Finding a foveal depression on an OCT can be challenging at times. In the presence of an epiretinal membrane (ERM), it can be like trying to find Waldo.
Although the pathogenesis of primary, idiopathic ERM is relatively unknown, the effect of ERM is certainly known. In advanced stages of ERM, there can be significant traction on the retinal layers, and result in edema. Patients complain of decrease vision and metamorphopsia, and progression of ERM may result in a macular hole.
Because of the tension that ERM inflicts on retinal tissue, the normal foveal depression becomes vaulted and flush with the level of the internal limiting membrane (ILM). This makes it difficult to identify the fovea and provide a proper scan of the retina.
The vaulted fovea will result in a peaked appearance on OCT and the apex of this peak is the center of the fovea. By moving the scan line, the peak will taper and fall as you move through the fovea. It’s important to move the scan until the image shows the tapered end of the fovea where it meets the top (ILM) of the retinal tissue.
In the scans below, a simple horizontal movement of the scan reveals a more peaked appearance to the fovea:
Note the rounded appearance to the peak of the fovea, as well as the top of the peak not reaching the top of the retinal tissue