What an eye exam covers and why you need one
An eye exam is a series of tests that measure how well you see, check the health of your eyes, and screen for diseases like glaucoma and diabetic retinopathy. You will sit in a darkened room while an optometrist or ophthalmologist uses machines and handheld tools to look at the front and back of your eye, test your vision at different distances, and check how your eyes work together. The exam takes 30 to 60 minutes depending on whether you need dilating drops and whether the doctor finds anything that needs closer inspection.
You should have an eye exam every one to two years if you have no vision problems or eye disease, every year if you wear contacts, and more often if you have diabetes, glaucoma, or a family history of eye disease. Even if your vision feels fine, an eye exam can catch diseases early, before you notice symptoms. Many serious eye conditions cause no pain or warning signs until damage is already done.
Key Takeaways
- An eye exam tests your vision, measures your prescription, and checks for diseases; it takes 30 to 60 minutes and requires no special preparation.
- Bring your insurance card, photo ID, a list of current medications, and your previous glasses or contact lens prescription if you have one.
- The doctor will use a phoropter (the machine with the clicking lenses), a slit lamp, and an ophthalmoscope to look at different parts of your eye.
- Dilating drops blur your vision for four to six hours afterward, so arrange a ride or plan to stay home if the doctor uses them.
- You will receive a written prescription for glasses or contacts that you can fill at any optical shop, not just the one in the doctor's office.
What to bring and how to prepare
Bring your insurance card and a photo ID. If you have vision insurance through your employer or a government program, the card will tell the office what your coverage is and whether you need a referral. If you do not have insurance, ask the office about their cash price before your appointment — eye exams typically cost between $100 and $200 without insurance, though this varies by location and whether the doctor is in a chain or independent practice.
Bring a list of all medications and supplements you take, including over-the-counter ones. Some medications affect eye pressure or can interact with dilating drops. If you wear glasses or contacts, bring your current prescription or your most recent pair of glasses so the doctor can compare. If you have had eye surgery, bring any paperwork from that surgery. You do not need to fast, avoid caffeine, or do anything else to prepare — just show up on time.
If you wear contacts, you can wear them to your appointment, but the doctor may ask you to remove them during the exam. Some offices ask you to leave them out for a few hours before the appointment so your cornea returns to its natural shape, which gives a more accurate measurement. Call ahead and ask whether you should wear them or leave them at home.
The step-by-step flow of a standard eye exam
When you arrive, you will fill out a form asking about your medical history, whether you have had eye problems before, and whether anyone in your family has glaucoma, macular degeneration, or blindness. Be honest about this — family history changes how carefully the doctor screens you. You will also answer questions about your current vision: whether you have trouble seeing far away, up close, or both, and whether you have had any pain, flashing lights, or floaters.
A technician will then test your vision using an eye chart (usually the big E at the top, getting smaller toward the bottom) and measure the pressure inside your eye using a small puff of air or a gentle probe. This pressure test screens for glaucoma. The technician may also take a photo of the back of your eye or scan it with a machine that measures the thickness of your retina.
The doctor will then have you look through a phoropter — the large mechanical device with the spinning wheels of lenses. The doctor will click through different lens strengths and ask "Is this better, or this?" until they find the prescription that makes the chart sharpest. This is called a refraction and determines whether you need glasses or contacts and how strong they should be.
Next, the doctor will use a slit lamp, a microscope with a bright light, to examine the front of your eye: the cornea, lens, and iris. They are looking for cataracts, scratches, infections, or other problems. If the doctor wants to see the back of your eye (the retina and optic nerve), they will put dilating drops in your eyes. These drops take 20 to 30 minutes to work and will blur your vision and make you sensitive to light for four to six hours. After dilation, the doctor will use an ophthalmoscope (a handheld light) or a special lens to look at the retina and check for signs of diabetes, glaucoma, macular degeneration, or detachment.
Understanding your prescription and what the numbers mean
Your prescription will have a line for each eye and will include numbers for sphere, cylinder, and axis. The sphere number (marked SPH) is your main prescription — it tells you whether you are nearsighted (negative number, like −2.50) or farsighted (positive number, like +1.75). The larger the number, the stronger the prescription. A sphere of 0.00 means you have no refractive error in that eye.
The cylinder number (marked CYL) and axis number (marked AXIS) explore only if you have astigmatism, a blurring caused by an irregularly shaped cornea. Not everyone has astigmatism, so these lines may be blank. If they are present, the cylinder is usually a smaller number (like −0.75 or −1.25) and the axis is a number between 0 and 180 that describes the direction of the blur.
Your prescription may also include an add number if you are over 40 and need help focusing up close. This is normal and does not mean your distance vision is getting worse — it is a separate correction for reading and close work. You can use bifocals or progressive lenses (which blend the distance and reading powers) to correct both at once, or you can use single-vision glasses for distance and separate reading glasses.
Your prescription is yours to keep and use anywhere. You do not have to buy glasses or contacts from the doctor's office. You can take the prescription to any optical shop, online retailer, or big-box store. The only exception is if you need a specialty lens (like one for a very high prescription or a specific type of progressive lens) — in that case, the optical shop may need to contact the doctor's office to confirm measurements.
What happens if the doctor finds a problem
If the doctor finds something that needs treatment — like glaucoma, a cataract, diabetic retinopathy, or a detached retina — they will explain what it is, show you images if available, and tell you what the next step is. Some problems need urgent care (like a detached retina, which can cause permanent vision loss if not treated within days), while others need monitoring over time (like early glaucoma or a small cataract that is not yet affecting your vision).
If the doctor finds a problem that is outside their scope, they will refer you to a specialist. An optometrist can diagnose most eye diseases but cannot perform surgery; if you need surgery, they will refer you to an ophthalmologist. If you have a retinal problem, you may be referred to a retinal specialist. If you have a problem with the muscles that move your eye, you may be referred to a neuro-ophthalmologist. Ask the doctor for a written referral and ask whether your insurance requires one before you see the specialist.
Dilating drops and what to expect afterward
Dilating drops (also called mydriatics) widen your pupil so the doctor can see the back of your eye without obstruction. The drops sting slightly when they go in, and your eyes may feel a little gritty for a few minutes. After 20 to 30 minutes, your pupils will be fully dilated and your vision will be blurry, especially up close. You will also be very sensitive to bright light — sunglasses are essential if you go outside.
The blurriness and light sensitivity last four to six hours, depending on the strength of the drops and your individual response. Some people clear the drops faster than others. During this time, you should not drive, operate machinery, or do anything that requires sharp vision. If the doctor dilated your eyes, arrange a ride home or plan to wait in the office until your vision clears enough to drive safely.
If you have narrow angles (a risk factor for angle-closure glaucoma), tell the doctor before they use dilating drops. Dilation can trigger an acute attack in people with this condition. The doctor will check for narrow angles during the exam, but if you know you have this condition, mention it upfront so the doctor can decide whether dilation is safe for you.
How often you should have an eye exam
If you have no vision problems, no eye disease, and no family history of eye disease, the American Academy of Ophthalmology recommends an eye exam every one to two years. If you are over 60, every one to two years. If you wear contacts, every year (because contacts can change the shape of your cornea and increase your risk of infection). If you have diabetes, every year, because diabetes can damage the blood vessels in your retina without causing symptoms. If you have glaucoma, high eye pressure, or a family history of glaucoma, every three to six months or as often as your doctor recommends.
If you have had eye surgery, cataract surgery, or LASIK, your doctor will tell you how often to return for follow-up exams. If you are taking medications that can affect your eyes (like tamoxifen for breast cancer or hydroxychloroquine for lupus), ask your doctor how often you should be screened. If you notice a sudden change in your vision, new floaters, flashing lights, or eye pain, do not wait for your scheduled exam — call your eye doctor right away.
Frequently Asked Questions
Can I wear my contacts during an eye exam?
You can wear them to the office, but the doctor will ask you to remove them during the exam so they can measure your cornea accurately. Some offices ask you to leave contacts out for a few hours before the appointment. Call ahead to ask what the office prefers.
What if I cannot see the letters on the eye chart?
The doctor has other ways to measure your vision. If you cannot read the chart, the technician will use a chart with pictures or symbols instead, or the doctor will use a technique called retinoscopy, where they shine a light in your eye and watch how it reflects to estimate your prescription. You will still get an accurate result.
Do I need an eye exam if I feel like my vision is fine?
Yes. Many serious eye diseases — glaucoma, diabetic retinopathy, macular degeneration — cause no symptoms until significant damage has occurred. An eye exam can catch these diseases early, when treatment is most effective. Even if you feel fine, you should have an exam at least every one to two years.
What is the difference between an optometrist and an ophthalmologist?
Both can perform eye exams and write prescriptions for glasses and contacts. An ophthalmologist is a medical doctor who can also perform eye surgery and treat complex eye diseases. An optometrist has specialized training in vision care but is not a medical doctor and cannot perform surgery. Both are may have access to to do a routine eye exam.
Can I get my prescription filled anywhere, or do I have to use the doctor's office?
Your prescription is yours to use anywhere. You can fill it at any optical shop, online retailer, department store, or big-box store. The doctor's office cannot force you to buy from them. The only time you might need to go back to the doctor is if the optical shop needs to verify measurements for a specialty lens.