Novel analytic model gauges progression

Oct 01, 2009

A novel analytic model, the Markov model, allows ophthalmologists to gauge the probability of progression of glaucoma in their patients over time simply by knowing their current mean deviation value.

Key Points

Fort Lauderdale, FL-A novel analytic model, the Markov model, allows ophthalmologists to gauge the probability of progression of glaucoma in their patients over time simply by knowing their current mean deviation (MD) value. The simplicity of such a model can prove to be helpful in the assessment of disease progression, impact of treatment choices, and estimation of the economic benefit of the prevention or treatment of glaucoma, said Steven M. Kymes, PhD, who spoke during the annual meeting of the Association for Research in Vision and Ophthalmology.

"There is little consensus on what constitutes glaucoma progression or how quickly it occurs in patients with the disease," said Dr. Kymes, research assistant professor, Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis.

The progression of glaucoma is assessed by evaluating the anatomic features of the ocular nerve for damage or by tests for visual field loss. One method of quantifying the visual field test is by use of MD, which is a measure of how the patient's perception of the visual field varies from that of the average person without visual field loss.

Assessments

The model was constructed using MD data from the participants in the Collaborative Initial Glaucoma Treatment Study, or CIGTS (n = 607), Ocular Hypertension Treatment Study, or OHTS (n = 1,619) and Advanced Glaucoma Intervention Study, or AGIS (n = 590).

These studies assessed treatment options in patients with ocular hypertension but no evidence of glaucoma (OHTS), patients with early glaucoma (CIGTS), and patients with advanced glaucoma (AGIS). The model was constructed to simulate the progression of glaucoma over 7 years with transition probabilities calculated for each level of MD for each year. At recent meetings, the group reported the results for four hypothetical patients with starting MDs of –1 dB, –4 dB, –10 dB, and –20 dB, respectively.

Visual field loss results

Results showed that over 7 years, 60% to 65% of patients with early glaucoma (that is, MD of –1 dB or –4 dB) are likely to see a worsening of their condition.

In contrast, slightly less than 60% of those with a loss of –10 dB are likely to lose –1 dB or more of visual field over 7 years. Of those with the worst disease tested (that is, –20 dB), more than 40% lost even more visual field. Of those with early disease, more than two-thirds experienced a loss > 3 dB of visual field during the 7 years.

"The high proportion of people with early disease who suffered clinically significant loss of visual field may speak to the importance of aggressive early treatment of people with even modest early field loss," Dr. Kymes said. "One purpose of this model is to examine the cost-effectiveness of such clinical policies."

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