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Contact lenses-2- Advanced Applications of Contact Lenses-2

- Complications of contact lens wear

Instructor: Areej Okashah7/1/2010

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Orthokeratology: i.e. contact lens corneal reshaping: is the planned

application of specially designed RGP contact lenses to reshape the cornea; this temporarily reduces myopic refractive error & improves unaided visual acuity.

This procedure allows patients to see well enough in order to perform daily activities without the need for spectacle or CLs correction for at least part of the day…

Orthokeratology has been practiced for more than 40 years; however its efficacy & safety still controversial

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… Overnight wear of ortho-K is relatively a recent

development

Remember that conventional rigid lenses have secondary & peripheral curves that are progressively flatter than the central (base) curve

Modern ortho-K lenses employs a reverse-geometry lenses to produce the desired corneal changes; these lenses have secondary peripheral radii of curvature that are steeper than the back optic zone radius (BCR). This alteration in design allows the lens to re-approach the cornea beyond the base curve which results in improved lens centration. & this steeper secondary curve causes the corneal tissue to redistribute radially from the centre of the cornea causing the central corneal epithelium to thin & the peripheral epithelium to thicken leading to refractive error changes

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…. Recently used ortho-k lenses have high oxygen

permeability; which makes it possible to apply the lens on extended wear bases or overnight wear schedule

Overnight wear of ortho-K lenses advantages include: convenience for patient as no optical devices are required during the course of the day; better ocular health as the wearing time decreased; little adaptation to lens is required; increased effectiveness because there is an increased eyelid pressure from closed eyes & rapid eye movement during sleep. & could retard myopia progression in children.

Ortho-K has been found in some clinical trials to correct 1.00-5.00 or 6.00 diopters of myopia & little or no astigmatism

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…. Some patient discontinue ortho-k use because of:

residual astigmatism; poor comfort; treatment failure; poor motivation; unideal lens fit

Overnight ortho-k could have some complications e.g. corneal staining; corneal ulcer; CL adherence these are relatively similar to complications of using conventional CLs..

Good candidates: patients with one to six diopters of myopia; & who have less than two diopters of with-rule-astigmatism; & who have pupil with small-or-average-diameter

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Ocular complications related to contact lens

wear…………………..

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Complications of CL wear:::

Corneal vascularization Immunologic complications Infectious keratitis Mechanical complications

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Corneal vascularization CV Vascularization i.e. neovascularization is the

appearance of new vessels within a tissue In general its not uncommon CL wear is the major risk factor for CV The risk of CV is not the same for all CL types;

e.g. RGP lens < soft When firstly detected; new vessels is a warning

sign for further damage,

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CV could scatter incident light & reduce corneal transparency; there could be a potential for visual interference

CV is an indicative sign for immune privilege within anterior the chamber this could increase the risk of infection or inflammation

Hypoxia, epithelial injury (could affect the integrity of tear film)& wearing time (longer wearing time is associated with higher risk for CV), significance of limbal hyperaemia are risk factors that can be associated with CV

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Treatment outcomes are better when CV is detected early….

firstly should remove the causative factor in this case CL

Evaluate lens fitting characteristics ; material properties; cleanliness (deposits); lens parameters

Advice: reduce wearing time; switch to another lens material; water content; DK

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Infectious keratitis Causes of non-infectious keratitis: tear film abnormalities;

immune reaction; chemical injuries etc. Causes of infectious include: bacteria; protozoa; fungi;

viruses

Risk factors in infectious keratitis: alteration of ocular normal flora (e.g. staphylococcus epidermidis; S aureus, propionibacterium acnes); noncompliance with standard CL disinfection and storage (mostly pseudomonas); virulent organisms (e.g. Serratia & Bacillus in CL solutions); contaminated CL (mostly pseudomonas); diabetes mellitus

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Bacterial keratitis non-related to contact lens wear mainly caused by gram-positive bacteria e.g. Staphylococcus, Streptococcus

Bacterial keratitis related to CL wear mainly caused by Gram-negative bacteria e.g. Pseudomonas; Serratia.

Protozoal keratitis related to CL wear: e.g. Acanthamoeba ; usually from contaminated lens solution

Viral infections related to CL wear are rare but could enhance other microbial infections of the cornea

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Common symptoms for infective keratitis: pain; photophobia; tearing; blepharospasm; reduced vision, discharge (watery, or purulent)

Treatment could include :antimicrobial agents (e.g. neomycin; chloramphenicol); steroids; penetrating keratoplasty

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Final exam: all the course material’s

except the 1st material

Good Luck with your finals