Well-known worldwide for his ETDRS test (Early-Treatment Diabetic Retinopathy Study), he is soon to launch two new tests that will completely change the measurement of low vision worldwide. On a recent visit to IMO, he spared us a few minutes to talk about his speciality.
Low vision has often been ignored, hasn’t it?
Yes, it has. Patients usually resigned themselves to their visual impairment, not expecting any improvement. When the ophthalmologist couldn’t do anything else medically, it was generally accepted. Also, since a lot of low vision is associated with getting older, many elderly people didn’t usually ask if there was a remedy. They assumed it was just another ailment. Low vision began to be studied in the 1950s, but not a lot of attention was paid to it, so it took some time before it was considered to have a role to play in eye health.
How does optometry and low vision contribute to ophthalmology?
The ophthalmologist is used to working with diseased eyes and with active processes. But, there are always people who end up with low or very low vision. That’s when the low vision specialist gets involved to help these people have as full and normal a life as possible, despite their visual limitations.
What was the purpose of the ETDRS test you invented?
It was used to measure visual acuity in a reliable, standardised and reproducible way. It was an extension of the original Snellen test, which was first used in 1862. Jan Lovie-Kitchin and I designed some new features and included an innovative way of measuring visual acuity in 1976. In each row, there had to be the same number of letters, five, and the space between them had to be proportional to its size. Currently, it’s the standard way of evaluating low vision in the world.
What do the new tests you are working on at the moment consist of?
What both tests have in common is simplicity, and they can be easily used in developing countries. They don’t require extensive clinical experience, or sophisticated technology.
The first is suitable for patients with extremely low vision. Most optometrists and ophthalmologists give up when measuring the visual acuity of a person, when it reaches 0.05, or they measure a patient’s low vision by asking how many fingers they can see, or if they can detect a movement of a hand or light, which are fairly inaccurate methods. The new test can quickly and accurately measure visual acuity as low as 0.00125.
Why did you decide to develop these tests?
The first reason was a request from the sports organisation The World Blind Cricket Council to review the standard for measuring vision. The council organises cricket competitions for the blind and those with low vision. Some teams broke the rules by allowing players with better vision than they should have had to participate. Another reason was to evaluate the effectiveness of implants used to stimulate the retina. These devices, installed in front of and behind the retina, receive signals sent by a video camera and create neuro-activity in the retina, which enables signals to reach the brain via the optic nerve, and provide the patient with some perception of light. I went to a meeting of experts, and they were still talking about counting fingers to measure the success of these implants. After that, I created a prototype of the test. It was much simpler and it standardised the results.
One of the most important benefits is that the tests can be used in developing countries, can’t they?
Yes, in those countries, there are many people with low vision, and the ophthalmologist needs to know if their vision is getting better or worse after surgery. On an epidemiological level, I’m also interested in identifying the needs of each population. In certain countries, there could be many people with serious eye diseases and major visual limitations who need to be acknowledged. This standardisation of measurements will help this cause.
Could you tell us about the new contrast sensitivity test you’re developing?
The first one was the Pelli-Robson test in the 1980s, which consisted of a panel, on which the letters at the top are very easy to see, because they have a higher contrast, and those further down have increasingly less contrast. In this test, all of the letters are the same size. Performing the test takes a little time, and it is necessary for the patient to know the alphabet. The test we are currently proposing consists of three cards printed on both sides, so they have six faces. Each face consists of six 75-mm squares, and within three of them there’s a 40-mm circle. On the first card, the circle is black; on the second, it’s dark grey, and, on the third, it’s light grey. The patient actually only needs to be shown three faces. We ask him to indicate the lightest circle he can see. If he only sees two on the other side of the card, there are intermediate levels of contrast that enable us to refine the measurement of his contrast sensitivity. The good thing about this test is that you can use it with illiterate people. It’s very quick and easy.