I've always hated going to see the eye doctor. Invariably, the madman would put dilation drops in my eyes sometime in the afternoon, and I would remain dilated not just into the evening, but often until the next morning as well. Of course, this prolonged dilation was nearly always accompanied by a splitting headache that only a dark room and sleep could cure. As it turns out, all of those previous visits could have ended much more happily had I just possessed a bit of knowledge about eye dilation, the chemicals that drive the process, and the eye itself.
The purpose of eye dilation in adults is to allow the doctor to easily look inside the pupil at the retina (back and sides of the eye). Normally, the pupil would slam shut when a bright light is shined directly into it. Dilation medicine forces the pupil to stay wide open even as painfully bright lights are repeatedly shined into and through it (causing the eyes to tear up, the eye lids to slam down, and the doctor to wonder out loud why being repeatedly blinded is such an uncomfortable procedure). That all makes a perverse sort of sense.
In children, who apparently have wildly active eyes, eye dilation also allows the doctor to more accurately assess the state of the eye's lens since the dilation solution also temporarily paralyzes the muscle that manipulates the lens. This paralysis is also why dilated adult eyes cannot focus since the lens cannot be manipulated to clearly view objects at a variety of distances.
Like most people in most professions, eye doctors operate on a least-common denominator paradigm. That is, if something works well for 95% of the population, and it works well enough for the remaining 5%, that process, procedure, or medicine is what eye doctors will use. When it comes to eye dilation solutions most doctors will direct their techs to use just one solution on all their patients. They do so regardless of the fact that eye dilation solutions come in a variety of strengths and chemical formulations.
Where this paradigm breaks down is that people are neither numbers nor machines and the least-common denominator solution is not always the best choice. The eyes of different people react differently to various eye dilation solutions.
The key variable is the amount of pigmentation present in the iris. Brown eyes have more pigment in the iris while blue and green eyes contain less pigment. The pigment (melanin) acts as a physical filter to slow and obstruct the dilation medicine from reaching the muscles responsible for pupil dilation. Brown eyes posess more melanin and therefore filter out more of the dilation chemicals and slow the transfer of the remaining chemicals to the muscles responsible for pupil contraction. If you have light eyes (small amounts of melanin) you possess a relatively weak filter that is easily overcome by the chemicals present in the dilation solution. In blue eyes the dilation medicine not only reaches the muscles faster, but it also reaches them in significantly higher quantities due to the reduced filtering done by the melanin. These higher quantities then lead to prolonged periods of eye dilation.
Eye doctors can afford to use just one solution for the most part because having one's eyes dilated for a prolonged period of time may be inconvenient, but it is hardly life threatening. If you possess blue eyes and if you call the eye doctor the next morning to complain about the fact that you're still dilated, he or she will essentially give you a version of the football "Walk it off!" speech dressed up in some medical-feel-good mumbo-jumbo.
I have light blue eyes; my current eye doctor has repeatedly commented on how lightly pigmented they are. That means I need less dilation solution to achieve the same results as a darker eyed person. But that's not what I was getting all these years. Because I didn't know, and because I didn't understand, I got the least common denominator solution. I was getting the same solution as a dark brown eyed person. It's no wonder that I was often dilated for periods of 16 hours or more and that I suffered some pretty awful headaches. That was something like asking a non-smoker to chain smoke two packs of unfiltered Lucky Strikes and then wondering why they were all fucked up by the experience.
Now when I go to the eye doctor, I know to direct the tech to check with the eye doctor before dilating my eyes. The doctor can then recommend a dilation solution appropriate for my level of pigmentation.
As it turns out a solution half the strength of the least-common denominator solution is still a bit too powerful. My eyes were dilated at roughly 15:00 yesterday with the half-strength solution and they were still ever so slightly dilated when I finally got tired of the whole mess and went to bed at 23:00.
The moral of the story is that if you have light blue eyes or green eyes, make the tech check with the doctor before dilating your eyes. As GI Joe says, "Knowing is half the battle."