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Accommodation in Myopia

Thirty years from now, half of the world’s population is predicted to be myopic, and approximately 10 % might have myopia of more than -5 D. A myopic eye has grown too long so that a focused object is placed in front of the retina. The refractive error can be corrected using spectacles, contact lenses, or laser procedures, however, the anatomical changes arising from the axial ocular elongation lead to severalfold increased risks for sight-threatening eye diseases such as glaucoma, retinal detachment, or myopic maculopathy. This means an enormous burden for the public health systems worldwide and researchers are challenged to receive a full understanding of the origins of myopia development.

The etiology of myopia is multifaceted, including genetic and environmental factors. As early as the 17th century, Kepler assumed myopia onset to be related to near vision and accommodation. Recent analyses found significant correlations between the prevalence of myopia and the level of education and the amount of time spent with nearwork. In 1892, the German ophthalmologist Cohn suggested a role for the ciliary muscle in myopia development: Periods of sustained contraction of the ciliary muscle during close work might lead to aftereffects such as a temporary lens myopia due to an increased lens curvature. Without providing the muscle with a period of relaxation, this transient type of myopia might slowly turn into a permanent one. Today, the temporarily experienced myopia after close work is termed “nearwork-induced transient myopia” and has been studied extensively over the last decades. Several investigations reported myopic subjects to be more susceptible to accommodative changes associated with periods of nearwork. Furthermore, myopes were found to exhibit larger inaccuracies during accommodation, larger under-accommodation when fixating a close target, the so-called lag of accommodation, as well as a lower resting state of accommodation (tonic accommodation). The relationship between myopia development and near vision has been controversially discussed for decades and is still being analyzed today. The development of new biomedical imaging tools facilitated the in vivo assessment of the ciliary muscle morphology. Previous studies predominantly applying optical coherence tomography (OCT) reported differences in the ciliary muscle anatomy depending on the refractive error. This led to a revived interest to investigate the ciliary muscle as possible factor in the development of myopia.

In this project, we compared the accommodation system of myopic and emmetropic young adults regarding changes in both crystalline lens power and ciliary muscle thickness (CMT) during regular and sustained accommodation. Moreover, we aimed to answer the question whether accommodation could be voluntarily controlled to improve its accuracy using auditory biofeedback training.

To allow a more detailed analysis of the ciliary muscle morphology within OCT images, we first developed and evaluated a semi-automatic segmentation software. This software, for the first time, allowed measuring the muscle thickness continuously along its boundaries instead of taking only incremental readings (Wagner et al., 2018). Applying this novel tool in the three-part study, we found that the ciliary muscle of myopic eyes was thinner anteriorly, close to the scleral spur, and thicker posteriorly than emmetropic ones. Furthermore, myopic anterior CMT changes during accommodation were smaller, but the muscle’s movement was larger. In contrast, lens power changes during a dynamic viewing task of the pattern far-near-far were not significantly different between the groups (Wagner et al., 2019a). The second part showed that after a continuous 30-min nearwork period, the ciliary muscle got significantly thinner in emmetropes and myopes, however, in different regions and to different amounts in the two groups, and only myopes developed a sustained relative myopic shift (Wagner et al., 2019b). Finally, accommodative accuracy after the biofeedback training was improved in both groups, with larger effects in myopes than emmetropes with habitual, but not multifocal soft contact lenses (Wagner et al., 2020).

The results provide supporting evidence for adaptation and malleability techniques of the accommodation system, which differ depending on the refractive error. An elevated activity of the sympathetic nervous system under sustained stress conditions or interstitial fluid changes might be possible explanations for the post-task muscle thinning found in both groups, and this needs to be further assessed. The differences between emmetropes and myopes in ciliary muscle thickness, shape, and responses raise the question whether the muscle is involved in myopigenesis. The investigation of a cause-effect relationship requires a larger database in the form of a longitudinal study in children with various refractive errors.

In the following, we want to investigate whether the neuronal signals controlling the ciliary muscle activity are correlated with its morphology and the refractive error.

Moreover, we aim to investigate whether the auditory biofeedback training can be applied to improve the myopia control effect of multifocal soft contact lenses in children when they perform near vision activities.

  1. Sandra Wagner, Eberhart Zrenner, and Torsten Strasser. 2018. “Ciliary Muscle Thickness Profiles Derived from Optical Coherence Tomography Images.” Biomedical Optics Express 9 (10): 5100. doi:10.1364/BOE.9.005100.
  2. Sandra Wagner, Eberhart Zrenner, and Torsten Strasser. 2019. “Emmetropes and Myopes Differ Little in Their Accommodation Dynamics but Strongly in Their Ciliary Muscle Morphology.” Vision Research 163 (October). Elsevier: 42–51. doi:10.1016/j.visres.2019.08.002.
  3. Sandra Wagner, Frank Schaeffel, Eberhart Zrenner, and Torsten Straßer. 2019. “Prolonged Nearwork Affects the Ciliary Muscle Morphology.” Experimental Eye Research 186 (September): 107741. doi:10.1016/j.exer.2019.107741.
  4. Sandra Wagner, Frank Schaeffel, and David Troilo. 2020. “Changing Accommodation Behaviour during Multifocal Soft Contact Lens Wear Using Auditory Biofeedback Training.” Scientific Reports 10 (1): 5018. doi:10.1038/s41598-020-61904-4.