Myopia, or nearsightedness, is one of the most common ocular disorders worldwide and a leading cause of visual impairment in children. Although specialized eyeglass lenses have been clinically tested to treat myopia progression, an in-depth optical characterization of the lenses has not yet been performed. Researchers from the ZEISS Vision Science Lab at the University of Tübingen and the University of Murcia undertook a comprehensive characterization to investigate the properties of spectacle lenses designed to slow the progress of myopia. The results of their study could help increase the efficacy of future lens designs. Myopia is typically caused when a person’s eyes become elongated, which affects how the eyes focus on faraway objects. The condition can progress in children and teens as their bodies grow. To reproduce pupil shape and myopic ocular aberrations, researchers developed an instrument that reproduced the aberrations in myopic eyes and enabled physical simulation of the pupil. They based their instrument on spatial light modulation (SLM) technology. “After exploring the state of the art, we didn’t find a method that could be used to characterize the optical properties of these eyeglass lenses under real viewing conditions,” said researcher Augusto Arias-Gallego. As a result, Arias-Gallego said, the researchers endeavored to build an instrument that can measure the lens’ optical response to different angles of illumination, while also reproducing the myopic eye’s pupil and refractive errors. The team’s instrument uses an illumination source mounted on an arm that rotates around the lens. After the light passes through the lens, it is guided to an SLM by a rotating mirror. The SLM is composed of tiny liquid crystal cells that modify the propagating light, boosting its spatial resolution. The SLM reproduces the refractive errors and pupil shape of myopic eyes, allowing the researchers to re-create myopic aberrations and to produce different aberrations depending on the angle of illumination. Using the SLM, the researchers programmed the aberrations as phase maps and induced programmed amounts of defocus to perform through-focus testing. Tests helped the researchers determine the image quality within the proximity of a simulated retinal position, shedding light on how the special lens interacts with eye elongation signaled at the retina. “By combining the through-focus results with light-scattering measurements, we were able to accurately characterize several types of eyeglass lenses,” Arias-Gallego said. The researchers then compared measurements for each lens with their reported clinical efficacy for slowing myopia progression, he said. The researchers quantified and compared the focusing and scattering properties of a single vision lens with two types of spectacle lenses for myopia progression management: defocus incorporated multiple segments (DIMS) and diffusion-optical technology (DOT). They calculated four optical metrics potentially related to myopia progress and quantified the scattered light from the peripheral lens zones. Scattering was quantified by implementing the optical integration method. Researchers used a spatial light modulator, shown here, illuminated by the interrogating beam, to reproduce real aberrations produced by different angles of illumination for different myopic eyes. This allowed them to rigorously analyze different types of eyeglass lenses that are used to slow myopia progression. Courtesy of Augusto Arias-Gallego/ZEISS Vision Science Lab. The characterization showed an increased contrast and sharpness of images through the DIMS lens at the peripheral retina when inducing myopic defocus, with respect to the single vision and DOT lenses. It further showed that contrast reduction by the DOT lens was dependent on the luminance at the pupil. According to Arias-Gallego, the results both raised new questions and pointed to potential strategies that could increase the efficacy of future designs. “Insights into the link between the optical properties of myopia progression management lenses and effectiveness in real-world scenarios will pave the way to more effective treatments,” Arias-Gallego said. “This could help millions of children and is fundamental in understanding the mechanisms by which these lenses work.” The researchers are working to adapt the SLM instrument to include sources with varying wavelengths. The research was published in Optica (www.doi.org/10.1364/OPTICA.486389).
