James E. Sheedy

Is all Asthenopia the Same

Purpose. Any of several conditions can cause asthenopia. The purpose of this study was to determine whether the particular sensations or their location vary dependent on the symptom-inducing condition. Methods. Twenty subjects with good vision performed eight reading tasks in random order during different conditions. Each condition used different stimuli to induce asthenopia. The eight conditions were mixed astigmatism, close viewing distance, upward gaze, dry eyes, lens flipper, small font, glare, and flickering light. Subjects were asked to read until attaining a level of discomfort self-defined as “barely tolerable.” After each task, subjects rated the magnitude of several symptom descriptors (burning, ache, strain, irritation, tearing, blurred vision, double vision, dryness, and headache) and their location. Results. Analysis of variance with repeated measures was used to determine that all of the individual symptom sensation measures (except blur) were significantly related (p values ranged from 0.003 to <0.0001) to the inducing condition. Principal factor analysis with orthogonal varimax rotation was used to test symptom by condition relationships and determined two latent factors, designated external and internal symptom factors (ESF and ISF), that related symptoms to inducing condition. The ESF pattern comprises burning, irritation, tearing, and dryness located in the front and bottom of the eye. ESF is caused by holding the eyelid open, glare, up gaze, small font, and flickering. ESF seems highly related to dry-eye symptoms. The ISF pattern comprises ache, strain, and headache located behind the eyes. ISF is caused by the close viewing distance, lens flipper, and mixed astigmatism conditions and is likely related to accommodative and vergence stress. Conclusions. Symptom descriptors and locations were able to distinguish discomfort on the basis of causative condition. Results support two different symptom constellations and, hence, at least two different afferent pathways for symptoms of asthenopia.

Association of symptoms with measures of oculomotor deficiencies.

&NA; Phoria, vergence, and fixation‐disparity were measured at near working distances for a nonclinical sample of 3rd‐yr Optometry students. A questionnaire divided the sample into 33 symptomatic and 44 asymptomatic subjects. Discriminant analysis was used to determine which clinical measures best predicted the group to which each subject belonged. Sheards criterion was a good discriminator for exo deviations, and a variant of Percivals criterion was good for eso deviations. Fixation‐disparity variables proved to be valuable diagnostically. The best fixation‐disparity measures were the curve slope, curve type, and amount of fixation disparity.

Visual acuity and chart luminance

ABSTRACT It is desirable to standardize the conditions under which visual acuity is measured because of its importance in determining whether subjects meet occupational vision standards and as an indicator of the extent or stability of pathological conditions. The chart luminance is one parameter which needs to be standardized, and the effect of the luminance level upon acuity measurement is a critical factor in this determination. These data are measured for a subject population using Landolt rings and British letters. Over a “normal” photopic range of 40 to 600 cd/m2 the relation between the logarithm of the minimum angle of resolution (log MAR)) and log L (luminance) can be approximated by a straight line. A doubling of the luminance level within this range improves the acuity measurement by approximately one letter on a five‐letter row. Landolt ring acuities are less affected by luminance than letter acuities. The application of these results to establishing a standardized luminance level and tolerance range is discussed.

Phoria, Vergence, and Fixation Disparity in Oculomotor Problems Printed in U.S.A

&NA; Measures of horizontal phoria, vergence, and fixation disparity were obtained for 2 samples: 28 optometry students without symptoms and 32 orthoptic patients with symptoms associated with binocular oculomotor difficulties. Discriminant analysis was used to determine which tests or group of tests best discriminated between the 2 samples. Analysis was done for both samples and for exophoric and esophoric subsamples. Sheards criterion was the best discriminator for the exophoric group, and amount of heterophoria was the best discriminator for the esophoric group. Fixation disparity was the next best discriminator for both groups.

Computer use, symptoms, and quality of life.

Purpose. To model the effects of computer use on reported visual and physical symptoms and to measure the effects upon quality of life measures. Methods. A survey of 1000 university employees (70.5% adjusted response rate) assessed visual and physical symptoms, job, physical and mental demands, ability to control/influence work, amount of work at a computer, computer work environment, relations with others at work, life and job satisfaction, and quality of life. Data were analyzed to determine whether self-reported eye symptoms are associated with perceived quality of life. The study also explored the factors that are associated with eye symptoms. Structural equation modeling and multiple regression analyses were used to assess the hypotheses. Results. Seventy percent of the employees used some form of vision correction during computer use, 2.9% used glasses specifically prescribed for computer use, and 8% had had refractive surgery. Employees spent an average of 6 h per day at the computer. In a multiple regression framework, the latent variable eye symptoms was significantly associated with a composite quality of life variable (p = 0.02) after adjusting for job quality, job satisfaction, supervisor relations, co-worker relations, mental and physical load of the job, and job demand. Age and gender were not significantly associated with symptoms. After adjusting for age, gender, ergonomics, hours at the computer, and exercise, eye symptoms were significantly associated with physical symptoms (p < 0.001) accounting for 48% of the variance. Conclusions. Environmental variability at work was associated with eye symptoms and eye symptoms demonstrated a significant impact on quality of life and physical symptoms.

Binocular vs. monocular task performance

ABSTRACT Functional advantages of binocularity were investigated by having 13 subjects perform a group of occupational‐type tasks under monocular and binocular conditions. Significant binocular advantages ranging from 29.5% (pointers in straws) to 3.7% (reading speed) were measured. Tasks with many disparity cues showed the greatest binocular advantage. This shows that patients with normal binocular vision use binocular cues, most likely stereopsis, to enhance performance. In a second experiment, three subjects with normal binocular vision underwent monocular occlusion for 5 days to investigate whether monocular skills improved to compensate for the loss of binocular vision. During that period binocular performance was consistently better than monocular performance, and both monocular and binocular performance improved, even though the subjects were only gaining monocular experience. Although the 5 day occlusion period does not simulate the long‐term denial of normal binocularity that strabismics or monocular patients experience, it shows that binocular superiority remains after shortterm loss of binocularity.

Visual effects of the luminance surrounding a computer display

The luminance surrounding a computer display can potentially reduce visibility of the display (disability glare), result in sensations of discomfort (discomfort glare) and result in transient adaptation effects from fixating back and forth between the two luminance levels. The study objective was to measure the effects of surround luminance levels upon these functions in younger and older adults to determine recommended surround luminance levels. The younger age group comprised 20 subjects (mean age 27.9 years, range 23 – 39) and the older group 17 subjects (mean age 55.5 years, range 47 – 63). The central task was presented with luminance of 91 cd/M2, tested surround luminance levels were 1.4, 2.4, 8.9, 25.5, 50, 91, 175, 317, and 600 cd/M2. Disability glare was tested with low contrast (20%) visual acuity charts, transient adaptation was tested with a task that required regular fixation between the two luminance levels, discomfort was measured with a questionnaire after reading stories with different surround luminance levels, and preferred luminance was measured by method of adjustment. The surround luminance significantly affected transient adaptation (p < 0.0001), optimal performance occurred at 50 cd/M2 and above for the young group and at 91 cd/M2 and above for the older group. Neither low contrast acuity (disability glare) nor symptoms when reading were significantly affected by surround luminance. There was wide variation in preferred surround luminance; however, average preferred surround luminance was 86.9 cd/M2 for the young group and 62.2 cd/M2 for the older group, slightly below the central luminance of 91 cd/M2. The effects of the surround luminance within the tested range are not large; however, the data show that the lowest surround luminance levels should be avoided and that surround luminance levels at or slightly below that of the central task are preferred.

The Effects of Visual Display Distance on Eye Accommodation, Head Posture, and Vision and Neck Symptoms

Objective: Determine the effects of display viewing distance on both the visual and musculoskeletal systems while the text height is held constant across viewing distances. Background: The distance from the eyes to a computer display may affect visual and neck comfort. If the angular size of the characters remains the same, it is recommended that the display be placed at a farther viewing distance (e.g., 70—100 cm). However, in common usage, the character sizes are not adjusted based on viewing distance. Method: Participants under the age of 35 years (N = 24) performed visually demanding tasks using a computer display for 2 hr each at three viewing distances (mean: 52.4, 73.0, and 85.3 cm) while torso and head posture were tracked. At the end of each task, eye accommodation was measured and symptoms were recorded. Results: The near distance was associated with significantly less blurred vision, less dry or irritated eyes, less headache, and improved convergence recovery when compared with the middle and far distances. Participants moved their torsos and heads closer to the monitor at the far distance. Conclusion: If the computer screen character sizes are close to the limits of visual acuity, it is recommended that the computer monitor be positioned between the near (52 cm) and middle (73 cm) distance from the eyes. Application: The location of a computer display should take into account the size of the characters on the screen and the visual acuity of the user.

Exophoria At Near In Presbyopia

&NA; The exophoria at near working distances through a plus lens addition which exists in presbyopia was investigated in order to explain the paradoxical lack of asthenopic symptoms associated with this condition. Fixation disparity measurements indicate that the exophoria which is measured by the von Graefe technique does not exist under binocular conditions. Further analysis indicates that presbyopes may have unrestrained use of accommodative convergence.

Stereoscopic Viewing and Reported Perceived Immersion and Symptoms

Purpose. Stereoscopic 3D displays heighten perceived immersion but elevate viewing symptoms for some viewers. The present study measured prevalence and magnitude of perceived immersion and viewing symptoms in stereoscopic viewing, and related them to viewers characteristics and viewing position. Methods. Two hundred three teens and adults viewed a movie in 2D or 3D while sitting at different angles and distances. Their prior viewing symptoms, as well as visual and physical discomfort immediately before and after viewing, were measured with questionnaires. They were also asked to report their perceived immersion after the viewing. Results. Twelve percent and twenty-one percent of 2D and stereoscopic 3D participants reported increases of measured symptoms during and/or after viewing. Stereoscopic 3D viewing incurred greater and more frequent perception of blurred vision, double vision, dizziness, disorientation, and nausea than 2D viewing. Reported ocular and physical symptoms were negatively correlated to perceived immersion in 3D viewing. Older viewers (age 46 years or older) reported greater ocular, visual, and motion sickness symptoms in 2D viewing, and younger viewers (age 24–34 years) reported greater visual and motion sickness symptoms in 3D viewing. Sitting in an oblique position attenuated perceived immersion but also reduced motion symptoms in 3D viewing. Prior viewing symptoms in 2D tasks also predicted ocular and physical symptoms in 2D but less so in 3D viewing. Conclusions. Stereoscopic 3D viewing provides greater immersion, but it can also lead to heightened visual and motion sickness symptoms. Viewers with prior symptoms in viewing TV and computer screen are not more likely to have increased ocular and physical symptoms in 3D viewing. Young viewers incurred higher immersion but also greater visual and motion sickness symptoms in 3D viewing; both will be reduced if a farther distance and a wider viewing angle are adopted.