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Editors Selection IGR 8-1

Progression

Comment by Paul Lichter on:

13374 Progression of visual field loss in open angle glaucoma in the Melbourne Visual Impairment Project, Zahari M; Mukesh BN; Rait JL et al., Clinical and Experimental Ophthalmology, 2006; 34: 20-26

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The interesting study by Zahari et al. (132) makes conclusions that sound quite reasonable - namely, that glaucoma patients can lose visual field over time while under treatment by their ophthalmologist. The numbers presented are a bit hard to follow since in the results section, it is said that "112 (not 118 as the abstract states) participants were identified with possible, probable, or definite open angle glaucoma." Then, the authors state that 78 (not 74 as the abstract states) patients returned for the follow-up examination. Of these, 49 patients had Humphrey Fastpac visual field data, but only 43 had reliable fields. Of these, 22 people had 'definite' glaucoma, seven had 'probable' glaucoma, and 16 had 'possible' glaucoma at the baseline examination. Of the 22 with 'definite' glaucoma, 13 (65%) were considered to have progressed by at least one of the three visual field assessment methods used in the study. Only three of these patients were found to have progressed by all three assessment methodologies. Just one visual field was performed at follow-up examination and a single visual field is known not to be acceptable to determine visual field progression.

Four patients had improved visual fields using AGIS criteria, but since the other two assessment methods do not use a score like AGIS does, the authors did not feel they could assess whether visual fields had improved by those methods, an important failing in the methodology. Statistics were conducted, but very small numbers of subjects were involved. In summary, then, while the study's conclusions may be valid, there are so many uncertainties in the data and testing that it would be a stretch to say that the conclusions are justified from the methodology.

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