Do you find that your vision at night is worse than during the day? When driving at night do you see star bursts or haloes around on-coming headlights? If so, you are not alone. This is a very common night time visual disturbance that can occur.
In order to understand why this phenomenon happens, we need to know how light affects vision. The iris is the coloured part of the eye and the pupil exists in the center of the iris.
In order to see, light passes through the pupil and eventually focuses on the retina. This information is then transmitted to the brain. Neural impulses from the brain control the muscles within the iris and ultimately the size of the pupil. In bright light situations, the pupil shrinks or constricts allowing only narrow rays of light to enter the eyeball. These rays of light are more likely to produce a sharp focus on the retina with low amounts of spherical aberrations. Conversely, in dimly lit conditions, the pupil enlarges or dilates. Wide rays of light enter the eyeball creating a blur pattern on the retina. Higher amounts of spherical aberrations are produced making it more difficult to see clearly. To simulate this concept at home, you can pop a tiny hole in a piece of paper with a ball point pen and then look at a distant object. You will see it more clearly through the hole in the paper as only the narrow rays of light are entering the eyeball.
For those who suffer from night time visual disturbances, there is hope to improve it. An essential starting point is to have a complete eye examination performed. Your optometrist may detect a small change in your eyeglass prescription which can greatly improve vision at night and reduce haloes. A small prescription change may not be noticeable during the day as your pupil is smaller or constricted. But at night when the pupil is dilated, that small prescription change increases blurriness as there are more spherical aberrations created by the dilated pupil.
For people who already wear glasses, an anti-glare coating on the front and back surface of the spectacle lenses can help reduce the amount of haloes and star bursts produced from on-coming headlights.
When large portions of the iris have been damaged by trauma to the eye, people will experience light sensitivity during the day and increase glare at night. To solve this problem, contact lenses with a coloured iris painted on the surface of the lens can be fitted.
In the past there were many reports of patients experiencing diminished night vision after having corrective laser eye surgery. These night vision complaints have dramatically decreased over the years due to improved technology of the lasers used. Most patients will experience haloes and glare at night immediately following laser eye surgery. However, the vast majority of people will notice remarkable reductions in glare by three months post-operatively. If some degree of night vision difficulties persists after three months either a surgical enhancement can be performed or a pair of glasses with a light prescription can be worn at night.
After understanding the ways in which light affects vision there are ways to manage the annoyance of night time vision disturbances. It is important to discuss your concerns with your optometrist to determine what course of action can be taken to show improvement.