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Diurnal variations in tonic accommodation.

A D Kurtev1, B D Stoimenova, M E Georgiev

  • 1Department of Physiology, Medical Academy, Sofia, Bulgaria.

Investigative Ophthalmology & Visual Science
|November 1, 1990
PubMed
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Tonic accommodation, a key aspect of vision, was previously thought to be constant. This study found that tonic accommodation exhibits predictable diurnal variations in individuals, challenging prior assumptions.

Area of Science:

  • Ophthalmology
  • Physiological Optics
  • Chronobiology

Background:

  • Visual function often exhibits diurnal variations.
  • Accommodation, the eye's ability to focus, was considered a potential exception to diurnal changes.
  • Understanding tonic accommodation is crucial for visual science.

Purpose of the Study:

  • To investigate whether tonic accommodation demonstrates diurnal variations.
  • To challenge the assumption that accommodation is not subject to daily fluctuations.
  • To characterize the pattern and magnitude of potential diurnal changes in tonic accommodation.

Main Methods:

  • Tonic accommodation was measured in three subjects using a modified Hartinger refractometer in complete darkness.
  • A red photodiode replaced the light source to eliminate accommodation stimulus during measurements.

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  • The method of limits was employed, with measurements taken every 4 hours over a day after a 10-minute dark adaptation period.

    • Main Results:

    • Tonic accommodation showed predictable diurnal variations specific to each individual.
    • One subject displayed a different pattern of peaks and troughs compared to the other two.
    • The daily amplitude of variation was approximately 1.0 D, with day-to-day stability within +/- 0.5 D.

    Conclusions:

    • Tonic accommodation is not constant and appears to be subject to diurnal variation.
    • Individual differences exist in the diurnal patterns of tonic accommodation.
    • These findings suggest a potential link between circadian rhythms and accommodative eye function.