Change in ocular refraction after tropicamide cycloplegia in preschool children.

PURPOSE: The aim of the study was to evaluate changes in ocular refraction after 1% tropicamide and its efficacy in diagnosing refractive errors in preschool children. MATERIAL AND METHODS: 116 children (232 eyes) at the age of 5 to 6 years participated in the study. An objective examination of refraction using autorefractor before and after 1% tropicamide cycloplegia (2 x 1 drop of the agent instilled 5 min apart) was performed in the study. RESULTS: After the instillation of tropicamide, the spherical component of the refractive error significantly increased by +0.78 D, while the cylindrical component (i.e. its power and axis) remained unaltered. In examining the refractive error, the mean value of the spherical component in children at the age of 5 to 6 years amounted to +1.55 D, in the cylindrical component mean value was -0.51 D, and the axis was 102 degrees. CONCLUSIONS: 1% Tropicamide appears an effective cycloplegic agent in preschool children, excluding children with high hyperopia, anisometropia, or strabismus.

Temporal order judgment in dyslexia.

Hari et al. (Brain 174:1373-1380, 2001) demonstrated that dyslexics showed a sluggish attention capture in both visual hemifields. Additionally, they indicated a left-right asymmetry in the perception of temporal order of two visual stimuli (they performed worse than controls only if the stimulus in the left hemifield preceded that in right hemifield). They suggested that a left-sided minineglect is associated with dyslexia. We hypothesized that if a kind of neglect syndrome is responsible for the asymmetry they found, dyslexics should not only show a left-right asymmetry in temporal order judgment of two laterally presented stimuli but also perform equally well as controls when the stimuli are vertically aligned. Our results indicated that in both tasks dyslexics performed generally worse than normal readers. The results suggest that dyslexics suffer from a more general problem of order discrimination.

Unstable Binocular Fixation Affects Reaction Times But Not Implicit Motor Learning in Dyslexia.

Purpose: Individuals with developmental dyslexia suffer not only from reading problems as more general motor deficits can also be observed in this patient group. Both psychometric clinical tests and objective eyetracking methods suggest that unstable binocular fixation may contribute to reading problems. Because binocular instability may cause poor eye-hand coordination and impair motor control, the primary aim of this study was to explore in dyslexic subjects the influence of unstable binocular fixation on reaction times (RTs) and implicit motor learning (IML), which is one of the fundamental cerebellar functions. Methods: Fixation disparity (FD) and instability of FD were assessed subjectively using the Wesson card and a modified Mallett test. A modified version of the Serial Reaction Time Task (SRTT) was used to measure the RTs and IML skills. The results for the dyslexic group (DG), which included 29 adult subjects (15 were tested binocularly, DGbin; 14 were tested monocularly, DGmono), were compared with data from the control group (CG), which consisted of 30 age-matched nondyslexic subjects (15 tested binocularly, CGbin; and the other 15 tested monocularly, CGmono). Results: The results indicated that the DG showed poorer binocular stability and longer RTs in the groups tested binocularly (RTs: 534 vs. 411 ms for DGbin and CGbin, respectively; P < 0.001) as compared with the groups examined monocularly (RTs: 431 vs. 424 ms for DGmono and CGmono, respectively; P = 0.996). The DG also exhibited impaired IML when compared with the CG (EFIML: 25 vs. 50 ms for DG and CG, respectively; P = 0.012). Conclusions: Unstable binocularity in dyslexia may affect RTs but was not related to poor IML skills. Impaired IML in dyslexia was independent of the viewing conditions (monocular versus binocular) and may be related to cerebellar deficits.

Posterior parietal cortex and developmental dyslexia.

Dyslexia is defined as a specific reading disorder despite normal intelligence and conventional teaching. One of the most influential theories attempting to explain problems suffered by dyslexics assumes that dyslexia is caused by deficits of the magnocellular system. This system, generally responsible for processing fast sensory information, projects mostly to the parietal cortex. Consistent with this theory, dyslexics should have problems with tasks which specifically involve parietal cortex. In the article, we review data and show that, indeed, dyslexics have problems with fast attention shifts, show some symptoms of mild unilateral neglect syndrome and have abnormal saccadic and pursuit eye movements. Little is known about visuo-motor coordination and mental rotation, the tasks in which the parietal cortex is thought to play important roles.

Mental rotation of letters and shapes in developmental dyslexia.

Extending the work of Corballis et al (1985, Cortex 21 225-236), we investigated mental rotation of letters (experiment 1), and of letters and shapes (experiment 2) in normal readers and developmental dyslexics. Whereas the overall response times were equal for shapes in both groups, for letters they were slower in dyslexics. For letters as well as for shapes, however, the same mental-rotation effects were obtained between the groups. The results are interpreted as support for the notion of developmental dyslexia as a deficit in functional coordination between graphemic and phonological letter representations.