Glaucoma Risk Calculator — Ocular Hypertension to Glaucoma Conversion

About

The Ocular Hypertension Treatment Study (OHTS, 2002, NEJM) was a landmark multicenter randomized clinical trial that established the benefit of IOP-lowering therapy in preventing or delaying the onset of primary open-angle glaucoma (POAG) in patients with ocular hypertension (IOP 24-32 mmHg). The study followed 1,636 patients for a mean of 72 months and identified baseline risk factors that predict conversion to glaucoma. The European Glaucoma Prevention Study (EGPS, 2005) independently validated these risk factors. The combined OHTS/EGPS model includes: age (older age increases risk), intraocular pressure (higher baseline IOP increases risk), central corneal thickness (thinner CCT = higher risk), baseline visual field pattern standard deviation (PSD >2 dB = higher risk), vertical cup-to-disc ratio (larger CDR = higher risk), and race (Black American or African Caribbean ethnicity increases risk). Diabetes was also independently associated with increased risk in pooled analysis. The risk calculator was externally validated in multiple populations including the Diagnostic Innovations in Glaucoma Study (DIGS). Clinically, a 5-year risk threshold of >15% is commonly used as a trigger for initiating IOP-lowering treatment in patients with ocular hypertension, as recommended by the AAO Preferred Practice Pattern for Primary Open-Angle Glaucoma (2020).

Formula

5-year risk = baseline risk + age contribution + IOP contribution + CCT contribution + PSD + CDR + race + diabetes

The risk calculation integrates multiple weighted risk factors from the OHTS/EGPS pooled analysis. Age >40 years increases baseline risk by approximately 2% per decade. Baseline IOP >22 mmHg contributes approximately 8% risk per mmHg above 22. Central corneal thickness <555 µm contributes approximately 1.2% risk per 10 µm below 555. Abnormal PSD pattern deviation on baseline visual field testing adds approximately 10% risk. Vertical cup-to-disc ratio >0.5 adds approximately 30% risk per 0.1 above 0.5. Black/African-Caribbean race adds approximately 15% risk. Diabetes adds approximately 8% risk. The total risk is capped at 100%.

Score Interpretation

The OHTS/EGPS risk calculator is the most validated tool for predicting glaucoma onset in ocular hypertension. Its practical applications include: (1) Shared decision-making — providing patients with their personalized 5-year risk helps them understand the benefits of treatment vs observation. A patient with 40% 5-year risk who chooses observation has a number-needed-to-treat of approximately 10 to prevent one case of glaucoma. (2) Treatment threshold — most guidelines use >15% 5-year risk as a treatment trigger. (3) Resource allocation — identifies high-risk patients needing more frequent monitoring. (4) Clinical trial inclusion — the calculator is used to enrich clinical trial populations with higher-risk patients. OHTS showed that treatment reduced 5-year glaucoma incidence from 9.5% to 4.4% in the overall population, but the absolute risk reduction was much higher (15-20%) in high-risk subgroups.

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