2020–2021 BCSC Basic and Clinical Science Course™
8 External Disease and Cornea
Chapter 8: Systemic Disorders With Corneal and Other Anterior Segment Manifestations
Nutritional Disorder: Vitamin A Deficiency
Vitamin A deficiency is a leading cause of blindness in developing countries and is responsible for at least 20,000–100,000 new cases of blindness worldwide each year. The earliest manifestation of vision loss is night blindness, or nyctalopia. At greatest risk are malnourished infants and babies born to vitamin A–deficient mothers, especially infants who have another biological stressor, such as measles or diarrhea. Superficial concurrent infections due to herpes simplex virus, measles virus, or bacterial agents probably further predispose these children to keratomalacia and blindness. Although xerophthalmia usually results from low dietary intake of vitamin A, decreased absorption of vitamin A may also be responsible. In cases of vitamin A deficiency and xerophthalmia occurring in countries with a low rate of malnutrition, the condition is usually caused by unusual self-imposed dietary practices, chronic alcoholism, or lipid malabsorption (seen in cystic fibrosis, biliary cirrhosis, and bowel resection). The increase in gastric bypass surgical procedures may lead to an increased incidence of vitamin A deficiency.
Vitamin A deficiency causes blindness by inhibiting the production of rhodopsin. Xerosis (abnormal dryness) of the conjunctiva and cornea due to vitamin A deficiency is associated with loss of mucus production by the goblet cells. Similar changes can occur in epithelial cells of the gastrointestinal, genitourinary, and respiratory tracts.
One ocular consequence is the Bitôt spot (Fig 8-13), a superficial foamy, gray, triangular lesion on the bulbar conjunctiva that appears in the palpebral aperture. This spot consists of keratinized epithelium, inflammatory cells, debris, and Corynebacterium xerosis. Corynebacterium bacilli metabolize the debris, producing the foamy appearance. Prolonged vitamin A deficiency may lead to corneal ulcers and scars and eventually cause diffuse corneal necrosis (keratomalacia). The World Health Organization classifies the ocular surface changes into 3 stages:
Figure 8-13 Clinical photograph showing a foamy Bitôt spot in the bulbar conjunctiva, close to the limbus, in a patient with anorexia.
(Courtesy of Stephen E. Orlin, MD.)
conjunctival xerosis, without (X1A) or with (X1B) Bitôt spots
corneal xerosis (X2)
corneal ulceration, with keratomalacia involving less than one-third (X3A) or more than one-third (X3B) of the corneal surface
Systemic vitamin A deficiency, best characterized by keratomalacia, is a medical emergency with a mortality rate of 50% if untreated. Although the administration of oral vitamin A will address the acute manifestations of keratomalacia, patients with this condition are usually affected by much broader protein-energy malnutrition and should be treated with both vitamin and protein-calorie supplements. Malabsorption may render oral administration ineffective in patients with acute vitamin A deficiency. Maintenance of adequate corneal lubrication and prevention of secondary infection and corneal melting are essential steps in treating keratomalacia, but identification and proper treatment of the underlying causes are vital to successful clinical management of the ocular complications.
Mannis T, Mannis MJ, Paranjpe DR, Kirkness CM. Nutritional disorders. In: Mannis MJ, Holland EJ, eds. Cornea. Vol 1. 4th ed. Philadelphia: Elsevier; 2017:676–687.
Sommer A. Vitamin A deficiency and clinical disease: an historical overview. J Nutr. 2008; 138(10):1835–1839.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.