Keratomalacia

Synonym - xerotic keratitis

Xerophthalmia is the term used for deficient tear production leading to dry eye (particularly affecting the cornea) associated with vitamin A (retinol) deficiency. There may be insufficient absorption, or poor metabolism, of the vitamin.

What is keratomalacia?

If left untreated, xerophthalmia progresses to keratomalacia: the cornea becomes thin and soft, eventually ulcerating. At worst, there may be perforation with secondary extrusion of the globe contents; however, other sequelae include corneal scarring, a permanent fibrotic deformity of the eyeball (phthisis bulbi) and blindness.¹

Keratomalacia epidemiology

• It is a common cause of acquired paediatric blindness worldwide.

• In western societies, it can occur amongst those with a poor nutritional status, due to a variety of factors (see below).

Risk factors²

• Primary vitamin A deficiency is prevalent in much of the developing world, particularly endemic in South and East Asia where rice is the staple food.

• Children have much lower vitamin A stores than adults.

• Protein-energy malnutrition is associated with keratomalacia - the diet is likely to be deficient in vitamin A, due to reduced intake, but starvation also affects the metabolism of vitamin A. Zinc deficiency and iron deficiency may contribute.

• It may be precipitated by a systemic illness such as measles ('measles blindness'),¹ pneumonia or diarrhoea.³

Keratomalacia symptoms (Presentation)⁴

• Night blindness (nyctalopia or poor dark adaptation) tends to be the earliest ocular symptom of vitamin A deficiency.

• Eyes become dry (cornea, lacrimal glands and conjunctiva are all affected) - known as xerosis.

• Keratomalacia presents with bilateral central grey, indolent corneal ulcers surrounded by a dull, hazy cornea, sometimes with photophobia.

• The cornea becomes soft and necrotic, usually progressing to perforation.

• Bitot's spots⁵ are areas of abnormal squamous cell proliferation and keratinisation of the conjunctiva, which look like foamy, wedge-shaped areas in the conjunctiva. They are usually temporal and are strongly associated with vitamin A deficiency, especially in young children.

• White spots on the retina have been reported in one case.⁶

Investigations

• Plasma retinol and retinol binding proteins are suppressed in advanced vitamin A deficiency.

• Iron and zinc levels may be relevant.²

• Electroretinography.^{4 7}

Keratomalacia treatment and management

Addressing the ocular problems

• Treatment will be on the aggressive end of the treatment spectrum of dry eye with intensive lubrication ± a bandage contact lens, depending on how far the condition has progressed.

• Topical antibiotics will be required to prevent secondary keratitis.

• Once the acute situation has settled, there will inevitably be some degree of corneal scarring. Depending on the extent and the individual's circumstances, keratoplasty may be considered. Success of this procedure for this condition has been limited³ but there are occasional case studies suggesting that this line of treatment may have a future as techniques improve.^{8 9}

Addressing the systemic problems

• Dietician advice for a vitamin A and protein-rich diet.

• Vitamin A supplements may be used (intramuscular or oral).¹⁰ Caution is needed in pregnant women because high vitamin A doses may be teratogenic.

• Underlying problems need to be addressed, eg, alcohol abuse, an eating disorder, gastrointestinal disease.

• Other micronutrients (iron and zinc) may be important.² Addressing zinc deficiency may be helpful.¹¹

• Optical iridectomy or penetrating keratoplasty may be required.³

Prognosis

• The prognosis for xerophthalmia is good if treated in the early stages (subclinical deficiency or early eye changes).³ However, as the condition progresses and keratomalacia develops, corneal changes may be irreversible.²

• Xerophthalmia and keratomalacia are associated with increased mortality in children. An Indonesian study showed mortality rates increased with night blindness (x 2.7), Bitot's spots (x 6.6) and both features(x 8.6) reflecting the severity of the underlying vitamin A deficiency.¹²

Prevention

An adequate and varied diet - good sources of vitamin A are liver, beef, chicken, eggs, fruit and vegetables (especially orange and green vegetables). Other prevention strategies are:

• Where there is vitamin A deficiency in a community, intervention is important, both to prevent blindness and to reduce child mortality.¹³

• High-dose oral vitamin A supplementation for children with measles in developing countries.¹⁴ and high measles immunisation coverage.

• Vitamin A supplementation in areas of high risk. There is a need for studies comparing different doses and delivery mechanisms.¹⁵