CONTACT LENSES

CONTACT LENSES

CONTACT LENSES Optical devices placed directly in front and adjacent to cornea To rectify refractive errors To provide protection To improve cosmetics

CLASSIFICATION OF CONTACT LENSES Anatomical position Scleral contact lenses Semi-scleral contact lenses Corneal contact lenses Nature of material Rigid non-gas permeable contact lenses(PMMA) Rigid gas permeable contact lenses(CAB) Soft contact lenses(HEMA) Mode of wear Daily wear contact lenses(hard contact lenses) Extended wear contact lenses(soft contact lenses) Disposable contact lenses PMMA-poly methyl metha crylate CAB-cellulose acetate butyrate HEMA-hydroxy ethyl metha crylate

CLASSIFICATION OF CONTACT LENSES FDA contact lens classification Group 1 – Low water content (<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) Color Green Brown Blue Uv blocking With or without UV blocker Toric contact lenses are used to correct cylindrical errors…. Torsion of a toric contact lens is prevented by incorporating +2.00 D base down prism to weight the lower pole of the lens or by removing the lower 0.5-1 mm of lens(truncation) to allow it to sit on the edge of the lower eyelid.

INDICATIONS OF CONTACT LENSES Optical indications Anisometropia Unilateral aphakia High myopia Astigmatism Keratoconus Anisometropia is a condition in which both eyes have different refractive powers i.e, are in different states of myopia or hypermetropia.it can adversely affect the development of binocular vision in infants and children if there is a large difference in the clarity b/w the 2 eyes.the brain will often suppress the vision of blurred eye in a condition called Amblyopia or lazy eye.it also leads to diplopia and Aniseikonia which is difference in the size of 2 eyes images.contact lenses are useful here because they have short vertex distance n are thin so the image size is changed less as compared to spectacles.unilateral aphakia also leads to image magnification,aniseikonia,diplopia and divergent squint in adults(esotropia in children).contact lenses cause significantly less magnification than spectacles.

Contd Therapeutic indications(BCLs) Corneal diseases Iris diseases Non healing corneal ulcer Recurrent corneal erosion syndrome(corneal dystrophy) Bullous keratopathy Filamentary keratitis Iris diseases Aniridia , coloboma , albinism Other conditions Post surgery(corneal transplant,LASIK,PRK) Bell’s palsy Bleb leak posttrabeculectomy Lid abnormalities(Entropion,lid lag,trichiasis) Promotion of epithelial healing Epithelial Defects can be healed more quickly by protecting the corneal regenerating epithelium from constant rubbing action of lids Recurrent corneal erosion syndrome if associated with corneal dystrophy Pain relief Bullous keratopathy can be managed by soft contact lens Filamentary keratitis – soft contact lens plus artificial tears

INDICATIONS OF CONTACT LENSES Preventive indications Symblepharon , restoration of fornices in chemical burns Exposure keratitis Cosmetic indications Corneal scars Cosmetic scleral lenses in pthisis bulbi To change color Occupational indications Sportsmen Pilots

INDICATIONS (CONTD) Miscellaneous Ptosis – haptic contact lens if no Bell’s phenomenon Occluders – amblyopia in children Vehicle for drug delivery – soaking a soft contact lens Protection of normal corneal epithelium in trichiasis or threatened exposure keratopathy

Advantages over spectacles Visual fields Optical aberration Accommodation and convergence Prisms Tint A contact lens moves with the eye…. Good vision in all positions of gaze…. Dec peripheral distortions…..inc VF… Inc demand for accommodation n convergence bcoz of no prismatic effect…myopic spectacles have base-in prismatic effect which reduces the amount of A n C reqd for near…. 3 D of prism power to contact lens easily without making it too thick to be practical…prism is base down…impossible horizontal prismatic correction… With scleral contact lenses,both vertical n horizontal prisms incorporated…6 prism D…

CLINICALLY IMPORTANT FEATURES Field of vision larger field avoid peripheral distortion Image size Spectacle frame reduces the field of corrected vision by about 20 degrees. Plus spectacles and contact lenses both increases the image size but contact lenses do so to lesser extent.vice versa for minus lenses.

CLINICALLY IMPORTANT FEATURES Accommodation Myopic correction– increased requirement Hypermetropic correction– decreased requirement Myopic spectacles base in effect. Visual axis is directed towards B when looking at a near point A. Contact lens correction of myopia increases the accommodative and convergence demands when focusing near objects proportional to the size of refractive error . reverse is true in hypermetropia.

CONTACT LENS FITTING

SCLERAL CONTACT LENSES Indications Astigmatism(keratoconus,post PKP) Ocular surface disease Diameter 25 mm……… Correct abnormal regular and irregular astigmatism e,g keratoconus, astigmatism after PKP E;g tear layer disorders,trichiasis,accelerate healig of persistent epithelial defects that are refractory to all other treatment strategies

COMPLICATIONS 1.Allergic conjunctivitis 2.Giant papillary conjunctivitis 3.Corneal epithelial oedema 4.Peripheral corneal neovascularisation 5.Sterile corneal ulcerations 6.Corneal infection/microbial keratitis 7.Corneal warpage 8.Mechanical or hypoxic keratitis 9.Superficial punctate keratitis/dendritic keratitis

Corneal oedema Commonest and earliest corneal change Occurs due to hypoxia of corneal epithelium.This occurs when lenses with poor oxygen transmission are worn overnight. Under the closed-eye sleeping conditions, oxygen availability is decreased to a level where endothelial cell dysfunction occurs leading initially to stromal than epitelial edema , finally bullae formation occurs

Contact Lens Red Eye with pain & photophobia

Giant papillary conjunctivitis is more common in patients wearing soft lenses . Immunological origin in which contact lens deposits esp protiens act as allergens.

Corneal neovascularization Ch hypoxia , tight or thick lens. Doesnot extend beyond 2 – 3mm If severe short course of steroids

Microbial keratitis The pattern of causal organisms is slightly different in contact lens wearers. There are relatively more Gram negative organisms, which reflects the alteration in commensal populations in contact lens wearers which, inturn, is due to the watery extraocular environment in which contact lenses are maintained. For the same reason, contact lens wearers are more susceptible to acanthamoeba keratitis

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