96
12.4 Pachymetry evaluation
The Pentacam® provides a detailed corneal thickness distribution map with 3 μm accuracy and
repeatability.
Display interpretation (pachymetry):
The pachymetric portion of the display includes the pachymetry map (corneal thickness), the two
graphs showing the current of this patient thickness progression versus a normal population and the
pachymetric indices. These identify the corneal thickness at the apex (the point on which the exam is
centered), the TP and the location and distance of the TP from the apex.
The location of the TP relative to the apex is described as temporal (T), nasal (N), superior (S) and
inferior (I) or intermediate (e.g. IT = inferior-temporal). The pachymetric difference between the TP
and the apex is > 10 μm in only about 12% of normal corneas.
We have found a positive correlation (r2 = 0.61) between the distance and the pachymetric
difference between the apex and the TP. The distance between the apex and the TP is significantly
higher (1.52 ± 0.58 mm) in keratoconic eyes than it is in normals (0.9 ± 0.23 mm) (p < 0.05).
Along with the TP the pachymetric display also evaluates the thickness profile of the cornea. The
basics and interpretation of the CTSP (Corneal Thickness Spatial Profile) and the PIT (Percentage of
Increase in Thickness) are explained in
chapter 11
.
12.5 Ectasia susceptibility revealed in the Belin/Ambrósio Enhanced
Ectasia Display
by Prof. Michael W. Belin
The case was sent over the internet from a colleague and I advised not to proceed with LASIK and
later this wise colleague said "if there are too many doubts, there is no doubt!"
So that, based on the evidences found in the tomography, we agreed to avoid corneal refractive
surgery and to wait for evaluating stability before going for custom surface ablation. It is a 28-year-
old female, candidate for LASIK
Refraction:
OD: sph -3.00 cyl -1.25 A 105° VA 20/20
OS: sph -3.00 cyl -1.00 A 70° VA 20/20
Central corneal thickness (CCT) was 515 μm in OD and 501 μm in OS.
Interestingly, the case was also documented on a very good Placido topographer with a good artificial
intelligence system, which classified it as "green" in both eyes, as shown in
Figure 115
and
Figure 116.
12 Belin/Ambrósio Enhanced Ectasia Display
