The term night blindness sounds alarming, as though some people are actually blind at night. There is a small percentage of the population that does in fact experience true night blindness, but it is rare and often the result of late stage eye disease. In optometry, it is not common to use the term night blindness although we do encounter a significant number of patients who complain of poor night vision. The symptoms are usually blur and dimming of vision at night, glare and haloes around lights and poor adaptation from light to dark environments. How do you know if what you are experiencing is normal or a result of something more serious?
There are a handful of eye conditions that can create symptoms of poor night vision.
- Patients who have had surgery to the corneas such as LASIK or corneal transplants may notice glare and haloes around light. They may also experience diminished contrast sensitivity which can cause images in the evening to appear more dim. Unfortunately, surgical results usually cannot be reversed.
- Cataracts are the number one cause of decreased night vision. Patients over the age of 40 will begin developing mild cataracts. This is when the natural lens inside the eye becomes more yellow and opaque as a result of age and ultraviolet exposure. Cataracts can cause haloes and dimming of vision in the dark and decreased contrast sensitivity. Fortunately, cataracts are easily removed thereby restoring problems with night vision.
- Corneal diseases such as keratoconus and severe dry eyes may also affect one’s vision in the evenings causing double vision or haloes. For some of these patients, specialty contact lenses or eyedrops will alleviate these symptoms.
- Newer technology has also allowed optometrists to detect higher order aberrations in some patients. For these patients, standard spectacle lenses may not improve night vision problems. An instrument to detect higher order aberrations will determine whether a patient requires a specialty custom-made spectacle lens to improve night vision.
Some patients do in fact have true night blindness caused by an eye disease in its late stage. Usually, symptoms begin slowly over time and progress to an inability to see in the dark. These patients usually suffer from one of two eye conditions.
- Retinitis pigmentosa is an inherited eye disease of the retina, the tissue that lines the back wall of the eye and captures visual images. Retinitis pigmentosa affects the rods of the retina and causes slow deterioration of these structures. The rods (unlike the cones) are responsible for night vision and for peripheral vision. As the disease progresses, patients will notice a decrease in their ability to see in the dark and in the periphery. Unfortunately, there is no current cure for retinitis pigmentosa.
- Glaucoma is an eye disease where the optic nerve slowly degenerates. Patients with glaucoma usually have no symptoms in the early stages of the disease. As the disease progresses, nerve fibers in the retina begin to deteriorate resulting in a decrease in peripheral vision as well as night vision. Usually, patients do not experience symptoms of poor night vision and poor peripheral vision until the late stages of the disease.
Now that you know the causes, what are some ways to alleviate or improve poor night vision? The simplest solution is to wear an updated pair of prescription glasses (if you have a prescription) with higher index lenses and an anti-glare coat. Your optometrist can also inform you if you require customized lenses to correct for higher-order aberrations. If your night vision problems are not a result of surgery or any eye diseases that you are aware of, then it is important that you visit your optometrist for a comprehensive eye examination.
– Cindy P. Wang, O.D., F.A.A.O.
California Optometric Association