Myopia has emerged as a major ocular health issue recentlybecause of its increasing prevalence worldwide1and its progressive nature in children. Myopia or near-sightedness is caused due to increase inaxial length or corneal curvature. The increase in axial length is governed bydifferent etiological factors2, among all near work3and peripheral retinal image formation4 have been formulated to beleading factors.
Animal studies5, 6have shown that elimination of signals from the fovea did not interfere withemmetropization, but inducing hyperopicdefocus on the peripheral retina promoted development of axial myopia in infantmonkeys. This experiment led to the proposal, peripheral retina defocus leadsto alternation of retinal shape causing axial elongation and myopia progression7-9.Donder10 and Helmholtz11 considered myopia to be anacquired anomaly associated with over-exertion in near work. It was observed that during near work myopicchildren shows lag of accommodation 12which results in a reduced power of the eye thus causing relative hyperopicdefocus at near, Since it is known from animal studies5, 6that a hyperopic defocus leads to the development of myopia, the Lag ofaccommodation might be a risk factor for the development and/ or progression ofmyopia.12, 13As peripheral hyperopicdefocus triggers myopia progression, the treatment modality for Myopia shouldbe potentially focused on modifying peripheral refraction to counterbalance theunknown stimulus that triggers the eye elongation and subsequent progression ofmyopia.
The conventional myopic spectacle lens increases hyperopic defocus inperiphery so to change RPR profile studies have tried adding tints(radiantrefracting lens) or pantascopic tilt which resulted in myopic defocus atperipheral retinal plane14, 15although study has shown that thesechanges are only for distance , hyperopic defocus still persists near work.16 Conventional soft andrigid gas permeable (RGP) contact lenses reduces relative peripheral hyperopia,and can even results in relative peripheral myopia, particularly in high myopia17, 18.Commercially available multifocalcontact lenses (MFSCL) intended for presbyopic correction served as myopiacontrol lenses in some studies 19, 20.
The peripheral add power area has shown to induce significant changes in theperipheral refractive error profile in myopic eyes as compared to distancepower in periphery19. Walline JJ et al 21in their study found 50% reduction in the progression of myopia and a29% reduction in axial elongation during the 2-year treatment period with MSCL. Reverse geometry contact lenses for corneal reshaping tendto have promising result in retarding eye elongation22-24. Ortho k lenses alter oculargrowth pattern by inducing relative peripheral myopic refractive error (RPRE)whereas the central refraction is fully corrected. Studies comparingconventional RGP and ortho k lenses have found ortho k lenses have significantlyreduced myopia in the central 20° VF in myopic children25.Majority of studies have measured RPRonly in horizontal meridian using different modalities of myopia correction,Atichson et al.,26 found that in vertical meridian myopeshad peripheral myopic defocus.
Study onsize and shape of myopic eye by Verkicherla et al.,9reported difference in peripheral refraction along horizontal and verticalmeridian. On measurement for near peripheral refraction in myopia by Calver etal.,27showed peripheral hyperopia in low myopes and peripheral myopia in high myopes.
However there is a lacunae in all the previous study as none of them havemeasured horizontal and vertical meridian PRP for distant and near with all themodalities such as single vision glasses, Anti-myopia lenses, spherical softcontact lens, multifocal contact lens and ortho-K. So, the aim of our study isto measure horizontal and vertical meridian PRP for distant and near withdifferent corrective modalities. References :1. Holden, B.A., et al., Global Prevalence of Myopia and High Myopiaand Temporal Trends from 2000 through 2050. Ophthalmology, 2016.
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