Orthokeratology (Ortho-K) for myopia control works through which optical mechanism to reduce myopia progression?

• A Corneal flattening reduces accommodative demand, decreasing convergence-driven axial growth
• B Flattening the central cornea creates relative peripheral myopic defocus that slows axial elongation ✓
• C Contact lens wear overnight increases choroidal thickness by increasing choroidal blood flow
• D Tear film redistribution under orthokeratology lens creates hypoxia that inhibits scleral remodelling

Explanation

Ortho-K lenses flatten the central cornea and simultaneously steepen the mid-peripheral cornea. This creates central emmetropia (clear vision) with relative peripheral myopic defocus — the peripheral image falls in front of the retina. According to the defocus theory of emmetropization, peripheral myopic defocus signals the eye to slow axial elongation (opposite effect to peripheral hyperopic defocus, which drives axial growth in myopia). Clinical trials show Ortho-K reduces axial elongation by ~40–50% compared to single-vision spectacles.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.