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Although developmental dyslexia (DD) is frequently associate to a linguistic deficit, the underlying neurobiological cause remains unclear. One prominent vision science hypothesis suggests a specific deficit in magnocellular (M) pathway in DD. However, a recent hypothesis proposes that M-deficits contribute to the etiology of phonological decoding ability (i.e., new word and nonword reading), impairing selectively the attentional orienting process onto letter string. Thus, a specific M-pathway impairment in association with an attentional orienting disorder in DD children with phonological decoding deficit was specifically predicted by this neurobiological hypothesis. In the present study we investigated the M-pathway and attentional orienting in 18 dyslexic (10 with phonological decoding deficit) and in 29 chronological age and IQ matched normally reading children by measuring dynamic stimuli sensibility (i.e., spatial frequency doubling illusion) and the time-course of automatic covert attention (i.e., target detection effect at different SOAs of a non-predictive and peripheral spatial cue), respectively. The results showed a specific deficit of the M-pathway task in dyslexic with phonological decoding deficit. More importantly, the same group of dyslexics with M-deficit presented a sluggish attentional orienting: attentional facilitation was present at longer cue-target SOAs compared with normal readers. These results highlight that a M-deficit linked to a parietal-attentional dysfunction might impair the phonological decoding mechanisms that are critical for reading acquisition.

PURPOSE. To study reading acuity in children and assess the reliability of its measurement using the Italian version of the MNREAD reading chart. METHODS. One hundred sixteen children from grades 3 to 8 with normal near vision were tested at a pediatric eye care institution in northeastern Italy. Visual acuity was evaluated with Early Treatment Diabetic Retinopathy Study (ETDRS) charts and reading acuity with MNREAD charts. Examination with charts 1 and 2 by the same examiner in the same visit were used as test–retest measurements. RESULTS. Mean improvement of performance from grades 3 to 8 was approximately 1 line for ETDRS acuity and 1.5 sentences for reading acuity and critical print size. Mean maximum reading speed increased from 96 to 167 words/minute. Regression analysis showed that a stable reading speed was obtained throughout sentences of decreasing size up to the critical print size. Measurement error, expressed as 95% limits of agreement, was 0.136 logarithm of the minimum angle of resolution (logMAR) and 0.142 logMAR for ETDRS acuity and reading acuity, respectively. Critical print size had the lowest reliability (0.193 logMAR). Maximum reading speed limits of agreement were 0.077 logarithm of words per minute (logWPM), or a 19% change in words per minute. There were no detectable effects of grade and refractive error on measurement errors. CONCLUSIONS. In children, MNREAD charts provide measurements of reading acuity as reliable as ETDRS chart measurements of distance acuity on a logMAR scale. They also provide highly reliable measurements of the maximum reading speed across all grades, independent of its noticeable increase. (Invest Ophthalmol Vis Sci. 2004;45:3349 –3354) DOI:10.1167/ iovs.03-1304