Comparison of Mean and Centroid of Surgically Induced Astigmatism After Standard Cataract Surgery

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.

Effect of Trabeculectomy on Mean and Centroid Surgically Induced Astigmatism

“…In the current study, our findings demonstrate that the C-SIA was much smaller than the M-SIA in post-trabeculectomy patients, possibly because individual SIA showed variations in astigmatism in magnitude and direction in these patients. Both SIA findings of trabeculectomy were in good agreement with our previous SIA findings of cataract surgery and phakic intraocular lens implantation [ 13 , 14 ]. Therefore, we believe that the C-SIA is theoretically beneficial to understand the overall trend of SIA.…”

“…To the best of our knowledge, this is the first study to unilaterally demonstrate the magnitude and the direction of SIA in a large cohort of patients undergoing trabeculectomy. It has been reported that standard cataract surgery through a 3 mm corneal incision caused a M-SIA of approximately 0.5 D [ 8 , 9 , 10 , 11 , 12 , 13 ]. We previously revealed that the C-SIA of cataract surgery and phakic intraocular lens implantation was far smaller than that of the M-SIA [ 13 , 14 ].…”

“…It has been reported that standard cataract surgery through a 3 mm corneal incision caused a M-SIA of approximately 0.5 D [ 8 , 9 , 10 , 11 , 12 , 13 ]. We previously revealed that the C-SIA of cataract surgery and phakic intraocular lens implantation was far smaller than that of the M-SIA [ 13 , 14 ]. In the current study, our findings demonstrate that the C-SIA was much smaller than the M-SIA in post-trabeculectomy patients, possibly because individual SIA showed variations in astigmatism in magnitude and direction in these patients.…”

Comparison of magnitude and summated vector mean of surgically induced astigmatism vector according to incision site after phakic intraocular lens implantation

“…The summated vector mean of SIA (SVM-SIA) consists of the magnitude and the meridian of corneal astigmatism. Hence, the SVM-SIA is considered clinically more meaningful in understanding general SIA tendencies [ 10 , 11 ] and might differ from the M-SIA [ 12 ]. Moreover, ICL surgery through a superior corneal incision may be beneficial for reducing astigmatism, especially when using a non-toric ICL in WTR astigmatic eyes.…”

Toric intraocular lenses: Evidence‐based use

“…This method tends to over-estimate the change that occurs due to the test-to-test variability of corneal power and axis measurement. 24 An alternative is to derive the flattening that occurs on average on the incised meridian by vector analysis. 25 Once again that value depends on possibly inaccurate corneal measurement.…”