The Efficiency of Using Mirror Imaged Topography in Fellow Eyes Analyses of Pentacam HR Data

Purpose: To investigate the effectiveness of flipping left corneas topography and analysethem quantitively along with fellow right corneas based on the assumption that they are mirror images of each other. Methods: The study involved scanning both eyes of 177 healthy participants (aged 35.3 ± 15.8) and 75 keratoconic participants (aged 33.9 ± 17.8). Clinical tomography data were collected for both eyes using the Pentacam HR and processed by a fully automated custom-built MATLAB code. For every case, the right eye was used as a datum fixed surface while the left cornea was flipped around in the superior–inferior direction. In this position, the root-mean-squared difference (RMS) between the flipped left cornea and the right cornea was initially determined for both the anterior and posterior corneal surfaces. Next, the iterative closest point transformation algorithm was applied on the three-dimensional flipped cornea to allow the flipped left corneal anterior surface to translate and rotate, minimising the difference between it and the right corneal anterior surface. Then, the RMS differences were recalculated and compared. Results: A comparison of the dioptric powers showed a significant difference between the RMS of both the flipped left eyes and the right eyes in the healthy and the KC groups (p < 0.001). The RMS of the surfaces of the flipped left corneas and the right corneas was 0.6 ± 0.4 D among the healthy group and 4.1 ± 2.3 among the KC group. After transforming the flipped left corneas, the RMS was recorded as 0.5 ± 0.3 D and 2.4 ± 2 D among the healthy and KC groups, respectively. Conclusions: Although fellow eyes are highly related in their clinical parameters, they should be treated with care when one eye topography is flipped and processed with the other eye topography in an optic-related research analysis where translation might be needed. In KC, an asymmetric disease, it was observed that a portion of the asymmetry was due to a corneal apex shift interfering with the image acquisition. Therefore, transforming the flipped left eyes by rotation and translation results in a fairer comparison between the fellow KC corneas.

Μελέτη του Contrast Sensitivity (ευαισθησία αντιθέσεων) και Aberration (εκτροπών κερατοειδούς) σε σχέση με τις μεταβολές του πάχους του επιθηλίου Corneal Apex και στο Pupil Center μετά από PRK και Lasik

Η διαθλαστική χειρουργική με χρήση των τεχνικών LASIK και PRK είναι ένα ταχύτατα αναπτυσσόμενο πεδίο της οφθαλμολογίας. Η αποτελεσματικότητα των επεμβάσεων και η προβλεψιμότητα του διαθλαστικού αποτελέσματος, σχετίζεται στενά με τον ακριβή έλεγχο της επουλωτικής αντίδρασης του κερατοειδή μετά το εισαγόμενο χειρουργικό τραύμα και ειδικά του επιθηλίου. Σκοπός: Ο σκοπός της εργασίας είναι η μελέτη των επιπτώσεων της διαθλαστικής χειρουργικής στην ευαισθησία αντίθεσης (C. S) του οφθαλμού λαμβάνοντας υπ όψη τη μεταβολή των εκτροπών σε συνάρτηση με την μεταβολή του πάχους του επιθηλίου στην κορυφή του κερατοειδούς (ET peak) και στο κέντρο της κόρης (ET center) που θα προκύψει μετά από διαθλαστικές επεμβάσεις (LASIK και PRK). Μελετώνται και συγκρίνονται οι μέθοδοι διόρθωσης οπτικής οξύτητας PRK και LASIK. Μεθοδολογία: Πενήντα εννέα ασθενείς (118 οφθαλμοί) με μέση ηλικία 31,39 +/- 6,95 (εύρος από 23 έως 50 έτη), 26 άνδρες και 33 γυναίκες συμπεριλήφθηκαν στη μελέτη. Είκοσι εννέα ασθενείς (29) υποβλήθηκαν σε επέμβαση LASIK και τριάντα ασθενείς (30) υποβλήθηκαν σε επέμβαση PRK. Όλοι οι ασθενείς εξετάστηκαν το χρονικό διάστημα από το Νοέμβριο του 2016 ως τον Ιούλιο του 2019. Η έρευνα είναι σύμφωνα με τη διακήρυξη του Ελσίνκι. Όλοι οι ασθενείς είχαν σταθερή διάθλαση για τουλάχιστον 2 χρόνια. Ασθενείς που ήταν σε κατάσταση εγκυμοσύνης ή είχαν συστηματική νόσο ή ιστορικό προηγούμενης οφθαλμικής νόσου ή χειρουργικής επέμβασης εξαιρέθηκαν από τη μελέτη. Η παρακολούθηση του κάθε περιστατικού έγινε για ένα χρόνο και με επανεξέταση του στην εβδομάδα, μήνα, τρίμηνο, εξάμηνο και χρόνο. Στη συγκεκριμένη έρευνα όλοι οι συμμετέχοντες υποβλήθηκαν σε προεγχειρητικό έλεγχο ο οποίος περιλάμβανε εξέταση του κάθε ενός οφθαλμού με τη συσκευή Pentacam HR προκειμένου να ληφθούν πληροφορίες τόσο από τον χάρτη “four maps refractive” όσο και από τον χάρτη των πολυωνύμων Zernike σχετικά με τις εκτροπές. Χρησιμοποιώντας την εφαρμογή Fract σε ηλεκτρονικό υπολογιστή ελήφθησαν μετρήσεις, εξετάζοντας κάθε ένα οφθαλμό ξεχωριστά, αλλά και διόφθαλμα - οπτικής οξύτητας (CDVA) αλλά και CS. Ακολούθως οι ασθενείς εξετάστηκαν ως προς το πάχος του επιθηλίου ET peak και στο ET center με το Oct Agiovue Avanti με φακό προσθίου ημιμορίου. Η εξέταση περιλάμβανε τον κάθε οφθαλμό ξεχωριστά. Οι ίδιες εξετάσεις επαναλήφθηκαν και στους μετεγχειρητικούς ελέγχους ώστε να προσδιοριστούν οι μεταβολές που πιθανόν προκάλεσε η επούλωση του επιθηλίου στην CDVA αλλά και στο CS. Όλες οι μεταβλητές εξετάστηκαν κατά την στατιστική ανάλυση με τη δοκιμασία Kolmogorov για κανονικότητα και έδειξαν ότι δεν ακολουθούν κανονική κατανομή. Χρησιμοποιήθηκε για την στατιστική ανάλυση το ειδικό στατιστικό λογισμικό SPSS v.26, και έγινε στατιστική ανάλυση spearman όπου μεταξύ των μεταβλητών διαπιστώθηκε σημαντική στατιστική διαφορά. Αποτελέσματα:Τόσο στο ET peak όσο και στο ET center τα αποτελέσματα μοιάζουν πολύ ως προς τη μεταβολή του E.T. Βρέθηκαν στατιστικά σημαντικές διαφορές μεταξύ των προεγχειρητικών και μετεγχειρητικών τιμών σε C.S, E.T και στις εκτροπές ανώτερης τάξης (HOAs) και στις δύο μεθόδους διαθλαστικής χειρουργικής. Στην ομάδα PRK, η μέση αύξηση του E.T peak ήταν 6,62 ± 1,31 microns και του E.T center : 6.39±1.32 microns και φάνηκαν να σχετίζεται με αλλαγή στο C.S και με αλλαγές στις εκτροπές, LOAs (Ζ00, Ζ02, Ζ11) και HOAs (Ζ31 και Ζ42). Ωστόσο, η αλλαγή στο επιθήλιο δεν φάνηκε να επηρεάζει το CDVA. Στην ομάδα LASIK, η μέση αύξηση του E.T peak ήταν 6,55±1,26 microns και του E.T center ήταν 6,03±1,22 microns αλλά δεν βρέθηκε καμία συσχέτιση με τη μείωση του C.S, τις αλλαγές στα HOAs και CDVA. Ωστόσο, υπήρξε συσχέτιση με την αύξηση του ET και των LOAs (Ζ00, Ζ02, Ζ11). Συμπεράσματα : Οι τεχνικές PRK και LASIK βρέθηκαν να έχουν παρόμοια μετεγχειρητική αύξηση E.T. Τόσο στο E.T peak όσο και στο E.T center στην PRK οι αλλαγές φάνηκε να συσχετίζονται ισχυρά με το C.S σε αντίθεση με το LASIK. Επίσης η διαφορά στην μεταβολή του C.S και των εκτροπών εκτός της μεταβολής του ET peak και ET center μεταξύ των δυο τεχνικών μπορεί να σχετίζεται με την αλλαγή στο σχήμα του κερατοειδούς, τη μετατροπή της εμβιομηχανικής, την επούλωση του κρημνού του κερατοειδούς αλλά και την ανακατασκευή του επιθηλίου και του στρώματος του κερατοειδούς. Τέλος οι αλλαγές του ET peak και οι αλλαγές στο ET center επηρέασαν τις εκτροπές και στις δύο τεχνικές, αλλά όχι με τον ίδιο τρόπο.

Chord Mu (µ) and Chord Alpha (α) Length Changes in Fuchs Endothelial Corneal Dystrophy before and after Descemet Membrane Endothelial Keratoplasty (DMEK) Surgery

This paper will evaluate chord mu and alpha length in patients with Fuchs endothelial corneal dystrophy (FECD) and its changes following Descemet membrane endothelial keratoplasty (DMEK). Patients with FECD that underwent DMEK surgery were included in this retrospective study. Scheimpflug Tomography was carried out in order to calculate chord mu and chord alpha lengths prior to surgery and at 3 and 12 months postoperative. This study included 27 eyes from 27 patients. Significant changes in chord mu were observed within the first three months (from 0.47 ± 0.32 to 0.29 ± 0.21 mm, p < 0.01) and remained stable 12 months postoperative (0.30 ± 0.21 mm, p > 0.05). However, chord alpha remained stable throughout the 12 months post surgery (from 0.53 ± 0.19 to 0.49 ± 0.14 mm, p > 0.05). In addition to the pupillary center distance from the corneal apex (from 0.35 ± 0.25 to 0.34 ± 0.20 mm, p > 0.05) also remain stable. In FECD patients undergoing DMEK surgery, chord mu length decreased, and chord alpha length remained stable after 12 months of follow-up.

The Influence of Analysis Mode Selection on Prediction Accuracy of Corneal Astigmatism Using Pentacam

Purpose: To evaluate the influence of analysis mode selection on prediction accuracy of corneal astigmatism using Pentacam.Methods: Fifty-nine eyes of 59 patients implanted with toric intraocular lenses (IOLs) were included in the retrospective study. Preoperative corneal astigmatism (total refractive power) measured with Pentacam was analyzed based on 2-, 3-, 4-, or 5-mm ring or zone mode either centered on corneal apex or pupil center. Actual corneal astigmatism was calculated based on residual astigmatism on the corneal plane, surgical-induced astigmatism, and effective toric power on the corneal plane. Prediction error, the difference between actual corneal astigmatism and measured astigmatism, was compared among different analysis modes. Influences of local topography on prediction error were also evaluated.Results: Based on the zone mode, prediction error was lower when centered on corneal apex than on pupil center at different diameters, whereas based on the ring mode, this difference was only seen at 2-mm cornea (all P &lt; 0.05). When centered on the corneal apex, the zone mode showed lower prediction error than the ring mode at 4- and 5-mm corneas (both P &lt; 0.001), regardless of asymmetric or symmetric astigmatism. In symmetric bowtie, the zone mode showed lower prediction error than the ring mode at 2-mm cornea of the small bowtie, and 4- and 5-mm corneas of the large bowtie (all P &lt; 0.05).Conclusions: For toric IOL planning, the corneal apex may be a better reference center. At a cornea diameter ≥4 mm, the zone mode is more accurate than the ring mode. Local topography affects prediction accuracy in the symmetric bowtie.

Corneal Parameters in Patients with Multiple Sclerosis: A Pilot Study

Objective To evaluate the corneal topographic parameter values measured with the Pentacam Scheimpflug system in patients with multiple sclerosis (MS). Methods A total of 108 eyes of 62 MS patients were studied. In addition to a complete examination of anterior and posterior segments, all patients were scanned using the Pentacam Scheimpflug camera. The diagnosis of MS was made according to the McDonald criteria. All MS patients were clinically assessed using the Multiple Sclerosis Severity Score (MSSS). Results The mean age was 38.89 ± 10.18 years (36.16 – 41.30) for MS patients and 40.94 ± 9.44 years (38.49 – 43.11) for the controls (p = 0.26). Only central corneal thickness (CCT) and corneal volume (CV) values were significantly lower in MS patients (p < 0.001). The other corneal parameters were not significantly different between the study eyes and control eyes (p > 0.05 for all). Pachymetric measurements at the corneal apex were 525.69 ± 29.35 (518.29 – 533.67) µm for the study eyes versus 563.13 ± 23.70 (562.13 – 576.36) µm for the control eyes. CV were 59.22 ± 4.11(58.18 – 60.20) mm3 for the study eyes versus 62.78 ± 3.09 (62.38 – 64.00) mm3 for the control eyes. Conclusion This is the first study that has reported lower CCT and CV measurements in MS patients than healthy subjects of a similar age. These results should be supported by further studies.

Comparison between two devices in the detection of corneal thickness changes after cataract surgery

This study compared corneal thickness (CT) changes obtained with specular microscopy (SM) and a rotating Scheimpflug camera (RSC) after conventional phacoemulsification surgery (PS). One hundred sixty six eyes of 83 patients were analyzed before and one month after PS. One eye underwent PS, while the fellow phakic one was used as control. CT was measured with SM at the center of the cornea and with RSC at the pupil center, at the corneal apex and at the thinnest point. In the operated eye, SM showed a larger CT mean increase than those one detected at the three different measurements’ points evaluated by RSC. Inversely, in the fellow phakic eye, SM showed a greater CT mean decrease than those one registered by RSC at its three measurement’s points. Thus, one month after surgery, even if cornea appears clear at the slit-lamp, a significant thickness increase is still present. This is even more evident if the slight decrease of the fellow phakic eye is considered. The differences between the two devices are probably related to the different measured areas.

The Effect of Body Posture Changes and Central Corneal Thickness on Intraocular Pressure among Healthy Malays

Purpose: To study the relationship between intraocular pressure (IOP), posture, and central corneal thickness (CCT) among healthy Malays. Method: Thirty-four young adults had their IOPs measured using a handheld tonometer (Accutome, Pennsylvania, USA) after maintaining 5 min at four different postures; sitting upright, supine, supine & 45° inclination, and prone positions. The sequences of the postures were made random. CCT was measured using Oculus Pentacam (Oculus, Wetzlar, Germany), and the value at the corneal apex was taken. Participants were grouped into Group A with CCT of < 550 μm, and Group B of > 550 μm. Results: The highest IOP was recorded at the prone position 23.77±2.71 mmHg (p < 0.001), and the lowest was at sitting upright 15.43±2.67 mmHg (p < 0.001). IOP at the supine position was 17.31±3.07 mmHg, and at the supine & 45° inclination position was 16.00±2.80 mmHg. IOPs were significantly different between sitting upright and supine (p = 0.03), between sitting upright and prone (p < 0.001), between supine and prone (p < 0.001), and between supine & inclined 45° and prone (p < 0.001). There was no significant difference in IOPs between Group A and Group B at different postures (p > 0.05). Conclusions: Change in body posture significantly affects IOP, with the lowest IOP during the sitting upright position, and the highest at the prone position. IOP change upon posture shifts was not affected by CCT.

Topographic, elevation, and keratoconus indices for diagnosis of keratoconus by a combined Placido and Scheimpflug topography system

Purpose:To determine the accuracy of various corneal parameters in keratoconus diagnosis using Scheimpflug camera combined with Placido disk corneal topography (Sirius, CSO).Methods:One hundred and fifteen keratoconic eyes (group1) and a 111 normal eyes (group2) were assessed prospectively between March 2018 and July 2019 for: corneal keratometric indices (K1, K2, sim K, apex curvature) at different corneal rings of both corneal surfaces, central corneal thickness (CCT), thinnest corneal thickness (TL), corneal asphericity (Q), elevation at thinnest point, root mean square (RMS), and root mean square per area (RMS/A) in spherical, aspheric and aspherotoric reference for both corneal surfaces and keratoconus summary parameters; surface asymmetry index of front and back (SIf, SIb respectively), elevation at keratoconus vertex front and back (KVf, KVb respectively), Baiocchi Calossi Versaci front and back index (BCVf, BCVb) and its vector summation (BCV) and convergence radius and cutoff value for each was calculatedResults:All studied indices were significantly different between the two groups. The highest predictive accuracy “Area under receiver operating characteristic curve (AUROC)” of 0.999 was observed for BCVf, KVb, RMS and RMS/A at 6 mm aspherotoric reference posterior surface. Keratoconus summary indices had high AUROC (0.986, 0.984, 0.948, 0.999, 0.999, 0.998 respectively). Curvature indices had lower AUROC than elevation indices, except for curvature of corneal apex at anterior (0.98) and posterior surface (0.99). Higher AUROC was noted with elevation at thinnest point especially at aspherotoric reference surface.Conclusion:Sirius topography showed high predictive accuracy in detection of keratoconus. Elevation indices and keratoconus summary parameters have the highest diagnostic ability.

Corneal thickness evaluation in healthy eyes: Comparison between two different Scheimpflug devices

Purpose To evaluate the correlation between corneal thickness (CT) measurements obtained with two Scheimpflug devices, Pentacam HR and Precisio, and to elaborate, if necessary, a regression formula which could make these results comparable. Design Retrospective, Comparative, Observational study. Setting Department of Medicine, Surgery and Dentistry, “Scuola Medica Salernitana” University of Salerno, Italy Methods One hundred twenty four healthy eyes of 124 volunteers (65 males; range: 20–32 years; mean age of 24.8 ± 1.7) were included in this study. CT was measured using Pentacam HR and Precisio in three different points: the pupil center (PC), the corneal apex (CA) and the thinnest point (TP). Results CT obtained with both devices at the PC, at the CA and at the TP showed a good correlation (r = 0.97, r = 0.97, r = 0.97, respectively), but Pentacam HR measurements were significantly thicker than those provided by Precisio (p < 0.01). The differences between Pentacam HR and Precisio were 21.9 ± 8.8 μm at the PC, 21.9 ± 8.9 μm at the CA, 19.1 ± 9.0 μm at the TP. The calculated regression formulas were: y = 0.9558x + 2.3196 for the PC, y = 0.9519x + 4.5626 for the CA, y = 0.9364x + 15.436 for the TP, where x is the CT measured with Pentacam HR and y is the Precisio measurement. Conclusions The findings provided by this study highlight that Precisio measures thinner corneas compared to Pentacam HR. The identified regression formulas could be utilized to make interchangeable the results obtained with these two devices.