Purchase this article with an account.
Nancy Coletta, Toco Chui, Ann Elsner; A Comparison of Acuity and Cone Density in the Temporal Retina. Invest. Ophthalmol. Vis. Sci. 2013;54(15):4064.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Cone spacing has long been thought to set a limit on visual acuity. While parafoveal acuity and cone density decrease at parallel rates with increasing myopia (Coletta and Watson, Vis Res, 2006; Chui et al., IOVS, 2008), parafoveal acuity has been reported to exceed the limit estimated from histological measures of cone spacing (Williams and Coletta, JOSA A, 1987). Recent advances in retinal imaging allow a comparison of acuity and cone spacing in the same eyes. We compared parafoveal acuity to cone density in several young adult individuals to determine whether acuity is matched to the limit estimated from cone density.
Measurements were made on five subjects with an average age of 28 years +/- 4.30 s.d., average spherical equivalent refractive error of -1.93 D +/- 3.32 s.d. and average axial length of 24.48 mm +/- 1.38 s.d. (IOL Master, Zeiss Meditec). Acuity was measured on the temporal retinal meridian using 543 nm laser interference fringes at a retinal illumination of 100 td; fringes were displayed in a 1 deg patch at 2 deg and a 2 deg patch at 7 deg eccentricity. Acuity was estimated at the 75% correct level for a 2AFC vertical/horizontal discrimination task. Cone densities in the temporal retinal meridian were assessed using a second generation Adaptive Optics Scanning Laser Ophthalmoscope. Densities were measured at a nominal 630 and 2070 microns from the foveal center with custom software (Matlab, Mathworks). Axial lengths were used to correct the cone sampling positions and retinal area, as well as to convert cone densities to Nyquist frequencies (NF) in units of c/deg.
The average acuity at 2 deg and 7 deg locations was 34.4 c/deg +/- 3.54 s.e.m. and 17.62 c/deg +/- 2.33 s.e.m., respectively, while the average cone NFs at 2 deg and 7 deg locations were 26.97 c/deg +/- 1.02 s.e.m. and 18.79 c/deg +/- 0.73 s.e.m., respectively. Individual ratios of acuity: cone NF ranged from 1.03 to 1.47 with a mean of 1.26 at 2 deg and 0.75 to 1.18 with a mean of 0.93 at 7 deg. A paired t-test of acuity and cone NF values at 7 deg was not statistically significant.
Visual acuity exceeded the cone NF at 2 deg eccentricity, confirming earlier studies that compared parafoveal acuity and histological measures from different eyes. However our results at 7 deg eccentricity suggest that interferometric acuity may provide a good estimate of cone density in the perifoveal region.
This PDF is available to Subscribers Only