Have you ever experienced a sudden drop in vision while driving back home at night after an exhaustive day at work? What felt like an hour-long drive back home can now feel like a defocussed camera. Or have you been experiencing difficulty in moving around or finding objects in the dark?
Night blindness, or nyctalopia, is a condition that makes it hard for an individual to see in dark places or for eyes to adjust to sudden changes between bright light and darkness. There are specialised cells of the retina called rod photoreceptors that are responsible for providing contrast in dim light, which get affected in numerous conditions, leading to difficulty in night vision.
What causes night blindness?
Vitamin A deficiency is a leading cause of preventable night blindness worldwide and hence a public health priority. Vitamin A is a direct precursor of rhodopsin, which is the most important pigment in rod function. Night blindness can be a presenting feature even before other signs are visible. This is mainly seen in children with chronic malnutrition, pregnant and lactating mothers, and in individuals with chronic malabsorption such as after bariatric surgery.
Other acquired causes include high myopia (short-sightedness), which leads to reduced rod density per unit area secondary to retinal stretching, and a specific variant of cataract (posterior subcapsular) seen at an early age, which causes glare or sudden decrease in vision because of headlight exposure of oncoming vehicles while driving at night.
Long-term use of drugs like chloroquine or hydroxychloroquine used in the management of arthritis causes retinal toxicity and hampers night vision. Hence, careful monitoring and periodic ophthalmic examinations are mandatory to reduce the dose or replace it to prevent further damage.
Other uncommon causes of night blindness include zinc deficiency, after retinal surgery or lasers, and chronic liver disease (liver being the main storage site of vitamin A).
Retinitis Pigmentosa is the leading inherited cause of night blindness globally. There is progressive photoreceptor degeneration leading to night blindness and peripheral visual field constriction.
When to consult your ophthalmologist?
Gradual worsening of night vision, associated peripheral field loss, white patches on the white area of your eye, night vision difficulty in children <5 years of age, pregnant and lactating mothers, after bariatric surgery and in patients on drugs like hydroxychloroquine or phenothiazine.
A detailed family and general history, ophthalmic evaluation and systemic testing, including vitamin A, Zinc, carotene, liver function tests play an important role in diagnosing the etiology for night blindness.
Treatment is directed at the specific cause. Vitamin A and Zinc supplementation, Cataract surgery, and withdrawal or replacement of medications, if any, can treat and/or prevent further progression of night blindness.
Dietary counselling to improve intake of vitamin A-rich foods such as carrots, egg, green leafy vegetables, and pumpkin can prevent progression and recurrence.
Genetic testing helps in confirming inherited mutations, which further aids in genetic counselling and family planning. Early identification also helps in enrollment in various therapeutic trials and planning of low vision aids. Delayed diagnosis may lead to permanent blindness, progression of retinal toxicity, loss of independence and functional vision and missed opportunities to diagnose systemic conditions.
Nothing is more expensive than a missed opportunity and hence timely vigilance, early diagnosis and management can help in improving the overall quality of life for a patient.
(The author is a Senior Consultant Ophthalmologist, Retina Services at Dr Agarwals Eye Hospital, Nehru Nagar, Ghaziabad)
The opinions expressed in this article are those of the author and do not purport to reflect the opinions or views of THE WEEK.
