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Editors Selection IGR 7-2
Types of glaucoma: Longterm OHT
Comment by Richard Parrish II on:
12114 A long-term prospective study of risk factors for glaucomatous visual field loss in patients with ocular hypertension, Bengtsson B; Heijl A, Journal of Glaucoma, 2005; 14: 135-138
A randomized prospective double-masked clinical trial, reported by Bengtsson and Heijl (206), the Malmo Ocular Hypertension Study, which recruited patients between 1981 and 1987, provides important information on risk factors that affect a predominantly white northern European population. Of the 90 patients who were randomized to topical timolol or placebo treatment and followed prospectively in some cases for a maximum of 17 years, 37 developed characteristic glaucomatous visual field loss. Interestingly, 18 patients who were initially randomized to timolol and 19 in the placebo group progressed. Not surprisingly, patients with a 'suspect disc appearance', older age, and those with higher mean IOP at baseline were shown to be at increased risk as in OHTS.1-3. The authors conclude that "suspect disc topography, defined as cup/disc ratio greater to or equal to 0,6 or cup /disc ratio discrepancy between the two eyes greater to or equal to 0.2, or marked cup asymmetry or disc hemorrhage […]" was the most important risk factor for progression with a univariate hazard ratio of nearly three. They describe allowing themselves to use the term 'risk factor' broadly by applying it to factors more likely to be an early manifestation of the disease than its cause. Historically, it is important to note that at the time the study was performed, disc
findings in the absence of visual field changes were viewed as risk factors rather than evidence of 'pre-perimetric glaucoma'. Higher IOP at baseline, defined as a mean of greater to or equal to 27 mmHg, doubled the risk for glaucoma compared to those with a baseline IOP less than 27 mmHg in a multivariate analysis. Too few patients with diabetes were recruited to determine if a protective effect existed as demonstrated in the OHTS.2 What does this study mean? That older patients with suspicious discs and higher IOP deserve more frequent follow-up care. How frequently should ocular hypertensive patients be seen? Often enough to assure that they will return for regularly scheduled follow-up visual field and optic disc examination to detect possible progression. The Malmo study examined patients every three months, somewhat more frequently than suggested by the European Glaucoma Society Terminology and Guidelines for Glaucoma, 2nd Edition.4 From a practical standpoint the question of whether newer technologies to assess optic nerve structure, such as scanning laser ophthalmoscopy, scanning laser polarimetry, and optical coherence tomography would have permitted the detection of earlier disease or progression earlier than determined by visual field criteria cannot be answered in the study. The conclusion that optic nerve examination is the key to identifying those at highest risk seems obvious.
References
1. Gordon M, Kass MA. The Ocular Hypertension Treatment Study: design and baseline description of the participants. Arch Ophthalmol 1999; 117: 573-583.2. Kass MA, Heuer DK, Higginbotham EJ, Johnson CA, Keltner JL, Miller JP, Parrish RK II, Wilson MR, Gordon MO. The Ocular Hypertension Treatment Study. A randomized trial determines that topical ocular hypotensive medication delays or prevents the onset of primary open-angle glaucoma. Arch Ophthalmol 2002; 120: 701-713.
3. Gordon MO, Beiser JA, Brandt JD, Heuer DK, Higginbotham EJ, Johnson CA, Keltner JL, Miller JP, Parrish RK II, Wilson MR, Kass MA. The Ocular Hypertension Treatment Study. Baseline factors that predict the onset of primary open-angle glaucoma. Arch Ophthalmol 2002; 120:714-720.
4. European Glaucoma Society, Terminology and Guidelines for Glaucoma IInd Edition, 2003.
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