Corneal topography and tomography have an important role as screening tools in patients seeking laser vision correction surgey and to diagnose and follow keratoconus and other corneal ectatic diseases.
This article was reviewed by Vishal Jhangji, MD
Advances in hardware and software make corneal topography and tomography useful tools for ectasia risk screening and for the diagnosis and follow-up of keratoconus and post-LASIK ectasia, but other factors and clinical correlation are important when interpreting the findings, according to Vishal Jhanji, MD.
“Corneal topography and tomography allow precise measurement of anterior and posterior corneal curvatures and corneal thickness and enable the diagnosis, classification, and monitoring of progression of corneal diseases, but there can be more to the picture,” said Dr. Jhanji, professor of ophthalmology, University of Pittsburgh, Pittsburgh. “Hopefully, these processes will be improved in the future through a combination of biomechanical factors, topographic indices, and surgery-induced risk stratification.”
Corneal topographers analyze the pattern of light rays reflected off the cornea and tear film-air interface and reconstruct the corneal shape. Corneal tomographers evaluate the whole cornea by obtaining information from the anterior and posterior corneal surfaces to reconstruct three-dimensional images of the anterior segment.
The corneal imaging technology has continued to evolve. Initial instruments based on Placido disk technology only analyzed the central anterior surface of the cornea and only provided anterior corneal shape-based indices. Subsequently, scanning slit-based technology was introduced that also imaged the posterior cornea.
Dr. Jhanji pointed out that with information about posterior surface elevation, keratoconus began to be diagnosed more efficiently.
Keratoconus affects 86 in 100, 000 people, resulting in visual loss due to increasing irregular corneal astigmatism, and the quality of life declines in patients. Ophthalmologists can stabilize the disease or improve vision by utilizing corneal cross-linking (CXL) and grafting, but these carry risks.
Scheimpflug camera-based devices were developed that could image the central anterior and posterior cornea as well as the peripheral cornea. Software for these systems was developed to generate comprehensive diagnostic indices for identifying subclinical and frank keratoconus.