A team of researchers has successfully created advanced instruments designed to accurately quantify and compare the light-focusing capabilities of specialized eyeglass lenses utilized for the purpose of slowing down myopia progression, also known as nearsightedness.
This novel approach to lens analysis holds great potential in providing valuable insights that can contribute to the development of even more effective lens designs, ultimately aiding in the prevention of visual decline.
In a publication featured in Optica, researchers from the ZEISS Vision Science Lab at the University of Tübingen (Germany) and the University of Murcia (Spain) present their latest instruments capable of assessing lens performance in real-world viewing scenarios. Their study includes findings from the measurement of light focusing properties in various lenses employed for the purpose of retarding myopia progression.
"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," said study author Augusto Arias-Gallego, from the ZEISS Vision Science Lab. "This could help millions of children and is fundamental in understanding the mechanisms by which these lenses work."
Myopia, often attributed to slight elongation of the eyes, causes distant objects to appear blurry as they focus in front of the retina instead of on it. While traditional eyeglass lenses can rectify this blurriness, they do not effectively halt the progression of myopia. The continued advancement of myopia can heighten the risk of various eye complications and irreversible vision loss.
Clinical trials have verified the efficacy of retinal signal-modifying lenses in reducing the progression of myopia, and these lenses are presently accessible in the market. It is believed by researchers that these lenses impede the elongation of the eyeball, thereby decelerating its growth. The design of these lenses includes various structures, such as microlenses or microdiffusers, to manipulate peripheral retina image characteristics while simultaneously addressing central vision. However, comprehensive investigations and comparisons of the optical properties pertaining to this relatively new technology are yet to be extensively explored.
The researchers used a spatial light modulator — shown here being illuminated by the interrogating beam — to reproduce, for the first time, 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. Credit: Augusto Arias-Gallego, ZEISS Vision Science Lab
In the new work, the researchers wanted to thoroughly characterize the currently available lenses under real-world viewing conditions. "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 Arias-Gallego. "Therefore, we developed a new instrument that can measure the lens's optical response to different angles of illumination while reproducing the myopic eye's pupil and refractive errors."
The newly developed instrument employs a rotating arm-mounted illumination source that revolves around the lens. Once the light traverses through the lens, it is directed by a steering rotating mirror towards a spatial light modulator (SLM). The SLM, comprising miniature liquid crystal cells, possesses exceptional spatial resolution and is crucial to the instrument's functionality.
The SLM serves as the instrument's focal point as it accurately replicates the refractive errors and pupil shape observed in myopic eyes. This groundbreaking feature enabled the researchers to simulate, for the first time, authentic aberrations resulting from different angles of illumination in various myopic eyes during lens testing. These aberrations were meticulously programmed into phase maps utilizing the capabilities of the SLM.
Additionally, the SLM allows for the introduction of programmed defocus levels, facilitating a comprehensive through-focus examination. This examination provides insights into the image quality at different simulated retinal positions, allowing for a better understanding of how the lens interacts with the elongation of the eye as perceived by the retina.
The researchers also quantified the light scattering characteristics of the tested lenses, which held significance as one of the lenses under evaluation incorporates contrast reduction through the addition of scattering. To accomplish this, they devised a customized setup that eliminates the need for specialized detectors and conventional moving components typically employed in quantifying scattering properties.
"By combining the through-focus results with light-scattering measurements, we were able to accurately characterize several types of eyeglass lenses," said Arias. "We then compared our measurements for each lens with their reported clinical efficacy for slowing myopia progression. The results raised new questions that need to be studied further while also pointing to potential strategies that could increase the efficacy of future designs."
In this study, the lenses underwent characterization using a single wavelength of light to streamline the analysis of image properties. However, since real-life illumination encompasses multiple wavelengths, the researchers are actively working on modifying the instrument to incorporate light sources with varying wavelengths. This adaptation aims to enhance the instrument's capability to capture and evaluate lens performance under more realistic scenarios.
Augusto Arias et al, In-depth optical characterisation of spectacle lenses for myopia progression management, Optica (2023). DOI: 10.1364/OPTICA.486389