Comparison of three monocular methods for measuring accommodative stimulus-response curves

Abstract

Purpose: The aim was to evaluate the repeatability of dynamic measurement of the accommodative stimulus-response curve (ASRC) at three different dioptric speeds using a modified instrument and its agreement with two other methods.

Methods: Twenty-nine adults (23.5 ± 2.0 years) were enrolled in the study. ASRC was measured monocularly using three methods: dynamic and static measurement using a motorised Badal system mounted on an open-field auto-refractor (WAM-5500, Grand Seiko Co., Ltd, Japan) and the minus lens technique. Dynamic measurements were conducted at three dioptric stimulus speeds to simulate continuous stimuli for ASRC (0.25, 0.40 and 0.55 D/s), with three repetitions for each speed. All three types of ASRCs were fitted with third-degree polynomial equations. The slope and objective accommodative amplitude of the ASRC were analysed.

Results: The repeatability of objective accommodative amplitude worsened as the speed of the stimuli increased. The repeatability of the slope was best at a speed of 0.40 D/s and worst at 0.55 D/s. The measurement method significantly influenced the objective accommodative amplitude values and slope (both, p < 0.001). The minus lens technique yielded the highest amplitude of accommodation (6.21 ± 0.84 D) and steepest slope (1.11 ± 0.14), followed by the static Badal method (5.60 ± 0.83 D and 0.89 ± 0.09 D). The objective accommodative amplitude decreased with increasing speed during dynamic measurements. There was no difference between the slopes at 0.25 D and 0.40 D/s (p > 0.05) and the slope was lowest at 0.55 D/s.

Conclusion: The accommodative stimulus-response curve values are method-dependent and the significant differences between three methods used to determine the ASRC based on slope and accommodative amplitude indicate that these methods are non-interchangeable. Using dynamic measurements, accommodative behaviour varies with the speed of dioptric-change of the stimulus. A speed of 0.40 D/s appears to be the best compromise in terms of time, results and repeatability for dynamic ASRC measurement.

Keywords: accommodation; accommodative stimulus-response curve; objective accommodative amplitude; repeatability; slope.

Figure 1

Schematic of the Badal stimulator mounted on a Grand Seiko WAM 5500 auto‐refractor (GS). BL and AL represent the Badal and movable auxiliary lenses, respectively.

Figure 2

Example of three accommodative stimulus–response curves (ASRC) obtained using three methods in one subject: dynamic ASRC (A), static ASRC using a Badal stimulator (B, triangles) and minus lens stimulated static ASRC (B, circles). AR_max and AR_min represent the maximum and minimum accommodative responses, respectively.

Figure 3

Mean objective amplitudes of accommodation obtained using different methods, namely, dynamic accommodative stimulus–response curve (ASRC) using a Badal stimulator (SB) at three speeds: 0.25 D/s‐DB, 0.40 D/s‐DB, 0.55 D/s‐DB, static ASRC using a SB and minus lens (ML) stimulated static ASRC. The objective amplitude of accommodation of dynamic ASRCs was determined as the mean of three measurements of amplitude of accommodation for each speed. The objective amplitude of accommodation of the corresponding method marked with * was significantly different from that of any other method. The error bars represent ±1 standard error of the mean.

Figure 4

Mean accommodative stimulus–response curve slopes (ASRC) obtained using different methods: dynamic ASRC using a Badal stimulator (SB) at three speeds: 0.25 D/s‐DB, 0.40 D/s‐DB, 0.55 D/s‐DB, static ASRC using a SB and minus lens (ML) stimulated static ASRC. The slope of the dynamic ASRC was determined as the mean slope of three measurements for each speed. The slope of the corresponding method marked with * was significantly different from that of any other method. The error bars represent ±1 standard error of the mean.