SS-OCT enables simultaneous visualization of the vitreous, retina, and choroid, and therefore may add a lot to our understanding of the pathomechanism of visual acuity loss associated with the epiretinal membrane.

Choroidal thickness has a very high intra-individual variability. It decreases in glaucoma or in nicotine abuse, and with age and refractive error [11]. It also depends on systemic vascular disease and caffeine or “energy drink” uptake. To make the measurements as reliable as possible, and thus useful for comparisons, they should be acquired at exactly the same time of the day. However, all choroidal thickness measurements should be evaluated very carefully. There is some primary data suggesting that choroidal thickness might slightly decrease three to 6 months after vitrectomy with ILM peeling for epiretinal membranes, which is not the case if vitrectomy is performed for other macular diseases [12]. The mechanism is not completely clear. It may be that choroidal thickness is slightly increased in the presence of epiretinal membranes and returns to normal values after surgery. It is not likely that vitrectomy causes choroidal thinning, as it was not confirmed for other diseases such as macular holes [13]. Thinning is not progressive, and was observed only three to 6 months after surgery. It must be considered, however, that those changes are very subtle.

A new finding observed with SS-OCT is that it is possible to visualize two lines at the choroidoscleral boundary, an upper, hyperreflective line and a lower, hyporeflective line. Together, the lines delineate the suprachoroidal layer (Fig. 10.4) [14]. The suprachoroidal layer is approximately 10–15 μm thick and is situated on the outer choroidoscleral boundary (CSB). It consists of five to ten layers of giant melanocytes interspersed between flattened processes of fibroblastic cells. As this layer was only recently recognized, little is known about its meaning. In idiopathic epiretinal membranes three factors were recognized, by multiple regression analysis, as being independently associated with the visibility of the suprachoroidal layer. First, this layer is more often visible in eyes with epiretinal membranes in which the outer plexiform layer forms waves on its outer surface, when compared to eyes with solely hyperreflective striae at the outer surface of the outer plexiform layer (Fig. 10.2). Second, it is associated with multiple adhesion points to the retina, and third, it correlates with central retinal thickness before surgery [13]. This might suggest that the suprachoroidal layer is more often visible in eyes with more prominent vitreoretinal traction and tangential traction between the epiretinal membrane and the retina.