The Cataract Assessment: Biometry, Eye-Health Checks and Consent
By Pauline Driscoll | Medically reviewed by Mr Lewis Pereira, FRCOphth
Published June 1, 2026 · Last reviewed June 12, 2026 · 2 min read
Key takeaways
- The cataract assessment confirms a cataract is the cause of your symptoms and plans the operation in detail.
- Biometry measures the length and curvature of the eye to calculate the power of the intraocular lens you need.
- The assessment checks overall eye health to spot other conditions that could limit the final result.
- Lens choice and target focus are discussed, since a monofocal lens still leaves most people needing reading glasses.
- Consent covers the benefits, the small risks, and the fact that surgery is offered when sight affects daily life.
The cataract assessment confirms that a cataract is causing your symptoms and plans the operation: it measures the eye with biometry to calculate your intraocular lens power, checks the overall health of the eye for conditions that could limit the result, and covers lens choice and consent1. It is the step where suitability, lens choice and timing are properly decided, rather than by preference alone2.
This assessment is the gateway to cataract surgery. If you are still deciding whether you are ready, see when to have cataract surgery and who needs cataract surgery.
Confirming the cataract and your symptoms
The assessment first confirms that a cataract is the cause of your blurred, dim or glare-affected vision3. Your vision is measured, the eye is examined, and your symptoms are matched against what is found in the lens.
This matters because surgery is offered when the cataract affects daily life, not at a fixed level of cloudiness2. When I went, I described how I had quietly stopped driving at dusk and turned every light up at home, and that everyday impact was as important to the discussion as the view through the microscope.
Biometry: measuring for your lens
Biometry is the set of painless measurements, including the eye’s length and the curvature of the cornea, used to calculate the power of the intraocular lens you need4. Getting these measurements right is what allows the new lens to focus your vision accurately.
It is usually done with a scanning device that does not touch the eye and takes only a few minutes. These numbers, combined with your chosen target focus, determine which lens power is implanted, which is why this step is so central to a good result.
Checking the health of the whole eye
The assessment checks overall eye health to spot other conditions, such as macular degeneration, glaucoma or diabetic changes, that could limit your final vision even after a successful operation1. A good operation can still give limited vision if the eye has other disease, so finding these beforehand allows honest expectations.
If you have one of these conditions, our companion guides cataract surgery with macular degeneration, cataracts and glaucoma, and cataracts and diabetes explain how they affect the picture.
Lens choice and consent
Lens choice and your target focus are discussed here, since a monofocal lens still leaves most people needing reading glasses, while premium lenses aim to reduce glasses use but can cause more glare and haloes3. Your surgeon helps match the lens to your eyes and lifestyle; see choosing a lens for cataract surgery.
Consent covers the benefits, the small risks including the roughly 1 in 1,000 chance of a serious sight-threatening complication, and what to expect on the day and in recovery3. It is your chance to ask anything, so it pairs well with our list of questions to ask before cataract surgery.
References
- Understanding cataracts: patient information, Royal College of Ophthalmologists. ↩
- Cataracts in adults: management (NG77), NICE. ↩
- Cataract surgery, NHS. ↩
- Cataract surgery, American Academy of Ophthalmology. ↩
Common questions
What happens at a cataract assessment?
The cataract assessment confirms that a cataract is causing your symptoms and plans the operation. It includes measuring your vision, examining the eye, taking biometry measurements to calculate the lens power you need, checking the overall health of the eye, and discussing lens choice and consent. It is also your chance to ask questions and raise any concerns before deciding to go ahead.
What is biometry for cataract surgery?
Biometry is a set of painless measurements of the eye, including its length and the curvature of the cornea, used to calculate the power of the intraocular lens you need. Getting these measurements right is what allows the new lens to focus your vision accurately. It is usually done with a scanning device that does not touch the eye and takes only a few minutes.
Why does the assessment check the rest of my eye?
The assessment checks overall eye health to spot other conditions, such as macular degeneration, glaucoma or diabetic changes, that could limit your final vision even after a successful operation. A good operation can still give limited vision if the eye has other disease, so finding these conditions beforehand allows honest expectations to be set and your care to be planned properly.
Will I choose my lens at the assessment?
Yes, lens choice and your target focus are usually discussed at the assessment. A standard monofocal lens gives excellent distance vision but most people still need glasses for reading, while premium lenses aim to reduce glasses use but can cause more glare and haloes. Your surgeon will help match the lens to your eyes, lifestyle and tolerance of night-vision effects.
What does consent for cataract surgery involve?
Consent means you understand and agree to the operation. It covers the benefits, the small risks including the roughly 1 in 1,000 chance of a serious sight-threatening complication, what to expect on the day and during recovery, and the fact that surgery is offered when your sight affects daily life rather than at a fixed level of cloudiness. You can ask anything and should feel comfortable before signing.
Does the cataract assessment hurt?
No, the assessment is not painful. The measurements, including biometry, are painless, and the eye examination uses lights and lenses rather than anything sharp. You will usually have dilating drops to widen the pupil, which can blur your vision and make you light-sensitive for a few hours, so it is wise to arrange not to drive straight afterwards.
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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