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CONTACT LENSES
DR PRATIBHA THILAK
CLASSIFICATION
 ANATOMICAL POSITION
 MATERIAL
 MODE OF WEAR
 WATER CONTENT
CLASSIFICATION OF CONTACT
LENSES
 FDA contact lens classification
Group 1 – Low water contenta(<50%),nonionic polymers
 Group 2- high water content(>50%),nonionic polymers
 Group 3- low water content(<50%),ionic polymers
 Group 4- high water content(>50%),ionic polymers
 Refractive correction
 Spherical contact lenses
 Toric contact lenses
 Bifocal contact
lenses(annular,segmental,diffractive,aspheric)
 Uv blocking
 With or without UV blocker

ANATOMICAL POSITION
 SCLERAL
 SEMI SCLERAL
 CORNEAL CONTACT
MATERIAL
 RIGID NON GAS PERMEABLE
 RIGID GAS PERMEABLE
 SOFT
MODE OF WEAR
 DAILY WEAR
 EXTENDED WEAR
 DISPOSABLE
WATER CONTENT
 LOW 0-40%
 MEDIUM 40-55%
 HIGH >55%
CONTACT LENS DESIGN
 SINGLE CUT
 LENTICULAR CUT
IDEAL MATERIAL
 BIOCOMPATIBLE
 TRANSPARENT,RI= TEARS
 GAS PERMEABILITY
 TOLERANCE
 MOULDING
 STERILITY
 STABILITY
 SURFACE CHEMISTRY
 WETTABILITY
 Complete= o *
 Partial=70*
 Non wetting=150*
 WATER CONTENT
 Wc =
 Wc=
oxygen tansmissibilty
thickness
 OXYGEN PERMEABILITY
 Coefficient of variable DK
 D=diffusion coefficient
 K=solubility
 OXYGEN TRANSMISSIBILTY
 DK/L
 L=thickness
 Light transmission
 Refractive index
 Heat resistance
 Dimensional stability
 flexure
RIGID NON GAS PERMEABLE
 PMMA
 Derivative of acrylic acid
advantages
disadvantages
High optical quality
Impermeable to oxygen
Excellent moulding
Hard
Non toxic
hydrophobic
RIGID GAS PERMEABLE
 Cellulose acetate butyrate
 Silicone acrylate
 Silicone
 Styrene
 fluoropolymers
HYDROPHILIC SOFT LENS
 HYDROGELS
 HEMA
 HEMA VP
 MMA PVD
INDICATIONS
 OPTICAL –refractive errors
 THERAPEUTIC-non healing ulcers,bullous




kp,recurrent corneal erosions,filamentary
keratitis,aniridia,coloboma,albinism
PREVENTIVE-symblepharon.exposure
keratitis,trichiasis
DIAGNOSTIC-gonioscopy,fundoscopy
OPERATIVE-goniotomy,vitrectomy
COSMETIC-corneal scars
CONTACT LENS vs SPECTACLES
Irregular astigmatism
Normal field of vision
Aberrations with spectacle use is eliminated
Binocular vision retained
Rain and fog do not condense
Clinical contraindications
 Active ocular disorders-inflammatory diseases of







lids,conjunctiva, cornea, anterior uveal tract
Corneal anaesthesia due to any cause
Caution-glaucoma and retinal detachment
Allergic predisposition,contact dermatitis
Pregnancy(fitting)
Lack of manual dexterity
Psychological factors
High altitudes
Optics of Contact lenses
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
 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
 Combined lens


Curvature of both surfaces contribute
Both glass lens & fluid lens give dioptric power.
CLINICALLY IMPORTANT FEATURES
 Field of vision
larger field
avoid peripheral distortion
 Image size
 Power of CL
Vertex Distance
The power of a lens is the reciprocal of the focal length, the
relative or effective power of a corrective lens changes with
the placement of the lens or the distance between the lens
and the eye.
This relationship is expressed by the formula
D= 1 /f
Where D = power in diopters, f = focal length in meters.
Example. In a +10.00 diopter lens, the focal length is 10 cm
(0.1 m):
D = 1/0.1
D= 10
- The closer a lens comes to the corneal surface
and nodal point of the eye, the greater the plus
power required and the less the minus power
needed to correct the refractive error.
-The formula for the change in vertex power of
the lens is
Δ= D²d
Where Δ = change in power due to vertex
distance; D = lens power; d = distance lens in
meters.
An aphakic spectacle correction of +13.00
diopters at 13 mm in from the eye.
power of the contact lens be?
Δ = 13² x 0.013
Δ = 169 X 0.013
Δ =2.197 diopters.
The power of the required contact lens corrected
for vertex distance is
+13.00 +2.20= +15.20 D
If a -10.00 lens is at 15 mm from the eye the power of the required
contact lens is calculated as follows:
Δ =D²d
Δ = -10² X 0.015
Δ = 1.5 D
The total required power is
-10.00 + 1.50= -8.50 diopters
- The power and position of the correcting lens must be such
that the focal point of the lens is conjugate to the focal point
of the eye.
DESIGN DESCRIPTION AND
PARAMETERS
Overall diameter
Linear measurement of greatest distance across physical
boundaries of lens
PMMA-7.5-8.8 mm
RGP-9-9.8 mm
Soft contact lenses-13-15mm
1.
 Optical zone diameter
 dimension of Central optical zone which is meant to
focus rays on retina
3. Curvatures
Ant. Curvatures:
•
C.A.C (Cental ant.Curvature)- ant surface of
optical zone,determines power of cl
•
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
 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.
CL can have bicurve, tricurve or even multi curve
contour design.
4. BlendSmooth area of transition
of radius of
curvature from one curve to other
Light
Medium
heavy
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
 Edge lift-extent to which peripheral curvatures differ
from base curve
 PPMA > RGP
 Greater need for tear renewal
 6.Power of CL-
determined by central ant & post surfaces at
O.Z. determined by the ammetropic correction
required
Measured in terms of posterior vertex power in
diopters
7.Tint- to reduce the glare for cosmesis
 Central thickness-measured at geometric centre
 Varies depending upon posterior vertex power of
lens
FITTING SPHERICAL
RIGID GAS PERMEABLE
CONTACT LENSES
CONTACT LENS FITTING
 Patient screening
 Preliminary examination & measurements
 Trial lens fitting
 Lens dispensing
 After-care
PATIENT SCREENING
Factors to consider in patient selection
 Anatomical and physiological
 Psychological
 Pathological
 Personal and occupational needs
 Refractive
HISTORY
 General health
 Ocular health
 Medication
 Ocular history
 Occupational, recreational, environmental
factors
 Refraction-Retinoscopy
-Subjective verification
-BCVA
-Spherocylinderical notation-Vertex distance
 Keratometry
PRELIMINARY MEASURES
 Corneal radius of curvature
 Corneal diameter
 Lid characteristics
 Pupil size
 Spectacle refraction
TRIAL LENSES
Range of designs required:
 For low and high minus
 For low and high plus
 Diameters
 BOZR
TRIAL LENS SELECTION
Based on:
 Corneal topography
 Corneal size
 Prescription
 Pupil size
 Lid position
 Lid tonus
TRIAL LENS SELECTION
Corneal topography controls:
 BOZR
 BOZD
 Total lens diameter
TRIAL LENS SELECTION
Corneal size controls:
 Lens total diameter
 BOZD
TRIAL LENS SELECTION
Prescription controls:
 Total lens diameter
TRIAL LENS SELECTION
Pupil size controls:
 BOZD
TRIAL LENS SELECTION
Lid tonus controls:
 Lens total diameter
TRIAL LENS SELECTION
 The trial fitting lens will be a guide
to the lens design which is
considered optimal for the patients
eye
Base curve
 Detemined from keratometry
 Flatter k reading
 Astigmatism-steeper k
 astigmatism 0.5-1.0-BC 0.25 D> steeper K
 1-2 D0.5 D steeper k
 > 2 D1/3 toricity added to K
TRIAL LENS
FITTING
ASSESSMENT
POSITION OF LENS &LID POSITIONS
EVALUATION:
Base curve determination
TRIAL FITTING: DESIRED RGP LENS
FITTING
EFFECTS OF DIAMETER
same BOZR
S2 > S 1 > S3
S1
S2
D1
‘Original Fit’
D2
‘Steeper’
same BOZR
flatter BOZR
S
S4
3
D4
‘Same’
S1
D1
 DS
D3
‘Flatter’
4
4
EFFECTS OF SAGITTAL HEIGHT
Constant Diameter
S2 > S1 > S3
S2
S1
D1
D1
Steeper BOZR
‘Original BOZR’
S3
D1
Flatter BOZR
Finalization of power
 Once a lens of satisfactory fit has been found,the
power to be ordered has to be finalized.
POST FIT MANAGEMENT
 Ordering rigid lenses
 Examination of ordered lens
 Evaluation of ordered lens
Ordering rigid lenses
 Specify known variables
 Base curve radius
 Optic zone diameter
 First back peripheral zone
 First peripheral curve radius
 Second peripheral curve radius
 Overall diameter
 power
AFTER - CARE
 Investigate complaints
 Perform general ocular examination:
 Over-refraction
 Slit-lamp microscopy
 Other tests particular to the patient
 Assess lens fit
 Review lens care regimen
 Schedule next after-care visit
FITTING SPHERICAL
SOFT CONTACT LENSES
SOFT LENS FITTING PHILOSOPHY
Corneal Apex
Limbus
Peri-Limbal Region
INITIAL PATIENT WORKUP: History
 General ocular examination
 Refraction
 Keratometry
 Corneal Diameter
SELECTING THE INTIAL TRIAL LENS:-
1- Selection of lens diameter :- Obtain patient's horizontal visible iris diameter
(HVID) measurement
- CL diameter = HVID + (1 to 3mm, average =
2mm)
- Increase or decrease lens diameter in 0.50mm step
if necessary during evaluation process.
- Most soft CLs are available from diameter of
13.50mm to 15mm.
2- Selection of Base curve (BC)
- SCL are usually fitted flatter than the flattest K
- The flattest K minus 3.00 diopter
BC = flattest K - 3.00D
- Convert the diameter value to millimeters
using a converting table.
- Increase or decrease BC in 0.30mm steps if
necessary.
 Measure Ks
 Select trial lens from manufacturer's fitting
guide for lenses
 Add 0.7 mm or more to flattest K for less
flexible lens materials (thicker, low water)
 Add 0.3 - 0.6 mm for standard and flexible
materials (thinner, high water)
3- Selection of lens power
- Refraction prescription must be converted to
minus cylinder from:
1- If cylinder in refraction is (less than or equal to)
less or equal ≤ 0.50D,
power = spherical component
2 - If cylinder in refraction is 0.750D to 1.00D,
the contact lens power = spherical equivalent
(spherical component + 1/2 Cyl)
EVALUATION OF TRIAL LENS FIT:1.Base curve Evaluation:- A well-fitted lens will show
five basic qualities;
 good centration,
 adequate movement,
 stable vision,
 crisp retinoscopic reflex,
 clear undistorted keratometry mires, and
 clear endpoint over-refraction
SOFT LENSES CENTRATION
DECENTRED SOFT LENS
 2.Lens diameter evaluation:-
IDEAL-should extend 1.0-1.5 mm over the cornea.
 3.Lens power evaluation:-
CONTACT LENS FITTING
APPROACHES FOR SOFT CL’S FITTING: Corneal Diameter Technique
 Corneal Curvature Technique
 Median Fit Technique
 Saggital Depth Tecnique
Corneal diameter technique:-
Corneal Curvature Technique:K-reading
Less < 41.00D
Soft CL Base Curve
Flat ( >9.00mm)
Between 41.00– 45.00 D
Medium (8.00-.00mm)
Larger > 45.00D
Steep (< 8.00mm)
Median Fit Technique:-
Sagittal Depth Technique:-
Correction
The following steps should be taken to correct a
loose lens:
- Either changing the base curve by decreasing it by
0.2 to 0.3 mm
OR
- Increasing the diameter of the lens by 0.5mm up to
15mm.
The following steps should be taken to correct a light
lens:
- Either changing the base curve by increasing it by
0.2 to 0.3 mm
OR
- Decreasing the diameter of the lens by 0.5mm.
Extended Wear Lenses: Fitting of Soft EWL’s:-
Base curves of 8-9 mm and
Overall diameter of 13.5 -14.5 mm are
commonly used
 Fitting of Rigid EWL’s:-
selected RGP-EW lenses should have a DK value
of 90
SPECIAL CONTACT LENS FITTING:
CONTACT LENS
FITTING IN
ASTIGMATISM
LENS TYPES: RGP LENSES-Front surface toric
Back surface toric
Bitoric
Peripheral toric
 SOFT LENSES-Spherical
-Toric
FRONT SURFACE TORICS
 Spherical back surface
 Base down prism
 Cylindrical front surface
 Circular design
 Truncated design
SPHERICAL BACK SURFACE
Start with:
 Optical zone about 7.70 mm
 Total diameter about 9.20 mm
 Tricurve
BASE DOWN PRISMS
 Meridional orientation
 Requires 1 - 1.75 prism dioptres
 Provide thickness/weight differential
 Nasal offset by 10-15 degrees
RIGHT EYE
UPPER LID
CORNEA
LENS
LOWER LID
PRISM BASE AT 280o
BASE DOWN PRISM
 The tendency for the lens to rotate with
a blink is counteracted by the thickness
differential of the lens
 The heavier prism base helps to
maintain meridional orientation of the
cylindrical correction
BASE DOWN PRISM
 There is a continuous variation in the
thickness across the lens
 Apex is the thinnest portion and the
base the thickest
CYLINDRICAL FRONT SURFACE
 The astigmatic correction is provided by a
plus cylinder on the lens front surface
CIRCULAR DESIGN
 Optical zone is centred
 Base down prism
 Easier manufacture and duplication
TRUNCATED DESIGN
 Inferior part of lens is truncated
 Resets against lower lid for stability
 Prism ballast
 Optical zone is decentred superiorly
TRUNCATED LENS
TRUNCATED DESIGN
Possible contour
 Taper from front to back
 Flat base
 Taper from back to front
a
b
c
TRUNCATED DESIGN
 Shaped to match lower lid contour
 Removes some of the prism ballast effect (more
in minus powers than in plus)
TRUNCATED DESIGN
TRUNCATION
DOUBLE TRUNCATION
A superior truncation can be added to
increase lens stability if a single
truncation is not sufficient
DOUBLE TRUNCATION
DOUBLE TRUNCATION
UPPER LID
LENS
CORNEA
TRUNCATIONS
LOWER LID
BACK SURFACE TORIC
The back surface toric design is chosen to
optimize the lens-to-cornea bearing
relationship that would be unsatisfactory with
a spherical lens
FITTING REQUIREMENTS
 Corneal cylinder of 2.00D or greater
 Physical compatibility with the cornea
 Stable meridional orientation
LENS DESIGN
 Back surface is toric
 Front surface is spherical
BITORIC
A bitoric lens is required when a back
surface toric/spherical front surface lens
results in an unacceptable amount of
residual astigmatism
LENS DESIGN
 Toric back surface for physical fit
 Toric front surface for astigmatism
correction
 Rotational stability
PERIPHERAL TORIC
 A toric periphery with a spherical back optic
zone is designed to improve the fit on the
cornea of moderate toricity
PERIPHERAL TORIC
 A toric peripheral curve(s) design allows
even bearing and/or clearance at the
periphery, resulting in improved centration
and comfort
LENS DESIGN
 Spherical back optic zone
 Toric back peripheral curves
 Spherical front optic zone and
peripheral curves
 oval shaped optic zone
10.60
8.6
0
9.0
0
11.00
Flatter secondary
and peripheral
curves
Steeper secondary and peripheral
curves
PERIPHERAL TORIC FEATURES
 Improved lens centration
 Reduced uneven bearing
 Prevents peripheral bubble formation
CONTACT LENS FITTING IN APHAKIA: RGP LENSES-Single cut
-Large lenticular cut
 SOFT LENSES-Particularly EWL
CONTACT LENS FITTING IN KERATOCONUS: Rigid CL’s fitted with 3
point touch technique:
 Sopper’s technique
 Piggyback lenses
CONTACT LENS FITTING IN PRESBYOPIA: Monovision CL’s
 Modified Monovision CL’s
 Binocular Bifocal CL’s- Annular Bifocal
- Segmental
- Aspheric
- Diffractive
CONTACT LENS FITTING IN MYOPIA: High myopia >-8.00 d
 Relatively flat ant. Surface
 Peripheral lenticular bevel
THERAPEUTIC CONTACT LENS
 Bandage lenses
 Provide mechanical support
 Facilitate wound healing
 Proper surface hydration
 Reduce discomfort from corneal surface disorders
 Drug delivery system
Types and choice
 Hydrogel therapuetic CL
 High water content-desmatocoele
 ABK/PBK
 Coexistent corneal or anterior segment
inflammation
 Moderate water content
 Low water content
 Epithelial defect
COSMETIC SOFT CONTACT LENS
 Indications
 Disfigured corneas
 Albinism/aniridia/iris
colobomas/photophobia/diplopia
 Occlusion therapy
 Pure cosmesis
COMPLICATIONS OF CONTACT LENS WEAR
 CORNEAL
 CONJUNCTIVAL
 CONTACT LENS RELATED
CORNEAL COMPLICATIONS
 Epithelial edema
 Epithelial microcysts
 SPKs
 3 and 9 o’clock staining
 Sterile corneal infiltrates
 Neovascularisation
 Microbial keratiti
 Warping
 Endothelial changes
CONJUNCTIVAL COMPLICATIONS
 Allergic conjunctivitis
 GPC
 SLKC
CONTACT LENS RELATED COMPLICATIONS
 Physical damage
 Discolouration
 Lens loss
 Deposits
CONTACT LENS SOLUTION
 For hydrophobic rigid CLs
 For hydrogel soft CLs
 For both
Wetting/cleaning/storage/rewetting/multifunctional
Vehicle/buffering agent/preservatives
 Low concentration of preservatives
 Benzalkonium chloride
 Chlorobutanol
 Thiomersal
 Chlorhexidine
 Ethylene diamine Tetra acetic acid
 Sorbic acid
 Potassium sorbate
Wetting solutions
 Minimise friction between lens and palpebral
conjunctiva and cornea
 Buffer or cushioning agent for brief period to be
replaced by lacrimal fluid
characteristics
 Wet thoroughly,spread entirely
 Form a film
 Non-irritating,non sensitizing
 Not leave a residue
 Cleaning antiseptic and self preserving
 Proper degree of viscosity
 Allow wear
agents
 Polyvinyl alcohol
 Polysorbate 80
 Polyethylene oxide
 Cellulose like derivatives
 PVP
CLEANING SOLUTIONS
 Detergent and bactericidal action
 Surfactant and enzymatic cleaners
 Surfactant-non-ionic
 Enzymatic- papain,lipase tablets
SOAKING SOLUTIONS
 Bactericidal
 Hydrated state maintainance
REWETTING AGENTS
 Rewet corneal surface or lens while it is on cornea
Agents in lens solutions
 Benzalkonium chloride
 Chlorbutanol
 Thiomersal
 Chlorhexidine
 Hydrogen peroxide and povidone iodine
 EDTA
 Polyvinyl alcohol
CONTACT LENS CARE
Personal hygiene
Removal of lens
Storage lens
Routine cleaning
Enzyme cleaning
Disinfection
Special lens care
 Personal hygiene
 Hands washed,dried,nails clipped
 Hand cream not to be used
 Removal of lens
 Lens cleaned before storage
 Storage of lens
 Hard lens-dry state,flat case
 Lens cases to be cleaned
 Soft lens-wet state,hydrating kit
 Routine cleaning
 Hands washed.dried,lens kept concave side up
 Solution added and rubbed for 15- 30 sec
 Lens held between finger and thumb
 Held in running water
 Soft lens
 Not washed with water
 Normal saline
Enzyme cleaning
 Once a week
 Papain
 For protein coating
Enzyme tablet+distilled water+lens for 4 hours
 Lens rinsed clear of enzyme
 Repeated enzyme cleaninglens decentres more
DISINFECTION
 Destroys vegetative microorganisms
 Moist heat and chemical methods
Thermal disinfection
 Saline based solution of thiomersal + EDTA
 boiling
 For 80 *C for 10-15 mins
 Suspending lens case over steam column
 Above procedure in >100 * C with 5 lbs of steam
pressure
Chemical disinfection
 Cold disinfecting system
 Thiomersal-alkyl triethanol ammonium chloride
 Thiomersal sorbic acid or potassium sorbate
 Hydrogen peroxide system
 Chlorine tablets with water
 Iodine based solution
Special lens care technique
 In womencontamination with cosmetics
 Insert lens before cosmetics
 In men contamination with hair oil
 In childrencarelessness
Special cleaning
 Laboratory cleaning to remove grease paint nail
polish etc