What is nyctalopia or night blindness

Our eyes have a phenomenal ability to adjust themselves according to the intensity of light in the environment. But due to different medical conditions, the eyes become unable to adapt to darkness or low lit areas thus results in severe loss of night vision in the affected person. This inability to see in the dark is called as Night blindness.

Night blindness, also termed as nyctalopia, is a visual impairment caused by the improper functioning of light receptors in the eye. Night blindness is not a disease; rather it’s a symptom to various underlying health conditions.  Despite of its name, night blindness does not mean complete blindness. It is the reduced ability of a person to visualize objects in the dark or at night. People with night blindness can face difficulty in switching vision from brightness to darkness such as entering any dark room or can find it hard to drive at night.

HOW VISION IS CREATED?

To understand the phenomenon more closely, let’s have a look over the functioning of eye.

Eyes are the visual windows of our body. Light enters the eye through cornea and lens and falls on the retina, the inner layer of the eye. Retina consists of photo-receptors that receive light rays and convert them into nerve impulse which is used to create an image. The two types of photo-receptors are rods and cones. Rods allow us to see in dim light because they don’t provide color vision. Cones are stimulated by bright light and allow colored vision. A person who loses rod vision mainly has difficulty seeing in dim light, which is the case with night blindness.

CAUSES OF NIGH BLINDNESS

Night blindness can be caused by a number of diseases or conditions. Some of them are listed below.

PRIMARY CAUSES:

1.      VITAMIN A DEFICIENCY:

Vitamin A, also known as retinol, is essential for proper retinal functioning. The rod receptors of retina contain pigment called rhodopsin which consists of retinol. It is responsible for detecting low intensity light rays. If vitamin A deficiency occurs in the body due to malnutrition or metabolic dysfunctioning, rhodopsin is not produced and the eye function is impaired. Vitamin A deficiency is a common cause of night blindness in children usually in developing areas.

2.      MYOPIA: (nearsightedness)

People who cannot see distant objects clearly, can also suffer from night blindness. It usually occurs at an early age.

3.      CATARACT:

Over the age, the proteins in the eye lens get degraded and start accumulating causing cloudiness in lens. This is called cataract. It results in an inadequate entry of light in the eye and produces poorly focused or blur images. Cataract can either occur genetically, due to diabetes or some injury to the eye.

4.      GLAUCOMA:

Sometimes the drainage tubes of the eye stop working properly which results in additional pressure buildup in aqueous humor (liquid in the ocular cavity). This pressure causes damage to the optical nerves which results in peripheral vision loss initially; but if remain untreated, can cause permanent blindness.

5.      RETINAL DETACHMENT:

It is a condition in which thin retinal lining at the back of eye starts to detach itself from the layers underneath. This may result in total or partial vision loss in affected person. Night blindness occurs as a first few symptoms for retinal detachment.

SECONDARY CAUSES:

1.      RETINITIS PIGMENTOSA:

It is an inherited disease in which gradual retinal degeneration occurs. The photoreceptors, usually rods are prone to damage at very initial stage. This damage to the photo pigments starts with signs like blur vision, poor color discrimination which ultimately leads to blindness.

2.      DIABETES:

High blood sugar levels cause damage to optical nerves and blood vessels leading to a condition called diabetic retinopathy. The symptoms include floaters in visual field, blurred vision, night blindness, and permanent vision loss.  Diabetes may also lead to cataract formation and glaucoma.

3.       CONGENITAL NIGHT BLINDNESS:

It is a genetic retinal disorder that occurs due to mutations on X chromosomes or sometimes on autosomal chromosomes. The disease is termed as congenital and non progressive which means the person is affected by birth and the deterioration of rod receptors does not worsen over the time but remain stationary.

4.        OTHER COMPLICATIONS:

Other conditions that can cause night blindness include improper liver or pancreatic functioning, post laser surgery complications, malnutrition, excessive sun exposure, aging, macular degeneration, xerophthalmia (dryness of conjunctiva), zinc deficiency etc.

PRECAUTIONARY MEASURES FOR NIGHT BLINDNESS

People with night blindness usually have sound vision at daytime but face difficulty at night or in any darker areas. So they should avoid travelling or driving at night and also take extra care when switching from brighter areas to dim light areas such as movie theaters. Supplements of vitamin A can also help increase the vision.

DIAGNOSIS AND TREATMENTS

Night blindness is not a disease itself but a symptom for any underlying disease or medical condition. To treat night blindness, the diagnosis of the causative disease is a prerequisite. Sometimes this symptom is over seen which leads to progression of the disease and unrecoverable vision damage to the person.

To avoid this, regular eye tests should be taken for people having diabetes or liver dysfunctioning. People who suffer from continuous headaches and find it difficult to focus should not delay to visit their ophthalmologists. Once the cause is identified, it is easier to recommend the treatment which either could be just medications, change of glasses or surgeries (in case of cataracts).