corneal topography and contact lenses

Corneal Topography

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?

360 eyecare - corneal topography appointment with optometrist

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 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.

Categories Corneal Topography
Corneal topography

What is corneal topography and why it is important

Corneal topography, also known as photokeratoscopy, is a medical imaging technique used for mapping the cornea’s anterior surface. This diagnostic tool creates a map of your cornea’s surface curvature. The data collected can then be viewed in different formats including axial, sagittal and elevations view.

Why corneal topography?

The human’s cornea is responsible for more than 70% of the eyes’ focusing power? Corneal topography helps detect irregular eye conditions such as Keratoconus, Pellucid marginal degeneration (PMD), and dry eye disease. Many of those are conditions that are commonly under-diagnosed. The approach outlines and marks a well-detailed visual description of the ultimate power and the shape of the cornea examined.

Useful information analyzed through corneal topography helps your optometrist monitor, diagnose, and treat dry eye conditions and other corneal disease. The collected data is then analyzed and used by optometrists and ophthalmologists for planning eye surgery and fitting contact lenses as well. Corneal topography is also used with other tests to determine the ideal ablation pattern to be used when correcting vision.

Role of corneal topography in contact lens fitting

custom hard contact lenses

Corneal topography is widely used by optometrists to describe and determine the shape of the cornea. This approach is recognized as an ideal diagnostic tool for monitoring and treating the cornea for various ocular conditions. However, the topographic parameters are also used in contact lens fitting providing reliable, repeatable, and accurate details. Topographical data for different parts of the cornea help your optometrist build custom-made contact lenses with varying curvatures to match your unique corneal shape.

Corneal imaging tools help in evaluation of eye conditions such as:

• Corneal deformities

• Astigmatism (regular or irregular such as Keratoconus)

• Corneal abrasions

• Other Corneal diseases

How corneal topography works

Corneal topography is a great tool that’s used with a repeatable approach to monitor for changes over time. Progression of certain corneal conditions is examined closely with serial topography over time which provides comparative analysis for best treatment plans and management. This approach is used in conjunction with other tests to help optometrists formulate better informed and more accurate decisions for their patients.

Basic test administration procedures:

• Patient sits facing a series of symmetrically arranged rings (illuminated patterns) where a set of data points are generated.

• The series of concentrated rings focus on the patient’s cornea, and later reflected back to the digital camera located at the bowl’s center

• The ultimate topography is thereby determined by the shape taken by the indicated sequence

• A computer is used to determine the height and position of the points across your cornea. The computer is linked to the corneal topography equipment to digitize the data points and produce a pattern of your corneal shape.

• A topographical map is then drawn using graphical formats.

Routine comprehensive eye examinations are important for accurate ocular disease detection. Most people should be seen for a comprehensive routine eye examination every one to two years. However, some patients need to be seen more frequently. Speak to your eye care professional on how often you should be seen for your routine eye exam. To book your comprehensive eye exam or dry eye assessment today with one of our optometrists, please contact our Queen St location in the Beaches.