Speciality Contact Lens Materials: Past, Present & Future
Hello there, welcome to another Contacts with Conway. My name is Martin Conway,
and in this video, we continue my earlier conversation with Dr Tom Arnold from
Sugar Land, in Texas. In the first part of the conversation, Tom described the use
of technology to allow the empirical fitting of scleral contact lenses.
In this, the second half of that conversation, he goes on to describe his wish list for
contact lens materials, the use of a revolutionary new hydra-PEG coating on
specialist lenses, and then we go on to discuss a new material, recently launched
onto the specialist lens market.
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Martin: And what about these new lenses now? These new generation of lenses.
What about the materials that you’re using currently?
Tom: Well, I think in the last couple of years, it’s been a very exciting time.
I think materials is a very, very important thing, as you well know, Contamac’s
been really great about introducing new materials that are stiffer.
You know, we want a stiff lens that can be cut thin, to allow oxygen.
We want high Dk lenses, stable materials, and there’s been great leaps
and advances in that area. And then of course we have the really good
coatings like Tangible Hydra-PEG, and I’m a big fan of that.
Martin: It coincided nicely with the arrival of interest in scleral lenses.
Tom: There’s a point, and this is interesting: a lot of people have dry eyes,
of course, a lot of keratoconus people are atopic, and we
fit scleral lenses for ocular surface disease, its an indication for it.
A couple of points about that: you put a
large diameter scleral lens on an eye, what does that do to the lid wiper?
What does that do to the blink of the eye? It certainly
pushes the eyelid forward, and the eyelid is coming down and
interacting not with the corneal surface but with the surface of that lens.
So, coatings are important but I think there’s a lot of work that has
been done and still to be done in the material science itself.
To make the material lubricious in itself, because, as good as Hydra-PEG is,
and I’m a huge fan and I’ve spoken for Tangible Science,
you well know that in patients with severe dry eye, severe atrophy –
I’m going to see a guy later this morning with ocular cicatricial pemphigoid and his eye is a disaster,
Steven Johnson’s syndrome – and so Hydra-PEG
doesn’t last all that long in patients that have poor tear film.
Now they’re coming out with Boost, which is a monthly replenishment – we’re
just waiting on that, that will help. But I think companies like
like Contamac still have work to do in the basic plastic science, chemical engineering.
Martin: Well as you know, we put a lot of effort into R&D,
the latest addition to the Optimum range has been the Infinite, which is different to what’s gone before.
Most of the materials, both from us and from competitors have all used
the basic silicone molecule called TRIS. This material uses a more
expensive monomer, it’s a styrene-TRIS monomer, which gives us more oxygen.
But it gives stiffness. With the conventional TRIS monomer,
if we just keep increasing, increasing silicone,
then what happens is the material starts to flex, and it’s the last thing you want to happen either
with an ortho-k lens or in particular with a scleral lens, where you’re actually
inducing astigmatism because of the flexure. Obviously, the stiffer we can make the material,
the thinner we can make it, again that’s going to be a boost to the oxygen coming through it.
Overriding all of this, is we have to maintain wettability, we have to make this material slippery for the lid
to flow over. And again, that’s the problem with conventional silicone,
is that by its nature its dry. We can see in silicone soft lenses and its no different in silicone GPs.
Tom: I was going to tell you an anecdote that’ll show my age: as an adolescent, I wore PMMA lenses,
and so did my wife. When I was in pre-optometry, doing my pre-optometry studies –
I was married at that time… still married – same wife!
– but we both wore these PMMA lenses, pre-optometry, and we found an optometrist in our college
in Boulder, Colorado. Gas permeables had just come out, and they were Polycon,
which I’m sure you remember. And we had PMMA lenses, which are like a piece of glass.
I remember my wife getting Polycon lenses, and they just flexed like this. Like a boomerang.
They were horrible. They flexed, they didn’t wet, but this was the good thing:
so, materials have come a long way since Polycon.
Martin: Yeah, in one of the lectures that I give to students, I mention Polycon –
I think it was Syntex that was the original lab that launched it.
Tom: Sounds right. Yeah that sounds right.
Martin: It think it had a Dk of about 8! Which was fantastic in those days.
But it achieved success, and people saw that the secret to success was more oxygen.
Then we ended up with this almost arms race amongst the manufacturers,
and unfortunately practitioners were carried along with this wave of enthusiasm –
they focus so much on Dk, to the exception of everything else.
I think now we’ve got enough oxygen; I think that with the likes of Infinite,
we don’t get that many problems now with oxygen at those levels.
Tom: I agree.
Martin: Now practitioners are realising that there are other attributes to materials that we need to focus on:
the wettability, the rigidity, and as you mentioned, this lubricity –
which is the new word that we’re all using. Not that we can measure it or tell you what it is!
Tom: Yeah, I really don’t care for it actually!
Martin: But we all know exactly what we want! So those are things that we’re working on steadily.
But these things take time. So we’ve just recently put Infinite out there,
and we’re getting good feedback from that. Based upon that, that’ll decide where we go next.
Have you had any experience with the Infinite material, have you tried it?
Tom: Oh, I have, yeah, I was going to tell you: I’m a big fan. Yes, I’ve used it a number of times…
It’s pretty much, I want to say in most cases it’s the lens of choice.
It’s certainly the material of choice when I fit a post-RK, you know when we’re worried about neovascularisation,
and the grafts, the PK’s, PKP’s. When oxygen is the premium.
And I find, as you said, the material is fine, it’s not less wettable, because of a higher Dk.
It’s not more flexible, it’s a great material.
Martin: It is, yeah.
Tom: There’s no reason not to use it in my opinion.
Thank you for watching
Martin: Thank you for watching this conversation with Dr Tom Arnold.
I hope you’ve enjoyed it, if you have, please remember to like, share and subscribe,
and I’ll see you next time. Thank you very much.