Myopia or short-sightedness is one of the visual defects that causes blurred distance vision. It is usually a progressive disorder that increases significantly between the ages of 10-20 years. Myopia progression can happen for a few reasons. Usually it occurs because the eye grows too long and light is not focused correctly onto the retina. Orthokeratology (or Ortho-K) lenses are placed on the cornea (the front of the eye) and worn overnight. These lenses use fluid trapped under the lens to temporarily reshape the cornea. The new corneal shape allows light to be focused correctly onto the retina after the lenses are removed, giving clear unaided vision during the day.
New research indicates that the progression of shortsightedness may be caused by peripheral retinal blur. This new theory states that while glasses and daytime contact lenses focus light accurately on the central retina (ie macula), they do not focus light on the peripheral retina very well. In fact, glasses and daytime contact lenses actually focus light behind the peripheral retina and not on it! New research shows this peripheral defocus will cause the eye to grow longer so that the peripheral retina comes into focus. Unfortunately, this excessive growth of the eyes leads to a progression in myopia.
With Ortho-K lenses, they reshape the front surface of the eye to focus light clearly on both the peripheral and the central retina. Glasses and daytime contact lenses cannot do this. Hence Ortho-K therapy is the most effective method for slowing (or sometimes halting) the progression of myopia.
In 2005, data from the Longitudinal Orthokeratology Research in Children (LORIC) study indicated that Ortho-k was effective in controlling childhood myopia progression. 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. The SMART study, a five-year study initiated in 2009, is currently underway to evaluate the effect of Ortho-k on myopia progression in 138 patients under the age of 15. The results from the first year showed that subjects wearing Ortho-k lenses had no progression in myopia 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. These results confirmed data from previous studies by showing that Ortho-k lenses slow or in some case halt the progression of myopia, in 2011 and 2013 further studies showed 43-64% reductions in the rate of progression compared to control subjects.
At this stage, researchers have also determined that substantial anatomic variations occur among children, which can reduce the clinician’s ability to accurately predict final visual outcome before starting Ortho-k therapy. Therefore we are not currently able to predict what your final prescription will be in 5-10 years, but the evidence is so compelling that we are able to state that with Ortho-k therapy, your final prescription will be significantly less than if only glasses or daytime contacts are prescribed.