K
Kanizsa figure See figure, Kanizsa.
kataphoria 1. A tendency of the visual axes of both eyes to deviate below the horizontal plane, in the absence of a stimulus to fusion. 2. Synonym of alternating deorsumduction. Note: also spelt cataphoria.
See depression; hyperphoria.
Kayser–Fleischer ring See ring, Kayser–Fleischer.
Kearns–Sayre syndrome See ophthalmoplegia, chronic progressive external.
Keith–Wagener–Barker classification See retinopathy, hypertensive.
Kennedy syndrome See syndrome, Foster Kennedy.
Kepler telescope See telescope.
keratectasia See ectasia; staphyloma, anterior.
keratectomy, photorefractive A surgical procedure on the cornea aimed at correcting ametropia. The epithelium is completely removed over a central diameter of about 7 mm and excimer laser ablation is then carried out on the stroma. A bandage soft contact lens is usually worn afterwards for a few days while the epithelium regenerates. Complications are more common than with either LASEK or LASIK. Useful vision recovers more slowly and pain lasts longer than with the latter procedures. Syn. keratorefractive surgery; laser refractive keratoplasty (LRK); refractive keratoplasty.
See ectasia, corneal; keratotomy, radial.
keratic precipitates (KP) Cells (e.g. leukocytes) deposited on the endothelium of the cornea which occur as a result of inflammation of the iris or the ciliary body. They often collect in a triangular pattern with the base down (Arlt’s triangle) on the inferior portion of the endothelial surface. They may also be distributed diffusely over the endothelium, as in Fuchs’ heterochromic iridocyclitis or anterior uveitis, or concentrated in one area, as in disciform keratitis or herpes simplex keratitis. In granulomatous uveitis they are larger than in nongranulomatous uveitis, greasy in appearance (called ‘mutton fat’). Following treatment of the primary cause they usually disappear.
See cornea guttata.
keratitis Inflammation of the cornea. It can arise from various sources, the most common being: infection by bacteria, fungi or viruses, hypersensitivity to staphylococcal exotoxins, nutritional deficiencies, failure of the eyelids to cover the cornea, deficiencies in the precorneal tear film, contact lens wear (especially extended wear), mechanical, radiation or chemical trauma or interruption of the ophthalmic branch of the trigeminal nerve. It is usually characterized by a dullness and loss of transparency of the cornea due to infiltrates, neovascularization, oedema and is accompanied by ciliary injection. The discomfort varies from a foreign body sensation to severe pain, with lacrimation, photophobia, blepharospasm and an impairment of vision. If the condition is severe, ulcers and pus (hypopyon) will appear and the iris and ciliary body may become involved. It is important to identify the cause and the organism in order to treat the condition. Keratitis of bacterial origin is treated with antibiotic drugs. Keratitis of viral origin (e.g. herpes) is treated with antiviral agents and that of fungal origin with antifungal agents.
See corneal infiltrates; keratomalacia; keratomycosis; keratopathy.
acanthamoeba k. A rare type of keratitis caused by the microorganism acanthamoeba, which invades the cornea. The symptoms begin with a foreign body sensation, which turns into pain, photophobia, tearing, blepharospasm and blurred vision. The signs are infiltrates that develop into a ring, and the cornea may eventually become opaque. Diagnosis of the disease is made by laboratory analysis of a corneal scraping. Contact lens wear has been found to be associated with this disease in about threequarters of the cases, especially when the patient has used homemade or unpreserved saline. The other cases were due to contact with stagnant water or following an abraded cornea. The therapy is with repetitive doses of antiamoebic agents (e.g. biguanide) and an antibiotic (e.g. propamidine isethionate) or a combination of propamidine and neomycin. However, strict compliance with contact lens regimens and avoidance of exposure to dirty, stagnant water diminishes the risks of contracting the disease.
See corneal infiltrates; disinfection; propamidine isethionate.
actinic k. See keratoconjunctivitis, actinic.
acute epithelial k. See herpes zoster ophthalmicus.
acute stromal k. A complication of scleritis in which there are superficial and mid-stromal infiltrates in the limbal region. Lesions can also be noted in the central cornea and may develop vascularization and permanent opacification. In cases of scleritis that are limited (i.e. not diffuse), corneal changes are noted only in the bordering corneal region.
dendritic k. See keratitis, herpes simplex.
disciform k. A deep localized keratitis involving the stroma, usually characterized by a disc-shaped grey area (Wessley ring) that may spread to the whole thickness of the cornea. It is due to a viral infection (e.g. herpes simplex virus) or to an immune reaction, or it may also occur as a sequel to trauma. It may heal without residue or may cause scarring and vascularization of the cornea. Treatment is with steroid and antiviral agents.
See clouding, central corneal; keratic precipitates; ring, Wessley.
epithelial k. See keratitis, punctate epithelial.
exposure k. See keratopathy, exposure.
filamentary k. Keratitis characterized by the presence of fine epithelial filaments. It can occur as a result of herpes, thyroid dysfunction, corneal abrasions, keratoconjunctivitis sicca, etc.
fungal k. A keratitis caused by a fungus, such as Fusarium, Aspergillus, or Candida albicans. The condition may develop after eye injury (e.g. fingernail or contact lens scratch, tree branch), especially in agricultural areas. However, it has become more common since the use of corticosteroids. It may also occur in eyes suffering from corneal disease, after keratoplasty, diabetes or extended-wear contact lenses. It is characterized by greyish-white, rough ulcers with indistinct and feathery edges with filaments infiltrating into the stroma (filamentary keratitis). There is ciliary and conjunctival injection and it may be accompanied by ring abscesses and, in severe cases, hypopyon. The ulcers have oval or round outlines with a plaque-like surface and the cornea is fully oedematous. Differential diagnosis is facilitated by corneal scraping or biopsy of the ulcer. Management consists mainly of antifungal agents. Syn. mycotic keratitis.
See keratomycosis.
herpetic k. Keratitis caused by either herpes simplex or herpes zoster viruses.
See herpesvirus; keratitis, herpes simplex.
herpes simplex k. An inflammation of the cornea, which occurs occasionally as a result of a blepharoconjunctivitis caused by the herpes simplex virus (usually type 1). The disease begins with skin vesicles typically spread over the lids, conjunctiva and periorbital area. Symptoms include irritation, photophobia, tearing, reduced corneal sensation and blurred vision if the central cornea is involved. The characteristic sign is a dendritic ulcer, which enlarges progressively resulting in a configuration referred to as a geographical ulcer. Treatment is with an antiviral agent (e.g. aciclovir) or debridement of the epithelium if unresponsive to antiviral agents. Syn. dendritic ulcer.
See herpesvirus; keratitis, disciform; keratitis, interstitial; keratitis, punctate epithelial; keratitis, ulcerative.
hypopyon k. Purulent keratitis with ulcer resulting in the presence of pus in the anterior chamber, which gravitates to the bottom. The ulcer is a dirty grey colour and the conjunctiva is also inflamed. The usual cause of the infection is the pneumococcus which gives rise to a corneal ulcer (often called serpiginous ulcer because of its tendency to creep forward in the cornea).
See hypopyon; keratitis, ulcerative; ulcer, corneal.
interstitial k. Keratitis involving the stroma. It is characterized by deep vascularization of the cornea and is often associated with iridocyclitis. Formerly, the most common cause was congenital syphilis (syphilitic keratitis). However, nowadays it is usually the result of a herpes simplex infection, or it may be part of a syndrome (Cogan’s) or other systemic diseases (e.g. leprosy, tuberculosis). Management involves cycloplegics, topical antiviral agents and in severe cases corticosteroids. Syn. stromal interstitial keratitis.
See ring, Wessley; sign, Hutchinson’s.
lagophthalmic k. See keratopathy, exposure.
marginal k. A condition characterized by subepithelial peripheral corneal infiltrates which may spread circumferentially and are separated from the limbus by a clear zone, which may eventually become invaded by blood vessels. It is a hypersensitivity response to staphylococcal exotoxins. There is discomfort, pain, redness and photophobia. Treatment is with topical steroids.
microbial k., contact lens induced A keratitis caused by a microorganism such as a bacteria (e.g. Pseudomonas aeruginosa, Serratia marcescens), amoeba (e.g. Acanthamoeba), or less commonly a virus or fungus. The incidence of the condition is relatively low. It has been estimated to be 2 to 5 individuals with daily wear of soft lenses and 10 to 20 with extended wear of soft lenses per 10 000 per year. High oxygen permeability leads to less infection. Signs and symptoms include pain, infiltrates, redness, lacrimation, photophobia, corneal oedema, reduced vision, discharge, swollen lids and aqueous flare. The condition may have been precipitated by non-compliance, poor hygiene, dirty lens case, etc. Management includes cessation of lens wear and drug therapy.
mucous plaque k. See herpes zoster ophthalmicus.
mycotic k. See keratitis, fungal.
non-ulcerative k. See contact lens acute red eye.
neuroparalytic k. Keratitis caused by a failure of blinking or infrequent or incomplete blinking causing inadequate spread of tears.
See keratopathy, exposure.
neurotrophic k. See keratopathy, neurotrophic.
peripheral ulcerative k. A severe form of keratitis most often associated with a systemic disease, the most common being rheumatoid arthritis, Wegener’s granulomatosis, lupus erythematosus and polyarteritis nodosa. It is characterized by pain, usually redness and peripheral ulceration with corneal thinning. Treatment is urgent and directed towards the primary cause.
phlyctenular k. See keratoconjunctivitis, phlyctenular.
punctate epithelial k. (PEK) An inflammation of the cornea characterized by either multiple, small, superficial, punctuate lesions or minute, flat, epithelial dots resulting from bacterial infection (e.g. chlamydial, staphylococcal), vitamin B2 deficiency, virus infection (e.g. herpes) and also from exposure to ultraviolet light, injury to the eye with aerosol products or contact lens solutions. The condition is usually associated with conjunctivitis. Treatment depends on the causative agent (e.g. antiviral agents will be used to suppress symptoms in herpes simplex keratitis). Syn. superficial punctate keratitis (SPK), although this term is more often used to describe a PEK of viral origin.
See conjunctivitis, adult inclusion; keratitis, Thygeson’ superficial punctate.
rosacea k. Keratitis associated with acne rosacea of the face. It is characterized by marginal vascularization at the limbus. The vessels extend into the cornea surrounded by a zone of grey infiltration. The infiltrates and vascularization are in the cornea proper and not raised above the surface (unlike phlyctens). There is little tendency to ulcerate. It is usually associated with an inflammation of the conjunctiva (keratoconjunctivitis). Treatment involves topical steroid drops as well as systemic antibiotic therapy.
See acne rosacea; keratoconjunctivitis, phlyctenular.
k. sicca See keratoconjunctivitis sicca.
superficial punctate k. See keratitis, punctate epithelial.
stromal k.; syphilitic k. See keratitis, interstitial.
Thygeson’s superficial punctate k. A rare type of punctate epithelial keratitis. It is characterized by circular or oval, grayish-white epithelial lesions commonly located centrally and slightly elevated with a cluster of granular dots. The lesions show punctate staining with fluorescein. The cause is unknown, although a virus is suspected. It gives rise to mild irritation, photophobia and slight blurring of vision. Treatment includes artificial tears, corticosteroids (but this may induce recurrence) and therapeutic soft contact lenses. Untreated, it may subside within a few years.
ulcerative k. Any keratitis in which there is an ulcer of the cornea. The cause may be bacterial or viral infection, trauma or contact lens wear (particularly extended wear). The ulcer is a dirty grey coloured area on the cornea, the eye is red, the pain can be severe, there is photophobia, lacrimation, and vision may be affected. Immediate treatment is necessary: if due to contact lenses, cessation of wear and topical antibiotics will be used.
See keratitis, herpes simplex; ulcer, corneal.
ultraviolet k. See keratoconjunctivitis, actinic.
keratocele Hernia of Descemet’s membrane through a hole in the cornea caused by a perforating corneal ulcer or wound.
keratoconjunctivitis Inflammation of the conjunctiva and the cornea.
See keratitis, punctate epithelial; keratitis, rosacea.
actinic k.
