Intraocular lens calculation is Dr. Stern’s main field of research; he founded and heads the Biomedical Optics Research Laboratory at Hadassah. This page explains what changes in cataract surgery after laser surgery on the cornea, and what the options are when the result of cataract surgery is not accurate.
Why does previous laser surgery change the lens calculation?
To choose the power of the intraocular lens, the length of the eye and the refractive power of the cornea are measured. The standard formulas assume a cornea with a natural shape. Laser surgery such as LASIK or PRK changes the shape of the cornea, and especially the relationship between its front and back surfaces – so the standard measurements and formulas may be wrong.
After laser surgery to correct short-sightedness, the error tends towards long-sightedness after cataract surgery, and after correction of long-sightedness – in the opposite direction. After RK (radial incisions in the cornea), the cornea may also change during the day and in the months after surgery.
How the calculation is made accurate
- Direct measurement of both corneal surfaces, front and back, with tomography – not just the front surface.
- Formulas developed specifically for eyes after laser surgery (such as Barrett True-K and Haigis-L), and comparison between several calculation methods – for example in the ASCRS calculator.
- Data from before the laser surgery (the prescription and corneal measurements) can help if they were kept, but they are not essential. If you have documents from the previous surgery, bring them to the consultation.
- Assessment of the astigmatism and of the optical quality of the cornea, before deciding on a toric or multifocal lens.
Which lens is suitable after laser surgery?
Most patients after laser surgery can receive a monofocal or toric lens. Caution is needed with multifocal lenses, because a cornea that has had laser treatment may add optical distortions; an EDOF lens suits some patients. The decision is based on the corneal measurements, not only on the type of previous surgery. About lens types
Realistic expectations
Even with the most advanced measurements and formulas, accuracy after laser surgery is slightly lower than in an eye that has not been operated on. So it is important to know in advance that some patients will need glasses for some activities, or a further correction once the eye has stabilised – with laser on the cornea or with an add-on lens.
Vision correction after cataract surgery
Sometimes, after cataract surgery, a residual prescription remains – short-sightedness, long-sightedness or astigmatism – or the lens chosen does not suit the patient’s needs. The first step is to understand the cause.
First – a diagnosis
- Wait for stabilisation: vision usually stabilises about 3 to 4 weeks after surgery.
- Rule out other causes of blur: dryness, macular oedema, or secondary cataract – which is treated with a YAG laser. About secondary cataract
- Re-measure the eye and the position of the lens – and with a toric lens, also its axis.
The correction options
- Glasses or contact lenses – the simple solution, without surgery.
- Rotating a toric lens – when the lens has moved from the planned axis, it can sometimes be returned to its axis in a short procedure.
- Laser on the cornea (PRK or LASIK) – to correct a small residual prescription, when the cornea is suitable.
- Add-on lens – an additional thin lens implanted in front of the existing lens, without removing it. Suitable for correcting prescription or astigmatism, and in some cases also for adding near vision.
- Lens exchange – removing the intraocular lens and implanting a different one. It is easier to perform in the first months after surgery.
The choice depends on the cause, the size of the residual error, the condition of the cornea and the time since surgery. At the consultation Dr. Stern examines the eye, recalculates the optics and explains which options suit you.
Frequently asked questions
Can I have cataract surgery after LASIK or PRK?
Yes. The cataract operation itself is the same; what changes is the lens calculation, which requires measuring both corneal surfaces and dedicated formulas.
Do I need the documents from my laser surgery?
They help if they were kept, but they are not essential – modern formulas allow an accurate calculation even without them.
Can I have a multifocal lens after laser surgery?
Sometimes. The decision is based on measurements of the optical quality of the cornea; for some patients an EDOF lens or a monofocal lens is more suitable.
I had cataract surgery and still need glasses. What can be done?
First the cause is identified. Depending on the findings, the options are glasses, laser on the cornea, an add-on lens, rotating a toric lens or exchanging the lens.
My vision became blurred again years after cataract surgery. Has the cataract come back?
A cataract does not come back, but the capsule behind the lens may become cloudy (secondary cataract). This is treated with a YAG laser in a short clinic visit. About secondary cataract