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Literature Review

Current Eye & Vision Science LiteratureDavid A. Goss, OD, PhD, FAAO, FCOVD-AIndiana University School of Optometry

Correspondence regarding this literature review can be emailed to dgoss@indiana.edu or sent to Dr. David Goss, School of Optometry, Indiana University, Bloomington, IN 47405. All statements are the author’s person­al opinion and may not reflect the opinions of the College of Optometrists in Vision Development, Optometry & Vision Development or any institution or organization to which the author may be affiliated. Permission to use reprints of this article must be obtained from the editor. Copyright 2010 College of Optometrists in Vision Development. OVD is indexed in the Directory of Open Access Journals. Online access is available at http://www.covd.org.

Goss DA. Current eye & vision science literature. Optom Vis Dev 2010;41(3):169-171.

Krupinski EA, Berbaum KS. Measurement of visual strain in radiologists. Academic Radiology 2009;16:947-950.

The authors hypothesized that the work done by radiologists could produce visual strain and fatigue. To test this hypothesis they measured accommodative error using an open view autorefractor, the Grand Seiko WAM-5500. With an open view autorefractor, fixation objects can be placed at various distances for viewing by patients or study subjects.

The subjects in this study were three experienced radiologists and three radiology residents. The radiologists were 47, 52, and 68 years old. The radiology residents were 28, 28, and 30 years old. Two of the radiologists had bifocals and one had reading glasses. One of the residents wore spectacles for myopia. All subjects wore their glasses or contact lenses during the study measurements if they wore them during radiographic image viewing.

Accommodative error was measured in the morning before reading radiographic images and later in the afternoon after an average of 5.7 hours (SD=1.2) of diagnostic reading from computer displays. Although the authors did not specifically define accommodative error for the purposes of their study, we might assume that it represented the dioptric amount by which the sum of the subject’s spectacle

corrections and their accommodative response differed from the accommodative stimulus. However, it was not stated whether the bifocal wearing subjects viewed through the distance or near portions of their spectacles during the accommodation recordings. Accommodation measurements were taken with viewing distances of 183, 152, 122, 91, 61, 50, 40, 33, 25, and 20 cm.

A graphical display of their results showed increases in accommodative error for all test distances after a day of work. Analysis of variance showed significantly greater accommodative error with decreasing target distance (p<0.0001), for the afternoon compared to the morning (p<0.0001), and for radiologists compared to residents (p<0.0001). Averaged across viewing distances, accommodative error increased from morning to afternoon by 0.51 D for residents and by 0.19 D for radiologists.

We may assume that the accommodative error of the radiologists increased less than that of the residents because of their lesser accommodative ability associated with presbyopia. The inclusion of the oldest of the radiologists as a subject is surprising because that individual at 68 years of age would likely have absolute presbyopia. Nevertheless, the study findings do show accommodative fatigue resulting in decreased accommodative response after a day of work, particularly for the residents. The authors expressed concern that visual fatigue could affect diagnostic accuracy in radiology work.

Tosha C, Borsting E, Ridder WH III, Chase C. Accommodation response and visual discomfort. Ophthalmic and Physiological Optics 2009;29:625-633.

In this study, accommodative response was measured for a two minute period of time in college students who were classified as having high or low levels of visual discomfort. Thirty-one students at Claremont Colleges in California served as subjects.

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They had at least 20/25 visual acuity at distance and near in each eye, no constant strabismus, normal stereopsis, no more than 0.50 D of myopia or 1.50 D of hyperopia, less than 1.00 D of astigmatism and anisometropia, and no “significant ocular pathology.”

The 23 item Conlon Visual Discomfort Survey was administered to each of the subjects. Each item on the survey is scored 0 (never occurs), 1 (occasionally, a couple times per year), 2 (often, every few weeks), or 3 (almost always). Thus total scores could potentially range from 0 to 69. Subjects whose total scores were less than 24 were considered the low discomfort group, and those with scores higher than 24 were defined as the high discomfort group. There were 16 subjects in the low discomfort group. Their average score on the survey was 11.1 (SD=5.1). The 15 subjects in the high discomfort group had a mean survey score of 33.1 (SD=7.4).

Accommodative response was measured with the Grand Seiko WAM 5500 open view autorefractor. Measurements were taken monocularly with the left eye covered with a patch. Subjects viewed a black filled-in five-pointed star on a white background. They were instructed “to keep the target in clear focus for the whole viewing time.” (p. 627) Accommodative response was recorded at 200 msec intervals for two minutes at viewing distances of 300, 50, 33, 25, and 20 cm.

The accommodative responses for the low discomfort group remained stable over the two minute recording period. Accommodative response decreased with time in the high discomfort group, particularly at the nearer test distances, resulting in higher lags of accommodation than in the low discomfort group.

The authors noted that their results “suggest that sustained viewing of 90 seconds or greater may be necessary to detect accommodative lag differences between the low and high visual discomfort groups.” (p. 631) They also pointed out that the high discomfort group’s “significant increase in lag with extended viewing… may indicate an accommodative fatigue effect.” (p. 631) However, we could ask whether an “accommodative fatigue” elicited after a minute or two as in this study is the same effect as that described in the study of accommodation after reading radiology images for several hours (discussed above).

It should be noted that this study involved monocular testing. It would be interesting to know whether results would be similar under the more

natural binocular conditions where there were interactions of accommodation and vergence.

Shin HS, Park SC, Park CM. Relationship between accommodative and vergence dysfunctions and academic achievement for primary school children. Ophthalmic and Physiological Optics 2009;29:615-624.

This study was conducted with 1,031 second, fourth, fifth, and sixth grade students (ages, 9 to 13 years) in a public primary school in South Korea. Subjects completed the College of Optometrists in Vision Development Quality of Life questionnaire. The questionnaire was administered a few weeks after the children had taken academic achievement tests. Visual symptom scores on the quality of life questionnaire were 20 or higher in 258 of the 1,031 children.

Eligibility criteria of no amblyopia, no strabismus, no ocular or systemic pathology, no contact lens wear, visual acuity 20/25 or better in each eye, and vertical phoria 1 prism diopter or less were met by 114 of the 258 children. Comprehensive eye and vision examinations were given to the 114 children. Testing on these examinations included case history, distance and near visual acuity, distance and near cover test, Worth dot test, stereopsis, inter-pupillary distance, autorefraction, subjective refraction, amplitude of accommodation by push up, near point of convergence, accommodative facility with +2/-2 D flippers, vergence facility with 8ΔBI/8ΔBO flippers, distance and near lateral and vertical von Graefe dissociated phorias, fusional vergence ranges, negative and positive relative accommodation, and direct ophthalmoscopy.

Based on the examination of the 114 children, 82 (71.9%) were diagnosed with accommodation or vergence disorders. The most common diagnoses were convergence insufficiency (n=23), accommodative insufficiency (n=15), accommodative infacility (n=11), and combined accommodative insufficiency and convergence insufficiency (n=24).

Academic achievement scores in reading and mathematics were compared in the 82 children with non-strabismic accommodation or vergence disorders to 761 children with quality of life symptom scores of less than 20, who did not have strabismus, amblyopia, ocular or systemic pathology, or current contact lens wear according to parent’s report. The academic

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achievement scores were significantly lower in those with accommodation and vergence dysfunctions in both reading (p<0.001) and mathematics (p<0.001).

Achievement scores in social science and science were not available for second graders. Scores in those areas were compared in 64 fourth through sixth graders with accommodation and vergence disorders to 581 fourth through sixth graders with low symptom scores on the quality of life questionnaire. The subjects with accommodation and vergence dysfunctions had significantly lower academic achievement scores in both social science (p<0.001) and science (p<0.05).

The authors wrote that a major finding of their study was “the significant relationship between general binocular dysfunctions and academic achievement for primary school children.” (p. 621) They noted: “It is clear that many children in this sample suffered from accommodative and/or vergence dysfunctions that made school work difficult…” (p.621). They further concluded that “it is important that accommodative and vergence functions, which are needed for accurate and efficient reception of visual input, should be tested in all children who have visual symptoms and/or academic difficulties.” (p. 622)

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