The apparent optical axis of an implanted intraocular lens (IOL) can be located by alignment of the examiner's hand light with the third and fourth Purkinje images from the front and back surfaces of the IOL. Tilt of the 101- can be estimated (or measured with an arc perimeter) by the angle between the apparent optical axis and the patient's line of sight (actual tilt ≈ 0.85 X apparent tilt). Decentration of the IOL is easily detected, equal to the distance of the 101 - optical axis from the center of the pupil. This simple technique can be used through the natural pupil with posterior chamber IOLs, providing the optical axis of the malpositioned IOL still passes through the pupil.
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