Re: How to perform retinoscopy
Dear Doug,
In order to measure your refractive STATE objectively -- with
a retinoscope -- you will need.
1. The instrument.
2. Technical training on the instrument, and some
basic optical information (analysis) of the eye.
3. Assuming you have a friend who has your interest then
BOTH of you can make this measurement on each other.
4. The Snellen/Trial-lens is quite good -- and is preferred
for a final refraction. But the retinoscope will give
a similar reading.
5. You can do this, but you can ot "freeze" the eye with
a drug. If you think that is more "accurate" then you will
need some one to prescribe that drug for you.
As Mike as said, he thinks the retinoscope is quite accurate
with no drug -- and I would agree with him on that point.
Enjoy,
On May 1, 7:14 pm, douglas <Protoman2...@gmail,com > wrote:
> On May 1, 3:31 pm, otisbr...@embarqmail,com wrote:
>
>
>
>
>
> > Dear Doug,
>
> > Subject: Best Visual Acuity -- METHOD
>
> > This is the standard that is preferred by most ODs.
>
> > Using a trial lens kit (or Phoropter), and a minus lens -- you do the
> > following.
>
> > Have the person read the Snellen. OK, 20/70
>
> > Now you place a weak minus lens in your trial-lens frame, of -1
> > diopter.
>
> > 20/30, OK
>
> > You then increase the power (asking 1 or 2 better) until you get the
> > sharpest
> > vision possible.
>
> > 20/20. OK with a -1.5 diopter lens.
>
> > Now let is see if we can do better. Using a cyl lens, you rotate the
> > lens
> > from zero to 90 degrees, looking for that to sharpen the image.
>
> > So you get to 20/15 for that person.
>
> > You think write the prescription for the Spherical and Cyl and angle.
>
> > Enjoy,
>
> > On May 1, 3:18 pm, douglas <Protoman2...@gmail,com > wrote:
>
> > > On May 1, 9:21 am, "Mike Tyner" <mty...@mindspring,com > wrote:
>
> > > > "douglas" <Protoman2...@gmail,com > wrote
>
> > > > > OK, I know how to check the base refractive error, but how do you
> > > > > check for astigmatism? I know the retinoscope has a protractor on it,
>
> > > > You don't see protractor markings on modern retinoscopes. The markings are
> > > > on the phoropter.
>
> > > > > I'm pretty sure you use it just for that, but...how?
>
> > > > Once you get a good reflex, you rotate the streak and sweep it in different
> > > > directions across the pupil. Many times it's obvious that the streak
> > > > neutralizes in one meridian (say, sweeping side-to-side) yet it's way off
> > > > 90 degrees away, when you sweep up-and-down. That's astigmatism, and the
> > > > trick is to determine the maximum and minimum meridians.
>
> > > > > If you did both a static cycloplegic and a dynamic non-cycloplegic
>
> > > > Dynamic retinoscopy isn't useful for determining refractive error. Many
> > > > doctors never use dynamic and have forgotten how, because it's only valuable
> > > > for determining accommodative response and there are other ways to do that.
> > > > A few years ago the "Prio system" was pushed out, basically an LCD nearpoint
> > > > card with a hole it it, thru which you could do dynamic retinoscopy. It was
> > > > gimmicky ("computer vision") and seldom indicated any unique sort of
> > > > treatment, but you were obligated to prescripe Prio lenses from it. It
> > > > wasn't that much better than a plastic nearpoint card with the same hole.
>
> > > > Retinoscopy is a dying art. Most retinoscopy used to be done to gain a
> > > > starting point for subjective refraction, an estimate. Many doctors now use
> > > > autorefractors for that, and consequently never pick up a retinoscope. I
> > > > wouldn't either, except sometimes I get ahead of my staff and patients
> > > > haven't had the autorefraction done yet.
>
> > > > Cycloplegic retinoscopy may be used to help determine latent hyperopia but
> > > > dry (non-cyclo) ret is often a good indicator of LH, revealing results that
> > > > are a half- or full diopter more plus than the patient's chosen subjective.
>
> > > > > Who makes good retinoscopes? Keeler?
>
> > > > Copeland and Welch-Allyn. Don't know the Keeler.
>
> > > > > And what's the diff b/w a
> > > > > retinoscope and an ophthalmoscope?
>
> > > > BIG diff. A ret just generates a streak of light. The streak can be focused
> > > > but it's designed to focus an image of the filament (the streak) to the
> > > > retina, such that you can see it moving in the pupil.
>
> > > > Ophthalmoscopes are illuminated too, but more important they have an
> > > > observation system that lets you see the details of what you're
> > > > illuminating. Direct and indirect o'scopes both produce an image of the
> > > > retina. In direct scopes, the image is upright and magnified. Indirect
> > > > scopes produce upside-down images that are wider-field (less detailed, not
> > > > as magnified.)
>
> > > > > Can you use a indirect
> > > > > ophthalmoscope for retinoscopy?
>
> > > > Not very well, I'm not sure it could be done because retinoscopes all focus
> > > > the streak in different planes. The ophthalmoscope generates only parallel
> > > > light for illumination.
>
> > > > >And has any beginning optometry student accidently held the
> > > > > retinoscope backwards, and temporarily blinded themselves?
>
> > > > Oh sure. Ophthalmoscopes are much brighter. But with all hand-held scopes,
> > > > it's habit to turn it on, then shine it somewhere like your hand or the
> > > > wall, to make sure it's working. Putting it to your eye backwards is dumb
> > > > but even dumber is getting up in your patient's face then finding the scope
> > > > is dead.
>
> > > > -MT
>
> > > But I'm sure you could use a direct ophthalmoscope for retinoscopy, if
> > > you lacked a retnoscope, would the procedure be any different for
> > > using an ophthalmoscope for static retinoscopy? Which provides better
> > > bva, cyclo, or non-cyclo?- Hide quoted text -
>
> > > - Show quoted text -- Hide quoted text -
>
> > - Show quoted text -
>
> That's subjectively. And, according to House, patients lie. So, how do
> we use retinoscopy to *objectively* determine our patient's refractive
> error? I believe its as follows:
>
> Dim the lights, instill cyclopentolate into the patient's eyes, and
> have them look at at a target at optical infinity. You stand 67cm away
> from the patient, and set the phoropter to -1.50D --please explain to
> me exactly why this is done? To set the effective curvature to zero,
> perhaps? And I know that -1.50D is the reciprical of 67cm--, and move
> the retinoscope across the pupil. If you see with-motion, add plus
> lenses; against-motion, add minus lenses. Stop when the pupil fills w/
> light, and there's no motion. Rinse and repeat for all meridians.
> Rinse and repeat for the other eye. Subtract -1.50D from the readings
> to get the prescription.
>
> How would you use the autorefractor to find an inital starting point
> for the static retinoscopy?- Hide quoted text -
>
> - Show quoted text -