title: Shape analysis of the peripapillary RPE layer in papilledema and ischemic optic neuropathy.
abstract: OBJECTIVE
  Geometric morphometrics (GM) was used to analyze the shape of the peripapillary retinal pigment epithelium-Bruch's membrane (RPE/BM) layer imaged on the SD-OCT 5-line raster in normal subjects and in patients with papilledema and ischemic optic neuropathy.
  
  
  METHODS
  Three groups of subjects were compared: 30 normals, 20 with anterior ischemic optic neuropathy (AION), and 25 with papilledema and intracranial hypertension. Twenty equidistant semilandmarks were digitized on OCT images of the RPE/BM layer spanning 2500 μm on each side of the neural canal opening (NCO). The data were analyzed using standard GM techniques, including a generalized least-squares Procrustes superimposition, principal component analysis, thin-plate spline (to visualize deformations), and permutation statistical analysis to evaluate differences in shape variables.
  
  
  RESULTS
  The RPE/BM layer in normals and AION have a characteristic V shape pointing away from the vitreous; the RPE/BM layer in papilledema has an inverted U shape, skewed nasally inward toward the vitreous. The differences were statistically significant. There was no significant difference in shapes between normals and AION. Pre- and posttreatment OCTs, in select cases of papilledema, showed that the inverted U-shaped RPE/BM moved posteriorly into a normal V shape as the papilledema resolved with weight loss or shunting.
  
  
  CONCLUSIONS
  The shape difference in papilledema, absent in AION, cannot be explained by disc edema alone. The difference is a consequence of both the translaminar pressure gradient and the material properties of the peripapillary sclera. GM offers a novel way of statistically assessing shape differences of the peripapillary optic nerve head.
authors: Department of Ophthalmology, Health Sciences Center, University Hospital and Medical Center, State University of New York, Stony Brook, NY 11794, USA. patrick.sibony@sbumed.org
authors: Patrick
authors: P
authors: Sibony
authors: Mark J
authors: MJ
authors: Kupersmith
authors: F James
authors: FJ
authors: Rohlf
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D016570:Bruch Membrane / Q000033:anatomy & histology / Q000473:pathology*; D048430:Cell Shape; D005260:Female; D006801:Humans; D019586:Intracranial Hypertension / Q000175:diagnosis*; D008279:Magnetic Resonance Imaging; D008297:Male; D009898:Optic Disk / Q000473:pathology*; D018917:Optic Neuropathy, Ischemic / Q000175:diagnosis*; D010211:Papilledema / Q000175:diagnosis*; D055213:Retinal Pigment Epithelium / Q000033:anatomy & histology / Q000473:pathology*; D012189:Retrospective Studies; D041623:Tomography, Optical Coherence; D055815:Young Adult