Southwest, FL | Measuring the Eye for Cataract Surgery | Cataract & Refractive Institute of Florida

Dr Croley describes the typical methods used for measuring the eye to determine the strength of the intraocular lens to be used during cataract surgery. There are three common instruments or technologies used for measuring the eye; ultrasound, IOL Master, and LenStar.


Dr. Croley: Hello, and welcome to Case of the Day. I'm Dr. Croley and today we're going to discuss some interesting things about how we determine what strength of lens or intraocular lens that we put inside an eye during cataract surgery.

Dr. Croley: A patient came in today to get scheduled for their cataract surgery and then had a lot of questions of why are we doing all this testing, and so we're going to cover that today. And so the basic test that we're doing is related to what strength of lens to put in your eye during cataract surgery. And cataract surgery involves taking your cloudy lens, your own lens inside your eye behind your pupil, has become cloudy. So we're removing that lens in cataract surgery and then inserting a clear lens so your vision will then be clear. And then we need to know what strength of lens to put in there, because if you're nearsighted or farsighted, we can then adjust that with the implant and then give you really good distance vision most of the time without glasses, unless we use a special lens of some other type that actually can give you distance and near.

Dr. Croley: So what are we measuring? So basically it's just purely optics. And so what these machines measure, and this is one of them called a LENSTAR, that is fantastic and very accurate. And so what are we doing? We're measuring actually the distance from the cornea back to your retina. So that actual length is extremely important in knowing whether your eye is nearsighted or farsighted. A farsighted person typically on average has a shorter than normal eye. A nearsighted person has a longer than normal eye, typically speaking. And so therefore, how long this is determines on whether your eye is nearsighted or farsighted. The other thing that determines that is how curved is your cornea, the clear part of your eye? So if you have a very steep cornea, then you're typically nearsighted, and if you have a very flat cornea, you're typically farsighted.

Dr. Croley: So the machines, like the LENSTAR, measures a lot of different things, but the main two measurements are axial length and curvature of your cornea. Another important measurement is how much distance is there from your cornea back toward your own lens sits or where the implant will sit. And then there's some other things that the LENSTAR measures as well, but then the computer inside the machine, then through formulas, calculates what strength of lens would we put in here that would then correct your vision. And so that is extremely important if you want a great result from your cataract surgery. There's lots of other tests that we're now doing as well to help us decide what's the best implant and how can we give you the best vision. And another one of those tests is called a Tracey Technology machine, and that machine measures different parts of your vision.

Dr. Croley: So it measures and does a wavefront analysis of your vision, which determines what type of aberrations you have in your vision system, because even if you have no glass prescription and are 20/20 you still have aberrations in your vision system. We don't have perfect eyes, and we don't have perfect vision. Say a animal like a hawk that's flying way up in the sky and looking for a tiny mouse down in some grass, they have a lot better vision than we do. We would not be able to see that mouse. So we don't have perfect eyes, but we certainly have vision enough to do what we need to do. So the Tracey Technology measure some of those aberrations in your vision system, and that way we can come up with a lens that matches more closely to what your own eye has as far as how it's shaped and what aberrations you have in your system, because then we have aspheric design lenses that can give you sharper, better vision. And what do we mean by aspheric?

Dr. Croley: In this drawing here, this cornea is fairly round, but in actuality a human cornea is not shaped that way. That is our corneas are steeper in the middle and flatter in the periphery. So we're not spherical. We're aspherical. And so we now have implants that are aspherical as well that better match the shape of our own eye, which then gives us a little better contrast sensitivity, a little less glare from the implant, and so these lenses give you a little bit better vision. It's like going from a regular TV to a high definition TV. It's just a little bit better. So a lot of people can choose that type of lens, and we're able to measure what that asphericity is.

Dr. Croley: And so that's another test that we do. A lot of times people want to do monovision. That is one eye for distance, one up close, but they're implants, just like they wear contact lenses that way. So we measure which is their dominant eye, because we typically put your nondominant for near and your dominant eye for distance. So that's the test we commonly do. Another test that we do is we measure the quality and health of your cornea, because that can determine a lot of times what type of lens would be good for your eye. And so we have a machine called a specular microscopy instrument that measures the inside lining of how healthy these cells are in your cornea. And we'll measure how thick your cornea is. And so that's valuable information that we use as well when we're sitting down with the patient and going over all your options of the different kinds of lenses we have today and what we're going to do about providing you the best result.

Dr. Croley: So if you have any questions about what we discussed today, about the tests that are vital in measuring you for cataract surgery, you can contact us through the website. If not, may God bless you with healthy eyes and great vision.