Frequency Doubling Technology Perimetry 2 (24-2) in the Evaluation of Homonymous Hemianopias

Abstract

Abstract: : Purpose: Frequency doubling technology 2 (FDT) perimetry is a method of visual field testing that uses smaller FDT stimuli (5°) with an approximately six-degree spaced grid of the central 27°. FDT 1 with its 17 separate 10° stimuli is an effective screening method for glaucomatous field loss but has an issue with stimulus detection in the hemianopic field by the uninvolved hemifield. The purpose of this study was to compare FDT2 to conventional automated perimetry (CAP) in the detection of homonymous hemianopias. Methods: FDT 2 (FDT2 24-2, 55 separate 5° stimuli) and CAP (SITA Standard 24-2, 54 separate size III, 0.43° stimuli) were performed on 25 patients with homonymous hemianopias. The total deviation and pattern deviation probability plots were compared by inspection of probability plots with respect to similarity (good, fair, poor). We also evaluated the extent (equivalent, FDT2, CAP) of the defect by two visual field readers; at least 25% more abnormal test locations needed to be present for one test to have greater extent. A preliminary database of 81 normals was used to generate the probability plots. Results: For the total deviation probability plots, the similarity of the defect shown on FDT and CAP was judged to be good in 54% of cases, fair in 33% of cases, and poor in 13% of cases; the extent of the defect on FDT and CAP was equal in 58% of cases, more extensive on CAP in 33% and more extensive on FDT in 8% of cases. For the pattern deviation probability plots, the similarity of the defect shown on FDT and CAP was judged to be good in 63% of cases, fair in 33% of cases, and poor in 4% of cases; the extent of the defect on FDT and CAP was equal in 67% of cases, more extensive on CAP in 25% and more extensive on FDT in 8% of cases. There were 5 instances of some stimulus detection by the uninvolved hemifield along the vertical midline. Conclusions: FDT 2 correlates well with CAP based upon similarity of shape and extent of visual field defects due to homonymous hemianopia. Stimulus detection in the involved hemifield along the vertical meridian is present in 1/5 of cases but is less prominent than with FDT 1.

Keywords: perimetry • visual fields • neuro-ophthalmology: cortical function/rehabil