What Is a Cataract? The Clouded Lens That Slowly Dims Your Sight
By Pauline Driscoll | Medically reviewed by Mr Lewis Pereira, FRCOphth
Published March 18, 2026 · Last updatedMay 7, 2026 · Last reviewed May 13, 2026 · 3 min read
Key takeaways
- A cataract is a clouding of the eye's natural lens, the clear lens behind the iris that focuses light onto the retina.
- As lens proteins clump with age, the lens turns cloudy and yellow, so vision becomes blurred, dim and washed-out.
- Cataracts are mostly age-related and very common; most people develop some lens clouding by their 70s.
- They are the leading cause of reversible blindness worldwide and a normal part of ageing.
- A cataract cannot be cleared with drops or glasses; the only proven treatment is surgery to replace the clouded lens.
A cataract is a clouding of the eye’s natural lens, the clear lens that sits behind the iris and focuses light onto the retina; as the proteins in the lens clump together with age, the lens turns cloudy and yellow, so vision becomes blurred, dim and washed-out, with glare and haloes around lights1. It is not a growth or a film over the eye but a change inside the lens itself, and it is one of the most common and ordinary changes that vision goes through with age2.
This article is the starting point for understanding the condition. Once you know what a cataract is, the natural next questions are about cataract surgery, the only proven treatment, and about what causes cataracts and the cataract symptoms to watch for.
What a cataract actually is
A cataract is a clouding of the eye’s natural lens, the clear focusing lens that sits behind the iris1. In a healthy eye that lens is transparent, and light passes straight through it onto the retina. Over the years the proteins that make up the lens begin to clump together, scattering and blocking light, so the lens loses its clarity and takes on a yellow or brownish tint.
The result is that vision becomes blurred, dim and washed-out2. Because the change is inside the lens, it cannot be wiped away or corrected with stronger glasses once it is established. I think of it as looking through a window that has slowly steamed up from the inside, where no amount of cleaning the outside makes any difference.
Why a cataract dims and yellows your sight
A cataract dims vision because the clouded lens scatters and absorbs light instead of letting it pass cleanly to the retina1. The yellowing matters too: as the lens browns, blues and whites look duller, so colours appear faded and less vivid.
This is exactly how it crept up on me. I am retired now, and for a long time I blamed dim hallways and dirty spectacles. My sight had dimmed so slowly that I had quietly turned every light in the house up and stopped driving at dusk without ever deciding to. It was only when I struggled to read a menu in good daylight that I booked a sight test, and that was when both eyes were found to have cataracts.
Who gets cataracts and when
Cataracts are mostly age-related and very common, and most people develop some degree of lens clouding by their 70s2. They are the leading cause of reversible blindness worldwide, which is striking given how treatable they are3.
While ageing is by far the commonest cause, cataracts can also follow diabetes, long-term steroid use, eye injury, some genetic conditions, and can even be present at birth as congenital cataract. For more on this, see what causes cataracts.
Why the only fix is surgery
A cataract cannot be cleared with drops, glasses, diet or lasers from the outside; the only proven treatment is surgery to remove the clouded lens and replace it with an artificial intraocular lens2. There is no eye drop or supplement shown to reverse the clouding.
The reassuring part is how successful that surgery is. Treatment is offered when the cataract starts to affect daily life, such as driving, reading or hobbies, rather than at a fixed level of cloudiness4. To understand the operation itself, read cataract surgery, and if you are weighing up timing, when to have cataract surgery.
References
- What are cataracts?, American Academy of Ophthalmology. ↩
- Cataract surgery, NHS. ↩
- Blindness and vision impairment, World Health Organization. ↩
- Cataracts in adults: management (NG77), NICE. ↩
Common questions
What exactly is a cataract?
A cataract is a clouding of the eye's natural lens, the clear lens that sits behind the iris and focuses light onto the retina. As the proteins in the lens clump together with age, the lens turns cloudy and yellow, and light can no longer pass through cleanly, so vision becomes blurred, dim and washed-out. It is a change to the lens itself, not a film growing over the front of the eye.
Is a cataract a normal part of ageing?
Yes. Cataracts are mostly age-related and very common, and most people develop some degree of lens clouding by their 70s. Worldwide they are the leading cause of reversible blindness. Developing a cataract does not mean anything has gone wrong; it is one of the most ordinary changes the eye goes through with time.
Can a cataract be cured without surgery?
No. A cataract cannot be cleared with drops, glasses, diet or lasers applied from the outside. Once the lens has clouded, the only proven treatment is surgery to remove the clouded lens and replace it with an artificial intraocular lens. Glasses may help for a while in the early stages, but they cannot reverse the clouding.
Will a cataract make me go blind?
Left untreated, a cataract can eventually cause severe sight loss, and globally cataracts remain a leading cause of blindness. The important point is that this blindness is reversible: cataract surgery removes the clouded lens and restores vision in around 9 in 10 people, assuming the eye has no other disease.
Can you have a cataract in only one eye?
Yes. Cataracts often develop unevenly, so one eye can be noticeably worse than the other, or one eye can be affected while the other stays clear for years. Because the better eye compensates, a cataract in one eye can go unnoticed for a long time until it is picked up at a sight test.
How do I know if I have a cataract?
Common signs are gradually blurred or misty vision, increasing glare and haloes around lights, faded or yellowed colours, and worsening night vision. These come on slowly, which is why many people do not realise how much sight they have lost until it is measured. An optometrist can confirm a cataract with a simple eye examination.
Written by Pauline Driscoll. Medically reviewed by Mr Lewis Pereira, FRCOphth.
Our guides are written from personal experience and reviewed by a qualified clinician for accuracy. Read our editorial policy.
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