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Report
from the International Congress of Ophthalmology in Sydney
Broadcast Monday 29 April 2002
with Norman Swan
Summary:
One of the speakers at this Congress
was Dr. Adrian Glasser who's trying to find ways round needing
reading glasses or bifocals as one ages. Another presentation at last
week's international eye congress was by Dr Christine Younan who
gave the results of an Australian study which suggested that the more
short-sighted you are, the greater your risk of developing cataract.
Transcript:
Last week eye specialists and researchers from around the world gathered in
Australia for the International Congress of Ophthalmology.
One of the speakers was Dr Adrian Glasser from the University of Houston in
Texas. He’s trying to find ways round needing reading glasses or bifocals
as you age. It’s called presbyopia.
Now you and I are too young to know what this is all about but they do tell
me that presbyopia and the problems it causes with something called
accommodation will happen to us one day.
Adrian Glasser.
Adrian Glasser: Accommodation is the ability that the young eye has
to change its focus. So for example if one is looking at the horizon and
then one wants to read print on a newspaper –
Norman Swan: What does it do?
Adrian Glasser: The crystalline lens inside of the eye actually
undergoes an increase in optical power to allow the eye to focus an image
on the retina. In optics we talk about refracting light, and that’s
important because it’s bending light so that it comes to focus on the
retina, just as one would use a magnifying glass, for example. The
important element as far as accommodation is concerned, is the lens inside
the eye which is behind the cornea. The lens is important in accommodation
because it has the capability of undergoing a change in shape. In fact it’s
an increase in its surface curvatures.
Norman Swan: It becomes in a sense a thicker lens by dint of muscles
around it squeezing it, or pulling and pushing it when you want to read a
book compared to looking in the far distance?
Adrian Glasser: Right. In fact what happens when the ciliary
muscles, which are the little muscles inside of the eye, they contract when
we try and read something at near, and the lens is then allowed to become a
little more spherical inside of the eye.
Norman Swan: And presbyopia which is really basically a difficulty
with reading as you get older, is what?
Adrian Glasser: Perhaps the most important change that occurs with
ageing is that the lens inside of the eye becomes hardened, and it loses
the ability to undergo accommodative optical changes.
Norman Swan: From what you’ve just said, you think well if it
becomes harder, you could just stick in an artificial lens like you do
after a cataract operation.
Adrian Glasser: Well typically cataract surgery requires putting
what’s considered a fixed focal length lens into the eye. In other words, it’s
a lens that’s not designed to accommodate, so it’s a rigid, hard optic, and
if accommodation is to occur, the same kind of surgical procedure could
conceivably be used. The difference is that a different kind of lens must
be put into the eye.
Norman Swan: So what have you been doing in this area?
Adrian Glasser: We have been studying a number of different kinds of
lenses. For example, if a lens is placed in the eye that allows the optic
to be translated, in other words moved closer to the cornea, that
potentially could produce an optical advantage. Another possibility is to
put a soft injectable polymer back into the capsular bag which is the
little elastic membrane that surrounds the lens, to actually create a soft,
malleable and optically clear accommodative interocular lens. In fact it’s
very similar to a standard cataract surgical procedure. What happens in
cataract is that the cataractous lens substance is removed by ultrasound
and aspiration, just by literally sucking it out of the eye, and in that
case you’re left with an empty capsular bag, this is that elastic membrane.
And typically in cataract surgery an interocular lens is then placed back
into that capsular bag. So all we’re suggesting is that instead of placing
a typical kind of interocular lens into the bag, you inject this polymer
back into the bag, and you end up with a soft, accommodative lens.
Norman Swan: How far have you got with that?
Adrian Glasser: Some of the things that we’re doing is to develop in
vitro, and when I say ‘in vitro’ I mean devices that can be used outside of
the eye, just with tissues for example, human eye bank eyes or animal eyes
for example, where we can do the surgical procedure on those eyes and then
we can do mechanical stretching tests and optical measurements to
understand if those polymer refilled lenses undergo the same kinds of
accommodative changes as the young natural crystalline lens should.
Norman Swan: And is it looking promising?
Adrian Glasser: They’re looking very promising. Certainly there are
many challenges. The surgical technique is a complicated one but the kinds
of optical changes that we’re seeing occur in these artificial lenses seem
to be very closely matching the accommodative performance of young
crystalline lenses.
Norman Swan: So it’s not ready to go to human trials yet?
Adrian Glasser: No, we’ve been doing some testing in animals.
Norman Swan: I don’t know many animals that can read, how are you
going to know that it works?
Adrian Glasser: Well in fact it turns out that monkeys for example
can be trained to perform tasks such as play video games, and one can
assess their visual capabilities by how well they perform those games for
example.
Norman Swan: Now I understand that some entrepreneurs in the United
States are touting an operation called scleral expansion for presbyopia;
what is this, and does it work?
Adrian Glasser: This is a procedure that is based on revisionist
ideas of how accommodation occurs and revisionist ideas about presbyopia.
Norman Swan: It sounds like Stalin in the ‘20s.
Adrian Glasser: Indeed. It’s absolutely remarkable to me that these
kind of procedures can be done based on so little supporting evidence for
them.
Norman Swan: So what’s the theory and what do they do?
Adrian Glasser: The theory is that presbyopia occurs because the
lens becomes too large, not too hard but too large. So expanding the sclera
of the eye –
Norman Swan: The sclera’s the white bit round the eye.
Adrian Glasser: That’s right, so expanding the sclera around the
lens is thought to be able to restore the accommodative ability and so the
surgical procedure is basically to insert these little plastic grain of
rice sized elements into the sclera.
Norman Swan: Is there any biological plausibility to this at all?
Adrian Glasser: No, I don’t believe there is, and the appropriate
testing that has been done post operatively really does not show that
accommodation is restored.
Norman Swan: And are there risks in this operation?
Adrian Glasser: Certainly placing these little plastic segments into
the sclera can in some instances block off blood flow, and that can have
detrimental effects on various parts of the eye that are no longer
receiving blood.
Norman Swan: Dr Adrian Glasser is in the College of Optometry at the
University of Houston, Texas.
Another presentation at last week’s international eye congress gave the
results of an Australian study suggesting that the more short-sighted you
are, the greater your risk of developing a cataract.
Here’s ophthalmic researcher Dr Christine Younan, who’s at the Centre for
Vision Research at the University of Sydney, Westmead. Christine has used
information from the Blue Mountains Eye Study to draw her conclusions.
Christine Younan: The Blue Mountains Eye Study is a study of common
eye diseases in an older Australian population. We’ve looked at
participants who live in two postal code areas of the Blue Mountains, which
is west of Sydney. We initially looked at about 3-1/2-thousand people
between 1992 and ’94, and then looked at those same people again about five
years later for the incidence of a number of common eye diseases, and it
included quite a comprehensive history as well as an examination of their
eyes.
Norman Swan: Now this particular part of the study you’ve been
looking at is the association between short-sightedness and cataract; well
just tell me what you found.
Christine Younan: Simply we found an association between a
particular cataract type, it’s called posterior sub capsular cataract,
which is an opacity at the very back of the lens.
Norman Swan: So just put this cataract into perspective for me? How
important is it?
Christine Younan: Posterior sub capsular cataract although it’s not
necessarily the most common type of cataract in itself, it’s the most
common type that’s associated with cataract surgery, and that’s because it
occurs in the very centre of the visual access, so it causes significant
visual symptoms very early on, and can progress to surgery very quickly,
and it has been shown in studies that this cataract type is most commonly
associated with surgery. And so we found an association between this
opacity at the back of the lens and short-sightedness, or myopia. We also
found an association between the incidence of cataract surgery, so people
who’ve had an operation for cataract and short-sightedness.
Norman Swan: How close is this association?
Christine Younan: We looked at different levels of myopia. People
who had any myopia which we defined as greater than one dioptre were at
about two times the risk of people who were ametropic or had no refractive
error.
Norman Swan: And was it dose related the worse your myopia, the more
likely?
Christine Younan: Yes, it was, and we again looked at people who
were more than 3-1/2 dioptres myopic, and their risk was over four times
compared to ametropic eyes.
Norman Swan: So that’s getting close to starting to believe there’s
a cause and effect relationship rather than just a chance association. What
other evidence is there that this might actually be a cause of cataract?
Christine Younan: The fact that our evidence is longitudinal in that
it’s shown over time is itself strong evidence. The Beaver Dam Eye Study
which is a similar study of common eye diseases in the United States has
also confirmed the relationship with cataract surgery, not with posterior
sub capsular cataract.
Norman Swan: And there are other eye studies in Australia, are any
of them showing the same thing?
Christine Younan: The Visual Impairment Project from Melbourne has
shown an association between myopia and cataract and the Melton Mowbray
Study in the United Kingdom has also shown an association between any
cataract. They didn’t look at different types, and myopia.
Norman Swan: So what’s going on here?
Christine Younan: There are a number of things that have been postulated,
but nothing is certain. It may be that the myopic eye being a little bit
longer has a relative impairment of the blood supply and therefore the
micro nutrient supply to the tissues at the front of the eye which
ultimately supply the lens.
Norman Swan: This that the short-sighted eye is a bit longer than
the normal eye?
Christine Younan: Yes, and it may be that little extra bit of
stretch causes that relative sort of impairment and also something that’s a
little bit more complicated relating to lipid peroxidation.
Norman Swan: This is part of the antioxidants, the free radical
process of damaging the eye?
Christine Younan: When there’s an imbalance between the free
radicals and the antioxidants which the body produces to neutralise these
free radicals, you can get damage to cell membranes, and it just happens to
be that the rod photo receptors, which are the cells at the back of the eye
that actually see the light and transform it into an electrical impulse
that goes to the brain, they have a very high concentration of
polyunsaturated fatty acids, these particular lipids that are very
susceptible to this sort of peroxidated damage. And it has been shown that
people with myopia have increased rates of lipid peroxidation, and these
products can be released into the vitreous, which is that gel-like
substance that fills about 80% of the eye.
Norman Swan: And then affect the back of the lens.
Christine Younan: Yes, this vitreous sits right in front of the
retina, and if these substances are released into the vitreous as they move
forward, what they’ve hit next is the very back of the lens, and that’s
where posterio sub capsular cataract occurs, at the back of the lens.
Norman Swan: Now isn’t that the same mechanism that some people
believe that macular degeneration works by?
Christine Younan: Yes.
Norman Swan: So is macular degeneration, that form of blindness as
one ages, where the macular, that part of the eye that is so exquisitely
sensitive to light, gets damaged, is that related to short-sightedness too?
Christine Younan: Myopia is related to a different sort of retinal
degeneration. Retinal degeneration is more common in myopic eyes but it’s
not exactly related to macular degeneration.
Norman Swan: Now if I remember my medical school days correctly, the
posterior sub capsular cataracts are also associated with being on
steroids, things like diabetes and so on, could that be the problem here,
not that it’s just an accidental finding about short sightedness?
Christine Younan: We’ve used statistical models in all our analyses
so that when we get to the end and we get our results, we’re more confident
that it’s not due to these confounding variables, but is a real association
between myopia and posterior sub capsular cataract.
Norman Swan: Does it have any meaning yet for an individual who’s
short sighted, which is a very large portion of the population?
Christine Younan: Yes, it’s part of quite a big picture for people
with short sightedness. People who are myopic tend to have high rates of
glaucoma, they tend to be more likely to develop this particular myopic
retinal degeneration, get retinal detachments as well, and it’s just one
more thing that they need to think about, so that as people with myopia are
ageing and they notice their vision start to deteriorate, there may well be
things that can be done about it.
Norman Swan: Dr Christine Younan works at the Centre for Vision
Research at the University of Sydney, Westmead.
Don’t forget Health Dimensions tonight at half past six on ABC Television,
where I speak to a man who cannot recognises faces.
Guests:
Dr Adrian Glasser
Assistant Professor,
College of Optometry,
University of Houston,
4901 Calhoun Road,
Houston, TX 77004,
U.S.A.
email: aglasser@popmail.opt.uh.edu
Dr Christine Younan
Centre for Vision Research,
University of Sydney,
Westmead NSW
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