Current Developments in Corneal Topography and Tomography

Abstract

Introduction: Accurate assessment of the corneal shape is important in cataract and refractive surgery, both in screening of candidates as well as for analyzing postoperative outcomes. Although corneal topography and tomography are widely used, it is common that these technologies are confused. The aim of this study was to present the current developments of these technologies and particularly distinguish between corneal topography and tomography. Methods: The PubMed, Web of Science and Embase databases were the main resources used to investigate the medical literature. The following keywords were used in various combinations: cornea, corneal, topography, tomography, Scheimpflug, Pentacam, optical coherence tomography. Results: Topography is the study of the shape of the corneal surface, while tomography allows a three-dimensional section of the cornea to be presented. Corneal topographers can be divided into large- and small-cone Placido-based devices, as well as devices with color-LEDs. For corneal tomography, scanning slit or Scheimpflug imaging and optical coherence tomography may be employed. In several devices, corneal topography and tomography have been successfully combined with tear-film analysis, aberrometry, optical biometry and anterior/posterior segment optical coherence tomography. Conclusion: There is a wide variety of imaging techniques to obtain corneal power maps. As different technologies are used, it is imperative that doctors involved in corneal surgery understand the science and clinical application of devices for corneal evaluation in depth.

Keratoconus: An updated review

“…In incipient cases, however, the use of a single parameter as a diagnostic factor is not sufficiently accurate, and pachymetry and corneal aberration data are now also commonly used in conjunction with corneal topography to aid early diagnosis and monitor progression and treatment outcomes [2,152]. In addition to corneal topography that provides two-dimensional imagining of the corneal surface based on curvature data, corneal tomography is a three-dimensional imaging technique that characterises the anterior/posterior corneal surfaces based on curvature data of the anterior surface and elevation data of both the anterior and posterior corneal surfaces, along with corneal thickness distribution [153], which have found critical to enhance the sensitivity and specificity for detecting corneal ectasia in comparison to corneal topography [133,154]. Furthermore, various machine learning algorithms have been developed using routinely collected clinical parameters that can assist in the objective detection of early forms of the disease [2,155].…”

Flap Thickness and the Risk of Complications in Mechanical Microkeratome and Femtosecond Laser In Situ Keratomileusis: A Literature Review and Statistical Analysis

“…In some investigations, OCT [ 24 , 27 , 28 , 29 , 36 , 37 , 38 , 39 ] or confocal microscopy [ 26 , 40 ] was performed postoperatively to evaluate flap thickness. Although subtraction pachymetry could be considered as the gold standard for flap thickness evaluation [ 41 ], OCT measurements were found to be more accurate with a tighter standard deviation [ 42 ]. Potentially, ultrasound pachymetry is subject to edema and compression, which are not present in postoperative OCT measurements [ 42 ].…”

“…Although subtraction pachymetry could be considered as the gold standard for flap thickness evaluation [ 41 ], OCT measurements were found to be more accurate with a tighter standard deviation [ 42 ]. Potentially, ultrasound pachymetry is subject to edema and compression, which are not present in postoperative OCT measurements [ 42 ]. Studies reporting the change in flap thickness over time in the postoperative period showed ambiguous results.…”

Current and new indications for corneal cross-linking in the therapy of corneal diseases

“…The current risk of developing ectasia after photokeratitis refraction procedures is very low due to the improved imaging techniques of the posterior corneal surface and biomechanical properties of the cornea [36]. The study results achieved by Hafezi et al demonstrated that CXL treatment can reverse the progressive iatrogenic keratectasia after LASIK, which manifests as a reduction in maximum keratometric values [37].…”