Atypical pattern of retardation on GDx-VCC and its effect on retinal nerve fibre layer evaluation in glaucomatous eyes.
OBJECTIVE
To assess the effect of atypical pattern of retardation (APR) on retinal nerve fibre layer (RNFL) measurements made by scanning laser polarimetry (SLP) with variable corneal compensation (GDx-VCC) in glaucomatous eyes.


METHODS
One eye each of 30 glaucomatous patients (average mean deviation (MD): -6.4+/-4.8) with APR on GDx-VCC retardation map were selected. In total, 34 glaucomatous, age- and severity-matched eyes (average MD: -7.0+/-5.3) and 36 age-matched healthy subjects, both with a normal pattern of retardation (NPR) represented control groups. APR on retardation maps was characterized by alternating peripapillary circumferential bands of low and high retardation, or high retardation areas arranged in a spokelike pattern, or high retardation nasal and temporal splotchy areas. Typical scan score (TSS) was extracted for each included eye. GDx-VCC parameters (mean+/-SD) in the two groups of glaucomatous eyes were compared with healthy eyes' corresponding values (Mann-Whitney U-test). Areas under receiver operating characteristic (AUROC) curves were generated to assess the APR effect on the parameters' diagnostic ability.


RESULTS
All parameters discriminated adequately between healthy and glaucomatous eyes with NPR (AUROCs > or =0.9 for nine parameters). On the contrary, considering healthy and glaucomatous eyes with APR, four thickness parameters could not separate the two groups and AUROCs > or =0.85 appeared only for Inferior and Superior Ratio, NFI, Max Modulation.


CONCLUSIONS
APR may void the effect of custom compensation and provide spurious RNFL thickness measurements. When a printout of glaucomatous eyes with APR is evaluated, it is proper to rely on ratios, modulation parameters, and NFI, since the diagnostic ability of thickness parameters is significantly reduced.
Da Pozzo
S
S
Eye Clinic, University of Trieste, Trieste, Italy. stefano34127@lycos.it
Marchesan
R
R
Canziani
T
T
Vattovani
O
O
Ravalico
G
G
D000368:Aged; D003941:Diagnostic Techniques, Ophthalmological; D018450:Disease Progression; D005260:Female; D005901:Glaucoma / Q000150:complications / Q000175:diagnosis* / Q000503:physiopathology; D006801:Humans; D008297:Male; D009412:Nerve Fibers / Q000473:pathology*; D009901:Optic Nerve Diseases / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology; D012372:ROC Curve; D012165:Retinal Ganglion Cells / Q000473:pathology*; D012189:Retrospective Studies; D012720:Severity of Illness Index; D014794:Visual Fields