What tests are done before cataract surgery — and which measurements actually determine the IOL?

Modern cataract surgery is partly a refractive procedure. Removing the cloudy lens is only half the job; selecting the right IOL power and identifying other eye disease determine how close the result comes to the visual target.

Biometry

Optical biometry measures the eye's axial length and other dimensions used in IOL power formulas. In dense cataracts, ultrasound biometry may sometimes be needed.

Keratometry

Corneal curvature measurements quantify corneal power and astigmatism. These values directly affect IOL calculation and decisions about toric IOLs or astigmatism management.

Corneal topography or tomography

Not every routine cataract patient needs every advanced map, but topography/tomography can be important when astigmatism is irregular, keratoconus is suspected, prior LASIK/PRK exists, or premium IOL decisions require more detail.

Ocular-surface evaluation

Dry eye can distort keratometry and topography. Treating the ocular surface before final measurements can improve calculation consistency.

Dilated retinal examination

The surgeon evaluates the retina, macula, optic nerve, and other posterior-segment structures to identify disease that may limit postoperative vision.

OCT of the macula

OCT can reveal epiretinal membrane, macular degeneration, edema, or other pathology that may not be obvious from symptoms alone. It can be especially useful before premium/multifocal IOL decisions.

Eye pressure and glaucoma evaluation

Intraocular pressure, optic nerve, visual fields, or angle evaluation may matter if glaucoma is known or suspected. Cataract surgery can sometimes be combined with MIGS when appropriate.

Corneal endothelial health

Patients with Fuchs dystrophy or low endothelial reserve may need specular microscopy or other corneal assessment because cataract surgery can worsen endothelial decompensation.

Prior refractive surgery changes the math

LASIK, PRK, or radial keratotomy can make IOL power calculation less predictable because the relationship between measured corneal curvature and true optical power has changed.

Toric and multifocal decisions

A toric IOL requires reliable astigmatism measurement and axis planning. Multifocal/EDOF IOLs require careful counseling about halos, contrast, ocular-surface quality, macular health, and residual refractive error.

Questions to ask before final lens selection

• What is my target: distance, near, or monovision?
• How much corneal astigmatism do I have?
• Is it regular?
• Is my macula healthy?
• Do I have dry eye that could affect measurements?
• How does prior LASIK/PRK change accuracy?
• What glasses might I still need?

Frequently asked questions

The cataract operation lasts minutes; the measurements made before it can shape your vision for decades.

Why two eyes can need different plans

The second eye is not automatically assigned the same IOL. Axial length, astigmatism, macular health, corneal shape, dominance, prior refractive result in the first eye, and patient satisfaction can all change the second-eye target.

Monovision simulation

If monovision is being considered, prior contact-lens experience or a trial can help clarify whether the brain tolerates one eye targeted for distance and the other for near.

Biometry after prior LASIK or PRK

Historical refractive data can help but may not always be available. Modern formulas and tomography-based methods can improve estimates, yet refractive surprise remains more likely than in untouched corneas.

Endothelial cell counting

Specular microscopy can help quantify endothelial reserve in Fuchs dystrophy or other corneal disease. This can influence whether cataract surgery alone is reasonable or whether endothelial keratoplasty should be combined or staged.

Retinal disease and premium IOLs

Multifocal optics split light and can reduce contrast. Significant macular disease, advanced glaucoma, irregular cornea, or unstable ocular surface may make those tradeoffs less attractive.

What “premium” does not mean

A premium-priced IOL is not universally better. The right lens is the one whose optical compromises match the patient's eye and priorities.

How to compare two surgeon recommendations

If two ophthalmologists recommend different operations, ask each to show the imaging or examination finding driving the choice. Then compare the underlying diagnosis, not merely the procedure names. Different recommendations can reflect different interpretations of anatomy, different acceptable risk thresholds, or different technical experience.

Travel and follow-up are part of the procedure

Eye surgery often has time-sensitive postoperative checks. Retinal gas, graft attachment, intraocular pressure, wound healing, or corneal epithelium can all create reasons to delay travel. International patients should plan around the surgeon's required checkpoints rather than buying a fixed return flight first.

What records to take home

• Exact diagnosis
• Operative report
• Implant, graft, gas, or device details when applicable
• Medication schedule
• Postoperative restrictions
• Warning signs
• Surgeon contact
• Relevant OCT, topography, retinal images, or visual-field results