Author Affiliations: G. B. Bietti Foundation–Istituto di Ricerca a Carattere Clinico e Scientifico, Rome (Dr Savini), and Studio Oculistico d’Azeglio (Dr Barboni) and Dipartimento di Scienze Neurologiche, Università di Bologna (Dr Carelli), Bologna, Italy; and Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles (Dr Sadun).
We read with interest the article by Scott et al1 on papilledema imaging by optical coherence tomography (OCT). Analyzing the whole peripapillary retinal thickness by OCT is worthwhile, as the edema is not limited to the inner layers, ie, the retinal nerve fiber layer (RNFL); it also involves the outer retina. The presence of a hyporeflective subretinal space around the optic disc in eyes with papilledema had already been described by our group and later manually quantified by Johnson et al.2,3 In 2006, we postulated 2 hypotheses to explain this finding. First, the extensive swelling of the optic nerve head pushes the disc anteriorly. The adjacent peripapillary fibers are attached and are also drawn forward. This may produce an upward traction to the peripapillary retina, generating negative pressure and a space below the retina, where fluid accumulation occurs. Second, the subretinal fluid may accumulate because of increased tissue and venous pressure caused by venous stasis at the level of the optic nerve head.2 The latter hypothesis was shared by Johnson et al,3 who considered the hyporeflective space the consequence of extravasated fluid from the optic nerve head. In a previous letter, Hayreh4 stated that the subretinal fluid leaks from the dilated retinal radial peripapillary capillaries secondary to optic disc edema. We would be interested in which mechanism Scott et al favor. Further, given that cases with papilledema were classified according to the severity of the disease, the authors may have missed an opportunity to separately investigate, in each stage of papilledema, the relative contribution to total retinal thickness of RNFL edema and subretinal thickening. This could easily be done by subtracting the RNFL thickness from the total retinal thickness.
Savini G, Barboni P, Carbonelli M, Carelli V, Sadun AA. Optical Coherence Tomography for Optic Disc Edema. Arch Ophthalmol. 2011;129(9):1245-1247. doi:10.1001/archophthalmol.2011.282