Cornea and anterior eye assessment with placido-disc keratoscopy, slit scanning evaluation topography and scheimpflug imaging tomography

Abstract

Current corneal assessment technologies make the process of corneal evaluation extremely fast and simple and several devices and technologies allow to explore and to manage patients. The purpose of this special issue is to present and also to update in the evaluation of cornea and ocular surface and this second part, reviews a description of the corneal topography and tomography techniques, providing updated information of the clinical recommendations of these techniques in eye care practice. Placido-based topographers started an exciting anterior corneal surface analysis that allows the development of current corneal tomographers that provide a full three-dimensional reconstruction of the cornea including elevation, curvature, and pachymetry data of anterior and posterior corneal surfaces. Although, there is not an accepted reference standard technology for corneal topography description and it is not possible to determine which device produces the most accurate topographic measurements, placido-based topographers are a valuable technology to be used in primary eye care and corneal tomograhers expanding the possibilities to explore cornea and anterior eye facilitating diagnosis and follow-up in several situations, raising patient follow-up, and improving the knowledge regarding to the corneal anatomy. Main disadvantages of placido-based topographers include the absence of information about the posterior corneal surface and limited corneal surface coverage without data from the para-central and/or peripheral corneal surface. However, corneal tomographers show repeatable anterior and posterior corneal surfaces measurements, providing full corneal thickness data improving cornea, and anterior surface assessment. However, differences between devices suggest that they are not interchangeable in clinical practice.

Keywords: Anterior corneal surface; corneal tomography; corneal topography; placido-based topographers; posterior corneal surface.

Figure 1

Placido-based topography (Keratograph, OCULUS) in orthokeratology patient. (a) Comparison between pre- and post- contact lens wear topographies in a myopic patient of - five-dimensional. Top-right shows baseline topography and down-right shows the topography after reverse geometry rigid gas permeable contact lens. Left-center shows the difference between both topographies (orthokeratologic effect). (b) Placido-based image captured by the topographer

Figure 2

Orbscan topography in a healthy eye with two-dimensional of astigmatism. (a) Axial power is showed and (b) three-dimensional image of the cornea

Figure 3

Corneal tomography (GalileiG4) in a patient with a corneal trauma. (a) Corneal tomography showing anterior axial curvature map (top left), pachymetric map (top right) and anterior (down left) and posterior (down right) elevation best-fit sphere maps. (b) Slit-lamp imaging showing corneal scar