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Interstitial Keratitis (IK)

URGENT — Cornea

Symptoms

gradual vision decrease, photophobia, and ocular pain (active)

tearing and redness; often bilateral (e.g., congenital syphilis)

symptoms typically manifest between ages 5 and 20 in congenital syphilis

systemic cues: hearing loss/vertigo (cogan) or skin anesthesia (leprosy)

Clinical Findings

Active phase

  • deep stromal edema with dense limbus-to-limbus haze
  • "salmon patch": pink sector of confluent deep stromal vessels (classic syphilis)
  • anterior chamber reaction (cells/flare) and mutton-fat keratic precipitates

Chronic / inactive phase

  • ghost vessels: pathognomonic empty, non-perfused stromal vessel channels
  • stromal clearing with persistent scarring or "ghost" lines

Hutchinson triad (congenital syphilis)

  • interstitial keratitis
  • sensorineural hearing loss (cn viii deafness)
  • hutchinson teeth: notched, peg-shaped permanent upper incisors

Cogan syndrome

  • autoimmune ik plus acute vestibuloauditory dysfunction (vertigo, tinnitus)
  • medical emergency: hearing loss can become permanent within weeks

Other etiology clues

  • hsv: most common adult cause; usually unilateral and sectoral
  • tuberculosis: unilateral, sectoral, often with peripheral phlyctenules
  • leprosy: "beads on a string" segmental thickening of corneal nerves

Etiology

Pathogenesis

  • non-ulcerative inflammation of the corneal stroma
  • typically a delayed immune-mediated reaction rather than active infection

Primary causes

  • syphilis: congenital (bilateral, 80%) or acquired (unilateral)
  • hsv/vzv: common adult triggers
  • tuberculosis, lyme disease, and ebv
  • autoimmune: cogan syndrome (associated with systemic vasculitis)

Red Flags

cogan syndrome: rapid hearing loss risk; requires high-dose systemic steroids

congenital syphilis stigmata (saddle nose, hutchinson teeth)

active stromal inflammation with neovascularization

corneal thinning or descemetocele formation

Investigations

Clinical diagnostics

  • check corneal sensation and look for madarosis (leprosy)
  • dilated fundus exam: salt-and-pepper chorioretinitis (syphilis)
  • audiology consult if cogan syndrome is suspected

Laboratory workup

  • syphilis serology: fta-abs (treponemal) and rpr/vdrl (activity)
  • tb screen: quantiferon-tb gold or ppd
  • lyme serology in endemic areas

Imaging

  • chest x-ray if tb is suspected; mri/mrv if neurosyphilis is a concern

Treatment

Ocular (active)

  • topical prednisolone acetate 1% (q2–6h) with a slow taper over months
  • topical cycloplegic (atropine 1%) for comfort and synechiae prevention

Systemic (etiology-specific)

  • syphilis: penicillin g iv (id consult for neurosyphilis staging)
  • cogan syndrome: high-dose systemic corticosteroids (urgent hearing rescue)
  • tuberculosis: ripe regimen; lyme: doxycycline or ceftriaxone

Refractive (chronic)

  • rgp or scleral contact lenses for irregular astigmatism from scarring
  • keratoplasty (corneal transplant) for visually significant central scars

Clinical Pearl

Ghost vessels in a non-inflamed deep stroma are a permanent record of old syphilitic or Cogan interstitial keratitis — they need no treatment but always prompt a history of untreated prior infection.

Differential Diagnosis

  • herpes simplex disciform keratitis
  • acanthamoeba keratitis
  • bacterial keratitis
  • syphilitic keratitis

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