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Robert W. Knighton, Xiang-Run Huang, David S. Greenfield; Analytical Model of Scanning Laser Polarimetry for Retinal Nerve Fiber Layer Assessment. Invest. Ophthalmol. Vis. Sci. 2002;43(2):383-392.
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purpose. To develop a quantitative understanding of scanning laser
polarimetry (SLP) for retinal nerve fiber layer (RNFL) assessment in
glaucoma diagnosis and management.
methods. The Mueller calculus was used to model the polarization optics of SLP.
A birefringent retinal structure (RNFL or macula) was represented as a
circularly symmetric linear retarder with a radial slow axis. The
birefringent cornea and a corneal compensator within the SLP instrument
were represented as fixed linear retarders. The model provided images
of the radial retarder that were compared with retardance images
obtained by SLP of the macula in eight normal subjects. Theoretical and
experimental images were quantified with circular profiles around the
center of the radial retarder or macula. Experimental retardance
profiles were varied by tilting the subject’s head to rotate the
corneal axis. The SLP model was fit to the experimental profiles by
nonlinear least-squares curve fitting.
results. The combined retarder formed by the cornea and corneal compensator
induced bow-tie patterns in images of the radial retarder. Macular SLP
images exhibited similar patterns. Retardance profiles could be
characterized by three parameters: modulation, mean, and axis. The SLP
model fit the experimental profiles very well
(r 2 = 0.8–0.9).
conclusions. The SLP model provided a quantitative framework within which to
interpret SLP studies. Modulation-based parameters were generally more
sensitive to retinal birefringence than mean-based parameters. Corneal
birefringence is an important source of variance in SLP, especially for
mean-based parameters. The theory developed for this study may guide
improvements in clinical SLP.
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