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Contact Lens
Dr Abdul Hannan
+Classification
1. Anatomical Position1. Scleral
2. Semi Scleral
3. Corneal
2. Nature of Material1. Rigid Non gas permeable
2. RGP
3. Soft contact lens
3. Mode of wear
+Classification
Mode of wear Daily wear Extended wear Disposible
Depending on Water Content Low water content Medium water content High water content
+Contact Lens Design
Single Cut design
Lenticular cut lens
+Terms Related to CL
Wettability
Water Content
Oxygen Permeability
Oxygen Transmissibility
Light Transmission
Refractive Index
Flexure
Dimentional Stability
+CL Materials
Ideal Material: Biocompatibility Optical Properties Gas permeability Tolerance Moulding Sterility Stability Surface chemistry
+RIGID non-gas-permeable PMMA
Advantages Light weight Excellent Moulding Non-toxic
Disadvantages Impermeable to O2
Hard – can cause corneal abrasion Resists wetting
+RIGID gas permeable lenses
Cellulose Good wetting Easy scratching Easy wraping
Silicone High oxygen permeability Lack of wetting
Styrene Surface durability and brittleness
+Present RGPs
Silicone Acrylate
Fluoropolymers
+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
+Indications
1. Optical
2. Therapeutics
3. Preventive
4. Diagnostics
5. Operative
6. Cosmetic
7. Occupational
+Optical
Anisometropia
Unilateral aphakia
High Myopia
Keratoconus
Irregular astigmatism
+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
+Therapeutics
Corneal Disease
Iris defect
Amblyopia
BCL after surgery
+Preventive
Symblephron
Restoration of chemical burns
Exposure keratopathy
Trichiasis
+Diagnostic
Gonioscopy
ERG
Fundal Contact Lens
Fundus Photography
Triple mirror
+Operative
Goniotomy
Vitrectomy
Endocular photocoagulation
+Contraindications
Mental incompetence
Lacrimal Disease
Disease of eyelids
Episcleritis or scleritis
Uveitis
Ocupational Hazard
Facial Palsy
Poor hygiene
Allergy to lens material
Dry eyes
+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
+Grip of CL
Cohesion of water molecules
Negative pressure
+Supply of Nutrition
Lid Pump Mechanism
20% replacement of post CL tear film is required
+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
+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
+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