Night myopia - Nocturnal myopia

At the moment the cause of night myopia (nocturnal myopia) is not entirely known. It is caused to some degree by spherical aberration (due to wide pupil in the dark environment), chromatic aberration (due to large share of short-wave blue green part of the spectrum at dusk) and mental causes - excessive accommodation to compensate for blurry vision.

The main cause of nocturnal myopia inheres probably in accommodation and in accommodated rest position. It was proofed that in rest position accommodation is not set on the point at the distance but on the position between near and far. In average it is the distance from 1 to 2 meters. Rest accommodation dawns when the visual field is without any stimulus, thus during nighttime or in empty space.

In other words, the substance of night myopia is that during nighttime the human eye reacts to the lack of light by dilating its pupil and by slightly moving the focal point before the point of the sharpest vision. Thus the so-called “quarter” myopia is formed. This holds true also for a person who does not suffer from any refractive disorder.

Nocturnal myopia not only decreases abilities of people working in some occupations (night watcher, forester, sailor, and driver) but it also plays part as far as the security of traffic is concerned. Low hypermetropic (farsighted) drivers see better at dusk without eyeglasses and on the contrary low myopic (shortsighted) drivers can drive without eyeglasses during daytime but has to use them when driving at dusk when visibility is lowered.

Dazzling caused by a car coming from the opposite direction increases the effect of nocturnal myopia. The reaction of pupils increases accommodation depending on the age and forced urge to fix the lights emitted by the car increases convergence.

Specially designed eyeglasses Night Vision from Tag Heuer company which compensate diopter diminution can serve as a solution. They have special color which helps to increase contrasts and also have double-sided anti-reflex layer on the surface of the lenses which markedly decreases unpleasant feeling of being dazzled by vehicles coming from the opposite direction.