Nobody likes getting their eyes dilated. It makes me sad. But it’s not because I love dilating drops so much. The tragedy in it is dilation is essential for a complete and accurate consultation. All the other pieces of the exam can be made less annoying or even enjoyable, but then there’s the dilation. I feel like it ruins the party. On the upside, eye exams used to involve that miserable puff-of-air test where you’d wait in horrified anxiety for a blast of air to shoot you in the eyeball. That one isn’t around anymore. So, hooray for that!
The reason you have to get dilated probably isn’t the one you’d think.
It’s not so we can examine the back of your eye to evaluate your retina and optic nerve. Is that the reason you would have thought? It’s times like this where I realize that I may be out of touch with how much people care about the details of their eye exam. I can’t tell if I’m like a wine sommelier saying, “I bet you’re thinking that a 2003 Sauvignon Blanc couldn’t have the raisin undertones to support such a smoky, plummy overbite.” Either way, dilation during a refractive surgery consultation isn’t really because of the view it gives of the back of the eye. We have cameras that can give us a photo of the same structures without dilation.
The real reason for dilation is not because of what it does to make the pupil bigger.
It is because the drug in dilating drops relaxes the focusing muscle in your eye. I bet you’re thinking, “you’re referring to a class called cholinergic antagonists,” and you’re absolutely right. Those dilating drops are used because of their ability to paralyze the muscle that allows the lens in your eye to focus. For a lot of people, it doesn’t change anything about their vision testing. But for a few, the refraction we get (the “better one, or better two” test) after dilation is significantly different after that focusing muscle is relaxed.
Some folks have, through no fault of their own, developed a great deal of tone to the focusing muscle in their eye. And it is no use to try and voluntary relax that tone. They could sit and try to let their eyes relax — like they’re futilely staring into one of those Magic Eye portraits — for an hour and it wouldn’t matter. That’s the nature of muscle tone. It doesn’t “un-flex” voluntarily. That’s good news if you workout and like to wear tank tops so people can appreciate your shoulder muscles. It’s bad news if you’re trying to figure out the real numbers of someone’s refraction.
With dilating drops, that focusing muscle can finally relax.
It loses the tone that can’t be undone with just a good refraction. We need the prescription that refraction gives us after dilation. It’s because that is the number that’ll be most accurate as the years go on and the tone in that focusing muscle starts to decrease with age and increased lens stiffness. Sadly, there’s no way to spot people with all that extra eye muscle tone in the general population. So everyone gets dilated to let us discover if your eyes are the ones that needed to relax to get a more accurate measurement. If there was any way possible, we would just dilate muscle-heads wearing tank tops... take them down a peg or two. As it is, for the good of the humble and unknowingly eye-muscle-toned among us, dilation makes the consultation more accurate overall.