Slowing Myopia Progression
Why is Ortho K recommended?
Ortho K now allows our optometrist eye doctors to correct a person or child’s sight without the need for glasses or contact lenses throughout the day. There are 2 benefits:
1/ The person or child will have natural clear vision throughout the day.
2/ Studies have shown that the treatment produced in orthokeratology also helps to slow down the progression of short-sightedness commonly seen in children and young adults between age 6 and 21.
Myopia in Children
Short-sightedness or myopia is known to progress at a constant rate of between -0.50 to -1.50 diopters on an annual basis until age 18-21. This is due to the child being at an age where the eyes are still developing and growing.
When is Ortho K recommended?
When the goal is to treat and slow myopia progression in children, then Ortho K is recommended as early as possible, usually from age 6 onwards if the child has developed myopia and is wearing glasses full time. In some instances, an established rate of change in a child is ideal which can occur over periodic visits every 6 months, however in cases of high risk of progression, I.e. when one or both parents are moderately myopic, over -4.00, then it is appropriate to consider commencing ortho K as soon as possible.
When the goal is to treat an adult with myopia, and eliminate the need for glasses or contact lenses throughout the day, the person may be of any age and can commence at any time. There is a period of transition usually between 1-2 weeks where the vision may be weak. It is recommended then that ortho K is commenced when the adult does not have any critical tasks to perform over that period.
The science behind Ortho K
It is now understood that vision correction with spectacle lenses and contact lenses for a child developing myopia will cause myopic progression. Studies have shown that these types of corrective lenses produce a hyperopic defocus in the periphery of the retina (Figure 2, meaning that the image of the world focusses beyond the plane of the peripheral retina.) This produces a stimulus that focusses outside and beyond the retina, thus causes the retina to elongate in an attempt to emmetropise (neutralise) itself to see the image more clearly. In doing so, it elongates the entire retina and sclera, causing a higher degree of myopia at the macula. In traditional scenarios, optometrists have corrected this with new increased prescription spectacles, which repeats the stimulus of peripheral hyperopic defocus, causing further elongation and change in another year’s time.
In orthokeratology, we are able to manipulate the peripheral image to alter the stimulus from a hyperopic defocus to a peripheral myopic defocus (Figure 3, meaning that the image of the world now focusses in front of the plane of the peripheral retina.) The retina again undergoes emmetropisation (neutralisation) in the periphery, however this time, instead of elongating to do so, it needs to reduce its length to so, which therefore helps to retard the progression of short-sightedness or myopia in children.
This effect is less seen in adults as the flexibility or rigidity of our eyes are such that we tend not to see progressing myopic adults.