PubMed · 13111599
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C BERGER, A MAHNEK, B KNUDSEN. 1953-11-12. [Visual fatigue].. https://pubmed.ncbi.nlm.nih.gov/13111599/
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A complex of measures for prevention, correction and rehabilitation of ground aviation personnel revealing symptoms of vision fatigue due to the work with electronic information display systems is proposed. Yet, the author point to the need to apply these measures as a part of an integral approach.
Samuel Pepys (1633-1703) is known for writing the finest diary in the English language. He was a man of remarkable accomplishments who transformed the English Navy, was president of the Royal Society, and was a member of the British Parliament. He survived the Great Plague and imprisonment in the Tower of London. During the years when he was writing the diary, Pepys began to experience great pain in his eyes when reading and writing and from photophobia, which caused him to give up writing the diary. Pepys also had an ultimately unjustifiable fear of blindness.
Unlike heterotropia (= manifest strabismus), heterophoria (= latent strabismus) is not a primarily existing condition but is a reaction to an interruption of the sensory-motor feedback control system. The reaction consists of a deviation from the orthovergence position. Binocular vision causes a continuous calibration of the vergence position. This "orthophorisation" explains that in most persons, heterophoria differs only slightly from zero. Nevertheless, a small heterophoria is common (70-80% of the population). The need to compensate for heterophoria by sensory-motor fusion can cause asthenopic complaints, such as headaches with prolonged reading. Since a variety of other defects can lead to similar symptoms, a causal relationship with heterophoria can be assumed only after a thorough differential diagnosis. Prism spectacles or eye muscle surgery for heterophoria should be recommended only after prism trials in free space, which include yoked prisms as a placebo control. Heterophoria should be distinguished from "Winkelfehlsichtigkeit", which is a deviation from orthoposition that results from the "measuring and correcting methodology after H.-J. Haase" (MKH) and is based on the idea that fixation disparity, a minute deviation from orthovergence position, indicates an inability to overcome a larger "vergence angle at rest". Objective recordings have, however, revealed that the subjective tests with stereo cues applied in the MKH can mislead to the assumption of a fixation disparity although both eyes are aligned exactly to the fixation point. A trial conducted in the Netherlands concerning the therapy of asthenopic complaints showed no statistically significant advantage of prism spectacles determined with the MKH over conventional spectacles.