Korean J Ophthalmol.  2018 Aug;32(4):265-272. 10.3341/kjo.2017.0108.

Improving the Toric Intraocular Lens Calculation by Considering Posterior Corneal Astigmatism and Surgically-induced Corneal Astigmatism

• Yoon CH
• Kim MK

• KMID: 2418146
• DOI: http://doi.org/10.3341/kjo.2017.0108

Abstract

PURPOSE
To investigate the effect of surgically induced corneal astigmatism (SICA) and total corneal astigmatism (TCA) estimation on the anterior corneal astigmatism (ACA)-based toric intraocular lens (IOL) calculation.
METHODS
Data from preoperative and postoperative corneal astigmatism, postoperative visual acuities, and refractive outcomes were collected. The incision was superior in with the rule anterior corneal astigmatism (WTRA) eyes and temporal in against the rule anterior corneal astigmatism eyes. The following five methods of calculating the toric IOL were compared: (1) ACA only and estimated SICA; (2) ACA with a fixed posterior corneal astigmatism (PCA) and estimated SICA; (3) ACA with a fixed PCA value and actual SICA; (4) and (5) TCA derived from the regression equations of ACA and actual SICA. The residual astigmatism was simulated. The Alpins method was used to analyze the astigmatism.
RESULTS
Sixty eyes from 46 patients were enrolled. Thirty eyes had WTRA and the other thirty had against the rule anterior corneal astigmatism. The vector and arithmetic means of the difference vector decreased when the information regarding the actual SICA and PCA was added to the calculation (from 0.59 diopters [D] @ 87.5° to 0.15 D @ 48.5°, and from 0.95 ± 0.53 to 0.71 ± 0.63 D, respectively; p < 0.001). The mean difference vector across the whole sample was lowest using model 5. The correction index was significantly closest to 1.0 in the WTRA group.
CONCLUSIONS
Researchers may improve the accuracy of post-implantation predictions by calculating toric IOL using exact SICA and TCA, with consideration of the PCA derived from the regression equation of ACA.

Keyword

Astigmatism; Lenses, intraocular; Surgically induced corneal astigmatism; Toric

MeSH Terms

Astigmatism*
Humans
Lenses, Intraocular*
Methods
Passive Cutaneous Anaphylaxis
Visual Acuity

Figure

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  Fig. 1 Double-angle plots of the difference vector with 95% confidence ellipses in eyes with with the rule anterior corneal astigmatism (red) and those with against the rule anterior corneal astigmatism (blue) in models 1 through 5.

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