Military Visual Requirements

Spherical Equivalent Conversion

Remarks: The minus lens "works" instantly. If you prefer it --
then use it. If you are 28 years old -- then the minus
will have little effect -- if you use it ONLY when
absolulty necessary. But if you have had -2.75 diopters
of myopia and cleared to 20/30 to 20/25, the "story" is
completely different. I each case the person who is
knowledgeable of these issues MUST make his decision
based on the best available information. Here is
information on the military 20/20 standard (4 out of 5
charaters) and the DMV standard is reading 1/2 the
characters to pass the line. (To the best of my
knowledge.)

Otis

++++++++++++++++++++

TOPIC: More on PRK

== 1 of 6 ==

Date: Wed 31 Aug 2005

From: "Yasar, Mehmet C PFC A Co 602d ASB"

Thank you to all ODs and friend who support me with their
feedback, yes it just didn't sink in well with me to get the PRK
with this prescription. Military OD at Hawaii who would perform
the surgery denied to do so. I got the email. I am not that
upset but I have some concerns, I'd appreciate some feedback.

He said* "Sorry, but we have decided not to do refractions
this low. Our cut off is a -1.50 spherical equivalent.

The results on anything below this usually are not worthwhile
and sometimes the risk is greater than the benefit."

* This is what I was thinking after I read your responses.
Though, what does "spherical equivalent" mean?

My concern is my right eye which is -0.75 + 0.25 x40 now, the
flight pyhsical consists of "transposing" these numbers and
standards must meet in both plus-cylinder and minus-cylinder
formats, after that calculation, my right eye seems to be -1.00
-0.25 x130(?) according to military technical bulletin.

This leaves me only half a diopter room before I would be
disqualified for flight duty. If my eye moves another half
diopter and transposed numbers equal a -1.50, can I be still
eligible for PRK? Maybe that is what spherical equivalent?

I will write more later... Thanks a lot... By the way,
Bill, my right eye was 20/30-1 and pin hole 20/20-2 and left was
with moisturizing drops 20/20. This exam was at 1430 hours so my
eyes were not so fresh as some call it. I wonder if the acuity
results would be different if it was done 0900 in the morning.

== 2 of 6 == Date: Tues 30 Aug 2005 20:43 From:
"otisbrown@..."

Dear John,

I wonder if you could check something for me.

I have been told that you must read 4 out of 5 characters to
pass the line.

Dr Judy says that reading 1/2 the characters pass the line.

(I like Judy's standard.)

Question: Is there any standard?

Best,

Otis

== 3 of 6 ==
Date: Wed 31 Aug 2005 12:57
From: "Yasar, Mehmet C PFC A Co 602d ASB"

* ATB - DISTANT VISUAL ACUITY TESTING (DD Form 2808, Block
61. 'DISTANT VISION' ) [As of: 1 May 2002]*

- IMPORTANT NOTE ABOUT 20/20 DISTANT VISUAL ACUITY STANDARD
FOR FDMEs! Per AR 40-501, paragraph 4-12, a (1), "...no more than
1 error per 5 presentations of 20/20 letters, in any combination,
on either the Armed Forces Vision Tester (AFVT) or any projected
Snellen chart set for 20 feet." -

Issue: AFVT line has 10 letters but is split into two sets
of five letters positioned next to each other on the same line.
You may still test the entire line, if desired, but the patient is
still only required to get *4 out of 5* letters that are on a
20/20 line to be considered a 'pass' for an FDME. Therefore,
entries of 20/20 or 20/20-1 are both passing entries. Most
projected Snellen charts have 6 letters (some have 4, 5, 7, or 8
letters) per line. The regulation allows for presentation of 5
letters "in any combination" so you may meet the requirement. If
in que stion, refer to the Eye Clinic for verification.


== 4 of 6 ==
Date: Wed 31 Aug 2005 04:07
From: "Mike Tyner"

"Yasar, Mehmet C PFC A Co 602d ASB"
<mehmet.yasar@...> wrote

> He said "Sorry, but we have decided not to do refractions
this low. Our cut off is a -1.50 spherical equivalent.

Very logical.

Spherical equivalent is the mean dioptric power, the average
of the two major meridians.

For -0.75 +0.25 x 040,
the SE is -0.62.

When you convert, honor the signs.

Your myopia would have to double before it threatens your
qualification. And the later myopia begins, the milder it tends
to be.

-MT

== 5 of 6 ==
Date: Wed 31 Aug 2005 04:25
From: "Mike Tyner"

<otisbrown@...> wrote

> Question: Is there any standard?

The standard they taught in physiological optics at UAB was
"smallest line with half or more right." But in the clinic, or in
a psychophysical experiment, the difference between one line and
another seldom alters anybody's career.

The AF and the FAA etc spell out qualification standards as
fairly as they can, and it isn't always what a purist would use.

-MT

== 6 of 6 ==

Date: Wed 31 Aug 2005 16:32
From: "Yasar, Mehmet C PFC A Co 602d ASB"

Mike Tyner wrote:


> Very logical.

> Spherical equivalent is the mean dioptric power, the
average of the two major meridians.

> For -0.75 +0.25 x 040,

the SE is -0.62.

When you convert, honor the signs.

> Your myopia would have to double before it threatens your
qualification. And the later myopia begins, the milder it tends
to be.

> -MT


Mike, Can you help me find where I am standing according to
Army regs? Let me quote the standard procedures for the Army
exam...

UPDATED ENTRY STANDARDS FOR CLASS 1/1A FLIGHT DUTY MEDICAL
EXAMINATIONS. (as of 28 March 2002):

Hyperopia greater than +3.00 diopters of sphere (in any
meridian by transposition in either eye) Myopia greater than -1.50
diopters of sphere (in any meridian by transposition in either
eye) Astigmatism greater than +/- 1.00 diopter of cylinder in
either eye.

Must meet above standards in both plus-cylinder and
minus-cylinder formats, so transpose to ensure patient meets
standards (spherical equivalent method does not apply).

For example, the cycloplegic refraction of:

-1.00 - 0.75 x 180 (in minus-cylinder format)

might appear qualified at first glance.

However, after transposition into plus-cylinder format of:

-1.75 + 0.75 x 090 (in plus-cylinder format)

it is apparent that this refraction is disqualifying because
the sphere amount exceeds -1.50.

Transposition Review:

1. Algebraically sum the sphere and cylinder powers

2. Change the sign of the cylinder power

3. Change the axis by 90 degrees.

Important Note for Eye Care Providers

A cycloplegic refraction is NOT necessarily equal to the
refraction you would give for spectacle lenses. If a patient is
"on the border" of being qualified or disqualified, it is best for
the Army and for the patient to use the "least amount of
prescription needed to see within standards" approach.

For example, if a patient has a cycloplegic refraction that
is +/- 0.25 diopters outside of standard but can still read to the
20/20-1 standard with the refraction amount that is WITHIN
standards, enter the lesser amount.

Do NOT, however, try to "push" the 20/20-1 on borderline
cases. These patients receive an entirely new cycloplegic exam
once they come to Fort Rucker to enter flight school.

If they are outside of the standard, they will be required to
request an exception-to-policy which will likely be disapproved.
Use your professional judgement but do not allow someone to come
to flight school knowing he/she has a good chance of failing their
detailed cycloplegic exam upon arrival.

So what is mine after this transposition? As far as I
understood, they are not doing the spherical eq. for flight duty
exams.