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S. A. Alanazi, C. Purslow, R. V. North, F. Ennis; Repeatability and Validity Measurements of Associated phoria using the near Mallett unit and the Saladin card. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3822.
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Associated phoria (AP) can be an important aspect of binocular vision assessment, however measurements are variable from one test to another (e.g. Mallett unit, Sheedy disparometer) in the clinical setting. Hence validity and repeatability studies are required. The Mallett Unit is commonly used in the UK, but the Saladin card has the advantage of being an inexpensive, lightweight and portable facility, making it particularly useful in non-traditional optometric settings such as in schools & nursing homes. The purpose of this study was to compare AP as recorded by the Near Mallett Unit (NMU) and the Saladin card (SC), and to assess the repeatability of both.
Ninety-three normal subjects (mean age: 22±4.3 years) were recruited who met inclusion criteria of : monocular VAs of 0.1 or better, absence of asthenopic symptoms; ortho or low heterophoria (5 eso to 7 exo distance, 4 eso to 10 exo near) and 60" or better stereoacuity. AP was measured using the NMU and SC placed at eye level at 40 cm at 300 lux background illumination. Thirty-two subjects (mean age: 23.1±4.45 years) repeated the tests after an interval of one week. All subjects provided written informed consent and this study conformed to the tenets of the Helsinki declaration.
The mean AP with the NMU was -0.086±0.503 and with the SC was -0.096±0.49 (meanΔ±SD) with no statistically significant difference between the two techniques (p>0.05). The mean difference in AP between the two techniques was 0.011 ± 0.59 Δ (95% limits of agreement -0.1125 and 0.134Δ). The inter-session repeatability indices for the two techniques did not differ significantly (p>0.05), the mean differences being 0.063±0.35 (mean±SD, 95% limits of agreement of -0.065 and +0.19).
The Saladin card and Mallett unit appear to give similar measures and repeatability level of AP in a clinical environment.
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