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Contact lenses-2Contact lenses-2

Advanced Applications of Contact Advanced Applications of Contact Lenses-1Lenses-1

31/12/200931/12/2009Instructor: Areej OkashahInstructor: Areej Okashah

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Presbyopia & Contact lensesPresbyopia & Contact lenses• Presbyopia is a gradual decrement of visual functions @ near

among elderly (40 years or older)

• Bifocal & multifocal contact lenses (either GP or soft designs) are designed to substitute bifocal or multifocal glasses; respectively.

• Bifocal contact lenses: provide two corrections (distance & near)

• Multifocal contact lenses: provide correction for more than two distances; usually in a progressive design..

• Either bifocal or multifocal contact lenses use simultaneous or alternating vision technique.

• Monovision: means that one lens corrects distance vision in one eye; & another lens corrects near vision in the fellow eye

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• Which is more effective for our patients ?a. Monovisionb. Multifocalc. Or bifocal designs&a. GP or b. Soft material

Answer: you should evaluate your individual patient: consider tear, tear film, lids, …..etc.

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• A good candidate for bifocal or multifocal contact lenses is the good candidate for contact lens wear in general….

Case history: surgical history; medications (e.g. antihistamines); visual requirements; occupational requirements….. Discuss with patients

External (anatomical) measurements: pupil size; lid position; palpebral fissure size; blink rate & quality

Tear quality & volume

Corneal integrity

Refraction

K/ corneal topographyAre very important preliminary evaluations

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• Patient satisfaction with presbyopic lenses starts after 6weeks of the initial application

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Single-vision CL & reading glassesSingle-vision CL & reading glasses

• i.e. a CL (GP or soft; sphere or toric) for distance correction; & a spectacle for near add.

• Provides good bilateral vision at D & N

• Low cost• Simplicity of fitting

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Monovision Monovision • i.e. anisometropic contact lens correction; one eye is

corrected for distance ; the other eye is corrected for near.. So, patients will be able to see D & N as they keep both eyes open

• Using conventional lens designs• Decrease professional effort• < expense for patients• This design is thinner than bi-or-multifocal CL

HowevereIt impairs stereoscopic depth perception & one eye produces a

dominant response (ocular dominancy) usually the one for distance; reduce the contrast sensitivity

If the patient has strong dominancy in one eye; it then be difficult to ignore the out of focus monovision image

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Fit patients who don’t require long time of critical D vision

Examine binocular function i.e. stereopsis

Select the proper eye for N correction; i.e. the better eye is usually for D correction

Prescribe the full amount of correction & underplus the N eye & overplus the D eye to reduce the anisometropia

Discuss adaptation time with the patient

• Check for VA for both D & near• Patient comfort & adaptation are important to consider

Consideration in fitting monovision

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Bifocal CLsBifocal CLs

• 70% of presbyopes who wear CLs are fitted with monovision; 30% are fitted with bifocal designs ????

• Bifocals are either simultaneous vision, or alternating vision designs

•

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Simultaneous vision i.e. bivisionSimultaneous vision i.e. bivision • Simultaneous vision is achieved

when the D & N power are positioned within the pupil at the same time; the patient will selectively suppress the most blurred image at the selected distance

• Three designs are available with simultaneous vision………cont

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contcont…..1) aspheric : has a gradual change of curvature

along one surface 2) concentric/annular : has small central zone (the central zone either for D or N; but D is more often) 3) diffractive : available in soft design only & is independent on the pupil size; central diffractive zone that focuses image at distance by refraction of light & at near through diffraction principle)

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Alternating/translating visionAlternating/translating vision• i.e. vertical movement results in one power zone to position

in front of the pupil at any one time (the distance zone is in front of the of the pupil when viewing @ D; & the near zone when viewing at N)

• Intentional shifting of lens position in which separate discrete images formed by the two power segments in the lens focus on the retina with a change of gaze from distance (up) to near (down) or vice versa..

• Prism ballast or truncation are usually involved in this design to maintain lens stability

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Therapeutic ClsTherapeutic Cls• Trauma• Disease • Surgery• Bandages• Corneal reshaping

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Ocular traumaOcular trauma• Contact lenses can cause trauma which causes visual

impairment and participate in rehabilitation • Trauma can be caused mostly by metallic injury & motor

vehicle accidents • Always check the corneal topography • Corneal staining; abrasion; scarring

• Cls may give a protective benefit against ocular trauma

• Cls is a useful tool to heal corneal & conjunctival wounds by allowing the regeneration of affected cells; & by the prevention of direct contact with lids while blinking

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• Cls also help in vision rehabilitation after trauma or injury

• It also help manages aphakia; irregular astigmatism; iris/pupil abnormalities; amblyopia management (e.g. instead of patch); gross disfigurement (e.g. lids)= post-trauma

• Bandage Cls: (soft, GP, or piggyback designs): after penetrating-keratoplasty; post-refractive surgery : to improve healing or to prevent infection or contamination; corneal abrasion

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Paediatric contact lenses Paediatric contact lenses • Usually CL wear in children is elective• Either to improve vision or to improve appearance • Correction of refractive errors among children depends on

the refractive error type; age; requirements; & parents motivation

• Myopia: is rare among children; & if low-to-moderate occasionally causes amblyopia

• Spectacle correction of high myopia results in image minification; peripheral distortion; reduced field of view; CLs reduce these effects

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Rigid CLs slow the progression of myopia in children …. “controversial”

• Hyperopia: the most common refractive error among children; however refractive error correction doesn’t alter emmetropization; many practitioners recommend correction of hyperopia to improve vision & to prevent the onset of accommodative esotropia

• With spectacle correction of hyperopia: plus lenses are heavy; magnify the patients eyes & the viewed object & they distort the peripheral vision… Cls avoid these

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• Cls in paediatric can be used to correct astigmatism as in adults; anisometropia (to reduce the retinal image disparity & to prevent amblyopia) as well as aphakia

• Children can be fitted with smaller diameter e.g. RGP OAD/ OZD = 9.2/7.88 mm because they have smaller palpebral fissure…

• Children can be fitted with larger diameter lenses because they may fall while on their eyes

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Corneal Cyl BCR

0.00 0.50 D flatter than flat k

=<0.75D 0.25D flatter than flat k

>0.75-<1.50D Fit on flat k

>=1.50D 1/3 times the toricity steeper than flat k

BCR selection:

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KeratoconusKeratoconus• Is a progressive disorder in which the cornea has

irregular shape• Onset: around puberty • Autosomal dominant• Usually bilateral; but assymetrical• Systemic association: e.g. Down syndrome;

Turner syndrome; Marfan syndrome• Ocular association: e.g. retinitis pigmentosa;

vernal keratoconjunctivitis;

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• According to morphology can be classified into

• Nipple cones: small size 5mm; steep curvature; the apex of the cone is central or infero-nasally

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• Oval cones: 5-6mm size; ellipsoid (oval) & displaced inferotemporally

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• Globus cones: the largest >6mm

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• Presentation: visual impairment due to progressive myopia & astigmatism (usually reported for one eye); changes in spectacle Rx; decrease tolerance to contact lens wear;

• Signs: central or paracentral stromal thinning; apical protrusion; irregular astigmatism; steepening of the cornea graded according to keratometry readings (mild <48D, moderate 48-54D, severe >54D)

Early in the disease: oil droplet reflex on ophthalmoscopy; irregular scissor reflex on retinoscopy; Vogt lines (i.e. deep vertical stromal striae) on slit-lamp exam; irregular astigmatism on keratometry; abnormal corneal topography

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Vogt striae (i.e. line) in keratoconusVogt striae (i.e. line) in keratoconus

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Late in the disease: Munson sign (i.e. bulging of the lower lid on downgaze); visual acuity worsens; watering; oedema; stromal scarring after beaks healing;

Munson sign in keratoconus

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• Treatment: spectacles to correct regular & mild irregular astigmatism; contact lenses (e.g. rigid; toric); Keratoplasty

• http://www.youtube.com/watch?v=8jDBvjbKMR4

• http://www.youtube.com/watch?v=Kwv9juznA7c

• http://www.youtube.com/watch?v=QRNzDC5xlc8