Your eyes, explained
How the eye works, what can go wrong, the tests you will have, and the words your doctor uses, in plain language.
How you see
- CorneaLight passes through the clear front window, which bends it toward the center of the eye.
- PupilThe iris opens or narrows the pupil to let in the right amount of light.
- LensThe lens fine-tunes focus so the image lands sharply on the back of the eye.
- RetinaLight-sensing cells turn the image into signals, with the macula handling fine detail.
- Optic nerveSignals travel to the brain, which turns them into what you see.
What 20/20 and 20/40 mean
The first number is the distance you stand from the chart, 20 feet. The second is the distance at which a person with typical vision can read the same line. 20/40 means you need to be at 20 feet to read what most people can read from 40 feet away. A bigger second number means blurrier vision.
Gary, one of our cataract patients, went from 20/400, the size of the big letter at the top of the chart, to 20/30 after surgery.
Tests you may have
None of these hurt. Most take a minute or two.
Visual acuity
Reading letters on a chart, one eye at a time, to measure how clearly you see.
Refraction
“Which is better, one or two?” Lenses are flipped in front of your eye to find your best prescription.
Tonometry
Measures the pressure inside your eye, a key check for glaucoma.
Dilated exam
Drops widen your pupil so the doctor can see your retina and optic nerve. Bring sunglasses.
Visual field
You press a button when you see small lights at the edge of your vision.
Optic nerve photos
Detailed photos of the back of your eye, compared over time to spot slow changes.
Who does what
Ophthalmologist
A medical doctor who treats eye disease and performs surgery, like Drs. James, Elena and Lucas Lumen.
Optometrist
Performs eye exams, prescribes glasses and contacts, and diagnoses and manages many eye conditions, like Dr. Michael Reed.
Physician assistant
A licensed clinician who works with our ophthalmologists on exams, follow-ups and care plans.
Call right away or go to the emergency room if you have
- Sudden loss of vision in one or both eyes
- A sudden shower of new floaters or flashes of light
- A shadow or curtain moving across your vision
- A painful red eye with blurred vision, halos, headache or nausea
- A chemical splash. Rinse with clean water for at least 15 minutes first.
Learn about a condition
Cataract surgery
Cloudy, dim or glaring visionGlaucoma
Pressure checks, laser and surgeryDiabetic eye care
Yearly retina exams and treatmentMacular degeneration
Central vision changesEyelid surgery
Droopy or heavy eyelidsCornea
Transplants and pterygium surgeryDry eye
Burning, gritty or watery eyesEye exams, glasses and contacts
Routine care with our optometristsWords your doctor might use
- Amsler grid
- A grid of straight lines with a center dot. Wavy or missing lines can be an early sign of macular problems.
- Astigmatism
- An unevenly curved cornea or lens that makes vision blurry at every distance. A toric lens can correct it during cataract surgery.
- Blepharoplasty
- Surgery that removes extra eyelid skin, and sometimes fat, from the upper or lower lids.
- Cataract
- Clouding of the eye’s natural lens, usually with age. Treated by replacing the lens.
- Cornea
- The clear front window of the eye that does most of the focusing.
- Dilation
- Drops that widen the pupil so the doctor can see the retina and optic nerve. Vision is blurry and light-sensitive for a few hours.
- DSAEK
- A partial corneal transplant that replaces only the inner layer of the cornea, with faster recovery than a full transplant.
- Extended depth of focus (EDOF)
- A lens design, such as Vivity, that gives a continuous range of clear vision from far to arm’s length.
- Glaucoma
- Damage to the optic nerve, often linked to high eye pressure. Usually painless and gradual.
- Intraocular lens (IOL)
- The clear artificial lens placed inside the eye during cataract surgery. It lasts a lifetime.
- Keratoconus
- A condition where the cornea thins and bulges into a cone shape, blurring vision.
- Macula
- The center of the retina, responsible for sharp detail.
- Macular degeneration (AMD)
- Age-related damage to the macula that affects central vision. Comes in dry and wet forms.
- Monofocal lens
- An intraocular lens that focuses at one distance, usually far. Readers are needed for close work.
- Ophthalmologist
- A medical doctor (M.D. or D.O.) who diagnoses and treats eye disease and performs eye surgery.
- Optic nerve
- The nerve that carries signals from the retina to the brain.
- Optometrist
- A doctor of optometry (O.D.) who performs eye exams, prescribes glasses and contacts, and diagnoses and manages many eye conditions.
- Posterior capsulotomy
- A quick in-office laser treatment that clears haze that can form behind a lens implant months or years after cataract surgery.
- Pterygium
- A noncancerous growth of tissue that spreads from the white of the eye onto the cornea.
- Ptosis
- A drooping upper eyelid, usually from a weakened lifting muscle.
- Retina
- The light-sensing layer at the back of the eye.
- SLT (selective laser trabeculoplasty)
- A gentle in-office laser that helps fluid drain from the eye to lower pressure in glaucoma.
- Tonometry
- A quick, painless test that measures the pressure inside your eye.
- Toric lens
- An intraocular lens that also corrects astigmatism.
- Visual acuity
- How sharp your vision is, written like 20/40.
- Visual field test
- A test of your side vision, used to track glaucoma and other conditions.
- Vitrectomy
- Surgery that removes the vitreous gel from inside the eye, for example to clear bleeding.
No matching terms. Ask us at your visit, we are happy to explain.
Questions about your eyes?
Our doctors will explain what they find at every visit, in words that make sense.