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Abstract
Corneal topography is a process for mapping the surface curvature of the cornea, similar to making a contour map of the land. The cornea is a clear membrane that covers the front of the eye and is responsible for about 70 % of the eye’s focusing power. To a large extent, the shape of the cornea determine 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 result.
Corneal topography instrument used in clinical practice are based on placido reflective image analysis. This method of imaging of the anterior corneal surface uses the analysis of reflected images of multiple concentric rings projected to the cornea.
The purpose of corneal topography is to produce a detailed description of the shape and the 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.
The map is interpreted much like other topography maps. The cool shades of blue and green represent flatter areas of the cornea, while the warmer shades of orange and red represent steeper areas.
This corneal map allow the physician to formulate a”3-D’’ perspective of the corneal shape .measuring astigmatism is important for planning refractive surgery, fitting contact lenses.
Corneal topography is not a routine test. Rather it is used in the diagnosis and management of corneal curvature abnormalities and diseases such as keratoconus, irregular astigmatism following corneal transplantation, in fitting some type of contact lenses and in preparing for refractive eye surgery such as -LASIK- 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.
Wavefront sensing and corneal topography are complementary tools in the diagnosis and management of refractive problems. They have very strong differences: different equipments, different technology, and different functions. Corneal topography measures shape and wavefront measures optics. Topography measures a large area of the cornea, while wavefront is limited to the pupillary area. both systems not exclude each other but used together to evaluate the refractive problems.