Corneal topography, also called corneal mapping, is a useful diagnostic tool that provides a detailed 3D map of the shape and curvature of the cornea and helps to detect various ocular disorders. The outer layer of the eye called the cornea is responsible for about seventy-five percent of the focusing power of our eyes. This test enables the detection of corneal diseases and irregular corneal conditions such as scarring, abrasions, swelling, and mild or chronic deformities. It can also check for irregular astigmatism-an imperfection in the curvature of the eye causing blurred vision. During the test, the patient is advised to sit in front of a lighted bowl that contains a certain pattern of rings. Corneal topography is a very simple test that can be performed in a few minutes time and does not have any complications.
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Also Read: Keratoconus - Causes, Symptoms and Treatment

Types Of Corneal Topography

Three different types of technologies are used for corneal topography. The first one is the Placido disc topography which checks the curvature, irregularities, foreign bodies, and other parts of the anterior cornea. The other two types of corneal topography are Scheimpflug and Scanning-slit topography which is primarily used to detect mild to severe corneal swelling. Besides, they are helpful in providing information about anterior and posterior cornea conditions.

Types Of Topographic Maps

Axial Display Map

The most traditional way of viewing a topography image, an axial display map gives an overview of the corneal power of the human eye.  However, since it collects very basic and average data, the results may vary. Therefore, it is considered less accurate as compared to other maps.

Tangential Display Map

This type of topography map gives an accurate measurement of the cornea’s power as well as of its curvature. It can be of great assistance in the effective placement of contact lenses; more so, when the patient is being fitted for a multifocal contact lens used for correcting myopia or poor far vision, and presbyopia- used for correcting poor near vision, or for the accurate positioning of lenses in the eye. It also helps to check the power of a contact lens while the lens is placed into the eye and to check for discrepancies in the corneal curvature due to corneal distortion (a problem that occurs due to wearing contact lenses).

Also Read: Contact Lenses: Types, Advantages and Here’s How You Care For These Ocular Devices

Elevation Display Map

This map is used to identify the shape of the cornea and choose the best contact lens for an irregular cornea. This display map is important while deciding between a corneal contact lens or an ‘Ortho K Lens’ which is a scleral gas permeable lens designed to reshape the cornea. This helps to enhance the focus of the eye, improving vision and providing options for ocular management.

Corneal Thickness Display Map

This map display is used to detect ocular keratoconus. Besides identifying the ailment, it also checks the thickness of the cornea during contact lens wear.

 Tear Break-Up Display

This map displays the quality of the natural tear film by showing how much of the tear quality has been impacted by the contact lens. It measures this quality before the patient begins to wear contact lenses and later a comparison is drawn with the measurement taken after the patient wears contact lenses.

When Is Corneal Topography Advised?

Corneal topography is used to check, monitor and detect the following related anomalies:

  • Planning refractive surgery
  • Monitoring ocular health, post an eye surgery
  • Detecting keratoconus
  • Determining appropriate lenses for cataract surgery
  • Evaluating and treating astigmatism
  • Detecting intricate corneal conditions such as corneal scars, and Salzmann nodules
  • Monitoring ocular diseases
  • Measuring corneal depth
  • Detecting infectious keratitis

Conclusion

Corneal topography is a 3-D corneal mapping technology that produces a detailed, visual description of the shape, condition and power of the cornea. Providing extremely intricate details regarding the condition of the corneal surface, it can help to identify, monitor, and treat various eye disorders and delay progressing eye conditions. It is an extremely useful test before any minor or major cataract surgery. This test has an edge over other technologies as it can detect conditions that cannot be evaluated and identified by most forms of conventional testing.