Pentacam analysis

A brief view of how to read a pentacam scans

1. Pentacam Analysis Dr Nikhil R P MBBS, MS, DNB, (FPRS)

2. QUAD MAP ANALYSIS PARAMETERS: QS : OK ( Abnormal: Data gaps/ Fix / Model ) Q- value: Normal  -1 to 0 ( ideal is -0.26- Least spherical ablation, myopic photoablation , after RK ) 0 Sphere >0 Oblate cornea <-1 Hyperprolate / prolate ( KC, Hyperopic phototablation K1 ( kf )  K flat. Normal - >34D , measured in 3mm zone K2( Ks)  Steep K. Normal <49D Km ( K- Avg )  Mean curvature of ant surface Km< 40 D  Free Flap complication may occur Km> 46 D  Button hole complication may occur Kmax  Maximum curvature power of whole anterior surface Normal  49D Kmax difference b/w 2 eyes  <2D Kmax-K2 diff in same eye <1D If difference >1D, Kmax to be used instead of K2 Astigmatism  SimK ( K2-K1) within 3mm zone To be compared with Manifest Refraction Pachy apex(.) : Thickness at corneal apex. “x” & “y” co-ordinates are there for location Pupil centre (+): Corneal thickness corresponding to pupil centre Normal : “x” is < 200µm ( or <5 deg ) Important to evaluate ANGLE KAPPA . Pupil Diameter : Photopic , Mesopic , Scotopic size. 11. Thinnest Location(TL) (o): Thickness & location of thinnest point of cornea < 470 µm in normal & < 500µm in abnormal topo Normal diff b/w both eyes  < 30 µm Diff b/w TL & Pachy apex  < 10 µm “y” co-ordinate: Normal : <-0.5mm ABNORMAL : <0.5/0.5 to 1/>1mm “-” sign indicates Inferior displacement of TL Safe parameters for ICL : Anterior chamber depth (ACD)> 3mm Anterior chamber Angle ( ACA)> 30 deg Anterior chamber volume( ACV)> 100mm3 ACD<24 deg , ACD <2.1mm, ACV < 100mm3  Risk of angle closure glaucoma.

3. QUAD MAP ANALYSIS ANTERIOR SAGITTAL MAP: Anterior surface dioptric power Steep areas  HOT colors – RED/ ORANGE Flat areas COLD Colors – GREEN/ BLUE Parameters to be read on 5mm circle Normal pattern is Symmetric bowtie (SB) Normal I-S difference < 1.5D . Inferior ( higher value than superior) SB- REGULAR ASTIGMATISM ( WTR / ATR ) +/- 15 degree of vertical/ horizontal meridian. Qblique astigmatism  SB is neither vertical or horizontal ABNORMAL PATTERNS: AB/SRAX > 22 ( angle between two lobes) AB/SS: SS- IS> 2.5D AB/IS: IS- SS> 1.5D Butterfly and Claw pattern : PMD Enantiomorphism: Sagittal map appears mirror shaped of that in other eye

4. QUAD MAP ANALYSIS ELEVATION MAPS : The patient’s cornea is compared to normative age related data base and the elevation/depressions are calculated in both ANTERIOR (A) and POSTERIOR (B) surface. Reference surface ( RS ) : 8mm IDEAL ELEVATIONS  (+) , DEPRESSIONS (-) Best Fit Sphere ( BFS )  Quantifies the shape measured Best Fit Toric Ellipsoid ( BFTE )  Quantifies parameters of that surface SHAPE: (BFS FLOAT Mode) : Normal : Symmetric hour glass ( WTR ) – Regular astigmatism ABNORMAL : Skewed hour glass: Seen in large angle kappa, Misalignment during capture, distorted cornea Tongue- Like extention & Irregular hourglass : distorted cornea Isolated Island : Distorted cornea PARAMETERS ( BFTE Mode): Highest plus within 5mm zone Cone Location : Can be central ( 3mm)/ paracentral ( 3-5mm)/ peripheral ( >5mm) If cone is peripheral  KISSING BIRDS SIGN A B µm Anterior Posterior BFTE >12 >15 BFS: Myopic 7.7 17.7 BFS: Hyperopic 6.5 27.8 Hour G lass Skewed hour glass Isolated Island KISSING BIRDS SIGN

5. QUAD MAP ANALYSIS PACHYMETRY MAPS: Corneal apex (+) Thinnest Location (o) Difference b/w Sup & Inf points ( < 30 µm ) Normal map : Concentric shape ABNORMAL pattern: Horizontal displacement of TL Dome Shaped: Vertically displaced TL Bell Shaped : Thin band of cornea inferiorly (PMD). Keratoglobus : Generalized thinning Horizontal displacement of TL Vertical displacement of TL Bell Shaped : PMD Keratoglobus Quick Slope S Shape Flat curve Inverted shape Details of CTSP & PTI in other slide

6. INDICES  Helps in differentiating normal corneas from KC. HIGHLY SENSITIVE Index of Surface Variance ( ISV ): Measured as standard deviation of individual sagittal radii from mean curvature ISV > 37 YELLOW  ABNORMAL ISV> 41 RED  PATHOLOGICAL Index of Vertical Symmetry ( IVA ): “mm” Mean difference b/w Superior & Inferior curvature IVA >0.28 ABNORMAL IVA >0.32 PATHOLOGICAL Keratoconus Index ( KI ): Ratio b/w mean radius values in upper half & Lower half of cornea KI > 1.07 ABNORMAL Central Keratoconus Index ( CKI ) : Ratio b/w mean radius of curvature in a peripheral placido ring & mean radius of curvature of central ring CKI > 1.03 ABNORMAL Index of Height Asymmetry ( IHA ): “µm” Mean difference b/w corneal elevation in superior hemisphere & inferior hemisphere in horizontal meridian IHA > 19  ABNORMAL IHA > 21  PATHOLOGICAL Index of Height Decenteration ( IHD ) : “µm” Measures vertical decenteration of elevation data on a ring with radius of 3mm IHD> 0.014 ABNORMAL IHD > 0.016 PATHOLOGICAL REFRACTIVE ANALYSIS 8. Topographic Keratoconus Index ( TKC ): Negative- 0 Possible- 0.5 Positive- 1 Abnormal- 2 Post – surgery- 3 R min : Denotes max steepness of cone Smallest radius of sagittal/ axial corneal curvature Rmin < 6.71mm ABNORMAL

7. BELIN AMBROSIO DISPLAY BAD_D A Elevation maps Enhanced/ Exclusion maps Difference maps B CTSP PTI Kmax , Q value, QS PPI, ART max C Parameters: Df , Db , Dp , Dt , Da Final D Multivariate Index Integrates Anterior Elevation, Posterior Elevation, Pachymetry Data Complete Overview of corneal shape Quick screening tool Standard Elevation maps: (A) Radius of BFS is noted eg : r= 7.7 float Diameter of zone used to complete the BFS dia =8mm Represents Anterior and Posterior elevation data relative to standard BFS Enhanced / Exclusion maps: (B) Anterior and Posterior elevation data relative to BFS located outside 4mm circle is calculated with EXCLUSION of central 4mm zone. This zone cant be modified. Exclusion zone is determined by the magnitude of astigmatism Difference maps: (C) Diff b/w standard & Exclusion map µm Anterior Posterior GREEN <6 <8 Normal YELLOW 6-12 8-20 Suspicious RED >12 >20 KC A B C

8. BELIN AMBROSIO DISPLAY Df : Front Elevation Db : Back Elevation Dp : Pachymetry Progression Dt : Corneal thickness at thinnest location Da : Corneal thinnest displacement Final D : is calculated considering all 5 parameters. These parameters denote the STANDARD DEVIATION from the mean of normative database. Individual parameter may be RED/ YELLOW & the “final D” can be normal. D values (SD) < 1.6 SD WHITE Normal 1.6- 2.6 SD YELLOW Suspicious >2.6 SD RED KC Corneal thickness spatial profile ( CTSP ) : (A) Average progression from thinnest point to periphery NORMAL: Av: 0.8- 1.1 ABNORMALS: Quick slope : Red line leaves before 6mm . Avg > 1.1 ( FFKC ) S- Shape: Red curve has SHARP “S”. Avg > 1.1 ( FFKC ) Flat curve: Red curve takes straight curve. Avg <0.8 ( edematous cornea, Fuch’s dystrophy) Inverted curve: Red curve follows upward course. Avg <0.8 & minus value might be there. ( few cases of PMD) Percentage thickness increase ( PTI ) : (B) Percentage thickness index . It denoted % of progression Normal Avg : 0.8- 1.1 Avg α Fast transition Pachymetric Progression Index ( PPI ): Calculates change in corneal thickness overall 360 deg of cornea Progression value at each meridian from the thinnest point is defined as progression index PPI – Max: Meridian with Max pachymetric increase (0.85±0.18) PPI - Min : Meridian with Min pachymetric increase (0.58±0.30) PPI- Avg : Avg of all meridians (0.13±0.33) Ambrosio relational thickness : Ratio b/w thinnest point & PPI Distinguishes KC eyes from normal eyes ART Max, ART Min, ART Avg ART Max < 412 µm  KC A B

9. 13 POINT ALGORITHM : Point No. 1: The quality specification of the capture (QS); Point No. 2: The maximum keratometry (K) value; Point No. 3: The corneal thickness at the thinnest location; Point No. 4: The y (vertical) coordinate of the thinnest location ; Point No. 5: The corneal asphericity at the 6-mm optical zone (Q-value); Point No. 6: The shape and value of the anterior sagittal curvature map; Point No. 7: The shape and values of the anterior elevation map; Point No. 8: The shape and values of the posterior elevation map; Point No. 9: The shape and value of the pachymetry map; Point No. 10: The shape of the corneal thickness spatial profile (CTSP) and the average of thickness progression; Point No. 11: The amount and axis of topographic astigmatism measured by the total corneal refractive power and compared with the manifest astigmatism; and Point No 12: A comparison between the patient’s two eyes Point No 13: BAD Display, BAD parameters, PPI, ARTmax * Sinjab M, Step by Step, Reading Pentacam Topography

10. SUMMARY * Sinjab M, Step by Step, Reading Pentacam Topography

11. µm Anterior Posterior GREEN <6 <8 Normal YELLOW 6-12 8-20 Suspicious RED >12 >20 KC BAD_D Difference Maps D values (SD) < 1.6 SD WHITE Normal 1.6- 2.6 SD YELLOW Suspicious >2.6 SD RED KC BAD_D PARAMETERS including Final D Yellow- Abnormal Red- Pathological ISV (SD) >37 >41 IVA (mm) >0.28 >0.32 IHA ( µm) >19 >21 IHD ( µm) >0.014 >0.016 KI >1.07 Abnormal CKI >1.03 Abnormal Rmin <6.71mm Abnormal PPI- Avg 0.13±0.33 PPI- Min 0.58±0.30 PPI- Max 0.85±0.18 ART Max < 412 µm KC SUMMARY * Sinjab M, Step by Step, Reading Pentacam Topography

12. CBI- Corvis Biomechanical Index Comprehensive biomechanical screening and keratoconus detection Based on corneal thickness profile and deformation parameters Developed by Riccardo and Paolo Vinciguerra from Italy Normal <0.5 Advantages: A higher safety, as patients at risk for developing ectasia after LASIK can be excluded A higher efficiency, as surgery can be performed when patients have a stiff and stable cornea * Vinciguerra , et al., J Refract Surg. 2016

13. TBI – Tomographic Biomechanical Index Integration of Pentacam data for a combined tomographic and biomechanical analysis TBI is calculated using an artificial intelligence approach to optimize ectasia detection By combining tomographic data with biomechanical data, one can further improve sensitivity and specificity in the detection of patients with a significant risk for developing ectasia after refractive surgery Normal < 0.29

14. Cut off values for border line cases/KC I-S >1.4 BAD-D >1.6 CBI >0.5 TBI > 0.29 CCT<480 µm * Vinciguerra , et al., J Refract Surg. 2016 * Ambrosio et al., J Refract Surg. 2017

15. A simplified algorithm to aid in decision making regarding suitability for combined refractive surgery with CXL * Brar S, Gautam M, Sute SS, Ganesh S. Refractive surgery with simultaneous collagen cross-linking for borderline corneas - A review of different techniques, their protocols and clinical outcomes. Indian J Ophthalmol . 2020 Dec;68(12):2744-2756. doi : 10.4103/ijo.IJO_1709_20. PMID: 33229650.

16. Classification systems for KC Severity : Mild, Moderate, Severe based on K- readings. Cone: Round or nipple, Oval , Globus Amsler Krumeich et al., : Stage 1, 2, 3, 4 Rabinowitz /Rasheed’s KISA % : KISA %= Central K x I-S Asymmetry x AST (degree of regular corneal astigmatism) x SRAX x 100/300. Normal : <50 % KC Suspect: 60-100% KC: >100% Belin ABCD classification system/ Progression Display: A,B & C- are autogenerated . A: Anterior Radius of curvature in 3 mm B: Posterior Radius of curvature in 3mm C: Thinnest pachymetry in microns D : Distance Best Corrected Visual Acuity ( to be entered )

17. Amsler Krumeich Staging

18. * Belin MW, Kundu G, Shetty N, Gupta K, Mullick R, Thakur P. ABCD: A new classification for keratoconus . Indian J Ophthalmol 2020;68:2831-4

19. Thank you