What Is Corneal Topography? - Ojaseyehospital

Posted by Dr Niteen Dedhia on March 14th, 2022

Corneal Mapping (Corneal Topography)

Corneal topography is an advanced device used by ophthalmologists to produce detailed images of the shape, curvature and thickness of their patients. These images give ophthalmologists excellent information about the condition of the corneal surface.

Different Types Of Corneal Topography

• Placido disc topography: Placido disc reflection systems measure curvature, irregularities and the quality of the tear film and the outer bodies and other parts of the anterior cornea.
• Scheimpflug and scanning-slit topography: They provide information about the anterior and posterior surface of the cornea, its shape and also give detailed information about the corneal thickness.

Different Maps Obtained Through Corneal Topography

The ophthalmologists may obtain the following maps through corneal topography:

• Axial Display Map: It is a standard mapping system and is not very accurate. Axial maps are a handy tool for selecting a primary curve for a soft contact lens due to displaying of average bending angle.
• Tangential Demonstration Map: They provide very accurate results for measuring the accurate shape and curvature of the cornea and are, therefore, useful for the application of contact lenses, especially ortho-k lenses. This map is also helpful in measuring contact lens power while the lens is in the eye. It helps the patient wear a multifocal contact lens to obtain appropriate visual acuity. They are ready to detect changes in corneal curvature that may occur due to corneal distortions due to contact lenses.
• Elevation map: This map helps determine the cornea’s actual condition and aids in selecting the best contact lens design for a person. The map display is very useful when deciding between scleral gas permeable lenses (GP) or a contact lens. Elevation mapping is also helpful in ortho-k management, as the shape of the angle is vital in determining whether ortho-k lenses will fit a patient and in choosing a double-axis or single-axis lens.
• Corneal thickness map: This map display is used to locate ocular diseases, such as keratoconus, but they help monitor changes in corneal thickness during contact lens contact.
• Tear-splitting indicator ( Tear Break Up time ) : This map shows the quality of the natural tear film and shows how the quality of the tears is affected by the wearing of a contact lens. It helps to measure the tear film before the patient wears contact lenses. They were then compared with the measurements taken after the patient wore contact lenses.

Purpose Of Corneal Mapping

Corneal mapping is used to diagnose, and monitor various eye conditions. The doctor uses this before advising of contact lenses and while planning for surgeries such as laser vision correction. The eye doctor utilizes corneal topography maps in conjunction with other tools regarding laser vision correction. It precisely determines how much corneal tissue needs to be removed to correct the patient’s vision.

Advantages Of Corneal Mapping

One of the advantages of corneal topography is that it can detect abnormal conditions (minute changes in corneal shape ) that are not detectable in a routine examination.

Corneal topography provides a detailed, visual description of the shape of the cornea. The doctor uses this information to diagnose, monitor, and treat various eye conditions. The doctor also implements corneal topography in prescribing contact lenses and surgical planning, including laser correction.

Differences Between Corneal Topography And Corneal Tomography

Following are some of the differences between topography and tomography:

• Corneal topography is a non-invasive method of mapping the upper extremities and the shape of the anterior corneal surface. It is performed using a Placido disc that examines the cornea based on the reflection of fixed rings. The devices used are Orbscan, Atlas, and NIDEK OPD.
• Corneal tomography makes 3D images of the cornea and examines the entire cornea from posterior and anterior regions. It is done using scheimpflug imaging that looks at the cornea using two cameras that images the cornea 360 degree as it rotates. Devices used are Pentacam, Galilei, and Sirius. This images both the front and back surfaces of the cornea hence giving more information about the corneal shape. Pentacam HR is a gold standard device.

Performance Of Corneal Topography

You are asked to sit in front of a lighted round device containing a ring pattern and rest your head against the headrest. A series of data points will be collected, and a colorful image of your cornea shape will be displayed on a computer screen. The images will contain various colors to differentiate the height, similar to a map.

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