JUN 22, 2016
Using data from the Idiopathic Intracranial Hypertension Treatment trial (IIHTT), investigators showed that abnormal visual fields were more likely a result of patient performance failure than an indicator of actual disease progression in idiopathic intracranial hypertension (IIH).
The authors recommend retesting when perimetric worsening occurs in otherwise clinically stable or improving IIH patients.
Treatment failures (TF) was defined when the participant’s VF mean deviation worsened more than 2 to 3 dB from the baseline, with a second retest confirming the visual deterioration. Performance failures (PF) was defined as either visual field results meeting treatment failure criteria on 1 field that were not confirmed on a second field or deterioration was confirmed on the retest but the adjudication committee concluded that true worsening due to IIH was unlikely.
The IIHTT randomized 165 participants with mild visual loss to either acetazolamide plus a low-sodium weight-reduction diet or placebo plus diet. TFs were rare, occurring in 4% of the participants. PFs were detected in 35/165 (21%) of the participants on at least 1 examination. However, when the test was repeated, the result was reversed. The authors attribute PF to possible treatment side effects such as drowsiness, fatigue and headaches.
Additionally, the study showed that 87% of the perimetry results classified as a performance failure had “reliability criteria” calculated by the perimeter software within normal limits. Therefore, the perimeter’s reliability criteria are not useful for judging whether a visual field change is real and it is only through repeat testing that this determination can be made.