Defining the residual vision in leber congenital amaurosis caused by RPE65 mutations

Abstract

Purpose: To quantify the residual vision in Leber congenital amaurosis (LCA) caused by RPE65 mutations.

Methods: Patients with RPE65-LCA (n = 30; ages, 4-55) were studied using electroretinography (ERG), full-field stimulus testing (FST), kinetic and static threshold perimetry, and optical coherence tomography (OCT).

Results: All patients with RPE65-LCA had abnormal ERGs even at the youngest ages. There were no detectable rod ERGs and only reduced cone ERGs. By chromatic FST, however, 59% of patients had measurable rod- and cone-mediated function. The remaining 41% had only cone-mediated function. Extent of kinetic fields varied widely in the first two decades of life but, by the end of the third decade, there was very little measurable field. Regional patterns of visual loss were evident using dark-adapted static threshold perimetry. The mildest dysfunctions showed relatively homogeneous sensitivity loss beyond the central field. Mid-peripheral dysfunction was a later feature; finally, only central and peripheral islands remained. Colocalized measures of visual function and retinal structure by OCT showed that visual function was detectable when a photoreceptor layer was detectable.

Conclusions: Residual rod as well as cone function is detectable in RPE65-LCA. The finding of different regional patterns of visual loss in these patients suggests that the optimal retinal site(s) for subretinal gene delivery to achieve efficacy are likely to change with disease progression.

Figures

FIGURE 1

Measures of residual function in RPE65-LCA. (A) Standard ERGs in patients with RPE65-LCA. Rod, mixed cone-rod, and cone ERGs from six representative patients with RPE65-LCA (age range, 5–23 years) were compared with ERGs of a patient with a rhodopsin (R135L) gene mutation showing residual, severely abnormal, cone-mediated function. A normal subject (age 20 years) is shown for comparison (left). Traces start at stimulus onset; calibrations are to the right and below waveforms. ERGs can be undetectable, even at early ages. Detectable ERGs show a pattern similar to that of the patient with a RHO mutation and severe rod dysfunction but residual and abnormal cone function. (B) Inset (left): FST sensitivity loss to a white stimulus in patients with RPE65-LCA ranked by age. Chromatic FST sensitivity differences (blue-red) in patients with RPE65-LCA ranked in decreasing order of magnitude (right). Results in normal subjects in the dark-adapted state (left) or at the cone plateau of dark-adaptation after light-exposure (right) served to define which photoreceptor mediates perception of each color (error bars, mean ± 2 SD). Labels above the bars denote photoreceptor mediation: R, rods; M, mixed; C, cones. Ages of the patients and their numbers are shown below each bar on the horizontal axis. Dashed line: delimits the upper limit for categorization as cone-mediated.

FIGURE 2

Kinetic perimetry in RPE65-LCA. (A) Kinetic field extent expressed as a percentage of normal and plotted as a function of age of patient. Longitudinal data are connected by lines. Representative kinetic fields illustrating early and later stage patterns are shown (above and to the right of the graph). All fields are depicted as right eyes. (B–D) Serial kinetic fields in one eye of three patients spanning 11 years in P8 (B), 7 years in P5 (C), and 3 years in P18 (D). Patients with illustrated visual fields are identified in (A).

FIGURE 3

Dark-adapted static threshold perimetry to a white stimulus in RPE65-LCA. (A) Sensitivities at 71 loci in normal subjects (N) and patients with RPE65-LCA are mapped to a pseudocolor scale representing 7 log units. Eight patient sensitivity maps are shown and ordered (left to right in each of three rows) by mean sensitivity calculated across the field. All data are depicted as right eyes to enable comparison. The normal blind spot is shown as a black square at the 12° temporal field. (B) Sensitivity as a function of eccentricity in patients with RPE65-LCA compared with normal subjects (top left). Patients are grouped by increasing severity of sensitivity loss (from top right to lower left to lower right; and within panels from top to bottom). Data traces are colored to show the two decades of ages represented (orange, 10–19 years; purple, 20–29 years). (C) Data from four patients of comparable age (19–23 years) that illustrate further the patterns of increasing severity.

FIGURE 4

Relationship between dark-adapted visual function and retinal structure in RPE65-LCA. (A) Vertical cross-sectional retinal images using OCT compared with the presence or absence of visual response in corresponding locations. A 48-year-old normal subject and two patients with RPE65-LCA (P10, P22) are compared. Each patient shows a different degree of ONL preservation (highlighted in blue on scan). Apparent peaks at the vitreoretinal surface at ∼4 to 5 mm eccentricity along some of these vertical scans are the nerve fiber layer bundles and arcade vessels. (B) Summary of data from 487 loci along the vertical meridian in 20 patients. ONL thickness is plotted for loci with absence (left, 95 loci) or presence (right, 392 loci) of dark-adapted visual sensitivity.