 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 lactasia 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. And so for patients with corneal lactages, 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. It takes a while for the 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 patients, 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 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 case of the patient. And 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. And 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 perperacane 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. At this point, 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's 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 the 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. And in this case, the contact lens's 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 2040 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. Good. So my retinoscopy was pretty close because you can read the 2040 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 fropter. 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. 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 one 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 fropter, he likes negative 3 power spherical and so that would mean that if we kept the same base curve of the contact lens, the final power would be a negative 6 because it's the contact lens that already has a negative 3 and the fropter 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. 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. To do that, typically we'll use the slit lamp with the cobalt filter. 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? 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 comfortable, 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 a 0.1 to 0.2 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. After you've done the assessment and you've done the over a fraction 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 of the bottom of the contact lens and pop it 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 and 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 sharp that he's comfortable and the contact lenses working as intended. Again, this is Dr. David Meyer. This video is about fitting a gas permeable contact lens and thank you for watching.