ACCURACY AND REPEATABILITY OF THE TOPCON K-3500 AUTOKERATOMETER ON CALIBRATED CONVEX SURFACES

The vertex (apical) radius and the p value of 30 conicoidal convex sur face plastic buttons were measured using the Topcon KR-3500 autokerato meter. The vertex radius was found using the equations derived in the introduction. The results were compared to those derived by the Form T alysurf technique, which was considered to give a precise indication o f both the vertex radius and p value. The results revealed a good agre ement between the two methods of measurement. The autokeratometer disp layed a tendency to underread the vertex radius, compared to the Talys urf result, but the maximum difference was 0.02 mm (95% confidence int erval). For the p value, the autokeratometer could over- or underread with a maximum difference of 0.035. The largest coefficient of repeata bility for the two observers using the Topcon autokeratometer was foun d to be 0.033 mm for vertex radius and 0.068 for the p value.