Krupa Philip, B.Optom, PhD
Padmaja Sankaridurg, B.Opt, MIP, PhD
Optical strategies such as orthokeratology and multifocal/extended depth of focus soft contact lenses are effective in slowing myopia, and their uptake is on the rise.1-4 In addition to correcting for the myopic refractive error, the lenses aim to control or reduce the hyperopic blur that results at the peripheral retina and/or hyperopic defocus at the central retina that occurs during accommodation. This reduction in hyperopic blur is achieved by having a zone/region/areas that have a power that is relatively more positive than the region that corrects for distance refractive error.
Optical strategies such as orthokeratology and multifocal/extended depth of focus soft contact lenses are effective in slowing myopia, and their uptake is on the rise.1-4
Hyperopic defocus that occurs at the retina with reduced accommodative effort is known as lag; some data indicates myopic eyes have greater or increased lag of accommodation, lower amplitude of accommodation, lower accommodative facility, reduced positive relative accommodation and an increased gradient AC/A ratio compared to non-myopes.5-9. However, other data show no difference in accommodative responses between myopic vs. non-myopic, progressing vs. stable myopes. Furthermore, results were found to vary based on the type of targets, experimental conditions, etc.10-13 Thus, the picture on whether myopic eyes suffer from some form of accommodative dysfunction is not clear. But operating under the assumption that there is hyperopic defocus due to accommodative lag, then the relatively positive power or ‘add’ power present in one or more areas in the multifocal contact lenses or induced as a result of treatment with ortho-k lenses may help to reduce the hyperopic defocus resulting from the accommodative lag and therefore, this should then slow eye growth.