Topography and tomography in the diagnosis of corneal ectasia

Abstract

For the modern day refractive surgeon, tomography has become an invaluable tool for selection of patients for refractive surgery; in addition it is essential for the diagnosis and treatment planning of ectatic disorders of the cornea. This review article attempts to compare the Scheimpflug with the Placido disc systems, stresses the value of elevation-based topography and the importance of posterior float. Finally, this article provides a comprehensive literature review of the most widely used tomographers, the Orbscan IIz, anterior segment optical coherence tomography, Pentacam, and Galilei Scheimpflug systems. Comparisons of the above tomographers provided in the available literature with respect to corneal elevation, corneal curvature (power) and pachymetry and calculation of intraocular lens power post-refractive surgery have also been discussed.

Keywords:

• corneal topography
• curvature
• elevation
• intraocular lens power calculation
• optical coherence tomography
• pachymetry
• Scheimpflug imaging
• slit scanning

Financial & competing interests disclosure

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.

Key issues

• A brief outline of the evolution of corneal imaging.

• The advent and relevance of elevation-based tomography.

• The features of the various slit scanning and Scheimpflug imaging systems.

• The importance of directly imaging the posterior surface of cornea and the advantages of the Scheimpflug systems.

• Use of optical coherence tomography in mapping the corneal epithelial changes, which mirror the changes in cornea ectasia.

• Analysis of comparative studies on corneal elevation and differences in its measurement between the slit scanning and Scheimpflug systems.

• Various methods of calculating IOL power in virgin corneas and after refractive surgery using the different tomographic systems and comparison of its accuracy and efficacy.

• Accuracy and repeatability of measuring corneal pachymetry of the various tomographers and comparison with ultrasound pachymetry.

Notes