Myopia or nearsightedness, a vision condition in which close objects are seen clearly, but objects farther away appear blurred, is extremely prevalent in our society and appears to be on the rise. A recent article estimated the prevalence of myopia in people aged 12 to 54 increased from 25 percent in the years in the early 1970s, to 41.6 percent in the years 1999 to 2004.
Now, a new study suggests that treating myopia early with bifocal lenses—glasses that use two corrective powers in each lens–instead of single-vision lenses may slow progression of the eye condition in children.
Many factors are felt to contribute to myopia, most important being genetic factors. Children who are myopic generally have parents who are myopic.However, environmental factors are possible contributors and attempts are being made to alter these to slow the progression of myopia.
One consideration is if computers or reading are causes of the increased incidence of myopia. As a possible explanation for this, we consider if prolonged focus (accommodation) changes the length of the eye. This theory serves as the basis for a recent study published in Archives of Ophthalmology.
The study recruited Chinese-Canadian children from age 8 to 13 with mild to moderate myopia. The patients were selected if they had evidence of a mild increase in myopia during the year prior to enrollment.
The children were randomized to one of three treatment groups: single vision lenses (standard treatment), or to one of two types of bifocal lenses. Adding a bifocal to their myopic correction theoretically decreases the amount of focusing necessary to see clearly up close.
Their results showed a statistical benefit to the use of the bifocal lenses over single vision lenses in decreasing the progression of myopia during a two-year period. We don’t know if this benefit would last if the patients were followed for a longer period of time.
The eyes treated with bifocals did show less eye growth than single vision lenses. The theory of increased focusing resulting in increased myopia warrants more investigation.
The difference in myopic progression between bifocal versus single vision lenses was small. This may alter how much an eyeglass prescription changes yearly but it will not eliminate the need for glasses.
The authors admit the modest benefit seen in their study needs to be weighed against the increased cost of bifocal glasses, the appearance of the bifocal and the attitudes of the patient and their family to the use of bifocals. They recommended caution in prescribing bifocals and I agree. For these reasons, this study won’t change my current eyeglass prescribing patterns.