Dear Don,

Subject: Ghosting -- differnt that Astigmatism

Re: Fincham -- 43 percent of eye's with excellent have
"ghosting".

I do not think there has been any effort to define a
difference between these to "artifacts".

My interest is in effective "prevention". The "ghosting"
issue came up because "Chet Thor" began to see it as he worked
towards very-sharp 20/20. When some one monitors his distant
vision as Chet did -- he might see this ghosting as described by
Fincham.

PERSONAL REACTIONS

Chect "accepted" that this ghosting (very slight) was part of
the optics of the natural eye. This ghosting never "prevents"
20/20. He continued to work with the plus -- and passed the JAA
test for pilot's vision.

John M. worked on vision-clearing with the plus -- and saw
the "ghosting". As a result he got very angry with me. Currently
he wants RPG, or Lasik done on his eyes to get that "perfect" zero
refractive status. (I am certain he does no understand how risky
Lasik is for him. Far worse that any ghosting he might see.) But
this poses another issue. If I were "medical" he could have sued
me! If an OD supported this work, John M. whould have suded the
OD. This is a tremendous dis-insentive to do any "preventive"
work.

In my judgment the ghosting was always there. For example,
let us say that a person has 20/40 vision.

The slight blur of 20/40 vision will effectively "hide" the
ghosting. As the person eye-chart begins to clear, towards 20/20
and 20/15, he begins to see the ghosting -- due to the success of
his work. Having never seen this before, he then believes TOTALLY
that the plus-clearing CAUSED the slight-ghosting.

DISCUSSION

In engineering we study "risk-benifit" relation ships.

Since ghosting is a possibility, the person (at 20/40) should
understand that fact -- BEFORE he starts clearing his vision.

If he judges that the "ghosting" is too great a risk, then he
should not attempt "clearing" with the plus.

If he understands this issue, then as he clears towards 20/20
-- he MIGHT see this ghosting.

Some more discussion:

At West Point, (from 201 files) the natural eye moves "down"
by about -1.3 diopters in four years. (Spread -1.1 D to -1.6
diopters).

If a person is at 20/40 entering a four year college, his
will pick up an additional -1.3 diopters -- average. He must
"trade off" the possibility of "ghosting" versus developing 20/100
to 20/140 vision while in college.

It is a decision and choice the person concerned with this
issue must make.

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

Dear Otis.

Don> the other day I looked up into the sky and saw a thin sliver
of the moon. Actually, I saw two slivers side by side. Saw
this with each eye separately.

Don> This is caused by astigmatism.

Don> Is this ghosting?

Otis> As defined above -- it is.

Don> Are people using the plus creating a little astigmatism they
never had before?

Otis> I don't know the answer to this question yet -- since there
have been so few who have done it. In a "formal" study you
could eventually estabish a relationship -- if any.

Don> If so, is this caused by upsetting the
accommodation/convergence relationship?

Otis> In going from 20/40 to 20/20, the natural eye's refractive
status has changed by about 0.6 diopters. The power of the
human eye is about 60 diopters, so the change is refractive
properties is about 1 percent. It is possible that small
changes in the properties of the eye MIGHT create slight
ghosting in this "change" process. I doubt that the issue
can be "accommodation/convergence" for that reason. What is
required is more consistent work and evaluation.

Best,

Otis

Don