Frequency Doubling Perimetry for Optic Nerve and Chiasmal Neuro-Ophthalmic Disorders

Abstract

Abstract: : Purpose: When a low spatial frequency sinusoidal grating undergoes counterphase flicker at a high temporal frequency, the spatial frequency of the grating is perceived as doubled. Frequency Doubling Technology 2 (FDT2) is a promising new modality for the evaluation of patients with neuro-ophthalmic disorders. The FDT2 24-2 program has 55 test points as compared to 17 for the previous FDT C-20 program. The purpose of this study was to compare the FDT2 perimeter with the Humphrey (HFA II) perimeter for optic nerve and chiasmal neuro-ophthalmic disorders. Methods: Four readers compared correlation between the FDT2 24-2 and HFA II SITA Standard 24-2 test patterns using 126 abnormal visual fields. Our analysis included patients with optic nerve and chiasmal neuro-ophthalmic disorders. The readers assigned separate correlations (Good, Fair, or Poor) to each eye using preliminary Total and Pattern Deviation probability plots for the FDT2 and standard Total and Pattern Deviation probability plots for the HFA II. The readers also ranked perimeters by the depth and extent of visual field loss (Equivalent, FDT2, or Humphrey). Results: For the Total Deviation probability plots, 66/126 (52%) had Good correlation, 35/126 (28%) had Fair correlation, and 25/126 (20%) had Poor correlation. For the Pattern Deviation probability plots, 44/126 (35%) had Good correlation, 47/126 (37%) had Fair correlation, and 35/126 (28%) had Poor correlation. The extent of the defect as seen on Total Deviation probability plots was equal in 58/126 (46%) of cases, more extensive with FDT2 in 36/126 (29%), and more extensive with HFA II in 32/126 (25%). The extent of the defect as seen on Pattern Deviation probability plots was equal in 38/126 (30%) of cases, more extensive with FDT2 in 47/126 (37%), and more extensive with HFA II in 41/126 (33%). Conclusions: The new FDT2 24-2 testing strategy provides a screening and quantitative visual field testing parameter for optic nerve and chiasmal neuro-ophthalmic disorders that correlates reasonably well with the HFA II SITA Standard 24-2 program. However, there are some clear differences in regard to correlation, extent, and depth of the defect. Further evaluation will be necessary to evaluate the differences between the programs for patients with optic nerve and chiasmal disorders.

Keywords: visual fields • neuro-ophthalmology: optic nerve • perimetry