Fourier-domain Anterior Segment Optical Coherence Research Articles

Comparison of Automated and Manual Measurement of Corneal Epithelial Thickness in Eyes With Limbal Stem Cell Deficiency.

The purpose of this study was to compare the outcomes of manual and automated corneal epithelial thickness (CET) assessments using anterior segment optical coherence tomography in eyes with limbal stem cell deficiency (LSCD). Eighty-seven eyes from 64 patients with LSCD and 65 eyes from 39 healthy subjects were included in this cross-sectional study. OCT images of corneas were acquired using a Fourier-domain anterior segment optical coherence tomography. The automated measurement of CET was obtained using the manufacturer's program and the manual measurements were obtained by 2 masked observers. The average CET was obtained from 3 consecutive epithelial profile maps. The average CET of manual measurement was obtained from 3 consecutive cross-line scans using 3-point measurement as previously described. The central CET was thinner in patients with LSCD compared with healthy individuals by both manual and automated measurements. Automated CET measurements were similar to the manually obtained CET in the healthy controls (r = 0.911). However, there is a lower correlation between the automated and manually obtained CET in the LSCD group (r = 0.497). Manual measurements of CET (39.8 ± 11 μm) in eyes with LSCD were significantly lower than the automated measurements (48.8 ± 7.2 μm, P = 0.001, 95% CI -11.0 to -6.9). The correlations between the automated and manually obtained measurements in the mild, moderate, and severe stages of LSCD were 0.623, 0.632, and 0.378, respectively. There is a large discrepancy between the manual and automated measurements in eyes with LSCD but not in normal eyes. Automated measurements in LSCD exhibited a higher rate of errors and nonuniform measurements due to the presence of subepithelial scars. Automated CET measurements appear to be unreliable in eyes with corneal scars in LSCD.

Longitudinal Epithelial Thickness Profile Changes 18 Months After Photorefractive Keratectomy.

Long-term evaluation of corneal epithelial thickness (ET) profile changes after photorefractive keratectomy (PRK) using Fourier-domain anterior segment optical coherence tomography. Three hundred twenty-six eyes of 163 patients were included in this prospective observational study. The corneal epithelial map was obtained across a 9-mm diameter area of the cornea before and up to 27 months after surgery. ET was assessed in 25 sectors and 4 annular zones (central 2 mm, paracentral 2-5 mm, midperipheral 5-7 mm, and peripheral 7-9 mm). There was a significant reduction in mean ET in all zones 1 month after PRK. Subsequently, ET increased in all annular zones. The change in mean ET became stable in the midperipheral and peripheral zones at 3 to 6 months and in the central zone at 12 months, and it continued to increase in the paracentral zone even after 18 months after surgery. The ET was 3.40 μm and 4.05 μm in the central and paracentral zones at 6 months, respectively. Postoperative spherical equivalent changed significantly only from 1 to 3 months (P < 0.04). There was a significant correlation between postoperative spherical equivalent at month 1 and ET change in the paracentral and midperipheral zones (P < 0.027). There is a significant reduction in ET 1 month after myopic PRK with a gradual thickening thereafter until it reaches stability at 12 months in the central zone. However, it continues to change even after 18 months in the paracentral zone. The greatest thickening is in the paracentral zone, followed by the central zone.

Agreement of corneal curvature and central corneal thickness obtained from a swept-source OCT and Pentacam in ectopia lentis patients

To assess the inter-device consistency of corneal curvature and central corneal thickness between Pentacam and a swept-source Fourier-domain anterior segment optical coherence tomography (AS-OCT) in ectopia lentis patients. Totally 72 eyes of ectopia lentis patients were recruited. Central corneal thickness (CCT), corneal curvature values and corneal astigmatism were obtained from both the Pentacam and AS-OCT (CASIA2). Repeatability was evaluated for both devices. The coefficient of repeatability (COR) and the relative COR was calculated. Bland-Altman plots were conducted to evaluate the inter-device agreement of measurement. Orthogonal linear regression was used to examine any proportional bias. The mean difference of CCT, steep anterior corneal curvature (anterior KS), flat anterior corneal curvature (anterior Kf), anterior corneal astigmatism (ACA), steep posterior corneal curvature (posterior KS), flat posterior corneal curvature (posterior Kf), posterior corneal astigmatism (PCA), steep true net power (TNP KS), flat true net power (TNP Kf) and total corneal astigmatism (TCA) between Pentacam and CASIA2 were 7.03±9.70 µm, -0.19±0.41 D, -0.27±0.35 D, 0.04±0.47 D, -0.17±0.23 D, -0.11±0.11 D, -0.02±1.02 D -0.41±0.43 D, -0.52±0.46 D, and -0.15±0.96 D, respectively. For measurement of TNP Kf with the Pentacam and CASIA2, a mean difference of 0.52 D and COR of 0.90 with P=0.02 was detected. There was no significant difference in CCT (P=0.393), anterior Kf (P=0.107), anterior Ks (P=0.414), ACA (P=0.131), posterior Kf (P=0.286), posterior Ks (P=0.418), PCA (P=0.105), TNP Ks (P=0.054), and TCA (P=0.977) between Pentacam and CASIA2. Our study reveals good agreement of CCT, corneal curvature and corneal astigmatism measured by CASIA2 and Pentacam in ectopia lentis patients. However, there was significant difference for CCT and corneal curvature values obtained by the two devices.

Screening for Subclinical Keratoconus Using Swept-Source Fourier Domain Anterior Segment Optical Coherence Tomography.

To discriminate between subclinical fellow eyes of patients with keratoconus (scKCE) and normal eyes (NE) using swept-source Fourier-domain anterior segment optical coherence tomography (SS-OCT). University Medical Center Hamburg-Eppendorf, Germany. Retrospective cross-sectional study. NE (both eyes with a KISA% Index <60; N = 213) and scKCE (KISA% Index <60, but an index of >100 in the fellow eye; N = 61) eyes were grouped according to the KISA% Index. Topography and tomography data were obtained by SS-OCT (Casia SS1000) and reviewed retrospectively. Receiver operating characteristics were performed for Casia SS1000 integrated automated parameters and newly computed indices. Additionally, discriminant functions were calculated for the automated single parameters, the computed indices, and the combination of both. An accuracy ≥0.7 was reached for 28 (8 automated and 20 newly computed parameters) of 785 parameters. Fourier analysis posterior higher-order irregular astigmatism revealed the highest accuracy with 0.81. By combining automated parameters with the newly computed indices in 1 discriminant function, an area under the curve of 0.92 with a corresponding accuracy of 0.85 was achieved. SS-OCT is able to discriminate between NE and scKCE with high accuracy. Automated single parameters and newly computed indices were combined to further improve this accuracy.

Effects of long-term soft contact lens wear on the corneal thickness and corneal epithelial thickness of myopic subjects.

To perform safe and successful corneal refractive surgery on myopic patients, corneal thickness (CT) and corneal epithelial thickness (CET) must be accurately measured. Numerous individuals with myopia wear soft contact lenses (SCLs) for the correction of visual acuity but may subsequently undergo corneal refractive surgery. The aim of the present study was therefore to investigate the effects of long-term SCL wear on the CT and the CET of myopic subjects in order to guarantee the safety and accuracy of subsequent corneal refractive surgeries. Fifty-six subjects prepared to receive refractive surgery at Jinan Mingshui Eye Hospital (Zhangqiu, China) from April to July 2013 were included in the study. CT and CET were measured in subjects immediately following discontinued SCL wear (group I, 56 eyes), and subsequently following >two weeks of discontinued SCL wear (group II, 56 eyes). Ninety-four subjects with no history of corneal contact lens wear were enrolled as a control group. The CT and CET were measured at positions with a radius of 0.0‑1.0, 1.0-2.5 (divided into eight quadrants) and 2.5-3.0 mm (divided into eight quadrants) away from the corneal center using the RTVue-100 Fourier-domain anterior segment optical coherence tomography system. A significant decrease in the CT of the subjects in group II was observed, compared with that of group I and the control group (P<0.05). A significant decrease was observed in the CET of groups I and II compared with that of the control group (P<0.05). Following discontinuation of SCL wear, CET increased. However, the increased CET was unable to reach the normal range exhibited by the control group. Edema and thinning of the corneal stroma, as well as thinning of the corneal epithelium were observed in groups I and II. In conclusion, it was proposed that in clinical practice, for myopic patients following long-term SCL wear, CT and CET should be determined ≥ two weeks following discontinuation of SCL wear, once a stable CT and CET are obtained.

Epithelial remodeling after partial topography-guided normalization and high-fluence short-duration crosslinking (Athens protocol): Results up to 1 year

To compare epithelial remodeling in keratoconic eyes that had photorefractive keratectomy and corneal collagen crosslinking (Athens protocol) with that in untreated keratoconic eyes and healthy eyes. Private clinical practice, Athens, Greece. Comparative case series. Fourier-domain anterior segment optical coherence tomography (AS-OCT) was used to obtain in vivo 3-dimensional epithelial thickness maps and center, superior, inferior, maximum, minimum, mean, midperipheral, and variability data. Group A comprised 175 treated keratoconic eyes (Athens protocol); Group B, 193 untreated keratoconic eyes; and Group C, 160 healthy eyes. The 1-year mean center epithelial thickness in Group A was 47.78 μm ± 7.36 (SD) (range 33 to 64 μm). At the first clinical visit, it was 52.09 ± 6.80 μm (range 36 to 72 μm) in Group B and 52.54 ± 3.23 μm (range 45 to 59 μm) in Group C. The mean thickness range in Group A at 1 year was -19.94 ± 7.21 μm (range -6 to -34 μm). It was -21.83 ± 12.07 μm (range -4 to -66 μm) in Group B and -6.86 ± 3.33 μm (range -3 to -29 μm) in Group C. The mean topographic thickness variability in Group A at 1 year was 4.64 ± 1.63 μm (range 1.6 to 8.1 μm) (P<.05). It was 5.77 ± 3.39 μm (range 1.3 to 17.8 μm) in Group B and 1.59 ± 0.79 μm (range 0.6 to 5.6 μm) in Group C. Anterior segment OCT indicated a thinner and more homogeneous remodeled epithelium in the keratoconic eyes treated using the Athens protocol. Dr. Kanellopoulos is a consultant to Alcon Surgical, Inc.; Wavelight Laser Technologie AG; Avedro, Inc.; and i-Optics Optikgeräte GmbH. Dr. Asimellis has no financial or proprietary interest in any material or method mentioned.

Accuracy of LASIK Flap Thickness Obtained Using 2 Types of Moria M2 Single-use Head Microkeratome Measured Postoperatively by Optical Coherence Tomography

Background: To investigate the accuracy of corneal flap thickness (FT) and to examine the potential factors that can influence flap thickness obtained using Moria M2 microkeratomes with two kinds of single-use heads. Methods: A retrospective review of the records of 90 patients who had undergone LASIK between Jun 2011 and Jan 2012 at Tri-Service General Hospital was performed. Creation of corneal flap was achieved by automated Moria M2 microkeratome with two different types of single-use head (SU90 and SU130). The right eye was operated before the left eye in each patient, using the same blade. Additionally, the corneal flap thickness was measured in all cases using the Fourier-domain anterior segment optical coherence tomography (AS-OCT) one week later. Results: The mean central thickness of corneal flap was 114.26±4.49μm (Range, 106~127μm) in the SU 90 head and 146.98±3.62μm (Range, 140~157μm) in the SU130 head. The difference between the first and second eye operated was not significant. There were no free flaps, incomplete flaps or flaps with buttonholes in any of our cases. Conclusions: Moria M2 SU 90 and SU 130 produce accurate, reproducible, safe and cost-effective corneal flap. Thin flaps achieved by both single-use heads did not increase the rate of flap-related complications. Furthermore, AS-OCT is a noncontact, rapid, and repeatable tool for measuring corneal flap thickness and making morphological observations.

Reliability and repeatability of swept-source Fourier-domain optical coherence tomography and Scheimpflug imaging in keratoconus

To evaluate the repeatability and reliability of a recently introduced swept-source Fourier-domain anterior segment optical coherence tomography (AS-OCT) system and a high-resolution Scheimpflug camera and to assess the agreement between the 2 instruments when measuring healthy eyes and eyes with keratoconus. Department of Ophthalmology, Medical and Health Science Center, University of Debrecen, Debrecen, Hungary. Evaluation of diagnostic test or technology. Three consecutive series of anterior segment images were taken with AS-OCT (Casia SS-1000) followed by rotating Scheimpflug imaging (Pentacam high resolution). Axial keratometry in the steep and flat meridians and astigmatism values were recorded. Pachymetry in the apex, center, and the thinnest position and anterior chamber depth (ACD) measurements were also taken. This study enrolled 57 healthy volunteers (57 eyes) and 56 patients (84 eyes) with keratoconus. Significant difference was found in all measured anterior segment parameters between normal eyes and keratoconic eyes (P<.05). In keratoconic eyes, the difference between repeated measurements was less with AS-OCT than with Scheimpflug imaging in every keratometry and astigmatism value, in apical thickness, and in ACD. For keratometry, the thinnest and central pachymetry measurement repeatability was better in healthy eyes than in keratoconic eyes with both instruments. In general, the mean difference between AS-OCT and Scheimpflug imaging was higher in cases of keratoconus. Significant differences in keratometry, pachymetry, and ACD results were found between AS-OCT and Scheimpflug imaging. However, the repeatability of the measurements was comparable. No author has a financial or proprietary interest in any material or method mentioned.

Age-related Variations of Human Tear Meniscus and Diagnosis of Dry Eye With Fourier-domain Anterior Segment Optical Coherence Tomography

To determine the age-related variations in the human tear meniscus using Fourier-domain anterior segment optical coherence tomography (FD-ASOCT) and evaluate its application in dry eye screening and diagnosis. One hundred forty-six patients with dry eye and 160 healthy controls were enrolled in this prospective, randomized, case-control study and grouped according to age: group A (0-19 years), group B (20-39 years), group C (40-59 years), and group D (>60 years). Tear meniscus height, tear meniscus depth, and tear meniscus cross-sectional area (TMA) were measured using FD-ASOCT (RTVue-100); corneal fluorescein staining, tear film breakup time, Schirmer I test, and a dry eye questionnaire were also estimated. Tear meniscus values were significantly correlated with clinical examination results and dry eye syndrome. Mean tear meniscus height, tear meniscus depth, and TMA values of patients with dry eye were significantly lower than those of the controls (P < 0.05). Tear meniscus values were negatively correlated with age in healthy Chinese subjects. Intraindividual variations in optical coherence tomography results were small in each group. Accuracy of dry eye diagnosis by FD-ASOCT was approximately 70%, and the clinical diagnostic critical point became lower with increasing age. Significant differences were observed in the tear meniscus borderline, TMA, and tear transparency between the 2 groups. FD-ASOCT provides blur-free imaging and precise measurement of the tear meniscus, which is consistent with clinical examinations. Therefore, FD-ASOCT is expected to become a valuable technique in dry eye screening and diagnosis.

Anterior segment optical coherence tomography evaluation and comparison of main clear corneal incisions in microcoaxial and biaxial cataract surgery

To use Fourier-domain anterior segment optical coherence tomography (AS-OCT)) to evaluate the main clear corneal incisions (CCIs) in microcoaxial and biaxial cataract surgery, the effects of incision enlargement, and the probable reasons for problematic healing. Atatürk Training and Research Hospital, 2nd Ophthalmology Department, Ankara, Turkey. Cohort study. Eyes that had microcoaxial cataract surgery through a 1.8 mm CCI or biaxial cataract surgery through a 1.2 to 1.4 mm trapezoidal CCI were divided into 2 equal subgroups based on incision enlargement. All surgeries were completed by stromal hydration. Incisions were evaluated 1, 8, and 30 days postoperatively. The CCIs in the microcoaxial group were longer, thinner, and more slanted than those in the biaxial group, with no statistical difference. The microcoaxial incisions had significantly more arcuate configuration at 1 day (P=.003); however, the configuration became linear in the following days in both groups. The endothelial gap rates were less and Descemet membrane detachment rates greater than reported in the literature. In eyes with enlarged CCIs, the endothelial gap rate was higher in the microcoaxial group and the Descemet membrane detachment rate was higher in the biaxial group (both P=.05). At 1 day, the intraocular pressure (IOP) was significantly lower in Descemet membrane detachment and endothelial gap cases (P=.006 and P<.001, respectively). Although closure was reliable in both groups, the microcoaxial group had slightly fewer undesirable effects on the incision site. Low postoperative IOP seemed to be a significant factor in problematic healing.

Angle changes before and after cataract surgery assessed by Fourier-domain anterior segment optical coherence tomography

To quantify angle changes after phacoemulsification extracapsular cataract extraction using Fourier-domain anterior segment optical coherence tomography (AS-OCT). Department of Ophthalmology, Tri-Service General Hospital, National Defense Medical Center, Taiwan. Case series. Fourier-domain AS-OCT examinations were performed in patients between 15 and 91 years of age 1 week before and 1 week after cataract surgery. The angle, angle-opening distance at 500 μm, and trabecular-iris space area at 500 μm in the temporal and nasal quadrants were obtained. Patients were then grouped on the basis of age (<60 years or ≥60 years) and the results compared between groups. Eighty-nine eyes of 80 patients were evaluated. The angle, angle-opening distance at 500 μm, and trabecular-iris space area at 500 μm increased significantly after cataract surgery in the entire study population (P<.001). There were larger postoperative differences in all 3 parameters in nasal and temporal measurements in patients 60 years or older (all P<.001). The angle changed significantly after cataract surgery, particularly in the temporal quadrant and its magnitudes. Postoperative angle changes were larger in older patients, which may be related to the increase in lens volume during the aging process. Fourier-domain AS-OCT can be used as a rapid and safe tool in addition to diagnostic gonioscopy in assessing anterior chamber angles.