Repeatability intraexaminer and agreement in amplitude of accommodation measurements

Clinical measurement of the amplitude of accommodation (AA) provides an indication of maximum accommodative ability. To determine whether there has been a significant change in the AA, it is important to have a good idea of the repeatability of the measurement method used. The aim of the present study was to compare AA measurements made using three different subjective clinical methods: the push-up, push-down, and minus lens techniques. These methods differ in terms of the apparent size of the target, the end point used, or the components of the accommodation response stimulated. Our working hypothesis was that these methods are likely to show different degrees of repeatability such that they should not be used interchangeably.

The AA of the right eye was measured on two separate occasions in 61 visually normal subjects of mean age 19.7 years (range 18 to 32). The repeatability of the tests and agreement between them was estimated by the Bland and Altman method. We determined the mean difference (MD) and the 95% limits of agreement for the repeatability study (COR) and for the agreement study (COA).

The COR for the push-up, push-down, and minus lens techniques were +/-4.76, +/-4.00, and +/-2.52D, respectively. Higher values of AA were obtained using the push-up procedure compared to the push-down and minus lens methods. The push-down method also yielded a larger mean AA than the negative-lens method. MD between the three methods were high in clinical terms, always over 1.75D, and the COA differed substantially by at least +/-4.50D. The highest agreement interval was observed when we compared AA measurements made using minus lenses and the push-up method (+/-5.65D).

The minus lens method exhibited the best repeatability, least MD (-0.08D) and the smallest COR. Agreement between the three techniques was poor.