The cornea is an important structure in the eye. It is the thin, transparent layer in front of your pupil and iris that acts as a protective layer to shield the sensitive inner structures from dust and debris. It also helps to bend and refract the light entering the eye, allowing it to hit the retina at the back of the eye and be translated by the brain into visible images. The cornea is unique to every patient in size and overall shape, and sometimes your optometrist needs to get a detailed image of your cornea for diagnostic or fitting purposes.
This is where corneal topography comes in.
What is Corneal Topography?
Corneal Topography is an advanced testing technique used for a variety of applications in vision correction, diagnostics and surgical evaluations. A corneal topographer measures the surface curvatures of the cornea, and produces a detailed map that reveals the unique shape of your cornea, much like how a cartographer will produce topography maps of mountains and hills, aimed at showing the changes in elevation over a wide area in detail.
Measuring corneal topography is non-invasive, quick and painless. The patient sits in front of a machine that projects a series of symmetric rings. These rings are lit up and reflect off the surface of the eye back at the machine, where a camera inside is able to see and record the reflections. The patient looks to the very centre ring while the trained operator (the optometrist or an optometric assistant) operates the topographer to line up the camera and capture a detailed image of the cornea. Through a series of calculations this image is then turned into a topographical “map” of the cornea’s surface showing the high and low points.
Corneal Topography and Diagnosis
Corneal topography can be used for diagnostic purposes, to help identify or rule out conditions and diseases that affect the shape of the cornea itself. For example, it is a common test used when a condition called keratoconus is suspected. Keratoconus is a progressive disease that causes the cornea to warp and grow thinner, typically bulging out into a more irregular “cone” shape. This will affect the quality of the patient’s vision, and will result in significant vision loss over time. Corneal topography is used to identify the corneal irregularities typical of keratoconus so that a diagnosis can be made and a treatment plan arranged.
Corneal topography is also used by ophthalmologists to help plan laser correction surgery. These surgeries permanently alter the shape of the cornea, so a successful surgery relies on topography data in order to map out what changes need to be made, and to evaluate how thin or thick parts of the cornea are. Topography is also used in post-operative care to monitor the healing and ongoing health of the cornea.
Corneal Topography and Contact Lenses
Corneal topography is also used for the purposes of making specialized contact lenses. Hard contact lenses such as RGPs (Rigid Gas Permeables) and Ortho-K (Orthokeratology) lenses are custom made for each patient and require the high detail corneal maps provided by corneal topography.
RGP lenses can be used to correct a larger range of prescriptions than what is available in most commercial soft contact lenses. This includes prescriptions with irregular astigmatism, or those that require much stronger powers that would be cumbersome to wear in glasses form. RGPs are made to be smaller than the patient’s cornea, with a series of specific curves in the lens itself to help with fit and comfort. As such, corneal topography is necessary to determine what angle the curves must be at and what size the lens has to be overall.
Ortho-k lenses are used to physically reshape the cornea as a form of myopia control. The lenses are worn overnight and removed in the morning, which temporarily reshapes the cornea. In this way, optometrists can reduce the strength of myopic or near-sighted prescriptions, sometimes helping to eliminate the need for glasses all together. This only works for certain prescriptions and is temporary, as the cornea will bounce back to its original shape if the ortho-k lenses are discontinued for a length of time. In order to ensure that the patient’s cornea is reshaped properly, a topography map must be made for each eye and sent to the manufacturer to create properly sized lenses.
Each 360 Eyecare location has been fitted with a corneal topographer machine in office to be able to provide specialized diagnostic testing or measurements for custom contact lenses. Reach out to one of our offices – 360 Eyecare Beaches or 360 Eyecare Rosedale – to learn more and book your next eye exam today.