The Role Of Safe Margin Of Hypermetropia In Protection Against Post Lasik Regression In Myopic Patients

Abstract

Purpose:To determine post lasik aim of refraction in young myopic patient that ensure slight over correction (safe margin of hypermetropiaSMH) which help in reducing possibility of regressionand post lasik myopic shift, however this SMH should be easily overcomedby accommodation , doesn’t affect UCVA or induce eyestrain. Patients and methods:400 patients (800 eyes) were taken in this study, all of them had myopia and myopic astigmatism with -1.0 to – 6.0 D(spherical equivalent) during the period between 2008-2014 in Nassirya city, south of Iraq. Those patients were divided into 5 groups each group with 80 patients (160 eyes) and planned to have post lasik refraction ofemmetrope,  +0.5, +0.75, +1.0 and +1.25 D, for groups from no.1 to no.5 respectively and these groups followed up in term of UCVA, spherical equivalent, myopic shift, and asthenopia (eyestrain) for three years. Result:Three yearsfollow up for the 5 groups showed that, in group no.1 (27.5%)  of eyes had VA of 6/9 or worse, (33.125%)  of eyes had myopic shift and(11.25%) of patients had eyestrain. In group no.2 (19.375%) of eyes had VA of 6/9 or worse ( 21.875%) of eyes had myopic shift and (8.75%)  of patients had eyestrain. In group no.3 (11.25%)of eyes had VA of 6/9 or worse (9.375%) of eyes had myopic shift and (2.5%) of patients had eyestrain. In group no.4 ( 4.375%) of eyes had VA of 6/9 or worse, no myopic shift and (2.5%) of patients had eyestrain. In group no.5(12.5%) of eyes had VA of 6/9 or worse, no myopic shift and (15%) of patients had eye strain.  Conclusion: In  young myopic patients with low to moderate myopia, we can choose post lasik aim of refraction of +1.0 D, this safe margin of hypermetropia SMH can ensure best UCVA without eyestrain (asthenopia), help in reducing regression and myopic shift.