Eye Checks & Tests

Common eye checks and tests at the doctor’s office

The most common eye test that they will start with after getting your eye and medical history is a nearsighted and farsightedness general vision test. This includes testing how well you can read letters up close and far away.

The test is usually performed at a distance of 20 feet away, hence the term 20/20 vision. However your eye doctor may use mirrors to get the effect of being 20 feet away while in reality you are much closer to the test.

20/20 vision actually technically means that you can read the standard letter while standing 20 feet away while wearing corrective lenses or while wearing nothing. So if someone says, “ I am special I have 20/20 vision. I have never had to wear any type of corrective lens.” You can say “I am special too or maybe you are not that special because I am currently wearing a corrective lens and because of that I too have 20/20 vision.”

20/15 vision means your vision is actually better than the standard or so called “perfect vision”. You can be standing 20 feet away from an image and see it just as clearly as a “normal” person or person with standard vision would be able to see the same image while standing only 15 feet away.

Near visual acuity is usually measured at the standard reading distance of 14-16 inches and they measure each eye on its own and together.

Near vision tests are often skipped on younger people who have no trouble reading or focusing because the doctor already knows they are able to read with no issues.

Refraction

Here the eye doctor is trying to help you find a combination of lenses that will result in your optimal vision. This can be done subjectively which is also known as subjective refraction and manifest refraction.

It can also be done objectively by shine light into your eye and neutralizing the light with lenses which is called retinoscopy. There are even computers that have automatic light refractors that are able to automatically and objectively find the best lens combination for your eyes.

Subjective refraction is usually only done to make small tweaks to the more objectively assigned prescriptions. The eye doctor will switch lenses as you look at a screen with letters, and will ask questions to judge how well you are able to see as they switch the lenses.

Objective is also used for younger children who are not able to focus for long enough to answer the subjective refraction questions accurately or correctly.

It is important to note that no one is required to wear glasses or contacts under any condition, even when they are prescribed. Wearing corrective lenses are 100%, completely your own choice, and if you would rather go without them then you are under no obligation to wear them.

The only exception to this rule is if you need the corrective lenses to pass the driver’s eye test, and in this case, you are required by law to wear your lenses while you are operating a motor vehicle.

If you use common sense and think about this it also makes sense because you would not want to put yourself or others in danger while driving if you cannot see well enough to drive.

External exam

Then the external eye exam comes where the eye doctor will look at your eye snot using any equipment.

They do this quickly and often do not write everything down. What they are looking for is how the face looks and how symmetrical it is, how the eyelid skin looks, how the edges of the eyelids and the eyelashes look, how the eyelids are positioned, how the eyelids open and close, how clear and shiny the cornea, iris, and pupil are, and how they react to light, the color, texture and moisturizing ability of the conjunctiva, and the movement and coordination of the eyes.

This external portion of the test is done very quickly and is mostly used to detect any abnormalities that need to be looked into more closely.

Testing the pupil

pupil

The black circle in your eye is called the pupil. Every image you see goes through your pupil before it is processed by your retina and seen by your brain. The pupil gets small in high light and opens to become very large in the dark in order to let in more light.

The eye doctor looks at your pupils because their shape and how symmetrical they are will give the doctor important information about your vision.

When your pupils are asymmetrical or irregular that can give the eye doctor information that you may have another disease in your body including a tumor, aneurysm or vascular disease.

This is because the pupil nerves travel throughout your neck and their long route means pupil health can provide information about the health of your whole body.

Inside the eye exam

The eye doctor will use a slit lamp which is a microscope that magnifies 10-40X or higher. It also produces slits of light that can light up a small section of your cornea, anterior chamber or lens so they can look at small parts at a time.

They can use the slit lamp to look through eye structures and to focus on a single eye structure. The slit lamp is also used to look specifically at the iris, the conjunctiva and the eyelids as well as the vitreous and retina.

Intraocular pressure measurements

To measure the pressure inside the eye, the eye doctor needs to use a machine that is calibrated specifically for this purpose. There are different machines and some use weights while others puff air into the eyes.

The most common tool is called the applanation tonometer which is put onto the slit lamp while it is used. To use this tool the eye doctor needs to numb the eye and put a dye in the eye which is called fluorescein. These medicines may cause the eye to sting slightly.

Then the doctor puts a cobalt blue filter on the light to cause a green light glow. Then they look through the tonometer and push until it flattens a small amount of the cornea’s surface.

They are able to calculate the pressure by measuring the relationship between the force needed to flatten the cornea and the surface area of the cornea that was flattened.

This allows the doctor to tell how much pressure was needed to flatten the cornea and how much of the cornea was flattened which allows them to get a standard measure of the intraocular pressure which is written in mm of mercury.

Retina Test

The eye doctor can use the slit lamp to examine the retina, and they can also use an ophthalmoscope instead. They examine the retina by shining a light into the patient’s eye which is reflected back out of the eye for them to look at.

They also can use the light of the ophthalmoscope to see deeply into the retina in 3D. Here the doctor can check to see if there is anything unusual going on in the retina as well as check out the optic nerve, the vitreous, and the retina’s blood vessels.

Since the retina can be more easily seen through a pupil that is huge and dilated, the eye doctor will put dilating eye drops into the patient’s eyes before doing the retina test.

These eye drops need to sit in the eye for over 15 minutes before taking full effect. Interestingly, people with a darker iris color will need longer for the drops to take affect.

The drops affect different people differently, although most people will not be able to see up close as well when their eyes are dilated. Most people are still able to see far away so they are able to drive home after the appointment.

The eye doctor will usually give you a pair of temporary sunglasses to wear home so you do not damage your dilated eyes by looking directly into the sunlight.

Remember, pupils dilate and get bigger naturally in the dark and shrink in the light, so it is unnatural to have huge pupils in bright light and therefore a good practice to wear sunglasses for as long as your eyes have been artificially dilated.

People who have a narrow anterior chamber angle need to be extra careful, and their eye doctor needs to be extra careful, when applying the eye dilation drops because they can actually cause acute closed-angle glaucoma in people with a thin anterior chamber angle.

Often the eye tests will stop after this and you will be free to go home. In other instances, additional tests may be offered.

One test offered may be a visual field test which can get very complex and use complex machinery. A simple test your eye doctor may give you to see if you need a more complex test is to ask you to focus on their face and to tell them when you see a pencil come into your sightline from underneath their face, above their face, and the sides of their face.

This is a screening test which can give them a quick indication of whether or not your visual field sight is up to par or not. These tests are unable to tell if you have glaucoma and they can’t tell us if any conditions get worse. Essentially this type of test is only a preliminary screening done to see if you need more extensive tests later.

Amsler Test

An Amsler grid test is a more in depth visual field test where you focus looking one eye at a time on a dot in the middle of a square. If any of the squares look blurred or out of shape to you then there is likely a retinal issue.

These are easy tests that can be self-administered at home as well. If you have had retinal issues in one of your eyes, then you are at risk for having similar issues in your other eye and should probably use the Amsler test yourself at home so you can be aware of any retinal onset issues in your other eye.

To use the grid at home place it in a place you know you will see it everyday such as the door on your fridge or your daily mirror. You should look at it in normal light from about one foot away. If you normally wear contacts or glasses then wear them while you take this test.

Then answer these questions: Can I see the dot in the center? Can I see all 4 corners in the grid? Are all the squares the same size? Are all the lines straight? Are any graph parts missing? Are there any distortions or movement? Are there any color abnormalities?

Then repeat the test with your other eye. If the test produces different results for each eye or if there are any abnormalities that you see in the grid, this indicates a retinal eye problem. Then you need to see your eye doctor right away to be tested so you can fix the problem as soon as possible.

Other people who should use this test daily is those at risk for macular or optic nerve issues including those who already have macular degeneration.

Here is a printable Amsler test you can use on your own including daily instructions:

amsler test instructions

amsler grid

Another self-diagnostic test is the online Zeiss test which can test for color, acuity and contrast, which is available online.

The Essilor online vision test is also a good one to try that helps you check if you need to go into an eye care professional to take a closer look at any vision problems you may have.

Gonioscopy

A gonioscope is as big as your thumb and can be fit to your cornea. The eye doctor will numb your eye and use the gonioscope to test for glaucoma. There is a mirror inside this device that allows the doctor to look at your eye where the cornea meets the iris at the space called the angle of the anterior chamber.

When the angel is too narrow or thin, this is a sign you may have glaucoma in your eye.

Exophthalmometry

Exophthalmometer is a ruler that has two extensons that sit on your eyes’ orbits. This instrument also has angled mirrors that let the doctor see if the eye sticks out more than a normal ee does. IT measures the protrusion of the eye. Excessive protrusion is an indication of thyroid disease.


Tearing Tests

Tearing test are used to find people who have dry eyes. One way is the Schirmer test which uses paper strips to see how many tears the eyes are able to produce. One paper strip is bent inside the lower eyelid while the rest hangs down onto your cheek.

Then how much of the strip that is wet due to tears is measured after 2-5 minutes. Many eye doctors disagree about how useful and accurate this test is although it is still used.

Another tearing test is called the rose Bengal dye test which places a drop of dye inside the lower lid. When you have dry eyes, the dye will leave small pink dots on your cornea and conjunctiva and are seen by he slit lamp. The dots are on the areas where your tear cells ie the corneal epithelial cells are not working or missing.

If you do have dry eyes, tear drops are a helpful solution.

Eye Coordination Tests

Eyes work together for people to see with, and the majority of people see the best using both of their eyes as opposed to one eye alone at a time. When eyes are unable to coordinate with eachother a plethora of vision problems can arise.

Eye coordination tests are used to diagnose and correct these problems.

One example that is harder to fix is an eye muscle problem where someone sees objects well with one eye but tilted with the other, a fix is to patch one eye temporarily and pray the other will improve on its own, or a more in depth eye muscle surgery can be attempted.

The easier to fix and more common eye coordination problem is horizontal or vertical muscle imbalances in the eyes. These can be detected using the cover uncover test, the alternate cover test, and the red glass test.

References
Cassel, Gary H., Harry G. Randall, and Michael D. Billig. The Eye Book: A Complete Guide to Eye Disorders and Health. Baltimore, MD: Johns Hopkins UP, 2000. Print.



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