Early detection of AMD

Print edition : August 23, 2013

ENGINEERS at the United Kingdom Astronomy Technology Centre (UK ATC), part of the country’s Science and Technology Facilities Council (STFC), who design state-of-the-art instruments for ground- and space-based telescopes, have used their expertise to develop a diagnostic test for the world’s most common form of sight loss in adults, age-related macular degeneration. AMD leads to the loss of the vision used when looking at something directly ahead, for example, at another person or when reading or watching television.

Collaborating with scientists from Cardiff University’s School of Optometry and Vision Sciences, they developed a “retinal densitometer”, which can pick up the earliest stages of AMD. AMD affects the macula, a pinhead-sized specialised area of the retina that contains a few million specialised photoreceptor cells called cone cells. Cone cells function best in bright light levels and allow us to recognise colours and to see fine detail for activities such as reading and writing. One of the earliest signs of AMD is a change in the way that the light-sensitive pigments in the macula regenerate after exposure to light. The retinal densitometer can assess this change by measuring, over time, the very small changes in the amount of light reflected by the retina after exposure to light.

Until very recently, there were few treatment options available for AMD, but some treatments to delay development of early forms of the disease, and to manage it, are being developed. Early diagnosis is one of the most crucial factors for developing new treatments and improving the management of this disease, but it is extremely hard to detect in the early stages and current tests are relatively crude.

The densitometer works by measuring the way the eye “dark adapts” after exposure to a bright light. It has several advantages compared with existing detection techniques in terms of its sensitivity and ability to measure responses to light from different parts of the retina. It is also completely non-invasive. Tests already carried out by the project team, on 10 patients with early-stage AMD and 10 control subjects, showed that the light changes on the macula can be highly accurately measured using this patented technology and that it has a high ability to distinguish between affected and non-affected groups.