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Shinichiro Nakano, Fumiyasu Amano, Seiu Takagi, Takahiro Hiraoka, Tetsuro Oshika; Day-to-day and diurnal variations of corneal refractive power and astigmatic axis measured with two different corneal shape analyzers. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4757.
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© ARVO (1962-2015); The Authors (2016-present)
Precise evaluation of corneal refractive power and astigmatic axis is essential to achieve good postoperative results in performing intraocular lens (IOL) implantation, and various corneal shape analyzers are used for achieving the purpose. Although many studies have been conducted to confirm the precision, reliability, and reproducibility of these devices, the day-to-day and diurnal variations of the corneal shape itself within the devices have not been fully investigated. In this study, we examined the day-to-day and diurnal variations of corneal refractive power and astigmatic axis in healty subjects by using two different corneal shape analyzers.
Eight eyes of four healthy volunteers (all men; mean age 33.3 ± 8.3 years old) without any ocular diseases other than refractive errors were enrolled. Corneal refractive power was measured in the 3 mm diameter region using two different corneal shape analyzers such as anterior segment optical coherence tomography (CASIA, TOMEY) and corneal topographer (iTrace, TRACY Technologies). From October 1 until 30, 2016, the measurements were performed every day three times a day as far as possible; in the morning (8 to 9 o'clock), daytime (13 to 14 o'clock), and evening (17 to 18 o'clock). We defined the day-to-day variation as standard deviation (SD) of all measurements for each eye over the study period, and diurnal variation as difference between 3 measurements (morning, daytime, and evening) for each eye during a day.
One hundred and two measurements were made in total (25.5 times on average for each subject). Regarding the day-to-day variation, SD of corneal refractive power varied from 0.13 to 0.22 D in the CASIA, and from 0.08 to 0.21 D in the iTrace, respectively. That of corneal astigmatic axis was from 1.93 to 3.66 and from 1.12 to 9.04 degrees, respectively. As for the diurnal variation, corneal refractive power varied from 0.02 to 0.58 D in the CASIA, and from 0 to 0.36 D in the iTrace, respectively, and corneal astigmatic axis varied from 0.17 to 8.59 and from 0 to 7.83 degrees, respectively.
The amount of day-to-day and diurnal variations of corneal refraction and astigmatic axis was relatively small. Thus, these influences on preoperative IOL power calculation were considered to be negligibly small.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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