Longitudinal Assessment of Retinal Structure in Achromatopsia Patients With Long-Term Follow-up

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Abstract

Purpose

To longitudinally characterize structural retinal changes in achromatopsia (ACHM) over extended follow-up.

Methods

Fifty molecularly confirmed ACHM subjects underwent serial spectral-domain optical coherence tomography (SD-OCT) and fundus autofluorescence (FAF) imaging. Foveal structure on SD-OCT was graded and compared for evidence of progression, and foveal total retinal thickness (FTRT) and outer nuclear layer (ONL) thickness were serially measured. FAF patterns were characterized and compared over time.

Results

Mean SD-OCT follow-up was 61.6 months (age range at baseline, 6–52 years). Forty-five of the subjects had serial FAF (mean follow-up: 48.5 months). Only 6 (12%) of the subjects demonstrated qualitative change on serial foveal SD-OCT scans. Among the entire cohort, there was no statistically significant change over time in FTRT ( P = 0.2459) or hyporeflective zone (HRZ) diameter ( P = 0.3737). There was a small—but statistically significant—increase in ONL thickness ( P = 0.0084). Three different FAF patterns were observed: centrally increased FAF (13/45), normal FAF (14/45), and well-demarcated reduced FAF (18/45), with the latter group displaying a small gradual increase in the area of reduced FAF of 0.055 mm ² over 43.4 months ( P = 0.0011).

Conclusions

This longitudinal study of retinal structure in ACHM represents the largest cohort and longest follow-up period to date. Our findings support the presiding notion that ACHM is essentially a stationary condition regarding retinal structure, and any change over time is likely to be small, slow, and variable across patients. This may potentially afford a wider window for therapeutic intervention.

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Most cited references 22

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The arrangement of the three cone classes in the living human eye.

A Roorda, D R Williams (1999)

Human colour vision depends on three classes of receptor, the short- (S), medium- (M), and long- (L) wavelength-sensitive cones. These cone classes are interleaved in a single mosaic so that, at each point in the retina, only a single class of cone samples the retinal image. As a consequence, observers with normal trichromatic colour vision are necessarily colour blind on a local spatial scale. The limits this places on vision depend on the relative numbers and arrangement of cones. Although the topography of human S cones is known, the human L- and M-cone submosaics have resisted analysis. Adaptive optics, a technique used to overcome blur in ground-based telescopes, can also overcome blur in the eye, allowing the sharpest images ever taken of the living retina. Here we combine adaptive optics and retinal densitometry to obtain what are, to our knowledge, the first images of the arrangement of S, M and L cones in the living human eye. The proportion of L to M cones is strikingly different in two male subjects, each of whom has normal colour vision. The mosaics of both subjects have large patches in which either M or L cones are missing. This arrangement reduces the eye's ability to recover colour variations of high spatial frequency in the environment but may improve the recovery of luminance variations of high spatial frequency.

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The cone dysfunction syndromes.

Steven Moore, M Michaelides, Kevin Hunt (2004)

The cone dystrophies comprise a heterogeneous group of disorders characterised by visual loss, abnormalities of colour vision, central scotomata, and a variable degree of nystagmus and photophobia. They may be stationary or progressive. The stationary cone dystrophies are better described as cone dysfunction syndromes since a dystrophy often describes a progressive process. These different syndromes encompass a wide range of clinical and psychophysical findings. The aim is to review current knowledge relating to the cone dysfunction syndromes, with discussion of the various phenotypes, the currently mapped genes, and genotype-phenotype relations. The cone dysfunction syndromes that will be discussed are complete and incomplete achromatopsia, oligocone trichromacy, cone monochromatism, blue cone monochromatism, and Bornholm eye disease. Disorders with a progressive cone dystrophy phenotype will not be discussed.