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Saturday, 12 February 2011

Early Treatment of Ocular Hypertension May Reduce Risk for Glaucoma

March 16, 2010 — Early treatment of ocular hypertension appears to reduce the risk for the development of glaucoma, especially in individuals at the highest risk, according to the results of a randomized controlled trial reported in the March issue of Archives of Ophthalmology.

"Elevated intraocular pressure (IOP) (ocular hypertension [OHT]) is a leading risk factor for the development of primary open angle glaucoma (POAG) and the only modifiable risk factor at present," write Michael A. Kass, MD, from Washington University School of Medicine in St. Louis, Missouri, and colleagues for the Ocular Hypertension Treatment Study (OHTS) Group. "It is estimated that 4% to 7% of the US population older than 40 years has OHT. There is substantial controversy on how to manage this large group of individuals who are at higher risk of developing glaucoma than the general population."

The goal of the study was to compare the safety and efficacy of earlier vs later treatment in reducing the risk for POAG in 1636 individuals with ocular hypertension, with baseline IOP ranging from 24 to 32 mm Hg in 1 eye and 21 to 32 mm Hg in the other eye. Participants were randomly assigned to observation or to receive topical ocular hypotensive medication. In the medication group, median duration of treatment was 13.0 years, whereas the observation group had a median duration of 7.5 years without treatment and then received medication for a median of 5.5 years.

To evaluate whether delaying treatment was associated with any harms, the investigators compared the cumulative proportion of participants who went on to have POAG in the original observation group and in the original medication group at a median follow-up of 13 years.

Overall, this proportion was 0.22 in the original observation group (95% confidence interval [CI], 0.19 - 0.25) vs 0.16 (95% CI, 0.13 - 0.19) in the original medication group (P =. 009), or a 27% reduction in glaucoma risk associated with early treatment. For participants at the highest tertile of baseline risk for the development of POAG, based on age, corneal thickness, and baseline IOP, the cumulative proportion of participants who went on to have POAG was 0.40 (95% CI, 0.33 - 0.46) and 0.28 (95% CI, 0.22 - 0.34), respectively.

"There was little evidence of increased adverse events associated with medication," the study authors write. "Absolute reduction was greatest among participants at the highest baseline risk of developing POAG. Individuals at high risk of developing POAG may benefit from more frequent examinations and early preventive treatment."

Limitations of the OHTS study include choice of a target IOP reduction of 20% from baseline, design not that of an epidemiologic study, use of very high thresholds for diagnosing POAG, and use of a convenience sample vs a population-based sample.

"We believe individualized assessment of the risk of developing POAG will be useful to patients and clinicians for deciding on the frequency of examinations and tests as well as the possible administration of preventive treatment," the study authors write. "Clinicians need to consider the patient's age, health status, life expectancy, and personal preferences when making such decisions. Ultimately, the full extent of the penalty for delaying treatment will require longer follow-up to ascertain the incidence and degree of visual impairment by randomization group."

In an accompanying editorial, Alfred Sommer, MD, MHS, from Bloomberg School of Public Health at Johns Hopkins University in Baltimore, Maryland, notes that clinicians should consider whether treating patients with IOP might do more harm than good.

"In the end, the physician is stuck with the persistent problem of whom to treat and whom to watch," Dr. Sommer writes. "The fascinating article by Kass et al provides interesting insights as to many of the issues at stake, but offers little definitive information to guide us. It probably still makes sense that young patients with lots of high risk factors should receive prophylaxis, while elderly patients with few risk factors should not. The endless symposia and debates on how best to manage patients with ocular hypertension will probably continue unabated."

The National Eye Institute and the National Center on Minority Health and Health Disparities, National Institutes of Health; Merck Research Laboratories; Pfizer Inc; and Research to Prevent Blindness supported this study. The study authors and Dr. Sommer have disclosed no relevant financial relationships.

Arch Ophthalmol. 2010;128:276-287.

Clinical Context

Glaucoma is one of the most common causes of blindness in the United States worldwide and has a higher incidence among African Americans than other racial groups. Elevated IOP is a leading risk factor for POAG, with 4% to 7% of the US population older than 40 years having ocular hypertension. Early medical treatment with topical hypotensive treatment in those with ocular hypertension has been shown to delay or prevent the onset of POAG but it is uncertain if duration of treatment affects the protective effects.

This is a randomized controlled trial conducted in adults with ocular hypertension to determine if medical vs delayed medical treatment in those with ocular hypertension is associated with reduced risk for POAG and if the effects differ in different risk groups.

Study Highlights

  • Inclusion criteria were ages 40 to 80 years, qualifying IOP of 24 mm Hg or higher or 32 mm Hg or less in 1 eye and 21 mm Hg or higher or 32 mm Hg or less in the other eye, gonioscopically open angles, 2 normal and reliable visual fields per eye, and normal optic discs.
  • Excluded were those with vision worse than 20/40 in either eye, with a history of ocular surgery, diabetic retinopathy, or optic disc degeneration.
  • The study involved 2 phases.
  • In phase 1, at baseline 817 participants were randomly assigned to topical ocular hypotensive agents and were observed for 13 years.
  • 819 were randomly assigned to observation only at baseline with no ocular hypotensive agents.
  • In phase 2, after 7.5 years, the observation group was given ocular hypotensive treatment for the next 5.5 years and thus received delayed treatment.
  • Follow up visits occurred every 6 months and included a medical and ocular history, determination of refraction and visual acuity, Humphrey white-on-white 30-2 visual field test, slit-lamp examination, IOP measurement, and direct ophthalmoscopy.
  • Participants also completed self-administered questionnaires consisting of the Glaucoma Symptom Checklist, the National Eye Institute Visual Function Questionnaire (every 24 months from 114 months), and the Medical Outcomes Study-Short Form with 36 questions.
  • POAG was defined as the development of reproducible visual field abnormality or clinically significant optic disc deterioration in 1 or both eyes that was attributed to POAG.
  • Optic disc degeneration was defined as generalized or localized disc thinning of the neuroretinal rim vs baseline stereoscopic disc photographs.
  • Primary endpoint was proportion of participants in whom POAG developed.
  • Mean age was 55 years, and median follow-up was 13 years.
  • Those in the observation with delayed treatment group had no medication for 7.5 years and were treated for 5.5 years.
  • The cumulative proportion of participants in whom POAG developed from baseline to 13 years was 0.19 overall, 0.22 for the observation with delayed treatment group, and 0.16 for the treatment group (P = .009), with a relative risk of 0.42 (P < .001) for the medication group.
  • In phase 2, the cumulative proportion who had POAG to 13 years was similar in the 2 groups (hazard ratio, 1.06; P = .77).
  • More participants in the observation vs the treatment group went on to have bilateral POAG at 13 years (6.2% vs 3.9%).
  • Similarly, more participants in the observation group vs the treatment group experienced glaucomatous visual field loss (2.3% vs 1.2%).
  • The cumulative proportion of African Americans in whom POAG developed was higher vs other races (0.28 vs 0.16).
  • The protective effect of treatment was significant during phase 1 for African Americans (hazard ratio, 0.47), but the proportions were similar in phase 2 when both groups received treatment.
  • African American status was a significant predictor of development of POAG (hazard ratio, 1.70).
  • The number of Hispanic patients was too small (n = 59) to determine risk.
  • When examined by baseline risk tertile, the cumulative proportion of participants who had POAG to 13 years were 6%, 6% to 13%, and more than 13% for the first, second, and third tertiles, respectively.
  • The numbers needed to treat to prevent 1 case of POAG during 13 years of treatment were 98, 16, and 7 for the first, second, and third tertiles of risk, respectively.
  • There were no significant differences in adverse effects or mortality rates in the observation and treatment groups.
  • The authors concluded that hypotensive ocular treatment reduced the risk for POAG in those with increased IOP, and the protective effect was greatest in those at highest risk and in African Americans.

Clinical Implications

  • Use of ocular hypotensive agents in those with IOP is associated with a reduced risk for POAG at 13 years.
  • The protective effect of ocular hypotensive medications is greatest in those with the highest baseline risk for POAG.

1 comment:

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