What is glaucoma?
Glaucoma is a group of conditions in which the optic nerve is damaged, usually in association with raised pressure inside the eye, and it typically affects peripheral vision before central vision.
- Subject
- Eye conditions
- Topic
- Glaucoma
- Kind of question
- What is…
- Last reviewed
- 22 September 2026
In more detail
Because the loss starts at the edges and progresses slowly, most people notice nothing until it is advanced. That is the whole argument for measuring eye pressure and examining the optic nerve on a schedule rather than waiting for symptoms.
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Where this answer sits
It is one of 483 answers in the vision and eye health knowledge base, filed under Eye conditions & diseases in Glaucoma . The subject page carries the answers either side of it, and the hub is searchable.
Subjects this question touches
The pages that answer the subject behind the question, rather than the question itself.
- Condition Glaucoma
- Condition Keratoconus
- Condition Retina and macula conditions
- Condition Diabetic eye disease
- Condition Eye infections, allergies and injuries
This information is for educational purposes and does not replace an examination by a qualified eye-care professional.
General answers cannot tell you what is happening in your own eyes. Only an examination by a qualified ophthalmologist can do that.
Sources & further reading
We prefer primary sources. Where a claim comes from a manufacturer, a single study or a regulator, it is labelled as such below.
- Eye Health Information
Condition-by-condition eye health information from a US government research institute, written for patients rather than for clinicians.
Used for Plain-language explanations of eye conditions and their symptoms; Healthy vision and screening guidance.
Link checked 23 September 2026
- EyeSmart: eye health information for the public
Patient-facing material from the largest ophthalmology professional body, covering conditions, tests and treatments outside refractive surgery.
Used for Cross-checking patient-facing explanations of non-refractive eye conditions; Describing what tests such as dilation and OCT involve.
Link checked 23 September 2026
- Cochrane Library
Systematic reviews and meta-analyses. Useful for readers who want to know how strong the pooled evidence is, not just what one trial found.
Used for Helping readers judge the strength of the evidence base.
Link checked 22 September 2026