“Cotton ball sign” may predict visual impairment

The authors of this retrospective case series in the March issue of Ophthalmology report a new OCT finding in eyes with vitreomacular traction (VMT) or epiretinal membrane (ERM) that they call the "cotton ball sign" due to its appearance. They describe it as a roundish or diffuse highly reflective region located between the photoreceptor inner segment/outer segment junction and the cone outer segment tip line at the center of the fovea.

They say it resolved or improved after surgical or spontaneous resolution of inward retinal traction. They speculate that it is indicative of inward traction and might predict visual impairment that may arise after chronic inward traction at the fovea.

The study included 45 patients (54 eyes) with symptomatic VMT or ERM. The highly reflective region was present in all seven cases of VMT and 30 of 47 cases of ERM. In the ERM cases, the mean central foveal thickness of cases with the highly reflective region was significantly thicker than in cases without it.

The exact mechanism that causes the highly reflective region was not determined. However, the authors say there is very little possibility that it is an optical artifact since it appeared when inward traction was forced to the outer retina, regardless of the existence of an ERM, and disappeared when the traction was released.

They note that the cotton ball sign was observed in patients with good vision. Four of seven eyes with VMT and 9 of 30 eyes with ERM with the sign had best-corrected visual acuity of 0.8 or better. This means that the cotton ball sign does not necessarily indicate a decrease in visual acuity, and it may be used as a predictor of visual impairment that would arise after longstanding inward traction at the fovea.

Since continuous foveal traction is known to cause microstructural damages in the photoreceptor layer, early detection of this sign may help in preserving good vision in these patients.