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April 2010

The Evolutionary Dichotomy of Human Visual Tilt

Author Affiliations

Author Affiliation: Departments of Ophthalmology and Neurology, Mayo Clinic, Rochester, Minnesota.

Arch Ophthalmol. 2010;128(4):496-498. doi:10.1001/archophthalmol.2010.43

The goal of scientific inquiry is to explain what happens, how it happens, and why it happens. The first level corresponds to observation, the second to analysis, and the third to understanding. Without understanding why something happens, we have knowledge without wisdom and cannot formulate a philosophy of science.

In 1866, Javal inferred the existence of human ocular torsion by noting that he was no longer able to see clearly through his cylindrical lenses when he tilted his head.1 Since that time, innumerable studies have documented the existence of a static ocular counterroll in humans.27 What is remarkable is that, despite the robust dynamic ocular counterroll in humans,2 its static counterpart is relatively miniscule (in the range of 5%-10% of the head tilt), leading many to conclude that it no longer serves a compensatory function and some to argue that it is virtually nonexistent.8 Jampel has recognized that one of the major functions of the vestibular system is to counteract the effects of gravity on the human body8 and that the oblique muscles function to actively constrain torsion under static conditions.9 Accordingly, our retinas are oriented gyroscopically to the brain and not the horizon.8

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