Artificial corneas offer hope

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Patients with impaired vision because of a damaged cornea could soon regain their sight without the need for a human donor transplant. Artificial corneas developed by a University of Ottawa scientist have shown promising results in early phase clinical trials.  The results, based on ten experimental transplants performed in Sweden, were published last month in the journal Science Translational Medicine.

The cornea is the clear dome of tissue on the outer surface of the eye.  It acts like a window and needs to be transparent to allow light in and help focus images properly on the retina at the back of the eye.  Diseases or injuries that cloud the cornea are a common cause of vision loss or blindness, and affect approximately 7 to 10 million people worldwide. The best treatment for permanently damaged corneas remains a transplant, but donor corneas are in chronically short supply

Developed by cell biologist May Griffith at the Ottawa Hospital Research Institute, the biosynthetic corneas are derived from genetically engineered human collagen that has been grown in yeast, purified, then treated and molded to resemble contact lenses.  The team removed tissue from the front of patients’ corneas and replaced it with the artificial corneas. Although they do not contain any live cells, the artificial implants mimic part of the natural corneal tissue, and act as a catalyst that coaxes the stem-like cells found in a patient’s own eyes to grow.  The implants provide an environment for the patients’ own cells and nerves to grow into, resulting in a cornea that looks and functions like a normal, healthy cornea, said Prof. Griffith.   

The patients were monitored for two years after surgery to observe how the implants were incorporated into the eye.  No one experienced rejection of the implant or needed to take immune-suppressive steroids in the long-term — two serious side-effects associated with human cornea transplants.  Six out of the ten patients had improved vision and postoperatively were able to see things four times farther away than before surgery. After the subjects were fitted with contact lenses, all had vision equivalent to conventional cornea transplants.  “This is because stitches on the implants introduced bumps that impaired vision and need to be smoothed by contact lenses,” says Griffith. Using different suturing methods or replacing the stitches by gluing the implants to the eye with tissue adhesives could solve this problem.  The research team has already had encouraging results testing such alternatives in preliminary follow-up work.  

The team also observed regenerating nerves in all the corneas, and in nine out of 10 patients, the nerves grew all the way to the center of the implant, a result Griffith is particularly excited about. “The nerves are really important for the long-term health of the rest of the cornea–but regeneration does not happen reliably even in donor corneas,” she says. Her long-term expectation is that the implant will slowly degrade and be completely replaced by the natural scaffold regenerated by the cells that have repopulated the cornea.

“These results are very gratifying to show that we’ve actually been able to make a prototype and we’re possibly on the right path,” Griffith said from Linköping, Sweden.  The implants need to be tested in more patients with different types of cornea disorders (all patients in this study were suffering from keratoconus). At least five more years of research and clinical trials will be needed before artificial corneas become available to the general public. If proven to be safe and effective at restoring vision, the artificial corneas could become a useful substitute in transplants that currently rely on donated human corneas.

Written by Cowichan

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