Fourier-domain Anterior Segment Optical Coherence Tomography Research Articles

Using Anterior Segment Optical Coherence Tomography (ASOCT) Parameters to Determine Pupillary Block Versus Plateau Iris Configuration.

Investigate anterior segment parameters to distinguish between 2 mechanisms of angle closure, PB and PIC, using swept-source Fourier domain ASOCT. Retrospective ASOCT images from narrow angle eyes were reviewed. PIC was defined either by ultrasound biomicroscopy and/or clinically when an iridoplasty was performed. Images were read by a masked reader using Anterior Chamber Analysis and Interpretation software to identify scleral spur landmarks and calculate anterior chamber, peripheral angle, iris size, iris shape, and lens/pupil size parameters. ASOCT parameters were summarized and compared using the 2-sample t test. Thresholds and area under receiver operating characteristic curve were calculated using logistic regression analysis. One hundred eyes (66 PB and 34 PIC) of 100 participants were reviewed. Of all ASOCT parameters, iris length in each quadrant, pupil arc, lens/pupil parameters (pupil arc, lens vault, and pupil diameter), all pupillary margin-center point-scleral spur landmark (PM-C-SSL) parameters, and all except superior central iris vault parameters were significantly different between PB and PIC. On threshold evaluation, lens/pupil parameters had the greatest area under receiver operating characteristic curve values (0.77 to 0.80), followed by PM-C-SSL angles (0.71 to 0.75). We propose that the pupil size parameters and PM-C-SSL angle are the most reliable novel ASOCT parameters to distinguish between PB and PIC eyes. These parameters do not rely on the visibility of the posterior iris surface, which is difficult to identify with ASOCT, but may be ambient lighting dependent.

In Vivo Evaluation of the Limbus Using Anterior Segment Optical Coherence Tomography.

PurposesTo investigate the limbal structure using anterior segment optical coherence tomography (AS-OCT) and compare the difference between a Chinese Han population and a Caucasian population.MethodsSixty healthy Chinese Han subjects (109 eyes, Chinese group) and 32 healthy Caucasian subjects (51 eyes, Caucasian group) were included in this comparative cross-sectional study. The central cornea and the superior, inferior, nasal, and temporal limbal regions of each subject underwent Fourier-domain AS-OCT. The following parameters were measured: corneal epithelial thickness (CET), maximum limbal epithelial thickness (LET), the mean LET, the width of limbus, distance between scleral spur and the location where limbal epithelium was the thickest (S-T), and limbal epithelial area between scleral spur and the end of Bowman's layer (LEA).ResultsCET was similar in both groups (P = 0.577). The width of limbus was more than 32.8% greater in all limbal quadrants in the Caucasian group (range, 1.25–2.20 mm) than in the Chinese group (range, 0.81–1.40 mm). S-T and LEA were also significantly higher in all limbal quadrants in the Caucasian group (all P < 0.001). The maximum LET and mean LET were 7.8% and 6.9% thicker at the nasal limbus and 8.1% and 8.7% thicker in the temporal limbus in Caucasian subjects than in Chinese subjects.ConclusionsThe limbal structures can be visualized using AS-OCT and differ significantly between the Caucasian and Chinese eyes.Translational RelevanceResearch of the limbus and surgeons performing procedures involving the limbal area should take into consideration of the anatomic differences especially when limbus is used as an anatomic reference.

Agreement of Anterior Segment Parameters Obtained From Swept-Source Fourier-Domain and Time-Domain Anterior Segment Optical Coherence Tomography.

PurposeTo assess the interdevice agreement between swept-source Fourier-domain and time-domain anterior segment optical coherence tomography (AS-OCT).MethodsFifty-three eyes from 41 subjects underwent CASIA2 and Visante OCT imaging. One hundred eighty–degree axis images were measured with the built-in two-dimensional analysis software for the swept-source Fourier-domain AS-OCT (CASIA2) and a customized program for the time-domain AS-OCT (Visante OCT). In both devices, we examined the angle opening distance (AOD), trabecular iris space area (TISA), angle recess area (ARA), anterior chamber depth (ACD), anterior chamber width (ACW), and lens vault (LV). Bland-Altman plots and intraclass correlation (ICC) were performed. Orthogonal linear regression assessed any proportional bias.ResultsICC showed strong correlation for LV (0.925) and ACD (0.992) and moderate agreement for ACW (0.801). ICC suggested good agreement for all angle parameters (0.771–0.878) except temporal AOD500 (0.743) and ARA750 (nasal 0.481; temporal 0.481). There was a proportional bias in nasal ARA750 (slope 2.44, 95% confidence interval [CI]: 1.95–3.18), temporal ARA750 (slope 2.57, 95% CI: 2.04–3.40), and nasal TISA500 (slope 1.30, 95% CI: 1.12–1.54). Bland-Altman plots demonstrated in all measured parameters a minimal mean difference between the two devices (−0.089 to 0.063); however, evidence of constant bias was found in nasal AOD250, nasal AOD500, nasal AOD750, nasal ARA750, temporal AOD500, temporal AOD750, temporal ARA750, and ACD. Among the parameters with constant biases, CASIA2 tends to give the larger numbers.ConclusionsBoth devices had generally good agreement. However, there were proportional and constant biases in most angle parameters. Thus, it is not recommended that values be used interchangeably.

Optical coherence tomography–derived corneal thickness asymmetry indices: Clinical reference study of normal eyes

To determine 3-dimensional corneal pachymetry distribution characteristics in a large pool of healthy normal patients. Private practice, Athens, Greece. Prospective case series. Spectral-domain anterior segment optical coherence tomography (AS-OCT) was used for measurements of central (CCT) and minimum corneal thickness, thickness asymmetry indices for superonasal-inferotemporal (SN-IT) and superior-inferior (S-I), and focal thinning indices (Min-Med focal thinning, Min-Max thickness range). The study enrolled 561 eyes. The mean values were CCT, 537.17 μm ± 30.99 (SD) (range 447.0 to 654.0 μm); minimum corneal thickness, 529.01 ± 30.02 μm (range 435.0 to 644.0 μm); SN-IT, 26.32 ± 15.06 μm (range -23.0 to 97.0 μm); S-I, 25.34 ± 15.06 μm (range -36.0 to 93.0 μm); Min-Med, -20.70 ± 5.99 μm (range -7.0 to -50.0 μm); Min-Max, -59.79 ± 16.55 μm (range -156.0 to -23.0 μm). There were significant age-related differences; the mean SN-IT was 22.19 ± 12.40 μm (range -6.0 to 63.0 μm) in the younger group and 30.44 ± 15.07 μm (range -4.0 to 97.0 μm) in the older group (P=.002). The mean S-I was 21.47 ± 12.92 μm (range -5.0 to 70.0 μm) and 29.76 ± 16.27 μm (range -8.0 to 93.0 μm), respectively (P=.001). Corneal-thickness asymmetry distribution in a healthy eye population obtained by Fourier-domain AS-OCT showed increased asymmetry in the older group; the asymmetry was not sex dependent. These findings may provide a benchmark for future comparative studies. Dr. Kanellopoulos is a consultant to Alcon Laboratories, Inc., Allergan, Inc., Avedro, Inc., Keramed, Inc., and i-Optics. No other author has a financial or proprietary interest in any material or method mentioned.

In Vivo Imaging of Radial Keratoneuritis in Patients with Acanthamoeba keratitis by Anterior-Segment Optical Coherence Tomography

To investigate in vivo corneal changes of radial keratoneuritis in early-stage Acanthamoeba keratitis (AK) using anterior-segment optical coherence tomography (AS-OCT). Single-center, prospective clinical study. Four eyes (4 patients with a mean age of 28.5 years) with early-stage AK showing radial keratoneuritis were included in this study. Definitive diagnosis was made by confirmation of AK cysts using in vivo confocal microscopy and culture. Anterior-segment OCT examination was performed on the initial visit and at follow-up visits paying special attention to radial keratoneuritis. Selected AS-OCT images of the cornea were evaluated qualitatively for the shape and degree of light reflection of abnormal neurons. With the use of AS-OCT, we successfully obtained high-resolution images of putative radial keratoneuritis in all patients as highly reflective bands or lines in the corneal stroma. The depth and width of the highly reflective bands/lines varied from case to case (anterior stroma to mid-stroma, from 20 to 200 μm). Some lines ran obliquely from the deep peripheral stroma toward the anterior stroma, and some were located at different depths (subepithelial and mid-stroma) and ran relatively parallel to the corneal layers. After appropriate treatment, radial keratoneuritis was resolved by both slit-lamp biomicroscopy and AS-OCT in all patients. High-resolution Fourier-domain AS-OCT provides novel and detailed visual information of radial keratoneuritis in patients with early-stage AK. Visualization of radial keratoneuritis by AS-OCT may be a useful adjunct to the diagnosis and follow-up of early-stage AK.

A novel OCT technique to measure in vivo the corneal adhesiveness for sodium carboxymethylcellulose in humans and its validity in the diagnosis of dry eye.

The purpose of this work was to gather preliminary data on tear film stability, and the adhesive properties of the corneal surface in dry eye patients and control group subjects, using a new, minimally invasive optical coherence tomography (OCT) imaging method. We screened 85 human subjects for dry eye and classified them in two groups, as dry eye or normal patients. Sodium carboxymethylcellulose (NaCMC) adhesiveness over the central cornea was measured using Fourier domain anterior segment OCT. The corneal adhesiveness for NaCMC was compared between the two groups, correlated with classical tests, and analyzed for diagnostic validity and repeatability. The corneal adhesiveness for NaCMC median and mode values was fair (between 1 and 3 minutes) for dry eye subjects (n = 36) and borderline (between 3 and 5 minutes) for control group subjects (n = 49), and was significantly different between the two groups (P < 0.001). Significant correlations were observed between the corneal adhesiveness measures and dry eye patients' symptoms (P < 0.001), Schirmer I test (P < 0.001), ocular surface staining (P < 0.001), and, particularly, fluorescein break-up time (P < 0.001). The area under the receiver operating characteristic curve was 0.94 (P < 0.001), suggesting reliable sensitivity and specificity of OCT imaging. A statistically significant intraclass correlation (ICC) value of 0.99 was found for measurements of corneal adhesiveness on two subsequent days at the same time (P < 0.001). This minimally invasive, novel technique of OCT imaging of the corneal surface following NaCMC drop instillation provides a measure of corneal adhesiveness. This technique may improve the clinician's ability in the understanding and diagnosis of the dry eye syndrome.

Anterior-Segment Optical Coherence Tomography Investigation of Corneal Deturgescence and Epithelial Remodeling After DSAEK

The aim of this study was to evaluate via Fourier-domain anterior-segment optical coherence tomography 3-dimensional corneal, epithelial, and graft thickness changes after Descemet stripping automated endothelial keratoplasty (DSAEK). Sixteen eyes were investigated preoperatively and up to 6 months postoperatively for preoperative and postoperative central corneal thickness (CCT), minimum corneal thickness, central graft thickness (CGT), and for epithelial topographic thickness variability. An age-matched and gender-matched control group of 32 healthy eyes was used for comparison. In the DSAEK group, the preoperative CCT was 582.32 ± 45.24 (550-615) μm. One-month postoperatively, the CCT was 736.26 ± 34.52 (713-771) μm, and the CGT was 210.42 ± 34.52 (145-243) μm. Three months postoperatively, the CCT was 641.39 ± 38.75 (569-684) μm, and the CGT was 171.23 ± 27.54 (119-185) μm. The preoperative center epithelial thickness was 55.74 ± 9.29 (45-74) μm, the minimum was 32.53 ± 14.30 (13-53) μm, the maximum was 76.00 ± 11.32 (64-105) μm, and the topographic thickness variability was 10.84 ± 4.09 (5.90-18.80) μm. Three months postoperatively, the center epithelial thickness was 47.21 ± 5.45 (43-56) μm, the minimum was 35.11 ± 4.70 (30-41) μm, the maximum was 58.11 ± 6.51 (49-65) μm, and the topographic variability was 4.77 ± 1.48 (2.90-6.50) μm. The average differences were -8.53, +4.53, and -17.89 μm for the center, minimum, and maximum (P < 0.001, <0.001, and <0.001). Similar results were obtained 3 and 6 months postoperatively. We present a near-term postoperative investigation of the corneal and epithelial thickness changes after DSAEK for bullous keratopathy, by in vivo, clinical anterior-segment optical coherence tomography. Epithelial thickness recovery and normalization and corneal deturgescence were noted as early as in the first postoperative month.

Limitations in imaging common conjunctival and corneal pathologies with fourier-domain optical coherence tomography.

Purpose:To describe the limitations of Fourier-domain optical coherence tomography (OCT) in imaging common conjunctival and corneal pathology.Materials and Methods:Retrospective, single-center case series of 40 patients with conjunctival and cornea pathology.Results:Fourier-domain OCT imaged laser in situ keratomileusis (LASIK) flaps in detail, including its relation to other corneal structures and abnormalities. Similarly, in infectious or degenerative corneal disorders, Fourier-domain OCT successfully showed the extent of infiltration or material deposition, which appeared as hyper-reflective areas. In cases with pterygium, the underlying cornea could not be imaged. All cases of common conjunctival pathologies, such as nevus or pinguecula, were successfully imaged in detail. Nevi, scleritis, pterygium, pinguecula, and subconjunctival hemorrhage were hyper-reflective lesions, while cysts and lymphangiectasia were hyporeflective. The details of the underlying sclera were not uniformly imaged in conjunctival pathologies. Fourier-domain OCT imaged the trabeculectomy bleb in detail, whereas the details of structures of the anterior chamber angle were not routinely visualized in all cases.Conclusions:Light scatter through vascularized, densely inflamed, or thick lesions limits the imaging capabilities of Fourier-domain anterior segment OCT.

Graft profile and thickness as a function of cut transition speed in Descemet-stripping automated endothelial keratoplasty

To determine the profile of endothelial keratoplasty lenticules prepared using a microkeratome and evaluate the impact of varying cut transition speed on cut depth and profile using anterior segment optical coherence tomography (AS-OCT). Department of Cornea and External Diseases, Moorfields Eye Hospital, London. United Kingdom. Experimental study. Fourier-domain AS-OCT was used to image 25 corneal specimens before and after microkeratome dissection with a 350 μm head. A pilot series of 7 corneas were cut and imaged with the following 18 corneas divided into regular cut transition speed and slow cut transition speed groups (9 in each). Proximal, central, and distal precut corneal thickness and post-cut residual bed thickness were measured using the integrated caliper tools of the Fourier-domain AS-OCT device. Cut depth was calculated by subtraction. The slower microkeratome pass speed produced significantly thinner donor lenticules (mean 148 ± 45 μm [SD]) than the standard pass speed (mean 234 ± 35 μm) (P ≤.0001). In both groups, significant asymmetry was observed in donor lenticules with a deeper cut depth and a thinner lenticule at the beginning of the microkeratome pass (proximal stromal bed). The mean difference between the proximal and distal stromal bed thickness was 61 ± 63 μm in the standard group and 52 ± 22 μm in the slow-pass group (P=.159). Reducing the transition speed in microkeratome dissection produced thinner donor lenticules. Thickness asymmetry is an inherent flaw with current microkeratome dissection that cannot be easily corrected by altering preparation technique.

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.

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.