The Effect of Machine Aging on the Measurements of Optical Coherency Tomography

Min Sun Kim; Dae Yune Kim; Young Joon Jo; Jung Yeul Kim

doi:10.3341/jkos.2016.57.7.1087

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Kim, Kim, Jo, and Kim: The Effect of Machine Aging on the Measurements of Optical Coherency Tomography

Original Article

J Korean Ophthalmol Soc 2016;57(7):1087-1092.

Published online: 25 September 2016

DOI: https://doi.org/10.3341/jkos.2016.57.7.1087

The Effect of Machine Aging on the Measurements of Optical Coherency Tomography

Min Sun Kim, MD¹, Dae Yune Kim, MD², Young Joon Jo, MD¹, Jung Yeul Kim, MD^1,

¹Department of Ophthalmology, Chungnam National University School of Medicine, Daejeon, Korea

²Jung Eye Clinic, Geoje, Korea

Address reprint requests to Jung Yeul Kim, MD Department of Ophthalmology, Chungnam National University Hospital, #282 Munhwa-ro, Jung-gu, Daejeon 35015, Korea Tel: 82-42-280-8433, Fax: 82-42-255-3745 E-mail: kimjy@cnu.ac.kr

Received 7 January 2016 Accepted 27 May 2016

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 evaluate the effect of instrument aging on optical coherence tomography (OCT) measurements.

Methods

Single eyes of 60 healthy participants (60 eyes) aged 20–30 years were examined twice using a 5-year-old OCT instrument and a new OCT instrument (Carl Zeiss Meditec, Dublin, CA, USA). The measurements and changes in signal strength were investigated using both instruments.

Results

The signal strengths of the new and aged instruments were 8.6 ± 0.8 and 5.0 ± 1.0, respectively, which was a statistically significant difference (p < 0.001). In addition, the central macular thicknesses (CMT) of the new and aged instruments were 201.1 ± 16.1 μ m and 210.3 ± 16.0 μ m, respectively. The thickness was significantly greater using the aged instrument (p < 0.001). Repeated measurements within the same eye were compared, and the difference in CMT was 3.2 using the new instrument and 10.5 using the aged instrument (p < 0.05). The intraclass correlation coefficient (ICC) was compared to evaluate the reproducibility of each instrument. The ICC values of nine areas of Early Treatment Diabetic Retinopathy Study in the aged instrument were 0.371–0.872, indicating low reproducibility. However, the new instrument showed high reproducibility with values of 0.806–0.947.

Conclusions

Higher signal strength and lower CMT were observed using the new instrument compared to the aged instrument. Additionally, there were no differences in signal strength errors between the instruments. However, the error in CMT measured using the new instrument was significantly smaller compared to that using the aged instrument. Therefore, the effect of instrument aging should be accounted for in analyses of OCT measurements.

Keywords: Aging of optical coherence tomography (OCT), Central macular thickness, OCT measurements, Signal strength

References

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Figure 1.

The nine Early Treatment Diabetic Retinopathy Study (ETDRS) subfield area. The diameters of central circle, inner ring, and outer ring were 1 mm, 3 mm, and 6 mm, respectively. F = fovea; SI = superior inner; TI = temporal inner; II = inferior inner; NI = nasal inner; SO = superior outer; TO = temporal outer; IO = inferior outer; NO = nasal outer.

Figure 2.

Representative images from one patient using aged instrument and new instrument. (A) Signal strengths measured using the aged instrument (left) and the new instrument (right). (B) Fast macular thickness maps measured using the old instrument (left) and the new instrument (right). OCT = optical coherence tomography.

Table 1.

Patient demographics

Number of patients (eyes)	60 (60)
Age (years)	28.3 ± 6.2
Gender (male/female)	16/44
Intraocular pressure (mm Hg)	15 ± 5
Refractive error (diopters)	–2.25 ± 1.75
Best corrected visual acuity (log MAR)	1.2 ± 0.2

Values are presented as mean ± SD unless otherwise indicated.

SD = standard deviation; log MAR = logarithm of the minimum angle of resolution.

Table 2.

Signal strength and macular thickness values

	Aged instrument	New instrument	p-value
Signal strength	5.0 ± 1.0	8.6 ± 0.8	<0.001
Fovea (μ m)	210.3 ± 16.0	201.1 ± 16.1	0.002
Superior 3 (μ m)	285.1 ± 17.8	275.0 ± 13.6	0.001
Nasal 3 (μ m)	284.2 ± 15.6	274.8 ± 12.0	0.002
Inferior 3 (μ m)	278.4 ± 16.0	267.5 ± 13.2	0.001
Temporal 3 (μ m)	269.8 ± 15.8	259.6 ± 10.9	0.003
Superior 6 (μ m)	243.5 ± 16.8	232.7 ± 13.4	0.004
Nasal 6 (μ m)	266.8 ± 17.0	256.7 ± 13.7	0.002
Inferior 6 (μ m)	239.5 ± 17.8	229.8 ± 15.0	0.005
Temporal 6 (μ m)	224.6 ± 16.4	215.5 ± 12.6	0.003

Values are presented as mean ± SD unless otherwise indicated.

Table 3.

Differences in signal strength and macular thickness values after repeated measurements

	Difference in values		p-value
	Measured using the aged instrument	Measured using the new instrument	p-value
Fovea (μ m)	10.5 ± 12.6	3.2 ± 2.3	0.021
Superior 3 (μ m)	12.0 ± 13.2	3.4 ± 3.8	0.010
Nasal 3 (μ m)	10.1 ± 12.0	3.0 ± 2.3	0.024
Inferior 3 (μ m)	10.0 ± 11.8	3.1 ± 2.5	0.022
Temporal 3 (μ m)	9.4 ± 11.6	2.6 ± 1.8	0.024
Superior 6 (μ m)	10.2 ± 12.4	3.2 ± 2.3	0.021
Nasal 6 (μ m)	10.4 ± 11.6	3.1 ± 2.4	0.028
Inferior 6 (μ m)	11.0 ± 12.6	3.6 ± 2.6	0.017
Temporal 6 (μ m)	9.6 ± 11.8	3.0 ± 2.4	0.042

Values are presented as mean ± SD unless otherwise indicated.

Table 4.

Intraclass correlation coefficient of macular thickness between the aged and new instruments

	Aged instrument	New instrument
Fovea	0.664	0.930
Superior 3	0.371	0.833
Nasal 3	0.454	0.828
Inferior 3	0.614	0.871
Temporal 3	0.631	0.806
Superior 6	0.780	0.906
Nasal 6	0.872	0.947
Inferior 6	0.728	0.894
Temporal 6	0.784	0.925

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