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Orthokeratology (Ortho-K) F.Fazel. MD

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Orthokeratology (Corneal Reshaping) Application of sequentially flatter PMMA hard contact lenses to flatten the cornea and thereby reduce the myopic refractive error.

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In the 1990s, there was a resurgence using highly gas- permeable rigid contact lenses for temporary corneal reshaping. In this technique, patients with myopia are fitted with reverse geometry rigid gas permeable contact lenses that are used only during sleep. The center of the contact lens is deliberately fitted flatter than central corneal curvature to transiently induce central corneal flattening, which will reverse myopia during the day when the lens is not worn. The contact lens must be used every 1 to 2 nights in order to maintain the effect. Food and Drug Administration approval has been granted for the use of this technique for temporary reduction of up to 6.0 D of myopia (in eyes with up to 1.75 D of astigmatism). Several other orthokeratology contact lenses are available

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The FDA has approved Paragon CRT corneal refractive therapy lenses for the treatment of up to -6.00 diopters (D) of myopia; VST overnight ortho-k lenses are approved for up to -5.00 D. Astigmatism also can be treated: up to -1.75 D with Paragon CRT, and up to -1.50 D with VST.

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Disadvantage Upon discontinuation of contact lens wear, the corneas of patients who have undergone orthokeratology tend to revert to their original shape. Earlier attempts to predict which patients will respond to orthokeratology based on ocular biomechanical or biometric parameters have not been successful, and the effects of orthokeratology were unpredictable and poorly controlled

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Complications The complications of orthokeratology overlap those of rigid contact lens wear. Corneal pigmentation rings have been reported, but these are reversible. Patients may also note a decreased quality of vision especially under low illumination conditions due to an increase in higher order aberrations. The most serious complication that has been associated is microbial keratitis, first reported in 2001.As with any overnight contact lens modality, orthokeratology is associated with an increased risk of microbial keratitis

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