Kenneth J. Bowman

Workstation variables and visual discomfort associated with VDTs

We have investigated the effects of a range of workstation factors upon the visual symptoms experienced by a group of 92 visual display terminal (VDT) users. Subjects in the study kept a diary over five consecutive working days in which they recorded the types of visual and postural symptoms which occurred and the types of work tasks being performed. Each subjects workstation was analysed for screen legibility and stability, discomfort and disability glare, and required head postures. By the use of multiple regression analysis techniques we have considered the relative contribution of these factors to the symptoms reported by the users of these workstations. Screen legibility significantly influenced the occurrence of symptoms of ocular discomfort and vertical head movements significantly affected the incidence of postural/headache symptoms.

Corneal topography and monocular diplopia following near work.

Monocular diplopia, reported by a subject following near work, was shown to be caused by changes in the corneal topography. Prior slit lamp biomicroscopy had revealed no corneal abnormality. The degree of corneal distortion and ray tracing calculations confirmed the presence and position of the resultant diplopia.

THE CLINICAL ASSESSMENT OF COLOUR DISCRIMINATION IN SENILE MACULAR DEGENERATION

The colour discrimination of 15 subjects manifesting senile macular degeneration was investigated, over a wide range of illuminances, using the Farnsworth‐Munsell 100‐Hue test and Panel D‐15. Ten subjects of similar ages with normal colour vision were investigated concurrently to provide a control group. Colour discrimination was shown to deteriorate with decreasing illuminance this being more marked for the subjects with senile macular degeneration than for the normal subjects. It is demonstrated that the FM 100 is the preferred test for assessment of colour discrimination loss in senile macular degeneration with early visual acuity loss. The Panel D‐15 is more useful as acuity loss becomes more marked.

Task variables and visual discomfort associated with the use of VDT's

We investigated task variables that may influence the incidence of visual discomfort amongst subjects who routinely spent a proportion of their day working with visual display terminals (VDTs). A diary was kept by subjects over five consecutive working days, in which they recorded visual symptoms, the visual tasks undertaken, the amount of time spent on workbreaks, work pressure, work interest, and personal moderating factors which may have influenced the symptoms recorded. The symptoms recorded by subjects were then treated as dependent variables in multiple regression analyses with the diary findings (task-related factors) as independent variables. The incidence of some types of symptoms was significantly associated with specific categories of work tasks, personal moderating influences, work pressure, work interest, time of day, and day of week.

Sensitivity to changes in size and velocity in young and elderly observers.

Thresholds for detection of change of size and for detection of change of velocity were measured in young and elderly observers. No differences in thresholds between these subject groups were found at the fovea or in more peripheral retina. The results indicate a degree of functional redundancy in the peripheral retina of elderly subjects, even though there is evidence of reduced numbers of functional photoreceptors in the periphery.

THE ROLE OF CORNEAL DISTORTION IN THE OCCURRENCE OF MONOCULAR DIPLOPIA

The measurement of anterior corneal surface topography before and during the occurrence of monocular diplopia can be used to predict the angular positions of any secondary images resulting from corneal distortion. The predictions correlate at a statistically significant level with direct measurements of the positions of the secondary images.

Peripheral Visual Acuity with Monovision and Other Contact Lens Corrections for Presbyopia

We have conducted two experiments to investigate the effect of monovision and other contact lens corrections for presbyopia upon peripheral visual acuity. In the first study, we measured binocular peripheral visual acuity using Landolt rings with seven subjects wearing a monovision correction. The Landolt rings were presented at eccentricities of 10, 20, 40, and 70° on each side of the subject, with near additions of +1.50 D, +2.50 D, and no addition. We found no significant effect of monovision correction on peripheral visual acuity. In the second experiment we measured the peripheral visual acuity of 11 presbyopic subjects wearing distance contact lenses with lookover spectacles, soft progressive bifocal contact lenses, soft concentric bifocal contact lenses, monovision contact lenses, modified monovision contact lenses, and hard bifocal contact lenses using Koenig bar targets. There were no significant differences in peripheral visual acuity between any of the contact lens corrections for presbyopia.

Spatial summation in young and elderly observers

We measured detection thresholds for targets over a range of sizes at both photopic and scotopic luminance levels in young and elderly observers, and used these data to estimate spatial summation areas 10 degrees in the retinal periphery. There were differences in detection thresholds between the young and old groups at photopic and scotopic luminances, but no differences in spatial summation areas at either background luminance level.

Symptoms associated with VDT use

Symptoms associated with the eyes were recorded by a group of 92 video display terminal (VDT) users over five days. A diary was maintained for the symptoms and other task related factors such as the type of work performed. Diary entries were recorded approximately every two hours. Symptoms were classified as either ocular (a range of discomfort symptoms), visual (blur or double vision) and systemic (headache or postural symptoms). Tired eyes and headaches were the most frequently reported symptoms. Comparing the symptoms reported during VDT work sessions and the clerical (non‐VDT) work sessions, there was a small but consistent trend towards more frequent symptoms during VDT sessions. Almost all types of symptoms showed a significant increase in frequency over the day (time of day effect).

Short term responses to soft contact lens corrections for presbyopia

Eleven subjects were each fitted with five different soft contact lens corrections for presbyopia. The correction types were distance contact lenses with lookover spectacles, concentric bifocals, monovi‐sion, modified monovision and progressive bifocal contact lenses. Subjects were asked to rate each contact lens correction in terms of distance, intermediate, near and peripheral vision, confidence when walking and climbing stairs, eye‐hand co‐ordination, performance on work tasks, vision difficulties in bright and dim ambient illumination and the correction most preferred for daily wear. There were few significant differences between ratings for the different corrections. Monovision, modified monovision and the concentric bifocal corrections were the preferred options for daily wear.