The purpose of this study is to quantify in-vivo repeatability of a new corneal topography measurement mode of an optical biometer, and the clinical performance of measurement in comparison to reference devices.
Study Type
OBSERVATIONAL
Enrollment
50
University Hospital Inselspital
Bern, Switzerland
In-vivo Repeatability of Corneal Topography Measurements With Lenstar LS 900 Topography: Sample Mean of Differences of Mean Power and Sample Mean of Std. Dev of Local Power Differences Between Two Consecutive Measurements
Corneal topography is a measurement of the shape of the anterior cornea. The shape of a cornea can be fully quantified by providing a map of local power. "Diopter" is the unit of refractive power of a lens. In case of the cornea, the power K \[diopter\] is related to the radius (curvature) R \[mm\] of the best fitting sphere by the relation K=337.5/R. Here, corneal topography measurements are implemented by the Placido method, i.e. by analyzing the reflection image of a ring-shaped illumination. According to International Standards Organization (ISO) 19980-2012, repeatability of corneal topography is assessed on the central cornea: area with diameter d\<=3mm, and middle cornea: 3mm\<d\<=6mm. "power difference (2 rep. meas.)": sample mean and 95% C.I. of differences of spatial mean of corneal power between two consecutive measurements. "power difference 2 std.dev.": sample mean of twice the deviation of local power differences (two consecutive measurements).
Time frame: 1 day of examination
Equivalence of Corneal Topography Measurement Between Lenstar LS 900 Topography and Atlas 9000: Sample Mean of Differences of Mean Power and Sample Mean of Std. Dev of Local Power Differences for One Measurement Per Device.
For definition of corneal topography, corneal power in "diopter", areas of evaluation and methods, see outcome 1. This outcome measure aims at testing the equivalence of corneal topography measurement between Lenstar LS 900 Topography (Haag Streit) and Atlas 9000 (Zeiss) by analyzing differences in measurement results for the same eye between both devices. "power difference (2 devices)" is the sample mean and 95% C.I. of differences of spatial mean of corneal power between two devices. This value quantifies systematic differences between devices (e.g. calibration), ignoring local variations of the power measurement. "power difference (2 std.dev.)" is the sample mean of twice the standard deviation of local power differences between measurements with both devices. This value quantifies the spatially resolved agreement of corneal shape measurement of the two devices.
Time frame: 1 day of examination
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