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R. C. Caruso, P. Lopez, L. M. Reuter; Microperimetry in Patients With Macular Disease: Adjusting for Location of Preferred Retinal Fixation Locus. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4163.
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© ARVO (1962-2015); The Authors (2016-present)
Fundus-controlled perimetry ("microperimetry") is used to correlate retinal sensitivity with fundus features. As in conventional perimetry, the array of stimuli is centered on the patient’s fixation locus. Most patients who have lost foveal function due to macular disease use an eccentric preferred retinal locus (PRL) to fixate. This implies that a different set of retinal loci are tested in each patient with a different eccentric PRL. This poses a problem when microperimetry is used to compare a cohort of patients. The purpose of this study was to assess the effectiveness of a method we designed to adjust for different PRL locations in patients with macular disease.
To date, 26 consecutive patients (8 women, 18 men), with an age range of 10 to 76 years, and macular lesions due to Stargardt disease (12 patients), age-related macular disease (9 patients), or other maculopathies (5 patients) have been included in this study. All had a central scotoma and eccentric fixation. A Nidek MP-1 microperimeter with fundus tracking was used for all tests. PRL position was assessed with a 60-second fixation measurement. The ensemble of x- and y-coordinates of the perimetry stimulus array was then displaced to center it on the anatomical fovea. The magnitude and direction of displacement were determined by the PRL coordinates. One of two stimulus arrays was used: a Humphrey 10-2 pattern (18 degrees in diameter), or a macular pattern (12 degrees in diameter). Threshold luminance was assessed with a 4-2 staircase.
The PRL had a mean eccentricity of 7.33 ± 3.98 degrees. Fixation was stable in 8 patients, relatively unstable in 14, and unstable in 4. For many patients, fixation stability was worse during the perimetry task (stable in 3 patients, relatively unstable in 12, and unstable in 11) than during the fixation task (p < 0.01). After adjusting for eccentric fixation, the mean distance between the estimated anatomical foveal locus and the center of the stimulus array was 1.43 ± 1.07 degrees. This distance was less than 1 degree in 11/26 patients, and less than 2 degrees in 21/26 patients. All remaining 5 patients had unstable fixation during the perimetry test.
The technique devised for this study allowed centering the stimulus array in the foveal area of most patients. This ensured that equivalent retinal loci were explored. This is a prerequisite for inter-patient comparisons of microperimetry results in the context of a clinical trial. The method was less successful in patients with very unstable PRL fixation. This technique can also be applied in conventional static perimetry and multifocal electroretinography.
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