Navigating the Dark: Insights Into Night Myopia

Kritika Gautam, M. Optom

Optometrist, Dr. Shroff’s Charity Eye Hospital, Delhi, India

 

The inclination of the eye to become myopic under low light conditions is known as Night Myopia (Figure 1). Decreased visual acuity in low light conditions can be corrected by treating night myopia. This issue may even arise in individuals who have 20/20 vision. Astronomer Maskelyne used minus lenses to correct his vision after realising that he tended to become near-sighted when gazing at the stars at night in 1797^{. (1)}  Under low illumination, the myopic shift of the patient i.e., change in refractive status of the eye towards myopia can be as great as 6.00 dioptres (D). ⁽¹⁾

Figure 1: Image formation on retina in day and night-time
Picture courtesy: https://winkoptometry.ca/night-vision]

Although several explanations, particularly those pertaining to accommodation or chromatic shift in scotopic light conditions, have been proposed in the literature, no conclusive explanation for its aetiology has been offered. The pupil dilates and subjectively noticeable retinal blur occurs when ambient luminance decreases. As a result, the eye appears to have become near-sighted when it was always near-sighted, but the myopia symptoms had not been observed.

According to Salmon and van de Pol, one explanation for this phenomenon is that most eyes exhibit positive spherical aberration (SA), when their accommodation is relaxed. Like defocus, SA’s blurring effect increases with pupil size, suggesting that low light will be the ideal setting for observing its effects visually. ⁽²⁾

Another possibility is that night myopia is an outcome of increased accommodation to offset the increased blurring effects of SA as the pupil dilates. Ocular SA that is positive decreases during accommodation. ⁽²⁾

Some of the symptoms of night myopia include:

Seeing glare or halos around lights

1. Blurry vision significantly more at night
2. Difficulty focusing on low light conditions
3. Squeezing eye to reduce effect of spherical aberration. ⁽³⁾

Treatment:

Decreased visual acuity in darkness specifically needs to be corrected in certain occupations such as driving professionals, pilots, soldiers and tactile units, rescue workers and lifeguards. Myopic changes under darkness are more common in young adults that gradually decrease with presbyopia. Due to these refractive changes under low light conditions, young drivers experience visual disturbances during driving at night. ⁽⁴⁾ Correction of refractive error is specifically more important in night driving due to greater blur associated with driving at night with a large pupil. Specific night driving prescriptions will be beneficial for driving at night to decrease blur.

Under corrected refractive error as low as −0.50 D affects night-time driving abilities and the ability to see road signs. ⁽⁵⁾

Increased myopic correction worn at night can be beneficial in patients with night driving difficulty. ⁽⁵⁾

• Anti-Glare Coatings: By adding anti-glare coatings to glasses, lessen the glare from street lights and headlights, improving the vision at night.

Enhanced Ambient Lighting: Improving ambient lighting in places where visibility is essential can assist lessen eye strain and enhance night vision.

• According to research, specially designed PALs (with maximised intermediate and distance zones, which are mostly used areas during driving) or Single vision night driving glass with extra minus power up to -0.25D is just the right amount to make driving comfortable at night. ^(6,7)

Avoiding night driving until a suitable therapy is discovered, restricting driving or other visually taxing activities in low light might help control symptoms.

 

References:

1. Kohen, Y. (2007). Relationship between night myopia and night-time motor vehicle accidents. Acta Ophthalmologica.
2. Norberto, A., Smith, J., & Jones, R. (2012). Shedding light on night myopia. Journal of Vision.
3. All About Vision. (2022). What is night myopia? All About Vision.
4. Charman, W. N. (1996). Night myopia and driving. Ophthalmic & Physiological Optics, 16(1), 1-6
5. Gene-Sampedro et al., (2024). Validation of a method to assess night myopia in a clinical setting. Scientific reports, 14(1), 293.
6. Fejer, T. P. (1995). Correction of night myopia and glare for night driving. Canadian Journal of Ophthalmology, 30(2), 91-95.
7. Pierce, L. (2024). How to treat night myopia with driving lens. IOT.