Limits...
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.

Show MeSH
Bland-Altman plot of anterior chamber depth (ACD) measurements, with zero-line (blue line), mean difference (red line) and 95% limits of agreement (green dotted lines), comparing AS-OCT (ZAP) and IOLMaster.X-axis units = mm/Y-axis units = mm.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3672133&req=5

pone-0065559-g001: Bland-Altman plot of anterior chamber depth (ACD) measurements, with zero-line (blue line), mean difference (red line) and 95% limits of agreement (green dotted lines), comparing AS-OCT (ZAP) and IOLMaster.X-axis units = mm/Y-axis units = mm.

Mentions: We summarized the anterior segment parameters comparing AS-OCT (ZAP) and the respective reference instruments in Table 2. We did not detect any violations in the assumptions of the limits of agreement – while the deviation of the mean difference from the zero-line in the Bland-Altman plots describes the presence of constant bias in all three comparisons. We found good agreement between the AS-OCT (ZAP) with the IOLMaster (at least 95% of all measurements were within the LOA), where a constant bias (mean difference 0.16 mm) was found as the AS-OCT consistently measured a deeper anterior chamber depth compared to the IOLMaster (95% LOA −0.24, 0.55) – Figure 1. This was similar to CCT measurements, where we found a good agreement between the AS-OCT and ultrasound pachymetry with 95% of measurements within the LOA (95% LOA −17.3, 50.8). There was an observed constant bias of 16.8±0.53 µm (3.03%) for the AS-OCT (ZAP) measuring a thicker CCT compared to ultrasound pachymetry– Figure 2.


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 anterior chamber depth (ACD) measurements, with zero-line (blue line), mean difference (red line) and 95% limits of agreement (green dotted lines), comparing AS-OCT (ZAP) and IOLMaster.X-axis units = mm/Y-axis units = mm.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0065559-g001: Bland-Altman plot of anterior chamber depth (ACD) measurements, with zero-line (blue line), mean difference (red line) and 95% limits of agreement (green dotted lines), comparing AS-OCT (ZAP) and IOLMaster.X-axis units = mm/Y-axis units = mm.
Mentions: We summarized the anterior segment parameters comparing AS-OCT (ZAP) and the respective reference instruments in Table 2. We did not detect any violations in the assumptions of the limits of agreement – while the deviation of the mean difference from the zero-line in the Bland-Altman plots describes the presence of constant bias in all three comparisons. We found good agreement between the AS-OCT (ZAP) with the IOLMaster (at least 95% of all measurements were within the LOA), where a constant bias (mean difference 0.16 mm) was found as the AS-OCT consistently measured a deeper anterior chamber depth compared to the IOLMaster (95% LOA −0.24, 0.55) – Figure 1. This was similar to CCT measurements, where we found a good agreement between the AS-OCT and ultrasound pachymetry with 95% of measurements within the LOA (95% LOA −17.3, 50.8). There was an observed constant bias of 16.8±0.53 µm (3.03%) for the AS-OCT (ZAP) measuring a thicker CCT compared to ultrasound pachymetry– Figure 2.

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