Orthokeratology (Ortho-K): Reverse Geometry Lenses, Corneal Reshaping, and Myopia Control

What Is Orthokeratology?

Orthokeratology (Ortho-K) is a non-surgical technique that uses specially designed reverse geometry gas permeable contact lenses worn overnight to temporarily reshape the cornea. The patient removes the lenses upon waking and experiences clear vision throughout the day without glasses or contact lenses. The corneal reshaping effect is temporary and reversible; if the patient stops wearing the lenses, the cornea gradually returns to its original shape.

Reverse Geometry Lens Design

Ortho-K lenses differ fundamentally from standard GP lenses in their curve structure. A standard GP lens has progressively flatter curves from center to edge. A reverse geometry lens has:

• Central base curve (treatment zone): Flatter than the central cornea, designed to apply gentle hydraulic pressure that flattens the central epithelium
• Reverse curve: Steeper than the base curve, creating a reservoir that pulls the mid-peripheral cornea steeper (this is the "reverse" that gives the lens its name)
• Alignment curve: Matches the mid-peripheral corneal curvature for lens stability
• Peripheral curve: Provides edge lift for tear exchange

Mechanism of Corneal Reshaping

The reshaping process involves epithelial redistribution, not stromal molding:

• The flat base curve creates positive hydraulic pressure on the central corneal epithelium
• Central epithelial cells are gently compressed and migrate outward toward the mid-periphery
• The reverse curve zone creates negative pressure that draws epithelial cells toward it, causing mid-peripheral thickening
• The result is a flatter central cornea that reduces myopic refractive error
• The effect develops over 1-2 weeks of overnight wear and stabilizes

The stromal layer is not permanently altered, which is why the effect reverses when lens wear is discontinued.

Clinical Applications

Myopia Correction

• Effective for myopia up to approximately -6.00 D, with most predictable results in the -1.00 to -4.00 D range
• Low amounts of astigmatism (up to -1.50 D) can also be managed
• Higher corrections require more aggressive corneal reshaping and may have less stable results

Myopia Control

Ortho-K has become a major tool for slowing myopia progression in children:

• The corneal reshaping creates a multifocal corneal profile with central flattening and mid-peripheral steepening
• This profile creates peripheral myopic defocus, which is believed to slow axial elongation of the eye
• Studies demonstrate 40-60% reduction in myopia progression compared to standard optical correction
• Particularly valuable for children ages 8-14 when myopia progresses most rapidly

Patient Selection

Good Ortho-K candidates typically:

• Have low to moderate myopia (-1.00 to -4.00 D for best results)
• Have low astigmatism (<1.50 D)
• Have healthy corneas with adequate corneal curvature and thickness
• Are motivated to wear lenses every night consistently
• Are comfortable with GP lens handling
• Want freedom from daytime correction (athletes, swimmers, dusty environments)

Fitting and Follow-Up

• Topography-guided fitting: Corneal topography maps are essential for lens design and monitoring treatment effect
• Post-wear topography: A "bull's eye" pattern showing central flattening with a mid-peripheral ring of steepening confirms proper treatment
• Over-correction initially: Some practitioners target slight over-correction initially because the effect partially regresses during the waking hours
• Follow-up schedule: 1 day, 1 week, 1 month, then every 3-6 months to monitor corneal health and treatment stability

Safety Considerations

• Ortho-K involves overnight GP lens wear, which carries inherent risks of microbial keratitis
• Proper lens care and hygiene are essential
• Children wearing Ortho-K need careful parent supervision of lens care routines
• Regular follow-up appointments are critical for monitoring corneal health
• The lenses must be high-Dk GP materials to ensure adequate overnight oxygen supply

Key Takeaways

• Ortho-K uses reverse geometry GP lenses worn overnight to temporarily flatten the central cornea
• The reverse curve is the key design feature that creates the hydraulic forces for epithelial redistribution
• The effect is reversible; consistent nightly wear is required for maintained correction
• Effective for myopia up to approximately -6.00 D, with best results in -1.00 to -4.00 D
• A major myopia control tool for children, reducing progression by 40-60%
• Topography is essential for fitting and monitoring treatment effect