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T. D. Martin, M. MacKeben, R. A. Schuchard, D. C. Fletcher; Foveal vs. Eccentric PRL Characteristics for Fixation in Low Vision Patients. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4103.
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To compare Scanning Laser Ophthalmoscope (SLO) foveal fixating characteristics with eccentric PRL fixating characteristics in low vision patients.
501 eyes of 273 patients referred for low vision rehabilitation had visual acuity (ETDRS) and PRL characteristic (SLO) testing performed in their initial evaluation. The PRL position relative to the fovea and fixation stability/size of the PRL were measured utilizing a SLO testing program with a gaze-contingent stimulus display (MacKeben et al, JOSA A 24/5, 2007).
Patient age median/range was 80/6 - 99 years and 59% were female. 77% had a maculopathy, with several other diagnoses in the remaining 23%. Visual acuity (VA) median/range was 20/200 and 20/20 - 20/3509. 50% (250/501) of eyes demonstrated fixation at the fovea. VA for the foveal fixation group median/range was 20/100 and 20/20 to 20/879 and for the eccentric PRL group was 20/401 and 20/46 to 20/3509. The median (range) of the diameter of the fixation area for the foveally fixating group was 2 (1-6) degrees while the eccentric PRL group median (range) was 5 (2-12) deg. The best possible fixation stability and VA decreased with distance from the fovea but there were many values that were worse than this best possible value at all distances from the fovea. There was a moderate significant relationship between VA and stability/size of the PRL with a floor effect also (RSquare 0.43).
This study of patients referred for low vision rehabilitation demonstrates that many have fixation at the fovea. An eccentric location of the PRL is associated with lower acuity and less stable fixation but VA at the fovea can be in the profound impairment category and the fixation area can be large and fixation can be unstable. In rehabilitation of low vision patients, it cannot be assumed that decreased acuity or unstable fixation indicate an eccentric PRL.
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