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Volume 49, 1999, p. 23–25

Visual Training and Reading
Creig S. Hoyt, M.D.

INTRODUCTION
It would seem difficult to find fault with the concept of "training" biological systems to maximize their normal function. It would seem equally valid to see training as a way to address inherent weaknesses within biological systems that may lead to physiologic disability. These general principles, however, need to be looked at carefully before applying them to the reading disabled student. In the case of the oculomotor system one must first define what eye movements are essential for the task under consideration. Having done so, one needs to then investigate whether abnormalities of these systems account for the disability experienced by the group of patients under study. In this presentation I shall assume that our primary concern is for the task of reading and not hand-eye coordination as it relates to athletic activities or other non-reading tasks said by some to be enhanced by eye exercises or training.

NORMAL EYE MOVEMENT FUNCTION NECESSARY FOR READING
Eye movement recordings of reading behavior demonstrate a highly stereotyped "staircase" pattern of eye movements consisting of alternate saccades and periods of fixation of about 100 to 500 milliseconds each.1 It is essential to recall that steady fixation on a visual target is not associated with the lack of eye movement. Rather three characteristic eye movements that occur during fixation have been identified. They are (1) microsaccades, (2) drift, and (3) high frequency tremor.2 During the periods of fixation semantic identification is made.3 Each saccade moves the fovea about eight letters to the right. At the end of a line a large saccade to the beginning of the next line occurs and the behavior is repeated.3 Note that three distinctly different saccades occur during reading. The first two-rightward moving approximately 8 to 10 letters at a time and jumping to the next line and to the left are essential and normal in all reading patterns. The third-backwards saccades (to letters previously viewed) is an apparent sign of failed comprehension. Under ordinary circumstances the vestibular, optokinetic, and pursuit movement systems are not involved in the reading process, If reading material is held at a near fixation point, of course, convergence is recruited to the reading effort. To summarize, reading primarily involves the saccadic system (including the microsaccades of "fixation.") The vergence system is necessary for material read at near fixation.

THE LEARNING DISABLED CHILD
Reasons for academic failure in childhood include mental retardation, a sensory disability such as blindness or deafness, a primary emotional disturbance or inadequate education. In addition, there is a small but significant proportion of children who, in the absence of any of the above explanations, show profound difficulties in one or more of the following: Listening, thinking, talking, reading, writing, spelling or mathematics. Are there abnormalities of the ocular motor systems that account for some of these academic failures and are they in any sense trainable? The literature relating to ocular movements and reading disability is a confusing one. This is partly because of the difficulty in defining "reading disability" and even more importantly because of a lack of normal age-matched controls in various treatment protocols. The normal maturation of ocular motor systems in children has been defined incompletely at the present time but it is apparent that it is completely inappropriate to use normative data obtained from adult eye movement studies when discussing whether a saccade, vestibular or pursuit movement is normal or pathologic.

In order to determine if there is an ocular motor abnormality(s) associated with a specific learning disability, a large study group must be assessed with objective eye movement recordings and an age-matched control group performing academically well must be studied in exactly the same fashion. A case can be made that no such studies have thus far been completed. However, a couple of noteworthy small studies should be cited.

A well-designed but small study of 40 learning disabled children (ages 8 to 12 years) from the Toronto area with age matched controls from the same area reveals interesting results. Saccadic pursuit and optokinetic movements were measured with standard eye movement recording techniques. The presence or absence of spontaneous and gaze-evoked nystagmus were also noted. No differences could be found between the test and control groups in any ocular motor function tested. Indeed, in case of pursuit movements, 25% of learning disabled students were judged to be dysmetric but 35% of normal students were found to have the same instability of pursuit movements.4 Ophthalmologists are far too familiar with the learning disabled child who is referred for evaluation because "there is something wrong with the tracking movements of the child's eyes." In the setting of this consultation one should recall that (1) pursuit movements play no role in reading and (2) in the Toronto study no abnormality of pursuit eye movements was characteristics for the learning disabled child rather than the normal one.

Second, the notion that post-rotational nystagmus is abnormal in dyslexics and indicates the presence of a vestibular dysfunction has been in the medical and educational literature for more than two decades. It has resulted in many children being treated with "motion sickness" medications. The notion that post-rotational nystagmus in dyslexic children is in some way abnormal has been conclusively disproved. Brown and co-workers at the Smith-Kettlewell Institute completed a study of post-rotational nystagmus (in the dark to exclude the optokinetic component) in a group of dyslexics and agematched controls.5 No difference between the two groups was identified. Scientific rationale for the use of anti-vertigo medications in a treatment of dyslexics is lacking.

What if anything do eye movement recordings tell us about the reading disabled student? At present, the only ocular motor abnormalities conclusively demonstrated in learning disabled children are an increase in the duration of eye fixation and the number of backward (or regression) saccades. Both of these findings can be explained as the ocular motor manifestations of comprehension failure rather than a primary abnormality of ocularmotor control systems. The question of whether there is an increased incidence of convergence insufficiency in the learning disabled child remains controversial .6-12 However, there is no disagreement that clinically significant convergence insufficiency should be treated in any child and vergence exercises are a fundamental part of this treatment protocol.

CONCLUSIONS
Normal reading at near requires saccadic and vergence eye movements. Pursuit, vestibular, and optokinetic nystagmus movements are not involved. To date, age-matched controlled studies with standard eye movement recordings are conspicuously few in the literature concerning eye movement abnormalities and the learning disabled child. No evidence at the present time conclusively indicates that there are any unique ocular motor abnormalities in the learning disabled student with the exception of prolonged fixation and increased number of regression saccades. With the exception of convergence insufficiency (the topic of a later paper) the case has not been scientifically made for ocular motor training in the student with learning disability.

REFERENCES
1. Abrams SG, Zuber BL: Some temporal characteristics of information processing during reading. Reading Res Q 1972; 8:40-51.

2. Yarbus AL Eye Movements and Vision. New York, Plenum Press, 1967, p. 36.

3. Rayner K: Eye Movements in reading and information processing. Psych Bull 978; 85:618-626.

4. Polatajko HJ: Visual-ocular control of normal and learning disabled children. Develop Med Child Neurol 1987; 29:477-485.

5. Brown. B, Haegerstrom-Portonoy G, Yingling C: Dyslexic children have normal vestibular responses to rotation. Arch Neurol 1983; 40:370-373.

6. Norn MS, Rindziunski A, Skysgaard H: Ophthalmologic and orthoptic examinations of dyslexics. Acta Ophthalmol 1969; 47:147-160.

7. Eames TH: Comparison of eye conditions among 1,000 reading failures, 500 ophthalmic patients, and 150 unselected children. Am J Ophthalmol 1948; 31:713-717.

8. Hammerberg E, Norn MS: Defective dissociation of accommodation and convergence in dyslexic children. Acta Ophthalmol 1972; 50:651-654.

9. Buzzelli AR: Stereopsis, accommodative and vergence facility: Do they relate to dyslexia? Optometry Vis Sci 1991; 68:842-846.

10. Stein JF, Riedell PM, Fowler S: Disorders of vergence control in dyslexic children. Br J Ophthalmol 1988; 72:162-166.

11. Latvala ML, Korhonen TT, Penttinen M, Laippala P: Ophthalmic findings in dyslexic children. Br J Ophthalmol 1994; 78:339-343.

12. Ygge, J, Lennerstrand G, Rydberg A, Wijecoon S, Pettersson BM: Oculomotor function in a Swedish population of dyslexic and normal reading children. Acta Ophthalmol 1993; 71:10-21.