快猫短视频

IMAGINE the horror of being told you are losing your sight and that nothing can be done to prevent it. This is the reality for millions of people with . But a novel laser treatment technique gives hope that this leading cause of blindness in the West could one day be preventable.

Unpublished results from a successful pilot trial which ended last year, described to 快猫短视频, have left researchers scratching their heads as to exactly how it works. The findings also challenge ideas about the basis of the disease. A larger, randomised placebo-controlled trial is now under way. It鈥檚 very early days but, if successful, the treatment could prevent vision loss in millions of people globally.

AMD corrodes the macula, a part of the retina at the back of the eye with the highest density of photoreceptors. The disease leaves people with a gaping hole in the middle of their vision, making reading and recognising faces difficult or impossible. AMD affects about 1 in 15 people at some point in their lives, and has a strong genetic component. It is most common among older white women, affecting about 1 in 6 over the age of 80. There is no treatment for the most common form of the disease (dry AMD), but drugs that slow its progression are available for the rarer, more aggressive form (wet AMD).

In most people, the condition starts with unusually large or numerous deposits of extra-cellular debris called 鈥渄rusen鈥� littering the retina. Drusen, which consist of proteins and lipids, are supposed to be cleared away by the retinal pigment epithelium (RPE) cells that they accumulate beneath (see diagram). But as those cells age they become less effective at doing that.

The exact cause of what happens next is not well understood. Either because of the extra drusen, or as a result of whatever is damaging the RPE cells in the first place, the RPE cells become starved of oxygen. As they die off, they stop providing energy to the photoreceptors, causing them to die too. This is a serious problem as the density of photoreceptors is highest in the macula, so any loss noticeably affects vision.

As early as the 1970s, there was some indication that laser treatment cleared away the drusen, but this did not come with an improvement in sight. In some cases, trials were even halted for fear they were making things worse. This is unsurprising as the lasers used were high energy and made visible burns on the retina. But today鈥檚 more sophisticated, low-energy lasers offer more subtle options.

In 2010, ophthalmologist at the University of Melbourne鈥檚 Centre for Eye Research Australia who were in the very early stages of the disease, with some build-up of drusen. They each had treatment in one eye with a specially designed laser which had previously been .

After treatment, the majority of the participants saw benefits 鈥� a reduction in the amount of drusen, an improvement in their sight, or both. In lab tests, some participants were able to notice small differences in the intensity of light that they hadn鈥檛 been able to before, indicating that the retina had regained some of its function. 鈥淭he sensitivity of the retina improved in the spots that were most at risk of running into trouble,鈥� says Guymer. 鈥淭here鈥檚 been no other intervention where you can improve the function of a person鈥檚 retina.鈥�

So why should lasering the already embattled RPE improve things? One theory is that the cells are so tightly bound that they never divide and regenerate, eventually becoming less effective at removing drusen. If the laser shot through that layer, killing some of the cells and breaking up the tight bonds, it may have allowed new RPE cells to be created. The laser should be able to do this because, rather than a uniform beam, it is made up of thousands of little beam spikes which turn its target into a pin-cushion. It kills a smattering of individual cells but leaves enough healthy cells in between to kick-start the regeneration of the RPE.

This cannot be the whole story, though. When Guymer conducted the pilot study she treated only one of each volunteer鈥檚 eyes in order to use the other as a control. To her surprise, among those participants who saw a reduction in the drusen, most of them experienced the effect in both eyes. 鈥淚t鈥檚 a little hard to explain how the other eye is affected by the [rejuvenation] mechanism,鈥� says Guymer. It seems something else is triggering a response in both eyes.

Guymer reckons the immune system might be responsible. To protect the eye from potentially damaging inflammation caused by an immune response, . Unfortunately, this means that the drusen are also 鈥渋n an immune privileged position鈥�, says Guymer, hidden by a tight layer of RPE cells. She thinks that when the laser kills some of the RPE cells, it effectively alerts the immune system to the presence of the drusen, triggering a double-whammy clean-up of the debris by both the immune system and the newly rejuvenated RPE cells. 鈥淭hat鈥檚 not proven,鈥� Guymer stresses, 鈥渢hat鈥檚 just the working hypothesis.鈥�

Philip Rosenfeld at the Bascom Palmer Eye Institute in Miami, Florida, is excited by the results and says the immune explanation is plausible. 鈥淵ou can come up with a lot of explanations but the most likely is that something is being stimulated in the immune system that鈥檚 been transferred to the other eye,鈥� he says.

Because of the surprising effects found in the pilot study, Guymer will be treating just one eye in each of the 300 people she aims to recruit for the larger trial, and is expecting both to benefit.

The results will be keenly anticipated. 鈥淪mall functional changes are very difficult to measure with precision and to repeat,鈥� says Emily Chew from the National Eye Institute in Bethesda, Maryland. 鈥淚鈥檓 waiting to see the next step, when patients are randomised. If there are truly differences, that will be very exciting and interesting for sure.鈥�

Although still a long way off, Guymer sees a future where the new laser is used as a preventative measure in people at high risk of AMD, in a similar fashion to the way heart attacks are prevented by treating blood pressure. 鈥淯ltimately, if your parents had AMD, you鈥檒l have a genetic test and if you鈥檝e got the gene you鈥檒l have this laser and you won鈥檛 get the disease. That鈥檚 where we would like to head. One lasering, perhaps once a year, for those who are genetically at risk,鈥� she says.

If Guymer had her way, this approach would be just the start. She imagines a time when people at genetic risk simply get vaccinated so their body recognises the drusen and clears it away. 鈥淲e just need to trigger the immune system to do a better job cleaning up that debris.鈥�

When this article was first posted, the diagram incorrectly labelled the choroid as the ciliary body