Association Between Cup-to-Disc Ratio and Structural and Functional Damage Parameters in Glaucoma: Insights From Multiparametric Modeling.

PURPOSE

To model the association between vertical cup-to-disc ratio (CDR) and clinically relevant glaucomatous outcomes.

METHODS

From a tertiary glaucoma clinic, clinician-estimated CDR, CDR derived from peripapillary optical coherence tomography scans, circumpapillary retinal nerve layer thickness, optic disc diameter, visual field (VF) mean deviation (MD), glaucoma hemifield test (GHT), and VF index were used to develop sigmoidal regression models of CDR, analyzed for floor/ceiling effects of functional or structural damage by model comparisons based on logarithms of Bayes factors (logBF, with logBF > 5 indicating very strong evidence).

RESULTS

We selected 17,509 eyes of 10,420 patients. For all outcomes, there was strong evidence for sigmoidal regression compared with linear regression (all logBF > 650). Model fits were characterized by plateauing for CDR toward 0, with ceilings for functional outcomes below the values denoting normal VFs (MD = 0 and VF index = 100). The clinician-estimated CDR was stronger associated with functional outcomes (all logBFs > 347) and optical coherence tomography-measured CDR with retinal nerve layer thickness (logBF = 243). Areas under the receiver operator characteristic curve for abnormal MD and GHT vs. CDR were 0.626 and 0.653, respectively. Optic disc diameter only marginally improved predictability (areas under the receiver operator characteristic curve increase for abnormal MD/GHT: 0.001/0.006).

CONCLUSIONS

CDR is subject to ceiling effects for glaucoma-related outcomes and poor at discriminating early glaucomatous damage. CDR values should be interpreted with care, particularly in screening settings.

TRANSLATIONAL RELEVANCE

This interpretable nonlinear model helps to better explain specific impacts on and limitations of CDR, one of the most frequently recorded parameters for glaucoma diagnostics.