Intra-retinal Cotton Wool Spots and Their Relation to Epiretinal Membrane Contraction and Induced Retinal Distortion

Background: Idiopathic Epiretinal membranes (ERM) may cause a wide variety of retinal abnormalities due to tangential traction on the retinal surface. These tractional changes may lead to retinal vascular leakage and oedema or rarely, a mechanical blockage of the axoplasmic flow resulting in a cotton wool spot (CWS). Aim: To follow the pre-operative location and time course of disappearance of cotton wool sports after ERM peeling and to document changes in retinal distortion in the post-operative period. Methods: This study examines four cases of epiretinal membranes associated with apparent cottonwool spots involving the central fovea. The time course of onset and disappearance of the white spots in relation to contraction and removal of the epiretinal membrane were examined. The retinal distortion produced by membrane contraction was evaluated by using four reference points on the perimacular vascular branches in preoperative and postoperative photographs taken with the same camera and projected at the same magnification. Results: The intra-retinal white spots, which appeared preoperatively to lie in the center of the fovea, proved to have been pulled in from more peripheral retina by the epiretinal membrane. These white areas were associated with surprisingly great distortion of the inner retina. Stretching of the inner retina seemed to play a larger role in the retinal distortion Conclusions: Tangential traction caused by ERM may cause interruption in axoplasmic flow and the resultant CWS indicate reversible visual loss.