HISTORY,MATERIAL,

NOMENCLATUREOf Contact Lenses

Presentor:- Dr.Pushkar DhirModerator :- Dr.OP GuptaModerator:- Ms Sheeba

D VINCI CODE• In 1508, Leonardo da Vinci sketched

the first forms of new refracted surface on the cornea.

• He used the example of a very large glass bowel filled with water; immersion of the eyes in water theoretically corrected vision.

• Sketches of a schematic eye

• Describes the mechanism of image formation from the cornea to the optic nerve

• Some drawings may represent the idea of a ‘contact’ lens

??DUMBULDORE??

RENÉ DESCARTES (1637)

• Understood that better vision could be achieved by enlarging the retinal image

• Sketched an elongated tube filled with water placed against an eyeball

• Demonstrated the principal of the telescope, not the contact lens

H2O

D GAME CHANGERADOLF E FICK (1888)• Fick was born in Germany in 1852.

• Used blown glass shells which appeared to be well tolerated.

• Observed corneal clouding, conjunctival and limbal injection.

• Discussed the need for lens disinfection and the concept of adaptation to lens wear.

• Observed that corneal clouding did not occur as quickly if an air bubble was inserted behind his lens along with a 2% glucose solution.

FA MÜLLER and SONS (1887)

• Artificial eye makers in Wiesbaden, Germany• Made lenses from blown glass• Very regular curvature, no sharp edges at the corneo-scleral junction• Designed a lens for ptosis correction

CARL ZEISS of JENA (1911)• Made lathe cut lenses from molds• Lathe cutting resulted in a better optical

performance• First commercially available trial lenses• Complete trial set contained 21 lenses• Lenses were afocal • Fitting determined by fluorescein and

white light

8

Evolution of Contact Lens

PMMA

40s 50s 60s 70s 80s 90s 2000

Silicone Hydrogel

+ silicone to increase Dk + surface treatment to

resist deposit

+ water to improve Dk & comfort

Hydrogel (HEMA based)Low water High water Ionic Non-ionic

+ silicone to increase Dk

RGP

• In 1954,• Professor Otto Wichterle &

Dr Drashoslav Lim suggested to experts in the medical plastics field that a plastic which more closely simulated living tissue would be more suitable for orbital implants than the metallic elements being considered.

IDEAL MATERIAL

BIOCOMPATIBILITY- should not harmful OPTICAL PROPERTIES- transparent GAS PERMEABILITY – wearing time TOLERANCE –gas permeability and design. MOULDING STERILITY STABILITY - in all dimentions SURFACE CHEMISTRY - easily wettable

CONTACT LENS CLASSIFICATIONBASED ON PURPOSE OF USE

Optical

Therapeutic

Cosmetic

ANATOMICAL

LOCATION Scleral contact lenses

Semi-scleral contact lenses

Corneal contact lenses

NATURE OF LENSRigid

non-gas permea

ble contact lenses(PMMA)Rigid

gas permea

ble contact lenses(CAB)

Soft contact lenses(HEMA)

BASED ON WATER

CONTENT

BASED ON WEARING SCHEDULE

Daily wear

contact lenses

(hard

contact lenses)Extended wear contact lenses

(soft contact lenses)

Disposable

contact lenses

12

Uses of Contact Lens

Purpose

Cosmetic

Spherical

Toric

Presbyopic

Optical

Keratoconus

Bandage Lens

Drug Delivery

Myopia Control

Therapeutic

Enhances Performance

Color Filters

C L WHICH COVER THE CORNEA & THE CONJUNCTIVAOVERLYING THE SCLERA

CONTACT LENSES THAT COVER THE CORNEA, BRIDGE THE LIMBUS & LIE PARTIALLY ON THE CONJUNCTIVAL TISSUE

CONTACT LENSES THAT CONFINED TO THE CORNEA

CLASSIFICATION OF CL BASED ON THE MATERIAL

NON GAS PERMEABLE

GAS PERMEABLE

PMMA, Lucite, Plexiglass, Perspex

Advantages-1. Lighter than glass2. Non toxic3. Easy to manufacture

Disadvantages4. 1-2% water content5. Dk = 0(not gas permeable)

1. Cellulose Acetate Butyrate

2. Silicone acrylate (Copolymer of pmma & silicone

containing vinyl monomer.

3. Silicone- D-Lack of wet ability , not popular. A- used in paeditaric aphakic in 1st yr of

life because eof high oxygen perm + tight fit

4. Styrene 5. Fluoropolymers- for extended wear.

RIGID GAS PERMEABLE

A-Low oxygen permeability – Dk of 4.5-10Relatively good wet ability – better than PMMA.Dis-Good protein resistance but prone to lipid deposits

Advantages of Rigid Contact Lens

• Better Quality of Vision• More Durable• Correction Of Astigmatism• Deposit Resistance• Less of Chance of infection• Cost is less• Less Stable• less comfortable,tough adapataion

Advantages of Soft Contact Lens

• Very comfortable & easy to adapt• Larger & adhere more tightly

to the cornea• No Spectacle Blur• Doesn’t correct Astigmatic Error

CLASSIFICATION OF CL BASED ON THE WATER CONTENT

LOW WATER CONTENTLOW WATER CONTENT Less then or equal to 50%

HIGH WATER CONTENTHIGH WATER CONTENT Greater than 50%

The amount of fluid taken up by a contact lens material

Ranges from 38% to 79%

Increase in water content increases oxygen permeability

20% increase in water doubles oxygen permeability

Low Water ContentAdvantages:

•Less susceptible to environment changes•Low protein deposition•Ease of manufacture•More wettable•Compatible with all lens care

product

Disadvantages: •Low Dk•Less flexible•Thin lenses difficult to handle

High Water Content

Advantages: •Higher Dk•More flexible•Faster restoration of shape following deformation.

Disadvantages:•More fragile•More deposit prone .•Difficult to manufacture•Lower tensile strength•Cannot be made too thin

CLASSIFICATION OF CONTACT LENSES

SOFT CONTACT LENSES

Ionic

Nonionic

---- ++ --

--__

__ ____

__

Ionic materials

Advantages:»More wettable»Less Denaturation of tear proteins

Disadvantages: »More deposits prone»Deposits may be bound

CLASSIFICATION OF CONTACT LENSES

Soft hydrogel contact lenses (FDA classification)

Group-1 Non- ionic, low water content CLGroup-1 Non- ionic, low water content CL

Group-2 Non-ionic, high water content CLGroup-2 Non-ionic, high water content CL

Group-3 Ionic, low water content CLGroup-3 Ionic, low water content CL

Group-4 Ionic, high water content CLGroup-4 Ionic, high water content CL

Contact Lens Parameters

• Base Curve• Diameter• Power

Base Curve

The curvature of the central part of the posterior surface of a lens.

It is at optic zone area

Expressed either in millimeters (mm) of radius of curvature or in diopters (D)

Calculated with help of Keratometer

Diameter–The maximum edge to edge width of a lens–Measured in millimeters (mm).–SCL diameter = HVID + (1 to 3mm, average = 2mm)

9.50mm 8.50mmTotal diameter

• Power»The ability of the lens to diverge or converge light

»Measured in diopters (D)

»FRONT VERTEX POWER: It is the reciprocal of the distance from the front surface of the contact lens to the first focal point

»BACK VERTEX POWER: It is the reciprocal of the distance from the back surface of the lens to the second focal point

FVP BVP

F1 F2

Parameters of

Contact Lens

Water content

Center thickne

ss

Optic Zone

Sagittal DepthWettabil

ity

Oxygen Permea

bility

Oxygen Transmissibility

Lens Curves

Lens Design

WettabilityThe angle that the edge of a bead of water makes with the surface of a contact lens is called wetting angleThe smaller the wetting angle, the greater the wettability of the lensIn vitro: Wetting angle

- Sessile drop- Wilhelmy plate - Captive buble

In vivo: Tear Coverage Tear Break-up time Drying time

70

• Low Dk material– Below 20

• Mid Dk material– 20 to 40

• High Dk material– 40 to 60

• Hyper Dk material– Above 60

O2

O2

O2

O2O2

O2O2

O2

O2O2

O2

O2

O2

O2O2

O2O2

O2

O2

O2

O2

O2

O2

O2

O2

OXYGEN PERMEABILITY

GAS TRANSMISSION

Oxygen transmissibility

Dk/L

D = Diffusion coefficient (cm/sec)

k = Solubility of gas in the material(cm3/cm2 mm Hg)

L = Thickness of material (mm)

Depends on:Permeability of the lens materialThickness of the lensTemperature at which the test is performed

Oxygen transmissibilityThe value for Dk/ t will decrease with increasing thickness of the lens

Daily wear, the recommended Dk/ t of a contact lens is around 30Extended wear, the recommended Dk/ t of a contact lens is 87

Low Oxygen transmissibility can result in corneal changes:• Microcysts• Polymegathism• Corneal pH• Edema• Blebs

O2O2

Ballasted Lens Fenestrated Lens

Lenticular Lens

Toric Lens

Truncated Lens

•Lens is made thicker at the bottom in order to prevent rotation & maintain orientation

•Rigid lens + small holes to allow more volume of oxygen & tear fluid to reach cornea

•Commonly used for aphakic patients

•Lenticular plus power lenses usually have thick central optic zone and a wide peripheral bevel

•Used to correct astigmatism

•In front surface toric lenses the two different radii are found on the anterior surface of the lens•In back toric surface lenses the two different radii are found on the back surface of the lens

A lens with an edge cut off flat

Used in some toric and bifocal contact lens design

References• Introduction: FREE download of the 'IACLE

Contact Lens Course' complete survey to access

• Download the 'IACLE Contact Lens Course'

• ICLC PPT Contact Lens Fitting • Making Contacts: Contact Lenses in History - Insig

ht Optometrists

• contact lens: Definition from Answers.com

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