AMD may be triggered by tiny mineral deposits in retina

Scientists from the University of Maryland School of Medicine have found that tiny lumps of calcium phosphate may be an important triggering factor for age-related macular degeneration (AMD). This is the first time these mineral deposits have been implicated in the disease, which affects more than 10 million Americans.

Credit: University of Maryland School of Medicine

A multidisciplinary international team studied retinal samples from a group of elderly patients, some of whom had AMD. They found that the AMD samples contained tiny spherules of a mineralized calcium phosphate known as hydroxyapatite (HAP). HAP is common in the body - it comprises the hard part of bones and teeth - but it had never been identified in that part of the eye before. 

AMD develops slowly over decades, with the buildup of fatty protein deposits in the retina, which cause damage by blocking the flow of nutrients into the light-sensitive portion of the eye, and of waste products out. Scientists have known about these deposits for over a century, but their origins remained a mystery. 

The researchers discovered that the deposits appear to form around the tiny bits of HAP. Once these chunks appear, the fatty protein material coalesces around it; over years, these globules build up. They discovered the possible role of HAP by examining tissue samples from patients using X-ray diffraction and fluorescent staining chemicals.

The scientists are looking into the possibility of using the presence of HAP as an early warning signal for AMD risk with a hope that this will aid early intervention before patients have suffered irreversible vision loss. Eventually, they say, it may be possible to devise methods to reduce HAP deposits or limit the growth and progression of the disease. The work was supported in part by the Bright Focus Foundation in the USA and the Bill Brown Charitable Trust in the UK. 

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