Yes we get it. Dilating the eyes isn't fun. When the eyes are dilated, your vision can be more blurry and lights will be incredibly bright. Why not just avoid dilation all-together! So during your eye exam, can you just refuse eye dilation?
Yes, you can refuse to have your eyes dilated. You have complete control over what happens to your eyes in an eye exam. But dilating the eyes does have benefits. It helps to ensure you have a healthy eye and good vision. You do give up some of those benefits by refusing eye dilation.
The dilated exam isn't an arbitrary part of the exam (as much as it may seem). So how exactly does dilation help the eye doctors?
Allowing a great view to the back of the eye.
Undilated eye; image byYlem, Public domain, via Wikimedia Commons
When you look inside an eye, you typically see the colored part of the eye, called the iris and a dark black circle called the pupil.
But there is so much more to the eye!
The eye; Image by Rhcastilhos. And Jmarchn., CC BY-SA 3.0, via Wikimedia Commons / modified from original
Beyond the pupil is a vast amount of real estate.
- Immediately beyond the pupil is the lens. The lens is responsible for giving us our ability to focus up close. Later on in life, this lens becomes cloudy and turns into a cataract
- Beyond the lens is a support structure of the eye called vitreous.
- And at the very end of this pathway through the pupil is the retina. The retina is a very important structure which converts the light that we see into signals to send to the brain to process through the optic nerve. It's like the light sensor in a digital camera.
These are all very important structures. If there is something going on with these structures, you will want to know about it.
You technically can see many of these structures through an undilated pupil. But looking through an undilated pupil is like looking through a keyhole. You don't have a very comprehensive view.
This is where dilation becomes important.
Dilated eye; image by Nutschig at the English-language Wikipedia, CC BY-SA 3.0, via Wikimedia Commons
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As you can tell with a dilated eye, the keyhole view becomes massive. With a dilated eye you can easily see the whole lens; all of the vitreous and all of the retina. That way nothing becomes missed in your eye.
What are some of the things in particular we are looking for?
Retinal Tears or Detachments
If the vitreous tugs on the retina, it can cause a tear in the retina. This tugging can occur after being hit in the head; it can also occur just naturally on its own (especially for those that are highly nearsighted).
If a tear develops, you typically notice flashing lights and floaters in your vision (dark spots that don't seem to go away).
Retina tears are important to diagnose and treat. If left untreated, fluid can get underneath the retina through a retinal tear and cause the retina to detach. A retinal detachment can lead to permanent loss of vision or blindness.
The way an eye doctor diagnoses retinal tears is by direct visualization (it is also how retinal tears are treated - a laser is used with direct visualization to put a “barrier" around the tear).
It also happens to be that retinal tears more often happen in the far periphery of our retina (this is where the vitreous is more firmly attached to the retina).
The far periphery is the hardest part of the retina to see without dilation. Dilation is essential in order to allow for prompt and proper diagnosis and treatment of a retinal tear.
Cataracts
A cataract is a clouding of the natural lens inside our eye. This causes blurry vision. While the majority of cataracts happen to individuals over the ages of 50 and 60, cataracts can happen at any age from children to adults.
The natural lens and cataract just happens to sit right behind our pupil and iris.
Through an undilated pupil, only a small part of the lens can be examined for cataract. We can roughly screen whether the center of the lens has developed a cataract; but not much else.
But there are multiple different types of cataracts. Not all cataracts involve the center of the lens. One type of cataract, called a cortical cataract, involves the center of the lens relatively late. When this cataract develops, it primarily develops in the periphery of our lens. This particular cataract causes lots of symptoms or glare or trouble seeing when lights are shining in the eye - such as when driving at night.
Given how close the lens is to the pupil, it is near impossible to see the periphery of the lens without any dilation. Having a full dilated eye exam is the only way to diagnose this type of cataract.
Getting a perfect glasses prescription for our eye
Beyond just making sure that the eye is healthy, having a dilated eye exam also can improve the accuracy of your glasses prescription.
As mentioned above, the natural lens in our eye is responsible for giving us our ability to focus up close. It does this by changing shape with the help of our ciliary body muscle. At least, the lens does this until we hit our mid-40s and this ability becomes weaker - something called presbyopia.
But just as how the lens is good at focusing on things up close, it is also good at focusing through extra prescription. While you still can see, this extra focusing of the lens can cause a headache and eye strain, especially when it also has to work harder to see up close.
This extra focusing can happen when we check your prescription during an eye exam. While there are some techniques we use to try to eliminate it, the best way to eliminate it is to prevent this focusing all-together. This is achieved with, you guessed it - dilation.
Certain dilating drops do more than just make the pupil big. Certain dilating drops also prevent the ciliary body muscle from working (temporarily). This prevents the lens from being able to focus. While it does have the side effect of not being able to see up close, it does improve how your eye is measured. When the lens is unable to focus, your prescription check becomes more accurate (since it measures the true prescription of the eye and not what the natural lens can focus through). Another great reason for dilation.
Alternatives to dilation
Can those benefits be achieved in other ways? Well yes and no.
- You can get great views of the retina with certain eye cameras. These can be used a general screening tool. These cameras have become sophisticated enough to take pictures of the far periphery of the retina to identify retinal tears and other pathology. In general these are a pretty good substitute for dilation, but you do miss out on having a full view of the natural lens to evaluate for cataracts as well as the benefits for getting the most accurate prescription available.
- Only dilating one eye can achieve half of the goal. Let's say you want to refuse eye dilation because you are concerned about driving home afterwards? That’s a legitimate concern. Ask your eye doctor if she can dilate one eye now and one eye later. That way you can at least get the full benefits eventually.
Summary
We get it, nobody actually likes their eyes being dilated. But it is a necessary step when you visit the eye doctor. You can refuse the eye dilation but in doing so you give up important benefits to the health and vision of your eyes. Instead of refusing the dilation, it is much better to postpone the dilation instead to a more optimal time for you.
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