X
xanthelasma A cutaneous deposition of lipid material that appears in the skin of the eyelids, most commonly near the inner canthi. It appears as a yellowish, slightly elevated area. It is a benign and chronic condition that occurs primarily in the elderly. It may be associated with raised blood cholesterol, high-density lipoprotein and triglyceride levels, leading to heart disease or diabetes. Syn. xanthoma; xanthelasma palpebrarum; xanthoma palpebrarum.
See arcus, corneal; plaque, Hollenhorst’s.
xanthogranuloma, juvenile (JXG) A benign proliferation of single or multiple, small yellowish-brown papules or nodules in the skin and the anterior uvea, especially the iris. The condition mainly appears in young children, although it may occur in adults. The lesions consist of dermal infiltration by histiocytes, lymphocytes, eosinophils and Touton giant cells. The skin lesions increase in size and number but eventually regress spontaneously into an atrophic scar, otherwise they may need to be treated by excision or corticosteroid injection. In the eye it is commonly associated with hyphaemia (in the anterior chamber), uveitis and secondary glaucoma with visual loss. Therapy includes topical and systemic corticosteroids. Syn. juvenile nevoxanthoendothelioma.
xanthoma See xanthelasma.
xanthopsia A condition in which all objects appear of a yellow colour. It may occur as a result of picric acid and santonin poisoning, or jaundice. Syn. yellow vision.
See chromatopsia.
x-axis See axis, transverse.
X-Chrom lens See lens, X-Chrom.
xeroderma pigmentosum An autosomal recessive inherited disease in which there is progressive pigmentary degeneration of the skin, especially in sun-exposed areas. It results from a deficient enzyme used in the repair of DNA damaged by ultraviolet light. The condition begins in infancy and is characterized by the appearance of numerous pigmented spots resembling freckles and telangiectases. Eventually atrophic patches appear as well as wart-like excrescence and often squamous cell carcinoma. Patients are photophobic and the eyelids are frequently affected with atrophy and ectropion, which may be accompanied with conjunctival inflammation and corneal ulceration. Protection of the eyes and skin is essential as well as surgical removal of the carcinomatous tumours, but many patients eventually succumb to metastases.
xeroma See xerophthalmia.
xerophthalmia Extreme dryness of the conjunctiva and cornea due to a failure of the secretory activity of the mucin-secreting goblet cells of the conjunctiva. The conjunctiva and cornea lose their lustre and become skin-like in appearance. The condition may even propagate to the cornea and give rise to keratoconjunctivitis sicca and, if severe, keratomalacia. Xerophthalmia may be due to trauma, exposure or systemic deficiency of vitamin A, etc. Syn. xeroma; xerosis of the conjunctiva (if the cornea is not involved).
See keratoconjunctivitis sicca; keratomalacia; mucin; spot, Bitot’s.
xerosis See xerophthalmia.
X-linked inheritance See inheritance.
