Why does my eye doctor… Part 1

Have you ever gone to the eye doctor and wondered “why do they do that”?
I know I have.
Before optometry school, despite my strong biology background, I honestly had very little understanding of the questions asked, the procedures done, and the outcomes discovered – let alone the actual workings of the eye!  And I’m guessing I’m not alone.
As optometrists, we can get push-back for asking questions or wanting to do procedures – which is totally understandable!  In a world where we’re taught to be skeptical of everyone and everything, it’s only natural to be on the lookout for someone trying to take advantage of you – making an extra buck by doing extra testing, etc.
This skeptisim is where I come in.
My goal in this series is to simply demystify the eye exam.
    -not to make all of you optometrists
    -not to try to be Dr. Google and help you diagnose all your problems.
Only to educate.

First up?  Everyone’s favorite: Dilation.

Understanding Dilation

Okay, let’s go back to biology for a moment.  Remember the autonomic nervous system?  It’s the one that automatically controls things in your body, and can be split into two components: the sympathetic nervous system, and the parasympathetic nervous system.
  • Sympathetic = fight or flight
  • Parasympathetic = rest and digest
Dilation is controlled by the sympathetic nervous system (because you need more light in your eye to see to run away from things trying to eat you!)
When it comes to the eye, the size of the pupil (black part) is determined by the iris (the colored part).  In the iris, there are two muscles – the sphincter (parasympathetic, shrinks pupil) and the dilator (sympathetic, dilates pupil) – that obviously then control pupil size, depending on the task and the situation.
Because two muscles and two systems are responsible for pupil size, we can target either (or both) of them to achieve dilation!
The first way is to activate the sympathetic nervous system.  The fancy name for these drops are sympathomimetics – which just means that they mimic sympathetic responses. The most common drop that we use is phenlyephrine (think epinephrine, or adrenaline).
The second way is to DE-activate the parasympathetic nervous system. Of course, that sounds too simple, so they’re called parasympatholytics – or medications that inhibit parasympathetic responses.  There are a number of drops in this category that we may use, but most general optometrists use tropicamide.
Here’s where it gets a bit tricky though.
The parasympathetic system, which is tied to the sphincter, causes more than a smaller pupil (miosis).  It also controls your eyes’ ability to focus (accommodate) and turn in (converge).  Together, these three components make up the near triad.

What does dilation do?

Now that we’ve got the science down, the effects are pretty simple.  First, dilation makes your pupil bigger.  And second, it makes it difficult to focus (especially at near).
These effects last for varying amounts of time, depending on the person in general.  For me, my near vision is the first to come back, generally within a few hours.  My (blue) eyes often remain dilated for at least 4-6 hours, sometimes longer, depending on the number of drops used.

Why dilate?

The basics purpose behind dilation is simply to get a better view of the back of the eye.
But, Hannah, can’t the doc see the back of the eye without adding the drops?
My favorite explanation goes something like this:
Have you ever tried to look into a room through a keyhole?  You can probably see a little bit, right? But it’s hard. And you have to move a lot to see just a little.
But what if someone opens the door? Of course, then it’s easy to look in and examine the whole room!
The exact same principle holds true with the eye.  Before dilation, sure, I can see some.  Most of the time I can get a look at the optic nerve and the macula, but seeing the rest of the retina?  It’s really hard.
With the dilating drops, however, it becomes significantly easier to see out into the far reaches, or the periphery, of the retina.

What is the doctor looking for?

Honestly, this depends a lot on your personal history in combination for your reason for exam.
For instance:
  • In near-sighted people: we’re especially looking to the peripheral retina, because that’s the most likely location for thinning, that may lead to a hole, tear, or detachment.
  • In people with diabetes: we’re looking for any spots of blood (hemorrhages) and other signs of diabetic changes.  As diabetes is one of the leading causes of blindness in the United States, finding changes and monitoring them is vital for optimal visual outcomes.
In general, optometrists may often be the first practitioners to see signs of systemic diseases (diabetes, hypertension, autoimmune disorders, brain tumors, and certain types of cancers) – all of which have better outcomes the earlier they’re found and treated, and so we’re looking for anything out of the ordinary.
Because we care about you, as an individual, not just your eyes.

 How often do I need to be dilated?

This again varies some by personal history.
In general, every adult patient (over age 18 and below age 65), with no known ocular or systemic history, should be dilated once every two years.  Those over 65 should be dilated yearly.
I am a firm believer in dilating every pediatric patient (under 16 years of age) at their first exam, and most subsequent exams (I’ll discuss this more later in a peds specific post).

What about that retinal picture? Isn’t that good enough?

Short answer: no.
Retinal photographs can, honestly, only show so much.  Yes, the wide angle imaging systems are improving, but they still may miss pathology that would be seen with dilation.  While I don’t view these as a full replacement for dilation, I understand advocating for their use as a measure of retinal documentation every other year in adults without known ocular or systemic conditions.

But, I’ve never been dilated…

Trust me, you’re not alone.  I personally was never dilated until my first year of optometry school.  While I do not judge the docs who do not dilate frequently, according to the American Optometric Association, routine dilation, as described above, is the standard of care for all optometric pracitices.

Can I drive after dilation?

The short answer, is: yes (for probably 90% of patients)!
If you are properly corrected with lenses (glasses or contacts), or have no prescription, your vision (at distance) should be minimally impacted by dilation.
However, due to the increased pupil size, everything will be brighter, so make sure you’ve got a good pair of sunglasses with you!
If you are uncomfortable with the thought of driving after dilation though, don’t worry! You’re always welcome to bring a driver, or to defer dilation to a day when you have a driver – just make sure you come back for the rest of the exam!
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If you have questions, or a topic that you’d like me to discuss, contact me here.  I’d love to hear from you!

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