Quantitative effect of subretinal fluid and intraretinal edema on visual acuity in uveitic cystoid macular edema

BACKGROUND: The effect of subretinal fluid (SRF) in uveitic cystoid macular edema (CME) is not fully understood. This study evaluates the quantitative effect of SRF and intraretinal thickness on visual acuity in eyes with uveitic CME. We separately measured SRF and intraretinal area on Optical Coherence Tomography (OCT) to determine the associations of each component with visual acuity and response to treatment. MAIN TEXT: Medical records were reviewed of patients with CME presenting to the University of Colorado uveitis clinic from January 2012 to May 2019. All available OCTs were reviewed to classify eyes as either having only CME or CME with SRF. Intraretinal area was manually measured using Image J along the central 1-mm section of B-scan OCT spanning from the internal limiting membrane to the outer most portion of the outer retina including both cysts and retinal tissue. SRF cross-sectional area was measured spanning from the outermost portion of the outer retina to retinal pigment epithelium. Response to treatment was assessed one to four months after presentation. Eyes with CME secondary to structural or non-inflammatory causes were excluded. Forty-seven (50.5%) eyes had CME alone and 46 (49.5%) eyes had SRF with CME. Measured SRF cross-sectional area was not associated (p = 0.21) with LogMAR at presentation. Conversely, intraretinal area was strongly correlated with visual acuity in eyes with SRF (p < 0.001) and without SRF (p < 0.001). Following treatment, there was a significant decrease in intraretinal area for both groups (p < 0.001), with a larger decrease in the SRF group compared to the non-SRF group (p = 0.001). Similarly, logMAR improved in both groups (p = 0.008 for SRF eyes and p = 0.005 for non-SRF eyes), but the change was more prominent in the SRF group (p = 0.06). CONCLUSIONS: There was no direct association observed between the amount of SRF and visual acuity. In contrast, increased intraretinal area was significantly associated with decreased visual acuity. This relationship between intraretinal thickening and visual acuity may explain differences observed in response to treatment between SRF and non-SRF eyes, with a larger decrease in the intraretinal cross-sectional area in SRF eyes associated with a greater improvement in logMAR visual acuity.