Purpose: To investigate the influence of pars plana vitrectomy (PPV) on the integrity of photoreceptor layers in eyes with diabetic macular edema (DME) by using parallelism (a parameter that comprehensively reflects photoreceptor-retinal pigment epithelium [RPE] complex alterations) in spectral-domain optical coherence tomography (SD-OCT) imaging.
Methods: A consecutive series of 64 eyes in 55 patients with diabetic macular edema who underwent pars plana vitrectomy were recruited into the study. Spectral-domain optical coherence tomography images were obtained preoperatively and 6 months after surgery. The morphologic features of the outer retinal layers were assessed quantitatively using parallelism and qualitatively by graders, including continuity of the external limiting membrane (ELM) line, continuity of the photoreceptor inner and outer segment (IS/OS) junction line, and the presence of hyperreflective foci in the outer retinal layers. The relationships between parallelism, visual acuity (VA), and photoreceptor layer status were evaluated.
Results: After surgery, foveal thickness significantly decreased (P < 0.0001) and visual acuity improved (P < 0.0001) from baseline level. Postoperative parallelism (0.632 ± 0.137) was significantly higher than preoperative parallelism (0.531 ± 0.172) (P < 0.0001). A number of eyes with hyperreflective foci reduced after surgery, while separate evaluation of the inner and outer segment junction and external limiting membrane lines did not show significant changes. Moreover, preoperative and postoperative parallelism values showed significant correlations with postoperative visual acuity and serum lipid levels. Foveal thickness and logMAR visual acuity did not show significant correlations with any blood test data.
Conclusion: Pars plana vitrectomy might be effective for resolution of hyperreflective foci in outer retinal layers. Parallelism is a potential marker for localization of hyperreflective foci and useful as a predictive factor for postoperative visual acuity.