Artificial eye lenses are regularly used by ophthalmologists to correct a variety of vision problems. Patients are typically elated after surgery as their vision significantly improves, unveiling the beauty of the world they only remembered before. Yet, modern artificial lenses are imperfect and act more like conventional glasses than the eyes’ surprisingly complicated own lenses.
Everyone knows from school about refraction and how lenses are used to focus light. Many teachers and textbooks use the lens of the eye as an example of a natural lens that’s just like what’s found in a photo camera. The fact is that most lenses found in optical equipment are made of solid glass pieces that only bend light at their surface. Once a beam enters the lens, it’s traveling in a straight line.
The eye’s own lens actually bends light continuously as it passes through, something called “GRIN”, or gradient refractive index optics. To make more perfect artificial replacement lenses, researchers from Case Western Reserve University, Rose-Hulman Institute of Technology, U.S. Naval Research Laboratory, and PolymerPlus (Valley View, Ohio) have created technology that allows the stacking of tens of thousands of ultra-thin layers of polymer to produce a continuous refractive gradient.
From the study abstract in Optics Express:
A synthetic polymeric lens was designed and fabricated based on a bio-inspired, “Age=5” human eye lens design by utilizing a nanolayered polymer film-based technique. The internal refractive index distribution of an anterior and posterior GRIN lens were characterized and confirmed against design by µATR-FTIR. 3D surface topography of the fabricated aspheric anterior and posterior lenses was measured by placido-cone topography and exhibited confirmation of the desired aspheric surface shape. Furthermore, the wavefronts of aspheric posterior GRIN and PMMA lenses were measured and simulated by interferometry and Zemax software, respectively. Their results show that the gradient index distribution reduces the overall wavefront error as compared a homogenous PMMA lens of an identical geometry. Finally, the anterior and posterior GRIN lenses were assembled into a bio-inspired GRIN human eye lens through which a clear imaging was possible.
Here’s an animation describing the M-GRIN manufacturing process used to make the new lenses:
Study in Optics Express: A bio-inspired polymeric gradient refractive index (GRIN) human eye lens