01/13/2025
Design and Theory Differences Between Hyperopic and Myopic Orthokeratology
Myopic orthokeratology (MOK) is widely used, while hyperopic orthokeratology (HOK) is less understood due to limited research. HOK design is essentially the inverse of MOK, targeting opposite corneal changes and refractive corrections. Advanced tools like 2D/3D corneal topography and custom software now help clarify these design differences.
Methods
Custom orthokeratology lenses were created for a myope (-3.00D) and a hyperope (+3.00D). Results were analyzed using:
Software lens curvatures and simulated tear film thickness
Fluorescein lens evaluation
Scheimpflug tomography and 3D Placido-disc topography
Results
Both HOK and MOK lenses achieved 20/20 vision, well-centered treatment zones, and good post-treatment physiological health.
MOK: Forces applied outward toward a single mid-peripheral fluid reservoir compressed the central cornea and thickened the mid-periphery.
HOK: Forces applied inward and outward toward two fluid reservoirs compressed the mid-periphery and thickened the central cornea.
Discussion
HOK thickens and steepens the central cornea to create a convex lens (plus power), while MOK flattens the central cornea for a concave lens (minus power). Though inverse in philosophy, both require precise peripheral lens alignment and centration for success.
HOK forms a central reservoir, shallower than MOK’s mid-peripheral reservoir, and uses a wider return zone to gradually thicken the central cornea. Mid-peripheral compression further emphasizes the convex reshaping.
Both HOK and MOK share similar edge lift designs, ensuring safe fits with adequate lens movement, no punctate staining, and no lens binding. These lenses can be designed using conventional corneal or translimbal orthokeratology techniques.
Success in orthokeratology depends on understanding corneal reshaping forces and lens design. Visualizing changes through fluorescein evaluation and post-wear topography supports optimal results, enabling more patients to benefit from this advanced treatment.
