Contact lens-all about

1. CONTACT LENS

2. INDICATIONS & C/I
• Artificial device whose front surface substitutes the
anterior surface of the cornea .
• Indications • Optical • Therapeutic • Preventive •
Diagnostic • Operative • Cosmetic • Occupational
• C/I: mentaly unsound,irresposible,unable to use
hands
:eye d/s
:occupational hazards
:Nerve palsy
:poor hygeine

3. TYPES OF CONTACT LENSES
Broadly : focons & filcons
Depending upon nature of material used
• Rigid non gas Permeable Lens :PMMA
• Rigid Gas Permeable Lens :CAB,silicone
• Hydrophilic Soft Lens :hydrogel lenses

4. RIGID NON GAS PERMEABLE CL
• PMMA/acrylic lenses.
• Advantage:optical quality,stability,light weight
:excellent moulding,easy manufacturing
:non toxic,non allergic.
• Disadv :o2 impermeable
:hard->corneal abrasions
:hydrophobic nature resists wetting

5. RGP CL/SEMISOFT LENSES
• Rigid as PMMA,but o2 permeable.
• Materials used :cellulose acetate butyrate
:silicone,silicone acrylate
:styrene
:fluoropolymers

6. Rigid CL –adv & disadv
• Better Quality of vision
• Durable
• Deposit resistant
• Low risk of infection
• Less cost & easy handling
• Correction of astigmatism
• Modified in office
• Less comfortable & adaptable
• Over wearing->pain
• Spectacle blur
• Difficult to achieve on eye stability.
• Glare,photophobia

7. SOFT CL
• Made of hydrogel[co-polymerisation products of
hydrophilic monomers with ethylene glycol
dimethyl acrylate].
• Hydrogel lens materials :HEMA
:HEMA VP
:MMA-PVD
:Glycidyl methacrylate

8. Soft CL –adv & disadv
• Easy adaptation & comfortable wear.
• Over wear reactions less
• No spectacle blur
• More on eye stability
• Varible vn :spoilage,dehydration,deposits.
• Less durable
• Correction of astigmatism not good
• Deposits high
• No office modification possible
• Not suitable in tear film abn/l p/ts
• Handling difficult
• High cost

9. MANUFACTURING,DESIGN PRESCRIPTION
& PARAMETERS OF CL
• CL blank :sheet /rod of diameter 12.7 & 15.9 mm
: thickness 3.00 & 6.5 mm.
• Semifinished blank : blank with p.curve
• Semifinished lens : both a&p curvature polished
• Finished CL : individually adjusted 4 cornea
: diameter,edge,peripheral &
intermediate areas of posterior
surface modified

10. • Diameter 1. Overall diameter (OD)
PMMA:7.5-8 mm
RGP:9-9.8 mm
Soft CL:13-15 mm
2. Optic zone diameter (OZ)

11. CURVES
• Base curve (BC) or central posterior curve (CPC)
• Peripheral curves : 1. intermediate (IPC)
2. peripheral (PPC)
• Central anterior curve (CAC) or front curve (FC)
• Peripheral anterior curve (PAC)
• Intermediate anterior curve (IAC)
• Blend:smooth area of transition between radii of
curvatures
:light,medium,heavy

12. • Edge : Union of the Peri.Postr.C & Peri.Antr.C of lens
: edge lift-extend to which the most peripheral
curve differs from the base curve radius
• Power : Measured in terms of posterior vertex
power in diopters
• Thickness : Measured at the centre of the lens
: Varies depending upon the postr. vertex
power of the lens
• Tint :Color of the lens

14. OPTICS OF CL
• Contact lens placed insitu has a thin fluid film in
between it & cornea & thus it eliminates surface
irregularity of cornea & cornea is no more a ref.
surface.
• Power of corneal surface is tear-air interface.
• Corneal RI :1.37,tear film RI: 1.333
• Tear lens neutralises almost 9/10th power of a.
corneal surface , it from +48D + 5.2 D.
• CL has a fluid lens & glass lens.

15. Correction of ammetropia
• Afocal lenses:
• correction is by different curvatures of fluid lens
surfaces,mainly back vertex power of fluid lens in
air(back +front surface power).
• Disadv:too many base curves needed
:poor fitting technique
• Powered lenses:
• correction is by different curvatures of contact lens
surfaces.
• P. surface curvature is already known & a.surface
curvature is decided based on an emperical
relationship to the corneal curvature.

16. Power & magnification of CL
• CL is placed on the vertex plane.so in myopes power of CL
needed is less & hyperopes needs power than their specs
power.
• +8 D specs  125 mm
• CL  125-13 =112 mm=+8.93 D
• CL produces a magnification of 7% in aphakia.
Influence of tear lens
• RGP & tear lens :power varies with BC of CL
• BC of CL =k plano power tear lens
• BC of CL steeper than k = +ve tear lens
• BC of CL flatter than k = - ve tear lens
• For every .05mm diff in BC of CL & k,power of tear lens is
0.25 D.
• Final CL power =SAM & FAP

17. CL & accomodation
• CL accomodative & convergence requirement of
myopic eyes and decrease those of hyperopic eyes
propotionally to the amount of their refractive
errors.

18. Fitting procedure 4 rigid CL
• H/O :r/o medical C/I
Reason 4 CL wearing
General & emotional status of p/t.
• Ocular examination:
 s/l examination:conjunctival,limbal,corneal injection
 TBUT
 blink characteristics noted
 measure – corneal diameter,pupil diameter & palpebral width
4 deciding CL diameter.
Refraction :retinoscopy,subjective refraction,back vertex
distance.
Keratometry 4 measuring corneal curvature in 2 principle
meridia
Trial lens fitting:with 2 diff diametre lenses of 0.25 D in BC.

19. • Diameter : 9mm in a p/t with avg corneal diameter &
palpebral aperture.
• BC  usually flatter k reading.
• Astigmatism: BC is steeper than flatter k.
• 0.5-1 D BC 0.25 D steeper than flatter k.
• 1.0-2.0 D BC 0.5 D steeper than flatter k.
• >2D 1/3RD toricity shud b added to k 4 BC.
K1=44 K2=47, BC= 44 + [ 47-44]
3
• Power of trial lens=spectacle power in minus cylinder form
corrected 4 zero vertex distance.
Specs power : -9.25/+0.50x90⁰
Minus power form : -8.75/-0.50x 180⁰
Vertex distance : 15 mm
CL power : -7.75/ -0.50X180⁰

20. • After adaptation period evaluate trial lens for
• Position of lens: High ride
• Low ride
• Horizontal decentering
• BC determination :flat
:steep
:ideal
• Finalisation of diameter
• Finalisation of power

26. • POST FITTING MANAGEMENT
• BC radius in mm
• Optic zone & overall diameter in mm
• First back peripheral zone in mm
• 1st & 2nd peripheral curve radius in mm.
• Power of the lens in D
• BC:OZD/1ST PC r:1ST BPZ/2ND PC r :overall diameter, power (D).
• EXAMINING ORDERED LENS:
• EVALUATION OF ORDERED LENS FIT
• EDUCATE THE P/T
care
wearing schedule
how to insert & remove
recentration
• POST FIT FOLLOWUP

29. SOFT CL FITTING
• CORNEAL DIAMETER: measured with transparent
ruler.
• : HVID
• TRIAL LENS FITTING :3 choices of BC & overall
diameter ids provided from which 1 is chosen.
• INITIAL TRIAL LENS SELECTION:BC
:overall diameter
:power
• EVALUATION OF TRIAL LENS FIT.
• POST FITTING P/T MANAGEMENT
• ORDERING SOFT LENSES
• EXAMINING ORDERED LENSES & EVALUATE FIT.
• EDUCATING P/T

30. EXTENDED WEAR LENSES
• Worn day n night even for months
EXTENDED SOFT CL
• Elderly p/ts with handling problems
• Young p/ts to avoid frequent handling
• Low compliance to DWL
• Irregular work shifts
• habitual over wearers
• eg: low,high ,medium water content lenses
EXTENDED RGP CL
• Metabolic,allergic,visual problems with soft CL
• toric bifocal /high plus/minus power lenses

31. DISPOSABLE CL
• Lenses used on daily wear basis,disinfected with H2O2
overnight & disposed weekly/fortnight.
• Adv:lens deposits,preservative induced
keratitis,infectious keratitis are less
THERAPEUTIC CL
• Wound healing,mechanical support,maintain surface
hydration in dry eyes,reduce corneal surface
disorders,as a drug delivery system
COSMETIC soft CL
• tinted cl used to alter the appearance of n/l eyes
• Used in disfigured cornea,vision disturbing conditions
needing CL,occlusion therapy,to change eye colour

32. Types of cosmetic CL
• Disadv:toxic effect of tint,corneal edema
,deposits,drying of lens,blanching of vessels

33. SPECIAL CASES 4 CL USE
ASTIGMATISM
• RGP : spherical lenses
:with toric peripheral curve
:bitoric RGP
:Front surface with toric RGP
• Soft CL :Spherical soft CL
:toric soft CL
APHAKIA
• RGP :Single cut lenses
:large lenticular lenses
• Soft CL :EWCL
:Lathe cut lenticular design

34. Keratoconus
• RGP with 3 point touch technique
• Soper lenses
• Mc Guine CL
• Rose k lens
• Piggy back lens
• Hybrid lenses
• Scleral RGP lens
• Custom toric soft CL
Presbyopia
• Monovivsion CL
• Modified monovision CL
• Binocular bifocal CL

35. Complications of CL use
conjunctival complicaions
• Allergic conjunctivits
• Giant papillary conjunctivitis
• Superior limbic keratoconjunctivitis
Corneal complications
• Epithelial edema,microcysts
• Corneal abrasions
• 3 - 9 o clock staining
• Sterile corneal infiltrates
• Corneal neovascularisation
• Microbial keratitis
• corneal warpage
• Endothelial changes
CL related complications
• Physical damage to CL,CL discolouration,deposits