Corneal Surgeries

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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). Diagram comparing PKP, DALK, DSAEK, and DMEK procedures

⭐ 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:
FeatureDALK (Deep Anterior)DSAEK (Descemet's Stripping Automated Endothelial)DMEK (Descemet's Membrane Endothelial)
Layers ReplacedStroma (to DM)Endothelium, DM, Post. StromaEndothelium, DM only
Key IndicationsKeratoconus, Ant. Stromal OpacitiesFuchs' dystrophy, PBK, Endo. DysfunctionFuchs' dystrophy, PBK (best VA)
Visual RecoverySlowerFaster than DALK/PKPFastest, near anatomical
Rejection RiskLow (stroma)Low (endo)Lowest (endo)

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).
TechniqueMechanismProsCons/Notes
LASIKFlap + excimer laser stromal ablation.Rapid recovery, less pain.Flap risks, dry eye.
PRKEpithelium removed, excimer laser on anterior stroma.No flap, for thin corneas/contact sports.Slower recovery, pain, haze risk.
SMILEFemtosecond lenticule extracted via small incision.Flapless, less dry eye, biomechanically strong.Myopia/astigmatism only; learning curve.

⭐ 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.

Practice Questions: Corneal Surgeries

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A patient presents with eye pain, redness, and blurred vision after sleeping in contact lenses. Fluorescein staining reveals a corneal ulcer. What is the most appropriate management?

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Flashcards: Corneal Surgeries

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What is the first line treatment of periocular BCC?_____

TAP TO REVEAL ANSWER

What is the first line treatment of periocular BCC?_____

Mohs micrographic surgery or wide surgical excision with frozen section margin control

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