LENS ENHANCEMENTLENS ENHANCEMENTOPTOM FASLU MUHAMMED

LENS ENHANCEMENTLENS ENHANCEMENTThere are various kinds of surface

treatments that are applied on either side of the spectacle lenses

1.Anti-reflection coating (ARC) 2.Scratch resistance coating 3.UV coating 4.Hydrophobic coating

Anti-reflection Coated Anti-reflection Coated LensLens

Anti-reflection coating are applied on the lens surface to efficiently manipulate the light transmission and reflection through it.

THE REFLECTION OF THE REFLECTION OF LIGHTLIGHT1.Frontal Reflection

2. Backward Reflection

3. Internal Reflection

4. Corneal Reflection

THE REFLECTION OF THE REFLECTION OF LIGHTLIGHT

PRINCIPLE OF ANTI-PRINCIPLE OF ANTI-REFLECTION COATINGREFLECTION COATINGTo reduce the loss of light due to reflection and increase the light transmittance through the lens to the eyes.

Based on destructive interference.

PRINCIPLE OF ANTI-REFLECTION COATING

PRINCIPLE OF ANTI-PRINCIPLE OF ANTI-REFLECTION COATINGREFLECTION COATING

SINGLE LAYER ANTI-SINGLE LAYER ANTI-REFLECTION COATINGREFLECTION COATING

The simple principle of single layer anti-reflection coating is that the substrate (lens) is coated with a thin layer of material.

PRINCIPLE OF ANTI-PRINCIPLE OF ANTI-REFLECTION COATINGREFLECTION COATING

The refractive index of the coating is the square root of that of the lens material.

The thickness of the coating, multiplied by its refractive index, is exactly one – quarter of a wavelength of light or any odd number of quarter wavelengths

MULTILAYER ANTI-MULTILAYER ANTI-REFLECTION COATINGREFLECTION COATINGThe limitations of the single layer

antireflection coating can be overcome by multilayer coating which are now capable of almost extinguishing surface reflections from one end of the visible spectrum to the other.

coating may be two layers or more.

In a two layer coating, the outer layer is made of a low refractive index and the inner layer is made of a high refractive index material compared to the substrate.

ADVANTAGES OF ANTI-ADVANTAGES OF ANTI-REFLECTION COATINGREFLECTION COATINGPeople see better with anti-

reflection.

Ghost images, particularly while driving at night.

Reflections from back lens surfaces can also be annoying. This is most noticeable with sun lenses because the dark lens acts like a mirror.

ADVANTAGES OF ANTI-ADVANTAGES OF ANTI-REFLECTION COATINGREFLECTION COATING

ADVANTAGES OF ANTI-ADVANTAGES OF ANTI-REFLECTION COATINGREFLECTION COATING

TECHNOLOGY OF ANTI-REFLECTION TECHNOLOGY OF ANTI-REFLECTION COATINGCOATING

Done inside a vacuum chamber.The lens to be coated must be

absolutely free of surface defects, perfectly cleaned and rid of dust or any other impurities before they are placed in the vacuum chamber.

glass lenses can be heated up to 300 deg C/570 deg F, plastics heated above 100 deg C/210 deg F.

HYDROPHOBIC COATINGHYDROPHOBIC COATINGAnti-reflection coating needs to be

kept clean.This problem can be eased if

hydrophobic coating is applied to the lens surface.

The basic principle is to create a high surface wetting angle, which allows the water or oil to run off rather than wetting and then drying on the surface.

HYDROPHOBIC HYDROPHOBIC COATINGCOATING

HYDROPHOBIC HYDROPHOBIC COATINGCOATING

HARD COATING or HARD COATING or Scratch-Scratch-Resistant Coatings (SRC)Resistant Coatings (SRC)Hard coating is a procedure by

which a thin layer of material usually 0.5 micron to 10 micron thick is applied to the lens surface.

The most common material used is lacquer which is applied either by dipping or by spinning procedure.

Thermally Cured Hard Coatingslenses are dipped in a “varnish”

and removed from the varnish at a consistent rate to control thickness of the coating.

The lenses are then thermally cured or “baked” over an extended period of time.

UV-Cured Hard Coatings

using a system that spins the coating on the lens.

HARD COATING or HARD COATING or Scratch-Scratch-Resistant Coatings (SRC)Resistant Coatings (SRC)

UV light comprises approximately 5% of total solar radiation.

Ozone in earth’s atmosphere absorb almost all solar UV –C radiation. of the reminder which strike the earth’s surface approximately 90% is UV-A and 10% is UV-B.

UV exposure may also come from arc welding and UV emitting light bulbs.

Ultraviolet filtersUltraviolet filters

UV COATINGUV COATINGUV exposure sunlight, welding arcs,

industrial sources, mercury vapour lamps, tubelight

Conditions Pterygium,

pingecula,cataract,cystoid macular oedema,skin ageing

IR wavelength near 1400 nm are very hazardous ;filters for these wavelengths are usually incorporated into protective goggles and face masks.

Blue light filters vary in tint between yellow and red. They increase contrast and facilitate distinction of light and dark areas and are used by mountaineers and skiers.

Tinted LensesTinted Lenses

A tinted lens modifies the spectral profile of the radiation passing through it .

Tints are either absorptive or reflective ; absorptive tints absorb light passing through them, whereas a reflective tint reflects unwanted wavelengths.

Tinted LensesTinted Lenses

Unequal absorption of different wavelengths produces a coloured tint. For example , a yellow tinted filter absorb all wavelengths of light except those in the yellow part of the spectrum, which it transmit.

A neutral density filter absorbs all wavelengths to the same degree and does not alter the spectral composition of the light.

SURFACE TINTING OF SURFACE TINTING OF LENSESLENSES

Tints are simply the methods of absorbing lights so that transmission is reduced.

If all wavelengths of light are equally absorbed, then a neutral grey is produced.

If the absorption is different for different wavelengths, then the tint has a particular colour.

The purpose of tinted lenses may be to screen out unwanted or harmful radiation (laser protective goggles) or cosmetic.

Varieties of tinted lensesVarieties of tinted lenses

PROCEDUREPROCEDUREThe lenses are placed in a suitable

bath of hot colour dye for an appropriate length of time.

Glasses can also be coated by vacuum process which has a unique advantage of uniform tint throughout the lens surface which is otherwise not possible in glass lenses.

Tinting of lensesTinting of lensesMixing dye to molten glass

materialBlowing layer of coloured glass on

the surface.Deposition of fine layers of tint on

the surface by vaccum process or electron beam process.

Deposition of mirror like coating

PHOTOCHROMIC PHOTOCHROMIC LENSESLENSESPhotochromic lenses are lenses that visibly darken and fade indefinitely under bright and dull light respectively.

A photochromic glass lens contains billions of microscopic crystals of SilverHalide.

When exposed to direct sunlight or UV light, these crystals absorb energy and cause the formation of metallic silver deposit on silver halide crystals..

Photochromic lensesPhotochromic lensesSilver halideMade up of two types of

materials; borosilicate glass and aluminophospahte glass.

Transmittance range Fading rate Reaction time

Darkening process of Darkening process of photochromatic lensphotochromatic lens

TINT OPTIONS IN TINT OPTIONS IN PHOTOCHROMIC LENSESPHOTOCHROMIC LENSESGlass photochromic lens usually

come in two basic colours – grey and brown.

Technically it is possible to obtain other tint.

RESIN PHOTOCHROMIC LENSRESIN PHOTOCHROMIC LENSPhotochromic compounds can be

incorporated into a resin lens by applying either a photochromatic coating or dye to the lens or by penetration of the surface, known as imbibitions

PHOTOCHROMIC PHOTOCHROMIC LENSESLENSES

POLAROID LENSESPOLAROID LENSESThe principle of polarized lenses

can be best illustrated by observing Venetian blinds.

The blinds block lights at certain angles, while allowing lights to transmit through it at certain angles.

Polarization implies restricting the light waves to one direction.

POLAROID LENSESPOLAROID LENSES

Polarized lenses block horizontally aligned light which causes glare, while allowing vertically aligned light to transmit.

Polaroid lens allows only useful Polaroid lens allows only useful vertical light wavesvertical light waves

ADVANTAGES OF POLAROID ADVANTAGES OF POLAROID LENSESLENSESFilters glares Enhances contrast and depth perception Reduces eye strain, greater comfort Improves visual acuity, provides safety Eyes feel restedRealistic perception Reduces reflection Comfortable and attractive – looking sun

wear.

ADVANTAGES OF ADVANTAGES OF POLAROID LENSESPOLAROID LENSES

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