Keratoconus

Keratoconus (KC) is a progressive, non-inflammatory ectatic corneal disorder characterized by thinning and protrusion of the central or paracentral cornea, leading to irregular astigmatism and visual distortion. The condition commonly manifests during puberty or early adulthood and may progress over several years. Understanding the pathophysiology, diagnostic approaches, and full spectrum of therapeutic interventions—ranging from conservative to advanced surgical techniques—is essential for optimizing patient outcomes.

Keratoconus involves biomechanical instability of the corneal stroma due to alterations in collagen fibrils and extracellular matrix degradation. Key pathological features include:

• Stromal thinning
   
• Fragmentation of Bowman’s layer
   
• Apoptosis of keratocytes
   
• Increased matrix metalloproteinase activity
   

Genetic predisposition and environmental factors (e.g., eye rubbing, atopy) contribute to disease onset and progression.

Keratoconus may be classified based on:

• Morphology: Nipple (central), oval (inferior-temporal), globus (>75% of cornea)
   
• Severity (Amsler-Krumeich classification):
   
  • Stage I: < 5 D myopia/astigmatism, K < 48 D
     
  • Stage II: 5–8 D, K < 53 D
     
  • Stage III: 8–10 D, K > 53 D, corneal thinning
     
  • Stage IV: >10 D, scarring, K > 55 D
     

• Placido-based and Scheimpflug imaging (Pentacam, Galilei, Sirius)
   
• Belin/Ambrosio Enhanced Ectasia Display for early detection
   

• CorVis ST, Ocular Response Analyzer to assess deformation response
   

• Quantifies higher-order aberrations (HOAs), particularly vertical coma
   

• Useful in epithelial mapping and pachymetric profiling
   

• Early keratoconus with minimal irregular astigmatism
   

• Improved visual acuity by masking corneal irregularity
   
• May cause lens intolerance with disease progression
   

• RGP center with soft skirt (e.g., SynergEyes)
   
• Enhanced comfort and centration
   

• Vault over the cornea, resting on sclera
   
• Indicated in moderate to advanced cases
   
• Excellent for visual rehabilitation and comfort
   

• Tailored to exact scleral shape via profilometry or impression molds
   
• Incorporation of custom optics addressing high-order aberrations ( with Ovitz or Oculus AXL Wave)
   
• Ideal for irregular corneas with decentered cones or prior surgical scars
   

• Progressive keratoconus with documented topographic worsening
   

• Epithelium-Off (Dresden protocol): Riboflavin + UVA irradiation (3 mW/cm², 30 minutes)
   
• Accelerated Protocols: Higher irradiance for shorter durations
   
• Epithelium-On (Transepithelial): Reduced efficacy, but better comfort and reduced risks
   

• Halts progression in >90% of cases
   
• Modest flattening effect (1–2 D)
   

• Intacs, Ferrara rings, Keraring
   

• Contact lens intolerance
   
• Mild to moderate keratoconus (K < 57 D, clear central cornea)
   
• Residual stromal bed > 450 µm
   

• Mid-peripheral flattening
   
• Improved symmetry and uncorrected visual acuity (UCVA)
   

• Femtosecond laser-assisted or mechanical tunnel creation
   
• Customized planning based on topography
   

• Customized ablation of the corneal apex
   
• Followed by CXL for biomechanical stability
   

• Mild to moderate KC with visual potential
   
• Irregular astigmatism limiting spectacle correction
   

• Improved UCVA and BSCVA
   
• Reduced HOAs
   

• Preserves Descemet’s membrane and endothelium
   
• Indicated in advanced KC with stromal scarring
   
• Better rejection profile compared to PKP
   

• Reserved for full-thickness opacification or failed DALK
   
• Long-term suture management and rejection risk present
   

• Spatially modulated UV exposure
   
• Targeted flattening and regularization
   

• Combined CXL with refractive surgery in early or forme fruste keratoconus (highly controversial)
   

• Biocompatible segments from donor tissue
   
• Alternative to synthetic ICRS in thin corneas
   

Management of keratoconus demands a tailored, patient-centric approach guided by disease severity, progression, and visual demands. Innovations in scleral lens technology, topography-guided interventions, and biomechanical enhancement have transformed the landscape of keratoconus care. As a refractive surgeon, integrating surgical skill with precise optical rehabilitation—particularly using HOA-customized and impression-based lenses—can significantly enhance quality of life for keratoconus patients.