Point Spread Function, Root Mean Square Wavefront Error and other Goodies

[qwopty99]

Hi folks

Hopefully some of you folks still in school can help out with this stuff. I remember coming across this in optom school, but I can't for the life of me remember in what course. And I don't have any textbooks with it (I didn't buy many texts to begin with).

Anyhoos - anyone know any decent resources that explain the basics of these things? I'm talking about point-spread functions of defocus blur e.g. what is the PSF of a 3-diopter myope? Or what is the RMS wavefront error of 2.5 D of astigmatism?

I don't really remember covering this stuff in detail, but I do remember coming across it.

Any help? Thanks.

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[eyestrain]

Oh dear Lord I'm having nightmares. Make it stop!!!

 

[qwopty99]

I'm writing something about refractive surgery that touches on this. It's critical to what I'm trying to say, so I have to find this stuff somewhere.

 

[iowaeyes]

Here's what I found in my Geometric and Visual Optics notes:

The Point Spread Function (PSF) is equal to B(as in beta) = d * K when the blur is limited by refractive error (so diffraction and abberrations are small).

d is the diameter of the pupil in meters

K is the absolute value of the refractive error in diopters

B (beta) is also known as the blur circle diameter in radians

I don't see anything about the RMS of the wavefront right now, althought I do remember covering it...

 

[qwopty99]

Geom and Visual optics... I'll have to pull those up.

I couldn't for the life of me remember where we covered it. I was thinking maybe a strab course or something - cause the "expert" in this stuff at our school was a BV teacher.

Is there a "chart" of some sort that equates point spread to visual acuity? i.e. "x" amount of spread equals a VA of 20/40 ? Do you know if this type of thing exists?

Do you happen to know how that equation changes for astigmatism? Or is it just spherical equivalent?
(But I can't see the two being equivalent in VA cause the spherical equiv of:

+1.00 DS -2.00 DC
and
+5.00 DS - 10.00 DC

are equal, but they certainly do not result in the same VA.)

But this is very helpful. I need an equation that includes the pupil size, and yours does.



Thanks for your reply. I'll go pull up my notes...

 

[IndianaOD]

Geom and Visual optics... I'll have to pull those up.

I couldn't for the life of me remember where we covered it. I was thinking maybe a strab course or something - cause the "expert" in this stuff at our school was a BV teacher.

Is there a "chart" of some sort that equates point spread to visual acuity? i.e. "x" amount of spread equals a VA of 20/40 ? Do you know if this type of thing exists?

Do you happen to know how that equation changes for astigmatism? Or is it just spherical equivalent?
(But I can't see the two being equivalent in VA cause the spherical equiv of:

+1.00 DS -2.00 DC
and
+5.00 DS - 10.00 DC

are equal, but they certainly do not result in the same VA.)

But this is very helpful. I need an equation that includes the pupil size, and yours does.



Thanks for your reply. I'll go pull up my notes...

PSF is used a lot in discussing higher order aberrations. I'd also research along those lines. Contact the optics gurus at Indiana, I believe they are know worldwide for their optics expertise. For example, Drs. Thibos and Miller.

 

[qwopty99]

For anyone just observing, I found this pretty good overview (although it is commerically influenced).

http://www.revoptom.com/index.asp?ArticleType=SiteSpec&Page=osc/105418/lesson.htm

Thibos is definitely the optics guy. I'm not as familiar with Miller.

 

[iowaeyes]

Miller actually taught part of our first year Geometric and Visual Optics class. Thibos doesn't teach it, but he researches in Optics and did teach in our Visual Science course.

 

[qwopty99]

What is Miller's full name?

 

[iowaeyes]

Donald T. Miller