Ortho-k for Myopia Control
Pediatric Eye Clinic
More than a decade ago, several eye care clinicians initially suggested that ortho-k lenses potentially could be used to control or even halt myopia progression. Then, in 2004, the results from the first report on ortho-k for myopia control––the Children’s Overnight Orthokeratology Investigation (COOKI) pilot study––were published. COOKI researchers evaluated refractive error, visual changes and ocular health for six months in myopic children who were fit with overnight ortho-k lenses. The researchers determined that overnight ortho-k was both a safe and effective treatment for curtailing myopia progression.
In 2005, data from the Longitudinal Orthokeratology Research in Children (LORIC) study indicated that ortho-k was effective at controlling childhood myopia.30 However, the researchers also determined that substantial anatomic variations among children can reduce the clinician’s ability to accurately predict final visual outcome before starting ortho-k therapy.
A) Optimally centered fit of an ortho-k lens.
B) Cornea following optimally centered lens removal. Note virtually no trace of an impression ring.
C) Superior-nasal decentered fit of an ortho-k lens.
D) Impression ring following decentered lens removal.
Results from more recent clinical trials, such as the Stabilizing Myopia by Accelerated Reshaping Technique (SMART) study and the Corneal Reshaping and Yearly Observation of Myopia (CRAYON) study, have yielded additional information regarding the safety and efficacy of ortho-k for myopia control.
SMART, a five-year study initiated in 2009, currently is evaluating the effect of ortho-k on myopia progression in 138 patients. At one-year follow-up, subjects wearing ortho-k lenses exhibited a mean progression of 0.00D, compared to an average of 0.50D in the control group.
In the two-year CRAYON study, researchers confirmed that patients who were fitted with ortho-k lenses experienced significantly less annual change in axial length and vitreous chamber depth than patients fitted with soft contact lenses.32 These results confirmed data from previous studies by showing that ortho-k lenses slow the progression of corneal changes in myopic patients.
Recently, there has been suggestion of low-level myopic orthokeratology with the use of a high-modulus silicone hydrogel lens intentionally worn in an everted position. The everted wear of a high-minus silicone hydrogel contact lens can induce alterations in corneal topography and subjective refraction. These refractive change range from plano to +1.75D sphere and +0.25D to +0.75D cylinder, but are unpredictable and vary from subject to subject.
In one study, the mean apical topographic power change was 1.11D with slight corneal steepening in both meridians as well as 0.23mm of corneal flattening in the horizontal meridian and 0.27mm of corneal flattening in the vertical meridian. Additionally, corneal eccentricity decreased by an average of 0.65e. These results suggest that this ortho-k technique may be suitable for patients with very low myopia.
Pediatric Eye Clinic.
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