Corneal tomography is a non-invasive imaging technique that evaluates the shape and specific optical details of the cornea. It analyses the contours, curvature and dimensions of the frontal structures, i.e. the structures in the visible part of the eye. Tomography systems can assess the entire cornea, including measuring:
- The curvature and elevation of the front and back surfaces of the cornea
- The iris-corneal angle, the structure that drains the liquids in the eye
- Anterior chamber depth, i.e., the space between cornea and iris
- Thickness of the cornea
Corneal imaging plays a critical role in the diagnosis and management of a broad range of ocular diseases. It generates a three-dimensional (3-D) image of the anterior and posterior segments and provides information about the spatial relationship between the two and details of the corneal architecture.
The exam is suitable for patients of all ages, including children. However, it is essential for the patient to be able to cooperate.
A corneal tomography exam can be done in the hospital, eye clinic or doctor's office by:
- A technician
- An optometrist
- An ophthalmologist
The evaluation is useful for all patients with corneal disorders, including:
- Corneal diseases
- Corneal scratches
- Corneal deformities
It is also useful prior to certain surgical procedures, such as postoperative cataract extraction with acquired astigmatism.
It is the most commonly used method for diagnosing keratoconus because of its ability to identify rear corneal elevation anomalies even in subclinical or mild diseases. Keratoconus is a disorder that occurs when the cornea becomes thin and slowly bulges out like a cone.
The cornea is the primary lens and accounts for close to 70 per cent of the focusing power of the eye. Changing its shape affects focus. It distorts light entering into the eye, making the patient's vision blurry and daily activities such as reading and driving, difficult. Usually, the condition affects both eyes. It can affect people in the age group of 10 to 25 years and progress gradually for ten years or longer.
Corneal tomography, along with other tests is also useful in:
- Glaucoma diagnosis and management
- Surgical planning for LASIK enhancements
- Keratoprosthesis post-surgical management
- Assessment of graft position after keratoplasty
- Surgical preparation for phakic intraocular lens implants
Preparation & Expectation
Patients with a family history of glaucoma should tell the doctor before the test. It may be necessary for the patient to stop using contact lenses for a while before the exam. It prevents changes in the curvature of the cornea and fingerprints that may influence the outcome. The tear film must be sufficient to enable reliable assessments that are not affected by surface irregularities.
Types of Examination
The methods of corneal tomography include:
The technique uses a slit beam to provide multiple slit images of the anterior section, anterior chamber depth and corneal thickness
Rotating Scheimpflug imaging
It is one of the most frequently used methods of corneal tomography. It produces cross-sectional images that are used to assess the posterior and anterior corneal surfaces.
Rotating optical coherence tomography
Anterior segment optical coherence tomography (AS-OCT) creates high-resolution imaging of the anterior chamber, iris, and cornea. It utilizes light waves to provide extremely high-resolution 3-D images of atomic ocular structures. The technique employs two scanning light beams that bounce on a visual structure and are then read and compared to a reference ray of light to produce a cross-sectional image
Arc scanning with high-frequency ultrasound
The technique uses ultrasound to produce precision measurement capabilities and microscopic resolution images of the cornea and anterior segments.
The patient will sit on a stool and place their chin on a chin rest and forehead on support. The patient will be fixed on a light source for several seconds, and a camera will conduct a series of corneal light scans. The computer processes the data according to the form of pathology under evaluation, or the required diagnostic.
Corneal tomography creates high-resolution imaging of the anterior surface and high-precision 3-D thickness of different areas of the cornea. It also provides a map of the curvature of the posterior surface of the cornea.
The information can be put to multiple use. For instance, it can enable the doctor to ascertain whether keratoconus is mild, moderate or severe. He/she can use repeat measures to assess whether the condition is progressing. It helps the doctor to determine the best vision correction options and can also serve to guide contact lens fitting.
For a patient who has undergone LASIK, the information can enable the specialist to accurately evaluate the anatomical changes induced in the cornea by the surgery.
Risks & Complications
Corneal tomography is a non-invasive imaging technology and there are no risks or complications associated with it.