Prognosis and Therapy
The initial goal of therapy is often to achieve a near 30% IOP reduction from a carefully determined baseline IOP. Once this is established, routine evaluations with appropriate individualized adjustments for target pressure are recommended. These adjustments should take into account relevant factors, including baseline severity of optic nerve damage and visual field loss, potential risks of therapy, comorbid conditions, and life expectancy of the patient. Target pressure may be reassessed and adjusted as needed during follow-up visits in order to maintain visual function.
In a secondary analysis of the Collaborative Normal-Tension Glaucoma Study (CNTGS; see Clinical Trial 7-3 at the end of the chapter), IOP lowering by at least 30% reduced the 5-year risk of visual field progression from 35% to 12%, supporting the role of IOP in NTG. It should be noted that the protective effect of IOP reduction was evident only after adjusting for the effect of cataracts, which were more frequent in the treated group. Considering the findings of the CNTGS, treatment of NTG is generally recommended unless the optic neuropathy is determined to be stable. Interestingly, about half of the patients who did not receive treatment in this study did not progress over the study duration, whereas 12% of patients progressed in that they had worsening glaucomatous visual field damage despite a 30% reduction of IOP. Factors in addition to IOP are likely important in patients with this disease. In those who worsened, the rate of visual field progression was highly variable yet slow in most but not all patients. In addition, this study showed a lower treatment benefit among patients with a baseline history of a disc hemorrhage.
Treatment of NTG differs little from that of other OAGs. Some glaucoma specialists are wary of treating NTG with topical β-blocker medications because of their association with low OPP (see the subsection “Lower ocular perfusion pressure”). The Low-Pressure Glaucoma Treatment Study showed a high rate of glaucomatous progression in patients treated with timolol. However, there was a significant loss of follow-up in this study, and its results must be interpreted with that in mind. In the Early Manifest Glaucoma Trial (EMGT; see Clinical Trial 7-4), IOP lowering with the combination of betaxolol and ALT was minimal in eyes with baseline IOPs of 15 mm Hg or lower. This finding suggests that patients with a lower baseline IOP who are progressing may need incisional surgery or medications other than β-blockers to stabilize their disease. Such tailoring of treatment to each patient is relevant to all forms of glaucoma. See Chapter 13 for further discussion of indications for surgery.
Bhandari A, Crabb DP, Poinoosawmy D, Fitzke FW, Hitchings RA, Noureddin BN. Effect of surgery on visual field progression in normal-tension glaucoma. Ophthalmology. 1997;104(7):1131–1137.
Collaborative Normal-Tension Glaucoma Study Group. Comparison of glaucomatous progression between untreated patients with normal-tension glaucoma and patients with therapeutically reduced intraocular pressures. Am J Ophthalmol. 1998;126(4):487–497.
Collaborative Normal-Tension Glaucoma Study Group. The effectiveness of intraocular pressure reduction in the treatment of normal-tension glaucoma. Am J Ophthalmol. 1998;126(4):498–505.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.