Partial posterior vitreous detachment as a classification criterion of epiretinal membrane.

Dear editor

I read with great interest the article “Relationship between variations in posterior vitreous detachment and visual prognosis in idiopathic epiretinal membranes” by Ota et al.1 The authors have compared visual prognosis of epiretinal membrane (ERM) patients according to type of vitreous detachment. Partial posterior vitreous detachment (P-PVD) was found to be related with poor visual acuity and prognosis. I appreciate the authors for this well-organized study.

Position of vitreous is very important in some retinal diseases. Vitreoretinal traction and adhesion affects prognosis of vitreoretinal interface diseases, macular hole, diabetic retinopathy, and age-related macular degeneration.2 Existence of vitreous detachment is a criterion of macular hole. Because of its importance in prognosis, I think vitreous detachment also should be a criterion for classification of ERMs. As stated in this study, P-PVD may cause a rapid worsening of clinical table by impairing structure of retinal composition and accelerating progression of ERM. Thus, revising classification of ERM according to existence of P-PVD may provide a better clinical approach to this disease.

Dear editor

We appreciate the comments of Abdullah Kaya, MD, about our article “Relationship between variations in posterior vitreous detachment and visual prognosis in idiopathic epiretinal membranes”.1 As Dr Kaya mentioned, it is very important to evaluate the vitreous pathology to determine its prognosis in many vitreoretinal diseases including epiretinal membranes (ERMs). I agree with his idea that vitreous detachment also should be a criterion for classification of ERMs.

Clinical grading of ERMs has been proposed by Gass, and it has been widely used.2 However Gass’s classification of ERMs is based on the configuration of the ERMs and macular retina but does not include the vitreal pathologies. An ERM with a grade 2 macular pucker is frequently associated with vitreomacular traction syndrome. It is obvious that a grade 2 ERM requires vitreous surgery. The ERMs with vitreomacular traction syndrome were not included in our article. We think that the vitreous condition, especially a partial posterior vitreous detachment (PVD) without shrinkage (M), which shows weak and chronic anteroposterior vitreous traction on the macula, independently affects the visual prognosis of ERMs regardless of the ERM configuration. ERMs with a partial PVD without shrinkage (M) have a worse visual prognosis than an ERM with no PVD and a complete PVD with collapse. However, it is difficult to detect the mobile vitreous gel on still images using optical coherence tomography. Slit-lamp vitreous biomicroscopy is more suitable for detecting mobile vitreous gel.

We strongly recommend a vitreous examination in which both biomicroscopy and OCT are performed to detect variations of PVD in vitreomacular diseases.3