This document discusses contact lenses, including their classification based on anatomical position, material, and mode of wear. It covers topics such as contact lens design, related terms, ideal materials, indications for use, contraindications, and optics. Rigid and soft contact lenses are described. Factors that affect contact lens fit and comfort are also summarized.

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Contact Lens
Dr Abdul Hannan

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Classification
1. Anatomical Position
1. Scleral
2. Semi Scleral
3. Corneal
2. Nature of Material
1. Rigid Non gas permeable
2. RGP
3. Soft contact lens
3. Mode of wear

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Classification
 Mode of wear
 Daily wear
 Extended wear
 Disposible
 Depending on Water Content
 Low water content
 Medium water content
 High water content

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Contact Lens Design
 Single Cut design
 Lenticular cut lens

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Terms Related to CL
 Wettability
 Water Content
 Oxygen Permeability
 Oxygen Transmissibility
 Light Transmission
 Refractive Index
 Flexure
 Dimentional Stability

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CL Materials
 Ideal Material:
 Biocompatibility
 Optical Properties
 Gas permeability
 Tolerance
 Moulding
 Sterility
 Stability
 Surface chemistry

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RIGID non-gas-permeable PMMA
 Advantages
 Light weight
 Excellent Moulding
 Non-toxic
 Disadvantages
 Impermeable to O2
 Hard – can cause corneal abrasion
 Resists wetting

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RIGID gas permeable lenses
 Cellulose
 Good wetting
 Easy scratching
 Easy wraping
 Silicone
 High oxygen permeability
 Lack of wetting
 Styrene
 Surface durability and brittleness

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Present RGPs
 Silicone Acrylate
 Fluoropolymers

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Hydrophillic Soft Contact Lens
 Combination of monomers and crosslinking agents
 Characteristics:
 Amount of Water Content
 Hydration of soft lenses
 Degree of swelling
 Average pore size
 Oxygen permeability
 HEMA, HEMA-VP, MMA-PVD

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Indications
1. Optical
2. Therapeutics
3. Preventive
4. Diagnostics
5. Operative
6. Cosmetic
7. Occupational

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Optical
 Anisometropia
 Unilateral aphakia
 High Myopia
 Keratoconus
 Irregular astigmatism

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Optical
 Advantages over glasses:
1. Normal field of vision
2. Irregular astigmatism
3. Aberrations
4. Binocular vision
5. Rain n fog don’t condense
6. Cosmesis

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Therapeutics
 Corneal Disease
 Iris defect
 Amblyopia
 BCL after surgery

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Preventive
 Symblephron
 Restoration of chemical burns
 Exposure keratopathy
 Trichiasis

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Diagnostic
 Gonioscopy
 ERG
 Fundal Contact Lens
 Fundus Photography
 Triple mirror

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Operative
 Goniotomy
 Vitrectomy
 Endocular photocoagulation

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Contraindications
 Mental incompetence
 Lacrimal Disease
 Disease of eyelids
 Episcleritis or scleritis
 Uveitis
 Ocupational Hazard
 Facial Palsy
 Poor hygiene
 Allergy to lens material
 Dry eyes

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CL and TEAR FILM
 Affect of CL on Corneal Nutrition:
1. Retards Evaporation
2. Barrier to Oxygen
3. Blocks Waste disposal
4. Traumatize the delicate epithelium

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Grip of CL
 Cohesion of water molecules
 Negative pressure

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Supply of Nutrition
 Lid Pump Mechanism
 20% replacement of post CL tear film is required

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OPTICS of CL
 Spectacles and its effect on eye:
 Are 12 to 13 mm away from the corneal vertex
 Are separated from eye by air
 No change in refractive status of eye
 Vergence of eye is not altered but the rays is altered
 CL changes the refractive power of eye ball the substituting the
cornea with its own surface

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Neutralization of Cornea
 Refractive index of Cornea: 1.376
 Refractive index of tears: 1.336
 With CL insitu it neutralizes the power of cornea by 90%
 From 48.83 to 5.19D

24. +Optics
Contact lens placed in contact with cornea with a
thin fluid film in between
It eliminates cornea as ref. surface
Afocal contact lens:
 ant & post curvatures of CL same as cornea
 No optical power
 Surface irregularities of cornea are taken care of

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Fluid lens
 Curvature of posterior surface of CL derives the
power of CL
Glass lens
 Post surface of CL same curvature as cornea
 CL power derived by curvature of ant surface of CL

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 Combined lens
 Curvature of both surfaces contribute
 Both glass lens & fluid lens give dioptric power.

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Physical factors of CL
1. Overall diameter of Hard lenses- 8mm, about 1.5-2mm
less than corneal diameter
• GP & soft lenses allow larger diameters
• Larger lenses are more stable
• Larger lenses – vaulting effect
2. Optical zone- central zone of 5-6mm
• Average of maximum & minimum pupil size

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3. Curvatures
Ant. Curvatures:
• C.A.C (Cental ant.Curvature)- ant surface of optical zone
• P.A.C. (Peripheral ant curvature): slope on the periphery
of ant surface
• I.A.C. (Intermediate anterior curvature) for high power
plus & minus lenses in between CAC & PAC

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 Posterior curvatures:
 CPC (central post curve )– Base curve to fit the front surface of cornea
 I.P.C.(Intermediate)- flatter than CPC
 P.P.C.(Peripheral)- flatter than IPC
These are meant to serve as tear fluid reservoir.
These form ski for contact lens movement.
CL can have bicurve, tricurve or even multi
curve contour design.

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4. Blend
Smooth area of transition of radius of curvature from one
curve to other
5. Edge-Polished & blended union of ant & post surfaces
• Too sharp- may dig into corneal epithelium
• Too thick- may irritate the lids
• Edge lift or Z factor- comfort & stability

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 Power of CL determined by central ant & post surfaces at O.Z.
determined by the ammetropic correction required
 Tint- to reduce the glare for cosmesis
 Ref. error determined by retinoscopy
 Curvature determined by keratometry
 Fit can be assessed by fluorescein pattern- flat , steep, ideal