What causes cataracts? Cataracts are caused when proteins in the lens break down and clump together, making the lens cloudy.
Cataracts form in the lens of the eye. As the lens becomes cloudy, it can look whitish, and vision can become hazy, blurred, or glary. If left untreated, the cloudiness can increase until the lens is largely opaque, and it becomes very difficult to see. The only effective treatment for cataracts is to remove the cloudy lens surgically and replace it with an artificial one.
The most common operation is called phacoemulsification. A small probe uses ultrasound to break the lens into tiny pieces, and these pieces are removed through a very small incision. During the operation, fluid is used to keep the front of the eye stable. Once the cloudy lens material has been removed, a replacement lens called an intraocular lens (IOL) is inserted, usually into the thin “capsule” that held the original lens. The artificial lens is commonly made of acrylic or silicone. Recovery often takes a few days for the eye to feel comfortable again, and vision usually improves quickly, although it can take weeks to fully settle.
The lens is the part of the eye that focuses incoming light onto the retina at the back of the eye. It sits just behind the pupil and the iris at the front of the eye. Muscles (the ciliary muscles) change its shape so that light can be focused for near vision or far vision. If you are near- or far-sighted, the light is focusing slightly in front of or behind the retina because of the length and shape of the eye and/or the focusing power of the cornea and lens. Glasses (or contact lenses) shift the focus so that the image lands in the right place on the retina.
The lens is made of highly packed lens fibre cells containing water and specialised proteins called crystallins. These proteins are arranged in a very organised way, which helps the lens stay clear and reduces light scattering. As lens fibre cells mature, they lose their nucleus and most of their internal structures, which also helps the lens remain transparent. The lens has to be clear to work properly, and this is what starts to change when a cataract forms.
Most cells in the body renew themselves. Some do this quickly, while others take longer. The core of the lens is different. The lens grows by adding new layers to the outside, a bit like the rings of a tree. The oldest fibres are in the centre and, once they are laid down, they stay there for life. Over time, newer layers press inward, which contributes to the lens becoming less flexible. This loss of flexibility is one reason many people develop presbyopia (difficulty focusing up close) and start needing reading glasses as they age.
These long-lived proteins are also the key to why cataracts happen. As the lens ages, some of its proteins and fibres are damaged and begin to unfold or stick to one another. Instead of staying neatly arranged, they start to clump together. A healthy lens is transparent because light can pass through with minimal scattering. Once proteins clump, they scatter and reflect light. That makes the lens look cloudy or white and prevents a clean image from reaching the retina. Vision can become blurry, colours can look duller, and glare (especially from headlights at night) can become a bigger problem. If the cataract progresses far enough, it can make it almost impossible to see.
The most common cause of cataracts is old age. The vast majority of people between 65 and 80 develop cataracts to some degree. It can happen faster or slower, but very few people escape it entirely. These days, at least in developed countries, it is usually a relatively simple problem to fix. However, there are other factors that can increase the risk of cataracts or bring them on earlier.
One of the main ways to increase risk is to smoke and drink a lot. Both smoking and alcohol expose the body to chemicals that increase oxidative stress, which can damage lens proteins and make clumping more likely. Cigarettes also contain heavy metals that can build up in the body over time, potentially worsening the situation. Diabetes can also increase cataract risk because high blood sugar changes the chemistry inside the lens. More sugar enters the lens, and some of it is converted into a sugar alcohol called sorbitol. Sorbitol draws water into the lens, which can damage lens fibres and disturb the arrangement of proteins.
Other risk factors include long-term exposure to ultraviolet light, long-term use of steroid medications, and eye injuries or inflammation. Cataracts can also be present from birth (congenital cataracts), although that is much less common than age-related cataracts.
On the other hand, one way to decrease risk is to eat a diet that includes plenty of fruit and vegetables. Vitamins and antioxidants help reduce oxidative damage, which may slow the protein changes that lead to cataracts. So, if you want your eyes to be healthy, eat fruit and vegetables, cut down on sugar, don’t drink and don’t smoke. Sounds like great advice for everything, not just the eyes. And this is what I learned today.
Sources
https://www.mayoclinic.org/diseases-conditions/cataracts/symptoms-causes/syc-20353790
https://en.wikipedia.org/wiki/Cataract
https://en.wikipedia.org/wiki/Phacoemulsification
https://en.wikipedia.org/wiki/Intraocular_lens
https://my.clevelandclinic.org/health/body/eye-lens-crystalline-lens
https://iris.ca/en/blogs/blog/what-is-the-crystalline-lens
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