Pentacam and Pentacam HR Interpretation Guideline 3rd Edition Sept 2015

Foreword We thank you for the trust you have put in us by purchasing this OCULUS instrument. In doing so you have chosen a modern, sophisticated product which was manufactured and tested according to strict quality standards. Our company has been doing business for over 120 years. Today OCULUS is a mediumsized company focused entirely on developing and manufacturing advanced and innovative instruments for examinations and surgery on the eye to help ophthalmologists, optometrists and opticians in their routine work. The Pentacam® is based on the Scheimpflug principle, which generates precise and sharp images of the anterior eye segment. This instrument takes extremely accurate measurements and is easy to use. If you have questions or desire further informations on this product, please turn to your OCULUS representative or directly to OCULUS. We will be glad to help you. OCULUS Optikgeräte GmbH

Note OCULUS Optikgeräte GmbH wishes to emphasize that the user bears full responsibility for the correctness of data measured, calculated or displayed using the Pentacam®. The manufacturer will not accept claims based on erroneous data or misinterpretation. This Interpretation Guide can no more than assist in the interpretation of examination data generated by the Pentacam®. In making a diagnosis physicians should not neglect to consider other medical information which may be obtainable through other methods such as slit lamp examination or ultrasound biomicroscopy, judiciously weighing the significance of each. This Interpretation Guide should be seen as a complement to the User Guide and Instruction Manual. The current version of these documents and the Interpretation Guide are on every Pentacam® Software USB drive and should be read by all users prior to use.

OCULUS has been certified according to DIN EN ISO 13485 and therefore sets high quality standards in the development, production, quality assurance and servicing of its entire product range.

Table of contents

Table of contents 1 Introduction...5 2 Description of the unit and general remarks...5 3 Differences between the various topography maps of Pentacam®...6-11 3.1 Calculation of corneal power...6 3.2 Sagittal power map (also called axial power map)...7 3.3 Refractive power map...8 3.4 True Net Power...9 3.5 Equivalent Keratometer Readings power map...10 3.6 Total Cornea Refractive Power map...11 4 Recommended settings and color maps, displays and values...12-14 4.1 Recommended settings...12 4.2 Recommended color maps, displays and values...13 4.2.1 Screening for corneal refractive surgery...13 4.2.2 Pre-op screening for iris fixated phakic IOL implantation...13 4.2.3 Glaucoma screening...14 4.2.4 Cataract surgery and IOL calculation for virgin and post refractive corneas...14 5 Differences between Placido and elevation-derived curvature maps by Prof. Michael W. Belin...15-19 5.1 Keratoconus in OD and OS?...15 5.2 Form fruste keratoconus?...18 6 Fast Screening Report as a first step in examining a patient and evaluating one’s findings by Ina Conrad-Hengerer, MD... 20-27 6.1 Case 1: Unilateral high astigmatism with suspicion of bilateral keratoconus...20 6.2 Case 2: Fuchs’ dystrophy with DMEK cataract surgery – progress evaluation...23 6.3 Case 3: Corneal injury sustained from an eye drop bottle after cataract surgery...26 7 Refractive Power Distribution display by Ina Conrad-Hengerer, MD...28-30 7.1 Visual acuity impairment during nighttime driving with distance spectacles – nocturnal myopia?... 28 8 Corneal ectasia...31-35 8.1 Case 1: Ectasia after radial keratotomy by Prof. Renato Ambrósio Jr ...31 8.2 Case 2: Ectasia after LASIK? by Prof. Michael W. Belin...33 9 Glaucoma...36-46 9.1 Case 1: General screening by Tobias H. Neuhann, MD...36 9.2 Case 2: YAG laser iridectomy by Eduardo Viteri, MD...37 9.3 Screening for narrow angles by Dilraj S. Grewal, MD...39 9.3.1 Case 1...39 9.3.2 Case 2...42 9.4 Evaluating the anterior segment in phacomorphic glaucoma by Dilraj S. Grewal, MD...45

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Table of contents

10 Screening for refractive surgery by Prof. Michael W. Belin...47-63 10.1 Screening parameters, 4 Maps Refractive display...47 10.1.1 Suggested installation settings...47 10.1.2 Proposed screening parameters...48 10.1.3 Strategy on how to go through the exams...49 10.2 Normal, astigmatic cornea...49 10.3 Astigmatism on the posterior cornea...52 10.4 Spherical cornea...53 10.5 Thin spherical cornea...54 10.6 Thin cornea...55 10.7 Borderline case of keratoconus...56 10.8 Displaced apex... 57 10.9 Pellucid marginal degeneration...58 10.10 Asymmetric keratoconus...59 10.11 Keratoconus with false negative findings on curvature map...61 10.12 Keratoconus greater in OD than OS...62 10.13 Classic keratoconus...63 11 Corneal Thickness Spatial Profile by Prof. Renato Ambrósio Jr ...64-79 11.1 Screening for ectasia by Prof. Renato Ambrósio Jr, Marcela Q. Salomão, MD...67 11.2 Case 1: Fuchs’ dystrophy by Prof. Renato Ambrósio Jr, Marcela Q. Salomão, MD...72 11.3  Case 2: Ocular hypertension by Prof. Renato Ambrósio Jr, Marcela Q. Salomão, MD... 74 11.4 Case 3: Early Fuchs’ dystrophy with glaucoma by Prof. Renato Ambrósio Jr, Marcela Q. Salomão, MD... 76 11.5 Screening parameters by Prof. Renato Ambrósio Jr ...79 12 Belin/Ambrósio Enhanced Ectasia Display...80-102 12.1 Why elevation is displayed by Prof. Michael W. Belin...80 12.2 Simplifying preoperative keratoconus screening by Prof. Michael W. Belin, Prof. Renato Ambrósio Jr, Andreas Steinmüller, MSc...88 12.3 Interpretation of the Belin/Ambrósio Enhanced Ectasia Display...94 12.4 Pachymetry evaluation...96 12.5 Ectasia susceptibility revealed by the Belin/Ambrósio Enhanced Ectasia Display...96 12.6 Early ectasia with asymmetric keratoconus by Prof. Renato Ambrósio Jr, Fernando Faria-Correia, MD, Allan Luz, MD...100 13 Locating the cone by Prof. Michael W. Belin...102 14 The corneal densitometry screen, Sorcha S. Ní Dhubhghaill, MB, PhD, Jos J. Rozema, MSc, PhD... 103-107 14.1 Keratic precipitates...104 14.2 Position and depth of INTACS® rings...106 14.3 DSAEK with specks at the interface...107 15 Using Pentacam® technology to evaluate corneal scars, planning and documenting surgery outcomes by Arun C. Gulani, MD, MS... 108-116 15.1 Case 1: Corneal scar with RK incisions and cataract...112 15.2 Case 2: Keratoconus with congenital cataract, high myopia and high astigmatism...115 2

Table of contents

16 INTACS® implantation...117-122 16.1 Case 1: by Prof. Michael W. Belin...117 16.2 Case 2: INTACS® after PRK by Alain-Nicolas Gilg, MD... 119 16.3 Case 3: INTACS® & crosslinking by Prof. Renato Ambrósio Jr, Fernando Faria-Correia, MD, Allan Luz, MD... 121 17 Holladay Report & Holladay EKR65 Detail Report by Jack T. Holladay, MD...123-136 17.1 Holladay Report...123 17.2 Holladay EKR65 Detail Report...129 17.3 Case 1: Holladay Report & Holladay EKR65 Detail Report of a normal exam...130 17.4 Case 2: Holladay Report & Holladay EKR65 Detail Report of a keratoconus exam...133 17.5 Case 3: Holladay Report & Holladay EKR65 Detail Report of a post LASIK exam...135 18 Corneal tomographic analysis is essential before cataract surgery 4 steps in screening candidates for premium IOLs by Prof. Naoyuki Maeda... 137-140 18.1 Corneal topography for selecting premium IOLs...137 18.2 Step 1: Evaluation of corneal irregular astigmatism...140 18.3 Step 2: Detection of abnormal corneal shape... 140 18.4 Step 3: Evaluation of corneal spherical aberration...140 18.5 Step 4: Evaluation of corneal cylinder...140 19 Dependency of effective phacoemulsification time on Pentacam® Nucleus Staging (PNS) by Mehdi Shajari, MD, Wolfgang Mayer, MD, Prof. Thomas Kohnen...141-142 19.1 Introduction...141 19.2 Case 1: Low PNS and low EPT...142 19.3 Case 2: High PNS and high EPT...142 20 Total corneal astigmatism for toric IOL by Giacomo Savini, MD...143-148 20.1 Case 1: Cylinder overcorrection from measurement of keratometric astigmatism in an eye with WTRA...144 20.2 Case 2: Cylinder undercorrection from measurement of keratometric astigmatism in an eye with ATRA...146 20.3 Case 3: Cylinder overcorrection from measurement of keratometric astigmatism...147 21 Overview about IOL power calculation formulas for different eye types... 149 22 Phakic IOL implantation ...150-160 22.1 Manual pre-op simulation and post-op control by Eduardo Viteri, MD...150 22.1.1 Pre-operative evaluation...150 22.1.2 Post-operative evaluation...151 22.2 3D pIOL Simulation Software and Aging Prediction by Prof. Burkhard Dick, Sabine Buchner, Optometrist...151 22.2.1 Myopic Artisan/Verisyse, 6/8.5 mm...151 22.2.2 Toric Artisan/Verisyse, 5/8.5 mm...155 22.3 Patient selection criteria by Prof. Burkhard Dick, Sabine Buchner, Optometrist...157 22.4 Case example of ectasia after LASIK, crosslinking and pIOL implantation by Prof. Renato Ambrósio Jr, Fernando Faria-Correia, MD, Allan Luz, MD...159

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Table of contents

23 Case reports from daily practice...161-172 23.1 Case 1: Cortical cataract by Tobias H. Neuhann, MD...161 23.2 Case 2: Remove sutures after corneal transplant surgery? by Tobias H. Neuhann, MD... 162 23.3 Case 3: Keratoconus and cataract by Tobias H. Neuhann, MD...163 23.4 Case 4: Corneal infiltrate by Prof. Renato Ambrósio Jr ...166 23.5 Case 5: Incisional edema, by Prof. Renato Ambrósio Jr ...168 23.6 Case 6: Corneal thinning after herpetic keratitis by Prof. Renato Ambrósio Jr ...169 23.7 Case 7: Epithelial ingrowth after keratomileusis in situ by Prof. Renato Ambrósio Jr ... 171 24 Scheimpflug and slit lamp images...173-178 24.1 Corneal dystrophy...173 24.2 Congenital anterior pyramid cataract...174 24.3 Posterior capsular cataract...175 24.4 Nuclear cataract...176 24.5 Posterior synechia...177 24.6 Pterygium...178 25 Orthokeratology, general screening by Alain-Nicolas Gilg, MD...179-181 26 Important studies and case reports...182-198 26.1 Refractive studies...182 26.2 Case reports...191 26.3 Cataract studies...191 26.4 Case reports...196 26.5 Glaucoma studies...196 26.6 Case reports...198 27 References... 199-201 28 List of illustrations...202-205 29 Tables directory...207 30 List of abbreviations...208-209 31 Authors and contact addresses...210-211

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1 Introduction 2 Description of the unit and general remarks

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Introduction

This guide is intended to assist Pentacam®/Pentacam® HR (referred to here as Pentacam®) users in interpreting the results and screens of the Pentacam®. We may not have covered everything which might be of interest, and we therefore ask anyone using the Pentacam® for their help in improving this guide step by step. Please forward us any cases or observations of particular interest, and we will be happy to incorporate them in this guide. This guide cannot, of course, replace the knowledge and experiences that only come from long years of medical studies and professional practice, but it will be of help in cases of doubt as well as to beginners. At the same time, since medical findings may also depend on the practitioner’s personal experience and perceptions, the individual patient’s history or the particular combination of instruments used, it is quite possible for results obtained by other means to differ from those shown in this guide yet be nonetheless valid.

2 Description of the unit and general remarks The OCULUS Pentacam® is a rotating Scheimpflug camera. The rotational measuring procedure generates Scheimpflug images in three dimensions, with the dot matrix fine-meshed in the centre due to the rotation. It takes a maximum of 2 seconds to generate a complete image of the anterior eye segment. Any eye movement is detected by a second camera and corrected for in the process. The Pentacam® calculates a 3D model of the anterior eye segment from as many as 25.000 (HR: 138.000) distinct elevation points. The topography and pachymetry of the entire anterior and posterior surface of the cornea from limbus to limbus are calculated and depicted. The analysis of the anterior eye segment includes a calculation of the chamber angle, chamber volume and chamber height and a manual measuring function that can be applied to any location in the anterior chamber of the eye. Images of the anterior and posterior surface of the cornea, the iris and the anterior and posterior surface of the lens are generated in a moveable virtual eye. The densitometry of the lens and cornea is automatically quantified. The Scheimpflug images taken during the examination are digitalized in the main unit, and all image data are transferred to the PC. When the examination is finished, the PC calculates a 3D virtual model of the anterior eye segment, from which all additional information is derived.

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Differences between the various topography maps of Pentacam®

3 Differences between the various topography maps of Pentacam® 3.1

Calculation of corneal power

Corneal Placido topographers measure geometrical corneal slope values. These values are converted into curvature values e.g. values of axial (sagittal) curvature or instantaneous (tangential) curvature which are initially given in mm. The Pentacam® measures geometrical height (elevation) values, which are likewise converted into values of axial (sagittal) or instantaneous (tangential) curvature and given in mm. These geometrical radius (mm) values are commonly converted it into refractive power values, which are given in diopters (D). This is normally done according the simple formula of D = (1.3375-1)*(1000)/Rmm. A. The refractive effect A sphere (sph) has the same radius of curvature at every point of its surface; however, due to the phenomenon of spherical aberration (SA) its refractive power is not the same everywhere. If the effect of SA is not taken into account, a corneal sphere with a radius of, say, 7.5 mm may be considered to have the same refractive power of 45 D at every point of its surface (assuming the keratometer calibration index of 1.3375, see below). Due to SA, however, the refractive power in the periphery is actually higher. The Pentacam® refractive maps, as they are called, are calculated on the basis of “Snell’s law” of refraction using precision ray tracing, thereby taking this effect into account. B. Inclusion of anterior/posterior surface By convention most keratometers use the refractive index of 1.3375 when calculating the dioptric power of the anterior radius; in doing so they assume the cornea to have a single refracting surface. However, it has been known for quite some time that this keratometric index is not the best approximation to the rather physiological power of the cornea. Due to the contribution of the posterior surface and the more rather refractive index of the cornea (n cornea = 1.376), the True Net Power of the cornea, calculated using thick lens models or high-precision ray tracing, is lower than the value reported by standard keratometry. The deviation between True Net Power and corneal power as determined by standard keratometry (Sim K’s) becomes even greater when dealing with corneas after excimer laser ablation (LASIK, LASEK and PRK) of the anterior surface. After refractive corneal surgery it is no longer possible to calculate corneal refractive power based only on the anterior surface, as the ratio between the anterior and posterior radius of the cornea has changed considerably. When the calcultio of the total corneal astigmatism comes into focus the effect of the posterior corneal surface cannot be disregarded anymore. Depending to the orientation of the anterior and posterior corneal kertometry the total corneal astigmatism can be over or underestimated and the axis of the total corneal astigmatism is influenced [1].

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Differences between the various topography maps of Pentacam®

C. The refractive index For historical reasons, most Placido topographers and keratometers use the refractive index of 1.3375 for calculating corneal refractive power. However, this refractive index is actually incorrect even for the untreated eye (n ≈ 1.332). It assumes the ratio between the anterior and posterior curvature of the cornea to be constant. Many intraocular lens (IOL) power calculation formulas use the incorrect ‘K-reading’, necessitating empirical correction to obtain the correct IOL power even in normal cases. Care should also be taken when using ‘K-readings’ from post-LASIK corneas or based on True Net Power or ray tracing, as the resultant D readings will be out of range for the applied IOL calculation formulas unless they are corrected for or converted into equivalent keratometer readings (EKR). Some modern formulas are able to deal with the rather measured curvatures of the front and back surface of the cornea, however. D. Location of the principal planes Calculation of corneal power by ray tracing involves sending parallel light through the cornea. It must take into account that each light beam is refracted according to the refractive index (1.376/1.336), the slope of the surfaces, and the exact location of refraction. This is necessary because the principal planes of the anterior and posterior surface differ slightly from one another due tocorneal thickness. The Pentacam® is able to measure the anterior as well as the posterior surface of the cornea. This allows further corrections to be made. The Pentacam® provides a number of different maps for predicting corneal power.

3.2

Sagittal power map (also called axial power map)

This is the common Placido style map with corneal power calculated using a refractive index of 1.3375 and the simple formula D = (1.3375-1)*(1000)/Rmm. It shows power values (Figure 1) similar to those of other Placido topographers.

Figure 1: Sagittal power map of a sphere, r= 8 mm

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Differences between the various topography maps of Pentacam®

3.3

Refractive power map

This map (Figure 3) uses only values from the anterior surface, but it also takes effect “A” (see above) into account. It calculates corneal power according to Snell’s law of refraction assuming a refractive index of 1.3375 to convert curvature into refractive power (Figure 2). This is a map that other Placido topographers also may show because it only considers the anterior surface.

Figure 2: Snell´s law of refraction

Figure 3: Refractive power map of a sphere, r = 8 mm

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3.4

Differences between the various topography maps of Pentacam®

True Net Power

This map (Figure 4) shows the optical power of the cornea based on two different refractive indices, one for the anterior (corneal tissue: 1.376) and one for the posterior surface (aqueous humour: 1.336), as well as the sagittal curvature of each. These results are aggregated. The True Net Power map thus takes effects “A” and "B" into account. The underlying equation is:

TrueNet Power =

1,376 -1 rant_surface

*1000 +

1,336 -1,376

1000 rpost_surface *

Figure 4: True Net Power map calculated by two spheric surfaces of anterior r = 8 mm and posterior r = 6.58 mm

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Differences between the various topography maps of Pentacam®

3.5

Equivalent Keratometer Readings power map

This map (Figure 5) was designed to take into account the refractive effects of both the anterior and the posterior surface. Another requirement was that it should output power values which in normal cases (no Lasik) would be comparable with simulated K (SimK) values, which are usually derived from sagittal curvature map. Its output is therefore also referred to as Equivalent Keratometer Readings (EKR). It calculates power according to Snell’s law using the refractive indices of corneal tissue and aqueous humour and aggregating the values for anterior and posterior power. Then the output is shifted such that for a normal eye (posterior corneal radius 82% of anterior corneal radius) its values (EKR) are identical to those of SimK readings from a sagittal map. In other words, the EKR map is corrected by adding the error that would be created by a refractive index of 1.3375 in a sagittal map. In this way it provides equivalent K-values (EKR) that can be used in IOL formulas that correct for n=1.3375. The EKR map thus takes into account effects "A", "B" and "C".

Figure 5: EKR power map calculated by twospheric surfaces of anterior r = 8 mm and posterior r = 6.58 mm

The study to validate the method was conducted using the Holladay 2 formula. Here it was determined that after LASIK the best correlation with the traditional method, with a mean prediction error of -0.06 D ± 0.56 D, is obtained using a mean zonal EKR for the 4.5 mm zone. For post-RK patients, the mean prediction error is –0.04 D ± 0.94 D [2].

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3.6

Differences between the various topography maps of Pentacam®

Total Cornea Refractive Power map

This map (Figure 7) uses ray tracing to calculate the refractive power of the cornea. It takes into account how parallel light beams are refracted according to the relevant refractive indices (1.376 and 1.336), the exact location of refraction and the slope of the surfaces. The location of refraction is a determinant of surface slope, since the anterior and posterior surfaces have slightly differing principal planes due to corneal thickness. In this way the map takes effects "A", "B", "C" and "D" into account. Its results are more realistic than any other, but they will deviate from normal (sagittal) SimK values so they cannot be used in conventional IOL formulas.

Figure 6: Calculation of power according to Snell´s law taking the different refractive indices and the different principal planes of the anterior and posterior corneal surfaces into account

Figure 7: Total Corneal Refractive Power map calculated by two spheric surfaces of anterior r = 8 mm and posterior r = 6.58 mm and pachimetry

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Recommended settings and color maps, displays and values

4 Recommended settings and color maps, displays and values Physicians who are starting to work with the Pentacam® often turn to us with questions on settings such as step width on the color scale, or which maps and values to consider before doing LASIK, PRK, RK or phakic IOL (pIOL) implantation or in keratoconus examinations etc. In the following chapter we present our recommendations on the more frequently addressed issues. Hopefully they will also cover most of your questions or even provide new insights as you work through them. They are no more than recommendations and not necessarily intended to discourage you from using other maps and settings that you may have found to work best for you.

4.1

Recommended settings

When working through the following chapters it is advisable to consistently use the same settings so as to be able to reproduce the values given. „„In the elevation maps, use a sphere fitted in float (BFS) and set the calculation diameter to

manual and use 8 mm or 9 mm „„In the scan menu, select “25 images per scan” and “auto release” „„Keratometer presentation: R flat/R steep, unitdiopter (D) „„Corneal form factor asphericity Q:

Q < 0: Untreated cornea, normal case Q > 1: Treated cornea LASIK/PRK/RK etc „„Color scale: American style „„Step width:

Normal (10 μm) for pachymetry maps Normal (1 D) for topography maps Rel. (2.5 μm) Minimum for elevation maps „„Use the 9 mm loupe function to obtain maps comparable with those of Placido based

topographers

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4.2

Recommended settings and color maps, displays and values

Recommended color maps, displays and values

4.2.1 Screening for corneal refractive surgery We recommend using the following maps and analysis displays: „„Fast Screening Report to check whether the displayed parameters are within normal limits „„4 Maps Refractive to check the pachymetry, topography and elevation maps of both corneal

surfaces „„Belin/Ambrósio Enhanced Ectasia Display to check whether there deviations from normal limits

which can be a sign of early ectatic changesor keratoconus „„Zernike Analysis to see whether the LOA or HOA are withon normal limits „„Important values: R flat and R steep, asti and axis, Q-value, QS, pachymetry at thinnest spot and

pupil centers, distance between the corneal apex and thinnest spot. In the elevation maps please use the parameters recommended in chapter 10.1.2 4.2.2 Pre-op screening for iris fixated phakic IOL implantation We recommend using the following maps and analysis displays: „„The 3D pIOL Simulation Software and Aging Prediction prior to iris fixated pIOL implantation

(available in the Pentacam® HR only). Calculate the required pIOL power using the implanted calculator. Use the database to find a pIOL that best matches the patient’s subjective refraction. Its fit in the anterior chamber is simulated in 3D and the minimum clearances are displayed. The aging simulation allows a simulation of the pIOL position in up to 30 years. Double-check your calculations and evaluations with the manufacturer of the respective pIOL „„For all further pIOL e.g. Intraocular Contact Lens (ICL): Scheimpflug images to obtain information

on the dimensions of the anterior chamber, the iris curve and the densitometry of the cornea and crystal lens. The view of the anterior chamber angle (ACA) shows whether there is an open or closed angle „„Evaluate the horizontal corneal diameter (HWTW). It is displayed automatically if the new iris

camera optic is built in. If not it can be measured manually in the Scheimpflug image at the 180° position (horizontal) „„Important values: R flat and R steep, asti and axis, HWTW, Q-value, QS, anterior chamber depth

(ACD) pachymetry in the thinnest spot and in the pupil center

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Recommended settings and color maps, displays and values

4.2.3 Glaucoma screening We recommend using the following maps and analysis displays: „„Fast Screening Report to check whether the displayed parameters are within normal limits „„General Overview display to view the chamber angle in the Scheimpflug images and corneal

thickness. While clicking to the button “Enter IOP” the tonometrically measured IOP can be entered manually or the respective IOP change can be viewed. The displayed IOP is based on pre-programmed IOP corrections tables. For more details refer to the Pentacam® User Guide „„Important values: ACD, ACV, ACA, Q-value, QS, pachymetry, IOP-correction

4.2.4 Cataract surgery and IOL calculation for virgin and post refractive corneas We recommend using the following maps and analysis displays „„Fast Screening Report to check whether the displayed parameters are within normal limits „„Cataract Pre-OP Display that offers a comprehensive overview. Prof. Maeda recommended the

4 following steps to select the IOL: 1. Evaluation of corneal irregularities 2. Corneal shape assessment 3. Evaluations of corneal spherical aberrations 4. Evaluations of the corneal astigmatism (An article was published in „The Highlights of Ophthalmology“ Assessment of Corneal Optical Quality for Premium IOLs with Pentacam®“ Highlights of Ophthalmology • Vol. 39, Nº 4, 2011) „„Zernike Analysis to determine the amount HOA and LOA „„ACD, manual horizontal white-to-white (HWTW) for keratometry readings from virgin eyes „„Scheimpflug images to obtain information on the dimensions of the anterior chamber and the

condition of the crystalline lens. Lens density can be quantified in a single location, a line, an area or a volume, as desired. The grading PNS can be used for optimizing Phaco settings (doi:10.1016/j. jcrs.2009.08.032) and for the effective phaco time (http://dx.doi.org/10.1016/j.ajo.2013.09.017) „„The Holladay Report and the Holladay EKR65 Detail Report for a comprehensive overview of the

cornea. This includes the topographic as well as the pachymetry map and the anterior and posterior elevation maps. For more information refer to chapter 17 „„The BESSt formula, developed from Edmondo Borrasio, MD. This requires Rm anterior,

Rm posterior, CCT and ACD doi:10.1016/j.jcrs.2006.08.037 „„Okulix or Phaco Optics, which are IOL power calculation software based on the ray tracing

principle. More information can be found under: www.phacoptics.com; www.okulix.de „„Important values: Keratometry, asti and axis, Q-value, QS, ACD, pachymetry in the thinnest spot

and in the pupil center

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5 Differences between Placido and elevation-derived curvature maps

5 Differences between Placido and elevation-derived curvature maps by Prof. Michael W. Belin 5.1

Keratoconus in OD and OS?

The case shown below explains the difference between suspicious and significant elevation maps and numbers. The topographic map (Figure 8) shows the left and right eye but gives no unequivocal statement if it is a keratoconus or not.

Figure 8: Placido based topography of OD and OS allowing no conclusion regarding keratoconus

The right eye seems to be fine. The left eye is a little steeper. The Pentacam® 4 Maps Selectable answers clearly the question.

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5 Differences between Placido and elevation-derived curvature maps

The right eye (Figure 9) has a regular corneal thickness, but the elevation maps of the anterior and posterior surface indicates this cornea as a suspicious cornea. Both sides show an inferior position of the cone with suspicious elevations.

suspicious elevation

Figure 9: 4 Maps Selectable showing keratoconus-suspicious elevations in OD

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5 Differences between Placido and elevation-derived curvature maps

The left eye (Figure 10) indicates an inferior steepening, but a smooth anterior elevation map. The reason for the thinning in the pachymetry map is the posterior elevation map, where there are significant elevations of more than 30 μm. Note that the position of the thinning in the pachymetry map and the highest spot on the elevation map are exactly at the same position.

significant elevation

Figure 10: 4 Maps Selectable showing significant elevation in OS

This is an excellent example to document that topography or anterior elevation only does not indicate keratoconus.

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5 Differences between Placido and elevation-derived curvature maps

5.2

Form fruste keratoconus?

A 47-year-old female presented for a second opinion. She had previously been told she was not a candidate for refractive surgery and that she had “form fruste” keratoconus. Her exam had revealed a BSCVA 20/20+ OD, and the slit lamp and external examination findings had been WNL. However, Placido topography showed the following (Figure 11):

Figure 11: Placido based topography of OD and OS

Pentacam® anterior segment analysis revealed normal pachymetry (normal distribution & central thickness > 650 µm). The anterior and posterior elevation revealed a slightly decentered apex. This had led to a “false positive” inferior steepening on the curvature map. Custom LASIK was performed without incident (Figure 12, Figure 13). Note: This case illustrates the limitations of curvature analysis in trying to analyze a shape abnormality. Curvature is a reference-based measurement and in this case, inaccurately reflects shape information. Elevation data are independent of axis or orientation and does not have the false positive rates as curvature maps commonly do.

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