Proper Fit and Evaluation of Gas Permeable Contact Lens

I'm Dr. David Meyer.

I'm the director
of contact lens services

at the Moran Eye Center,
and today's video is going to

focus on placing a
gas permeable contact lens

on a patient;

and we'll be looking at a proper fit
and an evaluation

of a gas permeable contact lens.

There are a number of reasons why
you would fit a gas permeable

contact lens, or a GP lens,
as opposed to a soft contact lens.

If a patient wants very sharp,
crisp vision,

GP lenses typically do a better job
than soft contact lenses.

Another reason you would fit a GP lens
is if the patient

has keratoconus or another form
or type of corneal ectasia,

or corneal irregularity,

GP lenses do a very good job
of neutralizing irregularities

on an abnormal eye, and they help
focus light

where it's supposed to go.

So for patients with corneal ectasias,
almost exclusively,

we use gas permeable contact lenses
to restore their vision

to be as sharp and clear as possible.

So for today's purposes,
for the patient,

I'm going to be fitting him
with a standard

gas permeable contact lens.

The one that we'll be using today

is the diameter is 9.4 millimeters.

That's a very standard size for
a gas permeable contact lens.

It's quite a bit smaller than
a soft contact lens,

so they tend to be a little bit easier
to put in and take out.

The biggest disadvantage
with these contact lenses

is adaptation.

Takes a while for a patient
to get used to it, it's a foreign body.

It's not quite as soft
as a soft contact lens,

but most patients, with a little bit of
time and with patience,

they end up doing just fine.

So for today, after I've taken
the keratometry,

I've done a full case history,

I've determined with with the patients

that a gas permeable contact lens
would be

the most ideal option for him,

and after I've cleaned the contact lens,

I've done a topography and found that

his average K-readings are about
45 diopters.

Now, in this case, for
a standard GP lens,

for a patient that has a normal cornea,

you typically pick a base curve

of a contact lens that's
slightly flatter

than the average Ks of the patient.

So in this case, I've got a contact lens

that's a 44.25 base curve for a patient

with a keratometry average
of 45 diopters.

So after cleaning the contact lens,

I'm going to actually have the patient
keep his head level

and look straight ahead,

and I'm going to pull down
on his lower eyelid

and kind of pull up on his upper eyelid

and set it directly on the front surface
of his cornea,

just like that, and have him
blink normally

and let it settle down a little bit.

It's very common to have some tearing,

especially with the GP lens when
you first place it on the cornea,

and so in some cases,
I will first put one drop

of proparacaine on the eye
before doing so.

In this case, we did this
with this patient.

It helps reduce tearing,
and it helps the patient adapt

to the contact lens at least
a little bit easier.

What's very, very important with
the gas permeable contact lens is,

after it's settled down,
to do an over-refraction.

Over-refraction is vital with GP lenses

because that's really the only way
to know

what power of contact lens to order.

In this patient's case, the contact lens

is lenses power is a negative 3.0

I can do an over-refraction

to determine what the ideal power

would be for this patient,
and with a base curve of 44.25.

To get a good baseline,
I'll often do retinoscopy

to get an idea of where to start.

So I'm going to show a large letter
across the room,

and I'm going to have the patient
look at

the large letter as I do retinoscopy.

In this case, the contact lens power
is a negative 3.0,

and in my over-refraction,
in the retinoscopy,

I can tell that you'll need a little bit

more power than that.

So for the over-refraction,
at this point,

I'm going to show them the 20/40 line,

and I'm going to take out some of my
working distance

and ask the patient:

Can you read any of those letters?

Yes.

Read them for me.

F, Z, B, D, E.

So my retinoscopy was pretty close,

because you can read the 20-40 line,

and so we know the power
of the contact lens

is going to be close to the negative 2.5
that I have

here in the phoroptor, and then you
refine it from there.

Ask the patient: What is more sharp
and clear?

Number one or number two?

Number one or number two?

Two.

Number one or number two.

One.

Number one or number two.

Two.

Now you keep going through this
until you refine it,

and as you can tell, initially,
I'll go in larger steps;

I'll go in .5, or sometimes even

.75 or 1 diopter steps

to get a really good idea
of the ballpark

of what his prescription is.

In this case, after refining
it a little more,

I found that in the phoroptor,

he likes -3 power spherical.

So that would mean that if we kept

the same base curve of the contact lens,

the final power would be a -6,

because it's the contact lens
that already has a -3,

and the phoroptor that's saying he wants

3 diopters more power;

3 minus 3 minus 3 is minus 6.

When it's time to assess a GP lens,

it's critically important
that you use fluorescein.

Fluorescein is really
the only way to see

how well the contact lens is moving,

how much it's vaulting over the cornea,

or if you have any problems
that you may run into,

like a small amount of edge lift or SPK

that's formed by the contact lens,

or any other issues like that.

In this case, I've got a small strip
of fluorescein,

and I've already wet it in some
sterile saline.

I'm going to have the patient look up
high toward the ceiling,

and just put a little dot of fluorescein

below his lower limbus
on his conjunctiva.

And then I have the patient blink
just for a few seconds,

let it spread around, and then I assess

the fluorescein pattern
of the contact lens.

And to do that, typically,
we'll use the slit lamp

with the cobalt filter.

So as I assess the contact lens,

you look for a number of things:

Is the contact lens centered?

At the center of the cornea,
is there touch on the cornea?

Or is there clearance?

And clearance means there's space

between the front of the cornea
and the back of the contact lens.

Now, an ideal fit of a contact lens

is to have an alignment fit,

and what that means is that
it just very, very lightly

touches that front surface of the cornea

in a very evenly distributed way.

You also have the patient blink
as you go through this

so you can see how much the lid pulls up

on the contact lens or moves it around.

Obviously, you don't want too much
movement

or else the contact lens will be very
uncomfortable,

but you want enough movement
so that enough tears

can spread on the front surface

and the back surface
of the contact lens.

Another very important aspect
is to look at

the edge of the contact lens.

The edge should have .1 to .2 millimeters

of fluorescein underneath the edge
of the contact lens.

If it's more than that, the patient

will probably be very uncomfortable,

and the lens would probably move
too much if there's not enough.

That usually means the contact lens
is too tight.

In this case, we have an alignment fit,

and that means that as you look
at the surface

of the contact lens and how it interacts
with the cornea,

there's very little fluorescein
that's built up

underneath the contact lens,
and that's an ideal fit.

In this case, if you see an area
of hard bearing,

what that means is there's no
fluorescein whatsoever

between the cornea and the contact lens,

and it may be pressing
too hard against the cornea,

which can eventually lead
to scarring or discomfort.

Now in this case, it's very important
to tell the patient

that when we order the contact lenses
to do a slow break in,

and what that means is,
when they first get it,

they don't want to wear it all day
the first day,

they want to slowly break into it;

meaning wear it one to two hours
the first day,

and slowly increase by a couple hours
every day after that.

Ater you've done the assessment

and you've done the over-refraction

and you've determined

what the vision is with
the contact lens,

it's time to remove the contact lens,

and there's a number of ways to do that.

The easiest way to do it as a
practitioner is the following:

Have the patient look straight ahead,

and I'm going to put my finger
on his upper eyelid to stabilize,

and also my finger on the lower eyelid
to stabilize,

and I'm going to be getting
his lower eyelid

to come up underneath the bottom
of the contact lens and pop out.

So look straight ahead.

So as you can see, I'm moving
the lower eyelid,

and I just pop it out just like that,

and it should come straight out.

Be sure to give the patient
extensive instructions

on the best way to take care
of the contact lens,

how to store it, how to wear it,

and it's very important to have
the patient come back

at a reasonable time to check
on how he's doing,

to make sure the vision's sharp,
that he's comfortable,

and the contact lens is working
as intended.

Again, this is Dr David Meyer.

This video is about fitting
a gas permeable contact lens,

and thank you for watching.