A model under development for in vivo visualization of human lens morphology could have clinical applications in patients at risk for changes in lens transparency. The device, which uses a rotating camera, creates a three-dimensional model of the lens and uses the relationship between contrast sensitivity measurements and lens optical density to evaluate visual function.
Chicago-With improvements, a novel computer-based software system to visualize in vivo human lens morphology and density could be an adjunct to slit-lamp biomicroscopy as a diagnostic tool.
Researchers from several Chicago institutions assessed the utility of a prototype system and also used it to examine correlations between contrast sensitivity, corrected visual acuity, and age with objective measurements of lens optical density in a group of adults with functionally transparent crystalline lenses.
"The system produced a reasonably accurate three-dimensional [3-D] replica of human lens morphology. In addition, assessment of the relationship between contrast sensitivity and lens density proved to be of considerable interest," Andrew C. Larson said. He conducted the study for his master's thesis while studying biomedical visualization in the Department of Biomedical and Health Information Sciences at the University of Illinois at Chicago with Zhuming Ai, PhD, who is research assistant professor in that department. Larson collaborated with Bruce I. Gaynes, OD, PharmD, and his colleagues at Rush College of Medicine as well as researchers at Northwestern University.
Suture geometry becomes more complex as the lens ages and more layers of fibers are added. At birth, sutures are Y-shaped but acquire more branches over time. By the age of 9 years, the shape is a six-point star, by age 19 a 9-point star, and by the mid-40s a 12-point star.
Researchers who have studied lens anatomy in detail have identified the above-mentioned developmental process as normal but also have noted abnormal changes caused by systemic disease or drug toxicity.
"That raises a number of important questions about lens sutures," Larson said.
He explained that researchers are interested in learning whether sutural abnormalities could be documented and correlated with various systemic diseases such as Alzheimer's, which lacks specific biomarkers accessible in a noninvasive fashion. Another question is whether a grading system for alterations in lens architecture could be established based on progressive changes in lens sutures. Such a system would be similar to the widely accepted Lens Opacification Classification System.
"These are all very important questions, but we can't do anything to answer them until we have a good way of studying lens sutures in detail in living subjects," he said. "Slit-beam Scheimpflug photography is a good candidate because of its ability to take cross-sectional photographs of the anterior segment and lens without being invasive in any way."
This process would involve a slit beam shined into the anterior segment to illuminate a cross-sectional image based on light backscatter. The scattered light could be captured at an angle with a camera lens.
"Because of the angles involved, the plane of focus and the cross-sectional image of the anterior segment coincide, and that allows us to have a perfectly clear image," Larson explained. "It is similar to how a view camera works."
He and his colleagues performed tests with a rotating Scheimpflug camera (Pentacam, Oculus Inc.) that is mostly used to evaluate corneal topography and tomography before and after refractive surgery. The camera was repurposed for this study. During a 2-second scan, the rotating camera captures both volumetric data and numerical values of lens optical density based on the light-scattering characteristics of the lens.
This device is ideal for longitudinal research, Larson said, because it automatically initiates scans upon determining that the eye is centered and rotates the same way for each scan, providing a consistent methodology.
The researchers' first objective was to determine whether the camera could be used to create a 3-D model of the in vivo lens that would be useful in studying sutures. They carried out the investigation in a group of 22 healthy individuals (44 eyes) sampled from refractive surgery consults and outpatient clinics.