How large a zone can orthoK go up to? 7mm? larger?

Due to my huge pupils, I will want the largest zone possible. I know
6mm is standard but theres also 5.5mm and 5mm as well as larger. I have
seen 7mm and heard of even larger! I googled it and orthoK is indeed
available in 7mm. Not sure if larger but 7mm is not bad as my pupil
probably wont get over 7mm except in near total darkness. I am willing
to accept mild halos and starbursts or rather, a mild increase over
what I have. I use my vision in the day much more than night and I dont
drive anyway so it wouldnt matter. If worse for worse comes, orthoK is
reversable and I can stop orthoK then resume it anytime.

 

your pupils wouldn't be so large if you quit eating mushrooms.
now go discover girls or something-- quit fixating on vision

 

Ace,

In my opinion, 7 mm is out of the question for your prescription. The
amount of correction is inversely proportional to the diameter of the
treatment zone. Look up Munnerlyn's formula for the exact
relationship. One generally has only 50 microns of tissue to play
with, so figure out the maximum depth is 50 microns, the diameter is 7
mm. How much correction in diopters can result?

Drg

 

Making a 7mm optic does not equate to the optic zone created on the
cornea.

Anyway, no-one would touch a douche like you anyway Nancy.

dr grant

 

This is true. But, since you are the "expert," exactly what
probability do you give to getting that accomplished, pretending that
the k's and eccentricity are "average"?

DrG

 

"One generally has only 50 microns of tissue to play
with, so figure out the maximum depth is 50 microns, the diameter is 7
mm. How much correction in diopters can result?"


OrthoK can only flatten 1/3 to 1/2 of that. If you have 50-60 microns
to play with, figure about 25 microns maximum to play with. With 6mm
orthoK, thats 6 microns per diopter so 4 diopter improvement is about
the limit. with 7mm zone, its 8 microns per diopter so the limit
becomes 3 diopters.


"In my opinion, 7 mm is out of the question for your prescription."


I wear -3.25 glasses most of the time.


"Making a 7mm optic does not equate to the optic zone created on the
cornea."


itll be about 6.75 mm for a 3 diopter correction. I will see if I can
get 7.5mm or even 8mm zone orthoK.

 

OK, Ace. You win. Nobody can tell you anything.

So, run along and get OK and report back to us.

The OK nomograms are derived from Munnerlyn's formula as any OK expert
will tell you. Of course the amount of tissue displaced will vary with
the thickness of the epithelium, and is not the same for everybody.

DrG

 

Actually most are derived from Jessen's formula, with the exception of
BE, which take a different tack.

However, you are correct in thinking that Nancy is a dickhead. She
really is. She does not listen, she thinks you are an OK expert, when
you have publically ridiculed OK (as is your right) and then tells you
how to prescribe RGP lenses.

I agree with you Lou, Nancy is one sick puppy.

Happy refracting brother in lenses.

dr grant

 

His formula says theres a .25 diopter regression after 4 hours and a .5
diopter after 10 hours. Wont make a difference to me since ill be
undercorrected anyway.

He also states a .75 diopter regression after 16 hours for 3 diopter
correction. Ok so ill just move a couple inches closer to the computer
monitor, no biggie.

He also found that when comparing the regression at seven-day, 30-day
and 90-day intervals, the amount of regression appeared to slightly
decrease with time

additionally, orthoK was preferred by a higher percentage of subjects
than glasses or soft contacts. This means your more likley to be happy
with orthoK than with glasses!


Before enrolling in the study, 82 percent of the subjects were soft
contact lens wearers, and at the conclusion of the study, only 18
percent of them preferred to continue to wear soft contact lenses. The
subjects who preferred soft contact lenses or spectacle correction over
Paragon CRT lenses were the ones who reported the most complaints of
lens discomfort and glare or flare.


I cant find much more info, but from what I can see, -6 diopters is the
limit for 5mm orthoK, -4 for 6mm and -3 for 7mm.

5mm orthoK displaces 4mm of tissue per diopter(4x6=24)
6mm orthoK displaces 6mm of tissue per diopter(6x4=24)
7mm orthoK displaces 8mm of tissue per diopter(8x3=24)

"Of course the amount of tissue displaced will vary with
the thickness of the epithelium, and is not the same for everybody."


The above figures are for a thick epithelium. If mine is average
thickness, ill expect an improvemen of -2.25 or -2.5 diopters plus a
reduction or elimination of my astigmastim.


DrG, you are presbyopic so you know full well the benefits of your -3.5
pescription in seeing clearly from 11.5 inches. If you sit about 2 feet
from the computer, a -1.75 undercorrection is needed. If you got OrthoK
and fully corrected, youd need reading glasses for near and
intermediate. If your OrthoK undercorrected you, you wont need glasses
except for reading fine print or for driving and watching movies.

 

****, I laughed so hard I nearly shat.

Lou Coma knows more about the math of OK than you and he doesn't know
the start of it as he does not do it. However, he does know math and he
knows that the bigger the zone, the smaller the change.

Now to you Nancy. You are stupid. You post crap that is not worthy of
posting and if I were moderator (Christ I wish I was) you would never
post here or anywhere again.

You don't know shit. You don't know the start of shit. You know OK even
less.

Just PISS OFF and stop annoying the general public with your shit.

dr grant

 

If you think you know so much, why dont you educate me instead of
spouting off vuglarities? Teach me about OK, o master!

 

Why would I waste my time. You are a parasite. You know noting and
learn nothing.

Go away.

dr grant

 

Your figures are close to mine. When I say thickness, I mean the
saggital thickness, which is the difference in thickness between the
center and the edge of the treatment area. OK causes the central
cornea to thin by pushing epithelium out into the mid-periphery, where
it piles-up. Helen Swarbrick published an excellent study on this a
few years back. She found that the average dioptric change was 1.66.
This was accomplished by an average central thinning of 9.3 microns and
an average mid-peripheral thickening of 10.9 microns. The effective
saggital depth is about 20 microns, or 12 microns/diopter for a 6 mm
zone. With a total of 50 microns to play with (25+25), this works out
to about 2.75 to 3.00 diopters of change for a 7.0 mm zone, ASSUMING
the lens mechanics would permit it.

The above is only theoretical, which is why I asked Dr. Mason to
comment from his personal experience. Instead, he made some obscure
reference to the founder and patron saint of orthokeratology, George
Jessen, and did not answer the question directly.

With respect to being presbyopic, my preference is for 100% clarity at
infinity, and 100% clarity at whatever nearpoint distance I am working,
which means that I prefer to wear progressive lenses over my contact
lenses. I have zero tolerance for blur, and zero tolerance for
fluctuating vision. This means that I would not be a good candidate
for either OK or LASIK.

DrG
http://www.coppellfamilyeyecare.com

 

Virtually all of the OK experts who publish make reference to
Munnerlyn's formula. For those who don't know, the Jessen to whom
Grant refers is George Jessen, the co-founder of Wesley-Jessen, and the
widely acknowledged founder of modern OK, who was still practicing and
lecturing in Chicago during the time I went to school there.

I have never publicly ridiculed OK, Grant. We have calmly and
rationally discussed different sides of the OK issue. Although I am
certified to do OK, I don't do much of it. For me, and for now,
overnight OK is not on the table. For me, OK is still a means by which
patients can extend the refractive effects after their lenses are
removed for the evening, or for sports and other activities.

DrG

 

No capital "D". No period. Does "dr" stand for Donald Randolph, or
"don't reply"?

 

The guys who design OK lenses all use Jessens formula, which is
prescribing a lens that is 4D flatter than flat K. The only exception
to this is the BE series, which chooses base curve according the the
required change in script. Munnerlyn's formula is only used in
publications to discuss corneal curve changes, not in calculation and
design of lenses.\\

dr grant

 

Here we go. Of course, that statement didn't sound right, and so I
called up a lens designer. He calculates the base curve from the
patients RX and the corneal curvature. He indicated that the method
you describe is somewhat outdated.

DrG

 

Actually, he just used Jessen's formula. Add the script to the flat K
(in D) and add an extra 0.50. This is the indicated base curve for your
lens. That is Jessen's formula. Your lens designer used it, CRT uses
it, Tabb uses it, Euclid uses it, R&R use it. This is why with all
these designs, you get a +0.50 overrefraction over your trial lens.

grant

 

Sorry, I was confused. In the previous post, you said 4 diopters
flatter than K. If you said just add 0.50 diopters of minus to the
script, I would have understood. In fact, I would have understood
better if you had said 0.75 diopters added to the script.

DrG

 

By the way, for those who don't understand, Grant is making the point
that shoots for an over-correction of 0.50 to 0.75 diopters in
orthokeratology to allow for the normal regression during the day.

So, in essence you wake up a little farsighted and go to bed a little
nearsighted.

DrG