Purpose
To evaluate associations between full-field and pattern electroretinographic (ffERG, pERG) responses, best-corrected visual acuity (BCVA), central color vision, visual field (VF) sensitivity, and structural abnormalities of the retina (assessed by SD-OCT) in patients with birdshot chorioretinopathy (BCR).
Methods
In a cross-sectional study, 17 patients with BCR and 44 normal controls received a standardized evaluation, including ffERG and pERG, which were recorded in accordance with standards set forth by the International Society for Clinical Electrophysiology of Vision. Abnormality was defined as a departure of >2SD from normative values. Central color vision was assessed with the Lanthony-D15 color test. VF mean deviation (MD) was determined by Humphrey automated perimetry. Presence or absence of any structural abnormality (e.g. disintegrity of ellipsoid layer, alteration of retinal architecture, atrophy, or intraretinal cystoid edema) was assessed on the macula volume scan by a masked reader.
Results
Response parameters of ffERG and pERG for the group as a whole differed significantly from control data (all p values<0.05). Regarding ffERG, 6 eyes (4 patients) had normal rod and cone function (Group 1); 11 eyes (7 patients) had normal rod and abnormal cone function (Group 2); 17 eyes (10 patients) had both abnormal rod and cone function (Group 3). Selective loss of the b-wave was observed infrequently. No eyes had abnormal rod and normal cone response. There was a weak association between groups and median BCVA (1.0, 0.8 and 0.5 for Groups 1, 2, and 3, respectively; p=0.078). There were statistically significant differences between Groups 1, 2 and 3 for the following factors: abnormal color vision (17% [1/6], 64% [7/11], and 94% [16/17], p=0.001); median VF-MD (-2.6dB, -6.8dB, and -13.0dB, p=0.022); abnormal SD-OCT findings (33% [2/6], 82% [9/11], and 100% [17/17], p=0.001); and abnormal pERG parameters (33% [2/6], 100% [11/11], and 88% [15/17], p=0.003).
Conclusions
The ffERG phenotype is associated with certain clinical measures of visual function (color, HVF) in people with BCR. Measures dominated by central cones (pERG, HVF) can detect dysfunction of vision even when ffERG response parameters are within normal limits. In addition, SD-OCT may show localized structural abnormalities in the absence of ffERG changes.