gms | German Medical Science

Toric intraocular lenses (tIOLs) are implanted to compensate corneal astigmatism. We evaluated the reproducibility of the axial position measurement of the eye using standard fundus photography ("rotational stability").

The rotational stability of the eyeball was evaluated using repeated standard fundus photographs (Zeiss telecentric fundus camera). A sequence of 2 fundus images was taken in 400 eyes of 200 patients (time interval of more than 6 months). The axial position of the eye was determined using characteristic markers on the fundus images (minimal distance 1 optic disc diameter). The angle between the two images ("autorotation angle") of each eye was measured.

The mean absolute autorotation was 2.3±1.7° (range 0 to 11.5°) ignoring laterality. Only 9% of the eyeballs did not rotate. A rotation of less/more equal than 3° was measured in 55%/36%. Patients younger than 50 years showed a smaller amount of rotation (2.2±1.5°) than older patients (2.5±1.8°; p=0.04). A best spectacle corrected visual acuity of more equal than 20/20 (p=0.02) and an astigmatism less than 1.75 D (p=0.01) were correlated with smaller amounts of eyeball autorotation. Potential causes of apparent eyeball autorotation induced by photographic technique included camera adaption (3° intrinsic error), slide mounting (<1°), slide projection (<0.5°), marking of characteristic fundus details (<1°), and head inclination.

The standard photography for evaluation of axial orientation of tIOLs is impaired by several intrinsic errors. Eleven and a half degrees (the maximal autorotation angle of the globe) tIOL rotation would correspond to a residual astigmatism of 40% or 10% of initial astigmatic power. Digital imaging and analysis could help to reduce the intrinsic errors in standard photography.