The researchers describe the custom design techniques and results of visual acuity tests in a paper published in Optics Letters.
Keratoconic eyes are rare but disabling. From the side, the eyes look cone-shaped. The apex shift from visual axis in the cornea causes people with the condition to see halos and double and triple images. About 1 in 2,000 people suffer from the disease, usually in both eyes.
‘The condition shows up in a relatively small population, but it causes huge optical problems,’ said Geunyoung Yoon, assistant professor in the Departments of Ophthalmology and Biomedical Engineering, the Center for Visual Science, and the
All three subjects reported their vision significantly improved with the custom-designed soft contact lenses.
The scientists tested several designs of custom lenses on the subjects’ eyes for high-contrast and low-contrast visual acuity. They compared vision with the custom-designed soft lenses to vision with conventional lenses and rigid gas permeable lenses, or hard contact lenses.
Corrections with the custom lenses resulted in an average improvement of 2.1 lines in visual acuity, or from 20/48 to 20/29, over the use of the conventional defocus and astigmatism corrections alone.
Conventional soft contact lenses do not work for keratoconic eyes, as they conform to the conical cornea shape. The custom-designed lenses have irregular front surface profiles designed to correct for specific aberrations of the cornea and crystalline lens. The scientists designed the front profiles by measuring with wavefront sensors exactly how light enters the subjects’ eyes through the misshapen cornea. In collaboration with Bausch & Lomb, an oscillating tool lathe sculpted the front surface of the lens.
Keeping the lenses exactly in place is still a challenge, as blinking shifts contact lenses. The scientists used existing stabilising techniques, such as making the lenses bottom-heavy, to coax them into correct orientation.