Parafoveal vision impairments and their influence on reading performance and self-evaluated reading abilities

Abstract

Patients with homonymous hemianopic field defects (HFD) after postchiasmatic cerebral brain injuries often complain about impairments in daily life activities, particularly problems in reading, and show considerable reductions of vision-related quality of life (QoL). This study aimed to assess the relation of "objective" reading performance and self-reported "subjective" reading abilities; it was further investigated whether parafoveal HFD characteristics have an impact on both parameters. In postchiasmatic-lesioned subjects with HFD (n = 43), "objective" reading performance was measured with Radner-Reading-Charts (reading speed, reading acuity). Vision-related QoL was assessed by the National-Eye-Institute-Visual-Function-Questionnaire (NEI-VFQ). Four reading-relevant NEI-VFQ items that assessed "subjective" reading abilities were separately analyzed. Macular sparing measures were derived from campimetry (+/-16 degrees vertical, +/-21.5 degrees horizontal); i.e., the vertical HFD border between +/-2 degrees and the proportion of intact parafoveal visual field within the "reading window". Since macular sparing may be a perimetric artefact, eye movements during campimetry were recorded in 26 subjects. Mean reading speed of the total sample (90.72 +/- 33.96 words per minute) was considerably reduced, as was the patients' vision-related QoL, which was revealed by diminished NEI-VFQ scores. Reading acuity was 0.12 +/- 0.13 LogRAD (0.81 +/- 0.26 according to the decimal system). There were significant but weak correlations between reading acuity and speed with all reading-relevant NEI-VFQ-items (r-range, reading acuity: -0.57 to -0.38, reading speed: 0.33 to 0.43) and 7/12 NEI-VFQ-subscales (r-range, reading acuity: -0.47 to -0.33, reading speed: 0.31 to 0.40). The intact parafoveal visual field correlated significantly with 2/4 reading-related NEI-VFQ-items and with 4/12 NEI-VFQ-subscales (r-range 0.31 to 0.52). Reading acuity and mean reading speed were both correlated with fixation accuracy during campimetry (r = -0.38 and 0.45). Correlations of spared areas between +2 degrees to -2 degrees and the relative and absolute defect HFD border with reading speed, but not reading acuity, tended to significance. Subjects deviated from the campimetric fixation mark in a SD-range of +/-5.2 degrees vertically and +/-6.5 degrees horizontally but eye movement ranges were not correlated with macular sparing measures. Patients with HFD showed severely reduced reading speed, which was reflected in subjectively diminished reading performance, and reduced reading-related QoL parameters. Larger areas of functionally intact parafoveal vision were associated with better reading performance. Although eye movements occurred during campimetry, these did not seem to constitute an artificially enlarged area of parafoveal intact vision.