Ranked-segment distribution curve for interpretation of optic nerve topography.
OBJECTIVE
The objective of this article was to evaluate whether a new method for analysis of optic nerve topography, the ranked-segment distribution (RSD) curve, can differentiate between normal and glaucoma eyes.


METHODS
Topographic optic nerve parameters of 39 normal subjects aged 50-79 years were measured using a confocal scanning laser ophthalmoscope (Heidelberg Retina Tomograph). Disc parameters were determined from the mean topography of three images of each eye obtained with a 15 degrees field of view. Rim area and retinal nerve fiber layer cross-section area were measured in 36 segments (each of 10 degrees) around the disc margin. For each parameter, the 36 segments were ranked in descending order and graphically depicted as the RSD curve. In normal eyes, the fifth percentile values for each of the ranked segments were calculated and graphed to compare with glaucoma eyes within the same age group. Evaluation of RSD curves was done automatically with a computer program using predefined criteria. Three primary open-angle glaucoma cases are presented to demonstrate the RSD curve method.


RESULTS
In these three glaucoma eyes, RSD curves demonstrated defects more consistently than stereoscopic disc photography, nerve fiber layer photography, and computerized visual field testing. In two cases, RSD curves differentiated between diffuse and localized defect as well as demonstrated the locations of the defects.


CONCLUSIONS
The RSD curve technique may assist in the interpretation of topographic optic nerve parameters and in the detection of glaucomatous optic neuropathy.
Asawaphureekorn
S
S
Glaucoma Center, University of California at San Diego, La Jolla 92093, USA.
Zangwill
L
L
Weinreb
R N
RN
D000328:Adult; D000368:Aged; D003937:Diagnosis, Differential; D005260:Female; D005901:Glaucoma / Q000175:diagnosis* / Q000473:pathology; D005902:Glaucoma, Open-Angle / Q000473:pathology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D018613:Microscopy, Confocal; D008875:Middle Aged; D009887:Ophthalmoscopy; D009898:Optic Disk / Q000473:pathology; D009900:Optic Nerve / Q000473:pathology*; D010781:Photography; D012016:Reference Values; D012160:Retina / Q000473:pathology; D014794:Visual Fields