JOIN USVitamin A deficiency is the most significant factor causing night blindness among lakhs of people, writes Dr Balakrishna Shetty.
Night blindness or nyctalopia is a condition in which a person experiences poor vision only during night. Nyctalopia also causes difficulty in visual adjustment to dark or low-lit surroundings after being exposed to a brightly-lit space, making motor driving risky during night. Vitamin A deficiency is the most significant factor which causes night blindness among lakhs of people every year.
Vitamin A is required for the synthesis of rhodopsin or visual purple, a light-absorbing pigment present in the rod cells of the retina of the eyes and essentially required for vision in dim light. Vitamin A deficiency impairs the synthesis of rhodopsin, making it difficult to perceive things in faint light. Night blindness is an early symptom of Vitamin A deficiency followed later by xerophthalmia (dry eyes unable to produce tears) and keratomalacia (thinning and ulceration of cornea). If diagnosed and treated in the beginning, the condition can be successfully reversed. However, if treatment is delayed and severe Vitamin A deficiency persists, there is a heightened risk of complete blindness due to intense damage to the cornea.
Although Vitamin A deficiency can affect people of any age, children below five years are particularly susceptible to it if they had not been breast-fed or given adequate dietary supplements or are malnourished. Vitamin A deficiency may also occur as a result of impaired absorption due to certain medical conditions such as celiac disease, cirrhosis, giardiasis, sprue or reduced storage of the vitamin in the body.
Vitamin A deficiency not just affects the eyes, but has other damaging effects as well. It weakens immunity and diminishes the ability to fight infections. If children are not immunised against childhood infections like measles, then Vitamin A deficiency can lead to higher mortality rates. Even mild deficiency of Vitamin A can increase a child’s risk of developing respiratory and diarrheal infections and lessen the possibility of survival from serious infections.
Including sufficient sources of Vitamin A in the daily diet is the best way to prevent Vitamin A deficiency and avoid night blindness and related complications. Animal foods such as cod liver oil, tuna, herring, salmon, liver, eggs and whole milk are rich sources of Vitamin A. Green leafy vegetables, yellow, orange and red-coloured fruits and vegetables such as papaya, mango, oranges, carrots, squash, pumpkin and tomatoes are other good sources. In plant foods, Vitamin A is present in the pro-vitamin form known as carotene, which is better absorbed in the body when taken with dietary fat.
Infants who cannot be breast-fed need to be given formula containing suitable amounts of Vitamin A and a paediatrician should be consulted to check for any deficiency. In older children and adults, any sign of night blindness should not be overlooked and medical consultation must be sought at the earliest.
In case clinically-evident Vitamin A deficiency is diagnosed in a child or adult, then supplementation should be immediately initiated as per the doctor’s recommendation.
(The author is senior ophthalmologist and chairman, Devi Eye Hospital, Bengaluru)