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Fernando Avellis, Alessandra Dassò, Arturo Carta, Vincenzo Scorcia, Stefano Gandolfi; Magnocellular Visual Pathway Deficit In Dyslexia: Analysis Of Possible Patterns Of Visual Field Alterations Tested With Frequency Doubling Illusion. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1214.
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© ARVO (1962-2015); The Authors (2016-present)
To identify a possible visual lack in specific areas of visual field in children with reading disabilities (dyslexia) by exploring the spatial frequency doubling responses characteristic of the magnocellular pathway.
Eighteen dislexic subjects and nine controls (mean age 8,4±1,4 years [range, 7-13 years]) consecutively enrolled, were compared on the average of threshold detection for frequency doubling illusion of 5 contiguous retinal sections amog 19 locations of visual field (VF) grouped by 7 topographic patterns: central (CE), superior-nasal (SN), outer superior-temporal (OST), inner inferior-temporal (IIT), inferior-nasal (IN), inner superior-temporal (IST), outer inferior-temporal (OIT). Participants spared from reading comprension difficulties and scored below the cut-off for either speed or accuracy in reading on the MT reading disability test were included in the group of dyslexics. A refractive defect superior than +/-2 Dioptres of spherical equivalent was excluded. Best corrected visual acuity (BVCA) was examined before treatment based on logopedic support. A control group, consisting of children without dislexia was examined as well. The enrolled children were free of any ocular morbidity, as shown by routine ophthalmological evaluation. The visual stimuli were presented on a Humphrey Instruments Frequency Doubling Technology (FDT) Visual Field Instrument: the default settings included measurements of both eyes separately at all 19 VF locations exploring the central 30 degree radius of eccentricity with a full threshold analysis program (N-30).
Right and left eye average of the thresholds of clusters of 5 contiguous points of VF for each pattern indicated was calculated: the 7 averages of thresholds obtained was compared for each eye between the control and dyslexics groups. For the right and left eye the results indicated a non statistically significant difference between control and affected cases for all patterns except for the patterns CE,OIT,IN of the left eye (P<0,05). The two groups were comparable for loss of fixation, false positive error and false negative error.
Dyslexic patients may be less sensitive in specific sections of visual field analyzed with FD illusions. This topographic failure may help to confirm that a deficit in magnocellular visual pathway correlate to reading difficulties.
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