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Comparison of anterior segment optical tomography parameters measured using a semi-automatic software to standard clinical instruments.

Ang M, Chong W, Huang H, Tay WT, Wong TY, He MG, Aung T, Mehta JS - PLoS ONE (2013)

Bottom Line: There was good agreement between the measurements from ZAP analysis and each instrument and no violations in the assumptions of the LOA; albeit with a systematic bias for each comparison: AS-OCT consistently measured a deeper ACD compared to IOLMaster (95% LOA -0.24, 0.55); and a thicker CCT for the AS-OCT compared to ultrasound pachymetry (16.8±0.53 µm 95% LOA -17.3, 50.8).This study demonstrates that there is good agreement between the measurements from the AS-OCT (ZAP) and conventional tools.However, small systematic biases remain that suggest that these measurement tools may not be interchanged.

View Article: PubMed Central - PubMed

Affiliation: Singapore National Eye Centre, Singapore, Singapore ; Singapore Eye Research Institute, Singapore, Singapore.

ABSTRACT

Objective: To compare anterior segment parameters measured using a semi-automatic software (Zhongshan Angle Assessment Program, ZAP) applied to anterior segment optical coherence tomography (AS-OCT) images, with commonly used instruments.

Methods: Cross-sectional study of a total of 1069 subjects (1069 eyes) from three population-based studies of adults aged 40-80 years. All subjects underwent AS-OCT imaging and ZAP software was applied to determine anterior chamber depth (ACD), central corneal thickness (CCT), anterior and keratometry (K) - readings. These were compared to auto-refraction, keratometry and ocular biometry measured using an IOLMaster, ultrasound pachymeter and auto-refractor respectively. Agreements between AS-OCT (ZAP) and clinical instrument modalities were described using Bland-Altman, 95% limits of agreement (LOA).

Results: The mean age of our subjects was 56.9±9.5 years and 50.9% were male. The mean AS-OCT (ZAP) parameters of our study cohort were: ACD 3.29±0.35 mm, CCT 560.75±35.07 µm; K-reading 46.79±2.72 D. There was good agreement between the measurements from ZAP analysis and each instrument and no violations in the assumptions of the LOA; albeit with a systematic bias for each comparison: AS-OCT consistently measured a deeper ACD compared to IOLMaster (95% LOA -0.24, 0.55); and a thicker CCT for the AS-OCT compared to ultrasound pachymetry (16.8±0.53 µm 95% LOA -17.3, 50.8). AS-OCT had good agreement with auto-refractor with at least 95% of the measurements within the prediction interval (P value <0.001).

Conclusion: This study demonstrates that there is good agreement between the measurements from the AS-OCT (ZAP) and conventional tools. However, small systematic biases remain that suggest that these measurement tools may not be interchanged.

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Bland-Altman plot of keratometric (K)-readings with the difference between the K-readings of the two methods regressed on the average of K-readings with its 95% prediction interval.X-axis units = D/Y-axis units = D.
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pone-0065559-g003: Bland-Altman plot of keratometric (K)-readings with the difference between the K-readings of the two methods regressed on the average of K-readings with its 95% prediction interval.X-axis units = D/Y-axis units = D.

Mentions: In terms of K-readings, we found that there was good agreement as at least 95% of the data points were in prediction interval, with a proportional bias observed between the AS-OCT (ZAP) and the auto-refractor. The AS-OCT (ZAP) overestimated the K-readings compared to the auto-refractor by a mean of 2.81±2.36. The difference between the K-readings of the two methods was regressed on the average of K-readings of the two methods with its 95% prediction interval drawn – Figure 3. Table 3 describes the correlations for ACD, CCT and K-readings between AS-OCT (ZAP) and the reference instruments. While ACD and CCT had Pearson correlation coefficients of more than 0.85 (p-value <0.001), K-readings had a relatively lower Pearson correlation coefficient.


Comparison of anterior segment optical tomography parameters measured using a semi-automatic software to standard clinical instruments.

Ang M, Chong W, Huang H, Tay WT, Wong TY, He MG, Aung T, Mehta JS - PLoS ONE (2013)

Bland-Altman plot of keratometric (K)-readings with the difference between the K-readings of the two methods regressed on the average of K-readings with its 95% prediction interval.X-axis units = D/Y-axis units = D.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3672133&req=5

pone-0065559-g003: Bland-Altman plot of keratometric (K)-readings with the difference between the K-readings of the two methods regressed on the average of K-readings with its 95% prediction interval.X-axis units = D/Y-axis units = D.
Mentions: In terms of K-readings, we found that there was good agreement as at least 95% of the data points were in prediction interval, with a proportional bias observed between the AS-OCT (ZAP) and the auto-refractor. The AS-OCT (ZAP) overestimated the K-readings compared to the auto-refractor by a mean of 2.81±2.36. The difference between the K-readings of the two methods was regressed on the average of K-readings of the two methods with its 95% prediction interval drawn – Figure 3. Table 3 describes the correlations for ACD, CCT and K-readings between AS-OCT (ZAP) and the reference instruments. While ACD and CCT had Pearson correlation coefficients of more than 0.85 (p-value <0.001), K-readings had a relatively lower Pearson correlation coefficient.

Bottom Line: There was good agreement between the measurements from ZAP analysis and each instrument and no violations in the assumptions of the LOA; albeit with a systematic bias for each comparison: AS-OCT consistently measured a deeper ACD compared to IOLMaster (95% LOA -0.24, 0.55); and a thicker CCT for the AS-OCT compared to ultrasound pachymetry (16.8±0.53 µm 95% LOA -17.3, 50.8).This study demonstrates that there is good agreement between the measurements from the AS-OCT (ZAP) and conventional tools.However, small systematic biases remain that suggest that these measurement tools may not be interchanged.

View Article: PubMed Central - PubMed

Affiliation: Singapore National Eye Centre, Singapore, Singapore ; Singapore Eye Research Institute, Singapore, Singapore.

ABSTRACT

Objective: To compare anterior segment parameters measured using a semi-automatic software (Zhongshan Angle Assessment Program, ZAP) applied to anterior segment optical coherence tomography (AS-OCT) images, with commonly used instruments.

Methods: Cross-sectional study of a total of 1069 subjects (1069 eyes) from three population-based studies of adults aged 40-80 years. All subjects underwent AS-OCT imaging and ZAP software was applied to determine anterior chamber depth (ACD), central corneal thickness (CCT), anterior and keratometry (K) - readings. These were compared to auto-refraction, keratometry and ocular biometry measured using an IOLMaster, ultrasound pachymeter and auto-refractor respectively. Agreements between AS-OCT (ZAP) and clinical instrument modalities were described using Bland-Altman, 95% limits of agreement (LOA).

Results: The mean age of our subjects was 56.9±9.5 years and 50.9% were male. The mean AS-OCT (ZAP) parameters of our study cohort were: ACD 3.29±0.35 mm, CCT 560.75±35.07 µm; K-reading 46.79±2.72 D. There was good agreement between the measurements from ZAP analysis and each instrument and no violations in the assumptions of the LOA; albeit with a systematic bias for each comparison: AS-OCT consistently measured a deeper ACD compared to IOLMaster (95% LOA -0.24, 0.55); and a thicker CCT for the AS-OCT compared to ultrasound pachymetry (16.8±0.53 µm 95% LOA -17.3, 50.8). AS-OCT had good agreement with auto-refractor with at least 95% of the measurements within the prediction interval (P value <0.001).

Conclusion: This study demonstrates that there is good agreement between the measurements from the AS-OCT (ZAP) and conventional tools. However, small systematic biases remain that suggest that these measurement tools may not be interchanged.

Show MeSH