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Thread: Assessing visual acuity

  1. #1
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    Assessing visual acuity

    Since there are so many different providers on this forum and so many different practice environments, it would be ideal to discuss how we all check vision. This is somewhat germane to another thread about checking vision through ophthalmic ointment.

    1. Any particular distance?
    2. Room light on? No room light on?
    3. Projected onto a wall or screen chart? Illuminated by a computer screen (CRT or LCD) or paper wall chart (a la Feinbloom, LogMar, Sloan, ETDRS)
    4. High contrast (standard card or projection) or low contrast (Pelli Robson etc)?

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    Just to start the thread, here are some examples I'v seen,

    1. Hand motion
    2. Finger Counting
    3. Light Perception
    4. 20/20 Snellen
    5. 20/20 Feinbloom
    6. 20/20 logmar
    7. 20/20 ETDRS
    8. 20/20 Sloan
    Near acuities?
    1. Jaeger 1
    2. 6 point
    3. 1.0M
    4. Single digits, multiple digits
    5. sentences

    Does it matter?
    1. If you had blunt trauma to the face and you see a swollen cornea, is there really any difference between CF at 8feet and 20/400. Is it ok just to do the FC at whatever distance than a 20/something reading
    2. A patient in intense pain ("10/10") says a vision? is it reliable
    3. A patient with illiteracy?

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    Quote Originally Posted by npdr View Post
    Since there are so many different providers on this forum and so many different practice environments, it would be ideal to discuss how we all check vision. This is somewhat germane to another thread about checking vision through ophthalmic ointment.
    1. Any particular distance?
    2. Room light on? No room light on?
    3. Projected onto a wall or screen chart? Illuminated by a computer screen (CRT or LCD) or paper wall chart (a la Feinbloom, LogMar, Sloan, ETDRS)
    4. High contrast (standard card or projection) or low contrast (Pelli Robson etc)?
    For standard eye exams... 20 ft (via mirrors) projection snellen chart, room light off, but dimmer lights on so there's a bit of light in the exam room, high contrast.

    For near point, I do single letter on a near point rod with gooseneck light illuminating for contrast.

    However, I think visual acuity doesn't mean all that much. It's a number to cover our posteriors from a legal standpoint and a way to track changes in vision. It is completely useless when it comes to describing functional vision, what a person actually sees. How many people see 20/20 but are completely debilitated by glare at night? Or see 20/20 with 10 degree visual fields? Or see 20/20 single letter, but throw a full sentence at them and are functionally reading heiroglyphics? Or the patient who's 20/400 and perfectly happy compared to the 20/20- patient who feels like they are totally blind?

    A number doesn't mean much, it's subjectively what the patient is telling me that truly matters more. If they come in seeing 20/20 but say that something isn't right with their glasses... then something really isn't right.

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    Excellent. I agree. I think there should be a difference between visual acuity and visually-related or -driven performance. In a injury case as was described in a thread on this venue, is the acuity adequate? or must it be greater in some degree?

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    Quote Originally Posted by npdr View Post
    Excellent. I agree. I think there should be a difference between visual acuity and visually-related or -driven performance. In a injury case as was described in a thread on this venue, is the acuity adequate? or must it be greater in some degree?
    For a screwed up cornea slathered in ointment, I don't get too hung up on acuity. I have a patient now with Bell's Palsy, I see her once a week, she's lubing the living daylights out of her eye, patching full time (taping it closed doesn't work on her, pulls off in about 30 seconds, springiest eyelid I've ever seen in a Bells' patient!). Her acuity when she first presented was 20/200 (she hadn't done any lubing of the cornea, only went to an ER, saw me the following Monday, so 3 days with a dry cornea, it was horrible looking). 1 week follow up, after following my directions to the letter, her acuity was 20/400, took a look at her cornea, it was roughly 8000000000 times better, but there was a glob of goo across the middle. I moved it with her eyelid, rechecked acuity, up to 20/100.

    Following other disease problems that do not involve ointment treatment, I use acuity only to monitor from one visit to the next.

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    8000000000 times better? thats some improvement. Your story reminds me of an elderly aphakic patient I dealt with years ago. She came in complaining of episodes of near complete vision loss in her right eye, and blamed the contact lens I had fitted. She had seen the ophthalmologist, and he found no problems, indicating va of 20/30+.
    A slit lamp check revealed nothing unusual, until suddenly a large clump of loose tissue "rolled" from within the posterior chamber, and lodged right behind the pupil, effectively blocking all incoming light. She blinked hard, and the tissue mass rolled back and away from the pupil. I was almost speechless for a moment, and called the ophthalmologist in a panic. I told him I was afraid the mass would pass through the pupil and lodge in the anterior chamber and cause an angle closure. He was quite amused by my call, and reassured me, and asked me to reassure the patient that there was no cause for concern.
    The tissue was a remnant from her cataract surgery, and to this day, I still don't know why there was no apparent risk of the remnant lodging in the meshwork.

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    Quote Originally Posted by Dave Nelson View Post
    8000000000 times better? thats some improvement. Your story reminds me of an elderly aphakic patient I dealt with years ago. She came in complaining of episodes of near complete vision loss in her right eye, and blamed the contact lens I had fitted. She had seen the ophthalmologist, and he found no problems, indicating va of 20/30+.
    A slit lamp check revealed nothing unusual, until suddenly a large clump of loose tissue "rolled" from within the posterior chamber, and lodged right behind the pupil, effectively blocking all incoming light. She blinked hard, and the tissue mass rolled back and away from the pupil. I was almost speechless for a moment, and called the ophthalmologist in a panic. I told him I was afraid the mass would pass through the pupil and lodge in the anterior chamber and cause an angle closure. He was quite amused by my call, and reassured me, and asked me to reassure the patient that there was no cause for concern.
    The tissue was a remnant from her cataract surgery, and to this day, I still don't know why there was no apparent risk of the remnant lodging in the meshwork.

    Yep, it was absolutely precicely 8000000000 times better :p I think most of us have had our moments behind the slit lamp where we wish we were anywhere but there, seeing something that makes us second guess ourselves or wonder 'wtf is that???' and hoping the patient doesn't see our facial pallor.

    Clinical pearl of wisdom, just don't say 'Oops' or "hmmmmmmmmm" when looking through a slit lamp. Unless you really want to mess with your patient's head :bbg:

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    In addition to normal acuities we have developed a snellen style chart in which any lighting condition (or light + any tint) can be emulated. The differences in acuity can be remarkable - even when brightness remains constant. This also applies to near vision and accounts for many currently very poorly addressed problems in optometry.
    We now know of over 100 physical effects that can be measured of optimum visual stimulus modification - and except in rare cases the optical professions completely fail the public by ignoring one of the most fundamental areas of vision - the stimulus. I feel sad that there are so many ostriches (head in sand types) in optics - for many patients the effects of accurate stimulus control is much greater than using any other optical intervention. For a few of the effects you can look at videos on our optometric clinic site www.jordanseyes.com - and they are just the start of what the optical professions should be doing. I am now being often called in as an expert witness in this area in the UK for legal cases in the area of poor optical physical knowledge - the numbers are growing fast - beware - optometry and opticians worldwide may be in a dangerous position if they don't use the current knowledge that is readily available and take pro active action!

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