# Optical Forums > Ophthalmic Optics >  Refracting Keratoconus

## Graduate

I know from books that i would get scissor retinoscopic reflex.How do you refract and manage keratoconus.

How often do you see keratoconus in your practise

Your input will prepare me to handle one if i ever come across.

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## chip anderson

A: Spelling  Keratoconnus

B:  Put a rigid contact lenses on, if it does not hold air or fall out, refract over it.  That's the best you can do unless it's a very early kone.

Chip

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## Graduate

> A: Spelling Keratoconnus
> 
> B: Put a rigid contact lenses on, if it does not hold air or fall out, refract over it. That's the best you can do unless it's a very early kone.
> 
> Chip


Thanks Chip for correct spelling.

More input please!

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## Graduate

> A: Spelling Keratoconnus
> 
> B: Put a rigid contact lenses on, if it does not hold air or fall out, refract over it. That's the best you can do unless it's a very early kone.
> 
> Chip


Chip,what kind or what strenght of rigid lens?

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## chip anderson

Does not matter but probably a high minus.  Make sure to know the parameters of the trial lens as you will have to interpolate this with the specs of the fitted lens.   Did I mention that a rigid contact lens is really the only avenue of hope for keratoconnus patients?  Glasses if of any use at all are for finding the contact lens and the bathroom.


Chip

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## Jedi

> A: Spelling  Keratoconnus
> 
> B:  Put a rigid contact lenses on, if it does not hold air or fall out, refract over it.  That's the best you can do unless it's a very early kone.
> 
> Chip


Sorry Chip, the proper spelling is Keratoconus. :cheers:

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## chip anderson

Not according to my spell check.

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## Jedi

Keratoconnus
Must be one of those funny spell checkers.:D

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## chip anderson

Jedii:  



I actually have two computers at my office and they both have different spellings for hydroxyappetite (both of which differ from the implant manufacturer) one insist that this be two words.  I just spell checked on this (my home) computer and it wants two words.

Chip     :cheers:

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## Stopper

Chip, I think Jedi is correct on the spelling. Check an old text book.

Cheers

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## drk

Chipster, you're wrong, here: k-e-r-a-t-o-c-o-n-u-s.  I won my fifth grade spelling bee.

You're talking about refracting a cone (irregular astigmatism) for spectacles, no?  Have you ever done a stenopaic slit refraction?  ( I haven't, but it was described in Optometry College.)  

First of all, a stenopaic slit is that thing in your trial lens set that looks like a, well, slit.  You put it in the trial frame, and you have the patient rotate it until a target (that's the tricky part: you'd have to have a readable chart; maybe would need a few diopters of minus to see the chart) is the clearest.  This is the least minus meridian.  Use trial lenses to optimize that meridian, write down the power and the meridian (say, -3.00 @ 45...not axis 45!), and start over, keeping the minus lens in place.

The clearest meridian again can be located, as before.  This, of course, by definition in irregular astigmatism, will NOT be 90 degrees away from the least minus meridian.  Find it, and refract it, and write it down.  Say you get an additional -4.50 @ 115 (not axis 115).

(I've heard there can be more than two meridians with cones, but let's keep this reasonable, here.)

The final step is to use vector analysis to combine the two cross cylinders, for a "best average" refractive power.  HUH?  VECTOR ANALYSIS, YOU SAY?  Right, I'm with you.

Instead, try to do it this way: in the trial frame, put pl-3.00 @ 45 (don't get confused with where the axis goes: 90 degrees away from where you found the power, so you'd do pl-3.00x135).  Then, in the cell on top of that, put pl-4.50x025.  Then, to resolve the cross cylinder formula, simply put the contraption on the lensometer and read the resultant, and order it.

Don't expect 20/20 vision, though, as the resultant is more of an average of the powers in the two meridia.  If you could theoretically fabricate a weird suface (what would be the name of that surface, BTW?  Someone here will know), then theoretically the k-e-r-a-t-o-c-o-n-u-s patient would get 20/20.

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## chip anderson

There can be more than one cone on a keratoconnic eye. I can guarantee that if the cone is more than rudimentary, the glasses will be just to find the bathroom and the contacts no matter what you do. 

Chip

And yes, I know about and have a stenopaic (I know I can't spell this) slit, it's basically an axial pinhole.

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## fjpod

> If you could theoretically fabricate a weird suface (what would be the name of that surface, BTW? Someone here will know), then theoretically the k-e-r-a-t-o-c-o-n-u-s patient would get 20/20.


What about wavefront lenses?

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## Graduate

> Chipster, you're wrong, here: k-e-r-a-t-o-c-o-n-u-s. I won my fifth grade spelling bee.
> 
> You're talking about refracting a cone (irregular astigmatism) for spectacles, no? Have you ever done a stenopaic slit refraction? ( I haven't, but it was described in Optometry College.) 
> 
> First of all, a stenopaic slit is that thing in your trial lens set that looks like a, well, slit. You put it in the trial frame, and you have the patient rotate it until a target (that's the tricky part: you'd have to have a readable chart; maybe would need a few diopters of minus to see the chart) is the clearest. This is the least minus meridian. Use trial lenses to optimize that meridian, write down the power and the meridian (say, -3.00 @ 45...not axis 45!), and start over, keeping the minus lens in place.
> 
> The clearest meridian again can be located, as before. This, of course, by definition in irregular astigmatism, will NOT be 90 degrees away from the least minus meridian. Find it, and refract it, and write it down. Say you get an additional -4.50 @ 115 (not axis 115).
> 
> (I've heard there can be more than two meridians with cones, but let's keep this reasonable, here.)
> ...


drk,so the technic is to combined multiple cross-cyl into best single sph-cyl.
i think there is a formula for this?

Thanks all for input.

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## drk

Chip, I was only busting your chops for misspelling "keratoconus".  You spelled "stenopaic" correctly, though, which is much more difficult!

The discussion about the SS refraction was aimed toward the thread starter, not yourself.  I wouldn't condescend to someone who has had the amount of experience you've had.

Yes, the acuity may be unspectacular with spectacles.

Wavefront, who knows?

Yes, there are cross-cylinder formulas, if you have the software.

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## Graduate

> Chip, I was only busting your chops for misspelling "keratoconus". You spelled "stenopaic" correctly, though, which is much more difficult!
> 
> The discussion about the SS refraction was aimed toward the thread starter, not yourself. I wouldn't condescend to someone who has had the amount of experience you've had.
> 
> Yes, the acuity may be unspectacular with spectacles.
> 
> Wavefront, who knows?
> 
> Yes, there are cross-cylinder formulas, if you have the software.


drk our MD says there is no such thing as SS refraction for keratoconus and there are no such formulas or softwares. He insisted it is bizarre irregular astigmastism and cross-cyl is irrelevent to conus.

Instead he told me to apply topographic +PMMA/Rigid lens techniques.

What do you say?

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## chip anderson

Graduate:  You M.D. has a firm grasp of what to do with kones.   Folks who want to put glasses on them, put soft lenses on them and exotic techniques are totally out of touch with the problem.

Chip

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## drk

Your MD is correct. I dreamed that one up, after a late night binge at Taco Bell. :Rolleyes:  

I was answering the question as to how to best refract a keratoconic or another irregular astigmatism patient.

I was not trying to infer, _CHIP_, or _MEAN, KNOW-IT-ALL-MD,_ that spectacles are the best method of managing keratoconics. *Obviously*, (and a big DUH, here) rigid lens correction is standard of care.

Some people LOOOOVE to argue! 

To prove that I'm not having a 7-layer burrito hallucination, have Doogie Houser, M.D. google "stenopaic slit refraction", or click on these two of 173 hits:

http://www.optvissci.com/pt/re/ovs/a...856145!9001!-1

http://www.ncbi.nlm.nih.gov/entrez/q...&dopt=Abstract

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## chip anderson

Had not ment to offend anyone here and I will probably stir up more trouble with this, but I will go on to say that when residual or bifocals encountered after fitting rigid lens.  The best thing to do is put this in forward lenses (which I am normally opposed to, as I like the contact to correct everything) is the only way to go.  If you try to fit bifocal contacts or toric contacts on kones, you will find that your sucess rate is near zero, with a few very rare very expensive exceptions.


Chip

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## drk

Chip, man, I'm just teasing you, you know.  I admire you, and anyone else who does the hard work that no one else will touch.

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## Graduate

> Your MD is correct. I dreamed that one up, after a late night binge at Taco Bell. 
> 
> I was answering the question as to how to best refract a keratoconic or another irregular astigmatism patient.
> 
> I was not trying to infer, _CHIP_, or _MEAN, KNOW-IT-ALL-MD,_ that spectacles are the best method of managing keratoconics. *Obviously*, (and a big DUH, here) rigid lens correction is standard of care.
> 
> Some people LOOOOVE to argue! 
> 
> To prove that I'm not having a 7-layer burrito hallucination, have Doogie Houser, M.D. google "stenopaic slit refraction", or click on these two of 173 hits:
> ...


 
drk no hard feeling please,just that our MD has never studied refracting kertaconic patient with stenopic slit.

Thank you for the good links,unfortunately I cannot open full article to read.Only abstract is available.I wanted to read the whole article.

Cheers:cheers:

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## drk

No offense.  Just having fun!:cheers:

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