Corneal topography consists of measuring the curvature of the cornea.
When to request:
- Medium-high astigmatism
- Astigmatism that changes
- Corneal transplants
- Corneal diseases that alter the curvature
- Corneal scarring
- Preoperative evaluation for refractive surgery
There are basically two techniques for measuring the radius of curvature of the cornea:
1) Placido disk: a series of concentric circles of a predefined thickness is projected onto the cornea. The image reflected on the cornea is acquired and the distortion compared to the original circles is measured.
2) Scheimpflug: the cornea is displayed in thin parallel and serial sections like scans, the images are recomposed and a 3D model of the whole cornea is obtained. With this technique it is possible to obtain the curvature of curvature also of the posterior face of the cornea.
The exam is not invasive and lasts the time of image acquisition usually a few seconds. A preparation with drops is not necessary. However, it is important to suspend contact lenses for 24 hours before the exam.