We analysed whether auditory biofeedback influences the variability of accommodation in myopic subjects.
Accommodative accuracy was trained in 31 myopic subjects for 3 distances (2, 2.5, 3D) using an eccentric photorefractor. Subjects were randomly assigned to an experimental and control group. Experimental subjects (n=15) received auditory biofeedback appropriate to the amount of accommodation and alternately a target tone proportionate to the tested distance. The task was to change accommodation to match the two pitches. Both a continuous training of 200s and 10 short sessions of 20s each were applied in random order. Control subjects received the same training without biofeedback. To analyze the influence of auditory feedback, accommodation variability was determined from the standard deviation of the response in both groups during both training methods. Power spectrum analysis was performed using the Lomb-Scargle periodogram.
Analysis of accommodation variability in the long training disclosed a significant influence of distance (univariate ANOVA p=0.018). Fluctuations were significantly larger at 3D than at 2D. Regarding the short training, accommodative variability was significantly greater in subjects without biofeedback (repeated measures ANOVA p=0.029). A dependence of variability on time (p<0.001) was also revealed.
The power spectrum density (psd) significantly varied with distance (p<0.001) and frequency class (p<0.001) for the long method, with significantly higher values for the sum(psd) at 3D than at 2D. In the short method, sum(psd) was significantly larger in the control group (p=0.001).
Biofeedback might be conducive to producing a steadier accommodative response during short near-vision intervals, affecting both the variability and its frequency composition.
Previous studies revealed that myopes exhibit greater accommodative variability than emmetropes, especially the late-onset myopes. It was suggested that the increased blur resulting from these microfluctuations could be a causal factor of myopia development. There are further indications supporting a possible link between myopia onset and near-vision behaviour. One hypothesis explaining this link is predicated on the so-called lag of accommodation, the under-accommodation that is found in most individuals during near-vision tasks.
A larger lag of accommodation, resulting in a larger hyperopic retinal defocus, is assumed to elicit further axial eye elongation and thereby myopia development and progression. Our previous investigation showed that auditory biofeedback training can improve the accuracy of accommodation, hence reducing the accommodative lag in some subjects with myopia at target distances ≥ 2.5 D (doi: 10.1016/j.visres.2016.10.002).
The detailed analysis of the accommodation behaviour could be instrumental in better understanding the process of myopia onset. I therefore aim to examine the dynamics of accommodation with respect to the refractive power changes of the crystalline lens, the ciliary muscle activity, and its morphology changes in subjects with myopia and emmetropia.
Sandra Wagner
I completed a Bachelor of Science in Optometry and Audiology and a Master of Science in Optometry and Psychophysics both at Aalen University, Germany, and I am currently a PhD candidate at the Institute for Ophthalmic Research, University of Tuebingen, Germany.
References
1 ZEISS Vision Science Lab, Institute for Ophthalmic Research, Eberhard Karls University, Tuebingen, Germany;
2 Carl Zeiss Vision International GmbH, Aalen, Germany;
3 Section of Neurobiology of the Eye, Institute for Ophthalmic Research, Eberhard Karls University, Tuebingen, Germany;
