Corneal Topography - a Review of Available Investigation Methods and Impact in the Diagnosis and Follow-Up of Keratoconus

Abstract

Keratoconus is a bilateral non-inflammatory ectatic disease of the cornea, with an asymmetrical evolution, that occurs in young people during puberty, progressing during the second and third decades and stabilizing around the age of 40. It is characterised by an insidious and progressive thinning of the cornea, myopia and astigmatism, which lead to a decrease in visual acuity. Slit-lamp examination findings in the early stages of keratoconus may appear normal. However, in advanced stages of untreated keratoconus, visual acuity is diminished, which leads to a lower quality of life. Corneal topography is essential in the early diagnosis of the disease, analyzing the corneal geometry and thus helping to establish the method of treatment and to follow patients' evolution. This investigation combines the projection of a light source and a video capture system of corneal images with computer processing, providing maps of the distribution of dioptric power over the entire surface of the cornea. Topography can be classified into measuring the anterior surface of the cornea (keratometry and reflection-based topography) as well as both the anterior and posterior surfaces of the cornea (Scheimpflug slit-lamp scanning and pinhole optics). Understanding and reading corneal topographies is essential in correctly diagnosing and staging a keratoconus case. The present review constitutes a comprehensive evaluation of available methods and expected typical results and interpretation, in order to support clinicians in better managing this underdiagnosed ectasia affecting young patients.

FIGURE 1.

Placido disk reflection on the anterior surface of the cornea (personal archive of author M.S.D.)

FIGURE 2.

Keratoconus stage 1, elevation maps with Pentacam (personal archive of author M.S.D.)

FIGURE 3.

Typical topographical aspect of keratoconus in the right eye, with the appearance of the inferotemporal cone of a yellow-orange color indicating the steeper curvature of the cornea compared to the left eye, which appears normal (personal archive of author M.S.D.)

FIGURE 4.

Keratoconus stage 2, integrated indices and Belin ABCD keratoconus staging with Pentacam (personal archive of author M.S.D.)