the effect of lateral head tilt on astigmatic axis

purpose: controversy has recently risen about the presence of compensatory ocular countertorsion (coct) after head tilt. this study was performed to define the functional range of this phenomenon. methods: cycloplegic autorefraction was performed on 80 eyes with regular astigmatism 2d. objective autorefraction was performed in normal position, right and left head tilt positions of 5º, 10º, 15º, 20º, and 25º. any change in astigmatic axis after head tilt was considered as coct defect. the authors designed a tiltometer which was fixed over the patient’s head without disturbing proper refractometry in various head positions. enrolled eyes had no other ocular disease except refractive error. results: seventy eyes completed the study process. mean age of the patients was 26.5±10 (15-48) years. mean amplitude of coct was 1.87°±1.81 (0°-5°) at 5° and 6.91°±4.96 (0º-20°) at 25° head tilt angles. coct values with left head tilt were significantly lower than coct values with right head tilt (p<0.026). incyclotorsional compensation in each eye was not necessarily equal to the excyclotorsional compensation of the fellow eye, but this torsional discrepancy was not overal significant (p>0.237). conclusion: coct was found to be an unreliable phenomenon. any minimal head tilt can induce erroneous measurement of astigmatic axis during refractometry.