Ординатура / Офтальмология / Английские материалы / Step by Step Reading Pentacam Topography (Basics and Case Study Series)_Sinjab_2010
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Case Study 91 
Fig. 5.3D: The elevation front map. Irregular shape with tongue-like extension, but with normal values.
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Fig. 5.3E: The elevation back map. Irregular shape with tongue-like extensionandabnormalvaluesgivingtheimpressionofcone-likeshape (arrow).
Case Study 93 
Fig. 5.3F: The Topometric map. Normal values (arrows).
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Fig. 5.3G: The keratoconus indices page. The curve lines are within the normal range, but they deviate before the 6 mm circle (red arrows). The average is abnormal (1.2) and the ABR is also abnormal.
Case Study 95 
•The Topometric map (Fig. 5.3F red arrows): Both the average vertical value and the lower value are normal (<-0.55).
•The keratoconus indices page (Fig. 5.3G): Although the curve lines are within the normal range, they deviate before the 6 mm circle (red arrows). The average is abnormal (1.2). One of the irregularity indices is displayed in red because of the slight irregularity of the anterior corneal surface. It is the corneal aberration coefficient factor (ABR), but there is no risk in treating the cornea with ABR less than 2.5.
The Quantifying Step
In the given example, to correct the refractive error of the right eye, we have to look at four important figures: the K- readings, the thickness at the thinnest location, Q-value and pupil center coordinates.
1.K-readings: Because the patient is hyperopic, we have to consider the steepest K, here is 45.4 dpt. The spherical refractive error is +5.5 dpt, this means after correction the steep K will increase by: +5.5 × 1 = 5.5 dpt, therefore the postoperative steep K will be = 45.4 + 5.5 = 50.9 dpt, which is very abnormal. We have to remember always when treating hyperopia that the steep K must not end up with more than 48 dpt. So, we can correct in this case only about +2.5 dpt (in case of good corneal characteristics).
2.Thickness: The hyperopic laser profile ablates the periphery of the cornea in order to steepen the central part depending on corneal biomechanics. Therefore, the peripheral thickness is the concerned part here.
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3.Q-value and pupil center coordinates: Correcting the +6 dpt leads to very negative Q-value, which means very prolate cornea. On the other hand, we have to consider angle kappa when treating hyperopia (this fully explained in my previous book). For these two important reasons, we should use the customized topography-guided ablation profile to conserve a normal Q-value and to compensate for angle kappa.
The Scoring Step and Discussion
Although our case here falls within score 2, which means low relative risk, I would not proceed with the operation. There are some reasons for that:
1.The K readings allow for +2.5 dpt correction only, which is not accepted by the patient.
2.The thickness map shows cone-like appearance and more than 30 µ difference between the two concerning points.
3.The thinnest location coordinates show abnormal displacement.
4.The posterior elevation map shows very high elevations.
5.The average of the progression index is 1.2, which is usually abnormal.
6.The shape of the red curves is suspicious.
All these findings are –at least in my opinion—sufficient
to postpone the operation; because of the very high risk of cone-like formation postoperatively. We can think about other treatment modalities such as phakic IOLs.
Case Study 97 
CASE 4: ANISOMETROPIA
A 34-year-old female came with stable refractive error. Her MR was:
Eye |
SPH |
CYL |
AXIS |
|
OD |
-6.00 |
-1.75 |
45 |
|
OS |
-2.00 |
-0.50 |
150 |
We will study the left eye first for educational purposes. Fig. 5.4A shows her left eye corneal topography (4 refractive maps).
The Qualifying Step
1.In a general look, the sagittal curvature front map has a slightly irregular pattern oriented as with-the-rule astigmatism. The elevation maps show irregular shapes more obvious on the posterior map. There is nothing suspicious in the thickness map in general.
2.Main page analysis reveals that the quality of the capture (QS) is OK. The K-readings in the central 3 mm are normal (42.1, 42.9) and the corneal astigmatism (the algebraic sum of anterior and posterior astigmatism) is also normal (-0.5 <-6). Q-value at the 6 mm circle of the cornea front is normal (-0.31). Corneal thickness at the thinnest location is normal (568) and has normal coordinates with pachy apex. There is also no significant difference in thickness between pachy apex and thinnest location.
3.Studying each map:
•Corneal thickness map (Fig. 5.4B): The shape of this map is normal with slight displacement of the
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thinnest location. The difference between the lower and upper points of the central 4 mm circle (superiorinferior difference) is 34 µ (red circles), which is slightly abnormal but not suspicious.
•The sagittal curvature front map (Fig. 5.4C): Asymmetrical bow tie/inferior steep (AB/IS). There is skew (angulation) between the lower and upper axes of the pattern, but this skew is about 10°, which is within normal limits. The difference between the upper and lower points of the 4 mm circle is less than 1.5 dpt (Fig. 5.4D red circles).
•The elevation front map (Fig. 5.4E): Irregular shape with tongue like extension, but the values within the central 4 mm circle are still within the normal range.
•The elevation back map (Fig. 5.4F): Irregular shape with abnormal 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 Topometric map (Fig. 5.4G): The average vertical value is normal but the lower value is not (red circle).
Case Study 99 
•The keratoconus indices page (Fig. 5.4H): The curve lines are within the normal range, no deviation before the 6 mm circle. The average is normal (0.9). One of the irregularity indices is displayed in red because of the slight irregularity of the anterior corneal
surface. It is the corneal aberration coefficient factor (ABR), but there is no risk in treating the cornea with ABR less than 2.5.
Now before moving to the Quantifying step, we should ask ourselves the following questions:
1.What is the reason behind anisometropia that the patient has?
2.What about the other eye?
Let us look at the right eye topography (Fig. 5.4I).
The Qualifying Step
1.In a general look, the sagittal curvature map has a clear asymmetrical pattern oriented as with-the-rule astigmatism. The posterior elevation map shows suspicious numbers. 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 and on repeating the capture the same QS appears, which means a problem in the cornea itself. The K-readings in the central 3 mm are normal (43.6, 45.7) and the corneal astigmatism (the algebraic sum of anterior and posterior astigmatism) is also normal (-1.75 <-6). Q-value at the 6mm circle of the cornea front is slightly high (-0.62). Corneal thickness at the thinnest location is normal (542) and has normal
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coordinates with pachy apex. There is also no significant difference in thickness between pachy apex and thinnest location.
3.Studying each map:
•Corneal thickness map (Fig. 5.4J): The shape of this map is normal. The difference between the lower and upper points of the central 4 mm circle is <30 µ (red circles).
•The sagittal curvature front map (Fig. 5.4K): Asymmetrical bow tie/inferior steep with angulation (AB/SRAX): as you see in this picture, the pattern is inferior steep and the difference between the upper and lower points of the 4 mm circle is 4.5, which is more than 1.5 dpt (see also Fig. 5.5L white circles), and the angle between axes of the segments according to SRAX low is more than 22°.
•The elevation front map (Fig. 5.4M): Shows irregular shape with tongue-like extension, but the values within the central 4 mm circle are still within the normal range.
•The elevation back map (Fig. 5.4N): Shows irregular shape with abnormal values within the central 4 mm circle. There are also some points where the difference between anterior and posterior values is >+5 µ.
•The Topometric map (Fig. 5.4O red circles): As you see, both the average vertical value and the inferior value are abnormal (the average vertical at 7 mm is -0.66 and the inferior value is -0.95 with very big difference between the inferior and superior values on the vertical meridian).