Purchase this article with an account.
A. Gentle, A. Jaworski, A.J. Zele, A.J. Vingrys, N.A. McBrien; Reduced Visual Sensitivity in Axial High Myopia: A Receptoral or Post–Receptoral Phenomenon . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5606.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose: High myopia results from an enlarged vitreous chamber depth (VCD), causing increased photoreceptor spacing and thus reduced retinal sampling. Reduced visual sensitivity has also been reported in high myopes, however this finding is equivocal. The current study investigated visual sensitivity in high myopes using different spatial psychophysical tasks to help localise sensitivity changes. Methods: Axial high myopes and age–matched controls were recruited (n=11 each group). All participants underwent clinical examination and ocular biometry measures, and demonstrated no clinically significant macular pathology with visual acuities >6/12. Foveal contrast thresholds were determined using a standard approach. Testing was performed under mydriasis and with spectacle correction. Data were analysed in terms of stimulus retinal image size. Spatial summation: White (0.2–5.4o diameter) and blue (0.6–5.4o) square–wave spot targets were presented, then data fitted with a two–component linear model. Spatial contrast sensitivity: Sinusoidal gratings (0.5–9.7 c/o) were presented, then contrast sensitivity (CS) functions fitted with a ‘difference of Gaussians’. Results: Spatial summation curves (blue and white) were vertically displaced in myopes relative to controls (p<0.03), indicating reduced CS at partial and maximal summation. Retinal image critical areas were not significantly larger in myopes, although the magnitudes of increase were consistent with estimates based on eye size. VCD was negatively correlated with both blue and luminance sensitivities at maximal summation (p<0.01). Myopes displayed CS losses at retinal image spatial frequencies ≥17.8 c/mm (p<0.01) but peak CS was not reduced. Conclusions: The findings of this study are most consistent with predicted spatial summation and CS functions that assume post–receptoral sensitivity losses and enhanced photoreceptor sensitivity. Although the spatial extent of luminance and S–cone receptive fields were not significantly larger in high myopes, the magnitudes of increase were consistent with the predicted increase in photoreceptor spacing.
This PDF is available to Subscribers Only