Ocular Biometry Before Cataract Surgery: How Lens Power Is Calculated
Quick answer: Ocular biometry is a set of measurements taken before cataract or lens replacement surgery to choose the power of the intraocular lens (IOL). It measures the eye's length (axial length), the curvature of the cornea (keratometry), the depth of the front chamber and lens thickness. Most clinics use optical biometry, a quick, contact-free scan; ultrasound is used when the cataract is too dense. Accurate biometry is what makes the final glasses prescription after surgery predictable.
Considering eye surgery? Start with an eye examination at Vision Concern for an assessment and referral advice.
What is measured
- Axial length: front-to-back length of the eye.
- Keratometry: corneal curvature and astigmatism.
- Anterior chamber depth and lens thickness.
- Sometimes corneal diameter (white-to-white).
These values are entered into IOL formulas to calculate the lens power for your target, usually clear distance vision.
Optical vs ultrasound biometry
Optical biometry uses light and does not touch the eye. Ultrasound (A-scan) biometry uses a probe on the numbed cornea or a water bath, and is used when a dense cataract blocks the light-based measurement.
How to prepare
If you wear contact lenses, your surgeon will ask you to stop wearing them for a set period beforehand, because lenses temporarily change corneal shape. Tell the team about any previous laser eye surgery, which changes the calculation. Dry eye may be treated first so readings are reliable.
How Vision Concern can help
Vision Concern is an eye-examination clinic and optical shop in Kathmandu with branches in Lazimpat, Boudha-Tushal and Makalbari. It does not perform surgery or injections. Its optometrists can examine your eyes, explain your prescription and findings, and advise on referral to an eye hospital or specialist; it can also provide glasses and contact lenses before or after treatment elsewhere.
Frequently asked questions
Is biometry painful?
Optical biometry is painless and contact-free; ultrasound uses numbing drops.
Why do I need biometry for both eyes?
Comparing both eyes helps check accuracy and plan a balanced result.
Can I still need glasses after cataract surgery?
Yes. Biometry makes the result predictable, but many people still need glasses for reading or fine-tuning, depending on the lens chosen.
This guide is general education and does not replace an eye examination or advice from your treating doctor.
Yes. Many visitors, particularly from Bangladesh and West Bengal (Kolkata), come to Nepal for cataract, retina, or other eye surgery at a hospital and also want new glasses, a general eye exam, or contact lenses at the same time, before or after their procedure. Vision Concern is an optical and eye-examination clinic, not a surgical hospital, so we work alongside hospitals such as Tilganga: we are happy to see you for glasses, contact lenses, or a routine check-up either side of your surgical treatment elsewhere.
No conversion is needed. Eyeglass prescriptions from Germany, France, the UK, the USA, China, Russia, and almost every other country use the same international format, SPH (sphere), CYL (cylinder), and AXIS, measured in diopters. Our opticians read this directly, so you can bring your prescription paper, a photo of it on your phone, or simply your current glasses, and we will use the same values. If your prescription is more than a year or two old, we recommend a quick, free re-check before we make your new pair.
Yes. Above roughly 3,000 metres, UV exposure increases sharply because of the thinner atmosphere and reflection off snow, and ordinary sunglasses (category 2-3) do not block enough UV to prevent snow blindness (photokeratitis). We recommend glacier glasses or category-4 sunglasses with side shields, and can fit these with your own prescription if needed. Vision Concern offers ZEISS polarized, UV400-certified sunglasses with prescription lenses, which we can prepare before you set off on your trek.