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

Case Study 111

Fig.5.4K:The sagittal curvature front map. Asymmetric bow tie/inferior steep with angulation (AB/SRAX): the superior-inferior difference is abnormal.

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Fig.5.4L:The sagittal curvature front map. Asymmetric bow tie/inferior steep with angulation (AB/SRAX): there is about 25° of angulation between the two axes, which is abnormal.

Case Study 117

•The keratoconus indices page (Fig. 5.4P): Although the curve lines are within the normal range and there is no deviation before the 6 mm circle, the average is abnormal (1.2). The diagnosis box displays KK1, which means keratoconus level one according to Amsler classification. Most irregularity indices are also abnormal.

P.S. Amsler classification is based on clinical signs and anterior curvature map (not elevation based) topography.

As we see, we should always study both eyes together, and wherever we find one eye is normal and the other eye is abnormal, this means both eyes are abnormal. In our case, the left eye seems to be an early stage of keratoconus; this is obvious when we look at the elevation back map. On the other hand, whenever we see abnormal findings in the topography of any patient, it is better to do topography to his/her father, mother, brothers or sisters. That is because there may be some relatives with keratoconus in early stages with no complaints or vice versa, as we are going to see in the next case study.

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CASE 5: SUSPECTED CASE

A 20-year-old male came with stable refractive error. His MR was:

Although as a sequence we should begin with the right eye topography, we are going to see the left eye topography first for educational purpose. Fig. 5.5A shows his left eye corneal topography (4 refractive maps).

The Qualifying Step

1.In a general look, the sagittal curvature map has a slightly irregular pattern oriented as oblique astigmatism. The anterior elevation map shows regular shape while the posterior map is slightly irregular. There is nothing suspicious in the thickness map in general.

2.Main page analysis reveals that the quality of the capture (QS) is not OK, but on repeating the capture the same quality remains, which indicates that the problem might be in the cornea itself. The K-readings in the central 3 mm are normal (44.8, 47.1) and the corneal astigmatism (the algebraic sum of anterior and posterior astigmatism) is also normal (-1.7 <-6). Q-value at the 6 mm circle of the cornea front is normal (-0.46). Corneal thickness at the thinnest location is normal (528) and has normal coordinates with pachy apex. There is also no significant difference in thickness between pachy apex and thinnest location.

Case Study 119

3.Studying each map:

•Corneal thickness map (Fig. 5.5B): The shape of this map is normal with a slight displacement of the thinnest location. The difference between the lower and upper points of the central 4 mm circle is 23 µ (red circles), which is normal.

•The sagittal curvature front (Fig. 5.5C): Shows a symmetrical bow tie, there is no skew (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 (Fig. 5.5C white circles).

•The elevation front map (Fig. 5.5D): Regular shape with normal values within the central 4 mm circle.

•The elevation back map (Fig. 5.5E): Slightly irregular shape with normal values within the central 4 mm circle. There are also some points where the difference between anterior and posterior values is >+5 µ.

P.S. In case of any irregularity or suspicious values on elevation maps with the BFS, it is recommended to see the elevation maps with Toric Ellipsoid float reference body; when the irregularities are due to corneal astigmatism, they will vanish, otherwise they stay when they are due to real corneal surface irregularity. The toric ellipsoid option eliminates the effect of corneal astigmatic slope on the elevation maps. This is important especially for the back surface where the subclinical keratoconus begins.

•The Keratometric power deviation map (KPD): Let us mention the importance of this map in this case. This map is calculated by excluding the effect of the

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anterior curvature power map from the true net power map, i.e. it represents the effect of the back surface of the cornea on the true net power map in every corneal point (Figure 5.5F).

The normal value at any point in this map should be <+0.75. Any value falling between +0.75 and +1.5 is doubtful and borderline, but it is not considered significant unless there is a corresponding posterior elevation. Any value more than +1.5 is abnormal, especially if it is in the inferior half of the map, or if there is a corresponding elevation at the back elevation map.

To understand the meaning of this map, let us imagine the back surface of a cornea with its elevations and depressions. The depressions are protrusions towards the anterior chamber, and the elevations are protrusions towardsthefrontsurfaceofthecornea,i.e.concavitieswhich appear on this map with values more positive than other areas. So, when we look at the illustration in Fig. 5.5G, we can see the concave marked area, which holds either the risk of posterior keratoconus, or the possibility of postoperative out bulging of the posterior corneal surface. The significance of this map becomes more obvious when compared with the posterior tangential curvature map, which displays the irregularity more clearly, and with the posterior elevation map, which displays corresponding elevations. As we see in our case (Fig. 5.5F), there are many pointsonthismapwithabnormalvalues.Thisisanindicator of irregular posterior surface, which brings to our mind the fear of very early keratoconus.

•The Topometric map (Fig. 5.5H red circle): Both the average vertical value and inferior value are abnormal.