Originally published in The Ottawa Citizen, July 25, 2005
Original title: Future Visions Now a Reality
Four exciting good-news medical stories warrant more exposure. Two of the stories report research into restoring the sight of visually impaired people. The other two stories demonstrate ultrasound technology advances to treat prostate cancer and improve medical diagnostic imaging.
The eyes have it.
Researchers at the Centre for Sight, Queen Victoria Hospital, in East Grinstead, West Sussex, spent five years perfecting a technique to restore the vision of patients who suffered severe corneal damage from acid, alkali and molten metal burns or from congenital disorders. These people were told at the time of their injury they had little hope of regaining their sight.
The cornea is the clear “window” covering the centre of the eye. When damaged, it can scar blocking light from passing through the pupil to the retina.
The treatment process involves harvesting stem cells that come from the eyes of donors. The cells, in turn, are grown into sheets. Once the sheet is complete, they are placed onto the surface of the eye and held in place by an amniotic membrane. This special membrane dissolves once the sheet fuses to the eye.
An unexpected outcome of the procedure was that the rejection rate of the transplanted tissue was almost nil. A year after the transplant, DNA analysis of the transplanted tissue showed no trace of the stem cell donor’s DNA; there was no donor tissue left. The recipient’s eyes took over the healing process and repaired the damage. This meant there was no need for long-term use of anti-rejection drugs to suppress the immune system.
Edward Bailey, who suffered a caustic acid injury to his left eye and lost his sight, said the operation has transformed his life. “It was the most emotional moment,” Mr Bailey, 65, said. “I couldn’t believe it. For 10 years all I had seen was shades of black and grey, then after I had the operation, the nurse came by and I saw a flash of blue from her uniform.
“I went home and when I took the patch off my eye, I had my vision back. It is only when you lose something like sight that you realize how precious it is.”
The team is now looking at other avenues to apply this technology to other damaged tissue around the body.
Another sight restoration procedure was reported by scientists from the University of Southern California and the Doheny Retina Institute in May at the annual meeting of the Association for Research in Vision and Ophthalmology. Six patients with retinitis pigmentosa, a progressive degeneration of the light-sensing cells of the retina, were given artificial retina implants or intraocular retinal prostheses.
The retinal prosthesis, developed and created in conjunction with Second Sight Medical Products of California, is a four-by-four grid of platinum electrodes set in a thin silicone rubber sheet about the thickness of Scotch tape. The sheet is implanted directly onto the retina.
The grid remains in constant wireless communication with a small external computer controller that is attached to the recipient’s belt. The image data is sent to the computer via a tiny video camera attached to special glasses worn by the patient. The computer digitizes the image and sends it to the platinum grid. The grid then stimulates the eye’s photoreceptor cells just like the retina once did. The signal is then carried to the brain’s vision centre to process the image.
Although the grid contains only 16 electrodes proving only 16 pixels of resolution (today’s consumer digital cameras typically have three million to five million pixels), patients were able to detect light, identify objects and even tell if an object was in motion.
In 2002, after being blind for more than 50 years, the first patient to receive the implant was able to see large letters and distinguish between a cup, a plate and a knife.
Mark Humayun of Johns Hopkins University, who has a doctorate in bioengineering and surgical training and started this project, will begin the next step to improve pixel density. This year he plans to use an implant that has 60 to 100 electrodes but is a quarter of the size of the original model. He hopes that 200 to 400 electrode models will be available in three years and plans to develop a prototype for a 1,000-electrode implant in five years.
The hope is that these devices will help restore the sight for people with retinitis pigmentosa and macular degeneration.
In the next column, we’ll look at amazing things you can do with ultrasound.
© Dr. Barry Dworkin 2005