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Issue 15May 2010

Sudheesh B R

Ayx Bt ̈ QFV¢×t

FV¢©×¡s¢iv

email : insight@keralaoptometry.orgwww.keralaoptometry.org

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Baburajan N SSub Editors

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PRESIDENT’S VOICE

Insight May 2010

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FROM SECRETARY’S DESK

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HOW WE CAN SEE......From the

beginning  humans havetried to explain thecomplex process ofvision.Vision is acomplicated process thatrequires numerouscomponents of thehuman eye and brain towork together.The initial step is carriedout in the retina of theeye. Specifically, thephotoreceptor neurons(called photoreceptors) in the retina collect thelight and send signals to a network of neuronsthat then generate electrical impulses that goto the brain. The brain then processes thoseimpulses and gives information about what weare seeing.The main structures of human eyeinclude the iris, lens, pupil, cornea, retina,vitreous humor, optic disk and optic nerve.

  By 19th century Thomas Young, aprominent physicist and physician, carried outa number of studies on the eye that resulted inan understanding of how the lens focusesimages onto the retina. He also showed thatastigmatism results from an improperly curvedcornea. We now understand that a number ofvision disorders, including both near- and far-sightedness, also result from an improperlycurved cornea. The lenses in eyeglasses functionby correcting for the improper corneal curve.

We now know the basic function of thecomponents of the human eye and how theyparticipate in the vision process. Light thatreflects off of objects around us is imaged ontothe retina by the lens. The retina, which consistsof three layers of neurons (photoreceptor, bipolarand ganglion) is responsible for detecting thelight from these images and then causingimpulses to be sent to the brain along the opticnerve. The brain decodes these images intoinformation that we know as vision.

Rod Cells and Cone Cells of theRetina

Although the microscope was firstused in scientific observation in thelate 16th and early 17th centuries,both the tool and the techniques ofits use reached a sufficient level ofsophistication by the 19th centuryto make it invaluable in examinationof the structures of the eye. It wasin the 1830’s that several Germanscientists used the microscope to

closely examine the retina. During this time thattwo different cells were discovered in the retina, therod cells and cone cells. These cells were namedbecause of their shape as viewed in the microscope.

A microscopic view of the rod cells of azebrafish shows us how these cells actually look inan animal. Additional research showed that the rodand cone cells were responsive to light. MaxSchultze (1825-1874) discovered that the retinalcones are the color receptors of the eye and theretinal rod cellswhile notsensit ive tocolor, are verysensit ive tolight at lowlevels. SeligHecht showed,in 1938, thee x q u i s i t esensitivity ofrod cells whenhe showed thata single photoncan initiate aresponse in arod cell. Cone

cells on the other hand are less sensitive to lightbut show great sensitivity to different colors. It isthe cone cells that allow us to see in color. It isbecause cone cells remain unstimulated in low light

Renju SajanPHC Vellangallur

Insight May 2010

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environments that we do not see color in dimly litplaces. Try this for yourself. Go into a closet anddecrease the light level. Soon you will see only shadesof gray. Slowly increase the light levels until you canbegin to see color. This demonstration usually workswell in a closet because of the many different colorsof your clothes.

In the human eye, there are many more rodcells in the retina than there are cone cells. Thenumber of rod cells and cone cells in animals is oftenrelated to the animal’s instincts and habits. Forexample, birds such as hawks have a significantlyhigher number of cones than do humans. This let themto see small animals from a long distance away,allowing them to hunt for food. Nocturnal animals, on

the other hand, have relatively higher numbers of rodcells to allow them better night vision.

A schematic drawing of rod and cone cellsare shown above.cells are divided into two sections.The bottom portion is called the inner segment. Itcontains the nucleus and the synaptic ending. Thesynaptic ending attaches to the neurons whichproduce signals that go to the brain. The top portionis called the outer segment. The outer segment iscomprised of a membrane which is folded into several

During the 1800’s the visual pigments werediscovered in the retina. Scientists, working bycandlelight, dissected the retinas from frog eyes.When the retinas were exposed to day light theychanged color. These scientists had discoveredthat the retina is photosensitive. They realizedthat the color they were observing was due topresence of a visual pigment, which was giventhe name rhodopsin. Later studies showed thatrhodopsin is a protein that is found in the disks ofthe rod cell membrane.

Pigments are also found in cone cells.There are three types of cone cells, each of whichcontains a visual pigment. These pigments arecalled the red, blue or green visual pigment. Thecone cells detect the primary colors, and the brainmixes these colors in seemingly infinitely variableproportions so that we can perceive a wide rangeof colors. Prolonged exposure to colors, forexample when staring at a particular object, cancause fatigue in cone cells. This results in achange in the way that you perceive the color ofthe object that you are viewing. 

The original theory of color vision wasintroduced by Thomas Young around 1790, priorto the discovery of the cone cells in the retina.Young was the first to propose that the humaneye sees only the three primary colors, red, blueand yellow and that all of the other visible colorsare combinations of these. It is now known thatcolor vision is more complicated than this, butYoung’s work formed the foundation of color visiontheory for the scientists that followed. Thephotoreceptor proteins of the cone cells have notyet been isolated. This may possibly be due tothe difficulty in obtaining them. There are manyfewer cone cells than rod cells in the retina. Alsomany animals do not have cone cells and hencedo not see in color.

An Important Protein in the Rod Cell:Rhodopsin

George Wald and his coworkers at HarvardUniversity pioneered our understanding of the

layers of disks. The disks are comprised of cellsthat contain the molecules that absorb the light.Visual Pigments

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molecules responsible for the first steps in the visionprocess. For this and other work on vision he wasthe recipient of the 1967 Nobel Prize in Medicineand Physiology. Wald’s group was the first toelucidate the molecular components of the rod cell’sfunctional protein rhodopsin. Prior to his work,rhodopsin was thought to be a chunk of molecular

material. Wald and his co-workers determined thatthe protein consists of two molecular parts: acolorless amino acid sequence called opsin and ayellow organic chromophore called retinal.

It is now known that the rhodopsin proteinhas a molecular weight of ~40 kDa. The proteinspans the membrane of the rod cell, and is thereforecalled a trans-membrane protein. The exactstructure of rhodopsin has never been determined,however experimental data lead scientist to predictthat it contains seven helices or turns.  About halfof the protein is contained within the membranewith approximately 25% of the protein lying bothabove and below the membrane.

It is the rhodopsin protein in the retina thatabsorbs the light that enters the eye. Specifically,it is known that the retinal molecule, which is

embedded inside rhodopsin, undergoes photo-excitation by absorbing light. In the photo-excitationprocess, the rhodopsin absorbs light and is excitedto a higher electronic state. Numerous studies havebeen carried out to try to understand what happensafter the rhodopsin absorbs light. Research hasshown that upon photo-excitation the retinal part ofrhodopsin undergoes a twisting around one of itsdouble bonds (see Figure 4). The retinal thendissociates from the opsin. The change in geometryinitiates a series of events that eventually causeelectrical impulses to be sent to the brain along theoptic nerve. Further research is needed to fullyunderstand this complex process.

Vitamin A and RetinalDuring the early part of the 20th century work

continued on the frontier of research aimed atunderstanding vision. It was also around this timethat the relationship between vision and propernutrition began being studied at universities andagricultural schools. It had been shown during WorldWar I that a vitamin A deficiency caused nightblindness. The link between vitamin A and nightblindness, however, did not become clear until GeorgeWald and his coworkers isolated vitamin A from theretina in 1933. Prior to this finding the importance ofvitamins was poorly understood. Additionally, thecomplete role of vitamins in physiological processeswas unknown.

It is now understood that the human bodymakes retinal from vitamin A. A picture of retinal andvitamin A is shown in Figure 5. Both the retinal andvitamin A molecules contain a long chain of doublebonds. When retinal dissociates from opsin, someof the retinal is destroyed. To replenish the destroyedretinal, it is important to have a source of vitamin Ain your diet. Without this source of vitamin A, nightblindness can develop as the rods can not functioneffectively without sufficient sources of retinal.

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An eye for an eye makes the whole world blind.Mahathma Gandhi

Many different lens manufacturing techniqueshave been used over the decades, some of which havenow been abandoned. They can, however, be dividedinto four basic types:

1. Casting, where a finished or semi-finished lensis produced from raw chemicals using a chemicalprocess (e.g. CR39 casting)

2. Moulding, where the lens material exists and itis reshaped by pressure and heat into the finishedor semi-finished lens form (e.g. polycarbonateinjection moulding)

3.Multi-part systems, such as laminating and fusing, where two or more pieces are joined to form the final lens (e.g. fused glass bifocals)

4.Surfacing, where the lens materials already exist and cutting and/or grinding and polishing is used to create the lens form (e.g. Rx surfacing)

Many lenses are produced by combinations ofthese four processes, the most common being the massmanufacture of semi-finished resin (e.g. CR39) bycasting, followed by surfacing in an Rx laboratory toproduce the second surface. Glass lenses are, of course,first moulded roughly to shape and then surfaced on bothsides.

Spectacle Lens ManufacturingFrom Casting To Freeform Generation

Casting

Casting is the mostcommon lens production methodin use today. It consists of plac­ingsome chemicals (e.g. CR39monomer plus a chemicalcatalyst) between two glass (ormetal) moulds held apart with aflexible gasket, and thensubjecting it to heat (or UVenergy). The material cures bypolymerisa­tion of the monomerinto a polymer. An ini­tial supplyof energy is required to start theprocess, but then thepolymerisation exotherms andcooling is sometimes requiredto prevent overheating. (Exotherm means that heat iscreated during the chemical polymerisation process.)

Because the material exotherms from the centre,this technique is difficult to use for thick lensesbecause of poor heat transfer through the lensitself.

During the conversion from monomer topolymer, the material shrinks (typically by 14%).About half of the shrinkage occurs while thechemicals are still liquid, and this necessitates aflexible gasket between the two mould surfaces.However, a bigger problem occurs during the secondhalf of the polymerisation, because the lens materialis then fairly rigid. For lenses where there is a bigdifference between the thickness of the edge andthe thickness of the centre of the lens, the front andback moulds, and/or the lens, must bend to preventseparation between lens and mould causing areject. Obviously, this causes difficulties whencast­ing high powered lenses.

Some companies have now replaced thespring and edge gasket with an edge taping system.The CR39 monomer is injected into the mould cavityeither at the edge of the gasket or through theedge tape, and a small gap allows any air to escape.Bubbles can easily be left within the mould andhence lens curing is done with the lensesposi­tioned, so that any remaining bubbles are atthe edge of the lens blank rather than in the centre.

Although many lens casting processes useair to heat (and cool) the moulds, somemanufacturers use water baths because ofimproved heat conduction. With a typical curing

cycle of about 18 hours, many lens massmanufacturing casting production processes areworked on a 24-hour cycle on what is called an ‘open-

Fig 1 Lens Casting Process

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and-shut’ system. It is very difficult to inspect mouldsfor surface defects, but relatively easy to inspectfinished lenses. Operators open the moulds, removethe new lens, inspect it for defects and if there arenone, immediately close the mould ready tomanufacture another lens. This is, of course, done inan ultra-clean environment. The process is illustratedin Figure 1, with a photograph of the componentsof a mould assembly shown in Figure 2.

Lens casting is primarily a massmanufac­turing process but many attempts have beenmade to cast lenses to prescription. This has notproved commercially successful. The biggestproblem (in the view of the author) is that to the uninitiatedperson, lens casting looks so incredibly simple; you just fillthe mould, heat cure and remove the lens. In fact, it is farfrom easy, with high reject rates for the very lenses that arerequired for spectacle prescriptions. As an example ofthis problem, the author was once told that the rejectrates in a factory were linked to the square of the lenspower, for example, pianos had almost no rejects, 3.ODDlenses had a 9% reject rate, 6.00D lenses a 36% reject rate

Figure 2C o m p n e n t sused for lenscasting - Flex-ible gasket,spring clip, top& bottom glassmoulds

and 9.00D lenses a 81% reject rate.Since the problems with casting relate to the

thickness of the lens, some interesting ways of makingprescription lenses have been attempted. For example,the Innotech Company took what were essentiallyfin­ished single vision lenses and then cast onto the frontsurface a thin multifocal/progressive segment. Being verythin, this could be done very quickly. In principle, thiswas a clever idea and some units were sold in the US. Apartfrom the production difficulties, the growth of AR coatinghas virtually eliminated the market for in-practice lenscasting systems; if the lens has to be sent away for coating,then the lens production might as well also be done bythe coating company. In fact, this is also sensible becausefull knowledge of the lens material and its method ofmanufacture can prevent problems in the coating process.

Moulding

By moulding (compared to casting) we mean‘reforming’ using pressure and heat. Originally used tocreate glass blanks (for later grinding and polishing)moulding is now more commonly used to createpolycarbonate lenses (remember that polycarbonate is athermoplastic material, whereas CR39 is a thermosetting

Figure 3 The Glass Slumping Process

resin).

The first stage of the process is for a chemicalcompany to produce the polycarbonate material, usuallyin granular form. These granules are then put into aninjection moulding machine, heated and then injected underpressure into a mould cavity. Rather like casting, lens mouldingis difficult for high power and thick lenses due to shrinkageas the newly formed lens cools. This can be alleviated bycomplex modern machines, which inject and then compressthe lens as it is cooling and solidifying. Typically six ormore lenses are produced at the same time, all connected bythe ‘sprue’ - the path along which the material is injected

into the mould. As all thermoplastic lenses are soft andneed hard-coating, this sprue is often used to hold a groupof lenses during a dip-coating process.

Another moulding process, only used by massmanufacturers, is called ‘slumping’. This process is usuallyonly used in the manufacture of semi-finished progressive powerglass lenses, and is best illustrated in Figure 3. First a ceramicblock is produced using a 3D, numerically controlled grindingmachine with the top side in the form of a progressive powerlens. A polished parallel sided piano glass blank is then laid overthe ceramic block and subjected to a carefully controlledheat process, sufficient to allow the glass to bend but not tomelt. This must be done in a clean and dust-free oven toprevent contamination of the upper surface (although dustcovers are also used). After the heating process, the lens(with its finished progressive front surface) is removed fromthe ceramic block. This semi-finished lens then undergoesthe normal Rx surfacing of the rear surface. A similar systemis now used to produce glass moulds for later use in castingthermosetting plastic (CR39) progressive power lenses.

Multi-part

There are a number of different multi-part processes.Probably the best known is the method used to produce glassbifocals by fusing a segment with a different refractive indexto make the reading addition section of the lens. Figure 4shows diagrammatically how this is done for a flat-topbifocal. Another multi-part system is the combination oftwo thin laminates to form a finished lens using a systemcalled ‘Instalens’ (Polycore Optical). It is intended for use bypractices with small optical laboratories who want toproduce multifocal and progressive prescription uncutlenses within a few minutes. A small stock of laminates isrequired. White and photochromic materials are available,with and without coatings, in bifocal and progressive lensforms. Essentially, the multifocal front laminate is glued (usingUV) to a rear laminate containing the distance prescription.In principle, this is a clever method that permits the rapid

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in-practice manufacture of finished coated lenses. Thecost of stockholding the large numbers of componentfront and back laminates is the major difficulty. Theproduction cost is relatively high because what areessentially two lenses are required to make each finishedlens. There are some other spectacle lenses produced bylaminating, such as laminated safety lenses, polarisinglenses and diving goggles.

SurfacingSurfacing is the most common lens

manufacturing technique (with the possible exceptionof mass production casting of single vision uncut lenses).There are three main types of surfacing processes, althoughwith many variants for special applicationsparticularly in relation to the production of progressivepower lenses. They are:

• Rough grind, smooth and polish, where allprocesses involve a lapping tool. Modern systemsusually do the initial roughing stage using alapping tool with a diamond abrasive embeddedinto a metal matrix. This system is only used inlarge volume glass production processes becauseit requires separate grinding, smoothing and polishinglaps for each curvature

• Generate, smooth andpolish, where a cup-shapedcutting wheel is used togen­erate a spherical ortoroidal curve, followed bylapping tool smoothing andpolishing. This is the methodused in most prescriptionlaboratories. Again, differentsmoothing and polishinglaps are required but acommon machine is used forthe grinding stage

• Cut, smooth and polish, wherea single point cutter is usedin a process usually referredto as ‘ freeform’. This isparticularly applicable toprogressive lens surfaces.After single point cutting,the surface can be smoothedand polished in the same wayas if a cup-wheel generatorhadbeen used. However, currentdevelopments are aimed atomitting the smoothing stage

Rough grind, smooth and polish

This is the oldest system in existence. Apart fromthe use of anelectric motorto rotate thelenses againstthe grindingtool, Leonardoda Vinci wouldhave fullycomprehendedany modernprocess ofg r i n d i n g ,smoothing and

polishing a lens surface. A poker arm machine is themost basic version, and is illustrated in Figure 5.

At each stage, finer and finer materials areused working on a ratio of about 10:1 between stages.For example, the first process is to obtain a roughshape by the removal of about 2mm of glass using a0.2mm diameter grit. This leaves imperfec­tions in thesurface of about 0.2mm. The second stage removes about0.2mm using 0.02mm abrasive, and leaves imperfectionsof about 0.02mm. The final polishing stage usuallyremoves about 0.02mm, using 0.002mm abrasive andleaves a surface with 0.002mm imperfect ions(0.002mm = 2 microns). Since the eye cannot see

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Insight May 2010

individ­ual particles less than about 20 microns, theresulting surface appears highly polished.

There are many clever techniques used inproduction to ensure that the correct curvature ofthe surface is achieved. For example, the lappingtool always oscillates so that a constant curvaturewithout surface waves is obtained, the radius ofcurvature can be gradually decreased by preferentiallyoscillating towards the edge of the tool and vice versa.More accurate curves can be achieved by multi-blocking a number of lenses onto a large ‘block’,and true flats can be achieved by interchangingthree flat tools.

Production systems for the massmanu­facture of spherical glass lenses using therough grind, smooth and polish process usuallystart with a tool that has fine dia­mond particlesembedded into a metal bond. The author introduceda system using this method into a UK Opticalfactory over 25 years ago. It enabled 30-secondgrind­ing, 30-second smoothing and two-minutepolishing to be achieved on spherical glass lenseswhere one operator produced a finished lens every30 seconds from a bank of 12 machines (a grinder,smoother and four polishers for the convex surfaceand the same for the concave surface).

This system of using lapping tools for all stages isonly suitable for mass production because of thelarge investment required in tooling. Most surfacingproduction uses a generation stage (see next), inwhich one machine can be adjusted to generatediffer­ent curves as described in the next section.

Generate, smooth and polishThe key component of a generate, smooth and polishsystem is the generating machine. This usuallyconsists of a tubular shaped ‘cup-wheel’ rotatingcutter with a curved end, as illustrated in Figure 6.The cutter is mounted on a swinging arm andcan be tilted so that the combination of swing

and t i l t canproduce thetwo differentcurves of atoroidal surface.

Cutting with at i l ted circularcutter does notactually producea circular cut, butan e l l ip t ica l

curve. The elliptical error is not large enough tobe significant to the optical power of a lens, butcan be significant to the manufacturing process. Itshould be remembered that the smoothing and

The key part of a generate, smooth and polishprocess is the generator itself. Very old machineshad to have the radii of the two curvatures set manuallybefore the cutting commenced, although this is nowdone automatically through electronic controls.Figure 7 shows a typical ‘conventional’ lens generator.

When a generator is combined with some smoothingand polishing machines, it cre­ates a prescription lensmanufacturing system suitable for a small Rx laboratory.Such a laboratory requires not only the generator,smoothing and polishing machines, but also a rackof lapping tools, a blocking and de-blocking unit andother ancillary equipment.

A considerable inventory of lapping tools is requiredto produce the combination of spherical andcylindrical curves commonly used in a prescriptionlaboratory. At the very least, tools for every quarterdioptre, from perhaps piano to 12.ODD curves withzero to 6.00 cylinders - not an inconsiderablenumber is required. Because of the wide variety ofdifferent refractive index materials now in use, manymore tools, normally in eighth dioptre incrementsare required, as well as a few tools of each sphere andcylinder combination. To prevent damage and wear tothe accurate tool curves, a system of applyingreplaceable abrasive and polishing pads onto the sametool has been evolved. The pads have a special shapeto allow them to adapt to the curvature of the tool.

Other techniques, where for example the polishingstage is replaced by lacquer coat­ing, have beencreated and these are described later in the sectionon recent developments.

Mention should also be made here of the number ofsmoothing stages. With modern equipment, it isusually possible to go from generating to polishingwith only one smoothing stage, but historically twostages of smoothing were often used. Obviouslythere is a trade-off between the amount of material

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polishing tools maybe accurate circularshapes, or may havebeen produced usinga process that alsoinvolves ellipticalerrors. It is thed i s c r e p a n c i e sbetween the ellipticalcurvatures of theg e n e r a t i o n ,smoothing andpolishing tools thatmay cause somedifficulties in the lensmaking process (seelater).

removed and the smoothness of the surface.Remember that sufficient material must be removed toclear surface cracks and curvature inaccuracy (includingelliptical errors) left by the generating stage. Adviceon the choice of smoothing and polishing pads isfreely available from the suppliers of prescriptionlaboratory consumables, who can provide completesystems as a turnkey operation, including operatortraining.

In addition to the generating, smoothing andpolishing machines, many other pieces of equipmentare needed to complete the surfacing process, includinglens tool calculation, lens surface protection, blockingand de-blocking, etc.

The first essential is to calculate the curva­ture ofthe lens surface to be produced. This requiresknowledge of the semi-finished curvature, the materialrefractive index and the desired lens power. For pluspower lens­es, a knowledge of the frame shape is alsorequired so that the thinnest possible uncuts may beproduced allowing just sufficient thickness at thecritical point around the circumference. For asphericand progressive power lenses, prism thinning may also

be required toproduce thebest balancedlenses. Thec o m p u t e rsoftware tocarry outt h e s ecalculations iscomplex, butis availablefrom thes u r f a c i n gm a c h i n e r ys u p p l i e r s .H a v i n gcalculated thes u r f a c i n g

require­ments, the next stage is to select thesemi­finished blank, protect it with surface saver tape(Figure 10) and then mount it onto an alloy block.Ready blocked lenses, together with the lens calculationcomputer printout, are then placed into a work-tray.The lenses then go through the generating, smoothingand polishing stages, are de-blocked and inspected.

Cut, smooth and polish

Using a traditional cup-wheel generatorrestricts the shape of the surface (ignoring ellipticalerrors) to either a sphere or to a toroidal section, thelatter being of course two circular arcs at right anglesto each other.

The key difference between a ‘generated’ curve anda ‘cut’ curve is that the latter is produced by a single

point cutter, and hence elliptical errors can beeliminated. A single point cutting tool has one bigadvantage (and a big disadvantage). In its favouris the ability to cut any curve, even a com­plexprogressive or aspheric, or even a com­bination ofthese. The disadvantages are the cost andcomplexity of the machinery, that it can takemuch longer for the whole sur­face to be cut,and also it is difficult to avoid a ‘pip’ at the centralpoint of the cutting action. Remember that a singlepoint tool is only cutting one point at a time,whereas a generator is cutting a whole sectionor arc at the same time.

When cutting a non-spherical curve, asingle point cutting tool needs to oscillate at rightangles to the lens surface. For a toric curve, thisrequires two in-out oscillations per lens revolution.This requires great accuracy and can involveconsiderable inertia forces. The cutter shouldtherefore be as light as possible, but must be veryrigidly mounted. The faster the lens rotation

speed, the greater are the inertia forces, and it isthis which may limit the total cutting time.

A close-up of a lens cutting tool is shownin Figure 12. Figure 12a shows the rough cuttool, and Figure 12b the fine cut tool. Oscillationof the tool presents considerable technicalchallenges due to the wear in mechanical parts.At least one machinery company has developedan air-slide mounted diamond tool assembly tominimise fric­tion and machine wear, and alsoa ‘voice-coil’ driven oscillation system therebyeliminating electro-mechanical motions.

The development of numericallycon­trolled ‘freeform’ surface cutting machinesmeans that it is now possible to produce one-offprescriptions for progressive power lenses allowingfor an individual’s personal requirements includingfacial features, different distance and readingPDs, different lengths for the corridor between

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Insight May 2010

distance and reading optical centres and otherfactors. Considerable computing power is requiredto calculate the motion required from the cuttingtool as the lens rotates, so a powerful computer isnecessary.

There is of course another major problem associatedwith a freeform surface shape and that is how tosmooth and polish it. This problem was overcomemany years ago when glass progressives were firstpro­duced. One system was to carry out the

smoothingusing avery smalldiameterf lex­i b l ed iamondp a d ,al thoughthis was ofcourse as l o wprocess.T h epolishingwas thendone onwhat wascalled a‘ d r u m ’pol­isher.

This consisted of a polishing material stretched acrosswhat looked like a drum, with compressed airunderneath the materi­al so that it flexed to take upthe progressive shape of the surface. Inevitably, flexiblesmoothing and polishing causes some degradationof the desired/designed surface (making it lessundulating) but nevertheless a satisfactory productcan be produced.

Also available are flexible soft-lap ‘balloon’polishing tools (Figure 13, which shows threesoft-lap tools which between them cater for all ofthe curvatures required). Inevitably, some accuracyis lost and so the smoothness of the cutting action iscrucial to the viability of the whole process. Thefiner the cut surface, the less smoothing is required,and hence less distortion occurs to the desired surfaceshape. In Figure 12, two cutting tools can be seen,one used to roughly shape the surface and the otherto create a finer surface. This two-stage single pointdiamond cutting reduces the amount of polishingrequired.

Many other methods have been tried, but the currentfavoured option is to use a hard-coating lacquer toconvert a smoothed surface into what looks like apolished surface. While it is still not possible to godirectly from cutting to hardcoating, this will no

doubt become possible in the future in what maybe called a ‘cut-and-coat’ process.

The ability of hardcoats to disguise minor defects(where very minor blemishes on lens surfaces can be‘filled-in’ with a lacquer) is already used in largeproduction operations result ing in a higherproduction yield. Obviously major defects cannotbe corrected - but very small defects can be disguisedresulting in a satisfactory final product.

Future developments

While the mass production of single visionlenses is likely to continue much as before, mainlyby using casting and moulding processes, the futurefor prescription lenses is more difficult to predict.Many attempts have been made to develop newprocesses, cast to Rx, front surface casting,laminating, etc. Most people think that the ultimategoal is the aforementioned cut-and-coat process.However, with a high percentage of lenses nowrequiring an AR treatment, it is the AR coating thatmay in future become the major delay in themanufacture of a prescription lens.

Large, complex high volume coatingmachines are now required to produce the latestgeneration of modern coatings, which includehydrophobic and oleophobic properties, and it islogistically difficult for these to produce prescriptionlenses rapidly. The future of lens manufacturetherefore needs a breakthrough in coating methods ifdelivery time is to be reduced. The production of a dip-coated, single layer AR coating has been attemptedand although this would reduce costs, it seemsunlikely to succeed commercially because of thecurrent requirement for multi-layer AR coupled with ahydrophobic topcoat.

Front-side coated, semi-finished lenses havealso been produced. This means that only one sideneeds to be AR coated after surfacing, reducing theproduction time. This development was done as acollaboration between a machinery company and aone-hour optical chain, which intended to use asmall four-lens AR coating machine needing only 15minutes for the plasma sys­tem coating process.

It now seems that the way forward for surfacingmay become the cut-and-coat system using lacquerhardcoating, but this does not resolve the problemof rapid AR coating to the modern sophisticatedstan­dards. Perhaps a dual market will evolve, withrapid relatively low cost production of less complexproducts in parallel with longer time scale, higher costsophisticated lenses.

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Insight May 2010

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Diseases have been affecting humans fromantiquity. An early diagnosis reduces morbidityfrom such diseases and cost incurred in treatingthem. There has been a paradigm shift in profile ofdiseases in ophthalmologic perspective; frominfectious diseases to non communicable diseaseslike diabetes, hypertension etc at least in our state.Though infectious diseases like conjunctivitis,infectious keratitis are common in community, theyare rarely misdiagnosed and most patients are treatedappropriately and early. But same is not the casewith noncommunicable diseases; they may notbe diagnosed early as rarely they are symptomaticenough to merit any investigations and late diagnosisleads to morbidity in such diseases.

Though a physician may be competent enoughto diagnose such noncommunicable diseases earlyfrom certain visible signs but he may not get enoughtime to properly examine a patient and thus earlydiagnosis is missed. So, how can a ophthalmicassistant help in this regard? They can bring visiblesigns indicative of internal diseases to attention oftreating physician & there by helping in early diagnosis.As eyes are windows through which mind sees theworld, eyes can be a portal to visualise derangmentswithin the body.

Xanthelesma are multiple yellowthickenings seen over medial aspect of eyelids whichif especially seen in young people may be marker ofincreased cholesterol in body. Trichomegaly meaningexcessive eyelash growth is seen in malnutrition,hypothyroidism, with certain drug intake, AIDS,porphyria. Madarosis meaning decreased number ofeyelashes may be due to myxoederna [severehypothyroidism],psoriasis, leprosy,systemic lupuserythematosus [disease in which body’s immunemechanism turn’s against itself & includessymptoms like joint pain, skin rash etc] & chronicanterior lid margin disease. Upper lid retraction meaninglid at or above level of superior limbus may be seen inhyperthyroidism, parkinsonism, uremia [advancedstage of kidney problem] & in some other neurologicalproblems, keratoconjunctivitis sicca meaning dry eyeis seen in elderly, contact lens users, people workingfor long time in AC, parkinson’s disease, atopickeratoconjunctivitis, posterior blepharitis, severeproptosis & many autoimmune conditions likerheumatoid arthritis, SLE etc. Seemingly harmlesssubconjunctival hemorrhage may be rarely sign ofdiseases like scurvy, blood diseases, malaria, elderlypeople with hypertension etc.Arcus if present belowage of 40 years may be sign of high cholesterol. A ringsimilar to arcus called KF ring may be seen in corneain a disease called wilson’s disease [a disease in which

copper excretion from body is defective]. Early indisease it may be seen only in one part of corneaespecially superiorly. Cataract [sunflower cataract]may be seen in this disease at an early age.

Signs seen in diabetes include iridopathydetected as increased iris transillumination, unstable-refraction, recurrent styes, xanthelesmata[multipleyellow thickenings seen over medial aspect of eyelids],accelerated senile cataract or even acute onsetcataract rarely, ocular motor nerve palsies [pupil sparingthird nerve palsy may be see] & reduced cornealsensitivity. Key retinal features in diabetes includemicroaneurysms, retinal hemorrhages [dot & blot],retinal lipid exudates, cotton-wool spots, macularedema, neovascularization, vitreous hemorrhage,retinal detachment & neovascular glaucoma.. Lidretraction, chemosis, proptosis, superior limbickeratoconjunctivitis, keratoconjunctivitis sicca anddiplopia are few signs that may be associated withhyperthyroidism. Dry eye, scleritis, ulcerative keratitisare a few external eye signs seen in rheumatoid arthritis.Dry eye, scleritis, madarosis, peripheral ulcerativekeratitis may also be seen in systemic lupuserythematosus [disease in which body’s immuneniechahism turn’s against itself & includes symptomslike joint pain, skin rash etc]. ’ Eye featuressuggestive of atopic eczema include madarosis,s taphy lococca l blepharitis, chronickeratoconjunctivitis, keratoconus & early onsetcataract. Signs of various forms of allergic conjunctivitisinclude papillary hypertrophy on superior tarsus,mucus deposition in between papillae, discretewhite spots near limbus, punctuate epithelialerosions, local area of arcus adjacent to allergicarea [called pseudogerontoxon],peripheral superficialvascularisation, conjunctival congestion predominantlyin interpalpebral area, angular fissuring & scaling.

A discussion of this sort is not completewithout mentioning about AIDS. Ocular featuresinc ludes b lephar i t is , multiple molluscumIesions[palunni], herpes zoster ophthalmicus,orbital cellulitis, conjunctival microangiopathy, skincancer of eyelids & conjunctiva, keratitis especiallyby unusual organisms, dryness of eyes, retinalnecrosis & retinitis from unusual organisms. Aneye sign seen in chronic depression is Veraguth’sfold. It is a triangular fold of skin seen in the nasalcorner of upper eye lid and is pathognomosic forit.

Finally a word of caution; the above mentionedsigns in isolation are not absolutely specific for adisease but rather it is the constellation of many signsalong with symptoms that are important in diagnosisof any disease.

Dr V P Praveen Kumar ShenoyMedical OfficerPHC Pizhala

The PortalsInsight May 2010

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           First After Care Visit

The first after care visit should takes place aftertwo weeks. Generally all patients may complain ofgenuine adaptive symptoms. Daily wear patientsshould be examined during  the afternoon followingseveral hours of contact lens use where as if thepatient is wearing the lens overnight if the effectsshould be observed in the morning.

Initial discussionThe initial discussion should cover many points

like whether the patient feels comfortable with  thelens ,any particular problems facing , maximumwearing time, whether handling satisfactory ,areinstructions being followed, solutions are being usedcorrectly, whether the soft lens is inside out etc.Examiner should carefully distinguished betweenvisual and physical symptoms.

Visual Acuity and Over Refraction  Snellen’ visual acuity  are recorded monocularlyand binocularly in the normal way. The quality ofretinoscopy reflex is important during assessment ofvision and over refraction.

Fitting Assesment  The following things may be noted with whitelight usually a torch in case of soft lenses.

1.Lens centration in primary position2.Lens movement on blinking3.Lens position with lateral and vertical movement.4. Blink rate5. Conjunctival injection6. Head position7. Eye movements.8. Palpebral aperture.

Hard Lens           Assessment OF fitting of hard lens should bedone with fluorescein. The flourescein examinationshould reveal the following,\.1.The central fitting inrespect of touch and clearence.2.Peripheral fitting andedge clearance.3.The speed of flourescein mixingasan indication of tear flow.4.three and four o clockstaining.5.Other areas of corneal staining ordesiccation.

         Slit lamp examination with lens in situ isdone to asses lens fit and to determine the grosscorneal

Oedema, bulbar conjunctiva for signs ofvessel irritation, the condition of lens, air bubblestrapped under the lens, debris trapped under thelens and wettability of lens surface etc,

Slit Examination With Lens RemovedThe lenses are removed and stored in

patients own case. Flourescein instilled and theeyes are examined for any corneal staining,eodema, foreign body and qualitative assessmentof tear film           After careful examinations the practitioneris now able to decide whether the symptoms areadaptive for some actions like alteration of poweror fitting or refitting with different materials, use ofdifferent solutions or adjustments of wearingschedules are needed. Reassurance concerningany subjective symptoms should be given.Recommend date of next visit.

Visual ProblemsDistant and near acuity should be assessed

separately. Contrast sensitivity measurements mayexplained visual problems where recorded acuityappear to be satisfactory. Retinoscopy reflex is animportant diagnostic aid. It can show opticalaberrations in a lens because of poor manufacture.A retinoscopy reflex improving after a blink with asoft lens indicate tight fitting. Spectacle blur maybe expected with PMMA lens.              An apparently unequal change in overrefraction is an indication that the right and leftlenses have been reversed.

Non Adaptive ProblemsAn increase in minus power may indicate

corneal oedema. Residual astigmatism can causeblurred vision. Foggy vision occur due to greasylens. Asthenopia may be due to residualastigmatism. Over refraction, binocular imbalanceor change in eye dominance (because of residualastigmatism in the dominant eye). Variable visionworse after blink suggest a loose fitt ing.Deterioration of vision during the course of the daymay be due to a lens dehydration.

After Care Of Contact LensBinoy R

CHC Anchal

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Wearing Problems

Oedema is common with PMMA and in soft lenswith hypoxia. Microcyst and bullae are other signs of corneal swelling. Subjectively patients maycomplaint of photophobia, cloudy vision or spectacleblur

· Staining : Arcuate staining with hard lenses foundin the superior mid-periphery of the cornea. Stainingcan be caused by1. Poorly finished edges,2. Insufficient edge by a sticky lens,3. Tight fit with excessive forced blinking,4. Blocked fenestration,5. Deposit on the posterior lens surface.·3 ‘O’ clock and 9’O’ clock staining·Central Staining.·Punctate staining·

Foreign body: Foreign body under the lens causepain and corneal scare

· Air bubbles (Dimpling): Small air bubbles trappedin a pool of tears beneath a contact lens act as aforeign body. If the lens is removed and the eye rinsedwith saline, irregular depression can be seen in thecorneal surface. It cause blurred vision if it occurswithin the papillary area. It can be helped by looseningthe fit to promote better tear flow, changing BOZD ortotal diameter.

Limbus

It is important to examine the limbus sincethe limbal vessels dilate in response to any adversestimulus such as physical irritation, insufficientoxygen or solution reaction.Staining at the limbus can occur in following reasons.

· Solution reaction· Abrasion from lens edges· Dessication· Hypoxia beneath upper lid

DellenMarked corneal thinning at the limbus

associated with severe conjunctival injection is calleddellen.

Bulbar Conjunctiva

Minor degree of redness is frequentlyadaptive. Severe conjunctival injection is due to· Solution reaction· Other allergies· Poor blinking· Infections· Physical Irritation

Lids

Papillary conjunctivitis is the commonproblem found with contact lens users. It is aninflammation of the papillary conjunctiva(upperlid) characterized by the presence of irregularpapillae.

Symptoms ;itching on lens removal,discharge in the morning ,severe lens depositcausing blurred vision, gradual deterioration ofcomfort .It may cause due to allergic response tothe lens material. Auto immune allergic responseto protein deposit, solution allergy, mechanical andenvironmental irritation.

Treatment

Consider medical referral for treatmentusually with steroids.Other measures are1. Discontinue lens wear for three months.2. Fit a new lens3. Ensure regular lens replacement.4. Eliminate all preserved solutions.5. Ensure regular use of enzyme tablets.

Environmental and General Factors.

Some of the problems are created not bythe lens but by the external factors.Air conditioning,low humidity , high altitude , computer use,polluted atmosphere, poor light etc. causediscomfort.

Alcohol use ,diet ,systemic drugs, oralcontraceptive, tiredness, poor health, pregnancy,mental tension etc. can increase the symptomsof discomfort .Poor blinking can cause dehydrationand deposit.

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The base curve of a spectacle lens and itsaffect on the wearing comfort of the patient is one ofthe most ignored and least understood principles ofrefractive optics. 

In order to understand the concept of the basecurve, it helpful to understand how a glasses lens ismade.  Although some labs make lenses in a mold,most lenses are ground from a lens blank.  The blankhas a front surface curve that is not changed in thefabrication process.  The prescription is made bycutting away material from the back of the blank toform one (sphere) or two (cylinder) ”ocular” curves. 

This is called “minus cylinder form”.  The backsurface minus curvature allows the lens to fit closerto the eye and maintain a more constant vertexdistance as the eye rotates.  The slightly plus or flatfront curve creates a cosmetically pleasing profile andforms a edge that fits well into the frame.  Lensblanks come with a range of front surface curves. Lens manufacturers apply mathematical formulasaccording to a “Corrected Curve Theory” thatcomputes the optimum front curves and back curvesfor a given prescription.  The idea is that there is anoptimum combination that will minimize lensaberrations.   There is more than one definition of the base curve:

·To the optician working in a lens fabrication

lab, the base curve may be the flattest curve on the

BASE CURVE

cylindrical surface of the lens.  With modern lensfabrication techniques, this would be the flattestcurve on the back side of the lens.· As optics technicians on the dispensingside of the processes, it is most practical to thinkof the base curve as being the singular front surfacecurve of the glasses lens. This is the definition wewill use. 

Lens blanks are generally made with basecurves in two diopter increments from plano through10 D (plano, 2, 4, 6, 8, 10).  A given prescriptioncan be ground in several combinations of frontcurves (base curves) and back curves (ocularcurves). Take for example a +4.00 D sphere: 

Each of the following base curve/ocular curvecombinations would yield a +4.00 D power lens. Algebraically add the front curve value and the backcurve value (+8-4 = +4).So how do you decide which combination is best? The Corrected Curve Theory tells you whichcombination is optimal to reduce aberrations andgive the patient comfortable viewing.  Generally,minus lenses will have base curves from plano (highminus) to 4 D (low minus).  Plus lenses will havebase curves from 6 D (low plus) to10 D (high plus). 

If the Corrected Curve Theory gives theoptimum curve combination for a given prescription,

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Insight May 2010

why might a patient have an adjustment problem whenthe base curve is changed?  Every glasses lens distortsthe image as compared to the view of the emmetropiceye.  It is the back curve (ocular curve), not the basecurve, that affects the patient’s view of the world.  Thepatient gets used to this distortion and it becomes thepatient’s “normal” view of the world.  If the back curveof a new prescription is changed significantly from theback curve of the old prescription,  the patientcomplains of distortion.   The patient might not usethis terminology.  The patient might simply say thatthe new glasses “just aren’t right.”  To eliminate thisproblem,  try to keep the new back curve within onediopter of the old back curve. 

Realize that, depending upon the Rx change,the back curve may change even if the base curve iskept the same,  and it may be necessary to changethe base curve in order to keep the back curve thesame.  When evaluating glasses problems, rememberthat it is the ocular curve (back curve) that mattersmost.  You will need to be able to read the base curveand calculate the ocular curve. The ocular curve is found with the following formula: Ocular Curve (OC) = Lens Power (P)  -  Base Curve(BC)Values in diopters Example:  Lens power = +2 D,  Base Curve =  8 D                        Ocular curve = (+2) - (+8) =  -6 Example:  Lens power = -4.00 D,  Base Curve = 4 D                     Ocular curve = (-4) - (+4) =  -8    Example 1: 

Mrs. Kadidlehopper comes into the office wearinga +4.00 diopter lens.  Her base curve measures 8 D. She has an early cataract and her prescription ischanged to +2.00.  Next week she comes backcomplaining of slanting lines when reading. Her glasses are checked and the new prescriptionmeasures +2.00 D with an 8 D base curve.  We can

calculate the ocular curve of the old prescriptionto be -4 D (4 - 8 = -4).  We measure the basecurve of her new glasses lens and it is also 8 D,just like her old glasses.  We calculate the ocularcurve on the new lens to be -6 D (2 - 8 = -6). 

So, Mrs. Kadidlehopper’s base curve waskept the same, at 8 D, but we have learned thatit is the ocular curve that really matters with Mrs.K’s perception of the world, and that changedfrom -4 to -6.  Could this two diopter change becausing her problem?  Probably.  It would beworth remaking the lens to find out.   

How would we keep the ocular curve thesame, at -4 D?  Of course there is a formula forthat too, and it is similar to the ocular curveformula: Base Curve (BC) = Lens Power (P) - Ocular Curve(OC) 

In our example, we want to keep the ocularcurve at -4, but we are changing the lens powerto +2.  What base curve will we need to changeto? 

BC = (+2) - (-4) = +6     So, we will bechanging the base curve from 8 to 6 in order tokeep the ocular curve the same.  Since the lensmanufacturer may use an 8 base curve for a +2D lens power, you would need to make a note onthe Rx that you are requesting a 6 D base curve.  

Example 2: 

Mr. Guy Wire has had cataract surgeryon his right eye.  Before surgery he was a +1.00D hyperope in each eye.  After surgery he becamea -1.00 D myope in his right eye.  After receivinga new right lens in his glasses, he comes backinto the office complaining that the glasses “don’tseem right”. 

A re-refraction confirms his prescription,the optical centers of the lenses match his PD,and the lens was ground to the correction.   A

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check of the old and new  base curves reveals thefollowing: Old right lens:  Rx = +1.00   BC = 6 D  OC = -5,change to:New right lens: Rx = -1.00   BC= 4 D  OC = -5 

At first glance it may seem that a change inthe base curve may be causing his problem. 

Remembering that it is the ocular curve thatmatters most, we calculate the ocular curve for eachlens: Ocular curve (OC) = Lens Power (P) - BaseCurve (BC) Old right lens: P = +1.00, BC = +6.00OC = +1.00 - (+6.00) = -5.00 D New right lens: P = -1.00, BC = +4.00OC = -1.00 - (+4.00) = -5.00 D 

So, the ocular curve in each lens is the same. It appears that someone has changed the base curveto keep the ocular curve the same, a procedure thatshould help the gentleman adjust to his newglasses.  In this case the base curve change isprobably not contributing to the patient’s problem. 

A more likely cause for his difficulty would bethe mismatch of having a plus lens in front of oneeye and a minus lens in front of the other eye.  Theplus lens causes a magnification of the image onthe retina of the left eye, and the minus lens causesa minification of the image on the retina of the righteye, making it difficult for the brain to fuse theimages. 

What can be done for this patient?  In termsof a glasses prescription, not much more, exceptperhaps slab-off grinding if the patient wears a bifocaland is complaining of reading difficulty.  If the patientneeds cataract surgery in the left eye, then theoutcome could be adjusted so that both eyes areslightly nearsighted after surgery.  If that is not aoption, contact lenses could be used to minimizethe retinal size difference.  With such a minimal

correction in each eye, this patient may do best byonly wearing glasses to read. How To Measure the Base Curve 

The base curve of a glasses lens is measuredwith a Geneva Lens Measure , sometimes called a“lens clock”.

The lens clock has an indicator that points to plus(black) or minus (red) diopter powers. It has threeprongs that are placed on the lens surface. The centerprong moves the indicator hand and is placed on theoptical center of the lens. The diopter power of the

base curve is read from the dial. Since the curve onthe front surface will always be either positive or flat,you will read the black numbers on the dial.

The prongs are placed in a perpendicularfashion on the front surface of the lens to measurethe base curve.  When reading a multifocal lens,  theprongs of the lens clock are placed horizontally withthe center prong placed over the optical center (justabove the line on a flat-top bifocal).

  The clock can be checked for calibration byplacing the prongs on a flat surface.  The clock shouldread zero in this position.

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With so many of us using computers at work,computer eye strain has become one of the majoroffice-related health complaints. Studies show thateye strain and other bothersome visual symptomsoccur in 50 percent to 90 percent of computer workers.These problems can cause physical fatigue,decreased productivity and increased numbers ofwork errors.

Computer vision syndrome (CVS) is atemporary condition resulting from focusingthe eyes on a computer display for protracted,uninterrupted periods of time. Some symptoms ofCVS include headaches,blurred vision,  neck pain,fatigue, eye strain, dry, irritated eyes, and difficultyrefocusing the eyes. These symptoms can be furtheraggravated by improper lighting conditions (ie. brightoverhead lighting or glare) or air moving past the eyes(e.g. overhead vents, direct air from a fan).

Pathophysiology

CVS is caused by decreased blinking reflexwhile working long hours focusing on computerscreens. The normal blink rate in human eyes is 16–20 per minute. Studies have shown that the blink ratedecreases to as low as 6–8 blinks/minute for personsworking on the computer screen. This leads to dryeyes. Also, the near focusing effort required for suchlong hours puts strain on ciliary muscles of the eye.This induces symptoms of asthenopia and leads toa feeling of tiredness in the eyes after long hours ofwork. Some patients present with inability to properlyfocus on near objects after a short duration. This canbe seen in people aged around 30–40 years of age,leading to a decrease in the accommodative focusingmechanisms of the eye. This can be a setting forearly presbyopia.

Therapy

Dry eye is a major symptom that is targetedin the therapy of CVS. The use of over-the-counterartificial-tear solutions can reduce the effects of dryeye in CVS.

Asthenopic symptoms in the eye areresponsible for much of the morbidity in CVS. Properrest to the eye and its muscles is recommended torelieve the associated eye strain. Various catch-phrases have been used to spread awareness aboutgiving rest to the eyes while working on computers.A routinely recommended approach is to consciouslyblink the eyes every now and then (this helps replenish

Computer Vision Syndrome

the tear film) and to look out the window to a distantobject or to the sky—doing so provides rest to theciliary muscles. One of the catch phrases is the“20-20-20 rule”: every 20 minutes, focus the eyeson an object 20 feet (6 meters) away for 20 seconds.This basically gives a convenient distance andtimeframe for a person to follow the advice from theoptometrist and ophthalmologist. Otherwise, thepatient is advised to close his/her eyes (which hasa similar effect) for 20 seconds, at least every halfhour.

Decreased focusing capability is mitigatedby wearing a small plus-powered (+1.00 to +1.50)over-the-counter pair of eyeglasses. Wearing theseeyeglasses helps such patients regain their abilityto focus on near objects. People who are engagedin other occupations—such as tailors engaged inembroidery—can experience similar symptoms andcan be helped by these glasses.

Here are some steps both workers andemployers can take to reduce computer eye strainand the other common symptoms of computer visionsyndrome (CVS):

Dr. BharathyDistrict Ophthalmic Surgeon, Manjeri

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1. Get a computer eye exam.

This is the most important thing you can doto prevent or treat computer vision problems.According to the National Institute of OccupationalSafety and Health (NIOSH), computer users shouldhave an eye exam before they start working on acomputer and once a year thereafter. Be sure to tellyour eye doctor how often you use a computer atwork and at home.

2. Use proper lighting.

Eye strain is often caused by excessivelybright light either from outdoor sunlight coming inthrough a window or from harsh interior lighting. Whenyou use a computer, your ambient lighting should beabout half that found in most offices.Eliminate exterior light by closing drapes, shades orblinds. Reduce interior lighting by using fewer lightbulbs or fluorescent tubes, or use lower intensitybulbs and tubes. If possible, position your monitorso that windows are to the side of it, instead of infront or back.

3. Minimize glare.

Glare on walls and finished surfaces, as wellas reflections on the computer screen can alsocause computer eye strain. You may want to installan anti-glare screen on your monitor and, if possible,paint bright white walls a darker color with a mattefinish.Again, cover the windows. When outside light cannotbe reduced, consider using a computer hood.If you wear glasses, have an anti-reflective (AR)coating applied to your lenses. AR coating reducesglare by minimizing the amount of light reflecting offthe front and back surfaces of your eyeglass lenses.

4. Upgrade your display.

If you have not already done so, replace yourold tube-style monitor (called a cathode ray tube orCRT) with a flat-panel liquid crystal display (LCD),like those on laptop computers.LCD screens are easier on the eyes and usually havean anti-reflective surface. Old-fashioned CRT screenscan cause a noticeable “flicker” of images on thescreen, a major source of computer eye strain. Evenif this flicker is imperceptible, it can still contributeto eye strain and fatigue during computer work.Complications due to flicker are even more likely ifthe refresh rate of the monitor is less than 75 hertz(Hz). If you must use a CRT at work, adjust thedisplay settings to the highest possible refresh rate.

When choosing a new flat panel display,select a screen with the highest resolution possible.Resolution is related to the “dot pitch” of the display.Generally, displays with a lower dot pitch havesharper images. Choose a display with a dot pitchof .28 mm or smaller.

Finally, choose a relatively large display. Fora desktop computer, select a display that has adiagonal screen size of at least 19 inches.

5. Adjust the brightness and contrast of yourcomputer screen.

Adjust the display settings on your computerso the brightness of the screen is about the sameas your work environment.

As a test, try looking at the white backgroundof this web page. If it looks like a light source, it’stoo bright. If it seems dull and gray, it may be toodark.Also, adjust the screen settings to make sure thecontrast between the screen background and theon-screen characters is high. And make sure thatthe text size and color are optimized for the mostcomfort

6. Blink more often.

Blinking is very important when working at acomputer; it rewets your eyes to avoid dryness andirritation.

When working at a computer, people blinkless frequently — about five times less than normally,according to studies.

Tears coating the eye evaporate more rapidlyduring long non-blinking phases and causedry eyes.Also, the air in many office environments is dry, whichcan increase the evaporation rate of your tears,placing you at greater risk for dry eye problems.

If you experience dry eye symptoms, askyour eye doctor about artificial tears for use duringthe day. By the way, don’t confuse lubricating dropswith the drops that only “get the red out.” The lattercan indeed make your eyes look better. They containingredients that reduce the size of the blood vesselson the surface of your eyes to “whiten” them. Butthey are not necessarily formulated to reducedryness and irritation.

Try this exercise: Every 20 minutes, blink 10times by closing your eyes as if falling asleep (veryslowly). This will help rewet your eyes.

7. Exercise your eyes.

Subscribe to free SMS servcie ofKerala Government Optometrists’ Association

OptoKeralaTo join Send

JOIN OPTOKERALATo 567678

from your mobile

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A component of computer eye strain isfocusing fatigue. To reduce your risk of tiring youreyes by constantly focusing on your screen, lookaway from your computer every 20 minutes andgaze at a distant object outside or down thehallway. Looking far away relaxes the focusingmuscles inside the eye to reduce fatigue.

Another exercise is to look far away at anobject for 10-15 seconds, then gaze at somethingup close for 10-15 seconds. Then look back at thedistant object. Do this 10 times.

This exercise reduces the risk of your eyes’focusing ability to “lock up” (a condition calledaccommodative spasm) after prolonged computerwork.Both of these exercises will reduce your risk ofcomputer eye strain. Remember also to blinkfrequently during the exercises to reduce your riskof computer-related dry eye.

8. Take frequent breaks.

To reduce your risk for computer visionsyndrome and neck, back and shoulder pain, takefrequent breaks during your computer work day.

Many workers take only two 15-minutebreaks from their computer throughout their workday. According to a recent study conducted by theNational Institute of Occupational Safety and Health(NIOSH), discomfort and eye strain weresignificantly lower when computer workers took fouradditional five-minute “mini-breaks” throughout theirwork day.

And these supplementary breaks did notreduce the workers’ productivity. Data entry speedwas significantly faster as a result of the extrabreaks, so work output was maintained eventhough the workers had 20 extra minutes of breaktime each day.

During your computer breaks, stand up, moveabout and stretch your arms, legs, back, neck andshoulders.

Check your local bookstore or consult yourfitness club for suggestions on developing a quicksequence of exercises you can perform during yourbreaks and after work, to reduce tension in your arms,neck, shoulders and back.

9. Modify your workstation.

If you need to look back and forth between aprinted page and your computer screen, this cancause eye strain. Place written pages on a copystand adjacent to the monitor. Light the copy standproperly. You may want to use a desk lamp, but makesure it doesn’t shine into your eyes or onto thecomputer screen.

Improper posture during computer work alsocontributes to computer vision syndrome. Adjust yourworkstation and chair to the correct height.

Purchase ergonomic furniture to enable youto position your computer screen 20 to 24 inchesfrom your eyes. The center of your screen should beabout 10 to 15 degrees below your eyes forcomfortable positioning of your head and neck.

10. Consider computer eyewear.

For the greatest comfort at your computer, youmay benefit from having a customizedeyeglasses prescription for your computer work. Thisis especially true if you normally wearcontact lenses,which may become dry and uncomfortable duringsustained computer work.

Computer glasses are also a good choice ifyou wear bifocals or progressive lenses, becausethese lenses are generally not optimal for thedistance to your computer screen. 

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 To

The Secretary9th Kerala Pay Revision Commission 2010Room No – 308, Legislature Complex,Vikas Bhavan P.O., Thiruvananthapruam

Sir,Sub:- Pay Revision – Views and Suggestions

Ref:-1. G.O(MS) 81/2010/Fin dt 20.02.20102. Notification of the 9th Pay Revision Commission dated 25.02.2010

 1. We are grateful to the 9th Pay Revision Commission for the opportunity offered to place our

grievances for favour of consideration by the Commission.

2. At the onset as part of this representation the following matters are presented in answer to part II.The questionnaire of the commission and our views in relation to part I are appended as annexureI.

3. The Posts causing us anxiety due to the repeated derogation by successive Pay Commissionsand refusal to effect rectification and their present scale, of pay are a s follows.

1. Ophthalmic Assistant Grade II – Rs. 6680 – 107902. Ophthalmic Assistant Grade I – Rs. 7990 – 129303. Senior Grade Ophthalmic Assistant – Rs. 10790 – 180004. Camp Co-ordinator – Rs. 11070 – 18450

The following posts in Ayurveda and Medical Education Departments are also allied ours in thematter of qualification and status and therefore are due for consideration along with our cadres.

1. Nethra Technician Ayurveda- Rs. 8390 – 132702. Tutor Technician Medical Education – Rs. 10790 – 18000.3. Orthoptic Technician Medical Education-  Rs. 10790 - 18000

4. We request that the injustice due to anomaly with effect from 01.07.2004 be looked into first andrectified before the revision of scales for our cadres is considered based on general principles.

5. Qualification and functional responsibilities are acknowledged by two of the main factorsfor consideration in award of pay scales. The relativity with other posts in the same department isanother factor. In consideration of award of scales in 2004 all these factors where given the go-bye, by the 8th Pay Commission and they were not rectified by the Government. We thereforerequest that at least the 9the Pay commission go into the mater and render justice.

I. Ophthalmic Assistant Grade IIUnlike other paramedical staff with very limited jurisdiction, the Ophthalmic Assistant has to attend to

work emanating from several Panchayaths. The main functions involve (1) Correctional treatment for variouseye disorders. (2) School eye health check-up, (3) contact lens fixing. Not only qualifications but alsoonerous nature of duties, coverage of population etc. are not reflected in awarding pay scales. A copy ofproceedings No EF4 – 53826/2000 DHS dated 24.01.2002 is enclosed.

Representation Given By Kerala Governemnt Optometrists’ Association toThe 9th Pay Commission

A junior heath inspector has to undergo a course for ten months whereas an Ophthalmic Assistanthas to undergo the course for two years after plus two. In 1997 the post of JHI was in the scale of Rs. 3500– 5400 and that Ophthalmic Assistant was in the scale of Rs 4000-6090. In derogation of the relativestatus, both posts are now equalized in the scale of Rs 6680 – 10790. Relativity is give ignored and thattoo in relation to posts in the same department. A physiotherapist in the department with comparableduration of qualifications enjoys scale of 9590 – 16650. The injustice meted out to Ophthalmic Assistantsis patent and we request sympathetic consideration and redressal at least at the hands of the 9the PayCommission. We request that the present scale be considers at least as Rs. 7990 – 12930, beforeeffecting further revision now.

II.  Ophthalmic Assistant Grade IPosts of Health Inspector Grade II and Ophthalmic Assistant Grade I were in the scale of Rs.

4600 – 7125 before revision in 2004. Now they are in scales Rs. 8390 – 13270 and Rs. 7990 – 12390respectively resulting in a hostile discrimination and derogation of Ophthalmic Assistant Grade I. in fairnesswe request that pre revision of scale 2004 be assumed to be Rs. 9180 – 15510 corresponding to HealthInspectors Grade I before their revision in 2009.

III.  Senior Grade Ophthalmic AssistantUnlike Health Inspectors with prospects for promotion as Health Supervisor, Technical Assistant,

Malaria Officer, Senior Grade Ophthalmic Assistant can aspire for promotion only to the post of camp –co.ordinator -  one in a district. Therefore the scale of senior Grade Ophthalmic Assistant may at least bedeemed to be Rs. 11070 – 18450 is the scale awarded in 2004 before further revision in 2009. IV.  Camp. Co.ordinator

As already indicated earlier there is only one post of a Camp. Co.ordinator in a district exceptMalappuram where there are two posts in two mobile eye units. A copy of orders on duties and responsibilitiesis enclosed. Order No. PH4/89024/92/DHSThe post of Camp Co.ordinator received derogated appreciation and a higher pay scale than of SeniorGrade Ophthalmic Assistant was granted after considerable difficulties and even interference by judiciary.We request that at least a pre revised scale of Rs. 11910 – 19350 in 2004 be accepted as basics for thepresent further revision.

V.  Tutor TechnicianThe post of Tutor Technician in Medical Education Department is the promotion post of Senior

Grade Ophthalmic Assistant. Even though repeated representations in the previous pay revisions, thescale of pay of tutor technician was not enhanced. Considering their duties in the teaching area andinstitutional responsibilities this post may be brought to the cadre of Camp Co.ordinator for the purpose ofaward of pay with a pre revised scale of 11910 – 19350, in 2004 be accepted as basis for present furtherrevision.

VI As the posts in our Cadre lack avenues for promotion, the denial of second higher grade allowed topersonnel after eight years of service in the first promoted post may be reinstated and the ratio 2:2:1 maykindly be revised as 1:1:1 in the present scenario. 

7. Though there was lack of appreciation and resultant award of low scales having little relativity to postsof similar status in the Health Service Department, the 8th Pay Commission in para 5-26-15 of theirreport had suggested charges of designation as follows.

 

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Post       Changed designationOphthalmic Assistant Grade II   OptometristOphthalmic Assistant Grade I   Senior OptometristSenior Grade Ophthalmic Assistant  Ophthalmic Officer

The recommendations was made because of All India pattern in optometry. In other countries andmiddle east, similar post are allied to the term ”Optometry”. The designation Ophthalmic Assistant doesnot reflect the nature of duties. The posts may be re-designated as Optometrist Grade II, OptometristGrade I and Senior Grade Optometrist to bring conformity to the duties and functions. Camp co.ordinatormay be re-designated as District Optometrist.

8. At present one of the Deputy Directors of the department in the office of DHS looks afterthe co.ordination activities under blindness control. In some other spheres like nursing there are exclusiveAssistant Directors. There has to be an officer in level of Assistant Director to co.ordinate and supportthe activities of our cadres for the smooth functioning of state blindness control activities and thisshould be allowed as promotion of our cadre. We request directions to the government as our entreatieshave fallen on deaf years.

We will be grateful for an opportunity to clarify doubts if at all any.   President               Secretary 

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Picture byPranoy S PS/o Preeja PrasadPHC Mundankunnu, Kottayam

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PROCEEDINGS OF THE DIRECTOR OF HEALTH SERVICESTHIRUVANANTHAPURAM

Sub: Establishment – Health Services Department – General Transfer 2010 – Transfer &posting of Camp Coordinator –Orders issued

Order No. EF4- 3069/2010/DHS dated 7.4.2010The following transfers and postings are ordered in respect of Camp Coordinator

In General Transfer 2010

Sl.No Name & Institution Station to which posted

1. Kumari Geetha.M.L General Hospital, ThiruvananthapuramDistrict Hospital, Kanhangad, In the existing vacancyKasargod

2. A.L.Amminikutty General Hospital, PathanamthittaDistrict Hospital, Palakkad In the existing vacancy

3. S.S.Babuji General Hospital, ErnakulamDistrict Hospital, Kannur In the existing vacancy

The date of relief and joining shall be reported promptlySd/-

Dr.M.K.JeevanDirector of Health Services

ToThe Incumbents

Copy toThe Accountant General, Kerala, ThiruvananthapuramThe District Medical Officer of HealthThruvananthapuram/ Pathanamthitta/ Ernakulam/ Palakkad/ Kasargod/ KannurSuperintendent, District Hospital / General HospitalThruvananthapuram/ Pathanamthitta/ Ernakulam/ Palakkad/ Kasargod/ KannurFile, Stock File

//Forwarded//

Senior Superintendent