One common finding in diabetic retinopathy (DR) is macular edema. Torcato Santos, MD, of the Association for Innovation and Biomedical Research on Light and Image in Coimbre, Portugal, presented findings on macular edema progression in nonproliferative DR eyes based on tissue optical reflectivity at the 2021 ARVO virtual meeting last week. He and his team found that macular edema progresses independently of DR stage and severity.

The study included 74 eyes of 74 patients with DR type 2 and 40 controls. Patients underwent OCT imaging annually over the three-year study. The researchers used both OCT angiography and OCT leakage, an algorithm for detecting sites of low optical reflectivity (LOR) in the retina and all layers. They defined the LOR area ratio as a fraction of the number of A-scans with LOR and the total number of A-scans within a specific area. They applied standards to classify eyes as subclinical and clinical macular edema, or center-involved macular edema (CIME).

The 74 eyes were graded on the ETDRS severity scale, with grades of 10 to 20 (n=23), 35 (n=31) and 43 to 47 (n=20). The researchers detected CIME in 8.7% of eyes during the first visit in the grades 10 to 20 group, in 9.7% of eyes in the grade 35 group and in 15% of eyes in the grades 43 to 47 group.

They noted that in eyes with increased central retinal thickness (CRT), the inner nuclear layer (INL) showed the most dramatic thickness increase (52.9%). In eyes with CIME at baseline, they found a strong correlation between INL OCT leakage LOR (LOR-INL) and CRT value differences from V01 to V04. “Changes in CRT and LOR-INL occur in parallel and are characterized by frequent fluctuations,” the researchers noted in their poster abstract. These variations in LOR-INL demonstrated a wide range from the average value.

The researchers concluded that eyes of diabetic patients in early DR stages with different ETDRS retinopathy grading show a similar prevalence of macular edema. They believe the severity and progression of DR may be better characterized by frequent volumetric fluctuations in extracellular space of the INL of the retina, as the OCT leakage measurements of INL correlated with the presence of CIME and its development over the four follow-up visits in the study period.

Santos T, Marques I, Madeira MH, et al. Characterization of macular edema in the initial stages of diabetic retinopathy: a 3-year longitudinal study. ARVO 2021 annual conference.