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S.S. Choi, J.M. Enoch; Extended Analysis of Traction-Induced Alterations in Retinal Sensitivity in Myopes . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2770.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To better characterize the tractional effects and events previously described in long and myopic eyes, we have extended our analysis of retinal responses at a number of selected loci. We now add data on increment thresholds defined by the classic Weber fraction as part of determinations of the Stiles-Crawford effect of the first kind (SCE-I). This allows assessment of sensitivity alterations as well as the orientation of retinal receptors. Test loci were selected in order to characterize the magnitudes and distribution of meaningful tractional strains found in long and myopic eyes. We sought to understand the implications of these alterations in retinal function. Methods: Here we greatly broaden the analysis presented at ARVO 2002. The increment threshold findings were derived from the same sets of data. SCE-I testing was conducted at fixation (0°), and at 5°, 10°, 15°, & 20° in the nasal visual field, at 5°, 10° in the temporal visual field (and temporal on the retina to the optic nerve head), at 22°, 27° in the temporal visual field (and nasal to the disc on the retina), at 16°/5° & 16°/10° in the inferior visual field (in the temporal visual field and superior to the disc), and at 16° /5° in the superior visual field (in the temporal visual field and inferior to the disc) of normal and myopic observers. Results: Retinal sensitivity was found to be reduced in areas exhibiting abnormal photoreceptor alignments. In the course of our larger analysis, individual differences were noted, but the overall trends were comparable, i.e. the greater the disturbance of alignment of receptors, the higher the measured increment threshold. This study served to re-enforce previous findings. The tractional effects sampled extended in eyes over a substantial area on the fundus, but they were not uniformly distributed. The anomalous effects were highly correlated with axial length of the eye and the magnitude of the myopia. Conclusions: Since all test loci assessed exhibited anomalous responses in individual observers, one may deduce these loci did not represent the boundaries of effects of tractional strains on the retina. The SCE-I is exquisitely sensitive as an indicator of photoreceptor sensitivities and alignments. These manifestations are secondary to factors inducing the traction. And a number of factors contribute to the tractional effects reported. These include: thinning of sclera, traction induced by external forces upon the eye, twisting of the disc, super-traction or super-involute effects as well as elongated axial length, etc. Clearly, this is not a minor set of issues. These effects influence the patho-physiology of myopic eyes.
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