Abstract
Purpose: To identify distinguishing visual field (VF) deficiencies in dyslexic children by exploring responses to spatial frequency doubling illusions, characteristically involving the magnocellular visual pathway. Methods: Eighteen dyslexic subjects and nine controls [mean age 8.4 ± 1.4 years (range, 7-13 years)] were consecutively enrolled and underwent VF examination on a Frequency Doubling Technology (FDT) Visual Field Instrument. Among the 19 locations of the right eye (RE) and left eye (LE) VFs, 7 topographic patterns were identified: central (CE), superior-temporal (ST), and outer superior-nasal (OSN), inner superior-nasal (ISN), inner inferior-nasal (IIN), outer inferior-nasal (OIN), inferiortemporal (IT). The default settings included measurements of both eyes separately at all 19 VF locations, exploring the central 30-degree radius of eccentricity. For each pattern indicated the thresholds of contiguous 5 point clusters of the VF in both eyes were averaged: the 7 threshold averages obtained were compared for each eye between the control and dyslexic groups. Results: For RE and LE there was non-statistically significant difference between control and affected cases for all patterns except for CE, IIN, IT patterns in the left eye (P<0.05). The two groups were comparable for loss of fixation, false positive error, and false negative error. These data indicate that the dyslexic reader's left eye presents less sensitivity to FD illusions in almost all inferior retinal hemifield. Conclusion: Dyslexics analyzed using FD illusions may be less sensitive in specific sections of the VF. This topographic failure may help to confirm that a deficit in the magnocellular visual pathway is correlated to reading difficulties.
Highlights
Dyslexia is a condition characterized by specific reading difficulties that can be partially explained by some failures in basic visual processing [1,2]
For the right eye (RE) and left eye (LE), 19 visual field (VF) locations were grouped by 7 topographic patterns, each consisting of 5 contiguous locations: central (CE), superior-temporal (ST), outer superior-nasal (OSN), inner superior-nasal (ISN), inner inferior-nasal (IIN), outer inferior-nasal (OIN), inferior-temporal (IT) (Figure 1)
On comparing the Frequency Doubling Technology (FDT) mean deviation index (MD) of the control and dyslexic groups we found a statistical difference for both RE (P=0.026) and LE (P=0.018)
Summary
Dyslexia is a condition characterized by specific reading difficulties that can be partially explained by some failures in basic visual processing [1,2]. It is a condition that affects boys and girls is not intelligence- related, and is usually first noticed during childhood. Dyslexia has historically been considered and clinically treated as a linguistic defect and not a visual problem. Treatments not founded on a linguistic process remain controversial: some evidence suggests that reading failures are unlikely to precede visual deficits [3]. It remains controversial that dyslexics may have a visual processing deficit of the magnocellular (M) dominated dorsal pathway, and that they could be less sensitive to visual stimuli mediated by the dorsal stream [4]
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