part 1 sinjab - official escrs · ... aquick%guideto%reading%corneal%tomography% ......

ESCRS 2015, IC-‐43 Course. How to Improve Your Refractive Outcomes by Skillful Mazen M. Sinjab, MD, PhD, FRCOphth(London)

www.mazensinjab.com www.sinjabacademy.com

Part One: A Quick Guide to Reading Corneal Tomography

First: Check 12 points on the Pentacam (Figures 1 and 2):

1. Quality specifications (QS): should be OK.

2. Maximum K-‐reading (K-‐Max): should be ≤ 47.2D.

3. Thickness at the thinnest location (TL): should be ≥ 470μm

4. Y-‐coordinate of the TL: should be ≤ -‐0.50mm.

5. Amount and axis of corneal astigmatism to be compared with the manifest

astigmatism: the difference should be ≤ 1.0D in amount and ≤15° in axis.

6. Q-‐Value: should be 0.0 to -‐1.0.

7. Anterior Curvature Map: shapes are classified into:

a. Symmetric: including the symmetric bowtie (SB), round, and oval

patterns. To consider these as normal, K-‐Max should be ≤47.2D.

b. Asymmetric: including inferior steep (IS), asymmetric bowtie/inferior

steep (AB/IS), superior steep (SS), asymmetric bowtie/superior steep

(AB/SS). To consider these as normal, the difference in K-‐readings

between the inferior and superior opposing points should be <1.5D.

c. Skewed: including symmetric bowtie with skewed radial axis

(SB/SRAX), and asymmetric bowtie with skewed radial axis (AB/SRAX).

To consider these as normal, the SRAX should be ≤ 22°.

d. Special shapes: including butterfly, claw, vertical D and irregular.

8. Anterior Elevation Map: It will be studied just like the posterior one (see

below).

9. Posterior Elevation Map:

a. Shapes are studied using the best fit sphere float mode (BFS) and

classified into:

i. Symmetric: including central island when there is insignificant

corneal astigmatism, if any; and hourglass when there is

corneal astigmatism.



ii. Asymmetric: including skewed, tongue–like, and irregular

patterns.

b. Values are either studied by using:

i. The best fit toric ellipsoid float mode (BFTE), where the normal

values, within the central 5mm zone, are ≤ 12μm and ≤15μm

for the anterior and posterior elevation maps, respectively.

ii. The BFS, where the normal values corresponding to the

thinnest location are shown in (Table 1) for 3SD.

10. The Pachymetry Map: shapes are classified into:

a. Symmetric: It is considered as normal when the difference in

thickness between the inferior and superior opposing points is

≤30μm.

b. Asymmetric: including horizontally displaced, dome, bell, and globus

patterns.

11. The Corneal Thickness Spatial Profile: shapes are classified into:

a. Normal: the red curves follow the slope and the average is < 1.2.

b. Quick: the red curves leave the slope before the 6mm zone.

c. S-‐shape.

d. Flat.

e. Inverted.

12. The Intereye Corneal Symmetry: Table 2 shows the cutoff points of the 5

parameters.

Second: Exclude pathologies:

In case of any asymmetry or abnormality, exclude the followings:

1. Contact lens usage: give a period of at least one week after the contact lenses

have been stopped.

2. Misalignment or large angle kappa.

3. Corneal opacities, scars or other pathologies.



4. Dry eye or excess tears.

5. Previous corneal surgeries.

Third: Rank the Tomography:

It can be ranked into high risk and moderate risk as shown in table 3.

Fourth: Take the right decision:

-‐ In case of one high risk factor or two moderate risk factors in the same eye,

keratorefractive procedure should be avoided in both eyes.

-‐ In case of one moderate risk factor in one or both eyes, go either for surface

ablation or for observing the patient after couple of months.

For further reading:

1. Corneal Topography in Clinical Practice 2nd Ed. 2011. Jaypee Highlight.

2. Step By Step Reading Pentacam Topography 2nd Ed. 2014. Jaypee Highlight.

3. Five Steps to Start Your Refractive Surgery. 2014. Jaypee Highlight.



Figure 1

Figure 2



Anterior Posterior

Myopic ≤ 8 ≤ 18

Hyperopic ≤ 7 ≤ 28 Table 1

Table 2. Reference: Galletti JD et al. Corneal Asymmetry Analysis by Pentacam

Scheimpflug Tomography for Keratoconus Diagnosis. J Refract Surg. 2015;31(2):116-‐23.

Table 3

part 1 sinjab - official escrs · ... aquick%guideto%reading%corneal%tomography% ......

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