Chemical Injuries

Introduction & Agents - Chemical Chaos Kickoff

• Definition: Ocular trauma from corrosive chemical agents, an emergency.
• Common Acids:
  • Sulfuric acid ($H₂SO₄$)
  • Hydrochloric acid ($HCl$)
  • Acetic acid
• Common Alkalis: (More dangerous)
  • Sodium hydroxide ($NaOH$)
  • Calcium hydroxide ($Ca(OH)₂$) (cement/plaster)
  • Ammonia ($NH₃$)
• 📌 Mnemonic: Acids Coagulate, Alkalis Liquefy. (Explains penetration difference)

⭐ Alkali burns are generally more severe and have a poorer prognosis than acid burns due to their ability to cause liquefaction necrosis and penetrate deeper into ocular tissues.

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Pathophysiology - Burn Breakdown Battle

• Acids:
  • Cause coagulation necrosis.
  • Proteins denature, forming an eschar.
  • This eschar limits deeper penetration.
• Alkalis: 📌 ALKALI = All Layers Kill And Liquefy.
  • Cause liquefaction necrosis.
  • Saponification of fatty acids in cell membranes.
  • Collagen hydration and destruction.
  • Results in rapid and deep penetration.
• Common Sequelae:
  • Stromal melt (via collagenases, MMPs).
  • Limbal stem cell damage (LSCD).

⭐ Alkali burns cause saponification of fatty acids in cell membranes, leading to cell disruption and significantly deeper penetration compared to the protein coagulation and barrier formation seen in acid burns.

Clinical Assessment - Signs, Symptoms & Scales

• Symptoms: Severe pain, photophobia, blepharospasm, ↓ vision, tearing.
• Signs: Conjunctival injection/chemosis/necrosis, epithelial defects, corneal opacification (haze to opaque), limbal ischemia (blanching - key prognostic sign), IOP (initially ↑ or ↓, later often ↑), anterior chamber reaction.

Management - Damage Control Protocol

Immediate:

• IRRIGATION: COPIOUS, 15-30 min (NS, RL, water) until pH $7.0-7.4$. Morgan lens. Remove particles, evert lids.

Medical Therapy: 📌 'LIT WASP'

• Lubricate: Preservative-free.
• Irrigate: (Primary step, already detailed).
• Tetracycline: Doxycycline 100mg BID.
• Witamin C: Oral 1-2 g/day.
• Analgesia / Atropine 1%.
• Steroids: Topical Prednisolone acetate 1%.
• Patch/Pressure (if indicated). Also: Prophylactic antibiotics; Na Citrate 10% (cement); ↓IOP (no PGs); Autologous serum.

Surgical (Severe Cases):

• Debridement, Amniotic Membrane Transplant (AMT), Limbal Stem Cell Transplant (LSCT), Tenoplasty, Tarsorrhaphy, Keratoplasty (delayed).

⭐ Cornerstone: Immediate, prolonged, copious irrigation to normalize ocular pH.

Complications & Prognosis - Aftermath & Future Focus

• Early: Persistent epithelial defect (PED), corneal ulcer/melt/perforation, 2° microbial keratitis, acute glaucoma, uveitis.
• Late: 📌 'SOS DD': Symblepharon, Opacity (corneal & vascularization), Stem cell loss (LSCD), Dry eye, Deformities (lid). Others: chronic glaucoma, phthisis.

  ⭐ Limbal Stem Cell Deficiency (LSCD) is a severe long-term complication, causing corneal conjunctivalization, vascularization, chronic inflammation, and poor vision.

• Prognosis: Chemical type/conc., contact duration, severity of initial limbal ischemia (most critical), pH at presentation, irrigation delay.

High‑Yield Points - ⚡ Biggest Takeaways

• Alkali burns are more severe than acid burns due to saponification and deeper tissue penetration.
• Immediate, copious irrigation (water/saline) for ≥30 minutes is the most critical initial step.
• Check conjunctival fornix pH with litmus paper; target pH 7.0-7.4.
• Roper-Hall classification grades severity and predicts prognosis of chemical eye injuries.
• Major complications: corneal opacity, symblepharon, limbal stem cell deficiency, glaucoma.
• Treatment includes topical steroids, cycloplegics, antibiotics, oral vitamin C, and doxycycline.