Purchase this article with an account.
Werner Eisenbarth, Johann Richert, Manfred MacKeben; Influence Of Refractive Errors In Letter Recognition In The Central Visual Field. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3609.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Visual acuity is highly dependent on refractive status. In addition, we used a topographic vision testing system (the Macular Mapping Test, MMT) to investigate letter recognition as a function of optical correction and different contrast levels within the central visual field. We calculated MMT "general field scores" (GFS) to assess the influence of refractive errors in young as well as elderly subjects and evaluated the current letter recognition performance in patients with AMD.
Testing the central visual field (10° radius) was performed with the MMT (using letter recognition in 33 parafoveal target locations at two contrast levels, 10 % and 100 %) in 10 young subjects (age: 25.7, SD ± 2.31), 10 elderly subjects (age: 67.0, SD ± 5.14) and 10 AMD patients (age: 76.4, SD ± 8,3). Influence of refractive errors on MMT performance was measured within the young and elderly subgroups. AMD patients were measured with the present optical correction and subsequently with the optimal present optical correction, which had been determined before. In all groups, VA was measured for 6.0 and 0.4 meters viewing distance.
GFS as a function of refractive error shows a mean loss of 3.89 points per one diopter within the young subjects for 100 % contrast and 5.90 points for 10 % contrast. Within the elderly subjects we found a mean loss of 2.61 points for 100 % contrast and 5.49 points for 10 % contrast. The GFS ratio (GFS at 10 % divided by GFS at 100 %) shows a decrease of 8 % for the young group and 11 % for the elderly group. MMT performance shows an increase of GFS after improvement of the refractive status in the AMD group: The 100 % performance increased from 21.5 to 24.1 (p < 0.008) and 10 % contrast from 8.85 to 10.15 (p = 0.285). The mean increase of visual acuity with the optimal optical correction was from 0.32 to 0.46 for far vision (p = 0.018) and from 0.28 to 0.44 (p = 0.018) for near vision (0.4 m).
At both contrast levels, the GFS declines with the amount of blur caused by refractive errors. The shape of this decline is more pronounced at the lower contrast level (10%). In both groups, junior and senior, optical blur by incorrect optical correction beyond 1 dpt can cause losses in the general field score. The prescription of the optimal optical correction for patients with AMD yields a significant increase of VA in general, but also better letter recognition in the parafoveal area.
This PDF is available to Subscribers Only