Vision is our main way of interacting with the world, and it can be debilitating when our vision deteriorates. Unfortunately, presbyopia – the gradual loss of ability to focus on nearby objects – is basically inevitable. Presbyopia affects nearly 25% of the world population; almost 2 billion people. People usually see symptoms in their 40s, but the path starts in childhood.
The exact cause of presbyopia is unknown, but the effects are well documented. The eye’s lens is the bit that changes shape, allowing us to focus at different distances. During childhood, the lens gradually becomes less flexible. Since it can’t change shape as easily, we stop being able to focus as rapidly and accurately. It gets more difficult to focus at close or mid-lengths. There are four broad methods suggested for increasing focal range, each with its own trade-off.
Changing focus over time is the first method. Think of it like having several pairs of glasses. When focusing on close things you might use readers. Different glasses may be used for mid-length, or distance viewing. This is what our eyes do naturally (when we’re young at least!). So far there are no pharmaceutical or implantable devices that can accomplish this. Using several glasses is a good – if bulky – approximation for millions of people, however.
Changing focus depending on where you look is the second method. Bifocals are the classic example. This solution is quick and convenient. There are downsides, however. Changing from near to mid-focus can be jarring, vision can be blurry, and eye strain occurs sometimes. One often overlooked issue is that bifocals can introduce other dangers, such as falls due to unfocused areas near the feet when walking.
Changing focus between eyes is an interesting method. With this approach, one eye is corrected for close vision, and the other stays focused at a distance. Each eye only focuses narrowly, but together you can see across a wide range. Even though this is easy to try by putting in only one contact lens, it can be hard to get used to and lead to a loss of binocular vision. Judging distances of objects may be more difficult with this method, and it can be uncomfortable for some people.
The final method is to increase the focal range across distances. This is an innovative method where the eyes are changed to have more in-focus at the same time. If you’ve ever had an eye exam where they dilate your pupils, this is the opposite. The pupils are artificially constricted. This extends your depth of field, making it easier to focus on things near and far at the same time! Some side effects may include a loss in quality and contrast, and a loss of low-light sensitivity. One of the big hurdles researchers have is the precision required to pull this off successfully. Methods to induce increasing focal range can be permanent, such as with implanted lenses; but mitigation of side effects may be easiest with special eye drops. Some of these eye drops are being tested currently in clinical trials.
With so many different angles to attack presbyopia, and volunteers helping with clinical trials, we may be looking at a universal treatment soon!
Written by: Benton Lowey-Ball, B.S. Behavioral Neuroscience
Source:
Chang, D. H., & Waring, G. O. (2021). Presbyopia Treatments by Mechanism of Action: A New Classification System Based on a Review of the Literature. Clinical Ophthalmology (Auckland, NZ), 15, 3733.
