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Thread: Refraction at 3.25 meters

  1. #1
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    Question Refraction at 3.25 meters

    Hey guys,

    I have some questions again for you guys since you know a lot more about optics than i do and i like to learn more about the field so here we go.

    To give a quick rundown of my workspace:
    We are using a tv screen which adjusts the sneller charts accordingly to the amount of distance you fill in the system. So the closer you fill in, the smaller the snelles chart letters become.
    I currently perform refractions at 3.25meters which translates to 10.67 Feet.
    The phoroptor an Essilor APH550.
    Our clients are mostly in their 20's. Only about 10% multifocal of all our sales.

    Before i worked at my current place i always used to perform refractions at 6 meters (19.69 feet) using a mirror.
    I learned that you need to use this distance to minimize accommodative impact.

    A guy from maintenance came over and mentioned that the room is very small and the tv too close to the seat.

    1) What is the impact of this? Should i try and get this changed to a mirror setup? This is going to to cost some money (not my money lol) so i'm not sure if they would comply. But i wonder if the implications of using this distance are severe or will the Tv compensate partially?

    and one more question.

    I have been using Humpriss method (fogging) but since we have 20 mins for the refraction, and i have to explain additional stuff, make an account etc. I was told by a co-worker to use pola duochrome (probably using the wrong word) instead. To save time and focus on practising using the slit-lamp.

    2) Is the pola duochrome enough or are there any other suggestions from you guys to try and minize accommodating in my current work setup?

    Thanks for reading, appreciate any feedback.

    Pardon any spelling errors.

  2. #2
    What's up? drk's Avatar
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    1. It's better to use a mirror system at that short an exam lane, period. But, as you said, the cost of remakes would have to be high enough to justify retro-fitting, mounting the LCD on the back wall, etc.

    2. Given the circumstances, I would do this:
    a. Don't freak out about accommodation. Just make the room as dark as possible, so the patient can't see the wall that the LCD screen is mounted on, to minimize stimulus to accommodation. (Heck, even painting the wall around the screen to a dark color would be nice.)

    b. Refract as usual. You will not be able to use any technique to compensate. However, a final correction will be needed: 1/3.25M = 0.3D, which is a really awkward number. If you can smush the chair farther from the screen, see if you can get the refracting distance to 4M, which will be a correction factor of 1/4D.

    c. If it were me, I'd just refract and add -0.25 to the finding. Theoretically, you could use the "duochrome" (i.e. "Red/Green) chart and make the "first green" your endpoint, which will do the same thing.

    d. https://www.thecrazytourist.com/15-b...r-netherlands/

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    a. I was the impression i should do exams in normal light conditions for normal pupil openings? Should i perform exams in a dark room instead? The LCD screen is just like a snellen chart with black letters on a white background.
    b. Unfortunately it is not possible since the chair is mechanical and the phoroptor & motor to raise and lower the chair are all mounted on it. You say there is room for about 0.25dpt for error with this setup?
    c. Sorry i forgot to mention it was about pola duochrome for binocular. I have more experience with humpriss. But i perform it in dark room, mine is without a white line so i think i should perform it in a light room instead? I thought to remember a co-worker once told me the white on the binocular is to force fusion?

    Much appreciated! i will really incorporate your advice in my exams!

    also, d. LOL

  4. #4
    What's up? drk's Avatar
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    Refracting with larger pupils is generally a better thing. It reduces depth of focus, and makes sphere check more sensitive. Yes, one could argue that you get peripheral cornea/lens input and you may get a little spherical aberration that would tend to make you overminus, but I doubt that's a factor.

    I don't know what "Pola" duochrome is, sorry. If it's just duochrome, and you're using it for the final binocular sphere check (good for you, because I like it, too), a dark room is best there, too. If the "pola" is short for polarized/vectograph, then it's best run in a dark room as well.

    I had to look up "humphriss" because I'm unfamiliar with that term, as well. https://www.eyedocs.co.uk/ophthalmol...ocular-balance. But you're right, bright lighting would be better with that sort of a test. The idea is that the fogged eye will still have enough vision to allow binocular fusion and therefore an accommodative "lock", and you can skip over the whole binocular balancing. It's quick and easy, I'll give you that. It was taught to me as a legitimate method, and I very rarely use it, usually when I can't get diplopia on the split prism binocular blur balance method.

  5. #5
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    Drk, first off I would like to thank you for taking the time to answer my questions, it truly shows your passion for your work answering questions for a guy halfway across the globe.

    I will start performing my exams in a dark environment as you suggested, if I understand correctly I can petty much do the entire exam in a dark room without having any major effects on accommodation.
    Yes sorry, I meant a polarized binocular red/green test after my monocular exams. I was already performing them in the dark and will keep it that way, good to see that you do it too, I was under the understanding that I don't need to perform one if I use the Humpriss method since it comes down to pretty much the same in terms of binocular balancing?

    Yes! My favorite test. However because I want to improve my exams as a whole, but I don't want to burden anyone on this forum with 3 pages of text of how I perform them, and if they could spot any points of improvement.
    I recently bought a book but it turned out to be more about pathology than the actual exams. So I keep browsing the net but the only way I can see to really improve or learn anything extra for my exams is to fork out the wallet and pay.

    I found this however and was wondering if you could give it a quick look about the ‘Hack Humphriss’ technique. http://assets.markallengroup.com/article-images/image-library/147/uploads/importedimages/eyeexam.pdft
    I was wondering what you think of this technique, it looks like a good one to me.

    Also, do you think it's worth to pay for a website like this and do these CET tests? Like: https://www.opticianonline.net/cet I'm unfamiliar with this.
    Since I've heard of the split prism binocular blur balance method, I have never actually used it or know how to perform it properly, maybe I could learn it off a site like that?


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