Abstract
Purpose::
To investigate (1) the variability of HRT measurements in normal and experimental glaucoma monkeys, (2) the correlations among HRT parameters, (3) the changes of HRT parameters in experimental glaucoma monkeys, (4) the relationship of HRT parameters to optic nerve fiber number in experimental glaucoma monkeys.
Methods::
4 normal monkeys and 16 laser-induced glaucoma monkeys were studied. Optic disc topography was measured in vivo with HRT three times. Coefficient of variance of each parameter was obtained from three measurements. Correlations among the topographic parameters were analyzed. The difference of each parameter between normal and experimental glaucoma monkeys was analyzed. Finally 4 normal and 8 experimental glaucoma monkeys were sacrificed. The nerve fiber number of each optic nerve cross section was estimated. The relationship between the nerve fiber count and each HRT parameter measured before sacrifice were calculated.
Results::
The coefficients of variation for rim area, mean cup depth and maximum cup depth were less than 10% both in normal and glaucomatous monkeys. The rim area (CV: 6.9% in normal and 4.7% in glaucoma) was the most reproducible parameter. The correlations among the topographic parameters (cup area, cup/disk ratio, cup volume, mean cup depth and maximum cup depth) in normal and experimental glaucomatous monkeys were strong, which was similar to human. The difference of all HRT parameters between normal and glaucomatous monkeys was distinguished except disk area. Rim area and cup/disk ratio were the most sensitive parameters. Cup/Disk ratio, Rim area, cup volume, disk volume, mean cup depth, maximum cup depth and cup shape measure correlate significantly to the optic nerve fiber number. Rim area(r=0.814), cup shape measure(r=-0.886) and cup/disk ratio(r=-0.833) showed strong correlation with the optic nerve fiber number.
Conclusions::
Rim area is a reproducible and useful parameter in experimental glaucomatous monkeys. The changes of optic nerve head in experimental glaucoma monkeys are similar to that of glaucoma patients. HRT could be used to evaluate optic nerve damage in glaucoma, and rim area is the best parameter.
Keywords: optic disc • optic nerve • nerve fiber layer