LASIK eye surgery, starburst

I have already asked a bit similar type of question before, but since I was
forwarded back here from elsewhere..

As many of you know, in an eye that has been treated with LASIK surgery,
there is a center area (about 6mm) that has perfect refractive correction.
Then there is a transition zone (about 2mm) which has a sliding correction
from perfect to the old (say -5 diopters). Now, if there's a bright light
(and the pupil is 8mm), what will be seen is a light with a starburst/halo
around it.

According to my tests and the picture I see (I have been lasered with
LASIK), I believe the starburst effect I see is completely caused by the
transition zone (I see also other halo layers, but they're not that bad and
we can dismiss them for now). When my pupil dialates, I can clearly see that
the starburst is enlarging from very small (5mm pupil) to quite big (7.7mm
pupil).

The starburst is identical on each lamp (I see many identical starbursts if
there are many lamps). I believe the starburst arm that points directly to
left is caused by the transition zone "slice" in my eye that points directly
to left. If I look at light from a laser pointer I can very accurately see
what's going on, the distortion is very accurate and moving head changes the
distortion.

What I still don't understand is how come I see starburst arms and not an
even halo. Does somebody have an answer for this or even speculation? I have
created a bunch of pictures that I can show and I can answer all your
questions if I forgot to give you some vital information.

Here is a rough approximation of how street lamps look to me (when they are
not close or big enough to change to halos, where individual arms are
duplicated to an even field) ->
http://www.glowfoto.com/viewimage.ph...=jpg&rand=7823

Let's say we have two video projectors with the same image pointing at the
same position on a wall and the other projector would have really bad focus
(somewhat similar to what the LASIK transition zone could be thought to
create). Then we would have just a good image and an evenly spreaded (bad
focus) image superimposed. What is the essential difference in a LASIK
treated eye that creates the starbursts?

PS. If there are any java (or similar) based simulations about eye and how
the image is forming depending on some variables, I would be really
interested to see them (I've seen only basic demonstrations with simple
two-ray representation).

Pauli Soininen wrote:
> I have already asked a bit similar type of question before, but since
I was
> forwarded back here from elsewhere..
>
> As many of you know, in an eye that has been treated with LASIK
surgery,
> there is a center area (about 6mm) that has perfect refractive
correction.
> Then there is a transition zone (about 2mm) which has a sliding
correction
> from perfect to the old (say -5 diopters). Now, if there's a bright
light
> (and the pupil is 8mm), what will be seen is a light with a
starburst/halo
> around it.
>
> According to my tests and the picture I see (I have been lasered with

> LASIK), I believe the starburst effect I see is completely caused by
the
> transition zone (I see also other halo layers, but they're not that
bad and
> we can dismiss them for now). When my pupil dialates, I can clearly
see that
> the starburst is enlarging from very small (5mm pupil) to quite big
(7.7mm
> pupil).
>
> The starburst is identical on each lamp (I see many identical
starbursts if
> there are many lamps). I believe the starburst arm that points
directly to
> left is caused by the transition zone "slice" in my eye that points
directly
> to left. If I look at light from a laser pointer I can very
accurately see
> what's going on, the distortion is very accurate and moving head
changes the
> distortion.
>
> What I still don't understand is how come I see starburst arms and
not an
> even halo. Does somebody have an answer for this or even speculation?
I have
> created a bunch of pictures that I can show and I can answer all your

> questions if I forgot to give you some vital information.
>
> Here is a rough approximation of how street lamps look to me (when
they are
> not close or big enough to change to halos, where individual arms are

> duplicated to an even field) ->
>
http://www.glowfoto.com/viewimage.ph...=jpg&rand=7823
>
> Let's say we have two video projectors with the same image pointing
at the
> same position on a wall and the other projector would have really bad
focus
> (somewhat similar to what the LASIK transition zone could be thought
to
> create). Then we would have just a good image and an evenly spreaded
(bad
> focus) image superimposed. What is the essential difference in a
LASIK
> treated eye that creates the starbursts?
>
> PS. If there are any java (or similar) based simulations about eye
and how
> the image is forming depending on some variables, I would be really
> interested to see them (I've seen only basic demonstrations with
simple
> two-ray representation).

Probably by examining what causes similar effects in nature would be
helpful. In astronomy, such "diffraction spikes" are caused by
something called the spider vanes which support the mirror in a
reflecting telescope. Perhaps in the eye they are caused by the
crystalline lens, or perhaps the natural irregularities of the edge of
the pupil. I agree with you that they are enhanced by the edge of the
ablation zone. I have seen many post-LASIK patients with starbursts.
They can be made to go away by correcting the outer surface of the
cornea with a contact lens.

DrG

> Probably by examining what causes similar effects in nature
> would be helpful.

If cameras, starbursts are formed in two main ways (as far as I know): first
one is when the aperture is a polygon, each corner will produce one or two
arms. I'm not sure, but I suspect this is an effect of diffraction. If
cornea causes the starburst (which would sound perfectly logical), it may
not be an effect of diffraction but just refraction (with some help from
irregularities). The other method on cameras is a "star-filter" with lots of
grooves. A bright point of light will spread along the grooves. This is also
not the case in an eye (although I guess a RK patient might have a situation
slightly similar to this).

> Perhaps in the eye they are caused by the crystalline lens,
> or perhaps the natural irregularities of the edge of the pupil.

Since the formation of the starburst is not even and there are shorter and
longer arms, it would seem to me that in my eye, some of the transition
zone's outer rim has less refractive error, which means shorter arm in that
angle. But the arm very near the shorter arm can be suddenly much longer,
which would indicate that also something else is very essentially
contributing to the effect.

If the arms would be solely caused by irregularities of the edge of the
pupil (which would be a nicely simple problem), then, it would seem that by
compensating (or somehow fixing) those irregularities, the arms would
completely go away. But that sounds impossible - where do the rays now go
that travel trough the transition zone?

That brings us to this question: If two patients have exactly the same
values before LASIK (same refractive error, pupil size, cornea thickness,
similar topography), how is it possible that the other one ends up with no
starbursts at all and the other one has huge starbursts?

> They can be made to go away by correcting the outer surface of the
> cornea with a contact lens.

How does this work? Does this lens make the outer surface relatively
thicker?

I have always compared the flare effects following LASIK to those
produced by a small rigid contact lens. In the early days of hard
lenses, this type of edge flare, or diffraction was common. A search
on this term turned up this excellent monograph on LASIK aberrations:

http://www.revoptom.com/archive/DEPTS/ro0200rs.htm

Enjoy.

DrG

> http://www.revoptom.com/archive/DEPTS/ro0200rs.htm

Thank you. After this I have again found new, essential information.

Let me comment on this article. It is reasonably recently written, though 5
years is "too much" already, I hope there are more recent articles about the
same issues with new, more accurate information. The first four visual
problems mentioned are blur, fog, flare (as a diffractive effect) and soft
focus. I'll make my own interpreatition.

a) blur

Simple spherical refractive error (too much + or -). No deviations.

b) fog (from scatter)

Caused by misaligned lamellar fibers in stroma (a result of microkeratome).
This makes sense. My own fog effect is not so bad or terribly visible, I
could live with it even if it wouldn't heal (and I believe it may well
heal).

c) flare (from diffraction)

There is mistake in the article. It should say "temporarily by contracting"
instead of "temporarily by enlarging".

There is talk about surgeries without a transition zone and so on
(outdated). There is no mention how the starburst arms are formed, that
information is missing. It does suggest though, that non-smoothness will
produce diffractive effects.

d) soft focus

In other words, a case where there is the good focus picture plus bad focus
picture superimposed. Which is probably what is the case on almost all LASIK
patients in some degree. It could be argued how much prolate/oblate will
affect and so on, but my logic would say, that if there is a transition zone
(or a zone with no correction) and the pupil size is somewhere near the
transition zone edge, a picture with bad focus will be present.

At the end, microstriae is mentioned. That makes sense as well. All in all,
I found misaligned lamellar fibers and microstriae particularly interesting.

About your speculation of the natural irregularities of the edge of
the pupil causing the starburst effect: I suspect that is not the case. If I
cover my eye with a card or look through "finger binoculars", I can simply
and clearly reduce the radius of the starburst where I cover the pupil. The
formation of the starburst doesn't change at all, only the radius. And when
the pupil is covered from the edges, I would believe rays of light are not
touching the edges of pupil. But the starburst formation stays intact. That
would indicate the starburst is created in cornea.

Pauli Soininen wrote:
> > http://www.revoptom.com/archive/DEPTS/ro0200rs.htm
>
> Thank you. After this I have again found new, essential information.
>
> Let me comment on this article. It is reasonably recently written,
though 5
> years is "too much" already, I hope there are more recent articles
about the
> same issues with new, more accurate information. The first four
visual
> problems mentioned are blur, fog, flare (as a diffractive effect) and
soft
> focus. I'll make my own interpreatition.
>
> a) blur
>
> Simple spherical refractive error (too much + or -). No deviations.
>
> b) fog (from scatter)
>
> Caused by misaligned lamellar fibers in stroma (a result of
microkeratome).
> This makes sense. My own fog effect is not so bad or terribly
visible, I
> could live with it even if it wouldn't heal (and I believe it may
well
> heal).
>
> c) flare (from diffraction)
>
> There is mistake in the article. It should say "temporarily by
contracting"
> instead of "temporarily by enlarging".
>
> There is talk about surgeries without a transition zone and so on
> (outdated). There is no mention how the starburst arms are formed,
that
> information is missing. It does suggest though, that non-smoothness
will
> produce diffractive effects.
>
> d) soft focus
>
> In other words, a case where there is the good focus picture plus bad
focus
> picture superimposed. Which is probably what is the case on almost
all LASIK
> patients in some degree. It could be argued how much prolate/oblate
will
> affect and so on, but my logic would say, that if there is a
transition zone
> (or a zone with no correction) and the pupil size is somewhere near
the
> transition zone edge, a picture with bad focus will be present.
>
> At the end, microstriae is mentioned. That makes sense as well. All
in all,
> I found misaligned lamellar fibers and microstriae particularly
interesting.
>
> About your speculation of the natural irregularities of the edge of
> the pupil causing the starburst effect: I suspect that is not the
case. If I
> cover my eye with a card or look through "finger binoculars", I can
simply
> and clearly reduce the radius of the starburst where I cover the
pupil. The
> formation of the starburst doesn't change at all, only the radius.
And when
> the pupil is covered from the edges, I would believe rays of light
are not
> touching the edges of pupil. But the starburst formation stays
intact. That
> would indicate the starburst is created in cornea.

If you really want an optical physicist's explanation of starbursting,
then I suggest you write to Ray Applegate c/o of the University of
Houston College of Optometry. The only reference sources I can find
refer to edge diffraction as well as artifacts in the pathway of the
light, including the crystalline lens. After the light passes through
the cornea, it has to pass through the lens. One thing is absolutely
clear to me, and that is the starbursting is an artifact of the LASIK
surgery. Another certainty is that a properly designed contact lens
will make it go away.

DrG

"Dr. Leukoma" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ups.com...

> If you really want an optical physicist's explanation of starbursting,
> then I suggest you write to Ray Applegate c/o of the University of
> Houston College of Optometry. The only reference sources I can find
> refer to edge diffraction as well as artifacts in the pathway of the
> light, including the crystalline lens. After the light passes through
> the cornea, it has to pass through the lens. One thing is absolutely
> clear to me, and that is the starbursting is an artifact of the LASIK
> surgery. Another certainty is that a properly designed contact lens
> will make it go away.

Probably not relevant but I wear Focus N & Ds and only get starbursts if I
squint.

> Probably not relevant but I wear Focus N & Ds and only get starbursts
> if I squint.

Squinting and starbursts. What causes starburst in that situation?

I was thinking it would be a diffractive effect caused by the eyelashes, but
I was not able to proove my theory with a laserpointer light and a
toothbrush. I just couldn't get long starburst arms as they occur when I
simply squint. One reason may be that the brushes in the toothbrush were too
thick (I did separate them a bit).

Anyone have ideas?

> I suggest you write to Ray Applegate c/o of the University of
> Houston College of Optometry.

Ok, I will. Thanks!

But what about this: Which is more powerful: aperture size effect itself and
transition zone unmasking in terms of the radius of starburst? Apparently
aperture size itself is a powerful factor to change the defocus radius, like
for example according to this:
http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=55

How is it possible that a person with large pupil and transition zone will
see no starburst (or halo)?

> I was not able to proove my theory with a laserpointer
> light and a toothbrush.

In my experiment I held the brush as near as my eye as I could, "simulating"
the eyelashes, but couldn't get long starburst arms at all.