Overview
A cataract is a clouding of the lens inside the eye, which makes vision progressively blurred, dim and glary. It is the leading cause of blindness worldwide and it is almost entirely reversible with a short operation.
That is what makes it so frustrating. WHO reports that one in two people globally who need cataract surgery do not have access to it, and that in the African Region three in four people needing surgery go untreated.
Disease Summary
- Category
- Non-Communicable Disease
- Cause
- Clouding of the lens of the eye
- Transmission
- Not transmissible
- Body System
- Eyes
- Preventable
- No
- Curable
- Yes
Symptoms
Common Symptoms
Cataract develops slowly over years, so people often adjust without realising how much vision they have lost.
Cloudy or Blurred Vision
Vision becomes hazy, as though looking through a misted window. This is the central symptom.
Glare and Haloes Around Lights
Headlights and bright sunlight become dazzling, and many people notice this while driving at night first.
Difficulty Seeing at Night
Night vision deteriorates earlier and more noticeably than daytime vision.
Colours Looking Faded or Yellowed
Colours lose their vividness gradually, and people often only realise after surgery on one eye how much had changed.
Needing More Light to Read
Reading becomes harder in dim conditions and needs brighter and brighter light.
Double Vision in One Eye
Seeing two images with one eye, which persists when the other eye is closed.
Frequent Changes in Glasses Prescription
Needing a new prescription repeatedly over a short period is a common early sign.
A Visibly Cloudy Pupil
In advanced cataract the pupil looks white or grey rather than black. In a baby this is an emergency.
Danger Signs
Seek urgent medical attention immediately if any of the following symptoms develop.
A White or Cloudy Pupil in a Baby or Child
This needs urgent specialist assessment. Cataract present from birth must be treated early for sight to develop properly.
Sudden Loss of Vision
Cataract develops slowly. Sudden loss of vision is a different problem and is an emergency.
Eye Pain With Redness and Blurred Vision
Pain is not a feature of cataract. This combination suggests another condition such as acute glaucoma and needs same-day assessment.
Flashes, Floaters or a Curtain Across the Vision
These suggest a problem at the back of the eye and need urgent assessment, whether or not cataract is present.
Vision Loss Interfering With Daily Life
Not an emergency, but the point at which surgery should be discussed rather than deferred.
Diagnosis
Vision Testing
Measuring how well each eye sees, both in ordinary light and with glare, establishes how much the cataract is affecting function.
Examination of the Eye With a Slit Lamp
A magnified examination of the lens shows the cataract, where it sits within the lens and how dense it is.
Examination of the Red Reflex
Shining a light into the eye shows whether the lens is clear. In babies this simple check is how cataract present from birth is found.
Examining the Back of the Eye
Checking the retina and optic nerve establishes whether the cataract is the only reason for the reduced vision, which predicts how much surgery will help.
Measurements Before Surgery
Measurements of the eye determine the strength of the replacement lens, which influences whether glasses will be needed afterwards.
Laboratory Tests
Visual Acuity Test
The basic measure of how well each eye sees, and the standard used to decide when surgery is indicated.
Slit Lamp Examination
A magnified view of the lens that confirms the cataract and grades its density.
Eye Pressure Measurement
Checks for glaucoma, which commonly coexists with cataract and needs separate treatment.
Examination of the Retina
Establishes whether the retina and optic nerve are healthy, which determines how much vision surgery can restore.
Biometry Before Surgery
Measures the eye to calculate the strength of the artificial lens that will replace the cloudy one.
Treatment
Cataract Surgery
The cloudy lens is removed and replaced with a clear artificial one. It is one of the most effective operations in medicine, and most people go home the same day.
Stronger Glasses in the Early Stages
Updating glasses and using brighter light help while the cataract is mild. They do not slow its progression.
Brighter Lighting and Magnification
Practical changes at home make reading and daily tasks easier while waiting for surgery.
Early Surgery for Cataract in Children
Where cataract is present from birth, early surgery followed by careful correction is what allows sight to develop. Delay causes permanent vision loss even after the cataract is removed.
Glasses After Surgery
Most people still need glasses for some tasks after surgery, usually for reading.
Prevention
Protect your eyes from strong sunlight
Sunglasses that block ultraviolet light and a wide-brimmed hat reduce the lifetime exposure associated with earlier cataract.
Do not smoke
Smoking is a recognised risk factor for cataract, alongside its many other effects on health.
Manage diabetes well
Diabetes is associated with cataract developing earlier, so good control matters for the eyes as well as everything else.
Protect your eyes from injury
Eye injury is a recognised cause of cataract, and protective eyewear during farm work, welding and construction prevents it.
Have your eyes checked regularly
Particularly after the age of 50, and sooner if you have diabetes. Checks also find glaucoma, which has no early symptoms.
Check every newborn's eyes
A simple light check at birth and at routine reviews finds cataract present from birth, which WHO notes is a leading cause of vision impairment in children in low-income countries.
Risk Factors
Older Adults
Cataract is overwhelmingly a condition of later life.
- Risk rises steadily from around the age of 50
- Most people will develop some degree of cataract if they live long enough
- WHO reports that over 94 million people are affected by cataract
- Age alone is not a reason to be denied surgery
People Without Access to Eye Surgery
This is what turns a treatable condition into permanent blindness.
- WHO reports one in two people globally needing cataract surgery do not have access
- WHO reports three in four go untreated in the African Region
- WHO Regional Office for Africa reports that one in every six blind people globally lives in Africa
- Cost, distance and the need for someone to accompany the patient are all barriers
People With Other Medical Conditions
Several conditions bring cataract on earlier.
- People living with diabetes
- People taking steroid medicines long term
- People who have had an eye injury or eye surgery
- People with high exposure to ultraviolet light through outdoor work
Babies and Young Children
WHO notes that cataract present from birth is a leading cause of vision impairment in children in low-income countries.
- Babies born with a cloudy lens
- Children whose cataract is found late, after sight has failed to develop
- Children with certain infections acquired before birth, including rubella
- Early surgery is essential, because delay causes permanent loss
Complications
Blindness
Untreated cataract progresses to complete loss of useful vision. It remains the leading cause of blindness worldwide.
Falls and Injury
Poor vision in older adults substantially increases the risk of falls and fractures.
Loss of Independence and Work
Losing the ability to read, cook, farm or travel independently has consequences well beyond the eye.
Isolation and Low Mood
Losing sight cuts people off from social contact, and the effect on mental health is substantial and under-recognised.
Complications of Very Advanced Cataract
A cataract left until it is extremely dense can cause raised pressure and inflammation inside the eye, and it makes surgery more difficult.
Permanent Vision Loss in Children
Where cataract in a child is not treated early, the visual pathways do not develop and sight is not restored even after surgery.
When to Seek Medical Care
Vision That Is Getting in the Way of Daily Life
This is the usual point at which surgery is discussed. Difficulty reading, cooking, farming or driving all count.
Glare That Makes Driving at Night Difficult
Often the first thing that prompts people to seek help.
A White or Cloudy Pupil in a Child
Urgent. This needs specialist assessment without delay.
Sudden Loss of Vision, Eye Pain or Flashing Lights
None of these are caused by cataract, and all need urgent assessment.
For a Routine Eye Check After Age 50
Particularly if you have diabetes. Checks find glaucoma too, which causes no early symptoms at all.
Prognosis
Surgery Restores Vision in Most People
Cataract surgery is one of the most effective operations available, and most people notice a substantial improvement within days.
The Operation Is Short and Usually Day-Case
It typically takes 20 to 30 minutes under local anaesthetic, and most people go home the same day.
Untreated Cataract Leads to Blindness
It remains the leading cause of blindness worldwide, almost entirely because of lack of access to surgery rather than any limitation of the treatment.
Other Eye Disease Limits the Result
Where glaucoma or retinal disease is also present, surgery still helps but may not restore full vision.
Differential Diagnosis
Uncorrected Refractive Error
Simply needing glasses causes blurred vision and is by far the commonest cause. It is corrected with spectacles rather than surgery.
Glaucoma
Causes gradual loss of side vision without pain in its common form, and is detected by pressure and field testing. It frequently coexists with cataract.
Diabetic Eye Disease
Causes blurred and fluctuating vision, and is found by examining the retina. People with diabetes often have both.
Age-Related Macular Degeneration
Causes loss of central vision with distortion, unlike the general haze of cataract.
Corneal Clouding
Scarring of the front surface of the eye, including from trachoma, also causes a cloudy appearance but is a different problem with different treatment.
References
World Health Organization: Blindness and vision impairment
WHO fact sheet on causes of vision loss including cataract, and the global treatment gap.
World Health Organization: One in two people facing cataract blindness need access to life-changing surgery
WHO on the scale of cataract and the gap in access to surgery, including in Africa.
CDC: About Common Eye Disorders and Diseases
Overview of cataract alongside the other common causes of vision loss.
National Eye Institute: Cataracts
Plain-language detail on symptoms, risk factors and what surgery involves.
Frequently Asked Questions
Can a cataract be treated without surgery?
No. There is no medicine, eye drop or diet that clears a cataract. Stronger glasses and brighter light help while it is mild, but surgery to replace the cloudy lens is the only treatment that restores vision.
When should I have the surgery?
When the vision loss is getting in the way of daily life, such as reading, cooking, farming, working or driving. There is no advantage in waiting until the cataract is very advanced, and a very dense cataract makes surgery harder.
Does cataract surgery hurt?
It is normally done under local anaesthetic, so the eye is numb. Most people describe pressure and bright light rather than pain. The operation usually takes 20 to 30 minutes and most people go home the same day.
Will I need glasses afterwards?
Usually for some tasks, most often reading. The artificial lens is chosen to give the best distance vision in most cases. Discuss what matters most to you before the operation, because it influences the choice of lens.
Why do so many people go blind from something curable?
Because of access, not because of the condition. WHO reports that one in two people globally who need cataract surgery do not have it, rising to three in four in the African Region. Cost, distance, the need for someone to accompany the patient and a shortage of eye surgeons all contribute.