Ulster University’s Professor Roger Anderson (pictured) will deliver the Janet Silver Memorial Lecture at the Hospital Optometrists Annual Conference (HOAC) in Belfast (Crown Plaza Belfast, 9–10 November). Professor Anderson led a research team based at the National Institute for Health Research Biomedical Research Centre to create the Moorfields Acuity Chart, which reduces variability in visual acuity testing.
Can you tell OT about your presentation at the HOAC?I am delivering the Janet Silver Memorial Lecture, which is quite an honour. Janet Silver was a pioneer in visual assessment in her clinical and research career. I will be looking at different acuity charts, what the state of the art version is at the moment and also looking at the history of the development of the Moorfields Acuity Chart, which is gaining quite a lot of interest for clinical use and clinical trials around the world.
What are the benefits of the Moorfields Acuity Chart?
The main reason we decided to design it was because of the very poor repeatability of current charts. If you have a test that varies in its result from one test to the next, even when you are not changing the conditions, it makes it very difficult to detect change and monitor disease progression in a patient. That was the idea behind it.
From previous work, we hypothesised that one of the causes of variability in conventional visual acuity charts was the fact that the letters differ very much in their spatial frequency content, particularly in the low spatial frequency content that makes up the overall shape of the letter. If we removed the low frequencies, the letters would become much more equally legible.
What has the uptake of the chart been like?
The chart is commercially available from Peter Allan Associates who do the specialised printing. It is used by hospitals like Moorfields and in clinical trials across the world. There are quite a few drug trials for age-related macular degeneration (AMD), for example, that are using the chart. The drug companies want a test that is more sensitive and repeatable than current measures.
How would you like to refine the chart further?
Computerisation is the big one. At the moment it is available only in the printed form. When you move to computerisation you can get much better standardisation of threshold scoring methods and what are called termination criteria – in other words, when you decide to stop the test and the patient has seen all they can see. That is something we are working towards.
Can you tell OT a little about the history of visual acuity testing?
One of the earliest recorded acuity tests was what was called the Arab eye test where subjects were asked to discriminate the separation of two particular stars. It was used by ancient armies as a measure of acuity for soldiers. Things went in fits and starts up until one of the most important events when Snellen designed his visual acuity chart to try and standardise testing in terms of distance, letter sizes and how you score it. Things changed very slowly after that, for well over a century, until the introduction of LogMAR charts in the 1980s.
“In the future instead of using one gold standard chart you might see different charts being used for different conditions”
How do you think visual acuity testing will change going forward?
Optometrists have historically used a letter chart as little more than a refraction target. It is fine for that. But increasingly optometrists are involved in detecting and monitoring eye disease and looking at the efficacy of different treatments. That requires very accurate and repeatable visual acuity measurement. I think in the future as new treatments come online for diseases like AMD optometrists are going to need good acuity charts more than ever before.
What we are increasingly realising is that different targets tap into different diseases in different ways. It may be that in the future we use different charts for different diseases. For example, you might need one chart if you are looking for optical blur, which is an optical loss, but you might want a different chart if you are looking for neural loss, like in AMD or diabetic retinopathy. In the future instead of using one gold standard chart you might see different charts being used for different conditions. It will be a development where optometrists increasingly tailor their testing to the patient in front of them and what they may or may not be suffering from.
Do you think visual acuity charts will ever become redundant as technology advances?
I think ultimately you are always going to have to have an assessment of what the patient can actually see because that is what determines their quality of life. While we have these fantastic developments in optical coherence tomography, which have revolutionised ophthalmic care, and the diagnosis and monitoring of conditions, visual acuity is not going away. It is always going to be a fundamental part of any comprehensive ophthalmic exam.