How dilation is checked depends on what part of the body you’re asking about. The two most common contexts are cervical dilation during labor and eye dilation during an eye exam. In both cases, the process is straightforward, though the techniques are completely different. Here’s what to expect for each.
How Cervical Dilation Is Checked
During labor (or late pregnancy), your provider checks how dilated your cervix is with a manual vaginal exam, sometimes called a “cervical check.” There’s no machine or imaging involved. The provider inserts two gloved, lubricated fingers into the vaginal canal and feels the opening of the cervix to estimate how far apart it has stretched, measured in centimeters from 0 to 10.
At the very beginning, the cervix may barely fit a fingertip. At 1 centimeter, one finger fits tightly through the opening. At 2 centimeters, one finger fits loosely. By 5 centimeters, the opening is a little wider than two loose fingers. From 6 to 9 centimeters, the fingers spread progressively farther apart. At 10 centimeters, the cervix is fully dilated, and the provider can no longer feel any cervix in front of the baby’s head. That’s when pushing can begin.
The whole check takes about 30 seconds to a minute. It can feel uncomfortable, especially during contractions, but it’s brief. Slow, steady breathing helps, and you can ask your provider to wait for a contraction to pass before starting.
What Else They’re Checking
Dilation is only one piece of the picture. During the same exam, your provider also assesses several other things:
- Effacement: How thin the cervix has become. This is expressed as a percentage. Zero percent means the cervix hasn’t thinned at all, 50% means it’s half its original thickness, and 100% means it’s paper-thin.
- Station: How far down the baby’s head has descended into the pelvis. This is measured on a scale from negative 3 (high up) to positive 3 (very low and nearly crowning), with zero meaning the head is right at the midpoint of the pelvis.
- Position: Whether the cervix is tilted toward the front, middle, or back. Earlier in pregnancy it tends to point toward the back, then moves forward as labor progresses.
- Consistency: How soft the cervix feels. A firm cervix feels like the tip of your nose. A soft, labor-ready cervix feels more like the inside of your lip.
All five of these factors together make up what’s called the Bishop score, which helps providers gauge how far along labor is and whether things are progressing normally.
How Fast Dilation Should Progress
During active labor, the current clinical standard considers 0.5 centimeters per hour a normal minimum rate of dilation. This is slower than the older guideline of 1 centimeter per hour that was used for decades. So if your labor feels slow, that doesn’t necessarily mean something is wrong. Every labor progresses differently, and providers now allow more time before intervening.
How Eye Dilation Is Checked
If you searched this because you have an eye appointment coming up, the process is very different. Eye dilation isn’t something the doctor checks for as a symptom. Instead, the doctor deliberately dilates your pupils using special eye drops so they can see inside your eye more clearly.
The drops work by relaxing the tiny muscles in your iris that normally make your pupil smaller in bright light. With those muscles relaxed, the pupil opens wide, giving the doctor a much better view of the retina, optic nerve, and blood vessels at the back of the eye. The most commonly used drops contain a medication called cyclopentolate, though several types exist. The drops typically take 20 to 30 minutes to fully work in an office setting, sometimes up to an hour depending on the type used.
What the Eye Doctor Does Next
Once your pupils are wide open, the doctor examines the inside of your eye using one of two main tools. The first is a slit lamp, which is that chin-rest microscope you look into at the eye doctor’s office. For a dilated exam, the doctor holds a small magnifying lens in front of the slit lamp to focus on the retina. The most commonly used lens is the +90D, considered the gold standard for retinal examination. Higher-magnification lenses let them look more closely at the central retina, while wider-field lenses let them scan the periphery.
The second tool is an indirect ophthalmoscope, a headband-mounted light the doctor wears while holding a lens in front of your eye. This gives a broader view and is especially useful for spotting problems in the outer edges of the retina. In either case, the bright light can feel uncomfortable since your pupils can’t constrict to protect your eyes, but the exam itself is painless.
Side Effects and Recovery Time
After a dilated eye exam, your pupils stay enlarged for 4 to 6 hours on average, though effects can linger up to 24 hours in some people. During that time, you’ll likely experience light sensitivity, blurry vision (especially up close), and difficulty focusing on screens or small text. Sunglasses help a lot if you need to go outside. Most eye care providers recommend waiting at least 4 to 6 hours before using digital devices. Some people are comfortable driving afterward, but if your vision feels too blurry, it’s worth having someone else drive you home.
How Often You Need a Dilated Eye Exam
The National Eye Institute recommends a dilated eye exam every 1 to 2 years if you’re over 60, if you’re African American and over 40, or if you have a family history of glaucoma. People with diabetes or high blood pressure typically need one at least once a year, since both conditions can damage the blood vessels in the retina without causing noticeable symptoms early on.
Pupil Dilation in Emergency Settings
There’s one more context where dilation gets checked: neurological assessment. If you’ve had a head injury, stroke symptoms, or are in an emergency room, medical staff will shine a penlight into your eyes to check your pupils. They’re looking for what’s abbreviated as PERRLA: pupils that are equal in size, round in shape, and reactive to light and accommodation (the ability to shift focus between near and far objects). Unequal pupil size, a pupil that doesn’t shrink when light hits it, or one that’s fixed and dilated can signal serious brain issues like increased pressure, nerve damage, or a stroke. This check takes only a few seconds and requires nothing more than a small flashlight.