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Editors Selection IGR 13-2

Medical Treatment: Does treating OH delay onset of glaucoma?

Comment by Robert Fechtner on:

25627 Delaying Treatment of Ocular Hypertension: The Ocular Hypertension Treatment Study, Kass MA; Gordon MO; Gao F et al., Archives of Ophthalmology, 2010; 128: 276-287

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The OHTS design randomized 1636 subjects to observation or treatment for ocular hypertension to determine if treating ocular hypertension prevents or delays the onset of glaucoma. Target IOP reduction for the treatment group was rather modest; IOP < 24 mmHg and 20% IOP reduction. Reduction of IOP below 18 mmHg was not required. Those results were published in 2002 demonstrating a clear benefit of IOP reduction with 4.4% of the treatment group and 9.5% of the observation group reaching a glaucoma endpoint. That left 95.6% of the treatment group and 91.5% of the observation group who DID NOT reach an endpoint.

Phase II of the OHTS began after June 2002. All participants were invited to continue, but ocular hypotensive medications were now offered to the observation group. By this decision, we lost the opportunity to learn more about the natural history of untreated ocular hypertension but could learn if a seven-year delay in initiating treatment affected later progression to an endpoint. Median follow-up was thirteen years with 90% of participants continuing through closeout.

Some of the key observations from this new report by Kass et al. (263) include the following: 1) a delay in treatment did not result in more severe visual field loss when glaucoma developed; 2) the likelihood of a bilateral glaucoma endpoint was higher in the observation group (n = 51 vs. n = 32); 3) the risk of developing glaucoma was greater during the period during which IOPlowering treatment was not administered; 4) the onset of glaucoma was about two and a half years earlier in the observation group for those who developed it (median 6.0 years vs. 8.7 years).

'Whom to treat and whom to watch' - as with so many other questions in glaucoma: 'it depends'

A high proportion of those in the highest tertile of risk as estimated by the OHTS/European Glaucoma Prevention Study risk calculator developed glaucoma (40% of the observational group and 28% of the treatment group). The number needed to treat to prevent one case of glaucoma in this group was seven. However, the risk calculator was based, in part, on this cohort so this estimate may be high. Perhaps more importantly, glaucoma developed rarely in the lowest tertile risk group. The number needed to treat to prevent one case of glaucoma was 98.

In an accompanying editorial, Alfred Sommer transforms Hamlet's lament 'To be or not to be' to our current dilemma of 'whom to treat and whom to watch.' As with so many other questions in glaucoma, the OHTS leaves us with the answer 'it depends.'

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