Validating and updating the OHTS-EGPS model predicting 5-year glaucoma risk among ocular hypertension patients using electronic records

Abstract

Purpose : To validate and update the OHTS-EGPS model predicting risk of conversion from ocular hypertension (OHT) to glaucoma using electronic medical records (EMR).

Methods : EMR data were extracted for patients newly diagnosed with OHT attending hospital glaucoma services in England. Inclusion criteria were: intra-ocular pressure (IOP) 22-32 mmHg in either eye, normal baseline visual field (VF) test, defined as Glaucoma Hemifield Test (GHT) ‘within normal range’ in a reliable VF test, at least two VF tests in total and no significant ocular co-morbidities.

Risk factors considered: 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. Conversion to glaucoma was defined as two 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 re-fitted by re-estimating the baseline hazard and regression coefficients. The updated model was cross-validated and several variants of the updated model were explored. 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 ten 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 re-fitted 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 externally validated the OHTS-EGPS model in a large English population. Re-fitting the model in the same population achieved modest improvements in performance. Further research on how these predictions might usefully be incorporated into clinical practice is warranted.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.