Why do eye doctors shine light in your eyes

Interviewer: What is a physician trying to find when they look into your eyes? That's next on The Scope.

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Interviewer: A lot of times on TV you'll see, or if you've ever even gone to the doctor yourself, they got the little flashlight and they start looking in your eyes and I've always wondered, what are they looking for? We're with Dr. Troy Madsen, emergency medicine at the University of Utah Hospital. In your particular situation, in the emergency room, if you get out the light and are looking into somebody's eyes, what are you trying to figure out?

Dr. Madsen:It's going to vary depending on who I'm looking at. But it's just part of a standard physical exam that when I see a patient I will document something that says on the chart, PERRL. What that stands for is the pupils are equal and reactive to light. And the pupil is the black part of your eye so I'm looking at that. I'm looking at are they the same size, and when I shine a light into it does it close? Does it react to that light and constrict like you'd expect?

And the relevance of that kind of varies from person to person. I mean, in the average person, it's not really a big issue. I can just kind of look at you and look at your eyes and say, "Oh, yeah, they look fine." But in different situations I'm looking for different things.

So if someone comes in after a head injury and they've been in a trauma, I really want to get a good look at those eyes to make sure the pupils are equal, because if they're not, that can be the sign of potentially something very serious in the brain that is affecting the brain's ability to send that message to the eye to have that pupil squeeze down and constrict. That can be a sign of some kind of bleeding in the brain, which is the more serious thing I'm really looking for there. So that's kind of the number one thing I'm looking when I do that.

The other thing I'm looking for often times, and this is a tough thing to do sometimes in the E.R., but sometimes I'll try and get a look at the back of the eye at what's called the fundus of the eye, called a fundoscopic exam, where I'm looking at optic nerve, so where the nerve inserts into the back of the eye. And if a person has a lot of pressure in their brain from bleeding in the brain or something like that, I can actually see swelling on that nerve. So that for me says this person potentially has something that's raising the pressure in their brain, like bleeding, a tumor, something like that. So that's kind of the other big thing I'm looking for when I do that.

Interviewer: All right. So two reasons you would look into somebody's eyes, none of them related to the eyes. Are there things you're looking in somebody's eyes for if they have an eye issue?

Dr. Madsen: Oh, certainly. Yep. And that's one of these things where if someone . . . and usually there I need to have something that's going to push me toward that, someone saying I'm having a lot of pain in my eye or I feel like just something is scratching my eye. And there, I'm going to do an even more detailed exam. I'll kind of flip their eyelid out, kind of like kids do to gross people out. So I'm doing that to look for some kind of piece of dirt or a splinter or something like that in the eyelid itself that's scratching the eye.

Interviewer: And that actually happens?

Dr. Madsen: It does.

Interviewer: That's gross.

Dr. Madsen: Oh, it does, yeah. And then I'm looking at the cornea, so the front part of the eye and sometimes you'll look at that, you'll see little pieces of metal that are stuck on there, say, from a welder or someone who is working with metal. I can see that. Sometimes I'll see a rust ring there. You can actually see rust on the eye itself from a piece of metal that may have been there and then came off.

And then I'll do a very detailed exam, something called a slit lamp exam. It's basically a microscope where I'm sitting down kind of with this microscope that focuses right on the person's eye. I'm looking in the front part of the eye for any, what we call just any cells, any inflammation there that would suggest a lot of irritation in the eye itself. And then I actually put a little thing on the eye that's kind of like a dye that will light up to look for any scratches.

Interviewer: Okay.

Dr. Madsen: Which is what's called a corneal abrasion.

Interviewer: Sure.

Dr. Madsen: So lots of different things you're looking for there on the eye.

Interviewer: So any of these tricks that people can try at home? For example, taking the flashlight and if a person's pupils aren't dilating properly, knowing that you might potentially have an issue?

Dr. Madsen: Yeah, and that's something you can do. If you've had a head injury and you feel comfortable looking at that, you can even look at your own eyes in a mirror and just say, "Do my pupils look like they're the same size?" If you have a family member who's had a head injury, you can shine a light in their eye, just watch, does that pupil squeeze down? And at the same time that one squeezes down does the other one do the same thing? And if it's not, those are concerning things.

Interviewer: Is time of the essence for any sort of eye injuries, generally?

Dr. Madsen: It is, yeah. So time is really of the essence for eye injuries if you actually have something that cuts the eye open. So if we have what's called an open globe injury, so the globe being the eye, the big eyeball, if something actually gets in there and cuts that where there's fluid coming out, time is absolutely of the essence. You need to get to the emergency department. We call our ophthalmologist and they'll oftentimes get you to the operating room to repair that emergently.

Interviewer: All right. Any final thoughts on the eyes?

Dr. Madsen: Final thoughts on the eyes. Obviously, a lot of these things are things we are going to need to do in the E.R. but, like you said, you can kind of take a look at the eyes at home. And certainly if anything comes up, make sure you come in so we can evaluate you further.

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updated: October 31, 2018

originally published: March 19, 2014

Why do eye doctors shine light in your eyes

A doctor inspects a patient's eye with the use of an ophthalmoscope.

Looking into a patient’s eyes can provide a doctor with a wealth of information regarding your general health. The following is a list of typical things your doctor will be on the lookout for when he holds that ophthalmoscope in front of your eye:

Around the eyes

Swelling or puffiness around the eyes may indicate allergies or infections or even kidney problems. Your doctor will compare both eyes and note any signs suggestive of allergies like redness, irritation or small lines that indicate persistent rubbing. 

Redness, warmth, tenderness and swelling may indicate soft tissue infections. When unusual swelling is present around your eyes, your doctor might also test your urine to check for protein that may suggest kidney problems.

Eyelids

If the inner lining of your eyelid (conjunctiva) is red, it may indicate to your doctor that you’re suffering from anaemia. One of the signs of anaemia is pale conjunctiva. He will also look for infections of the eyelid (blepharitis) caused by bacteria or infections of the inner lining of the eyelids.

He will ask you close your eyelids and look for any signs that your eyelids are not closing properly. This may indicate problems with the nerves or muscles responsible for closing your eyes.

Movement of your eyes

The muscles responsible for the movement of your eyes are controlled by nerves coming directly from your brain. Damage to or conditions affecting these nerves may have altered the movement of your eyes, causing squinting, or even the inability to move your eyes in certain direction. Your doctor will test the nerves by asking you to follow a light or object.

Position of your eyes in the socket

Masses behind your eyes or in your skull and even dehydration can have an effect on the position of your eyeballs in the socket. With abnormal growths, your one eye might protrude more than the other. With dehydration, the eyes often appear sunken.

With thyroid problems your eyes might appear as if they are protruding from their sockets, giving you an “amazed” look.

The eyeball 

On the eyeball itself your doctor will be on the lookout for burst blood vessels. He will also look for growths on the eyeball like a pterygium – a fleshy-pink, non-cancerous growth on the eyeball that extends toward the pupil (usually not covering the pupil).

A rare, but important find is what looks like a mole on the eye, which may be melanoma. Alert your doctor of any notable changes in the colour of your eyeball.

Read: Eye diagnosis: art or science?

The little black hole (pupil)

Your pupil regulates the amount of light entering your eye. This is controlled automatically by a brainstem reflex. Your doctor will test your pupils by briefly shining a light onto your eyeball to test how your pupils react to light. He will compare both sides and test each pupil individually.

The inside of your eye

Occasionally your doctor will look at the retina of your eye. The retina is the lining on the inside of your eyeball which allows you to see. The retina has a very rich blood supply from small blood vessels.

Chronic conditions like high blood pressure and diabetes can affect these small blood vessels and essentially affect the retina, causing a decrease in vision.

Looking at the back of your eye can be very uncomfortable as the doctor will need to come really close to your eye to get a clear picture of your retina. In some cases he will use eye drops that will temporarily cause dilation of your pupil to get a better view. As a result of the eye drops, you may experience significant blurry vision. It is best to lie down till the effect of the drop has worn off.

Your doctor will also look at the place where the optic nerve attaches to the eye, called the disc. The optic nerve comes directly from the brain.

If there is increased pressure in your skull (due to meningitis, bleeding from a stroke or brain swelling), the disc may look pale, or the blood vessels may have a different appearance.

Read: Your eyes are a window to your brain health

Pressing on your eyes

Measuring the pressure in your eyeballs is a test for glaucoma – a condition where the pressure in the front chamber of your eye is too high, causing pressure on the optic nerve. This may lead to vision loss if left untreated.

There are special tools available to measure the pressure exactly, but your doctor may make a gross estimate by pressing on your eyeballs with your eyelids closed. If he notes any difference in pressure, he will formally test the pressure in your eyes.

Examining the eyes forms an important part of any physical exam. To list every possible condition that may affect your eyes is not possible, but rest assured that your doctor is trained to identify and act on conditions affecting your eye.

An ophthalmologist (a doctor specialising in eye care) will do more indepth investigations.

Read more:

As the Optometrist questions about your eyes
Hypertension and your eyes
7 early signs of autism

Image: Doctor examining patient's eyes from Shutterstock