Scleral Lens Troubleshooting: Mid-Day Fogging. Conversations with Maria Walker.
Hello again, welcome to another Contacts with Conway, I’m Martin Conway and today I’m
in conversation with Maria Walker. Maria is a clinical instructor at the University of
Houston in Texas, and today she shares her views on the possible causes of that perennial
problem with scleral lenses: mid-day fogging.
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Martin: Obviously the big issue for most practitioners, and patients alike, is going to be this curse
of mid-day fogging. Perhaps you’d give us your views and your expertise on that, Maria.
Maria: Yeah, sure, so, it’s probably the most common complaint apart from handling
issues. I think it’s definitely that 2-week follow up, patients are going to start to
experience the blur of mid-day fogging. So, there’s two ways that it can occur, and
sometimes it occurs kind of as both. But some people will put their lenses in in the morning
and within 10 minutes it just feels foggy. You’re just looking through almost a cloud,
some people will describe. But there’s a few different ways that people will describe
it. When they put it in and it gets cloudy immediately. And actually, you’ll have to
troubleshoot it a little bit at that point, because if it gets cloudy really quickly you
also have to wonder if the lens itself is wetting properly. But once you troubleshoot
it through all of that and then they finally come into the office and you can see the actual
debris that develops in the tear reservoir. And that’s what we’re referring to when
we say mid-day fogging, it is literally just debris accumulates in the fluid reservoir.
Martin: It’s not on the outer surface of the lens and it’s not on the cornea, its
actually debris underneath the lens.
Maria: Correct, it’s within the lens itself, and so patients will often maybe confuse it.
I’ve had patients come in and think they’re having mid-day fogging, but really it was
a lens wetting issue. There’s a lot of stuff online that says if your vision is blurry,
it’s mid-day fogging. So, it’s important for the practitioner to really ask important
history questions like “how long does it take to get foggy?” And then ultimately
the diagnosis has to be made by seeing the actual debris in the reservoir. Usually, even
if patients don’t – so the other thing of course is patients will just develop a
gradual fogginess after a few hours of wear, so, three or four hours of wear. Then again,
you also still have to rule out things like corneal edema, which is usually accompanied
by some redness and discomfort. So, you usually know. The question I ask patients is “if
you take the lens out, clean the lens, even just rinse the lens, not even a full clean,
refill it and put it back in, does it go away?” And most of them will say yes. If they say
no, then you need to start going down the other routes. The interesting thing too about
patient symptoms, is I’ve had a few, probably 10 patients, that have come in and said that
they feel like the fluid is coming out of the lens. So, they’ll say after several
hours of wear, the fluid leaks out of the lens, they can feel the fluid leaking out
of the lens, and then it gets blurry. And there’s nothing there. I look and every
time its mid-day fogging. Which I think is very interesting, because its such a specific
symptom. So, if the patients are experiencing this, I always used to just say you know we’ll
do something else. But then I really started educating them, because I want them to understand,
the fluid is not leaking out of the lens. If the fluid was leaking out of your lens,
you’d have a lot bigger problem! It’s still frustrating to them. They don’t really
care what it is, they just want us to fix it. And the other thing you can do, the classic
thing that we look at as a reason for the mid-day fog, is just too much clearance.
Martin: Too much?
Maria: Yeah, too much clearance. Too much fluid thickness, right. Normally we maybe
start off with about 300 microns of clearance over the central cornea but inevitably some
patients will have 500. And you still send them home with it, and they’re still ok,
but that’s really the one thing where you think “they might come back with mid-day
fogging”. And sometimes they don’t, sometimes they’re fine, and sometimes those patients
have more clearance than other patients. Then you have the other side of the coin where
patients will have only 200 microns at dispense and maybe it settles down to only 100 microns
over the apex and they still are getting a thick fog and it’s bothering them. Then
you have to tick down your troubleshooting list. And there’s things that patients should
do as well. So, it starts with ocular hygiene and it starts at the level of treating ocular
surface disease that the patient might have. Things like morning eyewashes, things like
using eye wipes, or even just some soft soap and water to really clean the eyelids and
lashes.
Martin: I know at the practice that I worked at that we started off finding our way with
it, and then Mark, who owns the practice, he does his best to treat any dryness, any
blepharitis, any scaling. He won’t even start the fitting until that’s finished.
To remove the other symptoms, the other problems, before we start the fit.
Maria: Yeah, I think that will really pay itself back because it’s not just mid-day
fogging that can cause complications such as that with blepharitis. Anybody who is starting
to wear a scleral lens, everything should be done to make the ocular surface and the
eyelids as healthy as possible right? And sometimes there’s only so much we can do
because they’re diseased eyes in the first place. But I always explain to patients 2
things: 1 is how clean and healthy your eyes are is going to make a difference in your
success with this, and then 2 how clean you keep the lenses is going to be a success factor.
It’s so important to have everything on the ocular surface as healthy and clean as
possible. But you’ll still get people who have mid-day fogging.
Martin: What’s your theory on where all this gunge is coming from then? I know I have
my own thoughts but what’s your theory?
Maria: Yes, well there’s lots of different theories that have been floated. Probably
the oldest one is mucin, but we kind of debunked that actually, so we looked, and it wasn’t
published, but there were 5 samples all with mid-day fogging, and none of them had any
detectable mucin. But what they did have, which was interesting, was lipid. We found
a lot of free cholesterol which is relatively – about 10% of the lipids in tears naturally.
I thought that was really interesting. I think what it ultimately is, is a combination. So,
it’s not the exact same thing in patient A as it is in patient B. I think that at its
core, it’s a lipid precipitant.
Martin: And that’s coming in from outside? It’s coming in under the edge of the lens?
Maria: Yeah so, I think - well, maybe. Either yes, or if you have conjunctiva that’s under
that landing zone – right, it doesn’t always land right on the conjunctiva, even
if there’s half a mm of tissue in that area. I believe that that’s the root. Because
you see, if you close down that limbus, if you close down the limbal curve over the cornea,
it really reduces the forces that pull and suck that debris under. I think it’s coming
from the conjunctiva, and I think its lipid based but that being said, it could be what
we refer to as a glycoprotein, which is a lipid attached to a protein. We’ve got lots
of those all over the entire surface of the conjunctiva and cornea. You have these glycol-lipids
that’s job it is to tether the tears against the surface. So, when they’re in this completely
different environment and they’re covered in saline solution, yeah, is it unreasonable
to think that they loosen up and precipitate into the tear film? I think yes, but lipids
are really hard to test for in the tear film which is why you don’t see studies that
look at it. It’s not the most simple process.
Martin: Could it be remedied by amending the fitting do you think?
Maria: Well, yeah, I think you can do several things to the fit to help. So, the first:
I kind of start from the centre and go to the outside of the lens. So, decreasing the
absolute apical clearance. Which honestly doesn’t always seem to necessarily do a
tonne by itself. But it thins out that debris layer, so you’re looking through less of
a fog. And then, the limbal zone – constantly you’ll see patients that have mid-day fogging
and they have this lens where the cornea is like this and it just gets this huge angle
of vault over. So, I think if you bring that down, so that you’re a little bit more on
the actual contour of the eye, which flattens out in that area, that definitely helps. And
then finally, on the lens landing – its kind of the Goldilocks theory – you don’t
want it to be super tight, we have shown that if it’s really tight, that’s going to
make it worse; and I think it sort of clogs up the inside and sucks it in. But if it’s
really loose, the lens will move around and certainly debris will come under. So sometimes
doing a toric lens can be helpful. Oftentimes you’ll see people switch to some sort of
toric lens to maybe make a tight fit just a little bit looser; or to make a loose fit
a little bit tighter.
Martin: Any practical tips for the practitioners? How they can assess the fit or anything they
can do in practice to check for peripheral fit?
Maria: Yeah, what I like to do is when the patient comes in, and if they have the mid-day
fogging that’s perfect because then you can assess that as well, so after several
hours of wear. You can just put fluorescein, and I paint it right onto the conjunctiva.
So have them look down, so that the fluorescein goes down and around and lets gravity bring
it all the way around the lens. And then look for 2 things: 1 look for absolutely no fluorescein
coming through, which means you got a really tight fit probably and that could be a problem.
Or if you’ve got a little channel where you’re seeing fluorescein come through,
watch for that, because that’s going to let you know if there’s tear exchange, if
there’s not, and I wish I had the perfect answer to what that should look like, but
unfortunately - actually fortunately for our patients – there’s a whole wide variety
of tear exchange profiles that people will do very well with. So, what I usually like
to see is no fluorescein rushing in, but then if I push on the lens just a little bit or
have the patient give a couple of forced blinks, then I see just a little bit start to trickle
in in some areas. Honestly, when I see that I usually am not seeing mid-day fogging. But
if I see mid-day fogging and I’m looking for the relationship and I know probably we
need to change that, or if it looks really really good, then maybe it doesn’t matter.
Some patients, even if they have the perfect fit, they’re still going to get the mid-day
fogging. I always encourage practitioners - yes you can look at X, Y & Z, but don’t
create a problem where it’s just going to create more of an issue.
Martin: Obviously Contamac is a materials company, so, any bearing on this with which
material you choose? Obviously, you mentioned wetting, does the Dk of the material have
any effect on this do you think?
Maria: No, not anecdotally. But in theory, I might say you could try a higher Dk lens
in these patients. I don’t think we’ve got to a point where people have really played
around with that, certainly not in an organised, clinical study. But if you were going to do
that study or you were going to look at that, I would hypothesise that a higher Dk may have
a lower incidence of mid-day fogging. Just because you don’t have hypoxia, you don’t
have the same cell processes that are going to happen when you have a slight hypoxic environment.
If it’s more hypoxic, you might get cells secreting more histamine, you might get cells
secreting more when you create a hypoxic situation or a stressful situation, cells will usually
dump out a bunch of stuff, and vasculature dilate.
Martin: And you mentioned wettability, any experience with the Hydra-PEG system? Hydra-PEG
surface treatment?
Maria; Yeah so I’ve used the hydra-PEG some, and we’ve done some studies with them. I
find the hydra-PEG either really works well or just doesn’t work so well. Which, honestly,
is ok because it’s a coating on the lens, right, so it doesn’t change any of the underlying
lens properties that I know. So, say you have patient A, who loves the coating, and I have
those patients, and they typically are women of a certain age, maybe over 40, who have
some aqueous deficiencies. Dry eye, I think that is really the hallmark group for that
coating. And I’ve seen young people do really well with its hydrophilic coating. Where it
hasn’t worked as well for me is if I have the opposite, maybe a bigger man, who’s
got tonnes of blepharitis and tonnes of eye surface disease, and then you just slap on
the hydra-PEG and think it will fix the problem. Well now you’ve got this lipophilic coating
and MGD all over, so you can actually get more deposition on the lens. But with those
patients, what I haven’t tried, which would be interesting is really cleaning up the ocular
surface, and then introduce hydra-PEG. But like I said, if for some reason you get it
in a patient, I’ve had one patient who even had an allergy to it, but that was one patient.
You’re always going to have some patients that doesn’t tolerate something. And we
just used a super cleaner and cleaned it off and it was fine.
Thank you for watching
Martin: We’ll take a break now from this conversation and re-join Maria at a later
date. Thank you for joining us, and if you’ve enjoyed this video, please remember to like,
share and subscribe. Thank you very much and look forward to seeing you next time.