Intraocular lens and contact lens Keerthi N S Page 1
Intraocular lens• Implanted lens in the eye.• Replaces the existing crystalline lens, because:- It has been clouded by cataract Refractive surgery to change optical power Page 2
History:-• Sir Harold Ridley was the first to successfully implant an intraocular lens on November 29, 1949, at St Thomas Hospital , London.• That first intraocular lens was manufactured from Polymethylmethacrylate (PMMA.). Page 3
What would have made him think about the idea of implanting a lens in cataract surgery???
It is said that the idea of implanting an intraocular lens came to him after an intern asked him “ why he was not replacing the lens he had removed during cataract surgery”.
Why did he use acrylic plastic material???
The acrylic plastic material was chosen because Harold Ridley noticed that it was inert, after seeing RAF (Royal air Force) pilots of World War II with pieces of shattered canopies in their eyes.
Parts of IOL•Central partoverlying the opticaxis , called asoptic and• peripheral arms,called haptics• use of haptics:•to hold the lens inplace within thecapsular bag insidethe eye. Page 8
• Rigidity :-• flexible or rigid• Optic size :-• 5-7mm• Shape:-• Round or oval• Spheric or aspheric• Plano convex or biconvex Page 11
• Edge :-• Square or rounded• Holes in the optic:-• Present or absent• To keep IOL in position Page 12
Different types of haptic angulationrelative to the plane of optic:-For posterior chamber lens:- 100 anterior angulation to keep the optic part away from the pupil.For anterior chamber lens:- Posteriorly angulated lens to vault the intraocular lens away from the pupil
Suitable position for implanting IOL in eye • Best placed in posterior chamber in the capsular bag.
Other positions:-In the ciliary sulcus • Posterior capsule supported tear by the anterior • zonular dialysis capsule. In anterior chamber • If posterior chamber supportedby the angle is not feasible for of anterior implanting a lens chamber Page 17
Power of intraocular lens • To be calculated carefully to meet theImportance:- visual requirements of individual patient. Page 18
Power of intraocular lens• Calculated by various formula Widely used formula• Modified Sanders-Retzlaff-Kraff formula (SRK) Page 19
Modified Sanders-Retzlaff- Kraff formula Based on the statistical correlation between calculated and observed refractive error after ocular implantation.
Modified SRK Formula E=A - 2.5L - 0.9K Parameters used in the formula are estimated by A-scan ultrasonographic sonometry and keratometry
E=A - 2.5L - 0.9K E: A:Emmetropic Predeterminedpower of eye constant of IOL K: L: Average ofAxial length in keratometry mm readings
• Most IOLs fitted today are fixed monofocal lenses matched to distance vision. Page 24
Contact lensis a thin optical lensworn on the eyeResting on the surfaceof cornea.Contact lenses areconsidered medicaldevices and can beworn to correct vision,for cosmetic ortherapeutic reasons.
Adolf Fick• In 1888, Adolf Fick was the first to successfully fit contact lenses, which were made from blown glass
Purpose of wearing contact lens • . Aesthetics and cosmetics, to avoid wearing glasses • For more visual reasons.
Uses of contact lens
Corrective contact lenses To improve vision, by correcting refractive error By directly focusing the light with the proper power for clear vision Spherical contact lens :myopia and hypermetropia , aphakia Aniseikonia; in unilateral aphakia
Toric contact lens has a different focusing power horizontally than it does vertically, astigmatism Some spherical rigid lenses can also correct for astigmatism. Presbyopia presents an additional challenge in the fitting of contact lenses.
Other types of visioncorrection: colour blindness For those with certain color deficiencies, a red-tinted "X-Chrom" contact lens may be used. Although the lens does not restore normal color vision, it allows some colorblind individuals to distinguish colors better
Cosmetic contact lenses To change the appearance of the eye. Also correct refractive error.
Merits over spectacles Typically provide better peripheral vision Do not collect moisture such as rain, snow, condensation, or sweat. This makes them ideal for sports and other outdoor activities. Keratoconus and aniseikonia that are typically corrected better by contacts than by glasses.
Types of contact lens• Hard• Soft• Rigid-gas permeable
Hard contact lens 1930-1970 Made of PMMA Do not allow enough oxygen to reach the eye. Difficult to adapt But visual clarity is good Used in astigmatic corneas Less acute infective Indications for use are now restricted
Soft contact lens Made from gel like plastic, hydroxy methyl methacrylate Contains 79% water Better initial comfort But prone to deposits;is disposables;15 hrs Difficult to keep clean and and to handle
Continuous wear soft contact lens• Increased water content• Increased oxygen permeability• Allow up to 6 times more oxygen to cornea than ordinary contact lens• Can be worn upto 30 nights and day• But has increased risk of infections than daily wearing lenses.
Rigid gas permeable lenses• Oxygen permeable lenses• Made from:firm,durable plastic that transmits oxygen• A co-polymer of PMMA and silicone and cellulate acetate butyrate• Do not contain water; resists deposits; decreased risk of bacterial infections
• Easy to clean• Disinfect• Do not dehydrate• Last longer than soft lenses• Rigid; easy to handle than soft lenses• Retain their shape; provide sharp vision
Risks of cosmetic contact lens Carry risks of mild and serious complications ocular redness,pain irritation, and infection.
Complications due to contact lens wear affect roughly 5% of contact lens wearers each year Improper use of contact lenses may affect the eyelid, the conjunctiva, and the various layers of the cornea. Poor lens care can lead to infections by various microorganisms including bacteria, fungi, and Acanthamoeba
Measures to be taken prior to use a contact lens To measure • Retinoscopy anterior curvature of lens • keratometry To rule out dry eye,blepharitis • Tear film and cornea or pre-existing examined under slit lamp keratopathy Evaluation of • Trial lenses are evaluated Fitting under biomicroscope
Tear film examination • Fluorescein that Highlight tear film are useful in fitting rigid lens • Ideal lens show a minimal , uniform film behind the contact lens • Pooling of dye in centre denotes: a steep fit • Absence of dye in centre: a flat fit
HARD CONTACT SOFT CONTACT RIGID GAS LENSES LENSES PERMEABLE LENSESOxygen deliveryVisual clarityUse inastigmatismAdaptationDepositsDurability
HARD CONTACT SOFT CONTACT RIGID GAS LENSES LENSES PERMEABLE LENSESOxygen delivery Poor High Moderate to highVisual clarity Good Need to refocus Clear vision after a blinkUse in astigmatism Possible Less suitable PossibleAdaptation Required Not required RequiredDeposits Few Accumulate over Few timeDurability May scratch Tend to tear Do not scratch or tear