The Influence of Instruction on Frequency Doubling Technology Perimetry and Humphrey Matrix Results in Normals and Early Glaucoma Patients

Abstract

Abstract: : Purpose: To investigate the influence of instruction (detection versus pattern recognition threshold criteria) on visual field results determined by Frequency doubling technology perimetry (FDT) and the Humphrey Matrix (Matrix). Methods: FDT full threshold C–20 and N–30 tests, and the Humphrey Matrix full threshold (ZEST procedure) 24–2 test were performed on 20 clinically normal subjects and 20 early glaucoma patients (MD better than –6.0 dB for Humphrey Field Analyzer SITA results). For the detection task subjects were asked to respond when they could see anything. For the pattern recognition task subjects were asked to respond when they could detect the vertical lines, using the standard manufacturer’s instructions (i.e. the patient is asked to respond when they see patterns of flickering black and white vertical bars). Results: The mean sensitivity (MS) difference between detection and pattern recognition thresholds was about 2.5 dB for FDT and Matrix tests in normal and early glaucoma, with detection having higher threshold values. For FDT, there was a significant difference with respect to MS, mean deviation (MD) and the number of abnormal locations (P <0.05) on the total deviation probability plot (TD) for the two criteria in both normals and early glaucomas. For the Humphrey Matrix there was a significant difference for MD, the number of abnormal locations (P <0.05) on the TD, the number of abnormal locations (P <0.05) on the pattern deviation probability plot and the number of examinations outside normal limits on glaucoma hemifield test for the two criteria in both normals and early glaucomas. Conclusions: Instruction can have a significant effect on FDT and Matrix results. It was found that the pattern recognition task produced diffuse visual field loss rather than local visual field loss in comparison to the detection task results. The instrument’s normative database appears to be based upon a detection task rather than a pattern recognition task, and it is important for practitioners to be consistent in their instructions to patients, and that these criteria be clearly defined prior to testing.

Keywords: perimetry • visual fields • perception