Orthokeratology (ortho-k) uses GP lenses to reshape the cornea, primarily for myopia correction. Traditionally, ortho-k allowed adults to shed daytime corrective lenses. This technology is now also recognized as a safe and effective method for decreasing myopia progression in both children and adolescents.
Ortho-k lenses for myopia management should center well, and patients should be able to see their best-corrected visual acuity out of the lenses. After lens removal, the topography map should show a classic bull’s-eye pattern of an even, flattened treatment zone and a steepened reverse curve zone centered within the pupillary circumference. Proper centration of the reverse zone generates peripheral defocus completely inside of the pupil, thereby optimizing myopia retardation. Adjacent to the steepened reverse zone, a more pronounced flattened area 360º around should be visible, which represents adequate alignment and applanation of the alignment curve within the peripheral cornea.
Toric Ortho-k Lenses
Spherical ortho-k lenses on limbus-to-limbus, against-the-rule, or higher astigmatic corneas usually result in poor centration, leading to induced irregular astigmatism, glare, and poor visual outcome. Ortho-k mechanisms of action include a combination of central positive and midperipheral negative pressure forces (Mountford et al, 2004). This requires peripheral landing 360º around between the lens and the cornea to prevent tear film squeeze forces from escaping along the steepest meridian in an astigmatic eye. Thus, a toric ortho-k lens is the only option for correction of myopes who have limbus-to-limbus astigmatism (Korszen and Caroline, 2017; Chan et al, 2009). Corneal topography is used to determine whether a toric design is indicated. A sagittal height difference between the flat and steep corneal meridians of 30 microns or greater at the landing chord length of the alignment curve suggests that the treatment may benefit from adding lens toricity (Kojima et al, 2016).
A Case in Point Consider a 13-year-old Hispanic male who has a history of progressive myopia. This young man presented with a manifest refraction of –2.25 –1.25 x 180 in the right eye and –3.00 –1.50 x 180 in the left eye. He was originally fitted into a spherical ortho-k lens that resulted in poor treatment of both eyes (Figure 1). The patient was refitted into a toric ortho-k lens that gave him a best-corrected daytime vision of 20/20 and adequate treatment for myopia control in both eyes (Figure 2).
Effective for More Patients
Ortho-k can effectively stunt myopia in children. If treatment with spherical lenses is inadequate and/or corneal topography reveals peripheral astigmatism, toric ortho-k lenses may be indicated. While adding toricity modestly increases the complexity of the fit, the results are more than worthwhile. CLS
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