Elsevier

Ophthalmology

Volume 106, Issue 2, 1 February 1999, Pages 258-268
Ophthalmology

Yearly rates of rod and cone functional loss in retinitis pigmentosa and cone-rod dystrophy1☆,

https://doi.org/10.1016/S0161-6420(99)90064-7Get rights and content

Abstract

Objective

To provide the first measures of the relative rates of rod and cone functional loss in patients with retinitis pigmentosa (RP) or cone-rod dystrophy (CRD).

Design

Five-year, prospective natural history study.

Participants

Ninety-six patients (67 with RP and 29 with CRD) retaining measurable rod-mediated visual function and 5 normal subjects were tested at baseline and annually for 4 consecutive years.

Main outcome measures

Tests of visual function included visual acuity, dark-adaptation thresholds, dark-adapted static perimetry, and rod and cone computer-averaged electroretinograms (ERGs), which were obtained over a range of retinal illuminances. Intervisit variability for each measure was obtained in a subset of patients who were tested twice within a 2-month interval and was used to determine whether an individual patient had shown progression, regression, or no change over a particular study interval.

Results

Over a 4-year interval, a significant number of patients with RP (60%) and CRD (62%) showed a decline in cone ERG amplitude. For rod ERG amplitude, the percentage of patients with RP or CRD showing progression was 64% and 45%, respectively. Although visual acuity, dark-adapted threshold, and rod visual field area also declined significantly over the 4-year period, the mean rate of change and the numbers of patients showing progression on these measures were lower than those for ERG measures. On specialized ERG testing, the yearly change in rod ERG threshold in RP was greater than the yearly change in cone ERG threshold, and the rate of progression varied significantly among inheritance types. For patients with CRD, the yearly change in rod threshold was comparable to the yearly change in cone ERG threshold.

Conclusions

This study helps to define the natural progression of rod-mediated and cone-mediated functional loss in patients with RP and CRD.

Section snippets

Methods

This study was conducted with the approval of the Institutional Review Board of the University of Texas Southwestern Medical Center at Dallas. Informed consent was obtained from the patients and subjects participating in the study. One hundred two patients (71 RP, 31 CRD) were recruited from the database of the Retina Foundation of the Southwest; ages of patients ranged from 5 to 61 years. Inclusion criteria were a diagnosis by an ophthalmologist specializing in retinal disease, a measurable

Results

Examples of the data from standard and specialized tests administered on each yearly visit are shown in Figure 1 for a normal subject, Figure 2 for a patient with RP, and Figure 3 for a patient with CRD. The top left panels (A) show standard protocol6 ERG responses. These include a dark-adapted rod response, a cone response to 31-Hz flicker, a dark-adapted response to the maximum stimulus, and a light-adapted cone response to the maximum stimulus obtained in the presence of a 32-cd/m2

Discussion

The results of the current study support the generally held view that in RP, rod-mediated visual function declines more rapidly than cone-mediated function. Across all patients with RP, the mean annual increase in rod ERG threshold was 28% per year (0.14 log unit) compared to a 13% per year (0.06 log unit) increase in cone ERG threshold. In patients with CRD, the increase in rod ERG threshold was 0.08 log unit/year (17%) and comparable to the increase in cone ERG threshold of 0.06 (13%).

References (22)

  • D.G Birch et al.

    The relationship between rod perimetric thresholds and full-field rod ERGs in retinitis pigmentosa

    Invest Ophthalmol Vis Sci

    (1987)
    • ☆

    Supported by grants from the National Eye Institute (EY05235) and the Foundation Fighting Blindness, Inc., Hunt Valley, Maryland.

    1

    The authors have no financial interest in any aspect of this study.

    View full text
    Copyright © 1999 American Academy of Ophthalmology, Inc. Published by Elsevier Inc. All rights reserved.