Clinical evaluation of accuracy of horizontal meridian limbal marking

To assess the horizontal meridian misalignment of limbal marking under a slit lamp microscope by means of anterior segmental image assessment.

A consecutive series of the 32 eyes of 16 subjects (7 males and 9 females) aged 29 ± 6 years (range, 23-44 years), who had refractive errors but were otherwise healthy, were used in this study. With each subject seated at the slit lamp and a coaxial slit turned to the horizontal meridian, we aligned the subject's head vertically and placed two reference marks aligned with the 3- and 9-o'clock positions on the limbal conjunctiva, using a marker pen or a toric marker. We quantitatively evaluated the accuracy of axis aliment by determining deviation from the horizontal reference line using a corneal topographer with an anterior segment image.

The amount of the axis misalignment was 3.4° ± 2.2° (range, 0°-8°) when the marker pen was used, and 6.9° ± 5.0° (range, 0-24°) when the toric marker was used. Location identification using the toric marker showed a significantly larger deviation in axis alignment than that using the marker pen (Wilcoxon sign rank test, p < 0.001).

Horizontal limbal marking using a slit lamp microscope showed the axis misalignment by an average of 3.4° to 6.9°. These alignment errors led to a reduction of the effectiveness of astigmatism correction by an average of 10% to 20%, which was not necessarily negligible when we aim to correct astigmatism completely, if possible. For successful astigmatic surgical procedures, increased accuracy of preoperative limbal marking by decreased misalignment of the astigmatism axis is essential.