P 227 Measurement of corneal and crystalline lens misalignment relative to the visual axis

MEASUREMENT OF CORNEAL AND CRYSTALLINE LENS MISALIGNMENT RELATIVE TO THE VISUAL AXIS DUNNE M.C.M.1, BARRY J.C.2, HARTMANN A.2, CULPIN F.1, DE MAIN J.l, DUKE A.1 and FRENCH 1.1 I Department of Vision Sciences, Aston University (UK) 2 Department of Ophthalmology, RUTH Aachen (Germany) %rpare To measure the misalignment between the comeal and crystalline lens axes relative to the visual axis. To evaluate experimental errors involved in the Purkinje I and IV Reflection Pattern Evaluation technique for the assessment of eye rotations in strabismus detection. M&&&2& Pilot measurements were made in five cyclopeged eyes (one eye per subject) and repeated in two eyes. Ocular components were measured using a non-phakometric method. Horizontal misalignment of Purkinje images I, III and IV, relative to the visual axis, was measured using a modified slit lamp biomicroscope. Equations previously described by Phillips et al. (J. Cataract Refract. Sorg. 14, 129-135, 1988) for calculation of IOL tilt and decentration were applied to determine cornea1 and crystalline lens alignment. &x& Preliminary findings reveal that the comeal axis (rotated about a point 13.6 mm behind the comeal vertex, the eye’s assumed centre of rotation) is tilted by 0.4’ to 4.6” temporally relative to the visual axis (approximately angle kappa). Relative to the corneal axis, the lens also exhibits 2.4’ to 4.9” of tilt (lens rotation is assumed to occur about its anterior surface vertex) such that its nasal edge moves forward in addition to 0.08 mm nasalward to 0.10 mm temporalward decentration. Repeat readings indicate a precision of within 1.5” of comeal axis tilt, 0.5O of lens tilt and 0.10 mm of lens decentration. Conclusions Within the error limits of the technique, our results indicate that the comeal and lens axes are misaligned when the eye is in its primary position, onaccommodated. It follows that none of the eyes measured possessed a true optical axis. The likely difference in the relative orientation of the comeal and crystalline lens axes in right and left eyes yet to be established limits the accuracy of the Purkinje I and IV Reflection Pattern Evaluation techniaue, which ideallv assumes the existance of well-defined optical axes in both eyes. . Supported by DAAD grant 313, ARC VU 93i2 (Barry), DFG grant Ef 613-Z (Barry, Hartmann) and ARC grant 507 (Dunne).