Accuracy of Toric Intraocular Lens Axis Alignment Using Manual Slit Lamp Method and CALLISTO Eye Image-Guided System

Aims: Image-guided systems are the gold standard for determining toric intraocular lens (IOL) axis alignment. However, their high cost prevents widespread use of these systems. As an alternative, a simpler and affordable method could be performed manually using a slit-lamp biomicroscope. This study aims to compare the accuracy of manual toric IOL axis marking using a slit-lamp compared to the CALLISTO eye image-guided system.

Study Design: Prospective comparative

Methods: In this prospective study, toric IOL axis alignment of 42 eyes with cataract and coexisting corneal astigmatism were evaluated using manual slitlamp method and CALLISTO eye image-guided method. Preoperative and postoperative uncorrected visual acuity, best corrected visual acuity, amount of spherical and astigmatic refractive errors, and postoperative IOL axis alignment were evaluated. Intraclass correlation of the manual method was calculated and the difference of IOL axis alignment to the image-guided method was compared.

Results: Toric IOL implantation reduced the amount of astigmatic refractive error from -1.63 ± 0.65 D to -0.50 ± 0.19 D in the image-guided group and from -1.93 ± -0.90 D to -0.87 ± 0.26 D in the manual slitlamp group. As many as 90.5% of eyes in the image-guided group and 81.0% of eyes in the manual slitlamp group reached the target induced astigmatism (p=0.38). Manual axis marking showed intraclass correlation of 99.3%. However, when the manual method was compared to the image-guided method a mean difference in axis alignment of 10.98o (95% confidence interval: 9.32o - 12.63o) was observed.

Conclusions: Alignment of toric IOL axis using the manual method demonstrated a consistent result; yet producing a considerable difference to the result of the image-guided method.