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Alexandra Jaworski, Alex Gentle, Andrew J. Zele, Algis J. Vingrys, Neville A. McBrien; Altered Visual Sensitivity in Axial High Myopia: A Local Postreceptoral Phenomenon?. Invest. Ophthalmol. Vis. Sci. 2006;47(8):3695-3702. doi: 10.1167/iovs.05-1569.
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purpose. The present study investigated retinal integrity in high myopia using spatial psychophysical tasks.
methods. Ten axial high myopes (−8.5 to −11.5 D) and 10 age-matched control subjects (±1.0 D) were recruited. All participants underwent clinical examination and ocular biometry and demonstrated no visible macular disease with visual acuities better than 6/12. Foveal summation thresholds were determined for white and S-cone-isolating spots of various diameters up to 5.4° and spatial contrast sensitivity to luminance sine wave gratings (0.5–9.7 cyc/deg). Data were analyzed after correction for the magnification induced by eye size and correcting lens power.
results. Spatial summation for both white and S-cone-isolating spots showed a generalized loss of sensitivity at all spot sizes in myopes relative to control subjects (P = 0.01). Critical areas at maximum summation were significantly larger in myopes, for S-cone isolating spots only, after image size correction (P = 0.048). Sensitivity at maximum summation correlated negatively with vitreous chamber depth for both targets (P = 0.005). Sensitivities for S-cone and luminance spots also correlated (P < 0.001), indicating widespread dysfunction. Myopes displayed contrast sensitivity losses at high spatial frequencies (P ≤ 0.006) with a normal peak contrast sensitivity.
conclusions. These data can be interpreted to indicate that highly myopic eyes have either (1) a reduction in the number of receptors and/or a reduction in their sensitivity or, (2) a reduction in the sensitivity of postreceptoral processes. The presence of normal contrast sensitivity at low spatial frequencies indicates dysfunction at a postreceptoral level in high myopes.
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