[Impact of the eye's cyclorotation on axial orientation analysis of toric intraocular lenses: recommendations for an optimized evaluation of rotational stability of toric IOLs].
BACKGROUND
After the implantation of toric intraocular lenses (tIOLs) significant postoperative tIOL rotation angles were measured occasionally. We investigated the rotational stability of eyes during standardized photography and recommend two methods for an enhanced evaluation of tIOL rotation.


METHODS
1. The cyclorotation of the eye was investigated using standard fundus photography. A sequence of two fundus photographic slides was taken in 550 phakic eyes of 275 consecutive patients with a time interval of at least 6 months. With characteristic markers on the fundus photograph, the axial orientation of the eyes was defined and the cyclorotation between the two slides of each eye was measured. 2. Using bifocal photography (HRA II - Heidelberg Retina Angiograph), a sequence of anterior segment and fundus images was taken considering stable head position in 19 pairs of photographs of eyes with implanted tIOLs. The angle between reference fundus axis and tIOL axis was measured at both time stages (mean: after 3 months). The difference of the angle between bifocal-image samples was defined as the real tIOL rotation angle. 3. Ten pairs of anterior segment photographs of eyes with a tIOL were investigated using the Axenfeld loop analysis. In each photograph, the angle between the axis connecting two Axenfeld loops and the tIOL axis was measured. The difference of two angles of two photographs was defined as the rotational tIOL angle.


RESULTS
1. The mean absolute eye's rotation angle was 2.3 +/- 1.7 degrees (range: 0 to 11.5 degrees) in all 550 eyes. Only 9.1 % of the eyes did not rotate. In 57.3 % of the eyes a rotation of less than 3 degrees and in 33.6 % of more than or equal to 3 degrees was detected. The eye's cyclorotation correlated (p < 0.04) with an age older than 39 years and higher astigmatism (> 1.5 D). Because of the significant amount of spontaneous globe rotation we developed the following enhanced methods to minimize measurement errors of tIOL rotation: 2. Bifocal photography: comparing the 19 HRA anterior segment images, the amount of mean tIOL rotation was 5.4 +/- 4.8 degrees (range: 0 - 20.0 degrees). Using the bifocal photography, the mean tIOL rotation was 1.9 +/- 1.3 degrees (range: 0 - 5.0 degrees). The overestimated rotation of the tIOL (only anterior segment tIOL comparison) correlated with higher amounts of the eye's cyclorotation (r = 0.94; p = 0.01) and higher corneal astigmatism (r = 0.54; p = 0.05). 3. The simultaneous analysis of Axenfeld loops revealed significantly smaller amounts of tIOL rotation (2.3 +/- 2.5 degrees range: 0 - 7.0 degrees ) in 10 pairs of anterior segment photographs in contrast to the single analysis of tIOL axis (5.5 +/- 4.8 degrees range: 1 - 13.0 degrees p = 0.09). A reduction of up to 18.0 degrees tIOL rotation measurement failure was possible in single cases by applying the bifocal photography or simultaneous Axenfeld loop analysis.


CONCLUSIONS
Head inclination, head rotation, and incyclo- or excyclorotation of the eye may have a significant impact on the tIOL axis evaluation. Besides the bifocal photography the simultaneous Axenfeld loop analysis could be a promising alternative to the conventional axis evaluation of tIOLs.
Augenklinik mit Poliklinik der Universität Erlangen-Nürnberg, Kopfklinikum, Erlangen. Arne.Viestenz@t-online.de
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Viestenz
D016477:Artifacts; D019544:Equipment Failure Analysis / Q000379:methods*; D005260:Female; D006801:Humans; D019654:Lens Implantation, Intraocular / Q000379:methods*; D007910:Lenses, Intraocular; D008297:Male; D008875:Middle Aged; D009887:Ophthalmoscopy / Q000379:methods*; D010781:Photography / Q000379:methods*; D017410:Practice Guidelines as Topic; D011785:Quality Assurance, Health Care / Q000379:methods; D015203:Reproducibility of Results; D012399:Rotation; D012680:Sensitivity and Specificity; D016896:Treatment Outcome