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M. M. Shahimin, R. V. North, J. M. Woodhouse, J. T. Erichsen; Do the Measurements Agree? A Study on the Agreement of Cover Test Measurements Between Orthoptists, an Optometrist and an Infrared Portable Eye Tracker. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1830.
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Firstly, to evaluate the agreement of subjective cover test measurements between 2 clinical orthoptists and an optometrist. Secondly, to compare subjective and objective measurements obtained using an infrared eye tracker.
45 non-strabismic subjects, aged between 19 to 38 years (mean=24.28 ± 4.5SD), participated in this study. All 3 examiners assessed each subject independently in random order on the same session. All subjects wore their habitual correction at the time of examination. Cover test measurements were carried out at 6m and 40cm. The size of deviation was measured using prisms during an alternating cover test. The objective cover test measurement was performed on a subset of 7 subjects with an infrared eye tracker (Tobii X120; Tobii Technology AB, Sweden). Analyses were carried out using Intraclass Correlation Coefficient [ICC (3,1)] to assess for any potential systematic difference between subjective measurements made by the 3 examiners and the objective measurements performed with the eye tracker. Bland and Altman plots were also constructed to evaluate the 95% limits of agreement (LOA) between measurements.
The measurements ranged between 4 prism diopter (PD) esophoria to 20 PD exophoria. The ICC was high for both distance and near cover test with the values of 0.83 and 0.96, respectively. The 95% LOA from the Bland and Altman plots between 2 orthoptists ranged between -2.09 to 2.13 PD for distance and -4.02 to 4.46 PD for near measurements. The 95% LOA between orthoptists and optometrist was between -2.36 to 1.76 PD for distance and -3.47 to 3.52 PD for near measurements. Comparison of subjective and objective cover test findings revealed a high agreement, with an ICC of 0.92.
Subjective cover test measurements do not differ significantly between orthoptists and an optometrist. The objective cover test measurements, performed with the infrared eye tracker, also showed good agreement with subjective findings. This study provides evidence that an infrared eye tracker can be used as an alternative to assess eye alignment in a clinical setting.
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