Research must consider the significant effect of myopia’s rising prevalence when projecting future rates of visual impairment. Photo: Getty Images. Click image to enlarge.

With each diopter of myopia, patients face an increased risk of numerous vision-threatening conditions such as posterior subcapsular cataract, glaucoma, retinal detachment and myopic maculopathy. Given the rising prevalence of the disease, its current and future role in uncorrectable visual impairment may be underestimated in the literature. In fact, a new report predicts that in 2050, between 27% and 43% of cases in the US may be directly attributable to myopia.

To calculate these projections, the study authors first estimated the US prevalence of uncorrectable visual impairment in 2050 using census data and accounting for the changing distribution of age and myopia between now and then. The distribution of myopia was calculated using two prevalence estimates from the literature—58.4% ((≤ -0.5D; 2050 projection) and 33.1% (≤ -1D; reported prevalence from 1999 to 2004)—to provide both projected and conservative estimates. Lastly, the researchers identified the likely number of individuals in the US who will be visually impaired in 2050, defined as a best-corrected visual acuity of 20/40 or worse.

The study results, which were recently published in Scientific Reports, revealed that, “For a projected myopia prevalence of 58.4%, 222 million are projected to be myopic and 48 million will have high myopia (-5D or worse).” Of the 11.4 million projected cases of uncorrectable visual impairment, the researchers determined that 4.9 million (43%) will be directly attributed to increased risk of eye disease associated with myopia. Notably, the estimates showed that 2.4 million (49%) of these cases would be low or moderate myopes, emphasizing that “the impact of myopia is not restricted to high myopia,” the researchers elucidated in their paper.

On the other end of the scale, for a projected myopia prevalence of 33.1%, they noted that 8.9 million people are expected to have uncorrectable visual impairment, of which 2.4 million cases (27%) will be attributable to myopia.

The researchers relayed that “the established relation between myopia and visual impairment can be articulated further: [firstly], each 10% increase in the prevalence of myopia increases the number of visually impaired by about one million. Second, the visual impairment attributable to myopia increases with the underlying prevalence from 2.4 million at 33.1% to 5.1 million at 60%.”

The study authors also observed the possible effect of controlling myopia by 1D. “The result is that, for an underlying prevalence of myopia of 58.4%, the predicted visual impairment is reduced by two million (14%),” they wrote. However, they explain that this may not be the most realistic approach, as it “could only be achieved by treating every myope and also preventing the onset of myopia in a significant number of individuals.”

A more practical approach, the authors suggest, is to consider the impact of treating children who, if left untreated, are likely to progress to high myopia (-6D or worse). In theory, this could lower visual impairment by 0.6 million (5%). “Adjusting the criterion to -3D or worse would lower visual impairment by 1.3 million (11%), but of course, many more children would need to be treated to attain such a goal,” they added.

While the most appropriate method to reduce the future burden of myopia-related visual impairment has yet to be established, these updated projections suggest this is a critical area of research. “Efforts to prevent the onset of myopia and slow its progression should have a profound public health benefit,” the study authors argue. They add that, even with the more conservative prevalence estimate of 33.1% (with a more stringent criterion of 1D), “the analysis shows that myopia is, and will continue to be, responsible for a significant proportion of uncorrectable visual impairment in the US.”

The authors advise that to avoid underestimation of the prevalence of visual impairment in the US, future research must consider the increasing prevalence of myopia among the aging population. “Continued efforts to prevent myopia, delay its onset and slow its progression should have a profound influence on future levels of visual impairment,” they concluded.