Corneal Surgeries

Keratoplasty Fundamentals - Grafting New Sight

• Corneal transplantation: Replacing diseased cornea with healthy donor tissue to restore vision or integrity.
• Types:
  • Penetrating Keratoplasty (PKP): Full-thickness graft. Versatile for many conditions.
  • Lamellar Keratoplasty (LK): Partial thickness; replaces specific diseased layers.
    • Anterior (e.g., DALK): Replaces stroma, spares host endothelium. For keratoconus, anterior scars.
    • Posterior (e.g., DSAEK, DMEK): Replaces diseased endothelium. For Fuchs' dystrophy, bullous keratopathy.
• Indications: Optical (vision), tectonic (support), therapeutic (infection), cosmetic.
• Graft Rejection: Immune response to donor. Types: Epithelial, Stromal, Endothelial (Khodadoust line).

⭐ Khodadoust line: Linear endothelial precipitates, a classic sign of endothelial graft rejection, crucial for early diagnosis.

Lamellar Keratoplasty - Precision Layer Repair

• Selectively replaces diseased corneal layers, sparing healthy host tissue. Offers faster visual recovery, stronger wound, ↓ rejection risk vs. Penetrating Keratoplasty (PKP).
• Types & Key Features:

⭐ DMEK offers the best visual acuity and lowest rejection rates among endothelial keratoplasties due to minimal tissue transplantation.

Refractive Surgeries - Focus Perfected

• Goal: Correct refractive errors (myopia, hyperopia, astigmatism) by reshaping cornea.
• Pre-op: Pachymetry, topography. Aim for >250 µm residual stromal bed (RSB).

⭐ Munnerlyn's formula is crucial for determining excimer laser ablation depth.

• Formula: $t = S^2 \times D / 3$ ($t$=ablation depth µm, $S$=optical zone mm, $D$=diopters).
• Contraindications: Unstable refraction, keratoconus, thin corneas, active autoimmune disease.

Other Corneal Procedures - Shield & Strengthen

• Corneal Cross-Linking (CXL):
  • Halts progressive ectasia (e.g., keratoconus, post-LASIK ectasia).
  • Mechanism: Riboflavin (Vit B2) + UVA (365 nm) light → stiffens cornea by forming new collagen cross-links.
  • Key: Min. stromal thickness 400 µm (epithelium-off technique).
• Pterygium Excision:
  • Indications: Visual impairment, significant astigmatism, chronic inflammation, documented growth, cosmesis.
  • Best: Excision + Conjunctival Autograft (CAG) for ↓ recurrence rates.
  • Adjuncts (reduce recurrence): Mitomycin C (MMC), β-irradiation.
• Corneal Tissue Adhesives / Glue:
  • For small corneal perforations (<2-3 mm) or impending perforations (descemetoceles).
  • E.g., Cyanoacrylate glue.
• Amniotic Membrane Transplantation (AMT):
  • Promotes epithelialization, reduces inflammation & scarring.
  • Uses: Persistent epithelial defects, neurotrophic keratopathy, chemical burns, Stevens-Johnson Syndrome.

⭐ In Corneal Cross-Linking (CXL), the Dresden protocol is the standard epi-off technique, requiring a minimum corneal thickness of 400 µm after de-epithelialization to protect underlying structures like endothelium and lens from UVA toxicity.

High‑Yield Points - ⚡ Biggest Takeaways

• Penetrating Keratoplasty (PKP): Full-thickness graft for advanced keratoconus/scars; high astigmatism risk.
• DALK: Spares endothelium, reducing rejection; for anterior stromal opacities.
• DSEK/DSAEK: For Fuchs' dystrophy/PBK; replaces diseased endothelium; faster visual recovery.
• DMEK: Best visual acuity in endothelial keratoplasty; technically challenging.
• LASIK: Flap-based refractive surgery; dry eye is a common side effect.
• PRK: Surface ablation for refractive errors; no flap, but risk of corneal haze.
• CXL: Halts keratoconus progression using riboflavin and UV-A light.