A topography unit is a machine that takes a specialized photo of the cornea, the front transparent window of the eye. The resulting photo is a topographic map of the corneal surface, similar to satellite aerial colour-coded maps of mountains and valleys on the planet earth.
This map shows the bumps and valleys on the corneal surface and is used to ensure the cornea is regular and can be treated with the laser. People with irregular types of astigmatism or corneal disorders, such as Keratoconus, may be ruled as non-candidates prior to surgery. These patients may be good candidates for alternative vision correction procedures to LASIK. The topography is therefore essential in determining whether or not you are a candidate for LASIK surgery.
Orbscan Topography is a newer technology that not only allows your surgeon to detect these irregularities on the front surface of the cornea, but also allows mapping of the posterior corneal surface. Conventional topography machines can only give information about the front surface. Orbscan Topography can also determine whether the back surface of the cornea is healthy.
This ability to look at the back surface is essential for safety reasons. The added safety allows your surgeon to better determine the suitability of your cornea for surgery.
A pachymetry unit is a machine that takes a measurement of corneal thickness. It is vital to assess this before surgery in order to determine if there is adequate thickness to create the flap and to perform the laser ablation. It is also vital in assessing the candidacy for an enhancement. People with thin corneas may not have enough tissue for a primary or a secondary treatment.
Conventional pachymetry units take measurements at one point on the cornea. This point is where the probe of the pachymeter touches the cornea, usually in the centre. The Orbscan technology takes pachymetry (measurements) optically without touching the cornea. This allows a measurement reading for the entire cornea; rather than a measurement at just one point. The ability to determine the thickness at all points ensures that a thin point is not missed and contributes to greater safety.