Emmanuel Ojo
An optometrist at the University of Benin, Edo State, Prof Gladys George, discusses the causes and management of night blindness with EMMANUEL OJO
How will you define night blindness?
Well, for us in this profession, that is, as optometrists, our definition of night blindness is that it is a condition that is associated with the inability to quickly adapt from a well-illuminated environment to a poorly illuminated environment. What do I mean by that? It simply means that the person has a poor vision at night or in dim illumination, so, anytime the person leaves an environment that is well-illuminated and gets into a poorly illuminated environment, the person finds it difficult to appreciate things that are around him or her. So, it’s a condition of reduced vision in low light illumination or reduced vision in low light conditions. When the environment is dim or the illumination is low, the person has low vision in the environment. Another name for night blindness is what we call nyctalopia.
What causes this condition?
The causes of night blindness usually have to do with retina diseases. There is a portion of the eye we call the retina. It’s like a curtain at the back of the eye and it’s a light-sensitive tissue. It contains what is called a photoreceptor cell and the photoreceptor cells are both rods and cones, and usually, the rod cells are responsible for night vision, while the cone cells are responsible for daylight vision. So, anytime these rod cells are diseased, there will be poor or reduced vision at night or in dim illumination. Also, the diseases that affect the retina, particularly the peripheral retina, where we have a high concentration of these rod cells could lead to night blindness. So, the possible causes of night blindness include the condition we call retina pigmentosa, which affects the retina; diabetic retinopathy, a disease that affects the retina; and macular degeneration.
Can glaucoma cause night blindness?
Glaucoma, of course, can also affect or cause night blindness, though, glaucoma affects both day and night vision, likewise cataracts. But in young people, when we see night blindness, the first thing we want to check is their level of vitamin A, because vitamin A deficiency is a major cause of night blindness in young people and young children, especially when they are malnourished. So, we need to keep them by giving them high doses of vitamin A because vitamin A is a precursor for rhodopsin, which is a photopigment that is responsible for the blood cells. So, if vitamin A is deficient, there will be a reduced amount of rhodopsin and rhodopsin is the major photopigment cell that is responsible for vision at night. So, if that is deficient, it could cause night blindness. Other possible causes of night blindness are high myopia, cataracts, retinitis pigmentosa, or any form of retinopathy; such diseases often cannot be reversed with vitamin A treatment. That is why more often, sadly to say, we say night blindness has no cure or is not treatable when the cause is a result of vitamin A deficiency.
What are the common symptoms?
If someone is suffering from night blindness, often the patient will most likely complain of photophobia, especially if the cause in the elderly is a result of cataract formation. They complain of photophobia and they also complain of difficulty being able to navigate at night in a dim or poorly illuminated environment. They find it difficult to navigate at night.
What are the early signs before it becomes a full-blown case?
Most often, the patient discovers that if he or she comes from a bright environment into a dim environment, it takes quite a long while before he or she adapts because there is something that is called dark adaption and the photo recovery time, which is not supposed to be more than five minutes, but for those who are already developing night blindness, they find it difficult. Their photo recovery time is longer. So, they find it difficult to adapt quickly to a dim environment and for a patient who is already experiencing that, it’s an indication that they are beginning to experience night blindness.
The pupil has a way of controlling light rays that enters the eyes. There is a portion of the eye we call the pupil, which is like a window of the eye and it’s expected that when one is in a dark room, the pupil dilates (it opens up wide) and when one is in a bright environment, the pupil constricts. When one is in a dark environment whereby the pupil has dilated fully and then all of a sudden, light is shone because the pupil is fully dilated, too many light rays have got into the eyes, so, for that moment, the person is photophobic, that is, it is hypersensitive to brightness. So, the person will naturally just close the eyes because of the excessive rays entering the pupil that is dilated, but it is also expected that when the light comes in, the pupil constricts, and then because the pupil constricts, it will reduce the number of rays getting into the eyes.
Is this condition associated with age?
This condition can be associated with age, especially in certain disease conditions that come with age, for instance, cataracts, glaucoma and age-related macular degeneration. These conditions that I have mentioned are usually associated with age. When a patient suffers from cataracts, they will have difficulty navigating because it reduces vision both day and night and it is even worse at night. A patient suffering from glaucoma has both day and night vision reduced and it is worse at night.
Glaucoma affects the retina because in glaucoma, the peripheral retina is the first to go and that is where you have a high concentration of these rods, the rod cells that are responsible for night vision. So, a patient suffering from glaucoma, cataracts, age-related diseases and macular degeneration often will have trouble adjusting to that environment and when you see such patients, you will see them squinting, mostly at night. When they are in a dark place, their vision is blurry, so they tend to squint to reduce the blur they are experiencing and to improve their distant vision. For most patients, who have night blindness, one symptom they usually experience is that apart from having difficulty adapting to a dark environment, they also have difficulty seeing things afar, especially when they are in a dark environment.
Who is most prone to this?
Well, myopias, patients who are progressive myopes, that is, patients who are naturally short-sighted, are at risk of developing night blindness and you see them at the early stage of their symptoms complaining of headache, eye pain, blurry vision, hypersensitivity to brightness and difficulty seeing at a distance. Patients who are short-sighted have difficulty seeing things afar clearly, so, apart from this problem of seeing things at a distance, they will have associated symptoms like complaining of eye pain and headache all the time, because they are always straining to be able to see. The muscles controlling the accommodation are under stress, so they will experience eye pain, headache, and blurry vision, and most often, they tend to be hypersensitive to brightness, what we call photophobia. Myopes, generally, are at risk, even though they are young people. Also, albinos are at risk because there is what we call oculocutaneous albinism, that is, the albinism that not only affects the skin but also the eyes. The last set of people at risk is those with one form of retina disease or the other.
Is night blindness hereditary?
Yes. Night blindness is hereditary, though it’s usually carried by genetic traits, especially retinitis pigmentosa, because as I said, night blindness is a disease of the retina. Any diseased condition that is capable of affecting the retina, like retinitis pigmentosa, is a hereditary disease, which can be carried by the male chromosome and could be transmitted from the chromosome of the male to the female child. So, we can see it in female children whose parent or whose father is a patient of retinitis pigmentosa, which becomes dominant in the child.
Are there environmental and other factors that increase the risk?
Looking at environmental factors, we have to look at the diseases that can cause night blindness. For instance, dietary factors like poor feeding, unbalanced diets, and patients who do not have sufficient vitamin A can develop night blindness. Also, myopia is hereditary and because it is hereditary, patients who suffer from it run the risk of developing night blindness; and poor dieting, as children grow up, they are expected to be fed well, otherwise, they can fall victim to night blindness. But in the elderly, we know that diseases such as cataracts can cause night blindness and as such, if there is anything that can be done to prevent cataracts, it can, of course, prevent night blindness. For instance, exposure of the eyes to excessive ultraviolet rays (sun rays) can cause cataracts. So, if we try to prevent that early, we can prevent night blindness. Glaucoma is a hereditary disease and it is associated with diets if glaucoma can be prevented, night blindness can also be prevented.
What are the complications of this condition?
Most patients may have problems navigating, so they may have accidents. A patient suffering from night blindness should not be allowed to drive, because that patient is at risk and can also jeopardise the lives of other road users. So, we have to ensure that such patients are not allowed to handle the steering, especially at night. They are also not able to navigate, especially when walking at night. They are prone to accidents. It’s not as though they are completely blind, but they are referred to as partially blind or low-vision patients, so their central vision is still at risk. They may suffer from what is called scotomas or blind areas but their central vision is still preserved, so they can recognise colours. However, they will not be able to recognise black and white, because the rods are responsible for the recognition of black and white apart from being responsible for night vision.
Does their inability to recognise black and white also applies during the day?
During the day, the rods are not functioning, they are for night vision. It is the cones that one makes use of during the day. Cones are for daylight vision and they are for colours but at night, it is the rods that are functioning because rods are meant for night vision.
How can the condition be prevented?
Night blindness cannot be totally prevented, the reason being that if a patient has progressive myopia, for instance, that patient is already at risk. So, in a patient that has high myopia, since it’s not a result of something acquired, it cannot be prevented. The only way one can prevent night blindness is if it was caused by a deficiency in vitamin A. In that wise, the patient can be given high doses of vitamin A, carrots, or any other food that contains a high dose of vitamin A. In that case, it can be said that with such a balanced diet, we can try to prevent night blindness, that is, the one caused by vitamin A deficiency. But other retina diseases, which can lead to night blindness, are not preventable, so to say. Though in recent times, we know that cataracts, age-related macular degeneration and glaucoma tend to place patients on high antioxidants, especially, for the elderly. As one grows old or crosses 40, we advise them to go on high antioxidants, which are dietary supplements to prevent cataract formation and prevent the formation of age-related macular degeneration. So, patients are advised to start using high antioxidants, especially patients that are above 40.
How is it diagnosed in a clinic?
The diagnosis in the clinic is simple because most often, from the history, when patients come into the clinic to complain of poor vision at night or reduced vision at night, we know already from their case history that they are likely to have night blindness.
Can it lead to total blindness?
It can lead to low vision but not total blindness.
Is surgery an option for the treatment of night blindness?
Well, surgery is not an option for the treatment of night blindness because the major cause of night blindness is when there is a loss of rod cells and the rod cells responsible for night vision cannot be replaced. It’s not something that can be replaced, it’s not like cataract surgery where you remove the pacified lens and then you put in an ocular lens. In the case of retina disease such as lack of sunshine of these rod cells, once they are damaged, they are damaged. Like retinitis pigmentosa, once the rod cells are damaged, there is no way the rod cell can regenerate; so, we cannot say that surgery is an option.
Can recommended glasses be used to manage or improve the situation?
Night blindness is a disease. Glasses are meant to correct defects when there are refractive errors, in case of refractive errors like short-sightedness, or long-sightedness. Short-sightedness is not a disease; it’s just that the shape and size of the eyeballs are just too large or too small because short-sightedness means that the eyeballs are usually larger than they ought to be. So, when the rays of the light are coming in, they don’t get to the retina before they form focus, so when such a patient wears glasses, it pushes the rays to where they ought to be for the patient to be able to see and in contrary, short-sightedness is a situation where the eyeball is usually smaller than what it ought to be, so the rays might tend to go beyond the retina when the rays of light get into the retina.
So, when the glasses are put in the patient’s eye, they push the rays to fall on the retina and then the patient sees well. In the case of night blindness, it’s a disease condition, so even if you put a concave or convex lens before the patient’s eye, it doesn’t make any difference because it’s a disease condition that has damaged the rod cells. The rod cells are dysfunctional as a result of disease and there is nothing that can be done to regenerate those cells. So, it’s not something that glasses or surgery can fix.
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