Arlt's Triangle

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Article initiated by:

Marianna Kavalaraki MD, Msc

All contributors:

Ghazala A. D. O'Keefe, MD, Edmund Tsui, MD, Marianna Kavalaraki MD, Msc, Paulina Liberman

Assigned editor:

Paulina Liberman

Review:

Assigned status Up to Date

 by Paulina Liberman on October 18, 2025.

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Disease Entity

KPs distributed in a triangle-shaped area on the inferior cornea

Arlt's triangle is a distribution pattern of keratic precipitates, which deposit as an inverted triangle on the central to inferior cornea , forming a wedge-shaped region on the inferior corneal endothelium. The white-yellowish greasy precipitates of inflammatory cells (macrophages and epithelioid cells) are clumped in triangular fashion in the lower part of the anterior chamber due to gravity and the convection currents inside the anterior chamber. It is a clinical sign often associated with granulomatous inflammation, however not pathognomonic of granulomatous disease. Arlt’s triangle distribution is a general finding and not suggestive of any specific uveitis etiology.

History

A page from the 1858 textbook "Die Krankheiten des Auges : für praktische Ärzte" by Austrian ophthalmologist Ferdinand von Arlt. It shows his description of what would become known as Arlt's triangle. The text describes how inflammatory exudate settles "in the form of dots or spots" ("in Form von Puncten oder Flecken") on the posterior corneal surface ("an die hintere Wand der Cornea"), a classic sign of anterior uveitis.

The term is named after Carl Ferdinand von Arlt (1812-1887). An Austrian ophthalmologist, von Arlt was a highly regarded professor at the University of Prague and later at the University of Vienna.

His other major contributions include being the first to provide an accurate description of trachoma (1855), which led to the terms "Arlt's line" and "Arlt's syndrome." He was also the first to correctly understand the pathogenesis of myopia as a consequence of excessive axial length (1854). In his famous trilogy, "Eye Diseases for Practitioners," published during his time in Prague, he described inflammatory exudate settles "in the form of dots or spots" ("in Form von Puncten oder Flecken") that deposit on the posterior corneal surface ("an die hintere Wand der Cornea").

Etiology

Arlt's triangle distribution pattern of mutton fat keratic precipitates is suggestive of chronic granulomatous inflammatory process. The differential diagnosis should include anterior uveitis associated with sarcoidosis, syphillis, and tuberculosis.  Clusters of large, fluffy, lardaceous KPs with greasy appearance forming Arlt's triangle may also occur in other unusual chronic infections e.g. leprosy, brucellosis, coccidiomycosis.

Pathophysiology

Schematic diagram showing triangular distribution of keratic precipitates on the inferior corneal endothelium

Arlt's triange distribution occurs as a result of convection currents within the anterior chamber and the cooler temperature in the inferior cornea. The larger granulomatous KPs will pigment and then shrink as inflammation abates or is controlled by steroid therapy. They often fail to disappear completely, and they may alter the endothelium where they rest, leaving a halo on the endothelium.

Diagnosis

Clinical Diagnosis

Arlt's triangle sign is typically observed during slit-lamp biomicroscopy. The keratic precipitates forming an inverted triangle on the inferior corneal endothelium can be visualized during slit-lamp examination in diffuse illumination, as well as direct focal illumination or an optic section.

Granulomatous KP (keratic precipitates) plastered on the back surface of the cornea.

However, in some cases, this collection of sticky inflammatory cells on the central and inferior cornea is so large in size, that it's visible with the naked eye.

Mutton fat KPs form the wedge like area at the bottom of the cornea

Differential Diagnosis

Artl's triangle is suggestive, but not pathognomonic, of granulomatous inflammation. Differential diagnosis should also include unusual chronic inflammatory conditions including :

• Sarcoidosis
• Syphilis 
• Herpetic uveitis
• Tuberculosis
• Vogt-Koyanagi-Harada disease
• Sympathetic ophthalmia
• Lens-induced uveitis
• Brucellosis
• Lyme disease
• Leprosy
• Toxoplasmosis
• Toxocariasis
• Coccidioidomycosis (Valley Fever)

Diagnostic Work-Up

• FTA-ABS (or similar treponemal specific serology) test for syphilis with reflex Venereal Disease Research Laboratory (VDRL) test or RPR. A specific antitreponemal test must be obtained, as RPR or VDRL can provide false-negative results on RPR or VDRL.

• Chest radiograph to assess for sarcoidosis and pulmonary tuberculosis.
• IGRA for tuberculosis, depending on the patient's risk factors for tuberculosis

• Angiotensin-converting enzyme (ACE) test for sarcoidosis may be obtained but is not very sensitive or specific, especially in children. Soluble IL-2R in serum may also be obtained with the same purpose.

• Lyme serology if Lyme disease is suspected (eg, endemic area, tick bite, systemic manifestations)

• Toxoplasmosis enzyme-linked immunosorbent assay (ELISA) if mono or paucifocal retinitis with posterior uveitis is an associated feature

• In cases of suspected herpetic disease, anterior chamber fluid and/or vitreous may be examined via polymerase chain reaction (PCR) for HSV and herpes zoster virus nucleic acid.
• Cytology, polymerase chain reaction, and cultures of intra-ocular fluid may be needed when infection or masquerade suspected

Management

General treatment

Keratic precipitates typically resolve once the associated uveitis is adequately treated. Management may include antimicrobials, topical or systemic corticosteroids, and cycloplegia, depending on the specific type and etiology of uveitis.

Corticosteroids

• Topical corticosteroids are the mainstay of therapy and should be used aggressively during the initial phases of therapy.
• Subconjunctival injection of shorter-acting or depot steroids may be used if the patient poorly complies with topical therapy or if the inflammation is not responding to topical corticosteroids. Betamethasone (Celestone) is short and intermediate acting and can be used for exacerbations, whereas triamcinolone acetate is longer acting and is used more often for associated cystoid macular edema or vitritis. Depot steroids should be avoided in cases of uveitis secondary to any suspected infectious process because of their potentially severe adverse effects.
• Oral corticosteroids in severe cases may be added to the treatment regimen (after ruling out the infectious etiology or after under coverage of medication, which treats the infectious etiology).

Cycloplegia

Use a long-acting cycloplegic agent, such as cyclopentolate or homatropine, to relieve both pain and photophobia (if present) and to prevent the formation of posterior synechiae. However, this may not always be necessary in chronic disease, especially if the inflammation is well controlled. In any case, allowing for some pupil movement is helpful to prevent posterior synechiae formation in the dilated position.

Related concept

Turk’s line refers to a vertical linear accumulation of inflammatory cells on the inferior corneal endothelium.