Corneal topography is the most accurate tool available for measuring corneal curvature. It produces a map of the surface of the cornea and provides essential information about the cornea's shape, distortions, and astigmatism for patients considering refractive surgery or who are suffering from keratoconus.
At Berwick Eye Centre we use the Alcon EyeMap® EH- 290, a state-of-the-art corneal topographer from one of the leading manufacturers of ophthalmic instruments.
The EyeMap machine may look intimidating with its black and- white spiral, but don't worry -- it's a fast, easy and painless test. All you have to do is place your hands on the table, rest your chin on the ledge and lean your head on the bar.
The technician will ask you to blink a few times so the natural tear film on your eye is as uniform as possible, and then to open your eye wide. The machine will buzz a little and snap a picture. You'll see bright rings of light, and that's all. Those light rings are shining into your eye and reflecting back into the EyeMap machine.
Distortions in your cornea bend the rays of light, so when they bounce back, they arrive in slightly different positions. Computer software analyses the shifted light, calculates the surface characteristics of your cornea, and produces a highly detailed image. Within a few seconds you'll be able to see the image on the monitor. Different colours represent irregularities on the surface of the cornea like mountains and plains in a landscape. Blue and green indicate flatter sections of your cornea, while pink and red signify steeper areas
Corneal topography is a process for mapping the surface curvature of the cornea, similar to making a contour map of land.
The cornea is a clear membrane that covers the front of the eye and is responsible for about 70 percent of the eye's focusing power. To a large extent, the shape of the cornea determines the visual ability of an otherwise healthy eye. A perfect eye has an evenly rounded cornea, but if the cornea is too flat, too steep, or unevenly curved, less than perfect vision results. The purpose of corneal topography is to produce a detailed description of the shape and power of the cornea. Using computerized imaging technology, the 3-dimensional map produced by the corneal topographer aids an ophthalmologist in the diagnosis, monitoring, and treatment of various visual conditions.
How does corneal topography work?
The corneal topographer is made up of a computer linked to a lighted bowl that contains a pattern of concentric rings. The patient is seated in front of the bowl with his or her head pressed against a bar while a series of data points are generated on a Placido Disk, which has been projected on the cornea. Computer software digitizes these data points to produce a printout of the corneal shape, using different colors to identify different elevations. The procedure itself is painless and brief. It is a noncontact examination that photographs the surface of the eye using ordinary light.
The greatest advantage of corneal topography is its ability to detect conditions invisible to most conventional testing.
What are the uses of corneal topography?
Corneal topography is not a routine test. Rather, it is used in diagnosing certain types of problems, in evaluating a disease's progression, in fitting some types of contact lenses, and in planning surgery. It is commonly used in preparing for refractive eye surgery. The corneal topography map is used in conjunction with other tests to determine exactly how much corneal tissue will be removed to correct the visual defect.
Corneal topography is used in the diagnosis and management
various corneal curvature abnormalities and diseases
• Diagnosis of hidden astigmatism
• Keratoconus, a degenerative condition that causes a thinning of the cornea
• Corneal transplants
• Corneal scars or opacities
• Corneal deformities
• Fitting contact lenses
• Irregular astigmatism following corneal transplantation
• Planning cataract surgery
• Planning refractive surgery