Chemical injury and surface preservation

Chemical Ocular Injuries: Pathophysiology, Grading & Management

Chemical trauma accounts for up to $18\%$ of all ocular trauma presentations. It represents a true ophthalmic emergency where immediate treatment precedes any visual acuity testing or formal examination.

Pathophysiological Divergence: Alkali vs. Acid

Clinical Classification Systems: Roper-Hall vs. Dua

The prognosis of chemical ocular trauma depends directly on the extent of limbal ischemia (which destroys the limbal stem cells responsible for corneal epithelial renewal) and corneal stromal clarity.

Roper-Hall Classification (Modification of Ballen):

• Grade I: Corneal epithelial damage only; no limbal ischemia. Prognosis: Excellent.
• Grade II: Cornea hazy, but iris details remain distinctly visible; $<1/3$ limbal ischemia ($<4$ clock hours). Prognosis: Good.
• Grade III: Total corneal epithelial loss; stromal haze obscuring fine iris architecture; $1/3$ to $1/2$ limbal ischemia ($4-6$ clock hours). Prognosis: Guarded; high risk of recurrent erosion, neovascularisation, and visual reduction.
• Grade IV: Cornea completely opaque, obscuring view of iris and pupil; $>1/2$ limbal ischemia ($>6$ clock hours); significant ischaemic blanching of conjunctival and episcleral vasculature. Prognosis: Very Poor; high likelihood of corneal perforation, phthisis bulbi, and persistent limbal stem cell deficiency (LSCD).

Dua Classification (Modern Standard for Precision):

The Dua classification grades injury from Grade I to VI based on clock hours of limbal involvement and the exact percentage of bulbar conjunctival involvement:

• Grade I: $0$ clock hours limbal involvement; $0\%$ bulbar conjunctival involvement. Prognosis: Very Good.
• Grade II: $\le 3$ clock hours limbal involvement; $\le 30\%$ conjunctival involvement. Prognosis: Good.
• Grade III: $>3$ to $6$ clock hours limbal involvement; $>30\%$ to $50\%$ conjunctival involvement. Prognosis: Good.
• Grade IV: $>6$ to $9$ clock hours limbal involvement; $>50\%$ to $75\%$ conjunctival involvement. Prognosis: Guarded to Poor.
• Grade V: $>9$ to $<12$ clock hours limbal involvement; $>75\%$ to $<100\%$ conjunctival involvement. Prognosis: Poor.
• Grade VI: Total limbal ischemia ($12$ clock hours); $100\%$ bulbar conjunctival involvement ("porcelain cornea and dead white eye"). Prognosis: Very Poor.

Acute Emergency & Medical Management Protocol

1. Immediate Copious Emergency Irrigation:

   • Instill topical local anesthetic (e.g., proxymetacaine $0.5\%$) immediately.
   • Irrigate copiously with 1 to 2 litres of isotonic saline, balanced salt solution (BSS), or Ringer lactate using a Morgan lens or IV giving set for at least 15 to 30 minutes.
   • Neutralization Endpoint: Measure pH in the inferior fornix using litmus or indicator paper. Irrigation must continue until a neutral pH of 7.0 to 7.2 is achieved. Check pH again 5 to 10 minutes post-irrigation to confirm no persistent leaching from hidden reservoirs.
   • Eversion and Debridement: Perform double eversion of the upper eyelid using a Desmarres retractor. Sweep the superior and inferior fornices with a moistened cotton bud to mechanically dislodge entrapped particulate matter (especially calcium hydroxide in lime or cement burns).

2. Phase-Specific Medical Pharmacotherapy:

• Topical steroids: Use early anti-inflammatory treatment with specialist review of epithelial healing, infection and melt risk. Taper is individualised; there is no universal automatic day-ten stop.
  • Ascorbic Acid (Vitamin C): High-dose oral ascorbic acid ($1-2\text{ g daily}$) and topical $10\%$ sodium ascorbate eye drops (every 2 hours). Ascorbate serves as an essential cofactor for prolyl and lysyl hydroxylase, facilitating triple-helix collagen synthesis and reducing stromal ulceration rates.
  • Oral Doxycycline: Administered at $100\text{ mg}$ orally twice daily. Tetracyclines act as potent inhibitors of matrix metalloproteinases (specifically MMP-8 [collagenase-2] and MMP-9 [gelatinase-B]), directly preventing keratolysis and corneal perforation.
  • Topical Sodium Citrate (10%): Chelates extracellular calcium, thereby inhibiting PMN neutrophil membrane activation, respiratory burst, and enzymatic degranulation.
  • Supportive Therapy: Preservative-free artificial tears, therapeutic bandage soft contact lens, prophylactic broad-spectrum topical antibiotics (e.g., fluoroquinolones), and topical cycloplegics (cyclopentolate $1\%$ or atropine $1\%$) to relieve ciliary spasm and prevent posterior synechiae.
  • Surgical Adjuvants: Early amniotic membrane transplantation (AMT) within the first 7 to 14 days acts as an anti-inflammatory, anti-fibrotic substrate that fosters epithelial re-epithelialisation and preserves the limbal microenvironment. For chronic total limbal stem cell deficiency, late autologous or allogeneic stem cell reconstruction—such as Simple Limbal Epithelial Transplantation (SLET) or Cultivated Limbal Epithelial Transplantation (CLET)—is required.