Axial length
The distance from the cornea to the retina is one of the key measurements for calculating lens power.
Measuring the eye and calculating lens power
Optical biometry before cataract surgery
Before cataract surgery, we calculate the artificial lens power using biometry, including eye length and corneal power. Small measurement differences can affect the final refraction.
Understanding the procedure
Several measurements inform your individual lens calculation.
Optical biometers measure eye length, corneal curvature and other distances without contact. A formula combines these readings with the lens model and visual goal to calculate the required lens power.
A dense cataract may prevent an optical reading, making ultrasound biometry necessary. Corneal changes, contact lens use and dry eyes must be considered before the final calculation.
- Objective
- Calculate lens power
- Measured values
- Axial length and corneal refractive power
- Contact
- Optical measurement, usually without contact
- Alternative
- Ultrasound when the view is obscured
Used where needed
Which measurements matter most?
Calculations account for your anatomy, previous surgery and desired visual outcome.
Corneal refractive power
Curvature and astigmatism affect overall focusing power and the choice of toric lenses.
Anterior chamber depth and lens measurements
Additional anatomical measurements help modern formulas predict the artificial lens’s final position.
Visual objective
Together, we decide whether to prioritise distance vision, near vision or a coordinated monovision approach.
Step by step
How lens power is calculated
Stable corneal measurements and a clear visual goal matter more than extra decimal places.
Stabilize the eye surface
We account for dry eyes and contact lens effects before the final measurements.
Repeat measurements
We repeat measurements of eye length, corneal curvature and other parameters and check that the results are consistent.
Add special features
Planning takes account of previous laser treatment, corneal surgery, high prescriptions and retinal disease.
Choosing a lens and a vision goal
We bring together the calculation formula, lens model and desired focus during your consultation.
Understanding the results
Even a precise calculation is still a prediction.
Biometry reduces the risk of an unexpected remaining refractive error, but cannot eliminate it. Healing, the lens’s final position and individual anatomy still affect the outcome.
Toric and multifocal lenses require extra measurements and particularly stable corneal readings. Whether a premium lens is suitable also depends on your retina, optic nerve, cornea and visual needs.
Well prepared
How to prepare for your visit
- Leave contact lenses out as individually advised
- Previous laser treatment or cataract surgery records
- Your current glasses prescription
- Think about which everyday viewing distances matter most without glasses
Frequently asked questions
Clear, concise answers.
Why is it measured several times?
Repeated, consistent readings increase confidence and show whether the eye’s surface or fixation affects the measurement.
Does biometry guarantee freedom from glasses?
No. It allows precise planning, but a remaining refractive error or need for glasses is still possible.
Why do I need to stop wearing contact lenses temporarily?
Contact lenses can temporarily change corneal curvature and affect the calculated lens power.
Medical note
This page cannot replace an eye examination. Your symptoms, history and findings determine which tests are useful and how their results should be interpreted.
Medical basics
Sources and further information.
Related topics
All non-surgical eye care services