Scanning laser polarimetry of the normal human retinal nerve fiber layer: A quantitative analysis

PURPOSE: To provide a quantitative comparison of retardation values obtaine d with the scanning laser polarimeter (Nerve Fiber Layer Analyzer; Laser Di gnostic Technologies, San Diego, California) in normal subjects, with the k nown histologic properties of the human retinal nerve fiber layer. METHODS: Scanning laser polarimetry was performed on 48 normal subjects. Th e retardation values obtained from each eye were processed to remove reflec tions from the optic nerve head vasculature and to derive peripapillary pol ar retardation profiles. The location of the maximum and minimum retardatio n values superior and inferior to the disk was determined. Retardation valu es were also determined along lines running radially from the center of the optic disk to through the points of maximal retardation. RESULTS: Retardation values were greater in the superior and inferior quadr ants of the peripapillary retinal nerve fiber layer compared with the nasal and temporal quadrants. Superiorly, peak retardation values were nasal to the vertical meridian by 22.9 degrees (SD, 17.5) in right eyes and by 15.7 degrees (SD, 17.7) in left eyes. Inferiorly, the peak showed a closer corre spondence with the vertical meridian, lying nasal to this by 0.8 degrees (S D, 14.9) in right eyes and temporal to this by 2.8 degrees (SD, 15.4) in le ft eyes. Radial analysis showed that the peak retardation occurred approxim ately (0.5 to 0.7 disk diameters from the optic disk margin) at the superio r and inferior aspect of the disk. The degree of modulation of retardation around the optic disk was less than would be expected from the variation in peripapillary nerve fiber layer thickness seen histologically. CONCLUSION: The location sf the peak retardation values shows reasonable ag reement with the angular location of the peak values of nerve fiber layer t hickness published for humans. By contrast, the modulation of retardation v alues around the disk and the change with eccentricity from the optic disk center differ from the anatomic data. The Nerve Fiber Layer Analyzer appear s to measure a correlate of nerve fiber layer thickness, but it is importan t that any discrepancies between the retardation and anatomic data are reco gnized in the clinical interpretation of polarimetric data. (Am J Ophthalmo l 2000;129:76-82. (C) 2000 by Elsevier Science Inc. All rights reserved.)