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

Case Study 141

CASE 6: POST-LASIK ECTASIA

A 28-year-old female came to my office complaining of progressive reduction in her visual acuity (more severe in the left eye) since 3 years. Her history revealed Lasik treatment for myopia in 2003 (6 years ago) for both eyes. Her exam was as follows:

According to her complaint and history, one can think about post-Lasik ectasia (keratoectasia), and when looking at her refraction, there is low uncorrected and best corrected visual acuity in the left eye with an astigmatic refractive error that does not explain this reduction. Fig. 5.6A shows corneal topography of the right eye.

The Qualifying Step

1.In a general look, the sagittal curvature map has a highly irregular pattern. The anterior and posterior elevation maps show irregular shape with abnormal values. The thickness map shows a horizontally displaced thinnest location giving the shape of a conic pattern.

2.Main page analysis reveals that the quality of the capture (QS) is OK. The K-readings in the central 3 mm are normal (40.4, 42.4) and the corneal astigmatism (the algebraic sum of anterior and posterior astigmatism) is also normal (-1.3 <-6). Q-value at the 6 mm circle of the cornea front is abnormal (+0.39). Corneal thickness at the thinnest location is normal (489) and has abnormal

142 Step by Step Reading Pentacam Topography

horizontal coordinate with pachy apex. There is a significant difference in thickness between pachy apex and thinnest location (12 µ).

3.Studying each map:

•Corneal thickness map (Fig. 5.6B): The shape of this map is abnormal with a horizontal displacement of the thinnest location (red arrow). The difference between the lower and upper points of the central 4 mm circle is 2 µ (red circles), which is normal.

•The sagittal curvature front map (Fig. 5.6C): Shows the smiling face pattern, which is very abnormal pattern. When projecting the major axes on this map, you can see clearly the vortex pattern also (Fig. 5.6D). The difference between the upper and lower points at the 4 mm circle is much more than 1.5 dpt (Fig. 5.6D white arrows). So as you see, the K-readings of the central 3 mm are not enough to qualify the case, they are sometimes misleading and we should look at every single map.

•The elevation front map (Fig. 5.6E): There are an obvious cone and abnormal values (white arrow).

•The elevation back map (Fig. 5.6F): There are an obvious cone and abnormal values (white arrow).

P.S. There is no need of course in this case to see the toric ellipsoid; the diagnosis is clearly keratoconus.

•The Keratometric power deviation map (KPD): It is irregular and displays abnormal values (Fig. 5.6G).

•The Topometric map (Fig. 5.6H): All values in all meridians and on all circles are positive and abnormal indicating an oblate cornea, this is normal after Lasik treatment of myopia.

Case Study 143

•The keratoconus indices page (Fig. 5.6I): Look at the upper diagram; although the red curve begins within the normal range, it deviates rapidly. On the other hand, the lower diagram shows that the progression percentage is below normal. These findings are consistent with the diagnosis shown “Post Corneal Surgery?”. The average is high (1.7) and most of irregularity indices are abnormal, indicating irregular cornea.

•Fig. 5.6J is one of the Scheimpflug image sectors, it is difficult here to assess the ectatic part of the cornea even on other sectors, and this is opposite to what

we are going to see in the left eye topography.

Fig. 5.6K shows corneal topography of the left eye.

The Qualifying Step

1.In a general look, the sagittal curvature map and the anterior and posterior elevation maps show the pattern of just like keratoconus. The thickness map shows abnormal values within the central part.

2.Main page analysis reveals that the quality of the capture (QS) is OK. The K-readings in the central 3 mm are abnormal (53.1, 52.9) with very little amount of astigmatism, which indicates that the cone is not central but peripheral. Q-value at the 6 mm circle of the cornea front is abnormal (-1.36). Corneal thickness at the thinnest location is abnormal (423). There is a significant difference in thickness between pachy apex and thinnest location (17 µ).

Case Study 147

Fig.5.6D:The sagittal curvature front map. We can see here the vortex pattern after projecting the circles and the major axes. We can see also that there is no significant superior-inferior difference on the 4 mm circle although the pattern is abnormal (white arrows).

Case Study 149

Fig. 5.6F: The elevation back map. There are an obvious cone and abnormal values (white arrow).