External limiting membrane as a predictor of visual improvement in diabetic macular edema after pars plana vitrectomy

Abstract

Background: To evaluate the predictors of visual improvement using spectral-domain optical coherence tomography (SD-OCT) in eyes with resistant diabetic macular edema (DME) treated with pars plana vitrectomy.

Methods: Thirty-four eyes with resistant DME were evaluated in a retrospective manner. Several SD-OCT variables including photoreceptor inner segment/outer segment (IS/OS) junction, external limiting membrane (ELM) integrity, and central macular thickness (CMT) before and after the surgery, were evaluated by two experienced observers, masked to visual acuity. The visual improvement was used as the outcome measure for a stepwise regression, while the OCT factors were used as predictors.

Results: The strongest predictor of vision improvement was pre-operative damage to the ELM (p = 0.0277) compared to IS/OS junction (p = 0.03). Pretreatment central macular thickness was a very weak predictor (p = 0.18) of visual improvement. For each percentage increase of ELM integrity there was a 0.13 letter gain in vision. ELM integrity explained 16% of the visual acuity improvement after treatment, which rose to 21% with the addition of CMT. The addition of IS/OS junction in the model did not add predictive information.

Conclusions: Evaluation of ELM preoperatively predicts the vision improvement more accurately than the IS/OS junction and CMT in eyes with DME.