Comparison of retinal nerve fiber layer thickness measured by optical coherence tomography and scanning laser polarimetry (GDx)

Purpose： Optical coherence tomography (OCT) and scanning laser polarimetry (Nerve Fiber Analyzer， GDx) are optical devices that directly measure retinal nerve fiber layer (RN FL) thickness． ln this study， we compared the RN FL thickness measured by these two instruments under the same conditions， and also investigated the relationship between the visual field and RNFL thickness． Methods： Thirteen eyes of 13 glaucoma patients， 4 eyes of 4 patients with ocular hypertension， and 6 eyes of 6 normal subjects were studied (mean age±standard deviation， 56．0±13．6 year)． Mean deviation (MD) of the Humphrey Field Analyzer (HFA) was 一3．8±4．9 dB in glaucoma patients． Three consecutive measurements of peripapillary RNFL thickness were performed by a single operator using OCT and GDx． The same circular scan area with a radius of 1．7 mm centered on the optic disc was used for the determination of RNFL thickness using both instruments．The mean RNFL thickness was calculated for the total area and for each quadrant (superior， nasal， inferior， temporal) of the scanned circle． Cases with a coefficient of variance (standard deviation divided by mean RNFL thickness) greater than 10％ were excluded from analysis． Results： The mean overall RNFL thickness for OCT and GDx were 105．8±17．3 pt m and 79．3±14．6 pt m， respectively， and a significant difference was observed (p〈．OOO I)． A significant correlation between RNFL thickness measured by OCT and GDx was obtained in the total area and superior and inferior quadrants， but not in nasal and temporal quadrants． A significant correlation between corrected pattern standard deviation (CPSD) determined by HFA and RNFL thickness was observed for OCT but not for GDx． Conclusions： The RNFL thickness obtained using OCT is generally greater than that using GDx． Furthermore， a better correlation between visual function and RNFL thickness was obtained for OCT compared with GDx． 1． lntroduction In glaucoma， structural alterations of the optic disc and retinal nerve fiber layer (RN FL) often precede visual field abnormalities， and the importance of the ocular fundus test is emphasizedi・2)． Although the cup-disc (C／D) ratio is commonly used as a glaucomatous parameter in the clinical setting， this ratio does not allow reliable identification of structural changes of glaucoma because there is a broad overlap in distribution of glaucomatous and normal values and occasionally a lack of inter-observer reliability in measurement． Recently， several imaging technologies have been applied to the diagnosis of glaucoma， and allow quantitative and objective analysis of the optic disc and RNFL thickness． Among the optic disc parameters， the relative RNFL height has been reported to be the most effective parameter to distinguish between glaucoma