Cataract and Glaucoma: Two Very Different Problems People Confuse
Cataract and glaucoma are both common, both associated with ageing, and routinely mixed up. The difference matters enormously, because one is a correctable mechanical problem and the other is permanent nerve damage that you can only stop from getting worse.
Cataract: the lens clouds
Your eye has a clear lens behind the pupil that focuses light. Over decades, the proteins in it change and it becomes progressively cloudy. That is a cataract.
It is not a growth, not a film over the eye, and not something that spreads from one eye to the other. It is the lens itself losing transparency.
Symptoms develop slowly:
- Gradual blurring, like looking through a dirty window
- Glare and haloes around lights, especially night driving
- Colours looking faded or yellowed
- Needing more light to read
- Frequent changes in spectacle prescription
- Occasionally, a temporary improvement in near vision as the lens changes shape, sometimes called second sight
Risk factors include age, diabetes, prolonged steroid use, smoking, eye injury, and cumulative ultraviolet exposure.
Treatment is surgical, and only surgical. No drops, exercises or supplements reverse a cataract. Modern surgery removes the cloudy lens and replaces it with a clear artificial one. It is usually done under local anaesthesia, takes a short time, and is among the most commonly performed and most successful operations in the world.
The old advice to wait until a cataract is “ripe” is obsolete. Surgery is appropriate when vision affects what you need to do: reading, driving, working, or safety. There is no advantage to waiting, and very advanced cataracts are technically harder to remove.
Glaucoma: the optic nerve dies
Glaucoma is damage to the optic nerve, the cable carrying visual information from the eye to the brain. In most cases it is associated with raised pressure inside the eye, though it can occur at normal pressures too.
The critical difference: the damage is permanent. Lost nerve fibres do not come back. Treatment can only halt or slow further loss.
The second critical difference: the common form has no symptoms until late.
Open-angle glaucoma, the usual type, destroys peripheral vision first, slowly, and symmetrically enough that the brain fills in the gaps. People routinely lose a large share of their visual field before noticing anything. By the time central vision is affected, a great deal is gone permanently.
This is why glaucoma is found by testing, not by symptoms.
Risk factors: age over 40, family history, which is strong, African or Caribbean ancestry for open-angle, East Asian ancestry for angle-closure, high short-sightedness, diabetes, prolonged steroid use, and previous eye injury.
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Treatment aims to lower eye pressure: daily drops, laser treatment such as selective laser trabeculoplasty, or surgery. Drops only work while used, and poor adherence is the main reason glaucoma progresses in people who are being treated.
Acute angle-closure glaucoma is an emergency
A less common form in which drainage is blocked suddenly and pressure rises sharply within hours.
Symptoms: severe eye pain, headache, nausea and vomiting, blurred vision, haloes around lights, a red eye, and a fixed mid-dilated pupil.
This can destroy vision within a day. It needs emergency ophthalmology care immediately, not a next-week appointment. The nausea and vomiting lead some people to an emergency department thinking they have a stomach problem, which delays diagnosis.
Telling them apart
| | Cataract | Glaucoma | |—|—|—| | What is affected | The lens | The optic nerve | | Onset | Slow, over years | Slow and silent, or sudden in angle-closure | | Early symptom | Blur and glare | Usually none | | Vision lost first | Central clarity | Peripheral field | | Reversible | Yes, with surgery | No |
A person can have both, and cataract surgery does not treat glaucoma, though it can modestly lower pressure in some cases.
Who should be screened, and when
Because glaucoma is silent, screening is the entire strategy.
- A comprehensive eye examination at around 40 for everyone, earlier with risk factors
- Every one to two years after 40, more often with family history
- Annually from 60
- Annually for anyone with diabetes, regardless of age, for retinal screening as well
- Baseline testing at any age if a first-degree relative has glaucoma, since risk rises several-fold
A proper examination includes pressure measurement, examination of the optic nerve, a visual field test, and increasingly optical coherence tomography, which measures nerve fibre thickness and detects loss before the field test does.
Pressure measurement alone is not a glaucoma screen. A substantial proportion of people with glaucoma have pressures in the normal range.
Other causes of gradual vision loss worth knowing
Diabetic retinopathy, damage to retinal blood vessels, also silent until advanced, and the reason annual screening matters in diabetes.
Age-related macular degeneration, affecting central vision, with straight lines appearing wavy as an early sign. Sudden distortion needs urgent assessment because one form is treatable only if caught early.
Refractive change, which is the common and benign explanation for gradual blur and is corrected with glasses.
When to seek care urgently
- Sudden loss of vision in one eye
- A curtain or shadow across part of your vision
- A sudden shower of new floaters, or flashes of light, which can indicate retinal detachment
- Severe eye pain with nausea and haloes
- Straight lines appearing bent or wavy
- Double vision of recent onset
The short version
Cataract clouds the lens, announces itself with blur and glare, and is fixed by replacing the lens. Glaucoma kills the optic nerve, says nothing until the damage is substantial, and can only be slowed. The first you can wait on; the second is the reason to have your eyes examined on schedule even when your vision feels fine.