Keratic Precipitates in Arlt’s Triangle

Arlt’s triangle pigmented refers to a pattern of keratic precipitates (KPs)—clusters of inflammatory cells—deposited in a wedge-shaped, inverted triangular area on the central to inferior corneal endothelium. These precipitates are composed primarily of macrophages, epithelioid cells, and lymphocytes. In active granulomatous anterior uveitis, fresh KPs appear as white-yellow “mutton-fat” lesions; over time, as inflammation subsides or with steroid therapy, these larger granulomatous KPs acquire brown pigment granules, shrink, and sometimes leave faint halos when they detach, giving rise to the pigmented variant of Arlt’s triangle EyeWikiEnto Key. The shape results from gravity-driven sedimentation and convection currents within the anterior chamber, directing cells toward the cooler, lower corneal endothelium EyeWiki. The presence of pigment indicates a chronic or resolving process and can mark previous inflammatory episodes, aiding clinicians in assessing disease chronicity and treatment response.

Types of Keratic Precipitates in Arlt’s Triangle

Although Arlt’s triangle describes distribution rather than KP subtype, various KP morphologies can occupy this triangular zone:

1. Fresh Nongranulomatous KPs
   These are small, round, bright-white precipitates seen in early acute uveitis. They indicate active inflammation with predominance of polymorphonuclear leukocytes Review of Optometry.

2. Mutton-Fat (Granulomatous) KPs
   Large, greasy-yellowish clusters of macrophages and epithelioid cells form the classic Arlt’s triangle in granulomatous uveitis. Their size (up to 1 mm) and greasy appearance distinguish them from finer white KPs Vagelos College.

3. Pigmented KPs
   Represent older, degenerating granulomatous KPs that have taken up melanin pigment from iris melanocytes or degenerating cells. These brownish-black spots shrink over time and signal a resolving or past inflammatory event Ento Key.

4. Ghost (Descemet’s-Covered) KPs
   Long-standing precipitates may be overlaid by new Descemet’s membrane, appearing pale or glassy (“ghost” KPs). They reflect prior inflammation and endothelial remodeling Ento Key.

5. Red KPs
   Rare in hemorrhagic uveitis, these precipitates contain red blood cells and may deposit in Arlt’s triangle during severe inflammation or trauma Wikipedia.

Causes of Pigmented Arlt’s Triangle

1. Sarcoidosis
   A multisystem granulomatous disease often affecting the eye. Noncaseating granulomas trigger chronic anterior uveitis with mutton-fat KPs that pigment over time EyeWiki.

2. Syphilis
   Treponema pallidum infection can cause granulomatous keratic precipitates in Arlt’s triangle. Pigmented KPs may persist after antibiotic therapy EyeWiki.

3. Tuberculosis
   Ocular TB provokes granulomatous inflammation and mutton-fat KPs. Healing lesions often leave pigmented spots in the triangle EyeWiki.

4. Vogt-Koyanagi-Harada (VKH) Disease
   An autoimmune syndrome against melanocytes causes granulomatous uveitis. Pigmented KPs can mark past flares, and iris changes accompany them EyeWiki.

5. Sympathetic Ophthalmia
   Bilateral granulomatous uveitis following ocular injury. Mutton-fat KPs deposit in Arlt’s triangle; chronic cases develop pigmented residuals EyeWiki.

6. Lens-Induced Uveitis (Phacoantigenic)
   Exposure of lens proteins after trauma or surgery triggers granulomatous KPs. Pigmentation follows resolution under steroids EyeWiki.

7. Brucellosis
   Systemic Brucella infection can involve the eye, producing a granulomatous anterior uveitis with pigmented KPs in the inferior cornea EyeWiki.

8. Leprosy
   Mycobacterium leprae may lead to chronic anterior uveitis. The slow course fosters pigmented KP formation in Arlt’s triangle EyeWiki.

9. Toxocariasis
   Ocular larva migrans can cause granulomatous inflammation and pigmented KPs as lesions heal EyeWiki.

10. Coccidioidomycosis
    Valley fever fungus occasionally involves the eye, with granulomatous KPs depositing in the triangle and pigmenting on resolution EyeWiki.

11. Lyme Disease
    Borrelia burgdorferi can provoke chronic anterior uveitis; healing stages often show pigmented Arlt’s triangle lesions EyeWiki.

12. Herpes Simplex Virus (HSV)
    HSV anterior uveitis produces granulomatous KP clusters in Arlt’s triangle. Over time, these pigmented deposits can persist, marking prior flares PubMed.

13. Varicella-Zoster Virus (VZV)
    VZV uveitis yields medium-sized granulomatous KPs in the triangle; chronic cases develop pigmented remnants PubMed.

14. Cytomegalovirus (CMV)
    CMV anterior uveitis features coin-like or pigmented endothelial lesions often within Arlt’s triangle, especially in older patients PubMed.

15. Rubella Virus
    Fuchs heterochromic iridocyclitis (often rubella-linked) shows diffuse stellate KPs, but occasional wedge-shaped pigmented precipitates can localize in the inferior cornea AAO.

Symptoms Associated with Arlt’s Triangle Pigmented

1. Eye Pain
   A dull ache or sharp pain around the eye results from ciliary muscle spasm and iris inflammation Review of Optometry.

2. Photophobia
   Light sensitivity arises due to irritation of inflamed iris and ciliary body tissues Review of Optometry.

3. Redness (Ciliary Flush)
   Hyperemia around the limbus from inflamed perilimbal vessels gives the classic “red eye” Review of Optometry.

4. Blurred Vision
   Corneal edema or media opacity from KPs and anterior chamber flare reduces image clarity Review of Optometry.

5. Tearing (Epiphora)
   Reflex lacrimation occurs as the inflamed eye attempts to soothe irritation Review of Optometry.

6. Floaters
   Inflammation spill-over into the vitreous can produce moving spots in the visual field Review of Optometry.

7. Halos Around Lights
   Corneal edema from endothelial dysfunction causes diffraction of light, producing colored rings Review of Optometry.

8. Mucous Discharge
   Chronic inflammation may lead to sticky, mucous discharge coating the lashes canadianjournalofophthalmology.ca.

9. Headache
   Periocular pain often extends as a headache due to shared innervation pathways Review of Optometry.

10. Pupil Irregularity
    Posterior synechiae (iris-lens adhesions) from inflammation can distort pupil shape and responsiveness canadianjournalofophthalmology.ca.

Diagnostic Tests

Physical Examination

1. Slit-Lamp Biomicroscopy
   Uses a focused beam of light and microscope to visualize KPs, flare, and Arlt’s triangle directly EyeWiki.

2. Visual Acuity Testing
   Measures clarity of vision to gauge functional impact of anterior chamber inflammation Review of Optometry.

3. Tonometry
   Checks intraocular pressure, as uveitis can cause both spikes (from trabeculitis) and drops (from ciliary shutdown) Review of Optometry.

4. Pupil Examination
   Assesses for irregular shape or poor dilation due to synechiae, indicating chronic inflammation canadianjournalofophthalmology.ca.

Manual Tests

5. Gonioscopy
   A mirrored lens manually placed on the eye to inspect the anterior chamber angle for peripheral anterior synechiae or neovascularization Lippincott Journals.

6. Van Herrick’s Test
   Estimates peripheral anterior chamber depth by comparing corneal thickness to anterior chamber space, assessing angle closure risk Lippincott Journals.

7. Seidel’s Test
   Applies fluorescein dye and cobalt blue light to detect any aqueous leak from corneal perforations or postoperative wounds Lippincott Journals.

8. Iris Transillumination
   Shines a bright light through the iris to reveal defects or atrophy, aiding in diagnosing pigment dispersion and viral iridocyclitis OphthoGenie.

Laboratory & Pathological Tests

9. Complete Blood Count (CBC)
   Evaluates systemic inflammation, anemia, or infection markers that may underlie granulomatous uveitis educate.choroida.com.

10. Angiotensin-Converting Enzyme (ACE) Level
    Elevated in sarcoidosis; supports diagnosis when correlated with ocular findings educate.choroida.com.

11. Syphilis Serology (VDRL/RPR & FTA-ABS)
    Detects Treponema pallidum infection; essential in granulomatous anterior uveitis work-up educate.choroida.com.

12. Polymerase Chain Reaction (PCR) of Aqueous Humor
    Identifies viral DNA (HSV, VZV, CMV, rubella) to confirm viral anterior uveitis PubMed.

Electrodiagnostic Tests

13. Electroretinogram (ERG)
    Measures retinal function; may show indirect effects of chronic inflammation Wikipedia.

14. Visual Evoked Potential (VEP)
    Assesses optic nerve and visual pathway integrity, useful if inflammation extends posteriorly Wikipedia.

15. Electrooculogram (EOG)
    Tests the retinal pigment epithelium function; can detect subtle chronic changes from uveitis Wikipedia.

16. Multifocal ERG
    Maps localized retinal function; helps evaluate macular involvement in chronic cases Wikipedia.

Imaging Tests

17. Anterior Segment Optical Coherence Tomography (AS-OCT)
    Provides cross-sectional images of the cornea and anterior chamber to visualize precipitates and membranes Lippincott Journals.

18. Ultrasound Biomicroscopy (UBM)
    High-frequency ultrasound imaging of the anterior segment, detailing angle structures and ciliary body changes Lippincott Journals.

19. B-Scan Ocular Ultrasound
    Assesses vitreous and posterior segment for spillover inflammation when media are opaque canadianjournalofophthalmology.ca.

20. Fundus Fluorescein Angiography (FFA)
    Visualizes retinal vasculature leakage or ischemia in chronic uveitis, indicating posterior involvement Lippincott Journals.

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Last Updated: July 13, 2025.