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At least 631 records · Page 35Linked to original sources
PubMed1984

[Effects of visual and mental strain on VDT (visual display terminal) performance].

The progression of visual and mental strain in VDT work was investigated through an experimentally-designed VDT task providing a number of stressors including pacing, repetition, judgment and output decisions. We measured the effects of CFF (critical fusion frequency), TAF (the ability to maintain concentration), EEG (electroencephalogram) and near-point accommodation of various changes in the duration of the testing period. The subjects were seven male university students who performed single multiplication problems at a rate of 60 per minute. The problems were presented to them on a CRT screen and on paper for periods of 90 min each. The results obtained were as follows; CFF values and near-point accommodation of VDT performance were significantly decreased compared to Non-VDT's as a control. The TAF test showed that the mental strain in a VDT task is greater than that in a Non-VDT task. CFF values of VDT performance showed a tendency to decline in the 30th min after commencement, but in the 60th min and thereafter a significant lowering was noticed. In TAF and near-point accommodation of VDT performance, the greatest decline was in the 60th min, and this was significantly reduced only immediately after the work period. CFF values and near-point accommodation were not recovered after 60 min from the end of a 90 min VDT task. However, TAF X L values recovered in the 30th min after VDT performance. The peak level of alpha waves from the parietal region moved toward the slow alpha band with the elapse of VDT task time, but returned [or reverted] to the initial state 30 min after the test period ended.

Accommodation, Ocular↗
PubMed1982

The Kerala Decentration Meter. A new method and devise for fitting the optical of spectacle lenses in the visual axis.

Centring of spectacle lenses is much neglected field of ophthalmology. The prismatic effect caused by wrong centring results in a phoria on the eye muscles which in turn causes persistent eyestrain. The theory of visual axis, optical axis and angle alpha is discussed. Using new methods the visual axis and optical axis of 35 subjects were measured. The results were computed for facial asymmetry, parallax error, angle alpha and also decentration for near vision. The results show that decentration is required on account of each of these factors. Considerable correction is needed in the vertical direction, a fact much neglected nowadays; and vertical decentration results in vertical phoria which is more symptomatic than horizontal phorias. Angle Alpha was computed for each of these patients. A new devise called 'The Kerala Decentration Meter' using the pinhole method for measuring the degree of decentration from the datum centre of the frame, and capable of correcting all the factors described above, is shown with diagrams.

Asthenopia↗
PubMed1984

Nearpoint visual stress: a physiological model.

The nearpoint visual stress theory holds that a tendency for convergence to localize closer than accommodation is intrinsic to the nearpoint visual demands imposed by our culture. A physiological model is presented, suggesting that this effector system mismatch arises from the activation of autonomic reflexes related to stress, vigilant attention and information-processing. Autonomic arousal exerts a cycloplegic-like effect. Excess accommodative effort, which must be exerted to achieve required accommodation, produces a tendency towards overconvergence. The demand for integration of accommodation and convergence, essential for efficient nearpoint function, is thus incompatible with our own physiology, since autonomic arousal is inherent in task demands for attention and mental effort associated with reading. Additionally, autonomic arousal is generated by the high levels of stress pervasive in our society. Various refractive, binocular and accommodative deviations may arise adaptively in order to resolve this mismatch and facilitate efficient nearpoint visual function. These nearpoint stress-induced visual disorders parallel stress-induced systemic illness in that both result from the activation of physiological processes which are inappropriate for the demands and stresses of our society.

Accommodation, Ocular↗
PubMed1983

Convergence amplitude insufficiency.

There is a frequently overlooked group of patients, usually under 20 years of age, with typical symptoms of convergence insufficiency and diminished convergence amplitudes, but with normal near point of convergence. We studied ten cases of this type, which we call convergence amplitude insufficiency. The diagnosis in such patients will not be missed if convergence amplitudes are measured on every patient complaining of asthenopic symptoms during close work.

Accommodation, Ocular↗