Go.
We need this.
B
Go.
We need this.
B
Merriam simply says: "The normal refractive condition of the eye in which with accommodation relaxed parallel rays of light are all brought accurately to a focus upon the retina." Do the optometric colleges disagree or offer an alternative as a place to start?
I don't know I've heard a formal definition.
The way it's used is: no refractive error, normal accommodative function.
Now, what is "no refractive error"? Hmm.
As to what you'd treat as "refractive error", it would depend on symptoms. Sure, a half-diopter or less myopia can mean nothing or disability, depending on the person (and likewise with low amounts of astigmatism or hyperopia or even presbyopia).
To be as cautious as possible, I'd say emmetropia would be 1/4 D or less of any error (measurement error).
"Near emmetropia" or "normal vision" would probably be 1/2 D of myopia, 1 D of hyperopia, and say, halfway in-between for astigmatism.
As defined in Manual of Ocular Diagnosis and Therapy by Deborah Pavan-Langston:So there! One may draw similar definitions from a multitude of other sources but the meaning of emmetropia is quite clear to anyone with even a rudimentary ability to read and comprehend the English language. All that aside, I am willing to bet that this thread will come up with many other definitions, interpretations and above all obfuscations.
"An eye is considered to be emmetropic if parallel light rays from an object more than 6 m away are focused at the plane of the retina when the eye is in a completely relaxed state. An emmetropic eye will have a clear image of a distant object without any internal adjustment to its optics. Although most emmetropic rays are approximately 24 mm in length a larger eye can be emmetropic if its optical components are weaker, and a smaller eye can be emmetropic if its optical components are stronger"
Rather than partake in the upcoming discussion I am going down to my neighborhood pet shelter and watch them gas puppies.
Mmmm. Just as I thought. No consensus.
A recent OD grad stated:
"Light coming from infinity focusses to a point on the retina when the eye is fully relaxed."
Further discussion
B
As both rbaker and Uilleann listed Barry, yours is just a bit more concise. I also see drk ending up at the same conclusion in a round about way.
What is your definition?
I think we have to integrate, or at least discuss, end point acheivable acuity. For example, some people without correction, see 20/20. With correction, 20/13, or even 20/10.
So I ask: "If a -0.25-0.25 x 90 can raise uncorrected acuity from 20/20 to 20/13, should that person be classed emmetropic...or not?"
And if not, then MUST they wear that correction, even though they see fine or "adequately" with out it?
Further, must they see an eye doc every year before they buy a new Ray ban sunglass?
What is the exact difference between the above scenario, and one where uncorrected is 20/40 (legal driving), and with correction 20/20?
More discussion.
B
The definition of 20/20 is not the same as emmetropia. That's pretty academic isn't it?
It may well be. But only ametropes have expiration dates on their eyeglass Rxs, effectively simultaneously gatekeeping their eye health and restricting their buying freedom compared to emmetropes.
So I think an academic distinction is not robust enough for the discussions on regulation of eyewear that we are encountering today.
B
You're on point.Originally Posted by Uilleann
How about we do away with spRx expiration dates in cases where it is deemed safe? Let's encourage ODs who have patients that have stable refractive error give no expiration dates.
Next problem is deciding who has stable refractive error. Anyone know how to do that?
Look, an expiration date on a sp Rx is a form of a guarantee. "I guarantee this Rx is good for a year. Outside that, my treatment plan is expired." That's all.
Now, I don't think I have a problem with people deciding that they want another pair of glasses at year five. Just use the expired Rx. You can duplicate, right (which I don't advise)? It's better to know what the original Rx was.
(On the 364th day following the exam)
"I'm not feeling light I'm seeing as well." Can I get a recheck on these glasses and update the Rx state no charge?"
Yep. That one year time frame is, well...just like "manifest destiny"
B
Don't let one person get inside your head and scramble your thought processes.
What about the client who is a -1.00 OU and tells you they don't need or want glasses?
What we need to be able to offer from a retail point of view is the "Best possible correction"; I just wish we got exams from outside sources that actually where best possible correction but most of our exams come from MD offices.
We trial frame and if they cannot read the 20/20 line we suggest they visit our for a refraction to ensure it is as good as possible.
I see this as a huge opportunity in our industry; let folks who think they have perfect vision to understand that there is more available for them.
The definition in my opinion depends on the attitude of the patient much more than a clinical definition.
Thoughts from a retail guy.
I think some of the basic assumptions in the current refractive paradigm need review.
Many people do not have fully relaxed accomodation during rhe day
Many people have small pupils, effectively stopping down the eye, masking focus error.
Not everyone us looking at star points, but uf they are, even true emmetropes exhibit some form of night myopia, which means the the fully relaxed eye is not the gold standard by any means.
B
I take a nap and come back to find the waters have been muddied.
Trying to keep it simple:
all definitions assume accommodation is at rest, except for the last 5.
Emmetropia=0.00 refractive error
Myopia (aka near-sightedness, short-sightedness)=negative refractive error, using spherical equivalent when astigmatism is present
Hyperopia (aka far-sightedness, long-sightedness, hypermetropia)=positive refractive error, using spherical equivalent " ".
Ametropia=any refractive state other than emmetropia.
Regular Astigmatism=any toric or cylindrical refractive error that can be completely defined by adding a cylinder and axis to a spherical component
Irregular astigmatism=any toric or cylindrical refractive error than cannot be completely defined by sphere cylinder and axis.
Anisometropia=a significant difference in refraction between the two eyes
Antimetropia=myopia in one eye and hyperopia in the other
Presbyopia=age related decrease in accommodation function
Heterotropia (aka strabismus, squint)=a manifest misalignment of the visual axes of the two eyes. (Esotropia is inward deviation, aka crossed eyes, exotropia is outward deviation aka wall eyed, hypertropia/hypotropia are vertical deviations)
Heterophoria=a latent misalignment of the visual axes of the two eyes (esophoria, exophoria, hyperphoria, and hypophorias are similar latent tendencies as above)
Orthophoria=zero misalignment of the visual axes of the two eyes.
Amblyopia (aka lazy eye, amblyopia ex anopsia)=an otherwise healthy eye that is not correctible to normal acuity due to strabismus, or to moderate to large amounts of uncorrected ametropias in childhood.
Last edited by Dr. Bill Stacy; 09-11-2015 at 01:05 PM. Reason: expanded and corrected
So just because a lay person says or believes, or their doctor colloquially tells them, that they "don't need a prescription", we should NOT assume they are an emmetrope, correct?
B
I was asked for a glasses Rx from an on-line company recently and I asked where the lenses where being made. I was told: Utah. I asked how long eyeglass Rx's in that state were valid (I'm in MA) and I was told: "there's no expiration date of glasses Rx's written in Utah" -really???
Obviously, this is a flat out untruth. Doctors in every state, from every optometric school will write SRx and CLRx expiration dates on their prescriptions. Period. It isn't 100% of the time for a myriad of reasons, but in the general course of standard practice, that is the norm.
Of course, it is up to the dispenser as to whether or not to fill a given Rx after a written expiration date. In every state. To date, I've not heard of a single case of litigation from a patient/client against a dispenser from filling an expired SRx at the patients request. CLRx gets you into some murky water, for obvious reasons. But in any case, Utah isn't unique in this scenario. It's unique for lots of other reasons - almost all of them unsavory - but not that one. ;)
Absolutely. Of course "need" is a very poor choice of words in this context. One man's need is another's want. Need is one of those words that some docs like to throw around as a display of power.
And of course the definitions I gave all assume a reasonable measurement tolerance, I like to use ANSI, but depending on the equipment and skill of the refractionist, and the level of co-operation and intelligence of the subject. For example, emmetropia could be between -.25 and +.25 or even -.5 to + .5 under some circumstances (e.g. refraction of babies is always a challenge, as are some adults who have the mentality of a baby).
Ok. So: if we gatekeeping known ammetropes through Rx expiration dates, should ANY buyer of Any Eyeglass or sunglasses, when purchased in a licensed optical establishment, be stopped before you "fill" their (supposedly) emmetropic needs, and be advised/forced to have an eye exam first, before even getting replacement Plano sun lenses?
i know many see my comments as screwy. But I don't.
B.
I only use the term "need" in special circumstances, like when the patient wants to drive and is worse than 20/40 uncorrected, I'll tell them they "need" glasses or contacts. Otherwise I always answer the question "Do I need glasses, doc?" this way. "If you want to see clearly, or more comfortably, then yes, you need glasses to do that". And when they persist with "Then I don't need glasses, doc?" I answer, "Not if you don't need clear or comfortable vision. It's a free country."
Oh, there is one other situation where I will use the word "need". That's in the case of a child with moderate to large hyperopia and/or astigmatism. I will tell the parent this child needs glasses to prevent lazy eye or to help correct existing amblyopia.
"known ammetropes"??? sounds like some kind of brand or scarlet letter. I think it is nice to tell people about the importance of regular eye exams, but I don't think anyone is suggesting we have some kind of eyecare police out there "stopping" people, maybe writing them tickets for having expired eye registrations?
Naw, this is the USA. Let them do that in China or Russia.
There are currently 1 users browsing this thread. (0 members and 1 guests)
Posting Permissions
Reply With Quote
Bookmarks