Will Visual Discomfort among Visual Display Unit (VDU) Users Change in Development When Moving from Single Vision Lenses to Specially Designed VDU Progressive Lenses?

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Abstract
Three types of progressive additions lenses (PAL) specially designed for VDU-work and one single vision lens were compared in a prospective field study. The aim was to investigate if these progressive lenses created a difference in the development of visual discomfort compared to single vision lenses when working on an optimized VDU-workstation. The study had a prospective, parallel group design, with four groups of VDU-workers. Approximately 40 subjects in each group, selected after careful task analysis with special attention towards the visual angles and distances to the work tasks. The groups were followed over one year. A questionnaire concerning visual conditions, working conditions, discomfort in different body areas, the status of the subjects' optometric corrections, psychological factors both at work and at home, amount, frequency and duration of VDU-work etc. was filled in before the intervention, after six months and after one year. No other contact was made with the subjects. The VDU-lenses included were Interview (Essilor), Gradal RD (Zeiss) and Technica (American Optical). Pain intensity and duration were assessed on a 100 mm Visual Analogue Scale (VAS) before the intervention, and six and twelve months after the intervention. All subjects were given a complete optometric examination. Only small changes in the development of headache and visual discomfort were registered. However, the subjective evaluation of area of clear vision and overall satisfaction was significantly improved for the Interview and Gradal RD lens (p < 0.05). There were no significant changes for Technica and single vision lenses. Lens designs that cover viewing distances from near and out to approximately 2 meters work well compared to lens designs trying to cover greater range of clear vision. When tasks analysis shows that single vision correction may be used, this is still an acceptable solution.