Impact of atypical retardation patterns on detection of glaucoma progression using the GDx with variable corneal compensation.
OBJECTIVE
To evaluate the impact of atypical retardation patterns (ARP) on detection of progressive retinal nerve fiber layer (RNFL) loss using scanning laser polarimetry with variable corneal compensation (VCC).


METHODS
Observational cohort study.


METHODS
The study included 377 eyes of 221 patients with a median follow-up of 4.0 years. Images were obtained annually with the GDx VCC (Carl Zeiss Meditec Inc, Dublin, California, USA), along with optic disc stereophotographs and standard automated perimetry (SAP) visual fields. Progression was determined by the Guided Progression Analysis software for SAP and by masked assessment of stereophotographs by expert graders. The typical scan score (TSS) was used to quantify the presence of ARPs on GDx VCC images. Random coefficients models were used to evaluate the relationship between ARP and RNFL thickness measurements over time.


RESULTS
Thirty-eight eyes (10%) showed progression over time on visual fields, stereophotographs, or both. Changes in TSS scores from baseline were significantly associated with changes in RNFL thickness measurements in both progressing and nonprogressing eyes. Each 1-unit increase in TSS score was associated with a 0.19-microm decrease in RNFL thickness measurement (P < .001) over time.


CONCLUSIONS
ARPs had a significant effect on detection of progressive RNFL loss with the GDx VCC. Eyes with large amounts of atypical patterns, great fluctuations on these patterns over time, or both may show changes in measurements that can appear falsely as glaucomatous progression or can mask true changes in the RNFL.
Hamilton Glaucoma Center and Department of Ophthalmology, University of California, San Diego, La Jolla, California 92093, USA. fmedeiros@eyecenter.ucsd.edu
Felipe A
FA
Medeiros
Luciana M
LM
Alencar
Linda M
LM
Zangwill
Pamela A
PA
Sample
Remo
R
Susanna
Robert N
RN
Weinreb
D000368:Aged; D001369:Axons / Q000473:pathology*; D001718:Birefringence; D003315:Cornea / Q000502:physiology; D018450:Disease Progression; D005902:Glaucoma, Open-Angle / Q000175:diagnosis* / Q000503:physiopathology; D006801:Humans; D007834:Lasers; D009798:Ocular Hypertension / Q000175:diagnosis / Q000503:physiopathology; D009898:Optic Disk / Q000473:pathology*; D009901:Optic Nerve Diseases / Q000175:diagnosis* / Q000503:physiopathology; D010781:Photography; D012165:Retinal Ganglion Cells / Q000473:pathology*; D014786:Vision Disorders / Q000175:diagnosis; D058609:Visual Field Tests; D014794:Visual Fields