Test–retest variability of scanning laser polarimetry with variable corneal compensation is not affected by severity of glaucomatous damage.

Abstract

Abstract: : Purpose: To evaluate the reproducibility of peripapillary retinal nerve fiber layer (RNFL) thickness in normal eyes and eyes with pre–perimetric, early–moderate and advanced glaucomatous optic neuropathy (GON) using scanning laser polarimetry with variable corneal compensation (SLP–VCC). Methods: Complete examination, standard achromatic perimetry (SAP), and SLP–VCC imaging of the peripapillary retina were performed. GON was defined as cup/disc asymmetry between fellow eyes of greater than 0.2, rim thinning, notching, excavation, or RNFL defect and was classified by the following groups: pre–perimetric (normal SAP), early–moderate (MD <12dB) and advanced (MD ≥ 12 dB). Exclusion criteria were visual acuity < 20/40, diseases other than glaucoma, and unreliable SAP. Abnormal SLP–VCC measurements were defined as a cluster of ≥ 3 contiguous superpixels outside 95% normal limits with 1 outside 99% normal limits, or any retardation parameter outside 95% normal limits. A series of 3 measurements were obtained on a single day and 3 separate measurements on 3 separate days within a 3–month period. Intrasession and intersession reproducibility were evaluated using an intraclass correlation coefficient. Results: 47 eyes of 47 patients (12 normal, 15 pre–perimetric GON, 10 early–moderate GON, and 10 advanced GON) were enrolled (mean age 60 ± 18 years, range 25 –88). All eyes with glaucoma had associated visual field abnormalities (average MD = –0.5 ± 1.3, –0.6 ± 1.5, –5.4 ± 3.0, –26.3 ± 5.0 dB for normals, pre–perimetric, early–moderate and advanced GON respectively). The intraclass coefficients of intrasession reproducibility of TSNIT average and NFI were 94% and 86%; 98% and 93%; 96% and 94%; and 98% and 98% for normals, pre–perimetric, early–moderate and advanced GON respectively. The intraclass coefficients of intersession reproducibility were 94% and 89%; 78% and 84%; 92% and 94%; and 95% and 96% for normals, pre–perimetric, early–moderate and advanced GON respectively. The location and extent of RNFL loss on the retardation map was repeatable in 12/15 (80%), 8/10 (80%) and 8/10 (80%) eyes of pre–perimetric, early–moderate and advanced GON respectively. Conclusions: SLP–VCC provides high level of reproducibility in normal and glaucomatous eyes. Test–retest variability is not affected by the severity of glaucomatous damage.

Keywords: imaging/image analysis: clinical • nerve fiber layer