Characterizing Visual Fields in RPGR Related Retinitis Pigmentosa Using Octopus Static-Automated Perimetry

Abstract

Purpose: Peripheral visual fields have not been as well defined by static automated perimetry as kinetic perimetry in RPGR-related retinitis pigmentosa. This study explores the pattern and sensitivities of peripheral visual fields, which may provide an important end point when assessing interventional clinical trials.

Methods: A retrospective observational cross-sectional study of 10 genetically confirmed RPGR subjects was performed. Visual fields were obtained using the Octopus 900 perimeter. Interocular symmetry and repeatability were quantified. Visual fields were subdivided into central and peripheral subfields for analysis.

Results: Mean patient age was 32 years old (20 to 49 years old). Average mean sensitivity was 7 dB (SD = 3.67 dB) and 6.8 dB (SD = 3.4 dB) for the right and left eyes, respectively, demonstrating interocular symmetry. Coefficient of repeatability for overall mean sensitivity: <2 dB. Nine out of 10 subjects had a preserved inferotemporal subfield, whose mean sensitivity was highly correlated to the central field (r2 = 0.78, P = 0.002 and r2 = 0.72, P = 0.002 for the right and left eyes, respectively). Within the central field, sensitivities were greater in the temporal than the nasal half (t-test, P = 0.01 and P = 0.03 for the right and left eyes, respectively).

Conclusions: Octopus static-automated perimeter demonstrates good repeatability. Interocular symmetry permits use of the noninterventional eye as an internal control. In this cohort, the inferotemporal and central visual fields are preserved into later disease stages likely mapping to populations of surviving cones.

Translational relevance: A consistently preserved inferotemporal island of vision highly correlated to that of the central visual field may have significance as a possible future therapeutic site.

Figure 1.

Schematic of subfield definitions. Black points represent the 185-point testing grid. The central 30-degrees is within the innermost circle. The blind spot is highlighted in purple. Number of points in each subfield are as follows: central 30 degrees (n = 108); inferotemporal (n = 22); inferonasal (n = 17); superotemporal (n = 22); and superonasal (n = 16).

Figure 2.

Example of the generation of a volumetric measure of the hill of vision. (A) Point map of raw static perimetry data. (B) Interpolated data allowing the generation of heat maps. (C) Representation of the decibel sensitivities in the z-plane resulting in a 3-dimensional hill of vision with corresponding volume metric.

Figure 3.

Age versus overall mean sensitivity (n = 9 for the right eye, and n = 10 for the left eye). Shaded areas show 95% confidence limits of regression fit. Black and blue points and regression lines are for the right (OD) and left (OS) eyes, respectively.

Figure 4.

Example patient results across triplicate testing shown with point maps on the left, heat maps in the center and 3D volumetric plots on the right. Tests 1, 2, and 3 are labeled to show the order in which triplicate testing was performed over two consecutive days. dB-sr = decibel-steradians.

Figure 5.

Composite visual fields (full field) for all patients (n = 9 for the right eye, and n = 10 for the left eye) demonstrating the majority of patients have well preserved central and inferotemporal visual fields. Scotoma across superior fields likely due to eyelid effects. N = nasal, T = temporal.

Figure 6.

Correlations between mean sensitivity of the central 30-degrees. (A) Inferior temporal sensitivity, (B) superior temporal sensitivity, (C) inferior nasal sensitivity, and (D) superior nasal sensitivity (n = 10). Shaded areas show 95% confidence limits of regression fit. Black and blue points are for the right and left eyes, respectively. Bonferroni significance level is P = 0.0125. Nasal quadrants are dominated by floor effects whereby majority of subjects had little to no sensitivity.

Figure 7.

Correlations between volume of the central 30-degrees (V30). (A) Inferior temporal volume, (B) superior temporal volume, (C) inferior nasal volume, and (D) superior nasal volume (n = 10). Units of volume in decibel steradians (dB-sr). Shaded areas show 95% confidence limits of regression fit. Black and blue points are for the right and left eyes, respectively. Bonferroni significance level is P = 0.0125.

Figure 8.

Nasal-temporal asymmetry within the central visual field. Composite heatmap for our cohort of patients with RPGR-related RP (central 30-degree field; n = 9 for the right eye, and n = 10 for the left eye) demonstrating nasal-temporal asymmetry in retinal sensitivity. There were 47 points that were included in each hemifield due to exclusion of points lying directly on the vertical meridian, and the corresponding points in the nasal hemifield to account for the blind spot. Grey oval = blind spot, N = nasal, T = temporal.