Refractive errors, specifically myopia and hyperopia, are the main cause of visual impairment in the United States and throughout the world. As the population ages and more people are affected by refractive errors, more data is needed to help anticipate future healthcare needs. Up until this point, however, studies have only examined refraction over periods of five or 10 years.

To break this trend, a team of American researchers conducted a prospective study that analyzed the impact of cohort effects on refraction over a 20-year period among patients older than 40. The researchers used generalized estimating equations to evaluate the etiologic factors underlying refraction and changes in refraction. They discovered that nuclear cataract is the primary contributor to a myopic shift among older patients.

Of the total participants, the team found that only those with nuclear cataract experienced a myopic shift in refraction—a 0.25D decrease over a five-year period. They note that patients with mild to moderate nuclear sclerosis showed varying degrees of hyperopic shifts over five years.