Last month we started the conversation about the increasing prevalence of myopia and how environmental factors may play a significant role. This month we will concentrate on some of those factors and what current management options we have.
At birth, the human eye typically has a low amount of hyperopia (farsightedness). Throughout childhood, this hyperopia should reduce to leave a prescription near zero – a process known as emmetropization. If there is some type of disruption or error in this process then the eye is left with a refractive error and requires prescription. What feedback does the eye receive to help this process of emmetropization? Studies have shown that the eye uses defocus to determine whether it’s myopic or hyperopic and alters its growth to achieve the optimal refractive error. So by changing the focus of the eye, we can potentially change the way the eye grows.
Because myopia progression is usually due to the elongation of the eyeball, it is important to study what may trigger this to happen and how we can slow the rate of eye growth. The “peripheral hyperopic defocus” theory advocates that when light rays are focussed in behind the peripheral retina, it stimulates further elongation of the eye. This is the type of image that a nearsighted person can receive when uncorrected, or when corrected with traditional glasses or contact lenses. There is growing evidence to show that if we shift the focusing of the peripheral light rays inwards, it appears to help slow the eye growth and reduce myopia progression. This theory has led to the development of specialty contact lenses and glasses that have been shown to reduce the rate of myopia progression by up to 50-60%. Another method that has been found to successfully slow the rate of eye growth is by chemical means. Atropine eye drops have been used for decades for many eye conditions, and now appear to have a place in helping to slow the progression of myopia as well. While the mechanism is not yet completely understood, it is believed that atropine inhibits special receptors on the sclera and retina to slow the growth of the eye.
What else do we know about myopia progression? Studies have shown that the amount of time spent outdoors is important: myopia is more common in children who spend less time outdoors, and findings seemed to indicate that ensuring at least 2 hours per day of outdoor activity is likely to help prevent the onset of myopia. While the amount of time spent reading or other close work has not been proven to be directly related to the development of myopia, it is generally accepted that it is good practice to take visual breaks, ensure that near activities are not performed too close, and to try and limit near tasks outside of school to 2 hours daily. Inaccurate focussing and eye teaming skills can also play a role in stimulating myopia development, so it is important that these are checked with a complete eye examination.
Being highly nearsighted myself, it is exciting to know that we are making progress in the options for myopia management such that others may not need to follow the same path. At Cowichan Eyecare we are dedicated to staying at the forefront of this ongoing field of study. No longer should we just prescribe simple distance glasses and let myopia development go unchecked. Your optometrist can assess your child’s risk for developing myopia, or their risk for progression of their existing myopia and recommend options for treatment.