Validating and Updating the OHTS-EGPS Model Predicting 5-year Glaucoma Risk among Ocular Hypertension Patients Using Electronic Records

Abstract

Objective: To validate and update the Ocular Hypertension Treatment Study-European Glaucoma Prevention Study (OHTS-EGPS) model predicting risk of conversion from ocular hypertension (OHT) to glaucoma using electronic medical records (EMR).

Design: Evaluation and update of a risk prediction algorithm using EMRs and linked visual field (VF) tests.

Participants: Newly diagnosed OHT patients attending hospital glaucoma services in England. Inclusion criteria are as follows: intraocular pressure (IOP) 22 to 32 mmHg (either eye); normal baseline VF test, defined as Glaucoma Hemifield Test (GHT) "within normal range" in a reliable VF test; at least 2 VF tests in total; no significant ocular comorbidities.

Methods: Risk factors are as follows: age, ethnicity, sex, IOP, vertical cup-to-disc ratio, central corneal thickness, VF pattern standard deviation, family history of glaucoma, systemic hypertension, diabetes mellitus, and glaucoma treatment. Glaucoma conversion was defined as 2 consecutive and reliable VF tests with GHT "outside normal limits" and/or need for glaucoma surgery. For validation, the OHTS-EGPS model was applied to predict a patient's risk of developing glaucoma in 5 years. In the updating stage, the OHTS model was refitted by re-estimating the baseline hazard and regression coefficients. The updated model was cross-validated and several variants were explored.

Main outcome measures: Measures of discriminative ability (c-index) and calibration (calibration slope) were calculated and pooled across hospitals using random effects meta-analysis.

Results: From a total of 138 461 patients from 10 hospital glaucoma services in England, 9030 patients with OHT fitted the inclusion criteria. A total of 1530 (16.9%) patients converted to glaucoma during this follow-up period. The OHTS-EGPS model provided a pooled c-index of 0.61 (95% confidence interval: 0.60-0.63), ranging from 0.55 to 0.67 between hospitals. The pooled calibration slope was 0.45 (0.38-0.51), ranging from 0.25 to 0.64 among hospitals. The overall refitted model performed better than the OHTS-EGPS model, with a pooled c-index of 0.67 (0.65-0.69), ranging from 0.65 to 0.75 between hospitals.

Conclusions: We performed an external validation of the OHTS-EGPS model in a large English population. Refitting the model achieved modest improvements in performance. Given the poor performance of the OHTS-EGPS model in our population, one should use caution in its application to populations that differ from those in the OHTS and EGPS.

Financial disclosure(s): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Keywords: Electronic medical records; Glaucoma; Ocular hypertension; Risk prediction.