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The form of the human pupil
1Schnurmacher Institute for Vision Research, State University of New York, State College of Optometry, NY 10010, USA.
Vision Research
|July 1, 1995
Summary
Human pupils exhibit unique, stable shapes with predictable changes between light and dark conditions. Pupil noncircularity increases with age, showing individual variations and some consistent patterns across subjects.
Area of Science:
- Ophthalmology
- Human Physiology
- Biomedical Optics
Background:
- Pupil shape is crucial for visual function and optical quality.
- Previous studies have primarily focused on pupil size rather than detailed shape analysis.
Purpose of the Study:
- To quantitatively characterize the normal human pupil shape.
- To investigate the stability and individual variability of pupil form.
- To identify systematic changes in pupil shape between light and dark conditions.
Main Methods:
- Utilized a modified slit-lamp for pupil photography under steady illumination and after dark adaptation.
- Employed circular Fourier series and best-fit ellipses to represent pupil margin geometry.
- Analyzed pupil position relative to the limbus and quantified shape similarity.
Main Results:
- Average pupil noncircularity was minimal (0.0166), with best-fit ellipses accounting for roughly half of this deviation.
- Pupil shapes demonstrated stability within individuals over time but significant variation between subjects, especially in light.
- Systematic shape changes occurred, with a tendency for vertical elongation in darkness and horizontal elongation in light, indicating preferential contraction along the vertical meridian.
Conclusions:
- Human pupils possess individual shapes with underlying regularities.
- Pupil shape is relatively stable within an individual but varies significantly between individuals.
- Adaptation to light and dark involves predictable, systematic changes in pupil geometry, particularly concerning elliptical deformation.
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