How can an 11 diopter myope see 20/25 without squinting?

[drbizzaro]

Just a question to the doctors out there who are good with optics and physiology:

How is it possible for my 11 diopter patient to see 20/25 uncorrected without squinting? I mean, she functions fine without glasses. She has never had glasses and is currently 25 years old.

Here are the exam findings:

VAsc, OU: 20/25-2
VAcc, OU: 20/20

MR: OD: -11.00 DS
OS: -11.00 DS

RET: OD: -11.25 DS
OS: -11.25 DS

SLEX: WNL
FUNDUS: posterior staphyloma OU

Subjective comments: with corrective lenses, things are sharper, but not significantly sharper. Also, everything is more vivid and brighter. However, letter clarity is about the same as it was before.

Can anyone explain this? I was careful to notice if the patient squinted at all. And there was no squinting what-so-ever. I tested VA with lights on and off. In outdoor environments and indoor.

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[KHE]

Just a question to the doctors out there who are good with optics and physiology:

How is it possible for my 11 diopter patient to see 20/25 uncorrected without squinting? I mean, she functions fine without glasses. She has never had glasses and is currently 25 years old.

Here are the exam findings:

VAsc, OU: 20/25-2
VAcc, OU: 20/20

MR: OD: -11.00 DS
OS: -11.00 DS

RET: OD: -11.25 DS
OS: -11.25 DS

SLEX: WNL
FUNDUS: posterior staphyloma OU

Subjective comments: with corrective lenses, things are sharper, but not significantly sharper. Also, everything is more vivid and brighter. However, letter clarity is about the same as it was before.

Can anyone explain this? I was careful to notice if the patient squinted at all. And there was no squinting what-so-ever. I tested VA with lights on and off. In outdoor environments and indoor.

She is either the world record holder for PRA or there is something way off with that refraction.

 

[drbizzaro]

She is either the world record holder for PRA or there is something way off with that refraction.

That is what I was thinking. But I also had the other doctor do a quick recheck in case I missed anything. The other doctor found the same Rx.

Also, autorefraction was within 0.50D of the -11.00 OU (after tropic was utilized for dilation)

 

[vsarge0708]

Wow, that's one hell of a depth of focus. How teeny tiny were her pupils--was your patient a prostitute?

 

[gochi]

Wow, that's one hell of a depth of focus. How teeny tiny were her pupils--was your patient a prostitute?

Are you kidding me!

 

[vsarge0708]

Are you kidding me!

Yes and no, the magnitude of depth of field/focus is a function of pupil size--the smaller the pupil the larger the depth of field/focus [the caveat is that small pupil size increases diffractions]. There is syndrom called Argyll-Robertson's pupil in which the pupils are small and do not dilate well with atropine [the pupils also do not constrict when exposed to light, but constrict in the near triad constriction/convergence/accomodation]. A known etiology of this syndrome is neurosyphilis, hence its nickname "prostitute's pupils".

 

[gochi]

Yes and no, the magnitude of depth of field/focus is a function of pupil size--the smaller the pupil the larger the depth of field/focus [the caveat is that small pupil size increases diffractions]. There is syndrom called Argyll-Robertson's pupil in which the pupils are small and do not dilate well with atropine [the pupils also do not constrict when exposed to light, but constrict in the near triad constriction/convergence/accomodation]. A known etiology of this syndrome is neurosyphilis, hence its nickname "prostitute's pupils".

Dang...thats alot of info.

 

[Karnak]

She is either the world record holder for PRA or there is something way off with that refraction.

Dude that is one of the funniest things I've read all day

 

[eyepoker]

Does this have similar idea as a pinhole test?

I heard that if you use a pinhole probably, theoretically all the refractive errors can be corrected because the light would go through the hole in a straight line without bending ? so does having a small pupil have similar effects as having a pinhole test?

 

[vsarge0708]

Does this have similar idea as a pinhole test?

I heard that if you use a pinhole probably, theoretically all the refractive errors can be corrected because the light would go through the hole in a straight line without bending ? so does having a small pupil have similar effects as having a pinhole test?

Yeah sort of--a pinhole will increasing the depth of field/focus [about +/- 5 Diopters in the literature I've studied so far]. A pinhole probably won't "correct" all of the refractive error due to the decreased amount of illumination reaching the retina caused by having the pinhole infront of your face, as well as the diffraction effects of having such a small aperture. Having a small pupil will increase the depth of field/focus, but at a certain point the diffractions caused by having a smaller pupil will decrease visual acuity [If I remember correctly, I think going from a 3mm pupil to a 1mm pupil the diffractions increase exponentially, and going from 3mm to a 7+mm pupil the aberrations increase drastically, so 3mm was basically the best compromise between low aberrations and diffractions. I think the magic number for a pinhole is 1.2mm].

 

[Karnak]

I think the pinhole explanations are missing something...
Get any functional emmetrope to hold a +11.00DS in front of their eye, with a pinhole, and see how they go. Pinholes only get you so far...

 

[vsarge0708]

I think the pinhole explanations are missing something...
Get any functional emmetrope to hold a +11.00DS in front of their eye, with a pinhole, and see how they go. Pinholes only get you so far...

...reread my last post