Myopia, which affects the muscles used to focus the lens of the eye, appears to have clinical implications for “accommodating,” or focusing, intraocular lens (IOLs) implants that help the eye adapt to different visual distances, according to a study in the journal Optometry and Vision Science, titled “The Effect of Age, Accommodation, and Refractive Error on the Adult Human Eye.”
A better understanding of differences in the diameter of ciliary muscles used to focus at varying distances may offer patients a more “tailored” IOL fit in surgeries to correct presbyopia, or the decline in near vision that happens with age. IOL implants replace the eye’s natural lens after its surgical removal to restore focusing power.
To quantify alterations in ocular dimensions associated with age, refractive error, and accommodative response — or the ability to focus on objects near and far — researchers examined the right eye of 91 adults, ages 30 to 50, using methods that included ultrasonography, phakometry, keratometry, pachymetry, and high-resolution magnetic resonance imaging.
Accommodative response was assessed with a push-up test and with open-field autorefraction.
Differences in ocular parameters with age, refractive error, and accommodation were measured using regression analyses. Coherent with evidence from previous research studies, the results revealed that with age, the lens becomes less flexible, more sharply curved, and thicker.
Age was also associated with a reduction in the diameter of the ring of ciliary muscles that change the lens’ shape in the accommodation process. This constriction of the ciliary ring may also have implications for the development of presbyopia in aging eyes. There were also differences associated to refractive error: eyes with myopia (nearsightedness) were found larger, particularly front to back (called, axial elongation) and, confirming previous findings, myopia was associated with increased lens curvature.
Interestingly, the team found that eyes with myopia had a greater diameter of the ciliary muscle ring, and that the effect was considerably superior to the age effect — so that the ciliary muscle ring for a 40-year-old with myopia would be much larger than for a 60-year-old with hyperopia (farsightedness).
Study results help to explain why there are individual differences in the focusing capacity of accommodating IOLs. These individual differences depend on patients’ age and type of prescription. “The results provide the first evidence for why accommodating IOLs may not have the same effect in nearsighted people as they do in farsighted people,” Anthony Adams, OD, PhD, editor-in-chief of Optometry and Vision Science, said in a news release.
“The results of this study suggest that accommodating IOLs may need to be available in more than one diameter to allow for maximum benefit,” the authors wrote. Further testing and development of accommodating intraocular lenses should account for differences in patients’ preoperative refractive error, which could help to provide “customized” IOL fit to correct presbyopia.