Electroretinography May Help Detect Systemic Etiology in Retinal Vasculitis

Full field electroretinography (ffERG) is a beneficial clinical tool, but data is lacking on how its findings coordinate with other testing modalities in treatment of retinal vasculitis. A study at Byers Eye Institute, Stanford University, examines ffERG rod and cone responses, finding function is mostly maintained in retinal vasculitis, but certain low responses may hint at a systemic illness, as reported in the British Journal of Ophthalmology.

The retrospective analysis includes patients with retinal vasculitis who received wide-angle fundus fluorescein angiography (FFA) within 1 month of ffERG, and excluded those with various prior chorioretinal conditions, or factors leading to unclear images. Participants were treated from December 2017 to February 2021. FFA was graded according to a 0 to 40 rubric, with 0 indicating no inflammation. ERG measured amplitude and timing in scotopic, photopic, and flicker conditions; graded 0 to 6, with 5 the benchmark for normal and 6 as perfect.

The average age of the 20 patients (34 eyes) evaluated was 43.9±19.8 years, and 70% were women. Mean FFA result was 12.6±6.5 — scores correlated with delayed photopic 3.0 b-wave cone (P =.03) and 30 Hz flicker implicit timing (P =.016). Further, underlying ocular disorders did not result in differences of FFA (P =.42), or ffERG scores (P =.52).

The patients’ median ffERG score (measured on a scale of 0 to 6) was 5, with 91% achieving 4 or higher. Only 3 eyes of 2 patients scored 1 or less For 3.0 scotopic mixed response, 94% displayed normal timing and 79% normal amplitude. Although notably, results of photopic 30 Hz flicker timing revealed delayed responses in 65% of eyes, and greatly delayed at 2 or less for 50%. 

Lower ffERG marks correlated with systemic disease (P =.014) and vitreous haze, according to the investigators. Specifically, haze was associated with delayed photopic 3.0 b-wave cone timing (P <.001), flicker implicit timing (P =.002), and lower amplitude photopic flicker (P =.03). Peripheral vessel and macular leakage were also connected to delayed photopic flicker timing. Yet, reduced best corrected visual acuity (BCVA) only slightly correlated with delayed photopic cone timing (P =.046).

“Although we have found several statistically significant correlations with depressed ffERG responses, all of them, except for vitreous haze, were weakly correlated,” the investigators report. “Therefore, we suggest using ffERG to evaluate retinal function in retinal vasculitis, and not just rely on clinical criteria to assess its severity.” 

Previous research involving ffERG responses in uveitis — not specifically retinal vasculitis — demonstrates that cones are more vulnerable, and cone-produced responses may correlate with clinical assessment. The current investigators also note that most participants displayed normal or slightly lower ffERG, except those with systemic illnesses. This finding supports added exploration for systemic origins, with the caveat that masquerading conditions such as retinal dystrophy with leakage may present challenges. 

A study limitation relates to the 2 possible ffERG grading approaches. Researchers chose the z-score-based scale that is age compensated rather than the absolute, quantitative model. Also, this sample was relatively small with few presentations of occlusive retinal vasculitis. The analysis, though, offers unique clues on retinal function as measured by electroretinography.