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Chris A Johnson, John L Keltner, Michael Wall, Kim E Cello, NORDIC Idiopathic Intracranial Hypertension Study Group; Classification of Baseline VIsual FIeld Results in the Idiopathic Intracranial Hypertension Treatment Trial (IIHTT). Invest. Ophthalmol. Vis. Sci. 2014;55(13):3544.
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Purpose: Idiopathic intracranial hypertension (IIH) is a disorder of elevated intracranial pressure of unknown cause. IIH can produce swelling of the optic disc and visual field loss. The Idiopathic Intracranial Hypertension Treatment Trial (IIHTT) is a multicenter trial to evaluate the efficacy of weight reduction and/or a low sodium diet plus acetazolamide versus diet plus placebo in reducing or reversing visual field loss. The purpose of this investigation was to classify the pattern of IIH visual field loss at baseline prior to treatment.
Methods: Two sets of baseline visual fields from both eyes of 165 IIH patients were evaluated for quality control and visual field abnormality classification. All visual field examinations underwent quality control assessment. Three trained readers used 12 mutually exclusive categories representing four general types of IIH visual loss (localized nerve fiber bundle-like, neurologic-like, diffuse, and other). Superior and inferior hemifields were classified separately.
Results: There were few quality control errors (average of only 5.48 error points out of 100 per visual field). A total of 660 baseline visual fields (1,320 hemifields) were classified, with 95% (superior hemifield) and 91% (inferior hemifield) agreement for 2 out of 3 readers. Test-retest reliability for 20% of the total number of visual fields was 95% for both the superior and inferior hemifields. The majority of the baseline hemifields (74.9%) consisted of localized nerve fiber bundle-like visual field defects. Approximately 1/3 of the classifications were partial arcuate-enlarged blind spot determinations (a subset of nerve fiber bundle-like), with slightly more cases for study eyes than for non-study eyes. The inferior hemifields exhibited more abnormalities than the superior hemifields, especially in the study eye. Enlarged blind spot, partial arcuate, normal and pericentral-enlarged blind spot classifications were also more prevalent than the other patterns.
Conclusions: Arcuate nerve fiber bundle defects (nasal step, enlarged blind spot, partial arcuate, arcuate, pericentral) were the most common patterns of baseline visual field loss for study and non-study eyes. Certification of technicians and quality control assurance procedures minimized the number of testing and shipment errors in the IIHTT baseline visual fields.
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