Scanning-slit Topography Research Articles

Angle Kappa measurement pre-keratorefractive and post-keratorefractive surgery using Orbscan 3

Aim of the study Measurement of the mean angle Kappa pre-keratorefractive and post-keratorefractive surgery utilizing Orbscan 3. Patients and methods This retrospective study was conducted on patients who had refractive surgeries, group A included patients who underwent Lasik and group B included patients who underwent Photo Refractive Keratectomy (PRK). Mean age from 18 to 45 years. Preoperative, 1-week, and 1-month postoperative assessments included detailed ocular examination, slit-scanning topography done by Orbscan 3, and total ocular aberrations by Zywave 3 were done. Results The study comprised 146 eyes of 75 individuals. Preoperative data demonstrated that angle Kappa mean in Lasik group (group A) was 2.38±1.54 at 147.05±96.94, in PRK group (group B) was 2.31±1.17 at 137.67±85.7. Paired mean differences of the two groups between preoperative data and 1-week postoperative show no statistically significant difference in central corneal thickness (CCT) nor angle Kappa values. Paired mean differences of the two groups between preoperative data and 1-month postoperative show no statistically significant difference regarding CCT nor angle Kappa values. Preoperative, 1-week postoperative, and 1-month postoperative correlation of angle Kappa to refractive error, spherical equivalent, average K-reading, CCT and axial length, showed that both groups had a positive correlation with axial length. Conclusion Keratorefractive surgeries do not affect angle Kappa or its intercept measurements.

Comparison of Anterior Segment Measurements with a New Multifunctional Unit and Five Other Devices

PurposeTo evaluate the clinical availability of a multifunctional ocular biometric unit, MR-6000, for simultaneous keratometry, tonometry, topography, and pachymetry evaluation, and compare anterior segment measurements with five other devices: autokeratometer (KR-1), Scheimpflug camera (Pentacam HR), swept-source optical coherence tomography (IOLMaster 700), Placido disk scanning-slit topography (Orbscan II), and noncontact tonometry (FT-1000).MethodsThirty eyes from thirty patients who visited Severance Hospital for cataract surgery were examined using MR-6000 and the other devices. The mean keratometry, central corneal thickness (CCT), white-to-white (WTW) distance, and intraocular pressure (IOP) values were compared. Repeated measures analysis of variance, Wilcoxon signed-rank test, intraclass correlation coefficient (ICC), and Bland-Altman plot were used to assess the correlation and agreement between devices.ResultsThirty eyes of thirty patients were evaluated. Statistically significant differences in mean keratometry between MR-6000, KR-1, Pentacam HR, and IOLMaster 700 were not observed (p > 0.05). All five devices, including Orbscan II, had almost perfect agreement in measuring keratometry (ICC > 0.80, p < 0.05). CCT measured by MR-6000 was significantly different from that of Pentacam HR and Orbscan II measurements (p < 0.05) but correlated with that of Pentacam HR and Orbscan II measurements (ICC > 0.60, p < 0.05). The WTW distance measured by MR-6000 was not significantly different from that measured by IOLMaster 700 but was different from that measured by Orbscan II. IOP measured by MR-6000 was not correlated with FT-1000.ConclusionsKeratometric values obtained through MR-6000 can be used interchangeably with other devices based on good correlation and agreement. However, the CCT, WTW, and IOP values were not interchangeable with a single multifunctional unit for cataract surgery preoperative examination.

Comparison of central corneal thickness measurement by scanning slit topography, infrared, and ultrasound pachymetry in normal and post-LASIK eyes.

To compare central corneal thickness (CCT) measurements by scanning slit topography (SST), infrared pachymetry (IRP), and ultrasound pachymetry (USP), and their agreement in normal and post-laser in situ keratomileusis (LASIK) eyes. Sixty normal and 35 post-LASIK subjects were recruited. Only one eye from each subject was analyzed. Non-contact pachymetry was performed first, and the order for SST (Orbscan IIz) and IRP (Tonoref III) was randomized for each patient, to be followed by contact USP (Echoscan US-4000). Pearson's correlation, paired t test, and Bland-Altman plots were used to investigate association, difference, and agreement among different instruments respectively. The measurements obtained with the instruments were highly correlated. Compared to CCT determined by USP (CCTUSP), CCT determined by SST (after correction with acoustic factor) (CCTSSTC) was thicker by 7µm in normal eyes (P < 0.001). There was no significant difference between CCTSSTC and CCTUSP (P = 0.128), but a thickness-dependent deviation in post-LASIK eyes (P = 0.003). The CCT determined by IRP (CCTIRP) was thicker than CCTUSP in normal (P < 0.001) and post-LASIK eyes (P < 0.001) and demonstrated proportional overestimation with thinner corneas, with less predictable ultrasonic equivalent corneal thickness in normal eyes. Conversely, CCTIRP significantly underestimated CCT compared to CCTSST and showed increasing underestimation with thinner corneas in both normal and post-LASIK eyes (both P < 0.001). Central corneal thickness determined by SST, IRP and USP were not interchangeable or interconvertible, probably attributed to difference in methodologies. Compensation with algorithms may improve agreements amongst instruments.

The relationship of central corneal thickness with the status of diabetic retinopathy

BackgroundTo compare central corneal thickness (CCT) values measured by three different devices: slit-scanning topography (SST), ultrasonic pachymetry (UP), and optical coherence tomography (OCT) in diabetic eyes and compare the CCT values in patients with and without diabetic retinopathy.MethodsNinety-six patients with diabetes mellitus were included in this prospective study and divided into two groups according to the presence of diabetic retinopathy, as Group I with retinopathy and Group II without. The CCT of 96 eyes was measured by three different devices; SST (Orbscan II), UP and OCT. The results of CCT measurements with three different devices were compared. Also, the intergroup differences in CCT measurements were evaluated.ResultsThe CCT was statistically insignificantly different between the two groups. Although the three methods of CCT measurements correlated well with each other, SST showed significantly (p < 0,0001) higher CCT results compared to both UP and OCT.ConclusionsAccording to our results, neither the duration of DM nor the presence of diabetic retinopathy did have a significant effect on the CCT. The CCT values obtained with three devices were all in correlation. However, the results of SST were significantly higher compared to the other two. Our findings emphasize the value anterior segment OCT in CCT measurements, since it is a non-contact method and correlate very well with UP.

Scanning-slit topography in patients with keratoconus.

To evaluate the anterior and posterior corneal surfaces using scanning-slit topography and to determine the diagnostic ability of the measured corneal parameters in keratoconus. Orbscan II measurements were taken in 39 keratoconic corneas previously diagnosed by corneal topography and in 39 healthy eyes. The central minimum, maximum, and astigmatic simulated keratometry (K) and anterior axial power values were determined. Spherical and cylindrical mean power diopters were obtained at the central and at the steepest point of the cornea both on anterior and on posterior mean power maps. Pachymetry evaluations were taken at the center and paracentrally in the 3 mm zone from the center at a location of every 45 degrees. Receiver operating characteristic (ROC) analysis was used to determine the best cut-off values and to evaluate the utility of the measured parameters in identifying patients with keratoconus. The minimum, maximum and astigmatic simulated K readings were 44.80±3.06 D, 47.17±3.67 D and 2.42±1.84 D respectively in keratoconus patients and these values differed significantly (P<0.0001 for all comparisons) from healthy subjects. For all pachymetry measurements and for anterior and posterior mean power values significant differences were found between the two groups. Moreover, anterior central cylindrical power had the best discrimination ability (area under the ROC curve=0.948). The results suggest that scanning-slit topography and pachymetry are accurate methods both for keratoconus screening and for confirmation of the diagnosis.

Biometric evaluation of myopic eyes without posterior staphyloma: disproportionate ocular growth.

To evaluate changes in the anterior segment of myopic eyes and assess anterior biometry as a function of axial length (AL). Retrospective investigational study. Patients evaluated for phakic intraocular lens surgery at a tertiary eye care centre. Patients with corrected visual acuity >20/40 and AL>24.5mm were included in the study. Posterior staphyloma and maculopathy were ruled out in all the patients, and 176 eyes were included for analysis. AL was measured with partial coherence interferometry, while keratometry, central corneal thickness (CCT), anterior chamber depth (ACD), and horizontal white to white (WTW) were measured with slit-scanning topography. Group 1 included 55 eyes with AL<26.5mm, group 2 had 57 eyes with AL between 26.5 and 28.5mm while group 3 had 64 eyes with AL>28.5mm. Correlation of AL with anterior biometry. The mean AL of the study eyes was 27.88+2.14mm. The mean values of ACD (2.99mm), CCT (0.52mm), WTW (11.68mm), and keratometry (43.62D) were within the normal range. Overall, very weak correlations could be established between AL and CCT (R=0.17, p=0.02), AL and keratometry (R=-0.28, p<0.001), and AL and WTW (R=0.22, p=0.002), while ACD did not relate to AL significantly. The ACD and CCT did not relate significantly to AL in any of the three groups. Keratometry had a weak negative relation with AL in groups 1 and 2, while WTW had a weakly positive relation with AL in group 2 only. No variable had any significant relation with AL in group 3. There is disproportionate elongation of the eyeball in myopic patients with very weak or no correlation between anterior biometry and AL. This discord is more in longer eyes. Such a scenario can be challenging to a refractive surgeon treating highly myopic eyes and needs further evaluation.

Visual and Topographical Outcomes Following Accelerated Trans-Epithelial Corneal Crosslinking in Progressive Keratoconus.

To assess the visual and topographical outcomes following accelerated trans-epithelial corneal crosslinking (TE-CXL) in progressive keratoconus. Case series. Laser Vision Centre, Karachi, from January 2015 to December 2016. Forty-five eyes of 25 patients affected with progressive keratoconus and treated with accelerated TE-CXL with riboflavin (vitamin B2) and ultra-violet A(UV-A) irradiation were enrolled in this study. The visual outcome was measured by ETDRS chart as improvement in best corrected visual acuity (BCVA) of at least one line or more as compared to pre-CXLBCVA. The topographical outcome was measured as decrease in maximum simulated keratometry values, astigmatism and spherical equivalent (SE) and an increase in central corneal thickness (CCT). K-max was defined as the steepest radius of curvature of the anterior corneal surface. SE was measured by subjective refraction, and K-max, astigmatism and CCTby scanning-slit corneal topography. Patients were followed-up 12 months post-treatment. At the end of follow-ups, mean BCVAshowed improvement of one line from LogMAR 0.58 ±0.067 to LogMAR 0.48 ±0.077. Seven (15.5%) eyes showed two lines of improvement while 3 (6.7%) eyes showed worsening of one line in BCVA. The mean K-max flattened by 0.7D. Mean astigmatism and SE decreased up to -0.5D and -0.4D, respectively. Mean preoperative CCTwas 454.31 ±36.34 µm, whereas mean postoperative CCTwas 456.47 ±35.60 µm with an average increase of 2.15 µm. No postoperative complications were reported. Based on topographical outcomes, accelerated TE-CXL is effective in preventing the progression of keratoconus without any safety concerns with improvement of vision in majority of cases.

Comparison between Pentacam HR and Orbscan II after Hyperopic Photorefractive Keratectomy.

Purpose:The aim of this study was to determine the agreement between Pentacam HR (Scheimpflug imaging, Oculus) and Orbscan II (scanning slit topography, Bausch and Lomb) in measuring corneal parameters after photorefractive keratectomy (PRK) for hyperopia.Methods:In this prospective cross-sectional study, 38 hyperopic eyes undergoing PRK were examined before refractive surgery and 8 to 10 months postoperatively using Pentacam HR and Orbscan II. Ultrasound (US) pachymetry was also used to measure central corneal thickness (CCT). The radius of anterior (A-) and posterior (P-) best-fit sphere size (BFS), central elevation (CE), and anterior maximum tangential power in 3 mm (TG3) and 3-5 mm (TG5) zones, anterior chamber depth (ACD), and central corneal thickness (CCT) were collected and used in the analyses. To study the agreement between the measurements made by the two devices, the method described by Bland and Altman was used and the 95% limits of agreement were calculated.Results:The 95% limits of agreement show reasonable agreement between the measurements by Pentacam HR and Orbscan II for A-BFS, P-BFS, A-TG3, and CCT, but not for A-CE, P-CE, A-TG5, or ACD. CCT values obtained by both Pentacam HR and Orbscan II correlated well with the values determined by US pachymetry.Conclusion:Pentacam HR and Orbscan II after PRK for hyperopia show reasonable agreement for determining A-BFS, P-BFS, A-TG3, and CCT, but not for A-CE, P-CE, A-TG5, or ACD. CCT measurements with Pentacam HR have reasonable agreement with US pachymetry.

Estimation of axial curvature of anterior sclera: correlation between axial length and anterior scleral curvature as affected by angle kappa.

BackgroundThough the development and fitting of scleral contact lenses are expanding steadily, there is no simple method to provide scleral metrics for scleral contact lens fitting yet. The aim of this study was to establish formulae for estimation of the axial radius of curvature (ARC) of the anterior sclera using ocular biometric parameters that can be easily obtained with conventional devices.MethodsA semi-automated stitching method and a computational analysis tool for calculating ARC were developed by using the ImageJ and MATLAB software. The ARC of all the ocular surface points were analyzed from the composite horizontal cross-sectional images of the right eyes of 24 volunteers; these measurements were obtained using anterior segment optical coherence tomography for a previous study (AS-OCT; Visante). Ocular biometric parameters were obtained from the same volunteers with slit-scanning topography and partial coherence interferometry. Correlation analysis was performed between the ARC at 8 mm to the axis line (ARC[8]) and other ocular parameters (including age). With ARC obtained on several nasal and temporal points (7.0, 7.5, 8.0, 8.5, and 9.0 mm from the axis line), univariate and multivariate linear regression analyses were performed to develop a model for estimating ARC with the help of ocular biometric parameters.ResultsAxial length, spherical equivalent, and angle kappa showed correlations with temporal ARC[8] (tARC[8]; Pearson’s r = 0.653, −0.579, and −0.341; P = 0.001, 0.015, and 0.015, respectively). White-to-white corneal diameter (WTW) and anterior chamber depth (ACD) showed correlation with nasal ARC[8] (nARC[8]; Pearson’s r = −0.492 and −0.461; P = 0.015 and 0.023, respectively). The formulae for estimating scleral curvatures (tARC, nARC, and average ARC) were developed as a function of axial length, ACD, WTW, and distance from the axis line, with good determinant power (72 − 80 %; SPSS ver. 22.0). Angle kappa showed strong correlation with axial length (Pearson’s r = −0.813, P <0.001), and the different correlation patterns of nasal and temporal ARC with axial length can be explained by the ocular surface deviation represented by angle kappa.ConclusionsAxial length, ACD, and WTW are useful parameters for estimating the ARC of the anterior sclera, which is important for the haptic design of scleral contact lenses. Angle kappa affects the discrepancies between the nasal and temporal scleral curvature.Electronic supplementary materialThe online version of this article (doi:10.1186/s12886-016-0355-5) contains supplementary material, which is available to authorized users.

Polar Value Analysis of Corneal Astigmatism in Intrastromal Corneal Ring Segment Implantation.

Purpose. To evaluate surgically induced astigmatism (SIA) and the average corneal power change in symmetric intrastromal corneal ring segment (ICRS) implantation. Methods. The study included 34 eyes of 34 keratoconus patients who underwent symmetric Intacs SK ICRS implantation. The corneal pocket incision meridian was the preoperative steep meridian. Corneal power data were obtained before and 3 months after Intacs SK ICRS implantation using scanning-slit topography. Polar value analysis was used to evaluate the SIA. Hotelling's trace test was used to compare intraindividual changes. Results. Three months postoperatively, the combined mean polar value for SIA changed significantly (Hotelling's T 2 = 0.375; P = 0.006). The SIA was 1.54 D at 99° and the average corneal power decreased significantly by 3.8 D. Conclusion. Intacs SK ICRS placement decreased the average corneal power and corneal astigmatism compared to the preoperative corneal power and astigmatism when the corneal pocket incision was made at the preoperative steep meridian.

Comparison of central corneal thickness: ultrasound pachymetry versus slit-lamp optical coherence tomography, specular microscopy, and Orbscan.

BackgroundCentral corneal thickness (CCT) can be measured by using contact and non-contact methods. Ultrasound pachymetry (US pachymetry) is a contact method for measuring CCT and is perhaps the most commonly used method. However, non-contact methods like scanning slit topography (Orbscan II), slit-lamp optical coherence tomography (SL-OCT), and specular microscopy are also used. Not many studies have correlated the measurement of CCT with all four modalities. The purpose of this study was to compare and correlate the CCT measurements obtained by US pachymetry with SL-OCT, specular microscopy, and Orbscan.MethodThis is a prospective, comparative study done in an institutional setting. Thirty-two eyes of 32 subjects with no known ocular disease and best-corrected visual acuity of 20/20 were enrolled. CCT measurements were obtained using SL-OCT, specular microscopy, scanning slit topography (Orbscan), and US pachymetry. Three measurements were made with each instrument by the same operator. Mean, standard deviation, and coefficient of variation were calculated for CCT measurements acquired by the four measurement devices. Bland–Altman plot was constructed to determine the agreements between the CCT measurements obtained by different equipment.ResultsThe mean CCT was 548.16±48.68 μm by US pachymetry. In comparison, CCT averaged 546.36±44.17 μm by SL-OCT, 557.61±49.92 μm by specular microscopy, and 551.03±48.96 μm by Orbscan for all subjects. Measurements by the various modalities were strongly correlated. Correlations (r2) of CCT, as measured by US pachymetry compared with other modalities, were: SL-OCT (r2=0.98, P<0.0001), specular microscopy (r2=0.98, P<0.0001), and Orbscan (r2=0.96, P<0.0001). All modalities had a linear correlation with US pachymetry measurements.ConclusionIn subjects with healthy corneas, SL-OCT, specular microscopy, and Orbscan (with correction factor) can be used interchangeably with US pachymetry in certain clinical settings. The four modalities showed significant linear correlations with one another.

Comparison of corneal measurements in keratoconic eyes using rotating Scheimpflug camera and scanning-slit topography.

To compare the anterior segment measurements obtained by rotating Scheimpflug camera (Pentacam) and Scanning-slit topography (Orbscan IIz) in keratoconic eyes. A total of 121 patients, 71 males (58.7%) and 50 females (41.3%) (214 eyes) with the diagnosis of keratoconus (KC) were enrolled in this study. Following diagnosis of KC by slit-lamp biomicroscopic examination, central corneal thickness (CCT), thinnest corneal thickness (TCT), anterior chamber depth (ACD), and pupil diameter (PD) were measured by a single examiner using successive instrumentation by Pentacam and Orbscan. There was no significant difference between the two instruments for the measurement of CCT and TCT. In contrast, scanning-slit topography measured ACD (3.46±0.40 mm vs. 3.38±0.33 mm, P=0.019) and PD (4.97±1.26 mm vs 4.08±1.19 mm, P<0.001) significantly larger than rotating Scheimpflug camera. The two devices made similar measurements for CCT (95% CI: -2.94 to 5.06, P=0.602). However, the mean difference for TCT was -6.28 (95% CI: -10.51 to -2.06, P=0.004) showing a thinner measurement by Orbscan than by Pentacam. In terms of the ACD, the mean difference was 0.08 mm (95% CI: 0.04 to 0.12, P<0.001) with Orbscan giving a slightly larger value than Pentacam. Similarly, Orbscan measurement for PD was longer than Pentacam (95% CI: 0.68 to 1.08, P<0.001). A good agreement was found between Pentacam and Orbscan concerning CCT measurement while comparing scanning-slit topography and rotating Scheimpflug camera there was an underestimation for TCT and overestimation for ACD and PD.

Corneal Ectasis among Wrestlers: Report of Two Cases

Report keratoconus in two patients with a long history of wrestling without any risk factor for corneal ectasia and reviewing the possible pathogenesis. To confirm suspicion of keratoconus, corneal topography was performed using scanning slit topography system and Orbscan. In two wrestlers with the complaint of visual loss in their eyes and IOP raising, corneal topography was performed and development of keratoconus (KCN) was detected. Athletes involved in sports with high strenuous exercises m ight need routine eye examination and also a baseline corneal topography. This may provide an earlier detection of KCN in this group of athletics .

DETERMINATION OF VALIDITY OF CORNEAL THICKNESS MEASUREMENT BETWEEN ULTRASOUND PACHYMETRY (US), SCHEIMPFLUG IMAGING (PENTACAM, OCULUS) AND SCANNING-SLIT TOPOGRAPHY (ORBSCAN II, BAUSCH & LOMB) IN HYPEROPIC EYES AFTER LASEK SURGERY

Background and Aim: To determine the validity in central corneal thickness (CCT) peripheral corneal thickness (PCT) measured by Scheimpflug imaging (Pentacam, Oculus) and scanning-slit topography (ORBSCAN II, Bausch & Lomb) with that by gold standard method of ultrasound (US) in Hyperopic eyes after LASEK surgery . Materials and Methods: the present study which was based on descriptive and analytic census that carried out in hyperopic patients who undergone LASEK eye surgery in Farabi eye hospital in 2012 and collection of samples lasted for 9 months. The subjects were inspect by ultrasound (US), Scheimpflug imaging ( Pentacam ,Oculus) and scanning-slit topography (ORBSCAN II, Bausch & Lomb) .statistical analysis of collected data was performed using SPSS software version 18 and T-2test method. Results: CT and PCT were evaluated in 28 eyes. CCT measured by Orbscan II had good correlation with those measured by ultrasound pachymetry(r=0.083 and p<0.05) also Orbscan II had good correlation in CCT measurement with Pentacam HR (p<0.05 and r=0.072).PCT measured by Pentacam HR had good correlation with those ultrasound pachymetry readings and there is no considerable discrepancy between two method. Orbscan II had good correlation in superior, inferior and temporal corneal thickness but there was considerable discrepancy in nasal corneal thickness measured by Orbscan II with those of ultrasound pachymetry (sig=0.01, t=-2.74, p<0.05). Conclusion: Pentacam HR and ORBSCAN II showed good correlation with US in CCT measurement but in PCT measurement Pentacam HR had better correlation comparing with ORBSCAN II for hyperopic patient after LASEK refractive surgery Key Words: hyperopia, Pentacam HR, ORBSCAN, LASEK, Ultrasound

Comparison of Anterior Segment Measurements Using Scanning-Slit Topography and Optical Low-Coherence Reflectometry (OLCR) Biometry

Purpose: To compare the results of anterior segment biometry including white-to-white (WTW) between scanning-slit topography (ORBscan IIz, Bausch & Lomb), optical low-coherence reflectometry (OLCR) biometry (Lenstar, Haag-Streit), and Castroviejo calipers. Methods: Measurements on 72 eyes of 36 patients that underwent refractive surgery were measured using ORBscan, Lenstar, and calipers and compared. Ocular biometry parameters used in this study included the WTW, central corneal thickness, anterior chamber depth (ACD), keratometry, and pupil size. Results: The WTW measurements using ORBscan and calipers (11.57 ± 0.35 mm and 11.58 ± 0.34 mm, respectively) were statistically similar. However, the measurement using Lenstar (12.05 ± 0.40 mm) was significantly greater than with the other methods (p < 0.001). Central corneal thickness and keratometry measurements using ORBscan were greater than when using Lenstar (p = 0.01 for both). ACD and pupil size measurement using Lenstar were greater than when using ORBscan (p < 0.001 for both). Conclusions: Because WTW and ACD measurements using Lenstar were greater than when using ORBscan and calipers, unexpected high-vaulting may be observed due to the selection of a larger-sized posterior chamber phakic intraocular lens. Therefore, the differences in measurements obtained when using these methods should be considered. J Korean Ophthalmol Soc 2014;55(5):656-661

Corneal thickness and elevation measurements using swept‐source optical coherence tomography and slit scanning topography in normal and keratoconic eyes

To compare corneal thickness and corneal elevation using swept source optical coherence tomography and slit scanning topography. Prospective study. 41 normal and 46 keratoconus subjects. All eyes were imaged using swept source optical coherence tomography and slit scanning tomography during the same visit. Mean corneal thickness and best-fit sphere measurements were compared between the instruments. Agreement of measurements between swept source optical coherence tomography and scanning slit topography was analyzed. Intra-rater reproducibility coefficient and intraclass correlation coefficient were evaluated. In normal eyes, central corneal thickness measured by swept source optical coherence tomography was thinner compared with slit scanning topography (p < 0.0001) and ultrasound pachymetry (p = < .0001). Ultrasound pachymetry readings had better 95% limits of agreement with swept source optical coherence tomography than slit scanning topography. In keratoconus eyes, central corneal thickness was thinner on swept source optical coherence tomography than slit scanning topography (p = 0.081) and ultrasound pachymetry (p = 0.001). There were significant differences between thinnest corneal thickness, and, anterior and posterior best-fit sphere measurements between both instruments (p < 0.05 for all). Overall, reproducibility coefficients and intraclass correlation coefficients were significantly better with swept source optical coherence tomography for measurement of central corneal thickness, anterior best-fit sphere and, posterior best-fit sphere (all p < 0.001). Corneal thickness and elevation measurements were significantly different between swept source optical coherence tomography and slit scanning topography. With better reproducibility coefficients and intraclass correlation coefficients, swept source optical coherence tomography may provide a reliable alternative for measurement of corneal parameters.

Changes in Anterior and Posterior Corneal Parameters in Patients with Keratoconus After Intrastromal Corneal-ring Segment Implantation

Purpose: To compare changes in the anterior and the posterior corneal parameters and the anterior chamber depth (ACD) measured by a rotating Scheimpflug camera and scanning-slit topography before and after intrastromal corneal ring segment (ICRS) implantation.Methods: Twenty-five eyes of 21 keratoconus patients who had Intacs (Addition Technology, Sunnyvale, CA) ICRS implantation were included. The anterior segment parameters of the participants were measured before and 3 months after Intacs ICRS implantation with a rotating Scheimpflug camera and scanning-slit topography. Outcome measures included uncorrected (UDVA) and corrected (CDVA) distance visual acuities, refraction and corneal topography.Results: The UDVA improved in 21 eyes (84%) and CDVA in 18 eyes (72%). The anterior average keratometry decreased from 51.80 D preoperatively to 49.59 D postoperatively (p < 0.001) using the rotating Scheimpflug camera and Sim K decreased from 51.21 to 47.44 D using the scanning-slit topography. The posterior average keratometry decreased from −8.03 D preoperatively to −8.42 D postoperatively (p < 0.001) using the rotating Scheimpflug camera. ACD decreased from 3.44 to 3.32 mm (p < 0.001) and from 3.28 to 3.19 mm (p < 0.001) using the rotating Scheimpflug camera and scanning-slit topography, respectively.Conclusions: The implantation of Intacs segments induced corneal flattening of the anterior surface and corneal steepening of the posterior surface. Both anterior corneal flattening and posterior corneal steepening contributed to the decrease in the keratometric power.

White-to-white corneal diameter differences in moderately and highly myopic eyes: Partial coherence interferometry versus scanning-slit topography

To evaluate the differences between Orbscan scanning-slit topography and IOLMaster partial coherence interferometry (PCI) white-to-white (WTW) measurements in moderately and highly myopic eyes. IOBA-Eye Institute, University of Valladolid, Spain. Comparative case series. Myopic eyes were divided according to the degree of myopia as follows: Group 1 (<6.00 diopters [D]), Group 2 (between 6.00 D and 12.00 D), and Group 3 (>12.00 D). The WTW distance was measured with the scanning-slit topography and PCI devices. The study enrolled 328 eyes (64 subjects). The mean WTW in all eyes was 0.50 mm ± 0.26 (SD), lower with scanning-slit topography (11.69 ± 0.37 mm) than with PCI (12.19 ± 0.40 mm) (P<.01, paired t test). A low mean WTW was found in Group 2 (11.65 ± 0.34 and 12.15 ± 0.36 mm, scanning-slit topography and PCI, respectively) and Group 3 (11.51 ± 0.36 and 12.05 ± 0.46 mm, respectively) compared with Group 1 (11.79 ± 0.38 and 12.26 ± 0.40 mm, respectively) (P<.03, analysis of variance with Games-Howell correction). There was a low statistically significant relationship between WTW and spherical equivalent (SE) with both devices. Eyes with moderate and high degrees of myopia had lower WTW diameters than eyes with low spherical equivalent myopia measured with both devices. Scanning-slit topography provided less WTW distance than PCI in myopic eyes; thus, the devices are not clinically interchangeable.

Dependability of Pachymetry Measurements after Myopic Advanced Surface Ablation Using Scanning-Slit Topography and Specular Microscopy

To assess the repeatability, intersession and interobserver reproducibility, and agreement of central corneal thickness (CCT) measurements obtained by scanning-slit topography (SST) and noncontact specular microscopy (NCSM) after advanced surface ablation (ASA). To analyze repeatability, one examiner measured 63 post-myopic ASA eyes five times successively using both techniques randomly. To calculate interobserver reproducibility a second examiner obtained another CCT measurement in a random fashion. To study intersession reproducibility, the first operator obtained CCT measurements from another 24 eyes during two sessions 1 week apart. With regard to intrasession repeatability, SST and NCSM within-subject standard deviation (S(w)) and intraclass correlation coefficient (ICC) were 7.35 and 3.81 μm, and 0.97 and 0.99, respectively. For interobserver reproducibility, SST measurement variability showed correlation with CCT magnitude (r(s) = -0.38; P = 0.002), whereas NCSM did not. NCSM S(w) and ICC were 3.83 μm and 0.99, respectively. For intersession reproducibility, no difference in CCT measurements was found for any technique; S(w) and ICC estimates for SST and NCSM were 12.2 and 8.37 μm, and 0.94 and 0.95, respectively. We found a tendency for the difference (mean SST-NCSM = 13.39 μm) to increase in thicker corneas (r(s) = 0.45, P = 0.001). Both noncontact pachymetry techniques provided highly repeatable and quite reproducible CCT measurements in post-ASA patients having no clinically significant corneal haze, except for SST interobserver reproducibility, which decreased in thinner corneas. However, the techniques were not interchangeable. The estimates provided should help clinicians differentiate real CCT change from noncontact pachymetry measurement variability after ASA.

Measure of keratoconus progression in patients with vernal keratoconjunctivitis using scanning slit topography

To document topographic changes using Orbscan in patients with keratoconus and vernal keratoconjunctivitis over 1 year. Retrospective analysis of clinical and Orbscan data of 22 eyes of 11 patients with keratoconus and VKC with follow up over 1 year period was done. The parameters studied included patients demographics, clinical features, visual acuity, refraction and Orbscan IIz. The changes in various Orbscan parameters were studied over the 1-year period. Mean age was 14±4.1 years. 20 eyes had clinical keratoconus, while 2 had forme fruste keratoconus. 8 eyes of 22 showed evident progression (>1 diopter change in mean simulated (sim) K over 12 months). There was no significant difference in the visual acuity or clinical features over follow up. In patients with progression, statistically significant change (p<0.05) was found in posterior float curvature, sim K astigmatism and maximum astigmatism. Rest of the parameters did not show significant change. Among the patients without evident progression, none of the parameters showed significant change. On comparing the patients with clinical signs of keratoconus with those with only topographic signs of keratoconus, there was no difference between the two groups with respect to the rate of progression of keratoconus. Patients with both mixed type and pure palpebral type of VKC had comparable Orbscan parameters at baseline and 1 year follow up and similar progression rate of keratoconus. Serial topographic analysis provides numerical information about various corneal parameters in patients with vernal keratoconjunctivitis and keratoconus.