Human Foveal Cone Photoreceptor Topography and its Dependence on Eye Length

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PURPOSE. To assess the relationship between cone spacing and visual acuity in eyes with rodcone degeneration (RCD) followed longitudinally. METHODS. High-resolution images of the retina were obtained using adaptive optics scanning laser ophthalmoscopy from 13 eyes of nine RCD patients and 13 eyes of eight healthy subjects at two sessions separated by 10 or more months (mean 765 days, range 311-1935 days). Cone spacing Z-score measured as close as possible (average <0.258) to the preferred retinal locus was compared with visual acuity (letters read on the Early Treatment of Diabetic Retinopathy Study [ETDRS] chart and logMAR) and foveal sensitivity. RESULTS. Cone spacing was significantly correlated with ETDRS letters read (q ¼ À0.47, 95%CI À0.67 to À0.24), logMAR (q ¼ 0.46, 95%CI 0.24 to 0.66), and foveal sensitivity (q ¼ À0.30, 95%CI À0.52 to À0.018). There was a small but significant increase in mean cone spacing Z-score during follow-up of þ0.97 (95%CI 0.57 to 1.4) in RCD patients, but not in healthy eyes, and there was no significant change in any measure of visual acuity. CONCLUSIONS. Cone spacing was correlated with visual acuity and foveal sensitivity. In RCD patients, cone spacing increased during follow-up, while visual acuity did not change significantly. Cone spacing Z-score may be a more sensitive measure of cone loss at the fovea than visual acuity in patients with RCD.

Section: Methodsmentioning

confidence: 95%

Loss of Foveal Cone Structure Precedes Loss of Visual Acuity in Patients With Rod-Cone Degeneration

Bensinger

Rinella

Saud

et al. 2019

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“…The latter estimate translates to a visual acuity of 2.4 cpd (1 degree of visual angle = 82 µm across the retina in a guinea pig), which correlates well with behavioral visual acuity estimates. Equivalent calculations for the human eye used an average foveal cone density of 163,000 cones/mm 2 , 12 which translates to a sampling resolution of 215 cycles/mm and 62.5 cpd. Therefore, although optics limit human spatial vision, retinal ganglion cell density appears to limit the visual acuity of the guinea pig.…”

Section: Discussionmentioning

confidence: 99%

“…Although this difference in eye length offers the potential for greater spatial resolving power, the visual acuity of the guinea pig, based on behavioral measures, is reported to be relatively poor, between 1.0 cycles per degree (cpd) (Ostrin LA, et al IOVS 2011;52:ARVO E-Abstract 6296) and 2.7 cpd, 9 making it only slightly better than that of mice (0.5 cpd) 10 and much lower than that of chicks (6-8.6 cpd) 11 and humans (30-60 cpd). 12 Interestingly, albino guinea pigs and pigmented guinea pigs have very similar visual spatial resolution thresholds, despite the increased light scatter in albino eyes (Ostrin LA, et al IOVS 2011;52:ARVO E-Abstract 6296), raising the possibility that the optical quality of the guinea pig eye is inherently poor. Characterization of the high-order aberrations of the guinea pig eye can help to model image transfer in the guinea pig eye and inform the limits of its spatial resolution, with important implications for studies involving experimental visual manipulations.…”

mentioning

confidence: 99%

Optical Aberrations of Guinea Pig Eyes

Singh

Wildsoet

Roorda

2020

The guinea pig is widely used in studies of refractive error development and myopia which often involve experimental optical manipulations. The study described here investigated the optical quality of the guinea pig eye, for which there are limited data, despite its fundamental importance to understanding visually guided eye growth. METHODS. The ocular aberrations of eight adolescent New Zealand pigmented guinea pigs (6-11 weeks old) were measured after cycloplegia using a custom-built Shack-Hartmann aberrometer and fit with a Zernike polynomial function to the 10th order (65 terms). The optical quality of their eyes was assessed in terms of individual Zernike coefficients, and data were further analyzed to derive root-mean-square (RMS) wavefront errors, modulation transfer functions (MTFs), point spread functions (PSFs), Strehl ratios, and depth of focus. A 4-mm pupil was used in all computations. The derived data are compared with equivalent data from normal young adult human eyes. RESULTS. The guinea pigs exhibited low hyperopia and a small amount of positive spherical aberration, with other aberration terms decreasing with increasing order. Their average depth of focus, estimated from through-focus modulation, was 3.75 diopters. The RMS wavefront error of the guinea pig eye was found to be larger than that of the human eye for the same pupil size, reflecting a higher degree of aberrations, although the PSF (area) on the retina was smaller and sharper due to its shorter focal length. The radial average best-focus MTF derived for the guinea pig eye showed good performance at very low spatial frequencies, with a steeper decline with increasing frequency than for the human eye, dropping below 0.3 at 9 cpd. When converted to linear units (cycles/mm), the guinea pig eye had a higher spatial frequency cutoff and a slight contrast advantage for low spatial frequencies compared to the human eye. CONCLUSIONS. The optical quality of the guinea pig eye is far superior to their reported behavioral visual acuity. This implies a neuroanatomical limit to their vision, which contrasts with the close match of optical and neural limits to spatial resolution in human eyes. The significance for eye growth regulation of the relative optical advantages exhibited by guinea pig eyes, when optical quality is expressed in linear rather than angular retinal units, warrants further consideration.

“… 40 , 41 The PRL in eyes with normal central vision is generally within approximately 0.10° of the location of maximum cone density. 42 , 43 …”

Section: Methodsmentioning

confidence: 99%

“…40,41 The PRL in eyes with normal central vision is generally within approximately 0.10°of the location of maximum cone density. 42,43 Structure-Function Comparisons and Statistical Analysis. Correlations between cone density, IS and OS thickness, and AOMP sensitivity were assessed with Spearman correlation coefficients using bootstrap analyses clustered by person and excluding zero values.…”

Section: Cone Density Analysis Regions Of Interest (Rois)mentioning

confidence: 99%

Comparing Cone Structure and Function inRHO-andRPGR-Associated Retinitis Pigmentosa

Foote

Wong

Boehm

et al. 2020

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To study cone structure and function in patients with retinitis pigmentosa (RP) owing to mutations in rhodopsin (RHO), expressed in rod outer segments, and mutations in the RP-GTPase regulator (RPGR) gene, expressed in the connecting cilium of rods and cones. METHODS. Four eyes of 4 patients with RHO mutations, 5 eyes of 5 patients with RPGR mutations, and 4 eyes of 4 normal subjects were studied. Cone structure was studied with confocal and split-detector adaptive optics scanning laser ophthalmoscopy (AOSLO) and spectral-domain optical coherence tomography. Retinal function was measured using a 543-nm AOSLO-mediated adaptive optics microperimetry (AOMP) stimulus. The ratio of sensitivity to cone density was compared between groups using the Wilcoxon rank-sum test. RESULTS. AOMP sensitivity/cone density in patients with RPGR mutations was significantly lower than normal (P < 0.001) and lower than patients with RHO mutations (P < 0.015), whereas patients with RHO mutations were similar to normal (P > 0.9). CONCLUSIONS. Retinal sensitivity/cone density was lower in patients with RPGR mutations than normal and lower than patients with RHO mutations, perhaps because cones express RPGR and degenerate primarily, whereas cones in eyes with RHO mutations die secondary to rod degeneration. High-resolution microperimetry can reveal differences in cone degeneration in patients with different forms of RP.