Current Corneal Topography/Tomography Systems.

Corneal topography/tomography devices are among the most widely used diagnostic systems at the ophthalmology clinics. Parallel to the developments in refractive corneal and cataract surgery, substantial advancements have been made in these devices during the past 2 decades. Modern topography devices map a large area of the anterior corneal surface through analysis of reflected Placido disc images from the tear–cornea interface (Placido disc systems). Tomography devices, on the other hand, can construct 3dimensional images of the cornea through measurement and analysis of both the anterior and the posterior corneal elevations (scanning slit and Scheimpflug imaging devices). Today, there are devices that incorporate both the Placido disc and Scheimpflug principles into a single system. This advancement has enabled the clinician to use the advantages of the placido disc principle in anterior surface curvature measurements, whereas elevation data enabled the measurement of the posterior corneal surface and the mapping of corneal pachymetry. The cornea accounts for about two-thirds of the total refractive power of the eye. Thus, accurate evaluation of this tissue is of utmost importance in refractive surgery screenings, evaluation of postrefractive surgery patients, diagnosis and monitorization of ectatic dystrophies in relevance to progression, diagnosis of irregular/postsurgical corneas, monitorization of corneal reshaping therapies and orthokeratology, planning and monitorization of surgical options in ectatic diseases, planning of incision site and intraocular lens (IOL) power selection before cataract surgery, and in phakic IOL planning and monitorization. Today, advances in scientific knowledge and surgical techniques have increased the demands from the technology, and newer topography/tomography systems tend to incorporate as many data as possible from the anterior segment to help patient management in a more effective and time-saving manner. Incorporation of tear film analysis data such as noninvasive break-up time and tear meniscus height measurements into topography or tomography systems is one such advancement. Most of these devices that can evaluate the tear film are also capable of taking meibography measurements with the help of an infrared camera. Knowing the frequency of dry eye disease even in young population (thanks to the use of digital devices and cell phones), these devices can be helpful in diagnosis and management of a large patient population.1,2 Another common area of practice in ophthalmology clinics is cataract surgery, particularly “premium” IOL surgery. Premium IOL surgery requires accurate measurements of the anterior and posterior corneal power and the axial length.3 Topography/tomography devices that are capable of measuring the axial length have become available. Thus, at 1 setting, these devices can tell you whether the patient is a good candidate for premium IOL surgery, and what would be the ideal IOL power to choose.4 Since refractive surgery boosted around 1990s and 2000s, many cataract patients today are postrefractive surgery cases, in whom rather than assumptions, we need accurate measurements from both anterior and posterior surfaces of the cornea to calculate the correct IOL power; thus, we need tomographers and/or swept-source optical coherence tomography devices in this indication.5 Owing to their potential of viewing the anterior chamber, corneal tomography devices can also help planning phakic IOL or piggyback IOL surgery and monitorization of these patients after implantation of such phakic IOLs.6 Diagnosis and monitorization of patients with ectatic corneal diseases such as keratoconus and post-LASIK ectasia is another common indication of corneal topography/tomography devices. Despite advances in technology, there is no established topography/tomography index or set of indices for the diagnosis of preclinical corneal ectasia or for recognizing progression during the course of the disease. To help serve this purpose, corneal biomechanics has also been incorporated into Scheimpflug tomography technology. In addition to providing Scheimpflug tomography measurements, this technology can help evaluate biomechanical properties of the cornea and measure the intraocular pressure, thus potentially facilitating recognition of preclinical corneal ectasia.7,8 Application of machine learning algorithms and neural networks have also been explored to assist in the identification of corneas with preclinical and clinically evident ectasia.9,10 Although the definition of “progression” in ectatic eye diseases is still obscure, recently, such technology has been used to predict the level of keratoconus progression in nonsurgically treated corneas, in a preliminary study.11 Measuring the corneal epithelial thickness and generation of epithelial thickness maps with the use of swept-source optical coherence tomography was reported to help improve diagnosing corneal ectasia, screening refractive surgery candidates, and evaluating remodeling processes after ophthalmic surgery.12 Witnessing the developments in technology during the past 20 years, it is not impossible to imagine such technology being incorporated into topography/tomography systems in the near future. To summarize, today’s corneal topography/tomography technology features incorporation of other measurements/data from the external eye, the cornea, and anterior segment structures, as well as amelioration of available topography/tomography measurements using high technology, such as artificial intelligence to enhance reliable diagnosis and management of anterior segment diseases and surgery. As such, at least in the near future, topography/tomography systems will probably continue to be an indispensable part of the ophthalmology clinics. From the Department of Ophthalmology, Ankara University School of Medicine, Ankara, Turkey. The author has no funding or conflicts of interest to disclose.