Role of orthokeratology in refractive correction and an analysis of changes in corneal topography following overnight Orthokeratology.

INTRODUCTION : Orthokeratology The word ‘orthokeratology’ is derived from Greek roots and comes from ‘ortho’ meaning correct or proper and ‘keratology’ meaning having to do with the cornea. It thus means forming the cornea to a correct shape. Orthokeratology may also be considered to literally mean “the study of straight corneas”. Orthokeratology is defined as the reduction, modification or elimination of refractive error by the programmed application of specially designed rigid gas permeable contact lenses. It flattens the central anterior portion of the cornea, thus compensating for the abnormally long eye, in order to reduce or correct myopia. AIMS OF THE STUDY : a) To determine the amount of refractive correction after single overnight application of OrthoK lenses in myopes with and without low degrees of astigmatism b) To assess corneal topographic changes after overnight orthokeratology c) To determine the duration of maintenance of clear vision during daytime after a single application of OrthoK lenses d) To evaluate the side effects of OrthoK lens wear e) To assess the effectiveness of orthokeratology in the refractive correction of keratoconus patients INCLUSION CRITERIA : • Myopia (-1.0D to -10.0D) with or without astigmatism of -0.25D to -1.0D • No prior history of use of RGP contact lenses • In case of soft lens users, lens wear was discontinued for 1 week before OrthoK fitting • No prior documented history of anterior segment inflammation EXCLUSION CRITERIA : • Myopes with presbyopia • Astigmatism > 1.0D • History of corneal refractive surgery • History of allergic reactions following soft contact lens wear MATERIALS AND METHODS: This study was conducted at the Regional Institute of Ophthalmology and Government Ophthalmic Hospital, Chennai between February 2008 and October 2008. 40 eyes of 20 patients were included in the study. OrthoK lens fitting was done according to the topographic flat K value and the spherical equivalent of the refractive error. RESULTS: The mean refractive correction achieved after overnight orthokeratology was -2D. 50% of the eyes attained 1D to 2D correction and 35% eyes achieved 2D to 3D of myopia correction. 32.5% eyes showed a flattening of 1.5D to 2.0D in the central cornea and 22.5% showed flattening of 2D to 2.5D after a single OrthoK application. The corneal eccentricity values were indicative of a change in shape from prolate to oblate. SRI values increased after overnight orthokeratology but did not exceed the normal range and caused no significant impairment of vision SAI demonstrated a trend towards asphericity without significant visual impairment. 60% patients were able to maintain clear vision for 6 to 8 hours during the day. RESULTS The mean refractive correction achieved after overnight orthokeratology was -2D. 50% of the eyes attained 1D to 2D correction and 35% eyes achieved 2D to 3D of myopia correction. 32.5% eyes showed a flattening of 1.5D to 2.0D in the central cornea and 22.5% showed flattening of 2D to 2.5D after a single OrthoK application. The corneal eccentricity values were indicative of a change in shape from prolate to oblate. SRI values increased after overnight orthokeratology but did not exceed the normal range and caused no significant impairment of vision SAI demonstrated a trend towards asphericity without significant visual impairment. 60% patients were able to maintain clear vision for 6 to 8 hours during the day. There were no significant side effects reported. In case of the keratoconus patients, a mean improvement of 2.33 lines of visual acuity on Snellen’s chart was noted as compared to the best spectacle corrected visual acuity. Corneal topographic parameters did not show a significant change in keratoconus patients on a day wear ortho-k schedule. DISCUSSION: Overnight orthokeratology has an important application in the treatment of myopia especially in the young patients. It may have a role in retarding the progression of myopia and reducing the incidence of complications of pathological myopia.54,55 RGP lenses help retard axial elongation during the growth years.56 Orthokeratology gives better visual acuity as compared to spectacles in patients with keratoconus who can tolerate RGP contact lenses. It does not induce any topographic changes in keratoconic corneas when prescribed as day-wear lenses. CONCLUSION: Our study demonstrates that overnight orthokeratology is a safe and effective method for the correction of myopia. This is in accordance with certain studies in literature.21,57,58,59 The central corneal flattening is consistent as evidenced by topography. The asphericity induced in the cornea during the treatment process does not significantly impair vision. Orthokeratology provides unaided clear vision for most part of the day in a majority of the patients. It is a viable nonsurgical alternative to refractive surgery.