We appreciate Hanumunthadu and associates’ interest in our recently published manuscript, “Response of pigment epithelial detachment to anti–vascular endothelial growth factor treatment in neovascular age-related macular degeneration.” They have presented interesting data through correspondence about the repeatability of manual pigment epithelial detachment (PED) measurement on spectral-domain optical coherence tomography (SDOCT). The data indicated that mean PED height measurements derived from SDOCT are more repeatable than those derived from swept-source optical coherence tomography (SSOCT). Additionally, they suggested that a change of more than 34.6 μm in PED height measured with Spectralis SDOCT would be the result of an alteration in disease activity rather than measurement variability.
Recently, we read with interest their work about the repeatability of the measurement of retinal thickness and subfoveal choroidal thickness. They also suggested that a change of greater than 31 μm in Spectralis SDOCT–derived retinal thickness measurement and a change of greater than 35 μm in subfoveal choroidal thickness is necessary to detect a true clinical change associated with disease progression. We completely agreed with the point that manual measurement of the thickness of any retinal layer on an OCT image could entail a problem of repeatability in nature. Clinicians should be aware of this inherent measurement variability when they use an OCT image to measure various thicknesses, including PED height, retinal thickness, or choroidal thickness, and should pay attention to distinguish a true clinical change from a measurement variability.
The lack of correlation between PED height reduction and visual acuity is quite frequent; the visual improvements after anti–vascular endothelial growth factor (VEGF) treatment are more likely a result of improvement in other factors, such as intraretinal fluid or subretinal fluid, rather than a reduction in PED height. Hence, PED height has not been included in the conventional re-treatment criteria for pro re nata (PRN) treatment for neovascular age-related macular degeneration, and it is considered less useful as a clinical marker of treatment response. However, a recent study showed that the subretinal pigment epithelium lesion underlying PED may be the primary indicator for progressive disease activity, and PED seemed to be a trigger for consecutive vision loss in PRN treatment. In fact, in our study, the visual outcomes of patients with flattened PEDs after treatment were better than those of patients without flattened PEDs.
The importance of changes in PED after anti-VEGF treatment is undeniable. However, using current OCT technology, it is difficult to obtain detailed and accurate data, such as PED volume or PED lesion size, that could be more meaningful than PED height in determining therapeutic response. Further studies are necessary to better understand the mechanisms underlying and therapeutic responses of PED after anti-VEGF treatment.