Longitudinal Study of Nerve Fiber Layer Thickness Change in Open Angle Glaucoma

Lee, Hee Jeong; Choi, Kyu Ryong

Abstract

PURPOSE: To evaluate longitudinal retinal nerve fiber layer (RNFL) thickness change in patients with open-angle glaucoma (OAG) and to assess the possibility that RNFL thickness change may diagnose the progression of glaucoma earlier than visual field change.
METHODS
Eighteen OAG patients and twenty normal subjects who had had serial scanning laser polarimetry (Nerve Fiber Analyzer II : NFAII, version 2.1., LDT, Inc., U.S.A.) imaging and Humphrey C30-2 visual fields performed at average 27.5 months apart (8 months~48 months) were included in this study. These measurements were compared between groups at baseline and at subsequent follow-ups. Rate of change per month which was calculated by dividing the absolute value of measurements between baseline and follow-up by duration were also compared between two groups.
RESULTS
Significant differences in visual field parameter, such as MD, CPSD and IOP were found between OAG patients and normal controls at baseline. Over the same time, average reduction rate in RNFL thickness was 0.36 mu m/month in OAG patients while 0.14 mu m/month in normal controls. This represented the 2.6 times as great reduction rate in OAG patients as in normal controls. And there was greater RNFL thinning in OAG patients than in normal subjects, at the parameter of superior average (p=0.014), inferior average (p=0.024), temporal average (p=0.012). Visual field parameters did not change significantly in both OAG patients and normal controls.
CONCLUSIONS
Significantly greater reduction of RNFL thickness over time in OAG group , especially superior, inferior and temporal area, indicated that superior, inferior and temporal RNFL of OAG patients had thinned at a faster rate. Of all the NFA parameters, reduction rate of total polar average, superior average, inferior average and temporal average seemed to be helpful in early detection of glaucoma progression before the visual field deterioration.