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Mona Sane, Bilal Ahmed, Hoon Jung; Comparison of keratometry using optical biometry versus corneal topography and its effect on surgical decision making for toric intraocular lens implantation. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2472.
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© ARVO (1962-2015); The Authors (2016-present)
Accurate measurement of corneal power and astigmatic axis is essential for proper selection and correct placement of toric intraocular lens (IOL). Optical biometry is traditionally used for keratometry and measurement of axial length along with other parameters. The objective of the study is to compare the keratometry measurements obtained using optical biometry and corneal topography and determine the impact on surgical decision making.
This retrospective non-randomized comparative study included only patients with 2 or more diopters (D) of corneal astigmatism measured by the IOLMaster (Carl Zeiss Meditech, Germany), at a hospital based ophthalmology clinic. Keratometry was repeated in all these eyes using the ATLAS corneal topographer (Carl Zeiss Meditech, Germany) for confirmation of keratometry measurements, prior to finalizing the implantation of toric IOL. The corneal powers and axis of astigmatism were compared between the 2 instruments. Eyes with corneal astigmatism ≥ 2 diopters measured by both the instruments were selected for implantation of toric IOLs.
22 eyes of 17 male patients (age 46 to 99 years) showed ≥ 2 D corneal astigmatism by the IOLMaster. Out of the 22 eyes, 16 eyes (72.7%) showed corneal astigmatism ≥2 D by the ATLAS topographer. The IOLMaster measured a higher astigmatism in 17 eyes by an average of 0.79 D, and lower astigmatism in 5 eyes by an average of 0.23 D.
Our study showed clinically significant differences in magnitude and axis of astigmatism between the IOLMaster and ATLAS topographer. 27.3 % eyes did not receive toric IOL implants due to non-corresponding measurements between the 2 instruments. There can be a wide variation in measurement of astigmatic axis by the two instruments. Though most axis locations were within 5 degrees, about 9 % eyes showed a clinically significant difference. Our study was small and did not compare the refractive outcome of eyes implanted with toric IOLs to those not implanted with toric IOLs. Larger studies comparing the postoperative magnitude and axis of astigmatism to preoperative keratometry using the two instruments can determine instrument superiority and reliability for deciding eligibility for toric IOLs.
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