The Optical Effects Of Head Tilt On The Spectacle Corrected Astigmat.

It was found clinically that when a group of patients with astigmatic spectacle corrections tilted their heads toward either shoulder, many reported a subjective blurring of the visual acuity chart. The mechanism of this blur appears tobe due to the change in the location of the axis of the astigmatic refractive error . This change in the axis location
is caused by the compensatory counter-rolling of the eyeballs governed by the labyrinth reflexes . The topic of this study is based on the followi~ three
premises. (1) Upon any postural head tilt toward either shoulder
t he eyes will counter-roll reflexly in att empt to compensate
for the head tilt. (2) With an astigmatic spectacle worn, any
head tilt with associated count e r-roll of the eyes will result
in the movement of the exact correcting cylinder axis. The
correct axis of the astigmatic refractive error will rotate
an amount equal to the amount of the counterroll of the eye.
(3) Whenever a cylinder axis is pl a c e d in error of the true
location of the axis, the patient will no longer be perfectly
optically corrected.
The topic of this study is based on the following three premises. (1) Upon any postural head tilt toward either shoulder the eyes will counter-roll reflexly in attempt to compensate for the head tilt. (2) With an astigmatic spectacle worn, any head tilt with associated counter-roll of the eyes will result in the movement of the exact correcting cylinder axis. The correct axis of the astigmatic refractive error will rotate an amount equal to the amount of the counter-rol l of the eye. (3) Whenever a cylinder axis is placed in error of the true location of the axis, the patient will no longer be perfectly optically corrected. The above three premises infer the following theory which resulted in this study.