A cataract evaluation is a comprehensive eye exam that typically takes one to two hours and involves a series of tests to assess how much your vision is affected, determine whether surgery is appropriate, and gather precise measurements for planning the procedure. Some tests are familiar, like reading an eye chart. Others involve specialized imaging equipment that maps the surface and interior of your eye in detail. Here’s what to expect at each step.
Visual Acuity and Pressure Checks
The appointment usually starts with a standard eye chart test to measure how well you can see at various distances. This establishes a baseline and helps your eye doctor understand whether the cataract is meaningfully interfering with your daily vision. You’ll read letters on a chart from across the room, and you may also be tested for glare sensitivity, since cataracts often cause the most trouble in bright light or when driving at night.
Next, your eye pressure is measured using a procedure called tonometry. Normal eye pressure falls between 10 and 21 millimeters of mercury. The most common method uses a small probe mounted on the slit lamp (the microscope your doctor looks through) after numbing drops and a fluorescent dye are placed on your eye. You won’t feel pain, just brief contact. Some offices use an air-puff device instead, which requires no numbing drops at all. This pressure reading doesn’t diagnose cataracts directly, but it screens for glaucoma, a condition that could affect your surgical plan and visual outcome.
Slit Lamp Examination
The slit lamp is the centerpiece of the evaluation. It’s a microscope with a thin beam of light that lets your doctor examine the front structures of your eye in cross-section: the cornea, iris, and lens. To get a clear view of the cataract itself, your pupils need to be dilated. Eye drops (usually tropicamide) are instilled, and it takes about 20 to 30 minutes for your pupils to fully open.
Once dilated, your doctor grades the cataract’s density and type. The standard grading system, called LOCS III, uses a set of reference photographs to rate how cloudy and discolored the lens has become, on a scale from 1 to 6. Two features are assessed separately: how much the lens scatters light (opalescence) and how brown or yellow it has turned (brunescence). A higher grade generally means a denser cataract that requires more energy to remove during surgery, which influences the surgical technique your doctor selects.
Retinal and Optic Nerve Check
While your pupils are still dilated, your doctor examines the back of your eye, including the retina and optic nerve. This step is critical because a cataract can mask other problems. If you have an undetected condition affecting the macula (the central part of your retina responsible for sharp vision), removing the cataract alone won’t restore clear sight.
A standard dilated exam catches most issues, but subtle macular problems can hide behind a dense cataract. For this reason, many surgeons also order an optical coherence tomography scan, or OCT. This painless imaging test takes a detailed cross-sectional picture of the macula in seconds, and it works even when the lens is cloudy. It can reveal swelling, fluid buildup, or early degeneration that a visual exam might miss. Identifying these conditions before surgery helps set realistic expectations for how much your vision will improve afterward.
Eye Measurements for Lens Selection
If surgery is planned, your eye needs to be precisely measured so that the replacement lens (intraocular lens, or IOL) is the right power for your eye. This process, called biometry, is done with a laser-based device that takes several measurements in one sitting:
- Axial length: the distance from the front surface of your eye to the retina, which is the single most important number for calculating lens power.
- Corneal curvature (keratometry): how steeply curved your cornea is, which affects how light bends as it enters your eye.
- Anterior chamber depth: the space between your cornea and the lens, which determines where the new implant will sit.
The machine does all of this without touching your eye. You simply rest your chin on a support and look at a target light while the device takes readings. The whole process takes a few minutes.
In some cases, your doctor also orders corneal topography, a mapping scan that creates a detailed picture of your cornea’s surface shape. This is especially useful for detecting astigmatism or irregular curvature, and it becomes essential if you’ve had previous laser vision correction like LASIK, since those procedures alter the cornea in ways that complicate standard lens calculations.
Contact Lens Wearers: Plan Ahead
If you wear contact lenses, you’ll need to stop wearing them before your measurement appointment. Contacts temporarily reshape the cornea, and if it hasn’t returned to its natural shape, the biometry readings will be off, potentially resulting in the wrong lens power. The general guideline from the Royal College of Ophthalmologists is to leave soft lenses out for at least one week and rigid (hard) lenses out for four weeks before measurements are taken. Some clinics use slightly different timelines, so confirm with your doctor’s office when you schedule the appointment.
Corneal Cell Count
Not everyone needs this test, but if you have a history of eye trauma, prior eye surgery, or a condition called Fuchs’ dystrophy, your doctor will likely perform specular microscopy. This non-invasive scan photographs the innermost layer of cells lining the back of your cornea. These endothelial cells keep the cornea clear by pumping fluid out of it, and they don’t regenerate. If the cell count is already low, cataract surgery carries a higher risk of causing corneal swelling or cloudiness afterward.
The results help your surgeon decide whether to proceed with cataract surgery alone or combine it with a corneal transplant procedure. Even when the cell count is adequate but borderline, knowing the number in advance allows the surgeon to take extra precautions to protect the cornea during the operation.
Choosing Your Replacement Lens
A significant part of the evaluation is a conversation about which type of IOL best fits your life. The main categories break down by what distance they correct:
- Monofocal lenses provide sharp vision at one distance. Most people choose distance focus and wear reading glasses afterward. If you prefer, the lens can be set for near vision instead, or your surgeon can set one eye for distance and the other for near (called monovision).
- Multifocal lenses have zones built in for near, intermediate, and distance vision, similar to bifocal glasses. They reduce dependence on glasses but can cause halos or glare around lights, particularly at night.
- Extended depth-of-focus (EDOF) lenses stretch a single corrective zone to cover distance and intermediate vision, with fewer glare issues than multifocals, though near vision may still require reading glasses.
- Toric lenses correct astigmatism and are available in both monofocal and multifocal versions. People with moderate to high astigmatism tend to be much happier with these than with standard lenses.
Your doctor will recommend a lens based on your measurements, eye health, and how you use your eyes day to day. If you drive frequently at night, multifocal or EDOF lenses may not be ideal because of their glare effects. If you have glaucoma, macular degeneration, or other eye disease, multifocal and EDOF lenses are generally not recommended because they let less light reach the retina, which can worsen vision in eyes that are already compromised.
Medication Review and Surgical Risk Factors
Your doctor will ask about all medications you currently take. One class of drugs is particularly important: alpha-blockers prescribed for an enlarged prostate (benign prostatic hyperplasia). Common examples include tamsulosin (Flomax), terazosin, and doxazosin. These medications affect the muscles inside the eye that control the pupil, and they can cause the iris to become floppy during surgery, making the procedure more complicated. If your surgeon knows ahead of time, they can adjust their technique and dilation approach accordingly.
Blood thinners, diabetes medications, and drugs that affect the immune system may also come up in the discussion, since they can influence healing and infection risk.
What to Expect After the Evaluation
Because your eyes will be dilated, your vision will stay blurry and light-sensitive for several hours after the appointment. The American Academy of Ophthalmology advises arranging a ride home, since it may not be safe to drive with dilated pupils. Bring sunglasses if you have them. The blurriness varies from person to person, and your doctor can’t predict exactly how long it will last, but most people find it resolves within three to six hours.
By the end of the evaluation, your doctor will have a complete picture: how much the cataract is affecting your vision, whether any other eye conditions need attention, the precise measurements for your new lens, and which lens type suits your needs. If surgery is recommended, the next step is scheduling the procedure, which is typically done as an outpatient operation lasting under 30 minutes.