Corneal topography is a map of the anterior corneal surface. This is a simple diagnostic method based on the fact the tear film on the surface of the cornea functions as a mirror. The basis of this method is Placido-disc technology. By the end of the late 1800s, doctors were evaluating corneal irregularity by assessing the reflection of a set of concentric rings off the anterior corneal surface. Today’s instruments measure the corneal shape very precisely.
Every corneal image recorded is very carefully analyzed by a special software, and the data are presented in maps. Combined maps give a detailed picture of corneal curvature, refractive potential, shape, and optical quality of the surface of the eye. The data are presented in different colors. Warm colors represent the steeper zones, and cold colors – flatter zones.
The cornea is of vital importance to the vision. It protects the eye from outward influences but it has to be transparent so the light can go through and enter the eye undisturbed. All kinds of corneal bulges lead to uneven light refraction. Based on the topography, the doctor sets a diagnosis among many conditions and disorders, some of them being astigmatism and keratoconus. This specialist report is also significant for the suggestion on what type of correction to use for the refractive error.
The checkup is done without any direct contact. After the patient places his chin and the forehead to the delimiter of the instrument, he should focus on the fixation light target for a couple of seconds while the photo of the corneal surface is taken.