In this analysis of the Advanced Glaucoma Intervention Study (AGIS), Joseph Caprioli, MD, and Anne L. Coleman, MD, considered only patients who had one surgical intervention (ALT or trabeculectomy). They collected intraocular pressure data beginning at three months after the intervention and concluding at the first detection of visual field (VF) worsening (if any).
The baseline characteristics of this subgroup of AGIS patients was similar to those of the original cohort of patients described in previous AGIS reports.
The authors detected VF progression in approximately 26 percent of eyes, which is consistent with the number of eyes showing progression in the overall AGIS study (27 percent). They identified three variables associated with a higher probability of VF progression: greater IOP fluctuation (P = 0.009), argon laser trabeculoplasty (P = 0.004), and older age (P = 0.05).
The odds for VF progression increased by approximately 40 percent for each 1-mmHg increase (of SD) in IOP fluctuation, 280 percent for ALT performance as opposed to trabeculectomy, and about 20 percent for each five-year increment in age. A 1-mmHg increase of mean IOP was associated with 12 percent increased odds of VF progression, which was of borderline significance.
IOP fluctuation was associated with VF progression in the low mean IOP group, but not in the high mean IOP group.
The authors suggest clinicians may want to rethink target pressure, perhaps considering "IOP modulation" rather than "IOP reduction" when exploring treatment options.
"Target IOP is an IOP range deemed unlikely to cause further optic nerve damage from glaucoma. Estimation of target pressure is based on a patient's risk factors for progression, the level of IOP that caused damage, the severity of disease, and longevity. There is, of course, no way to determine in advance which IOP will prevent or slow further damage. Some patients may even have an IOP-independent component of damage. Perhaps we should consider IOP modulation rather than IOP reduction as the most appropriate treatment. This may include not only robust IOP reduction in patients at risk for visual loss, but also the goal of reducing IOP fluctuation, particularly in patients who progress at lower pressures. Specific guidelines, however, must await a better understanding of the pathophysiologic consequences of long-term IOP fluctuation in glaucoma."