Why can't we see things at night..

Patient's question:

Why can't we see things at night

Doctor's answer:

It may be caused by a lack of vitamin A. It is recommended to see a doctor early for symptomatic treatment. Nyctalopia refers to poor night vision or the inability to see things in the dark, meaning poor visual function from daylight to dark environments. It is mainly due to the dysfunction of rod cells in the retina, with symptoms such as dark adaptation disorders or peripheral fundus lesions. Nyctalopia can be caused by eye diseases themselves or by systemic diseases. It can be congenital or acquired, and sometimes has a genetic cause, such as:
(1) Systemic Nyctalopia: Due to vitamin A deficiency caused by systemic diseases such as insufficient intake, malnutrition, wasting diseases, artificially fed infants, liver disease, digestive diseases, etc., nyctalopia may appear early, followed by conjunctival and corneal dryness. In severe cases, the cornea may erode, ulcerate, or perforate.
(2) Refractive Intermediate Nyctalopia (Pseudo-Nyctalopia): If the corneal disease is peripheral or more severe, night vision will be poor. Cloudiness in the periphery of the lens, such as corneal cataracts, traumatic cataracts, or early senile cataracts, can cause poor vision in the dark.
(3) Nyctalopia Caused by Iris and Pupil Abnormalities: Conditions such as posterior synechiae of the iris, deformed pupils with only a small central opening, or drug-induced pupil constriction can lead to nyctalopia.
(4) Ocular Nyctalopia: Congenital cases include retinal dysplasia and retinitis pigmentosa. Acquired cases include progressive glaucoma, optic neuritis, optic atrophy, retinal periphlebitis, diabetes, hypertension, and arteriosclerotic retinopathy.
Why do children get nyctalopia? How should it be treated?
Nyctalopia is primarily a disease caused by vitamin A deficiency, most common in infants and young children. The reasons for vitamin A deficiency include:
- Long-term feeding of infants with starchy foods, skimmed milk, and legumes without timely addition of vitamin A-rich foods.
- Digestive system diseases (e.g., diarrhea) or liver and biliary diseases (e.g., chronic hepatitis) in infants that affect vitamin A absorption and utilization.
- Rapid growth in infants with insufficient vitamin A supply.
Infants with vitamin A deficiency often have difficulty seeing in low light, frequent blinking, photophobia, and even dry, dull, cloudy, softened, or ulcerated corneas. Additionally, symptoms such as dry, scaly skin, brittle hair, and easy hair loss may occur.
For mild cases, vitamin A can be taken orally in doses of 25,000–50,000 IU per day, divided into 2–3 doses (e.g., concentrated vitamin A soft capsules, each containing 25,000 IU). Severe cases may require intramuscular injections of vitamin AD, 0.5–1 mL daily, with improvement expected within 3–5 days. Additionally, keeping the eyes clean and using 0.75% chloramphenicol eye drops can be helpful.
How to prevent nyctalopia?
Prevention of nyctalopia involves the following four points:
1. Pregnant women should have a varied diet, consuming foods rich in carotenes and vitamin A, such as eggs, animal livers, carrots, and vegetables like tomatoes.
2. Actively prevent or treat chronic diseases in infants and supplement vitamin A early. Breastfeeding infants or those on artificial feeding should be given vitamin A-rich foods promptly. The physiological daily requirement of vitamin A for infants is generally 30 IU per kg of body weight. Premature infants should be given concentrated cod liver oil, 3,000–5,000 IU daily.
3. Avoid restrictive diets blindly, especially during measles, and ensure adequate vitamin A supplementation.