Xerophthalmia is a progressive eye disease caused by a severe vitamin A deficiency. Without adequate vitamin A, the eyes begin to dry out, leading to conditions affecting the conjunctiva and cornea. This disease is a significant cause of preventable blindness in children, particularly in developing countries where nutritional deficiencies are more common. If left untreated, xerophthalmia can escalate from mild symptoms to permanent vision loss.
The Role of Vitamin A in Eye Health
Vitamin A is a fat-soluble nutrient that performs multiple functions for vision. Its primary role is in the visual cycle, where it is a component of rhodopsin, a protein in the retina that absorbs light. Rhodopsin is necessary for the retina to convert light into nerve signals sent to the brain, allowing for vision in low-light conditions. A lack of this protein leads to difficulty seeing at night.
Beyond its function in the visual cycle, vitamin A also maintains the health of the cornea and conjunctiva. It supports the production of mucus, which keeps the eye’s surface moist and protected. Without sufficient vitamin A, these tissues lose their ability to secrete moisture, leading to dryness and cellular damage. This process, known as keratinization, causes the eye’s protective outer layers to become thick and dry.
Signs and Progression of Xerophthalmia
The initial symptom of xerophthalmia is an impaired ability to see in dim light or darkness, a condition called nyctalopia, or night blindness. As the vitamin A deficiency persists, the disease progresses to affect the physical structures of the eye’s surface.
The next stage is conjunctival xerosis, where the conjunctiva—the thin membrane covering the white of the eye and the inside of the eyelids—becomes dry, thick, and wrinkled. Following this, deposits of keratin and epithelial debris may build up on the conjunctiva, forming distinct patches. These triangular, foamy, or cheesy-looking spots are known as Bitot’s spots and are a characteristic sign of the disease.
If the deficiency is not corrected, the cornea becomes involved in a stage called corneal xerosis, appearing dull, hazy, and dry. This condition can advance to the most destructive stage, keratomalacia, which involves the softening and melting of the cornea. This severe stage often leads to corneal ulceration, perforation of the eyeball, and the formation of scars that cause permanent blindness.
Medical Diagnosis and Treatment
Diagnosing xerophthalmia involves a clinical eye examination to identify its characteristic signs. A healthcare provider will look for evidence of dryness, Bitot’s spots on the conjunctiva, and changes to the cornea. The patient’s medical history, particularly regarding diet and any difficulties with night vision, provides important context for the diagnosis.
To confirm the underlying deficiency, a blood test can be performed to measure serum retinol levels. In some cases, specialized tests like an electroretinogram, which measures the electrical response of the eye’s light-sensing cells, may be used to assess retinal function. Another diagnostic tool is impression cytology, where a sample of cells is taken from the conjunctiva to check for changes related to vitamin A deficiency.
Treatment for xerophthalmia is a medical emergency to prevent permanent vision loss. The standard intervention is a high-dose vitamin A supplementation regimen, administered orally or by injection. The dosage depends on the patient’s age and the severity of the condition. For patients with corneal damage, doctors may also prescribe antibiotics to prevent secondary infections.
Dietary Prevention Strategies
Long-term prevention of xerophthalmia is centered on ensuring an adequate intake of vitamin A through a balanced diet. Vitamin A is available in two main forms in food: preformed vitamin A (retinoids) and provitamin A (carotenoids). Both types are effective in preventing deficiency.
Preformed vitamin A is found in animal-based products and is ready for the body to use. Rich sources include:
- Liver from beef or chicken
- Fish liver oils
- Eggs
- Dairy products like milk and butter
Provitamin A carotenoids are found in plant-based foods and are converted into retinol by the body. The most well-known carotenoid is beta-carotene. Excellent sources include:
- Carrots
- Sweet potatoes
- Mangoes and papayas
- Dark leafy green vegetables, such as spinach and kale