October 8, 2012
Researchers Find Easier Way To Perform Macular Degeneration Eye Test
Lawrence LeBlond for redOrbit.com - Your Universe Online
Age-related Macular Degeneration (AMD) is a condition that generally occurs in people over the age of 50, but also occurs in higher numbers of people who smoke, who are white, and people who have a family history of the often debilitating condition. And for those who had gone through AMD testing, they had generally had to sit in a darkened room for 20 minutes before testing had begun.
Their study shows that AMD can be just as easily and effectively diagnosed under bright lights, as it can after patients sit in a dark room for 20 minutes. The study also shows that the new method is less costly.
Professor Ted Maddess, from The Vision Centre and The Australian National University, said AMD accounts for nearly half of cases of legal blindness in Australia. “It affects one in seven people over the age of 50, costing the nation $2.6 billion a year. Globally, it affects 25 to 30 million people, with an annual cost of $343 billion.”
“While current tests for AMD are done in the light, scientists have proposed that it might be better if the patient has their vision adapted to the dark prior to the test,” Madess remarked. “This is because they had found that rod receptors — vision cells that we use to see in black and white and in low light — die earlier in AMD than the cone receptors we use to see in color during the day.”
Because of this, many scientists have “suggested that AMD tests would be more accurate if they were based on the health of a person´s rods.”
However, Maddess noted, recent research has shown that the eye´s cones, while dying later than rods, start to deteriorate at the same time as the ℠night´ vision cells.
Maddess and his colleagues wanted to know if the cones “become just as sick as the rods, and if yes, would it make a difference if we test for AMD under bright lights?” To find out, he and his team examined people´s vision at light levels suitable for rods and cones.
To test how pupils respond to images on LCD screens, Maddess developed a device, the TrueField Analyzer, with the help of Australian company Seeing Machines. Using the device, multiple stimuli were provided for each eye, at 24 locations in the person´s visual field. Two cameras using infrared lighting recorded the instantaneous response of the pupils, which was then processed by a computer.
Maddess said the pupils´ response was a good indication of “how well the eyes are working — healthy eyes, being more sensitive to stimuli, will produce larger pupil contractions than damaged eyes.”
“We found little to no difference in the results — with the TrueField Analyzer, we could diagnose AMD just as well regardless of how much light the eyes were exposed to during the test,” he said in a news release. “This means that the cones of an AMD patient are about as damaged as the rods, so tests that are based on a person´s cone vision are just as accurate.”
“To ℠switch off´ your cones and activate your rods, a process known as ℠dark adaptation´, you´d have to be in a dark environment for at least 20 minutes, as in our dark tests. This means a long test to find out if you have AMD,” Maddess added.
Maddess noted that his team´s research showed that it is not necessary for people to be acclimated to a darkened room before testing begins, eliminating long wait times and the need for dark rooms. Because of this, it is a much “easier test than was previously thought.”
The study, “Photopic and scotopic multifocal pupillographic responses in age-related macular degeneration,” is published in the latest issue of Vision Research.