A study published last week from the US suggests that the rate of age-related macular degeneration (AMD) at specific ages has fallen by about 60% with each successive generation, since the beginning of last century.
This study examined the offspring of people studied in the famous Beaver Dam Eye Study (the US predecessor of the Australia's landmark Blue Mountains Eye Study).
After accounting for smoking, sex and cardiovascular disease, there was still a remarkable 60% reduction in the number of new cases of AMD with each successive generation at any given age as illustrated in the graph below.
The study has not been replicated, although several other studies, including the Blue Mountains Eye Study have also found that the rate of vision impairment has declined over generations.
The new study has not been able to determine the specific reason for the dramatic fall, although the most logical explanation is changes in diet over generations.
In an interview with ABC Radio's Norman Swan, the Foundation’s National Research Advisor Professor Paul Mitchell said, “I want to introduce some of the issues. This is called a cohort effect whereby the frequency of disease alters over the course of time. And in a sense it's fantastic news because macular degeneration is such an important cause of vision loss. We have to still put it into perspective. So firstly is the study real? It's not been replicated, so no one else has done a study like this, except that there have been a few studies that have suggested it.”
“So first of all they adjusted for the things you could try to adjust for; age, sex, smoking, which we know increases the risk, cardiovascular disease, obesity, but there's two things they didn't adjust for that are critical. Firstly they didn't adjust for the genes that cause macular degeneration… we don't know whether the frequency of these key genotypes could have changed a bit. Second, they didn't adjust for people's diet.” he added.
Many people born at the beginning of the 20th century, and into the 1930s, experienced long periods of poor diet and poor health, which may have had long-term consequences. With successive generations, diet has improved - although obesity is causing other health problems.
If this research is replicated, it is clearly very good news for the future. However, we are now living much longer, and as the rate of AMD increases dramatically with increasing age, we will continue to see significant numbers of cases in the future.
Source: Cruickshanks K et al, JAMA Ophthalmology, Published online November 16
You can listen to the original interview and read the transcript here
28 November 2017