Evaluating the eye's rotational stability during standard photography

Abstract

To evaluate the rotational stability of the eye during standard photography and determine its effect on the measurement of toric intraocular lens (IOL) orientation. Department of Ophthalmology, University Erlangen-Nuremberg, Erlangen, Germany. The rotational stability of the eye was evaluated using standard photographs taken with a telecentric fundus camera (Zeiss). Two sets of fundus images were taken at least 6 months apart in 400 eyes of 200 patients. The axial position of the eye was determined using 2 characteristic markers of the fundus. The angle between the 2 images (autorotation angle) was measured in each eye. The mean absolute autorotation was 2.3 degrees +/- 1.7 (SD) (range 0 to 11.5 degrees). Nine percent of eyes did not rotate. The rotation was less than 3 degrees in 55% of eyes and was 3 degrees or greater in 36% of eyes. Eyes of patients younger than 50 years rotated less than eyes in older patients (mean 2.2 +/- 1.5 degrees and 2.5 +/- 1.8 degrees, respectively) (P=.04). A visual acuity of 20/20 or better (P=.02) and a refractive cylinder of less than 1.75 diopters (P=.01) were correlated with smaller amounts of autorotation. Potential causes of artificial eye rotation induced by the photographic technique included camera adaptation (3-degree intrinsic error), slide mounting (<1 degree), slide projection (<0.5 degree), marking of characteristic fundus details (<1 degree), and head inclination. Cyclorotation of the eye during standard photography may lead to overestimation or underestimation of the presumed spontaneous rotation of an implanted toric IOL. Results show that 11.5 degrees of toric IOL rotation would lead to residual astigmatism that is 40% of the initial astigmatic power and 3 degrees, 10% of the initial power. Digital imaging may reduce the intrinsic errors of standard photography.