Contact lenses

1. CONTACT LENS

2. DEFINITION
 Artificial device whose front surface subtitutes the
anterior surface of the cornea

3. HISTORY OF CONTACT LENS
 1508, Leonardo Da Vinci used bowl half
filled with water.
 1637, Descartes used tube filled with water.
 1887, Muller used glass shell
 1888, Fick formulated term C.L
 Initially 2 types were available-
 - Blown glass lens from Muller
 - Ground glass lens from Zeiss
 1937, Feinbloom 1st used plastic polymer for
manufacture
 1938 – Orbig & Muller – Transparent MMA
 1946 – PMMA CL
 1948 – Plastic CL – Kevin Tuchy
 1961 – Hydrophilic CL - HEMA CL - Wichterle

4. CLASSIFICATION
ANATOMICAL POSITION
 I. Scleral contact lens
 II. Semi-scleral contact lens
 III. Corneal contact lens
NATURE OF LENS MATERIAL
 I. Rigid non-gas permeable/hard C.L.
(PMMA)
 II. Rigid gas permeable/semi-soft C.L.
(Cellulose acetate butyrate - CAB)
 III. Soft C.L. (HEMA).

5. CLASSIFICATION
MODE OF WEAR
 I. Daily wear
 II. Extended wear
 III. Disposable
PURPOSE OF USE
 I. Optical
 II. Therapeutic
 III. Cosmetic
WATER CONTENT
• Low (0-40%)
• Medium (40-55%)
• High (>55%)

6. DESIGN
 1. Single cut lens -
single continuous front surface
back surface – base curve and peripheral curve
 2. Lenticular cut lens
Front surface- central optic portion surrounded by peripheral carrier
portion

7. PHYSICAL PROPERTIES
 Wettability
 High water content
 O2 permeability
 O2 transmissibility
 Light transmission
 Refractive index
 Heat resistance
 Dimensional stability
 Flexure

8. WETTABILITY
 Adherence of liquid to surface of solid despite of cohesive forces holding liquid
together
 The angle that the edge of a bead of water makes with the surface of a contact
lens called a wetting angle.
 The smaller the wetting angle the greater the wettability of lens.
 Complete wetting – wetting angle 0’
 Partial wetting – wetting angle 70’
 Non wetting – wetting angle 150’

9. OXYGEN TRANSMISSIBILITY
DK/L
 D= Diffusion coefficient (cm/sec)
 K=solubility of gas in material(cm3/cm2mmhg)
 L= thickness of material(mm)
Depends on:
 permeability of lens material
 Thickness of lens
 Temperature at which test is performed

10. OXYGEN PERMEABILITY
 Low Dk material
 Below 20
 Mid Dk material
 20 to 40
 High Dk material
 40 to 60
 Hyper Dk material
 Above 60
 Property of the polymeric material to
transmit gaseous substances
 Unit from which O2 passage for a specific
lens is derived

11. OXYGEN PERMEABILITY
 Daily wear, the recommended Dk/L of a contact lens is around 30
 Low oxygen transmissibility can result in corneal changes:
 - Microcysts
 - Polymegathism
 - Corneal Ph
 - Edema
 - Blebs

12. IDEAL MATERIAL
 BIOCOMPATIBILITY
 Should not harmful
 OPTICAL PROPERTY
 Transparency
 Refractive index approximating to tears
 Gas permeability
 Tolerance
 Moulding
 Sterility
 Stability
 Surface chemistry – wettable – cover by tears

13. OPTICAL INDICATIONS
 Myopia / Hypermetropia / Astigmatism
 Presbyopia
 Unilateral Aphakia
 Anisometropia & Anisoconia
 Keratoconus

14. COSMETIC INDICATON
 Aniridia
 Albinism
 Coloboma / Large iredectomy
 Heterochromia
 Microcornea / Microphthalmos
 Corneal scars
 Inoperable cataract

15. OCCUPATIONAL INDICATION
 Actors / public speakers
 People using telescope / microscope
 Sportsman
 Protection from steam, spray, mist etc.

16. THERAPEUTIC
[ BANDAGE SOFT C.L.]
 Decreases pain
 Prevent mechanical trauma by touch
 Increases proper hydration and proper healing
 Corneal edema
 Corneal perforation
 Corneal burns
 Corneal grafts

17. THERAPEUTIC
[ BANDAGE SOFT C.L.]
 Bullous keratopathy
 Leaking conjunctival blebs
 Keratitis
 Symblepharon
 Lagophthalmos
 Chronic and indolent ulcer

18. THERAPEUTIC
 Trichiasis / entropion
 Post pterygium operation
 Dry eye syndrome
 For drug delivery(glaucoma)
 Melanosis of conjunctiva – use to deliver high dose continuous to conjunctiva
 In glaucoma –vehicle for drug delivery
 Amblyopia – opaque CL for occlusion

19. DIAGNOSTIC USE
 Fundoscopy
 ERG
 Gonioscopy
 Applanation tonometry
 A-scan biometry

20. CONTRAINDICATIONS
OCULAR PATHOLOGIES
 Blepharitis
 Chalazion / stye
 Conjunctivitis
 Large pterygium / pinguecula
 Chronic hyperemia

21. CONTRAINDICATIONS
OCULAR PATHOLOGIES
 Pannus
 Corneal anesthesia
 Tear film abnormalities
 Epithelial dystrophies
 Scleritis,
 Episcleratis
 Iritis

22. CONTRAINDICATIONS
 Mental incompetence
 Diabetes
 Pregnancy
 VIIth cranial nerve palsy
 Crippling arthritis – inability to use hands
 Poor personal hygeine
ALLERGIES
 Contact dermatitis
 Asthma
 Atrophic rhinitis

23. CONTRAINDICATIONS
OCCUPATIONAL HAZARD
 Smoky, dusty hot environment
 Chemical fumes & irritants
 High altitude flyers
 Construction worker / automobile mechanics.

24. ADVANTAGES OVER SPECTACLES
 No peripheral aberration
 No chromatic aberration
 Prism distortion can be controlled
 Less minification / magnification
 Astigmatism can controlled
 No fogging
 Increases field of vision
 Cosmetically more pleasant
 BSV in high anisometropia (u/l amblyopia)

25. DISADVANTAGE
 Problem for old / very young patient
 Require a lot care
 Supervision required
 Costly

26. HARD CONTACT LENS
(RIGID NON-GAS PERMEABLE LENS)
 Made of PMMA.
 Confirm to the cornea.
ADVANTAGE
 Light in weigh
 High optical quality
 Non toxic
 Easy to manufacture

27. HARD CONTACT LENS
(RIGID NON-GAS PERMEABLE LENS)
DISADVANTAGE
 Low wettability
 Low O2 permeability (DK value = 0)
 Hard
 Now obsolete

28. RIGID GAS PERMIABLE LENS
(RGP) / SEMI SOFT LENS
 Initially made of Cellulose Acetate Butyrate.
 Silicon Acrylate
 Copolymer of PMMA & Silicon containing vinyl monomer
 Styrene
 Fluropolymers-for extended wear.
 Size- usually 9-10mm.
 Best in high myopes, astigmatism >2d, keratoconus.

29. SOFT CONTACT LENS
HIGH WATER CONTENT
 Up to 85 % of H2O
 Made of hydrogel
 HEMA
 HEMA-VP (Vinyl pyrrolidone)
LENSES –max hydration 45%
 MMA-PVD LENSES
 Glycidyl methacrylate
LOW WATER CONTENT
 38 – 45 % of H2O
 High DK value
 Made of silicone hydrogel

30. SOFT CONTACT LENS
HIGH WATER CONTENT
 Advantage
 Higher DK
 More flexible
 Faster restoration of shape following
deformation.
 Disadvantage
 More fragile
 More deposit prone
 Difficult to manufacture
 Lower tensile strength
 Cannot be made too thin
LOW WATER CONTENT
 Advantage
 Less susceptible to environment changes
 Low protein deposition
 Ease of manufacture
 More wettable
 Compatible with all lens care product
 Disadvantage
 Low DK
 Less flexible
 Thin lens difficult to handle

31. ADVANTAGES OF RIGID CONTACT LENS
 Better quality of vision
 More durable
 Correction of astigmatism
 Deposit resistance
 Less of chance of infection
 Cost of lens
 Less comfortable, tough

32. ADVANTAGE OF SOFT CONTACT LENS
 Very comfortable and easy to adapt
 Larger & adhere more tightly to the cornea
 No spectacle blur
 Doesn’t correct astigmatism

33. TERMINOLOGY USED FOR C.L.
 1. Diameters:
 Overall diameter / chord diameter
 Optic zone diameter
 2. Curves:
 Base curve / central posterior curve
 Peripheral curves (reservoir of tears)
 Central anterior curve / front curve (power of CL)
 Peripheral anterior curve
 Intermediate anterior curve
 3. Blend: smooth area of transition of radius of curv from 1 curve to
another curve
 Light (transition b/w 2 post. Curves visible), Medium , High (transition not
visible)
 4. Edge: polished blended union of peri post & ant curves
too sharp – digs cornea, too Thick – irritates lid
 5. Power
 6. Central thickness
 7. Tint

34. CONTACT LENS FITTING
PRE-FIT CONSULTATION
 Complete history
 Detailed eye examination
KERATOMETRIC METHOD
 Pupil diameter [with IPD scale] is measured.
 HVID is measured.
 Corneal diameter is measured.
 Radius of curvature is measured with a keratometer.

35. CONTACT LENS FITTING
KERATOMETRIC METHOD
 BASE CURVE, back surface of lens.
 Rest on cornea responsible for good fit.
 Long radius of curvature – flatter base curve.
 TD depends upon lid diameter & corneal diameter OR HVID.
 Optical zone should be at least 7 mm.
 Posterior surface – Aspheric.
 Anterior surface –convex with power.

36. CONTACT LENS FITTING
TRIAL LENS METHOD
 Various lens from trial set tried until appropriate B.C. achieved.
 Very tedious and cumbersome
 A large trial set has to be maintained
INVENTORY FITTING METHOD
 Combination of both above
 More time efficient and more convenient to patient.

37. FACTORS TO BE KEPT IN MIND
 The total diameter should 1-1.5 mm greater than HVID.
 BC should be 0.3-0.6 mm flatter than the flattest k reading.
DETERMINATION OF LENS POWER
 • Spherical power + ½ cylindrical power [ if cyl is b/w 0.5D to 2.00D ]
 • If cyl is < 0.5D Drop cylinder.
 • If cyl is > 2.00D , go for toric CL.

38. EVALUATION OF TRIAL LENS FIT
1. Position of lens: (optic zone must cover pupillary area)
 Lens Ride high- upper edge of lens crosses upper limbus in straight gaze
 Higher position of lowerlid – reduce diameter of lens
 Tight upper lid –Thin edge will slip under upper lid
 Large lens / with the rule astigmatism – small or steep lens
 Lens ride low – lower edge touches the limbus
 Lens heavy (single cut aphakic lens)– making minus carrier lens
 Lens small/flat – large or steep lens
 Exophthalmos - large lens / steep& small lens

39. EVALUATION OF TRIAL LENS FIT
2. Base curve determination – Tear exchange - pumping action - Blinking
 Flat base curve
 Excess lens movement
 High / low riding / horizontal
 Flourescein pattern
 Corneal abrasion, irregularity, distortion
 Steep base curve
 Little or no movement
 Air-bubble under surface of lens
 Flourescein pattern
 Burning sensation, edema, hazy vision
 Ideal base curve

40. FLOURESCEIN PATTERN
Flat base curve
 Black area at apex – no tear
 Diffuse green in periphery and intermediate zone
 Astigmatic cornea – broad black band overlying flattest meridian and
remaining area bight green
FLAT FIT

41. FLOURESCEIN PATTERN
Steep base curve
 Pooling of tear fluid in apex – bright green central area
 Bright green peripheral band and broad black intermediate zone (heavy
touch)
 Astigmatic cornea –black crescent under intermediate zone and bight
green centre & periphery
STEEP FIT

42. FLOURESCEIN PATTERN
Ideal base curve
 Apical appearance, mid peripheral touch and peripheral clearance (periphery –
bright green & central area faintly)
 Astigmatic cornea –black band under central apical zone over the flattest
corneal meridian, faint green pool over the steepest corneal meridian and dark
band over intermediate zone and bight green periphery
IDEAL FIT

43. EVALUATION OF TRIAL LENS FIT
1. Base curve evaluation: (fluorescein is never used in soft CL)
a) Movement of lens over cornea: <0.5-1mm, flat/loose fit moves rapid, steep /tight fit
doesn’t move
b) Centring – proper fitting will centre well
c) Effect of blinking – Visual acuity, retinoscopic reflex, keratometermires
steep fit – clears after blink
flat fit – blurs after blink
d) Compression of blood vessels, indentation on sclera
2. Diameter evaluation: diameter should extend 1-1.5 mm over cornea
3. Lens power evaluation: clear vision

44. LENS WITH IDEAL BASE CURVE
1. Maintains 0.5-1.0 mm movement
2. Movements good centration
3. Doesnot cause compression of the conj. Vessels
4. Maintains stable VA with and without blinking
5. Maintains sharp and crisp retinoscopic reflex and keratometric mires before
and after blinking

45. TECHNIQUES OF WEARING

46. RIGID LENS PROBLEMS
 Blurred vision – Distance:
 Blurred vision – Near:
 Blurred vision – when wearing specs:
 Awareness of presence of lens:
 Burn, hot & scratchy eyes
 Lens touching eyelids
 Discomfort in morning
 Tilting back of head
 Excess blinking
 Swelling of lid in evening
 Difficulty in removing
 Lens fall out frequently
 Discomfort in eye movements
 Photophobia
 Watering
 Pain

47. Rigid contact lenses Soft contact lenses
Advantages Disadvantages
Quality of vision Better Variable vision despite good fit – lens
dehydration, lens spoilage, deposits
Durability More durable Less durable – scratch /torn
Correction of
astigmatism
Spherical rigid CL-can
correct mod astigmatism
Toric rigid CL-best to correct
high astigmatism - KC
Spherical soft CL - Since moulds to
cornes –not corrects astig
Toric soft CL for astig but rigid is better
Deposit formation Deposit resistant Protein / mineral / lipid deposits
Risk of infection less more
Dry eye and tear
film irregularities
Are not contraindicated Not suitable
Cost and handling Less cost & easy handling More costly and more difficult to handle

48. Rigid contact lenses Soft contact lenses
Disadvantages Advantages
Comfort Less comfortable and more
difficult to adapt
Very comfortable and more
easy to adapt
Wearing
problems
Prob with irregular schedule
Over wear - pain
Intermittent wear – no
problem
Over wear – less severe
Spectacle blur May occur Not occur
Lens stability Less eye stability, lost
frequently
Larger & adhere more tightly
and so dislodges less freq

49. WEAR AND REPLACEMENT SCHEDULE
 DW-daily wear:
 • Traditional replacement cycle> 3 months
 • Monthly replacement
 • Daily replacement
 EW-extended wear: Allowing lenses to be worn for 7 days/6 nights without
removal.
 During one night per week the eyes are free of lenses. Weekly replaced by new
lenses

50. WEAR AND REPLACEMENT SCHEDULE
 FW-Flexible wear: Compromise between DW & EW.
 Depending upon the demand of the patient to once a while sleep in lenses

51. HYBRID RGPs
 Central optical zone, formed by Rigid GP ,surrounded by peripheral soft
contact lens material.
 Second generation silicone hydrogel CL, called Duette, having highly
oxygen permeable GP centre , surrounded by a soft silicone hydrogel “skirt”
for comfort.

52. CONTACT LENS FOR ASTIGMATISM
RGP
1. Spherical RGP – Mild – moderate astigmatism
2. RGP with toric peripheral curves – 1.5 – 2.5D
Steeper peripheral curves (equal to D of corneal astig) in the steepest meridian
3. Bitoric RGP- >2.5D
Post toric surface – lens tear interface becomes toric - induced astigmatism – addnl ant toric curve – Bitoric lens
4. Front surface Toric RGP
spherical cornea with significant Lenticular astig – residual astig: spl change in shape to prevent rotation of cyl
axis – Prism blast (base down prism 1.5D), truncated (edge is cut short in 1 meridian by 0.5-1mm)
Soft CL
5. Spherical soft CL (upto 1D and total astig < 1/3rd
of sph correction)
6. Toric soft CL (>1D) Prism blast, truncation, combined, Double slab off

53. CL IN PRESBYOPIA
1. Monovision CL
2. Modified Monovision CL
3. Binocular Bifocal CL
a) Annular
b) Segmental
c) Aspheric
d) Diffractive
Annular
Diffractive

54. ORTHOKERATOLOGY
 Reversible and noninvasive technique of reshaping cornea by wearing
specially designed RGP lenses over a period of time
 Correction of Myopia
 Overnight Ortho K lenses- worn during sleep 8hrs - Corneal flattening – need
not wear in day time
 Effect is temporary and return to original shape if discontinued
 FDA approved for myopia correction – corneal refractive lenses

55. SPECIAL CONTACT LENS
COSMETIC CONTACT LENS
1. TINTED LENS-
 Can be opaque OR transparent
 Used for cosmetic purpose
2. PAINTED LENS-
 Painted with pigment to stimulate iris
 Useful in occlusion therapy, disfigured cornea, vision-disturbing conditions such
as albinism, aniridia , iris coloboma.

56. TYPES OF COSMETIC LENSES
 A. Iris painted with clear pupil [Albinotic lens]
 B. Black pupil and iris painted
 C. Pupil painted
 DISADVANTAGE
 Toxic effect
 Corneal edema

57. CONTACT LENS FOR COLOUR
BLINDNESS
 Using customize filters to change the wavelength of each color.
 Example- X-Chrome lens, Golden yellow lens

58. FUTURE ADVANCES
 Antibacterial CL – resist contamination
 Soft CL – that slow progress of Myopia
 Customised CL – correct individual ocular irregularities
 CLs with embedded circuit - For monitoring IOP in glaucoma
 CL measuring glucose levels in DM
 Drug delivery CL
 3D Cl for gaming

59. COMPLICATIONS
 Corneal
1. Epi edema due to hypoxia
2. Epi microcysts – depressed corneal metabolism – extended wear CL
3. Corneal abrasions – insertion , removal
4. SPKs – Mech inj, chemical toxicity – CL solutions
5. 3&9oCP staining – desiccation of cornea – interruption of tear flow dt pooe lens edge
fitting
6. Sterile corneal infiltrates – inflammatory response to specific antigen
7. Neovascularisation – hypoxia – deposits – tight thick lens
8. Microbial Keratitis – Mcc pseudomonas aeruginosa, Acanthameba
9. Warping – hypoxia-lactate accumulation-elevated CO2-reduced pH- endothelial bleb,
polymegathism, pleomorphism

60. COMPLICATIONS
 Conjunctiva
1. Allergic conjunctivitis – thiomersal containing CL solutions
2. GPC

61. CL SOLUTIONS
1. Wetting – buffer /cushioning agent – Polyvinyl alcohol, Polysorbate 80,
Polyethylene oxide,cellulose like derivatives
2. Cleaning – detergent to remove lacrimal film and mucus deposits and
bactericidal agent
1. Surfactant – emulsify lipids, solublise debris, remove accumulated contaminants
2. Enzymatic – cleans bound proteins and lipids
3. Soaking – bactericidal and hydate CL
4. Rewetting – artificial tears – polyvinyl alcohol, methycellulose

62. Thanks

64. IDEAL CONTACT LENS MATERIAL
 Meets corneal ’s oxygen requirements
 Physiologically inert
 Biocompatibility
 Excellent in vivo wetting
 Resists spoliation

65. IDEAL CONTACT LENS MATERIAL
 Dimensionally stable
 Durable
 Optically transparent
 Requires minimal patient care
 Cost effective
 Easily moldable

66. CONTACT LENS DESIGN
1. Monocurve / single-cut lens
2. Bicurve
3. Tricurve
4. Multicurve
5. Toric lens- has toric back surface
6. Bitoric lens-
Prism blast lenses
Truncated lenses
7. Lenticular lenses
8. Bifocal lenses

67. SIGN OF TIGHT FIT
 Lens coverage-uniform
 Movement <0.5 mm
 Fluctuating vision clears on blinking
 Progressive discomfort on wearing
 Circumciliary congestion
 Edge indentation of limbus
 Retinoscopic image is fuzzy
 To correct this-
 Increase B.C. by 0.2-0.3 mm
 Decrease T.D. by 0.5 mm

68. SIGN OF LOOSE FIT
 Poor centration
 Movement >1 mm
 Variable vision blurs on blinking
 Edges stand off , ejection of lens
 Retinoscopic image blur on blinking
 To correct this-
 Increase T.D. by 0.5-1 mm
 Decrease B.C. by 0.2-0.3 mm

69. Schematic flow chart of soft contact
lens fitting procedure
1. Insert trial lens symptom
 -comfort
 -visual
2. Slit lamp examination
 -Corneal coverage
 -Edge alignment
 -Primary gaze movement
 -Centration
Assessment of initial fit
 -vision assessment
 -visual acuity
 -over refraction