Relationship Between Dry Retinal Volume and Visual Acuity in Diabetic Macular Edema

Background and objective: To evaluate the relationship between a novel spectral-domain optical coherence tomography (SD-OCT) parameter, predicted dry retinal volume (DRV), and visual acuity (VA) in subjects with diabetic macular edema.

Patients and methods: Twenty-eight eyes of 26 subjects with macular edema secondary to diabetic retinopathy (cases) and 10 healthy eyes of normal volunteers (controls) were included. Spectral-domain optical coherence tomography volume scans (512 × 128) were obtained before and 6 months to 12 months after anti-vascular endothelial growth factor therapy. The borders of the neurosensory retina, nerve fiber layer (NFL), and vitreous were manually defined using previously described grading software. NFL reflectivity was used to normalize the signal between eyes, allowing a normalized total retinal intensity to be computed for each eye by summing the brightness of every pixel in the retina on all B-scans. Using this normalized retinal intensity, a ratio of retinal intensity of cases over retinal intensity of normal was generated. The predicted DRV was computed by multiplying this calculated ratio with total retinal volume at baseline for each eye. Correlation analysis was performed between DRV at baseline and VA at baseline and final follow-up.

Results: The mean ± standard deviation age of the cohort was 69 years ± 9.8 years, and 28% were female. Mean best-corrected VA (logMAR) improved from 0.56 ± 0.36 at baseline to 0.44 ± 0.32 at follow-up (P = .001). The uncorrected ("wet") total retinal volume of 13.25 mm³ ± 2.73 mm³ at baseline declined significantly to a posttreatment retinal volume of 10.92 mm³ ± 1.42 mm³. The predicted DRV (10.79 mm³ ± 1.42 mm³) was statistically similar to the post-treatment, actual retinal volume. No significant correlation was observed between DRV and post-treatment VA.

Conclusions: The predicted DRV at baseline showed good agreement with the actual observed posttreatment retinal volume. Thus, DRV may be a potentially useful parameter to estimate the extent of retinal tissue loss that may be obscured by the presence of concomitant edema. The lack of correlation between DRV and VA, however, suggests that other parameters, such as the integrity of the outer retinal bands, are likely important for visual outcome prediction. [Ophthalmic Surg Lasers Imaging Retina. 2018;49:510-515.].