Abstract
Purpose: :
To compare total retinal thickness (TRT) and nerve fiber layer thickness (NFLT) to light sensitivity (LS) in the central macula using microperimetry and retinal topography in normal and glaucoma patients.
Methods: :
Spectral OCT/SLO (Ophthalmic Technologies Inc., Ontario, Canada) was used to map macular topography and perform microperimetry on 10 eyes (7 patients). Retinal topography was performed of a 5.5mm x 5.5mm area of the central macula via a 200 x 200 cube scan. NFLT was extracted from TRT by edge detection method. Microperimetry "Humphrey 10" protocol was chosen with a stimulus size of 400 miniarc squared (corresponding to Goldman III). TRT and NFLT maps were overlain on microperimetry results by computer assisted recognition. Point by point comparison was made for 44 points in a rectangular grid within the central macula corresponding to microperimetry testing sites. Statistical analysis was performed using NCSS 2007. Linear regression analysis was performed at each of the 44 points comparing both and RT and NFLT to LS in decibels. A second linear regression analysis was performed to determine the correlation of the data sets in their entirety. Unpaired t-tests were used to compare mean TRT and NFLT for glaucoma vs. normal subjects.
Results: :
Demographics: 10 eyes (7 patients), 64yr -73yr, 4M/3F, best corrected visual acuity 20/20 to 20/50, refractive error + 4.0 to -4.0 d. Four eyes had glaucoma of varying severity, 2 eyes were glaucoma suspects and 4 eyes were age-matched normals. LS was weakly associated with both TRT (R Square = .132 (1,395) p<.001) and NFLT (R Square = .132 (1,395) p<.001). A stronger association was found between TRT and NFLT (R square = .382 (1,395) p<.001). Point by point analysis showed the lowest correlation in the fovea and parafoveal areas. When averaged across all points, NFLT in glaucoma eyes was 59% less than that of age matched controls (p<.001). When TRT was corrected for NFLT at each point, mean for glaucoma patients was 3.2 % less than age matched controls (p<.001).
Conclusions: :
Although globally there was a decreased light sensitivity, total retinal thickness, and nerve fiber layer thickness among glaucoma patients when compared to normal, a limited association exists between these variables when compared at specific retinal foci. When NFLT was subtracted from TRT, the average thickness measurements for glaucoma and normal eyes were more closely approximated, confirming a preferential loss of NFL in glaucomatous eyes. Retinal topography used in conjunction with confocal microperimetry may prove useful in the management of glaucoma patients; further study is warranted.
Keywords: imaging/image analysis: clinical • nerve fiber layer • macula/fovea