Visual Field Outcomes for the Idiopathic Intracranial Hypertension Treatment Trial (IIHTT)

Abstract

PurposeThe Idiopathic Intracranial Hypertension Treatment Trial (IIHTT) showed that acetazolamide provided a modest, significant improvement in mean deviation (MD). Here, we further analyze visual field changes over the 6-month study period.MethodsOf 165 subjects with mild visual loss in the IIHTT, 125 had perimetry at baseline and 6 months. We evaluated pointwise linear regression of visual sensitivity versus time to classify test locations in the worst MD (study) eye as improving or not; pointwise changes from baseline to month 6 in decibels; and clinical consensus of change from baseline to 6 months.ResultsThe average study eye had 36 of 52 test locations with improving sensitivity over 6 months using pointwise linear regression, but differences between the acetazolamide and placebo groups were not significant. Pointwise results mostly improved in both treatment groups with the magnitude of the mean change within groups greatest and statistically significant around the blind spot and the nasal area, especially in the acetazolamide group. The consensus classification of visual field change from baseline to 6 months in the study eye yielded percentages (acetazolamide, placebo) of 7.2% and 17.5% worse, 35.1% and 31.7% with no change, and 56.1% and 50.8% improved; group differences were not statistically significant.ConclusionsIn the IIHTT, compared to the placebo group, the acetazolamide group had a significant pointwise improvement in visual field function, particularly in the nasal and pericecal areas; the latter is likely due to reduction in blind spot size related to improvement in papilledema. (ClinicalTrials.gov number, NCT01003639.)

The Idiopathic Intracranial Hypertension Treatment Trial: A Review of the Outcomes

“…PMD in the fellow eye also showed greater improvement in the acetazolamide group (acetazolamide 0.87 dB, from −2.28 dB to −1.41 dB; placebo 0.42 dB, from −2.28 dB to −1.86 dB; treatment effect 0.44 dB; 95% CI .01‐0.87 dB, P = 0.45). The greatest areas of improvement were in eccentric test points around the physiologic blind spot and the nasal field . The pattern of improvement was similar for both treatment groups, with a marked increase in the number of normal hemifields at 6 months.…”

“…The average PMD at baseline was −3.5 dB (SD 1.1) in the worst (study) eye and −2.3 dB (SD 1.1) in the best (fellow) eye . Glaucoma‐like, nerve fiber bundle (arcuate) field loss was the most common visual field abnormality, slightly more common in the inferior hemifield compared to the superior hemifield in both eyes.…”

“…Therefore, each clinical site had a certified visual field technician, the testing procedure and instructions were standardized, and all visual field tests were analyzed at a central Visual Field Reading Center. Three experienced readers reviewed all of the visual fields, and if two of them did not agree on the interpretation, the group adjudicated the visual field to achieve group consensus …”

“…Glaucoma‐like, nerve fiber bundle (arcuate) field loss was the most common visual field abnormality, slightly more common in the inferior hemifield compared to the superior hemifield in both eyes. Less commonly observed visual field defects were an isolated enlarged blind spot (without a contiguous nerve fiber bundle defect), a normal hemifield, or diffuse depression of the field …”

“…The study intervention used two of the most common treatment approaches, weight loss and acetazolamide therapy. While multiple aspects of visual function can be affected by IIH, perimetry was chosen as the primary outcome because it generates quantitative data, and visual loss in IIH occurs across the visual field and increases with eccentricity from central fixation . Previous investigations also suggested that visual field assessment is more sensitive for detection of visual defects than visual acuity and contrast sensitivity .…”