Light on night blindness.
Night blindness is not uncommon in our vast population. One needs a careful understanding of its causes so that, if treatable, it is treated at the earliest and, if controllable, it is be adequately controlled. Night vision is a function of small cells in the retina called rods, also known as photoreceptors.
Broadly speaking, night blindness can be either nutritional — vitamin A deficiency, or a familial degenerative disease known as retinitis pigmentosa. The less common causes are high myopia (nearsightedness) and advanced cases of glaucoma. The opposite of night blindness is day blindness which is caused by the advancing central cataract; people feel better at night in this situation.
Let us understand nutritional vitamin A night blindness. It is still the leading cause of childhood blindness. Approximately, three million children develop vitamin A
deficiency annually and three lakh of them become blind. A combination of strategies is required for the sustainable control and elimination of the vitamin A deficiency. A revised schedule of vitamin A intake is as follows: The first dose of one lakh international units should be given at nine months of age. The second dose of two lakh international units should be administered at 18 months of age. The third dose of two lakh international units should be given at the age of two years.
The second cause of night blindness is retinitis pigmentosa, a degenerative condition, which is inheritedly determined and difficult to treat. This disease usually starts manifesting itself in the second decade of life, between 12-20 years. A good thing here is that patients do not go blind until late in life.
A severe loss of vision is caused by the associated retinal disease of glaucoma for which treatment should be taken. These cases develop cataract early but they tolerate cataract surgery very well.
As the central vision is very good in these cases, cataract surgery without an intraocular lens is beneficial because of the magnifying effect of the spectacles which act as a low-vision aid.
There has been a resurgence recently in the role of vitamin A therapy in delaying the progression of retinitis pigmentosa. The timely diagnosis, regular yearly check-ups and the treatment of the associated eye disease, along with reassurance, constitute the mainstay of the management in this disease.
The blanket statement that retinitis pigmentosa patients would not have children is not desirable without knowing the background of inheritance. Most of these patients have simplex inheritance with no family history. Less than 20 per cent of the patients have the autosomal dominant form of inheritance. So, the chances of transmitting the disease to the offspring in general are very limited. Well-informed and reassured patients can plan their career and lead a useful and reasonably good life.