BY KENNETH DANIELS, OD, FAAO
As myopia among children is being described as ‘epidemic,’ a variety of techniques for treating them are coming to the forefront.A 6-year- old Asian female who presented for an exam already had –1.00D of myopia, and both her parents were significantly myopic. As studies have shown, early manifestations of myopic refractive error and the number of myopic parents are significant predictors of the child’s risk of myopia progression. Her young age and the onset of myopic shift related to refractive error and axial length before the onset of juvenile myopia.
The clinical question we have with this patient: What options do we have for slowing this patient’s myopic progression?
We could obviously prescribe glasses to correct the presenting ametropia and re-evaluate in six months, or flat-top bifocals or progressive addition lenses could be used to relax accommodative stress. However, these options will not have a lasting effect on myopic progression, delaying it by only 0.25D to 0.50D.
We could also consider using atropine in conjunction with corrective spectacle lenses. Studies suggest that might be appropriate, particularly if the child is not ready to be fit with contact lenses.
There are also behavioral modifications, such as an extra 40 minutes of time outdoors, which research shows can reduce the progression of myopia, and following the 20-20- 20 rule (a 20-second break to view something 20 feet away every 20 minutes) to reduce eyestrain from increased use of digital devices.
The other option: using contact lenses to halt the progression of myopia.
The simple essence of myopia control is to focus all incoming images into the fovea centralis and bring parafoveal defocused images (the image shell) into focus to prevent accommodative stress.
The goal of a proper contact lens design is to control the stress of accommodation in which the eye tries to refocus the image shell. The result of this stress is increased axial length of the eye, which causes myopia to progress.
Standard gas permeable contact lenses cannot control this stress successfully because the basic lens design only provides refractive correction. To control accommodative stress, a gas permeable design requires central cornealepithelial compression, with the spread of the tissue to the periphery. This allows the paracentral region to refocus the image shell onto the peripheral parafoveal retina.
Standard gas permeable designs do not provide significant control of axial length and myopic progression. Myopia control with orthokeratology, however, is highly achievable.
Orthokeratology dates back more than 70 years. Eyecare practitioners used a progression of polymethyl methacrylate (PMMA) lenses in a sequentially flatter base curve to compress the central cornea.
As we approached the mid-1990s, manufacturers began using more advanced lathe and computer designs, which enabled them to take the original reverse peripheral curve lenses developed in the 1980s and advanced the study of orthokeratology. This led us to the “modern day” reverse geometry accelerated corneal reshaping with overnight ortho-k lenses.
There are a variety of orthokeratology lenses for controlling myopia. Each has a unique design but follows similar concepts of method. Ortho-k can reduce theamount of myopic refractive error and affect the progression of myopia as a childages.
SOFT CONTACT LENS
But, can a child at a younger age, such as my 6-year- old patient, perform the task of contact lens insertion, removal and care? This patient and even an older child may initially do better with a soft contact lens. However, there is a problem. Standard soft lenses only prolong the issue of myopia progression rather than cause a clinically relevant decrease.
A distance-center multifocal soft contact lens may be the best place to start because it can result in 50% reduction in the progression of myopia and a 29%re-duction in axial elongation, suggesting the potential for soft multifocal contact lens myopia control.
Two designs from CooperVision, the Proclear and Biofinity Multifocal, allow for adistance zone of 75% of the child’s average pupil. The peripheral region of the lenses, which progress to intermediate and near plus power, refocus the image shell for the para visual axis rays. This allows for sustained myopic defocus (refocusing of the image shell) and can slow myopia progression without compromising visual function even when presented to the retina simultaneously with a clear image. When fitting this design, I tend to use a multifocal add power of no less than +1.50D to +2.00D (“D” design), with the appropriate distance power centrally.
CooperVision also has entered the arena of myopic control with the MiSight daily disposable myopia control contact lens, which has alternating visual correction and treatment zones. A study comparing this lens to a single-vision daily dispos-able contact lens in 144 myopic children demonstrated that the dual-focus lenseffectively slowed myopic progression by 59%, as measured by cycloplegicrefraction, and 52%, as measured by mean axial elongation of the eye.
Another new entry to the market is the NaturalVue Multifocal 1 Day Contact Lenses with Neurofocus Optics from Visioneering Technologies, Inc. The lens isdesigned to provide spectacle-level stereo acuity and vision at near, intermediateand at a distance. A study from the University of Waterloo found the lens designs of–10.00D led to nearly complete inhibition of defocus-induced myopia in chickens compared to control lenses (also –10.00D).
The lack of significant axial length increase seen with the NaturalVue test groups indicates that these lens designs reduced the progression of defocused-induced myopia by inhibiting axial elongation. The optical design suggests a reduction inaccommodative lag, another risk factor for myopia progression, while having minimal effect on visual acuity, PREP score quality of life and MN-READ scoresin children of the age that myopia progresses quickly. They found in additionalstudies that the corrected peripheral hyperopia so that each meridian was focused within the retina, an improved amplitude test accommodation by 1.00 Dimproved lag of accommodation by 0.50D. Visual quality was rated as the same or better visual quality as compared with a single vision soft lens.
Myopia control is a complex management decision based on many factors. Theprimary factors are the awareness and con-cern of the parents, while otherconcerns are the capabilities and understanding of the child. Each approachmust be planned from a long term perspective using a building block approach.