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.php?img=18-161234L&y=2005&m=04&t=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

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).

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?

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.

 

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

 

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

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

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

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.

 

My guess is that it is something other than edge diffraction, i.e.
possibly some type of prism effect from the tear film as a meniscus is
created along the edge of the eyelid. So, instead of diffraction, it
may be refraction, with some modification or contribution by
diffraction, small irregularities in the pupil, lens, etc....but,
mainly refraction.

DrG

 

possibly some type of prism effect from the tear film as

Sounds reasonable. This would be so easy to confirm... If there was a
program for this kind of purpose. I have experimented with a software called
Zemax, which is a optical designer software. I'm not sure if it is able to
render "end-result" images in a "normal" way. It is full of different types
of image analysis, but so far I wasn't that successful.

 

A tear meniscus is formed at the point where the eyelid comes into
contact with the ocular surface. It has a base and an apex, much like
an ophthalmic prism, which causes light to be deviated.

Expanding on this concept, one can also imagine the edge of the
ablation zone to behave similarly.

DrG

 

A tear meniscus is formed at the point where the eyelid comes into

I was thinking about this. I think your theory is right, it makes perfect
sense.

When the lower lid is lifted, there will be a long set of few starburst rays
upwards in the picture. (When the lower lid covers the pupil's bottom, there
will be a pyramid of no starburst down in the picture.)

Let's go further with the theory: In the eyelid experiment, why do I not see
just a solid part of halo like a filled V but discreet rays instead? It
makes sense that the arc length is not minimal but the rays open up a bit
instead, because the lower lid is not straight (the meniscus is curved). But
why can I see lets say three distinct rays, the meniscus surely doesn't have
three distinct planes in that case, does it??

 

Perhaps eyelid as well as the ablation has an irregular border.

Paul, why are you obsessing over this seemingly trivial point? If you
want to get rid of this problem, then get your ablation zone blasted
out to 8.0 millimeters, or get a post-refractive RGP contact lens.

DrG

 

Perhaps eyelid as well as the ablation has an irregular border.

And if this irregularity would be shaped to non-irregular, what would be the
visual result? No starburst rays, but uniform halo?

How do you define trivial point... I understand that the science of today
does not exactly know how visual problems are formed after LASIK. What is
the absolutely exact cause of starburst and what would be the exact action
to completely eliminate it? And how is it possible that some patients do not
get starburst even if their ablation and other specifications have been the
same as with the non-lucky patient?

I may go to a corrective surgery, but that will be earilest in the autumn.
And meanwhile, I want to make sure that the corrective procedure will be the
best possible in Europe or so. I already have ablation zone over 8mm, though
the perfect correction zone is only 6.0mm (pupils max 7.66, -5D/-5D before
surgery, MEL-80 used). But also I want to just understand as much as I can
about LASIK now that I have really started to study it.

Why I'm interested specifically about starburst is that I find it possibly
the greatest common problem of LASIK.

 

And how is it possible that some patients do not

Perhaps your premise is wrong.

DrG

 

Perhaps your premise is wrong.

Do you mean that if the doctor or the patient claims, that there is no
starburst after surgery or it is smaller than before surgery, they are not
telling the actual truth?

Or on the second thought, I think you mean that there will be no starburst
only if the specifications are optimal already before surgery (and naturally
no complications in the surgery)? We know that even with large pupils it is
possible to achieve vision with no starbursts, isn't that right? Or am I
wrong here - is it a certainty, that if pupil diameter exceeds the perfect
correction diameter, starburst will be present? If that is the case, there
is no way that time could possibly heal transition zone related starburst.

 

I think that you are bright enough to draw the correct conclusion
without me correcting the dots. The problem is "planned" vs "actual"
results with respect to ablation diameter and centration.

Have you requested a look at your post-operative topographies?
Certainly your surgeon took post-op topographies.

DrG

 

I think that you are bright enough to draw the correct conclusion

With all respect, I don't entirely follow or understand the facts here. If
you mean that my ablation diameter and centration have failed somehow, I'm
not sure if that is the case. I think my doctor would say that centration is
perfect in both eyes.

Of course both doctor and I knew that there is a risk of not achieving
blur-free vision. As far as I know it was a (high) risk only, it wasn't
certain that vision will be blurred and starbursted.

Post-op topographies I didn't get to take home for some reason (too bad),
but I did see them at the reception. To me they look quite far from perfect
but on the other hand they don't seem to relate to starburst so much (?).
Topographies were very different in each eye, but the starburst is somewhat
similar and even in both eyes. I should have the topographies home though
and examine more carefully.

I'm interested in my eyes particularly, but also in the whole field of
refractive surgery, how it could be improved.