Abstract
Purpose: To compare the arithmetic mean of surgically induced astigmatism (M-SIA) and the centroid of surgically induced astigmatism (C-SIA) after standard cataract surgery.Methods: We retrospectively examined 200 eyes of 100 consecutive patients undergoing bilateral cataract surgery through a 2.8 mm temporal clear corneal incision. We quantitatively measured the magnitude and axis of corneal astigmatism preoperatively and 3 months postoperatively using an automated keratometer (TONOREFF-II, Nidek). We assessed the M-SIA, the C-SIA, and the double angle plots for the display of the individual SIA distributions.Results: For bilateral data analysis, the magnitude of corneal astigmatism significantly increased from 0.66 ± 0.39 D preoperatively to 0.74 ± 0.46 D postoperatively (paired t-test, p = 0.012). The M-SIA was 0.50 ± 0.36 D. On the other hand, the C-SIA was 0.18 ± 0.60 D at an axis of 97°. For unilateral analysis, we obtained similar outcomes between the right and left eye groups.Conclusions: According to our experience, standard cataract surgery induces the M-SIA by approximately 0.5 D. The magnitude of the C-SIA largely decreased to approximately 40% of the M-SIA, and the direction of the C-SIA showed a tendency toward with-the-rule astigmatism. It should be noted that the M-SIA was considerably different from the C-SIA, especially when selecting the appropriate toric IOL model and power.
Highlights
Toric intraocular lens (IOL) implantation has been widely acknowledged as a safe and effective means for the treatment of cataract patients with corneal astigmatism [1,2,3]
We found no significant differences in the preoperative biometrics, such as uncorrected visual acuity (p = 0.509), or best spectacle-corrected visual acuity (p = 0.619), manifest sphere (p = 0.604), manifest cylinder (p = 0.710), corneal astigmatism (p = 0.751), mean keratometry (p = 0.599), central corneal thickness (p = 0.128), or axial length (p = 0.389), between the right and left eye groups
In the entire study population, the magnitude of corneal astigmatism significantly increased from 0.66 ± 0.39 D preoperatively to 0.74 ± 0.46 D postoperatively (Figure 1)
Summary
Toric intraocular lens (IOL) implantation has been widely acknowledged as a safe and effective means for the treatment of cataract patients with corneal astigmatism [1,2,3]. Modern sophisticated cataract surgery does not largely induce astigmatism due to a 2.0 to 3.0 mmincision size as well as the unnecessity for sutures to the wound, it is essential to accurately predict surgically induced astigmatism (SIA) to maximize visual function and subsequent patient satisfaction, especially in toric IOL-implanted eyes. The arithmetic mean (M-SIA) calculation is based on the magnitude of astigmatism, but does not include the direction of astigmatism. The centroid of SIA (C-SIA) is determined by both the magnitude and the direction of astigmatism. The bilateral differences in these two SIAs between the right and left eyes have not been fully understood. It may give us intrinsic insights into the current understanding of astigmatic correction, especially when using a toric IOL model in daily practice
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