Popperian falsification of methods of assessing surgically induced astigmatism.

To test several methods of assessing surgically induced astigmatism (SIA). Department of Ophthalmology, Arhus University Hospital, Arhus, Denmark. Assessment methods can be divided into 3 groups. Group 1 includes methods that consider only astigmatic magnitude and disregard astigmatic direction, such as the algebraic and simple subtraction methods. Group 2 can be termed "astigmatic magnitude not considering axis" and includes several almost identical techniques known as the methods of Naylor, Jaffe, Kaye, Holladay, and Olsen. Group 3 includes Naeser polar value analysis and the methods later described by Alpins and Holladay. The methods were tested in situations in which the expected result was known. When this result was not produced, the specific assessment method was considered falsified in a classical Popperian manner. The simple falsification experiments revealed that the methods in Groups 1 and 2 are erroneous. Mathematical analysis disclosed that the methods in Group 3 are similar, although derived from different concepts. The algebraic, simple subtraction, astigmatic magnitude not considering axis, and vector decomposition methods for assessment of SIA are erroneous and should not be used. The Naeser, Alpins, and Holladay methods are identical and in agreement with current research in optometry.