This study will examine the accommodative behavior in young adults wearing multifocal soft contact lenses. undergoing myopia control treatments. Subjects will undergo auditory biofeedback training while wearing the multifocal contact lenses to improve the accommodative. This pilot study is divided into three separate experiments and aims to assess:

1. the time course of the effect of biofeedback training in young adults wearing MFCLs -- the time course group
2. whether repeated biofeedback training increases the efficacy in young adults wearing MFCLs -- the repetition group
3. whether a longer training duration, given repeatedly, increases the efficacy in young adults wearing MFCLs -- the longer duration group

The results of this study will be used to design a larger clinical trial to investigate whether increasing accommodative responses through the multifocal contact lenses increases multifocal lenses' treatment effect on myopia management in children.

The public health systems worldwide might soon face an increase in highly myopic patients and with this a rising number of cases with severe eye diseases. By 2050, about five billion people are expected to be myopic and one billion might suffer from a myopia of more than -5 D. According to the World Health Organization, myopia is one of the top factors leading to avoidable blindness. For decades, researchers have been investigating the etiology of this refractive error as well as methods to prevent its progression in children myopic. Among the currently available treatments to slow myopia progression, optical interventions were shown to be a promising and feasible non-invasive approach. Hyperopic retinal defocus is known to induce ocular axial elongation and may be a factor in the progression of myopia. Positive defocus has been shown to reduce axial elongation and contact lenses with bi- or multifocal power profiles that add positive power to the central distance have been used to reduce myopia progression in children. Clinical trial outcomes show progression to be reduced, on average, by 38% on average, but with variable results. This variability may be related to the ways patients accommodate through the lenses. An earlier study found that children wearing multifocal lenses may under-accommodate at near, which could reduce the efficacy of the lenses.

Biofeedback training has been used to change accommodation. Earlier studies attempted to reduce accommodation based on the hypothesis that functional myopia results from a spasm of the ciliary muscle. In contrast, a recent study with young adult myopes successfully applied auditory biofeedback training to *increase* accommodation accuracy and reduce the accommodative lag in individuals by 0.3 D or more at different dioptric distances and while myopic subjects wore multifocal contact lenses. If accommodation was increased by means of auditory biofeedback training in myopic children wearing multifocal soft contact lenses, the treatment efficacy of the lenses might be improved.

The purpose of this pilot study is to investigate whether the frequency and duration of auditory biofeedback training affect their efficacy in increasing accommodative responses through the multifocal lenses.

• STUDY POPULATION

Thirty subjects will be randomized to one of the three study groups:

1. The time course group: The time course of the effect of biofeedback training (one episode) on accommodation in young adults wearing MFCLs will be measured weekly
2. The repetition group: The effect of repeated biofeedback training (one episode per week for 3 weeks) on accommodation through the MFCLs will be measured weekly
3. The longer duration group: The effect of repeated biofeedback training with longer duration (one episode per week for 3 weeks) on accommodation through the MFCLs will be measured weekly

INCLUSION CRITERIA

• Best corrected monocular Snellen visual acuity (VA) ≧ 20/25
• Age 18 to 30 years
• Refractive error spherical equivalent between -0.75 D and -10 D
• Astigmatism ≤ 0.75 D
• Age-appropriate amplitude of accommodation
• No suspected or confirmed eye disease (anamnesis)
• No accommodative or binocular function abnormalities
• Agreement to participate in the study (informed consent of subjects)

EXCLUSION CRITERIA

• Persons who are incapable of giving consent
• Refractive error spherical equivalent < -10 D and > -0.75 D
• Astigmatism > 0.75 D
• Abnormal binocular functions
• Medication affecting accommodative response or causing dry eye

Inclusion Criteria:

• Best corrected monocular Snellen visual acuity (VA) ≧ 20/25
• Age 18 to 30 years
• Refractive error spherical equivalent between -0.75 D and -10 D
• Astigmatism ≤ 0.75 D
• Age-appropriate amplitude of accommodation
• No suspected or confirmed eye disease (anamnesis)
• No accommodative or binocular function abnormalities
• Agreement to participate in the study (informed consent of subjects)

Exclusion Criteria:

• Persons who are incapable of giving consent
• Refractive error spherical equivalent < -10 D and > -0.75 D
• Astigmatism > 0.75 D
• Abnormal binocular functions
• Medication affecting accommodative response or causing dry eye