Eye Care Eye Care Basics

Blindsided by Night Blindness

Walking into a dark movie theater, it may take a little while for your eyes to adjust to the dim lighting before finding your seat. But for someone who has night blindness, this process can take much longer. Night blindness causes problems seeing in any dark or dim lighting. These symptoms can lead to problems getting around at night-or even a fear of the dark.

Night blindness can be caused by a variety of problems, and some are easily treated. Donald Schwartz, MD, associate clinical professor of ophthalmology at the University of California, Irvine and the University of Southern California's Doheny Eye Institute explains what a doctor can do to help restore your night sight.

What is night blindness?
Night blindness can be a number of things. One of the things that is called night blindness is a decreased ability to see at night. Some people become more nearsighted at night as the pupil dilates in dark conditions, a condition called spherical aberration. People with this condition become more nearsighted in the dark. In this case, signs off in the distance, such as freeway signs, may not be as clear at night.

Another situation is where people have problems adapting to light changes. For example, when they go to the movies, they find that it takes a very long time for their vision to come back in the dark room. This may simply be caused by a deficiency in vitamin A, or it can reflect an underlying medical condition.

Lastly, there is a completely different kind of night blindness, which is quite significant, involving the loss of receptors. These cells in the back of the eye and the retina, called the rods, allow peripheral vision and vision in dim light. The loss of these rods can indicate a problem such as retinitis pigmentosa, which leads to progressive vision loss.

How does a doctor determine the cause of night blindness?
When a patient says that he or she is night-blind, it is important to find out specifically the conditions they're addressing: if a distant object is blurrier at night, if they are unable to be mobile at night or in dark conditions or if they're unable to see off to the side and their peripheral vision is compromised. Those types of things need to be determined to get proper treatment.

How is night blindness treated?
If a doctor thinks that night blindness might be caused by simply being more nearsighted at night, the first thing they will do is check visual acuity to see what the vision is in the normal office setting. Then they should check refractive error, to see how far out of focus the patient's eye might be. If the night blindness is found to be caused by nearsightedness, the patient may need to wear glasses at night, and this sometimes means that a different type of lens is needed at night as opposed to during the day.

If nearsightedness is determined not to be the cause, and there is concern about the possibility of night blindness caused by a loss of some of the function of the rods, then a visual field examination is performed. This examination determines the extent of the person's peripheral, or side, vision, which is the vision that uses low-level light. Tests would need to be done to determine whether the receptor cells in the retina are not functioning well or if the problem is in the ganglion cells, other important cells needed for vision. These can be evaluated, but many times there's nothing that can be done if those cells are damaged.

If a doctor determines that there is simply a need for vitamin A to help the night blindness, then that would be recommended. For those patients who have retinitis pigmentosa, vitamin A is being used to help, but there's no cure at this time.

When should someone with night blindness see a doctor?
Someone doesn't need to see a doctor in the space of days if he is having trouble seeing at night, but certainly he should speak to a doctor within a couple of weeks or a month, after determining how different circumstances impact vision. It is helpful to be able to tell the evaluating doctor what the problem is like: if it's looking at signs, if it's difficulty when the lights are very dim or off in the house at night, if it's going from the bed to the bathroom or walking down the hall. Those kinds of difficult situations would be very helpful to the physician to determine what the problem might be. Additionally, retinitis pigmentosa is usually inherited, so people that have relatives with this disease should be sure to tell their doctor, as their chances of getting the disease are particularly high.