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L.M. Hurvitz; Measurement Ring Size as a Possible Error in Calculation of Corneal Compensation for Laser Polarimetry . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3400.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: to evaluate the effect of ring size on estimation of anterior segment polarization in scanning laser polarimetry Methods: A retrospective case review was undertaken in eyes that were found to have anterior segment undercompensation during GDx scanning of the macular area. 30 consecutive such eyes were identified. In these eyes, the macula was scanned once with the same size ring that was used during scanning the nerve fiber layer around the optic nerve, as directed by the manufacturer. A second scan of the macula was again performed using the smallest ring possible. Both scans were centered on the fovea. A qualitative analysis was made of the difference in the two scans of the macular area of each patient. A statistical analysis is difficult, as no methodology for analysis of macular area scanning has been established. Results: A large qualitative difference was seen in the macular area laser polarimetry scans for many of the tested eyes. A "spotty" type of undercompensation is often observed, which is not equally measured by one or the other of the tested rings. Conclusions: A variable anterior segment compensator is in development by the manufacturer of the GDx machine. The smallest ring is always used in the calculation of the anterior segment compensation, prior to scanning the nerve fiber layer around the optic nerve. This calculation is likely to be flawed by use of only the small ring, which may not accurately represent the anterior segment polarization. A better standard of measurement of anterior segment polarization is needed.
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