Eye Health As Clear As PLANO
Recently, an interesting discussion on Optiboard got me thinking about how vision care professionals view emmetropia, visual acuity and eye health
Q: How do you define emmetropia?
- 20/20 uncorrected acuity
- Absence of any correction to obtain 20/20 or better
- Light is brought to a point focus on the retina in the absence of any accommodation
- The Rx is PLANO, aka 0.00D
I was going to go through each choice above and expound, but just thinking about the choices a bit is, I believe, sufficiently expositive.
Now let's move on to the meat of the matter.
In 1862, when Dr. Herman Snellen, a student of the Dutch ophthalmologist Dr. Franciscus Donders, introduced his chart of optotypes to facilitate collecting data to help define the normal or commonly found limit of human acuity. He wanted the assistance of researchers in a variety of different locals and countries. Therefore, he needed to create a standardized chart of objects to be discerned as well as a set distance for the chart was to be used at. Although he had initially favored an outside setting of 30 yards to ensure complete relaxation of focus, he settled on an indoor setting in order to be free of the vagaries of the weather. Checking around, he saw that most homes or buildings would contain at least one room of 20 feet in length. And this is where the numerator in the 20/20 fraction comes from. It's not really optical infinity, but its close enough because light from this distance turns out to have just a 0.16D vergence.
And while what Dr. Snellen found did not represent the actual limit of human vision, he did find that 20 feet was a conveniently test distance, given all the vagaries and imprecision of testing in his time. And somehow, someway, 20/20 evolved to become the gold standard for describing excellence in human vision.
Docs are often overheard to say:
"Your eyes are perfect. They're healthy, and you don't need a prescription. You're seeing 20/20."
This statement begs 2 questions:
- Does the lack of receiving an actual Rx reveal evidence of perfect vision?
- Does having no Rx automatically mean someone does not need any correction to see their personal best?
And therein lies the rub.
Today, the 'standard of care' in the US eye exam frequency is a one year exam interval, aka the Vision Council's advice to "Check yearly. See clearly." Eyeglass Rxs increasingly feature a one-year expiration date. It is a convenient time frame, and has been designed to safeguard a person’s eye health by limiting the need for intermediate, refractive-only vision testing. But it has become an unintended obstacle for those wanting to buy new prescription eyewear, who are emphatically counseled that they must have a complete eye health check-up accompanying every refraction. Supporters argue that we can't allow any insidious, asymptomatic eye diseases, such as glaucoma, going undetected in an optician’s quest to make additional profits, can we?
Yet when was the last time you encountered an Rx written for PLANO?
Today, we stop anyone who wants to buy new glasses for fashion, sun, computer, reading or simple replacement, who has a history of ametropia, dead in their tracks... on the 366th day after their last eye exam. Is this really logical? Is it fair?
In a word, no.
Why? Because it disenfranchises anyone who doesn't currently posses either an Rx or is know to be emmetropic ー whatever that is (see above). Applied uniformly for all people, regardless of their need for any type of correction, Rx expiration dates make sense. But we never think that PLANO people are left out receiving the same eye health gatekeeping.
So sweet reader, have you ever heard this dialogue in any optical shop?
"Hi! I'd like to look at (Plano) Ray Bans."
"Sure. When was your last eye exam?"
"Oh, over a year ago."
"Sorry, no Ray Bans for you. Not without an eye exam first."
How about asking your doc to start writing Rxs for PLANO people. And be sure they put on an expiration date.
Can't be too careful now, can we?
Ridiculous you say? Look at the fallacy of eye health gatekeeping that our present system of Rx expiration dates for what it is. IMHO, divorcing refraction-only testing from the complete eye exam will only serve to improve the clarity in the message to tend to one's eye health by scheduling a routine eye exam. But that would mean a change in the way we think about the relationships between eye health, acuity, refraction, emmetropia and our lost son...PLANO.