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Corneal Topography - Eye Test By Dr. Himanshu Mehta

Corneal topography is a computer assisted diagnostic tool that creates a three-dimensional map of the surface curvature of the cornea. The cornea (the front window of the eye) is responsible for about 70 percent of the eye’s focusing power. An eye with normal vision has an evenly rounded cornea, but if the cornea is too flat, too steep, or unevenly curved, less than perfect vision results. The greatest advantage of corneal topography is its ability to detect irregular conditions invisible to most conventional testing.

Corneal topography produces a detailed, visual description of the shape and power of the cornea. This type of analysis provides your doctor with very fine details regarding the condition of the corneal surface. These details are used to diagnose, monitor, and treat various eye conditions. They are also used in fitting contact lenses and for planning surgery, including laser vision correction. For laser vision correction the corneal topography map is used in conjunction with other tests to determine exactly how much corneal tissue will be removed to correct vision and with what ablation pattern.

Computerized corneal topography can be beneficial in the evaluation of certain diseases and injuries of the cornea including:

  • Corneal diseases
  • Corneal abrasions
  • Corneal deformities
  • Irregular astigmatism following corneal transplants
  • Postoperative cataract extraction with acquired astigmatism.

corneal topography eye test by Dr. Himanshu Mehta

The corneal topography equipment consists of a computer linked to a lighted bowl that contains a pattern of rings. During a diagnostic test, the patient sits in front of the bowl with his or her head pressed against a bar while a series of data points are generated. Computer software digitizes these data points to produce a printout of the corneal shape, using different colors to identify different elevations, much like a topographic map of the earth displays changes in the land surface. The non-contact testing is painless and brief.

What exactly is the corneal topography?

The corneal topography (corneal topography) is a special test by which we can acquire useful information (through a series of coloured maps e.g. axial, elevation, tangential, refractive maps) on the curvature of the cornea (anterior & posterior segments – optical scanning of the anterior and posterior surface of the cornea). The different colours in a topographical map represent the distribution of refractive power on the corneal surface (center and periphery). The different colours in a corneal topography (corneal map) depict areas with higher or lower refractive power. The range of colours also helps to compare different eyes but also changes in the same eye.

When do we use corneal topography?

  • in consideration for keratoconus (conical cornea shape). The coloured topographic maps actually define the position, size and curvature of the cone and the keratoconus indices, the stage (keratoconus stage)
  • in the preoperative control if a patient is to undergo refractive surgery with excimer laser. In refractive surgery, the corneal topography is an important exam of primary importance, not only preoperatively and postoperatively. The topographic changes (e.g. contact lenses), the suspicion indicator for keratoconus, the configuration of the corneal surface, the distribution of refractive power, corneal thickness, the keratometry etc. are taken into account seriously. Many times the decision to refractive technique derives from corneal topography (PRK, conventional LASIK, Z-LASIK with femtosecond laser)

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