Soderberg, I., Calissendorff, B., Elofsson, S., Knave, B. and Nyman, K. G.
Investigation of visual strain experienced by microscope operators at an electronics plant.  Applied Ergonomics 14: 297-305 (1983).

This investigation was concerned with the examination of 75 microscope operators at an electronics plant, with reference to eye function and visual strain. It consisted of three separate parts: (1) standardised interviews dealing with symptoms of visual strain, (2) examinations of the refractive state as well as possible diseases of the eye, and (3) examination of binocular vision.

It emerged that 80% of the microscope operators engaged in full time microscope operation experienced various symptoms of visual strain. A statistically verified relationship was found to exist between these manifestations of visual strain on the one hand and uncorrected astigmatism, fusion insufficiency (poorer eye co-ordination) and the length of time spent at the microscope during the working day on the other.