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Editors Selection IGR 15-3

Glaucoma and Systemic Diseases: POAG and diabetic retinopathy

Comment by Rupert Bourne on:

117110 Association of Primary Open-Angle Glaucoma with Diabetic Retinopathy among Patients with Type 1 and Type 2 Diabetes: A Large Global Database Study, Chauhan MZ; Elhusseiny AM; Kishor KS et al. et al., Ophthalmology, 2024; 131: 827-835

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The association between diabetes mellitus (DM) and primary open-angle glaucoma (POAG) has long been studied, with several studies reporting an increased risk of POAG in individuals with diabetes mellitus, with a prevalence around twice as high as the non-diabetic population.^1-4 IOP is an important confounder in the relationship between diabetes mellitus and POAG. There has also been a variation in the findings regarding the association between diabetes and POAG progression. In this retrospective study by Chauhan et al., the risk of diabetic retinopathy (DR) among those with POAG is explored, using a very large global patient database. The authors used propensity score matching (PSM) to harmonize two cohorts one of diabetics with POAG (n = 44,359) and another of diabetics without glaucoma (4,393,300), such that the two cohorts (each with 39,680 patients) could be compared for first-time onset of diabetic retinopathy, at intervals up to ten years. PSM attempts to reduce the bias due to confounding variables that could be found in an estimate of the POAG effect obtained from simply comparing outcomes among those with POAG versus those without. In this case an array of covariates included co-morbidities, demographics, blood glucose and cholesterol, and care-seeking behaviors, were used in the PSM process. The authors report a greater risk of proliferative diabetic retinopathy (PDR) among patients with Type 1 DM within the POAG group compared to those without glaucoma at one year (relative risk, RR, 3.0) and at ten years (RR, 7.0) and that the elevated risk of any DR was sustained over an extended period (adjusted Hazard Ratio, 3.74; at ten years). The risk of first-time DR and PDR in Type 2 DM patients was also higher across the time period.

These findings concur with a much smaller clinical study⁵ and also findings from the Danish Registry of Diabetic Retinopathy, which included almost 10,000 patients with glaucoma or ocular hypertension.⁶ The authors refer to the common mechanisms associated with both DM and glaucoma such as compromised autoregulation of retinal blood flow, ischaemia, and an interesting concept whereby loss of retinal ganglion cells in POAG may disrupt 'neurovascular coupling' ‒ a process that involves adjustment of blood flow in response to neural activity.⁷ Despite limitations of selection and information bias (which are well-described), there was a significant effort by the authors to control for potential confounders, which makes it an important addition to a body of evidence that suggests eyecare providers should adjust surveillance strategies in DR screening programs when glaucoma is already known.

There was a significant effort by the authors to control for potential confounders, which makes it an important addition to a body of evidence

Additionally, DR screening programs offer the opportunity for glaucoma case-finding, which increasingly can become automated, and the heightened risk of DR in a glaucomatous diabetic flagged.

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