so the first lens we have here is a diopter flatter than K remember our C ratings are 42x 44 at 90 got a 41 diopter lens on the eye and when we click on this video you can see that the center of the lens uh is coming in contact with the center of the cornea and what happens is that the lens displaces laterally so one time it goes temporally sometimes it goes nasally but after the patient blanks and gravity pulls the lens away from the upper lid the lens will displace to one side or the other this is obviously not an ideal fitting relationship now when we look at a lens that is uh a 42 diaper base curve which is exactly on flat k in this particular instance you can see our simulated florene pattern shows 20 microns of clearance and when we fire up this video you can see that that when the patient blinks the lid pulls the lens up gravity pulls the lens down away from the lid because the lens is coming in contact at 3 and 9:00 it keeps the lens centered along the horizontal axis um and you can see how nicely that lens centers you know after each blank so this is what we would consider a nearly ideal fit um and you can see those touch points at 3 and 9:00 out where the optical Zone comes to an end and the peripheral curve system begins but really an ideal fitting relationship uh in this particular case which happened to be on flat k now the other the secondary the second GP fitting Factor we need to look at is that there should be a mid peripheral contact point along the horizontal Meridian and this just very simply means that you know we're again we're clearing the center of the cornea as The Lens comes down on the eye the contact point should be at 9:00 and 3:00 um and that'll keep the lens from moving laterally along the horizontal axis and with our 18 microns of clearance remember the ideal number being between 10 and 20 you can see those contact points where the Florine thins out the Lens comes in contact with the eye here at 9:00 and over here at 3 3:00 this would be considered an ideal fluorine pattern and in this case we would expect uh you know for a very well centered contact lens now what makes this a little bit tricky is that the contact points in the periphery uh depending on the eccentricity of the eye uh can vary rather dramatically so most of us have been taught to fit rigid lenses using Central keratometric readings and this just shows you maybe one of the built-in flaws of of using a keratometer to fit rigid lenses not that it can't be done but why it may be a little challenging on some patients more than others let's look at three patients with different eccentricity values well patient one here has an eccentricity value of 020 so the corne is um you know much steeper in the in the mid periphery the second patient has a value of 0 40 um kind of a more normal eccentricity value and then finally one with a 6 value when we put a 4 E2 diopter lens on each of these three patients it'll fit ideally on one of them and in this case the 0 40 but in the other two eccentricity values we're going to have a lens that's either too flat or too steep so ideally if we could measure the cornea in the periphery where the Lens comes in contact with the eye instead of in the center where we want it to actually clear the central cornea we may have some more valuable information and what we found with like the 95 CAD design if we go out 1 2 3 millim temporally and determine this point on our topographer on the axial map we have a very good starting point for what the base curve should be for uh our 95 diameter lens and it's just a very simple way for those of you that have topography to kind of get a good starting point um in in your diagnostic fitting again it certainly can be done using the flat K on Central keratometry just a little bit more accurate when you have you know peripheral topography to work with now the final uh GP fitting factor that I want you to consider is that the lens should maintain unobstructed movement along the vertical Meridian and it's what we call unobstructed uh vertical movement basically and it just means that the lens is not impinging along the along the vertical axis of the eye so as the patient blinks we want the lens to Pi be picked up by the lid move freely in the along that vertical position to keep from it you know rubbing against the cornea and causing discomfort when we do see a patient wearing a contact lens that has restricted movement along the vertical axis we find that they're usually uncomfortable around 4 hours of wearing time so the the the cornea can only maintain uh comfortable wear for about four hours when there's impingement somewhere along that axis and it's simply because the patient's blinking so many times during the day that lens just cannot take the drag just the mechanical rub of the lens against the cornea so we really want freedom of movement from a from a topography standpoint when we're designing these lenses using a topographer we're looking for about 40 microns of clearance here in this position right here where the lens you know is up off the eye about 40 microns so we're going to expect to see a little brighter florene pattern at 6:00 and 12:00 then certainly we would at 3:00 and 9 clock or even in the center of the lens so you know it's it's a very simple system where we're looking for the lens to clear the center of the cornea have bearing points at 3 and 9:00 and clear the cornea freely at 6 and 12:00 now the ideal person for doing this on is is the patient with with the rule of stigmatism patients uh uh with the stigmatism fortunately for us most of them have with the rule of stigmatism are really ideal fits with the rigid gas per perable lenses um you can see what this map allows us to you know really preview is that the lens is going to come in contact with the cornea where the cornea is the flattest in the mid periphery it's going to be loosest or come off the eye the most where the cornea is the steepest and this patient with with the rule of stigmatism we've got touch points at 9:00 and 3:00 clearance points at 12:00 and 6:00 and looking at this we would expect a successful fit with a spherical rigid gas permeable lens we have that unobstructed vertical Movement we have um we we're clearing the central cornea and we've got touch points at 3 and 9:00 and we would just expect this to be a very successful outcome let's look at an example of a patient with K readings of approximately 4175 by 4375 so we've got about two diaps of with the rule of stigmatism we've got a flat k of approximately 41 175 and you can see just looking at the map because we're flat out here in the mid periphery at both 9:00 and 3:00 we expect our touch points there we expect unobstructed movement along that vertical axis and we can start our design now again if you don't have a topographer you're going to be using diagnostic lenses to do this but if we put a 4175 on this particular patient because of the eccentricity of the eye you can see that the center of the lens is touching it's very flat flat so we can we can visualize this on the topographer and say we probably need to go steeper than 4175 if we do put a 4175 on there's likelihood that it's going to touch in the center and let's go through the process of taking a look at that so we've got our 4175 lens on the eye see if we can start up the video when the patient blinks The Lens comes up with the lid as it should but as the lens is gravity induced down we can see that it tends to move laterally left and right so in this particular case we've got a lens that's too flat and typical of a flat lens the lens is Riding High now when we go with the lens that's a half a diopter steeper than K our simulated Florine pattern is represented with about 20 microns of clearance in the center about just over 40 microns of clearance out in the periphery along the vertical axis and when we look at that lens on ey and unfortunately this is not a video but when we look at that lens on ey you can see the touch points again at 9:00 and 3:00 and you can see how well that lens is centered and you can uh you can appreciate that there is no touch here in the center there's touch here in the mid periphery but it's clearing the center of the cornea to a point of about 20 microns of clearance and we would expect that to be a very very successful fit now let's go one step further and create a lens with a with a base curve of 4275 which um would be considered a diopter steeper than K and maybe just a little of half adapter steeper than the last lens we looked at you can see now that we're clearing the corny in the center more than 20 microns we're uh we're still just over 40 microns out here in the periphery so we should still be okay there and when we look at this lens on eye this one diopter steeper than K lens on ey you can see that uh there's a significant amount of pooling in the center of this contact lens so let's run this video and see what happens now the lens is still picked up drops pretty pretty rapidly though into place that's because of the impingement up here above we've got a little more impingement than we had at a at a half adapter steeper than K we've got more tier film than we need in the center of the lens and we probably are running the risk of three and N staining that could lead into vascularized limbal keratitis or VK and I would consider this a slightly steeper lens than what we'd necessarily need still Center well probably could be considered a successful fit more chance for lens flexure little more tiar foam than we need under the center little more risk of three and :00 staining not an ideal fit but not a terrible fit and then finally you know want once we've determined our diameter first our base curve second we need to determine the power of the lens and we certainly do this most of the time with just a simple spherical over refraction but uh often times we can use if we're doing empirical fitting especially the old sfap rule samap basically says if the base curve of the lens is steeper than the patient's flat k we're going to add minus power an equal amount of minus power um you know for every quar of adopter we are steeper than flat k we're going to add a a quarter adap or more minus and we're going to add plus if the if the lens is flatter so if the base curve of the lens is flatter than the patient's fla a we're going to be adding plus the basic Sam fap Rule now my intention is to do a series of these webinars where we're talking about boric design we're talking about uh you know U uh konus designs reverse geometry designs multifocal designs so I I really appreciate uh uh you know Josh and Janice's uh you know support with us at Valley context and hopefully you'll follow along as we kind of walk through step by step how to design some of these more complex fits I appreciate that you took the time to listen to this and I want to wish you the best of luck and uh designing and working with rigid lenses and hopefully I've convinced you that this is a very viable option for your practice and your patience thank you very much