Interobserver and intraobserver reliability of a classification scheme for corneal topographic patterns

Abstract

Aims: To determine the interobserver and the intraobserver reliability of a published classification scheme for corneal topography in normal subjects using the absolute scale.

Method: A prospective observational study was done in which 195 TMS-1 corneal topography maps in the absolute scale were independently classified twice by three classifiers--a cornea fellow, an ophthalmic technician, and an optometrist. From these observations the interobserver reliability for each category and the intraobserver reliability for each observer were determined in terms of the median weighted kappa statistic for each category and for each observer.

Results: For interobserver reliability, the median weighted kappa statistic for each category varied from 0.72 to 0.97 and for intraobserver reliability the range was 0.79 to 0.98.

Conclusion: This classification scheme is extremely robust and even in the hands of less experienced observers with minimal training it can be relied upon to provide consistent results.

Figure 1

(A) Diagrammatic representation of the various topographical patterns used by this classification scheme. See text for detailed definitions. (B) A bow tie is considered to have "skewed radial axes" when the smaller of the two angles between the two lobes (θ₁) is less than 150 degrees.

Figure 1

(A) Diagrammatic representation of the various topographical patterns used by this classification scheme. See text for detailed definitions. (B) A bow tie is considered to have "skewed radial axes" when the smaller of the two angles between the two lobes (θ₁) is less than 150 degrees.

Figure 2

(A) Transparent overlay placed over a TMS 1 map. The outermost circle occupies the area that a TMS 1 map would occupy when all points on all 25 rings are digitised. The intermediate circle occupies an area equal to two thirds of the entire map. This area is used to determine the classification of a map. The innermost circle occupies an area equal to 10% of the central two thirds area of the entire map. (B) The overlay being used to assess whether a colour occupies 10% of the central two thirds area of the map.