Age-related macular degeneration (AMD) is one of the most common eye disorders – and threatens to deprive its millions of sufferers of their vision, as well as causing misery and frustration for those battling the condition.
However, there have been a number of scientific discoveries in recent weeks, which could help ophthalmologists across the industry address the issue and perhaps lead to more effective treatments for AMD.
At a recent meeting between the American Academy of Ophthalmology (AAO) and the Middle East-Africa Council of Ophthalmology (MEACO), researchers reported progress on two of the most challenging eye disease issues.
The first development was in the treatment of advanced AMD and the other in preventing blindness in people with diabetes. The joint conference was held between October 16th and 19th in Chicago.
While eye doctors have a number of medications at their disposal for patients with vision-threatening 'wet' AMD, there are currently no effective treatments for advanced 'dry' symptoms – a more common disorder.
At the meeting in Chicago, however, a research team led by Jason Slakter, from New York University's School of Medicine, reported on a clinical trial of fenretinide – a synthetic derivative of vitamin A.
The risk of developing wet AMD was found to have decreased almost two-fold when patients with the dry form of the condition were administered the drug.
Geographic atrophy (GA) lesion growth was similarly reduced among the group who took the fenretinide compound. This finding correlated with lowered blood levels of the biomarker retinol blinding protein (RBP) – an indication that the experimental treatment was working successfully.
Patients whose RBP decreased by 60 per cent or more were also found to have shown the most considerable reductions in lesion growth. GA lesions damage an area of the eye called the retinal pigment epithelium (RPE), which can result in significant loss of sight.
Advanced AMD, in either dry or wet form, can destroy the detailed, central vision we require to recognise faces, read and generally enjoy day-to-day life. It is a major cause of blindness across the world.
In the advanced wet form, abnormal blood vessels develop beneath the retina, then leak fluid or bleed, eventually forming scars.
Fenretinide was found to work on three key AMD disease mechanisms. Firstly, it has strong anti-inflammatory properties, it inhibits abnormal growth in retinal blood vessels and finally it reduces toxins derived from vitamin A. These toxins accumulate in the RPE and can interfere with its ability to nourish light-receptor cells in the eye.
"Evidence from our study and others points to fenretinide's potential to treat and prevent diseases of the retina," Dr Slakter said.
While these experimental treatments certainly represent good progress in the battle against AMD, they remain in the research and development phases of drug discovery.
In separate findings published recently, newer treatments for AMD, including injections of a chemotherapy drug into the eye – were found not to be associated with increased risk of heart disease when compared with existing therapies.
Since 2005, ophthalmologists have been treating AMD with the cancer drug bevacizumab – an antibody which also blocks blood vessel growth.
Later, in June 2006, ranibizumab – an antibody fragment with similar mechanisms – was approved in the US for treatment of the condition.
"In chemotherapy regimens, bevacizumab is associated with an increased risk of thromboembolic events," when a blood clot forms and travels through blood vessels, potentially causing a stroke or heart attack, the authors noted in the October issue of the journal Archives of Ophthalmology.
"However, intravitreous bevacizumab is administered at a dose of 1 to 2.5mg - 150 times less than the systemic dose. Despite the regulatory approval of ranibizumab, off-label use of bevacizumab continues, likely because of the cost difference ($1,950 per dose of ranibizumab vs. $30 per dose of bevacizumab). The relatively safety of the therapies is unknown," they added.
The scientists found no differences in the risk of death or heart attack between the bevacizumab group and any other therapy group – and bleeding events or stroke did not differ by treatment group.
"We found no evidence of increased risks of mortality, myocardial infarction, bleeding or stroke among Medicare beneficiaries who received intravitreous ranibizumab or bevacizumab for neovascular age-related macular degeneration," the authors concluded.
by Martin Burns