Calcium deposits may trigger degenerative blindness

Chuck Bednar for – Your Universe Online

Age-related macular degeneration (AMD), one of the major causes of blindness in seniors, may be caused by deposits of microscopic calcium phosphate spheres in the eye, a team of researchers report in the latest edition of the Proceedings of the National Academy of Sciences.

In the study, scientists from University College London and the University of Maryland School of Medicine note that this is the first time these mineralized calcium phosphate spheres have been implicated in AMD, a condition affecting one-fifth of people over the age of 75.

AMD causes the vision of those affected to slowly deteriorate, and the cause of the primary form of the disease remains a mystery. The possible involvement of these tiny calcium spherules, also known as hydroxyapatite (HAP), could ultimately lead to early detection of the disease.

Not so HAP-py (sigh)

As the researchers explain, HAP is common in the body. It makes up the hard part of teeth and bones, but it had never before been detected in the retinal samples of elderly patients. This discovery could help scientists learn how AMD develops, as well as how to better diagnose and treat the condition that affects a reported 10 million people in the US alone.

AMD is characterized by a build-up of drusen (deposits of fat and protein) in the retina, which prevents essential nutrients from reaching light-sensitive cells called photoreceptors. Photoreceptors are regularly recycled by cellular processes, which creates waste products. Drusen can trap this material, however, causing it to build-up in the retina.

Previously, scientists did not fully understand how drusen formed and grew to clinically relevant size, but the new study shows that HAP particles could be responsible. The study authors believe that the calcium spheres could attract proteins and fats to the surface, causing them to accumulate over the course of several years or even decades to form drusen.

The research began with the question, “What’s HAP-pening, here?” (We’re getting canned any day now.)

The researchers made their discovery through post-mortem examination of 30 eyes from donors between 43 and 96 years old. Using fluorescent dyes, they were able to identify the miniature calcium spheres. They also examined tissue samples from AMD patients using X-ray diffraction and fluorescent staining chemicals, which helped reveal the role of HAP in the process.

“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 lead investigator Dr. Imre Lengyel, a senior research fellow at the UCL Institute of Ophthalmology and Honorary Research Fellow. “Eyes with more of these spheres contained more drusen.”

Dr. Lengyel noted that the spheres appear long before the drusen itself becomes visible during a clinical examination, and that the new techniques can be used to identify drusen build-up long before it becomes visible using current techniques. The findings could potentially advance AMD diagnoses by at least a decade, she added.

“Our discovery opens up an exciting new avenue of scientific research into potential new diagnostics and treatments, but this is only the beginning of a long road.” added Dr. Richard Thompson, an associate professor of biochemistry and molecular biology at the University of Maryland School of Medicine.


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