Macular perimetry in low vision

Abstract

Background: Detection of residual visual function is critical for vision rehabilitation. Macular perimetry may provide essential information in this regard. In the presence of reduced vision, fixation maintenance is paramount for perimetric test validation. We performed a study to determine the validity of perimetric test results in the presence of low vision, as expressed by the relation between scotoma location, acceptable fixation maintenance and visual acuity.Methods: The study was a prospective observational case series. Macular perimetry testing was performed with the Humphrey Automated Perimeter in eyes of consecutive patients attending our low-vision clinic between July and December 1999. The main outcome measures referred to scotoma location, acceptable fixation maintenance and visual acuity.Results: We tested 46 eyes of 46 patients, 24 men and 22 women aged 33 to 88 years (mean 69.0 [standard deviation 15.41 ] years). Of the 35 eyes with best corrected visual acuity of 20/200 or better, 18 (51.4%) had acceptable fixation maintenance (p = 0.052), and 31 (88.60 had scotoma patterns displaced eccentrically (p < 0.001).Interpretation: We conclude that in the presence of residual vision of 20/200 or better, acceptable fixation maintenance is possible, probably with a new preferred retinal locus, and, as a result, scotoma patterns are recorded eccentrically. Therefore, perimetric results in such cases should be viewed as valid, and interpretation should always account for eccentric fixation. Concomitant testing with scanning laser ophthalmoscopy or eye tracking equipment could further clarify this issue.