OcuLearning › Trauma

Corneal and Conjunctival Foreign Bodies

URGENT — Trauma

Symptoms

Foreign body sensation.

Tearing and redness.

Pain.

Clinical Findings

FB and rust ring

  • Presence of conjunctival or corneal foreign body on slit lamp.
  • Rust ring (iron/steel): begins within 3–4 hours; fully developed by 12–24 hours.

Subtarsal FB signs

  • Vertical linear corneal abrasions or "ice-skating rink" SPK pattern.
  • Mandates single or double upper-lid eversion to inspect the tarsal conjunctiva and superior fornix.

Associated signs

  • Conjunctival injection and lid edema.
  • Mild anterior chamber (AC) reaction.
  • Small reactive/sterile infiltrate may surround an embedded FB.

High-velocity red flags (suggest occult IOFB)

  • Microhyphema or pupil peaking/irregularity.
  • Iris transillumination defects or lens capsule perforation.
  • Shallow or asymmetrically deep AC; low IOP in the affected eye.
  • Any Seidel-positive wound.

Etiology

Mechanisms

  • Metal grinding or hammering: highest risk for intraocular foreign body (IOFB).
  • Organic matter, glass, or insect parts: common in the superior fornix.

Complications

  • Retained iron leads to rust ring formation.
  • Organic material carries a high risk of fungal keratitis.

Red Flags

High-velocity injury (metal-on-metal) → occult IOFB; obtain CT orbits.

Seidel-positive wound with iris prolapse → open globe; use shield and prepare for surgery.

Vegetable/organic material → high fungal risk; requires prolonged monitoring.

Persisting rust ring → remove with burr at 24 hours to prevent scarring.

Investigations

Clinical assessment

  • Document visual acuity before any procedure.
  • Slit-lamp exam: assess FB depth, entry sites, and AC reaction.
  • Check for pupil peaking, iris tears, or lens opacities.
  • Measure IOP: look for asymmetrically low pressure.

Lid eversion

  • Evert eyelids and inspect fornices (Desmarres retractor for double eversion if necessary).
  • Inspect conjunctival lacerations to rule out underlying scleral perforation.

Imaging and dilation

  • Perform dilated fundus exam to rule out posterior segment IOFB.
  • CT orbits (1-mm thin cuts; axial, coronal, and parasagittal): preferred for IOFB.
  • B-scan or UBM: if the view is hazy or to localize scleral wounds.
  • WARNING: avoid MRI if a metallic FB is possible.

Treatment

Corneal FB

  • Remove with FB spud, jeweler's forceps, or needle at the slit lamp.
  • For multiple superficial FBs, consider saline irrigation.
  • Diagram the dimensions of the resulting epithelial defect.

Conjunctival FB

  • Remove with a cotton-tipped applicator or irrigation under topical anesthesia.

Pharmaceuticals

  • Topical antibiotic prophylaxis until the epithelium heals.
  • Update tetanus immunization.

Clinical Pearl

Always evert the upper lid; a hidden subtarsal foreign body will continue to scratch the cornea despite optimal drops and a "normal" primary gaze exam.

Differential Diagnosis

  • Corneal abrasion
  • Corneal ulcer
  • Subtarsal foreign body
  • Metallic rust ring

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