Background  

The purpose of this study is to compare the effectiveness of pars plana vitrectomy (PPV) and dye-enhanced peeling of the internal limiting membrane (ILM) with modified grid laser photocoagulation in patients with diffuse diabetic macular edema and to determine if any correlation exists between improvement in visual acuity (functional improvement) and reduction in foveal thickness and macular volume (anatomical improvement).

Design  

This is a randomized, prospective, comparative, interventional study.

Method  

In this study 24 eyes of 24 patients with metabolically stable diabetes and with diffuse diabetic macular edema were evaluated. The patients were randomized to either pars plana vitrectomy with removal of ILM which was done in 12 eyes (ILM group) and modified grid laser photocoagulation carried out in the remaining 12 eyes (laser group). Main outcome measures were (1) the postoperative visual acuity in the form of ETDRS log MAR values, (2) foveal thickness and (3) macular volume as measured by optical coherence tomography. The correlation between improvement in visual acuity and the reduction of foveal thickness and macular volume in both the groups were also evaluated. The results were all subjected to statistical analysis.

Results  

The ETDRS log MAR visual acuity difference between the two groups at the end of 6 months was not clinically significant (P = 0.525). However, foveal thickness and macular volume decreased significantly more in the ILM group compared to the laser group (P = 0.001, P < 0.001, Mann Whitney U test). There was no correlation between the improvement in visual acuity and the reduction of foveal thickness (r = −0.158, P = 0.6) (ILM group), r = −0.155, P = 0.7) (laser group) in both groups.

Conclusions  

PPV with ILM peeling was shown to be beneficial by inducing a statistically significant reduction of macular thickness and macular volume. Visual acuity also demonstrated a trend towards improvement in both the ILM peel group and the grid laser group; however, the comparative VA outcome analysis between the two groups was not significantly different. Besides, there was also no correlation between the reductions of foveal thickness and macular volume with the improvement in visual acuity in either of the groups.