Ординатура / Офтальмология / Английские материалы / Step by Step Reading Pentacam Topography (Basics and Case Study Series)_Sinjab_2010

62 Step by Step Reading Pentacam Topography

In this chapter, we will apply all the previously mentioned data on many clinical cases. Each case will be studied according to the following strategy:

1.The Qualifying step: in this step, we have to look for abnormal findings and risk factors if any.

2.The Quantifying step: in this step, patient’s data will be studied according to the topographical features.

3.The Scoring step: apply the “Ectasia Scoring System” to score the case for degree of risk, which helps taking the right decision.

CASE 1: MYOPIC ASTIGMATISM

A 21-year-old male came with stable refractive error. His manifest refraction (MR) was:

Fig. 5.1A shows his right eye corneal topography (4 refractive maps).

The Qualifying Step

1.In a general look, the sagittal curvature map has a symmetrical bow tie pattern oriented as with-the-rule astigmatism. The elevation maps seem to be symmetric with no isolated islands.

2.Main page analysis reveals that the quality of the capture (QS) is OK. The K-readings in the central 3 mm are normal (43.3, 45.6) and corneal astigmatism (the algebraic sum of the anterior and posterior astigmatism)

Case Study 63

is also normal (-1.6 <-6). Q-value of the cornea front is normal at the 6 mm circle (-0.20). Corneal thickness at the thinnest location is normal (535) and has normal coordinates with the pachy apex. There is also no difference in thickness between pachy apex and thinnest location.

3.Studying each map:

•Corneal thickness map (Fig. 5.1B): The shape of this map is the normal shape, i.e. no displacement of the thinnest location (please compare with Fig. 5.1C to understand this point: the white arrow points to the thinnest location). The difference between the lower and upper points of the central 4 mm circle is <30 µ (Fig. 5.1B red circles).

•The sagittal curvature front (Fig. 5.1D): Symmetrical bow tie, no skew or angulation between the lower and upper axes of the pattern, the difference between the upper and lower points of the 4 mm circle is less than 1.5 dpt (white arrows).

•The elevation front map—Based on the BFS as a reference body—presents regular shape with no isolated island or tongue-like extension, normal values within the central 4 mm circle (Fig. 5.1E).

•The elevation back map—Based on the BFS as a reference bodypresents regular shape with no isolated island or tongue-like extension, normal values within the central 4 mm circle, but there are some points where the difference between anterior and posterior values is >+5 µ (Fig. 5.1F).

•The Topometric map (Fig. 5.1G red arrows): Both the average vertical value and the lower value are normal (<-0.55).

66 Step by Step Reading Pentacam Topography

Fig. 5.1C: The corneal thickness map in an abnormal cornea. Notice thebigdisplacementofthethinnestlocation(whitearrow)andtheconiclike shape of the map.

68 Step by Step Reading Pentacam Topography

Fig. 5.1E: The elevation map of the anterior corneal surface. There are two important things to look at: regularity and values within the central 4 mm. In this case the shape is regular and symmetric and the values are within normal limits.