Scleral Lenses, Fogging and Limbal Clearance. Conversations with Pat Caroline.
Hello there, my name is Martin Conway welcome to contacts with Conway with a
difference. During the lockdown period I've obviously not had access to
patients and my normal consulting room equipment so in this series I'll be in
conversation with leading figures from the contact lens world, around the world.
The first of which is my old friend Pat Caroline from Pacific University in
Oregon and he's been involved in the research of eye shape and contact lens
design for as long as I can remember. You join the conversation with Pat as
I've asked him the question how long has he actually been involved and with
scleral lenses. If you would prefer to watch this video with English or Spanish
subtitles please go to the cog in the bottom right hand corner of the screen
and press to select your preferred options.
When did you start working with scleral lenses?
Well, you know, our work began
in about 2009 and really compared to the rest of the world
we were very very late. Individuals like Don Ezekiel and Perry Rosenthall had
been using early versions of scleral lenses for actually many years. Actually,
started out back in the early days of the Boston 2 - material which actually
became the first material for a scleral lens with all its you know Dk
limitations and everything.
Yeah I mean when we first started working together
they were basically spherical lenses with spherical peripheries, and we
were concerned if I remember about oxygen - whether we were getting enough
oxygen through the material and through the subsequent tear layer.
And we did a series of experiments with you at Pacific - remember those?
Where we fitted patients, I can’t recall exactly how many, but we
fitted patients with identical lenses but we did them in a range of
different Dk materials, and if I remember it clearly demonstrated that the higher
the Dk, the less swelling we got underneath the scleral lenses. Which pointed
us as Contamac in the direction that we wanted to go, which is you know develop a
higher Dk material and with scleral lenses in mind, specifically. Initially
I think we were concerned that this was going to be a flash in the pan. That we
were going to do a lot of developmental work a lot of cost involved and it was
going to remain a very specialized small market. You know, how wrong could we have
been at that point. It's simply exploded after that. Yeah. One of the
earlier issues that we encountered and we asked you to investigate was
fogging. Mm-hmm. And maybe you'd like to sort of bring us up to date on where we are
with that now. Well it's still very much an intriguing topic you know we our
incidence of fogging when we first came out with the initial scleral lenses was
very high - it was probably in the area of around 30 to 35 per cent of our
patients. Those are the figures that I remember. Yeah and we
switched over to using the toric haptic and creating a more sealed
lens
our early work with OCT imaging and scleral shape showed us clearly that
there's about a hundred and fifty micron differential in scleral height between
the two principal meridians of the sclera. And therefore when we went to
the 150 micron differential in the haptic shape
we noticed rather quickly that our incidence of fogging went down rather
significantly. Still today, it's a problem probably in about ten percent of
individuals. So it really is a question of making a better seal around the
the peripheral. Anecdotally, that seems to be the case, that there's some type of
contaminant coming in from the sclera from the bulbar conjunctiva
that seems to be contaminating the tear film. Now we did a lot of studies a
number of years ago on that and found that it wasn't a protein underneath
there but actually a lipid. When we stained these fogged lenses with oil red O
a lipid specific stain, it really did demonstrate that compared to normal
patients with no fogging, those with fogging had significant amounts of
increase in lipid contamination underneath the lenses. When we started
narrowing down that limbal clearance, we definitely noticed a significant
decrease in the lipid. So that kind of told us that the contaminant is probably
entering in from the bulbar conjunctiva. The outside rather than the inside.
I think if I remember back, the the concept of fitting either close to or
even on even a mild touch on the peripheral cornea was just not
acceptable in the marketplace and so although I think that kind of
fitting is still being used in and around Europe, for the US market and the markets that have developed subsequently...
It's always hard when we are constantly hearing the fact that we need limbal
clearance, we need limbal clearance. And I gotta admit that's an area we've
really not studied. It's become sort of anecdotal in our industry and our
industry is noted for that. That its just repeating what other individuals have
said from the podium without any real substantial research into what is the
optimum amount of clearance in the peripheral cornea and limbus.
Some discussion later...
But I think inadvertently, we were sealing the cornea, the tear layer, from the external
contaminants without realizing what were doing. So we achieved the
result, but not by design it was really just by chance. What you're now
doing by designing the periphery around the actual scleral shape, you're
achieving much the same.
Well most of what we do in clinic is by chance.
There is no doubt that we've had to relearn scleral lenses since a few of us
were actually trained with PMMA scleral lenses, we really did have to learn a lot
of this from scratch. And I think today though now the peripheral designs
on these lenses, the haptic designs and so on are really pretty darn good.
We've been very impressed with how the industry has responded.
I think I've said it before but I've never ever known
a lens modality which has undergone so much intense research and development.
If you look at where we are now versus where we were in 2010 to 2012
it's miles miles better. I've never seen that rapid a development
partly fueled by the success in the marketplace and competition and
particularly in the US market but also I think advances in instrumentation have
led that research and led our understanding of the shape that we're
actually fitting the lenses to. Pacific have led the research,
known for research into metrology and you must get to play with every new
gadget that comes out what can you tell us about that what's in
the pipeline now that you've got access to that the rest of us they could only
wish for?
Well you know, we're still playing around a lot with scleral shape.
We have the Eaglet system and the SMap 3D which are profilometry based
systems for measuring scleral shape. We also have OCT imaging and those do
need to be added to that list because a lot of the work we did early on was
with OCT imaging which is more of a direct physical measurement of the shape
of the sclera. Although all three instruments seem to be providing some
really good information about scleral shape and about the fact that
there's a tremendous variety in scleral shapes in the marketplace
even in normal eyes. So we've got a lot to learn yet in that area.
Thank you for watching
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