Night myopia is reduced in binocular vision.

Area of Science:

• Ophthalmology
• Physiological Optics
• Vision Science

Background:

• Night myopia, a change in eye refraction with decreasing light, is a known phenomenon but its underlying mechanisms remain incompletely understood.
• Existing research highlights the influence of light levels on visual perception, yet a comprehensive quantification of night myopia under varying conditions is lacking.

Purpose of the Study:

• To precisely quantify night myopia using a novel infrared open-view binocular Hartmann-Shack wavefront sensor.
• To investigate the accommodative response, aberrations, pupil diameter, and convergence in both monocular and binocular viewing conditions across a range of light levels.

Main Methods:

• Simultaneous measurement of ocular parameters including accommodation, aberrations, pupil size, and vergence.
• Utilized an infrared open-view binocular Hartmann-Shack wavefront sensor for precise measurements.
• Tested subjects under controlled light conditions, from photopic to scotopic levels and complete darkness.

Main Results:

• In monocular vision, reduced luminance induced a myopic shift in accommodation, aligning with the eye's dark focus or tonic accommodation.
• A corresponding change in convergence was observed, following the induced accommodative error.
• The majority of subjects exhibited a reduced myopic shift when viewing binocularly, suggesting a mitigating effect of binocular vision.

Conclusions:

• The findings support the hypothesis that night myopia originates from accommodative state changes in response to decreasing luminance, moving towards the eye's resting state.
• Binocular vision plays a crucial role in restraining night myopia, potentially through fusional convergence acting as an additional accommodative cue.
• Binocularity effectively reduces the impact of night myopia on visual acuity in low-light conditions.