Major cause of blindness linked to calcium deposits in the eye

Microscopic spheres of calcium phosphate have been linked to the development of age-related macular degeneration (AMD), a major cause of blindness, by UCL-led research.

AMD affects 1 in 5 people over 75, causing their vision to slowly deteriorate, but the cause of the most common form of the disease remains a mystery.* The ability to spot the disease early and reliably halt its progression would improve the lives of millions, but this is simply not possible with current knowledge and techniques.

The latest research, published in Proceedings of the National Academy of Sciences, has implicated tiny spheres of mineralised calcium phosphate, 'hydroxylapatite', in AMD progression. This not only offers a possible explanation for how AMD develops, but also opens up new ways to diagnose and treat the disease.

AMD is characterised by a build-up of mainly protein and fat containing deposits called 'drusen' in the retina, which can prevent essential nutrients from reaching the eye's light-sensitive cells, 'photoreceptors'.

Photoreceptors are regularly recycled by cellular processes, creating waste products, but drusen can trap this 'junk' inside the retina, worsening the build-up. Until now, nobody understood how drusen formed and grew to clinically relevant size.

The new study shows that tiny calcium-based hydroxyapatite, commonly found in bones and teeth, could explain the origin of drusen. The researchers believe that these spheres attract proteins and fats to their surface, which build up over years to form drusen. Through post-mortem examination of 30 eyes from donors between 43 and 96 years old, the researchers used fluorescent dyes to identify the tiny spheres, just a few microns - thousandths of a millimetre - across.

What Qualifies as Blindness?

People who are going blind often first deal with vision impairment, which then progresses into blindness. Blindness can affect one or both eyes, and doesn't necessarily cause total darkness. Many people who are considered blind can still see some light or shadows, but cannot see anything clearly.

Likewise, "legal blindness" does not mean that a person cannot see anything, but that their vision is so impaired that they need a lot of help perceiving images.

The United States typically defines someone as legally blind when the person’s central vision has degraded to 20/200, or the person has lost peripheral vision so that he sees less than 20 degrees outside of central vision. Normal vision is 20/20, and people can usually see up to 90 degrees with their peripheral vision. An estimated 1.1 million people in the United States are considered legally blind.

"We found these miniscule hollow spheres inside all of the eyes and all the deposits that we examined, from donors with and without AMD," explains Dr Imre Lengyel, Senior Research Fellow at the UCL Institute of Ophthalmology and Honorary Research Fellow at Moorfields Eye Hospital, who led the study. "Eyes with more of these spheres contained more drusen. The spheres appear long before drusen become visible on clinical examination.