Comparison of Axial Length and Postoperative Refraction between Applanation Ultrasonography and Low-coherence Reflectometry

Yoon Pyo Lee; Young Joo Shin; Kayoung Yi

doi:10.3341/jkos.2018.59.7.629

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Lee, Shin, and Yi: Comparison of Axial Length and Postoperative Refraction between Applanation Ultrasonography and Low-coherence Reflectometry

Original Article

J Korean Ophthalmol Soc 2018;59(7):629-639.

Published online: 25 September 2018

DOI: https://doi.org/10.3341/jkos.2018.59.7.629

Comparison of Axial Length and Postoperative Refraction between Applanation Ultrasonography and Low-coherence Reflectometry

Yoon Pyo Lee, MD, Young Joo Shin, MD, PhD, Kayoung Yi, MD, PhD

Department of Ophthalmology, Kangnam Sacred Heart Hospital, Hallym University College of Medicine, Seoul, Korea

Address reprint requests to Kayoung Yi, MD, PhD Department of Ophthalmology, Hallym University Kangnam Sacred Heart Hospital, #1 Singil-ro, Yeongdeungpo-gu, Seoul 07441, Korea Tel: 82-2-829-5196, Fax: 82-2-848-4638 E-mail: kayoungyi@yahoo.co.kr

Received 14 February 2018 Revised 9 May 2018 Accepted 26 June 2018

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose

To compare axial length applanation ultrasonography (A-scan) (CineScan B-Scan; Quantel Medical, Bozeman, MT, USA) and low-coherence reflectometry (Lenstar LS900^®; Haag-Streit, Bern, Switzerland), the accuracy of the predictive post-operative refraction of both instruments, and the intraocular lens (IOL) calculators.

Methods

A total of 250 eyes of 191 patients who received cataract surgery were included in the study. The axial length was measured by the A-scan and Lenstar LS900^®. The SRK-2, SRK/T, and Olsen formulas were used to calculate the IOL power, and the difference between the predictive and actual postoperative refractions after 6 weeks and the probability that they were within 0.25 diopters (D) and 0.5 D were compared.

Results

The mean axial lengths measured by the A-scan and Lenstar LS900^® were 23.42 ± 0.94 mm and 23.55 ± 0.95 mm, respectively, which showed a statistically significant difference (paired t-test, p = 0.000). When comparing the difference between the predictive and actual postoperative refractions, the results of the A-scan using the SRK-2 and SRK/T formulas were significant toward the hyperopia, and the results of the Lenstar LS900^® using the SRK-2, SRK/T, and Olsen formulas were significant toward the myopia (paired t-test, p = 0.001 and p < 0.001, respectively). When comparing the mean absolute difference between the two refractions and the probability that they were within 0.25 D and 0.5 D, the Lenstar LS900^® using the Olsen formula significantly showed the highest accuracy (McNemar test, p = 0.045 and p = 0.002; p = 0.010 and p = 0.002, respectively).

Conclusions

The A-scan using the SRK-2 and SRK/T formulas showed that the actual postoperative refraction was more hyperopic than the predicted refraction, whereas the Lenstar LS900^® resulted in more myopic findings. The accuracy of predictive postoperative refraction was highest with the Lenstar LS900^® using the Olsen formula.

Keywords: Applanation ultrasonography, Axial length, Cataract surgery, Low-coherence reflectometry, Postoperative refraction

References

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Figure 1.

Correlation between biometric data (axial length, keratometry) measured by Lenstar LS900® and other devices (Pearson correlation analysis). Axial length measured by Lenstar LS900® and A-scan (A). Keratometry measured by Lenstar LS900® and autokeratometer (B). r = Pearson correlation coefficient.

Figure 2.

Bland-Altman plot of axial length and keratometry. Bland-Altman plot of axial length between A-scan and Lenstar LS900® (A), keratometry between autokeratometer and Lenstar LS900® (B). LOA = limit of agreement.

Figure 3.

Comparisons of accuracy of predictive postoperative refraction by mean prediction error (A), mean absolute error (B). ‘A-scan (SRK-2/T)’ is ‘measurement of A-scan using SRK-2 and SRK/T formulas’, ‘Lenstar (SRK-2/T)’ is ‘measurement of Lenstar LS900^® using SRK-2 and SRK/T formulas' and ‘Lenstar (Olsen)’ is ‘measurement of Lenstar LS900^® using Olsen formula’. Bold line in gray box means ‘median value’, bottom line of gray box means ‘first quartile’, top line of gray box means ‘third quartile’, lower end of vertical line means ‘minimum value’, and upper end of vertical line means ‘maximum value’. ^* p < 0.05, Statistically significant (Paired t-test).

Figure 4.

Comparisons of accuracy using probability within 0.25 D and 0.5 D. Comparisons of probability that the difference between the predictive and actual postoperative refraction is within 0.25 D (A) and within 0.5 D (B). ^* p < 0.05, Statistically significant (McNemar test).

Table 1.

Demographic data of enrolled patients

	Mean (SD)	Range
Age (years)	70.90 (8.82)	39 to 89
Preoperative refraction (SE)	−0.11 (3.09)	−14.50 to 6.00
Postoperative refraction (SE)	−0.38 (0.64)	−3.25 to +1.50
IOL power (D)	21.07 (2.46)	+9.0 to +27.0
Central corneal thickness (μ m)	534.06 (30.49)	447 to 626
Anterior chamber depth (mm)	2.57 (0.39)	1.57 to 3.64
Lens thickness (mm)	4.58 (0.39)	3.42 to 5.47

SD = standard deviation; SE = spherical equivalent; IOL = intraocular lens; D = diopters.

Table 2.

Comparison of biometric data (axial length, mean keratometry, central corneal thickness, anterior chamber depth, lens thickness) by Lenstar LS900^®, A-scan and autokeratometer

	A-scan and Autokeratometer		Lenstar LS900^®		p-value^*
	Mean (SD)	Range	Mean (SD)	Range	p-value^*
AL (mm)	23.42 (0.94)	21.43 to 26.85	23.55 (0.95)	21.55 to 26.96	<0.001
Mean keratometry (D)	44.13 (1.47)	40.22 to 47.53	44.17 (1.47)	40.22 to 47.53	0.089

SD = standard deviation; AL = axial length.

^* Paired t-test.

Table 3.

Values of mean absolute error and probability that it is of within 0.25 D and 0.50 D according to axial length (IOL formula) and IOL model

		Mean absolute error (D)				Probability of mean absolute error within 0.25 D and 0.50 D (%)
		Mean absolute error (D)				Within 0.25 D			Within 0.50 D
		n	A-scan (SRK)	Lenstar LS900^® (SRK)	Lenstar LS900^® (Olsen)	A-scan (SRK)	Lenstar LS900^® (SRK)	Lenstar LS900^® (Olsen)	A-scan (SRK)	Lenstar LS900^® (SRK)	Lenstar LS900^® (Olsen)
AL (IOL formula)	<25 mm	232	0.513	0.517	0.398	34.9	30.6	43.1	58.2	56	66.8
	(SRK-2)		(<0.001^*)	(<0.001^*)		(0.079^‡)	(0.003^‡)		(0.050^‡)	(0.011^‡)
	≥25 mm	18	0.754	0.595	0.410	11.1	16.7	27.8	44.4	44.4	83.3
	(SRK/T)		(0.010^†)	(0.008^†)		(0.375^‡)	(0.500^‡)		(0.039^‡)	(0.016^‡)
IOL model	ZCB00	142	0.536	0.519	0.407	35.9	25.4	40.1	54.9	54.9	67.6
			(0.002^*)	(<0.001^*)		(0.519^‡)	(0.004^‡)		(0.023^‡)	(0.021^‡)
	SN60WF	108	0.524(0.003^*)	0.527(<0.001^*)	0.388	29.6(0.034^‡)	35.2(0.175^‡)	44.4	60.2(0.243^‡)	55.6(0.045^‡)	68.5

IOL = intraocular lens; AL = axial length.

^* p-value of paired t-test compared to mean absolute error of Lenstar LS900^® (Olsen)

^† p-value of Wilcoxon signed ranked test compared to mean absolute error of Lenstar LS900^® (Olsen)

^‡ p-value of McNemar test compared to probability of mean absolute error within 0.25 D and 0.50 D of Lenstar LS900^® (Olsen).

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