There is poor agreement between visual field (VF) testing and scanning laser polarimetry (SLP) in the detection of glaucoma progression among healthy eyes, eyes with suspicion of glaucoma, and glaucomatous eyes, report US researchers.
The team carried out testing using both fast mode (FM; population-derived) and extended mode (EM; individual variability) criteria, but neither proved superior at detecting glaucoma progression compared with VF, as reported in the British Journal of Ophthalmology.
"Taken together, we cannot ascertain the most effective SLP method of progression detection," say Gadi Wollstein (University of Pittsburgh School of Medicine, Philadelphia) and co-workers, adding: "It is therefore recommended to acquire three SLP scans at each visit, to allow either EM or FM to be performed."
The study included 16 healthy eyes, 34 with suspected glaucoma, and 26 with glaucoma, which was defined as having a glaucomatous VF at baseline.
Participants undertook a mean of six visits involving SLP analysis, which uses a polarization-modulated light source directed on the retina to identify retinal nerve fiber layer (RNFL) thickness changes indicative of glaucoma, as well as VF testing.
A total of 10 eyes were identified as having glaucoma progression using VF testing (seven with glaucoma, and three with suspected glaucoma), with four eyes detected as progressing according to FM criteria, and four progressing according to EM criteria.
For FM-detected progression, the rates of change were 0.13, 0.43, and 0.22 µm/year for healthy, glaucoma suspect, and glaucomatous eyes, respectively, while the corresponding rates of change with EM in these eyes were 0.18, 0.45, and 0.31 µm/year.
These results represent significantly different rates of change between glaucoma suspects compared with healthy eyes for EM- and FM-detected progression, and significant differences in rates of change between glaucomatous eyes compared with healthy eyes for EM, but not FM.
Furthermore, the difference in temporal-superior-nasal-inferior-temporal average rate of change between VF-defined progressors and nonprogressors (whether FM- or EM-detected), was significant, indicating a lack of agreement between the methods of detection.
"Vision loss and RNFL changes occur at different times and exhibit different rates of progression, making agreement difficult to detect," remark Wollstein and colleagues.
"A model that accounts for these differences and relates structural and functional changes in glaucoma may provide a better assessment of disease," they conclude.
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