Inefficacy of Longitudinal Cup-to-Disc Ratio Measurements in Identifying Glaucoma Progression.

Abstract

To assess whether longitudinal change in cup-to-disc ratio (ΔCDR) is predictive of glaucoma progression on optical coherence tomography (OCT) or standard automated perimetry (SAP). Retrospective cohort study. Subjects in the Bascom Palmer Glaucoma Repository. We extracted CDRs from the electronic health record. We identified OCT and SAP tests performed within ±6 months of CDRs. Baseline and final CDRs were defined as CDRs closest to the baseline and final tests, respectively. Eyes were required to have ≥5 tests spanning ≥2 years. ΔCDR was calculated as CDR _final - CDR _baseline. Using ordinary least squares regression, we calculated eye-specific rates of change in OCT retinal nerve fiber layer (RNFL) and SAP mean deviation (MD). We classified eyes as progressors if they had statistically significant negative eye-specific slopes (P < .05). We then evaluated how well ΔCDR predicted progression on OCT or SAP. Area under receiver operating characteristic curve (AUC) predicting OCT or SAP progression using ΔCDR. In the OCT analysis (N = 3313 eyes), ΔCDR ≥0.20 was observed in only 7.1% of OCT progressors and 4.8% of non-progressors (P = .04). Only 2% of the variation in OCT RNFL slopes was explained by ΔCDR. AUC was 0.55. At 90% specificity, ΔCDR had a sensitivity of 15% in detecting OCT progressors. In the SAP analysis (N=2,174 eyes), ΔCDR ≥0.20 was observed in only 7.7% of SAP progressors and 5.7% of non-progressors (P = .23). Only 1% of the variation in SAP MD slopes was explained by ΔCDR. AUC was 0.53. At 90% specificity, ΔCDR had a sensitivity of 16% in detecting SAP progressors. Longitudinal CDR data performs similar to random selection in identifying glaucoma progression on both structural and functional testing. Given this weak association, clinicians should gauge glaucomatous progression using both a comprehensive optic nerve head examination and ancillary testing.