PAGE 17

Page 17

More recently, research has shown that disabled readers demonstrate reduced functional magnetic resonance imaging (fMRI) responses to moving stimuli,^152-154 have less subjective sensitivity to the detection of motion,^116,155-156 and have abnormalities in reflexive, stimulus-induced visual attentionThe magnocellular pathway is thought to be closely associated with the serial deployment of focal visual attention during saccadic eye movements in reading.¹⁵⁸ A magnocellular pathway deficit could produce32 Learning Related Vision Problemsthe perception of overlapping text or illusory text movement,^159-160 disrupting the proper timing and accuracy of saccadic eye movements,^161-162the proper spatial and temporal disposition of visual attention,^163-169 the temporal order of letter processing in words,^170-173 visual search,¹⁷⁴ and the effects of luminance and color on reading.^175-179 This association of the magnocellular pathway with ocular motility and visual attention processes are distinct from the higher order inattention and impulsive behaviors associated with ADHD.¹⁸⁰ Presently, there are no standard clinical tests readily available to clinicians for the evaluation of magnocellular function. The most promising tests are visual evoked potentials using low-contrast, low-spatial frequency stimuli, and psychophysical motion detection paradigms.¹⁸¹F. ASSESSMENT AND DIAGNOSISAll data obtained from testing should be evaluated to establish one or more clinical diagnoses and to develop a management plan. Examination of the patient history, clinical signs and symptoms, test results and behavioral observations, and review of previous reports and present levels of care are necessary to accomplish this. Low test scores should be referenced to the expected signs and symptoms of that deficiency.In the analysis of the visual efficiency performance data obtained, it is necessary to examine all of the data collectively by a standard clinical protocol, rather than relying on a single finding to arrive at a diagnosis. The Optometric Clinical Practice Guideline for Care of the Patient with Accommodative and Vergence Dysfunction provides lists and descriptions of common accommodative and vergence dysfunctions and methods of data analysis.²¹For testing visual information processing the use of z (or standard) scores is recommended. The z-score is the deviation of a specific test score from the mean, expressed in standard deviation units. It allows the expression of any score as a percentile rank by comparing it to a standard normal distribution. A test result with a z-score that is ≥1.5 standard deviations below the mean (percentile rank = 6.68) should definitely be considered anomalous and clinically significant.¹⁸² Scores fallingThe Care Process 33between 1.0 and 1.5 standard deviations below the mean should be considered suspicious and perhaps clinically relevant, depending on the overall clinical picture, the nature and type of the learning problem, and the level of overall cognitive function.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25