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Do you really need your oblique muscles? Adaptations and exaptations
1Department of Ophthalmology, University of Arkansas for Medical Sciences, Little Rock, USA.
Archives of Ophthalmology (Chicago, Ill. : 1960)
|June 7, 2002
Summary
Human oblique muscles, crucial for eye counterrotation in animals, retain rudimentary torsional functions in humans. These muscles are exapted for stereoscopic vision and tilt perception, not vestigial.
Area of Science:
- Ophthalmology
- Evolutionary Biology
- Neuroscience
Background:
- Lateral-eyed animals possess oblique muscles for counterrotating eyes during pitch and roll.
- In humans, these torsional eye movements are considered rudimentary.
Purpose of the Study:
- To investigate whether human oblique muscles are vestigial.
- To explore the evolutionary adaptations and exaptations of oblique muscles in human binocular vision.
Main Methods:
- Review of primitive oblique muscle adaptations.
- Analysis of exaptations in human binocular vision.
Main Results:
- Human oblique muscles produce measurable rudimentary torsional movements (cycloversion and cyclovergence).
- The human system modulates cyclovergence for stereoscopic pitch perception and uses oblique muscles for saccades enabling nonstereoscopic roll perception during head tilt.
Conclusions:
- Human oblique muscles are exapted for detecting slant (pitch) and tilt (roll).
- Primitive adaptations persist and can reappear in cases of strabismus or neurological disease.