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Michael Wall, Gideon Zamba, NORDIC Idiopathic Intracranial Hypertension Study Group; Pointwise Visual Field Change in the Idiopathic Intracranial Hypertension Treatment Trial. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2234.
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The Idiopathic Intracranial Hypertension Trial (IIHTT) showed acetazolamide provided a modest but significant improvement in global visual field function using mean deviation. Here, we aim to further analyze 1) the rate and 2) the magnitude of individual visual field test location change in the treatment groups from baseline to primary end point (six months).
We evaluated 121 of the enrolled IIH subjects who had visual field testing at baseline, six months and 3 of 4 interim visits. At entry the SITA Standard 24-2 mean deviation was between -2 dB and -7 dB in the worst eye (study eye). Subjects from multiple study sites were randomized in a placebo-controlled trial of acetazolamide with both treatment groups receiving a weight reduction program. We used pointwise linear regression to classify each of the 52 visual field test locations in the study eye as improving or not using the criterion of a positive slope. In a separate analysis, differences in magnitude in dB from baseline to final visit for the groups were computed and ANOVA was used to determine the significance of differences at each location.
On average, subjects had 36 of 52 test locations with improving visual thresholds over six months in the study eye. While slopes of both groups improved, there were no significant differences in slopes between the treatment groups. Thresholds improved across the visual field with the magnitude of the change from baseline to final visit in dB greatest and statistically significant around the blind spot and the nasal area especially in the acetazolamide group. The figure shows the difference in dB between the groups (effect size of acetazolamide point by point).
While there were significant positive trends (slopes) in visual thresholds over time for most participants there were no significant differences between the groups. However, acetazolamide treatment resulted in significant improvement in visual field function with the magnitude of the changes greatest in the nasal and pericecal areas; the latter is likely due to reduction in blind spot size related to improvement in papilledema.
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