Night Blindness

It is very well known that some people are not able to see properly in the dark. But, some individuals have a considerable amount of difficulty while seeing in poor light or at night. This condition is known as night blindness. The medical term for the condition is nyctalopia. Night blindness does not imply that the individual is unable to see at night, it just means that the concerned person’s vision is poorer than other people without night blindness. This condition is not considered to be a disease by itself, but most often it is a sign of some other vision related problem. This condition is also known as nocturnal amblyopia, nyctanopia or day sight.

Night Blindness which might also be known as impaired dark adaptation makes affected people have difficulty in seeing when it is dark but the person is able to see perfectly when it is not dark. There is just difficulty in seeing and difficulty in driving when it is dark. This condition, if not accompanied by any other eye problem is not true blindness. Even in the night or when it is dark, the eye is not blind. The reason is not blindness but the inability of photoreceptor cells which are required for seeing in the dark to function properly.

The ability of the eyes to shift from objects in light to dark and view them quickly is an important aspect of an individual’s visual health. The ability to see things in dim light or at night is very important. When the eye is not able to do so, the condition is known as night blindness. This might occur due to different conditions that lead to the degeneration of the sensory cells in the retina also known as rods. It can also be due to a deficiency in the rhodopsin or visual purple which refers to the pigment of the rods in the retina. This deficiency can be inherited. This abnormality in the sensory cells of the retina might also arise due to Vitamin A deficiency. The pigment of the rods maintains the photosensitivity only in case Vitamin A is present in adequate amounts. Some sources of Vitamin A include yellow and green leafy vegetables, milk, animal liver etc. due to the presence of carotenes which are chemically related substances which are converted into vitamin A once in the body.

This condition might be existing in a person from birth, or might be caused by injury or be due to malnutrition. Retinitis pigmentosa is one of the most common causes of night blindness. In this disorder, the rod cells present in the retina lose the ability to respond to light. People who suffer from this condition have night blindness which is progressive in nature, and eventually the affected person might impair his or her daytime vision also. In case of X-linked congenital stationary night blindness, the rod cells are impaired from birth. The cells might not function at all or might function a little, but this condition does not worsen with time. Another major factor that leads to night blindness is the deficiency of vitamin A or retinol, commonly found in liver, dairy products and fish oil.

The outer area of the retina comprises of more number of rods as compared to cones, therefore loss of peripheral vision might lead to night blindness in many cases. People affected with this condition not only have difficulty seeing, but also find it difficult to adjust from bright light to dimly lit areas. The contrast vision of the person is also highly reduced. The opposite problem of night blindness, the inability of the eyes to function properly in bright light is known as hemeralopia and is very rare.

Some forms of night blindness are treatable and some types are not. Determining the correct cause associated with this problem can help in proper treatment of the condition.

Symptoms of Night Blindness

The only symptom associated with night blindness is the difficulty to see in the dark. The individual is likely to experience this problem while transitioning from an area of bright light to a dimly lit environment. The person is also likely to suffer from poor vision while driving because of the intermittent brightness and the change in lights from headlights to street lights.

Causes of Night Blindness

Retinitis pigmentosa: This is a genetic condition that leads to vision loss in the affected person. The symptoms of this condition include difficulty seeing at night and loss of peripheral vision. The symptoms come on gradually and are not sudden. The probability of the person going completely blind is extremely uncommon. This disorder is inherited from the family. There is no known cure for retinitis pigmentosa. Vitamin A supplements might be useful. The problem can be managed by using low vision aids, guide dogs or portable lighting.

Retinal Detachment:

In this disorder, the retina detaches from the layer underneath it. The common symptoms of this condition include sudden increase in number of floaters, flashes of light, loss of central vision etc. This happens because of a break in the retina which leads to the fluids in the eyes to take space behind the retina. Males are more at risk than females for this disorder. The outcomes for the condition depend on the duration of the retinal detachment and if the macula was detached or not. Outcomes are positive if the condition is treated before the detachment of the macula.

Oguchi disease:

Also known as congenital stationary night blindness, this involves discoloration of the fundus and slow adaptation to darkness. This condition occurs most frequently in people of Japanese ethnicity.

Cataract:

This condition leads to clouding of the eye lens which leads to decrease in vision. This condition might affect one or both eyes. The symptoms of cataract include blurry vision, trouble seeing at night, faded colours, trouble with bright light and halos around light. This often leads to the individual experiencing trouble while driving, reading and while recognizing faces. This might be caused due to aging and can also develop because of trauma or radiation exposure to the eyes. Risk factors for developing cataract include smoking, alcohol, excessive exposure to light and diabetes. Prevention can be done by wearing glasses and not smoking. If it does not lead to any improvement, performing surgery to remove the lens that has turned cloudy is the only other effective treatment option.

Choroidermia:

This is a very rare form of retinal degeneration that affects around 1 in 50000 males. This leads to a gradual vision loss, which starts from night blindness during childhood which is followed by peripheral vision loss and goes on to the loss of central vision later on in life. The progression of vision loss continues throughout the affected person’s life, but the extent of vision loss and the rate of decline differs from individual to individual. This results because of the lack of a protein in the retina cells which results in the gradual decline of vision. There is no known treatment of this condition as of now.

Some other major causes of this condition include pathological myopia which is near sightedness or short sightedness in which the light is focussed in front of the retina rather than on the retina, some medications like phenothiazines, Glaucoma, Vitamin A deficiency, Macular degeneration or Sorsby’s Fundus Dystrophy, Refractive surgeries like LASIK, photorefractive keratectomy and radial keratotomy etc.

Diagnosis of Night Blindness

Night blindness is not just a disease but also a symptom caused by several other eye diseases. The doctors will check the history of loss of vision in the patient’s family. The doctors or the ophthalmologist will also check for other symptoms of retinitis pigmentosa. Retinitis Pigmentosa is a disorder of the eye that results in the loss of vision. Retinitis pigmentosa affects how the retina of the eyes will react to light. The symptoms include decrease in peripheral vision which leads to tunnel vision and trouble seeing at low light or during night time. The doctors will also check for symptoms for congenital stationary night blindness such as reduced acuity or reduced sharpness of images in the eye, severe myopia or near sightedness, involuntary movement of the eyes and strabismus or eyes being unable to look in the same direction together. Congenital stationary night blindness is caused by genetics and occur at birth. It remains stationary over the time. The ophthalmologists or the doctors will conduct a test called electroretinogram which measure the function of the retina. The doctors will also check for cataracts in the patient’s eyes. The doctor will also conduct tests to check for any deficiency of Vitamin A in the patient and also for presence of any benign tumours. The doctors will also check for other causes such as retinal detachment, glaucoma, chloroideremia and pathological myopia. The doctors will also ask the patient questions about past surgeries and medications as both surgeries and certain medications can also result in night blindness. The patient will also be asked to provide the doctor with blood samples for blood tests to measure glucose levels and vitamin A levels.

Night Blindness Treatment

-  Night blindness caused due to the deficiency of vitamin A, cataracts and near sightedness or myopia can be treated.

- Near sightedness: The most common treatment is done by correcting the vision disparity using corrective contact lenses or eye glasses. This helps the patient improve vision at night and day. The corrective lenses help the patient see clearly in low light settings. Laser eye surgery or refractive surgery can also be done to permanently correct the near sightedness of the patient. The laser eye surgery procedure reshapes the patient’s cornea to focus the light onto their retina.

- Cataracts: Cataracts are the clouded portions in the lenses of the eyes. If the patient has cataracts, they don’t necessarily require surgery to remove them. Some patients who have cataract can see normally with the use of just prescription level glasses or by relying on bright lighting. But cataracts can grow and cause more severe symptoms such as blurred, yellow or dim vision. Cataracts can also cause double vision if they see through the cataracts in the eyes, which means that the patient will see more than one of the same objects at a time. Cataract makes it hard for the patient to drive or work on a computer. The doctor will perform a surgery on your eye to remove the cataracts. The doctors will numb the patient’s eye and then use a laser to make a small cut on the front of the eye. Through the cut the doctor will insert the small tools used to break the cataract and suction it out gently. The doctors then replace the lens with an artificial one made of acrylic or silicone and close off the cut. The surgery usually takes an hour to be complete. If the patient has cataracts in both their eyes, they will have to get two surgeries a few weeks apart. The doctors will prescribe the patient an eye drop to help them see clearly.

- Vitamin A deficiency: The doctors will prescribe the patient with vitamin A supplements if they suffer with vitamin A deficiency.  Most people living in developed nations don’t usually have a Vitamin A deficiency because of the availability of proper nutrients. The doctors will prescribe the vitamins according to the patient and the symptoms they have. Vitamin A deficiency occurs when diets of the patient don’t have sufficient vitamin A. Vitamin A is important for growth and development of children, managing stress caused by any illness or other physiological functions. One of these physiological functions in maintaining proper eyesight of the individual. The doctors will also suggest consuming food rich in vitamin A along with the supplements prescribed.

-  Genetic defect: Night blindness is also caused due to genetic defects or disorders. Disorders such retinitis pigmentosa are not treatable. Many other eye diseases that may cause night blindness do have treatments and specific surgeries available to correct any vision problems.

Last updated on : 19-09-2018

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