Spectral-domain optical coherence tomography for evaluating palisades of Vogt in ocular surface disorders with limbal involvement.

Spectral-domain optical coherence tomography (SD-OCT) has been used to observe the morphology of the palisades of Vogt (POV) with satisfactory resolutions. In this study, we used SD-OCT to examine the microstructure of the POV in ocular surface disorders with limbal involvement. We detect subclinical limbal pathologies based on five parameters, including (1) decreased epithelial thickness, (2) loss of the sharp stromal tip, (3) loss of the smooth epithelial-stromal interface, (4) dilated stromal vessels, and (5) decreased POV density. Eighteen eyes of 10 patients with advancing wavelike epitheliopathy (AWE) and 15 eyes of 9 patients with phlyctenular keratitis/ocular rosacea were recruited. SD-OCT could detect abnormal changes in the POV in 100% of the lesion sites. In presumed-healthy areas of the diseased eyes diagnosed by slit-lamp biomicroscopy, SD-OCT detected abnormal changes in the POV in 100% of the eyes in both groups. In patients with unilateral disease, abnormal changes in the POV were detected by SD-OCT in 50% and 100% of presumed-healthy eyes diagnosed by slit-lamp biomicroscopy in the AWE group and phlyctenular keratitis/ocular rosacea group, respectively. SD-OCT is powerful in detecting POV changes in ocular surface disorders and can provide useful information that cannot be provided by slit-lamp biomicroscopy.

Anterior Segment Optical Coherence Tomography in Locating the Insertion of Horizontal Extraocular Muscles After Strabismus Surgery.

PURPOSE: To evaluate the accuracy of anterior segment optical coherence tomography (AS-OCT) for locating horizontal extraocular muscle (EOM) insertion after strabismus surgery. METHODS: The distance from the limbus to the postoperative muscle insertion was measured with calipers intraoperatively and by AS-OCT during the postoperative visit of adults undergoing strabismus surgery. Images were collected by masked technicians. Intraclass correlation coefficients (ICC) were used to evaluate the agreement between measurements. RESULTS: Twenty-eight patients were recruited. Measurements were taken from 31 eyes, including 17 lateral and 14 medial rectus muscles. EOM insertion was successfully identified by AS-OCT for 14 (45%) cases. The ICC between intra-operative and AS-OCT measurement was 0.886 when the distance from the limbus to the insertion of EOM was less than 8 mm and 0.001 when the distance from the limbus was between 8 and 10 mm. EOM insertion was undetectable if distance to the limbus was greater than 10 mm. CONCLUSIONS: AS-OCT can accurately identify post-surgical horizontal muscle insertion if the insertion is less than 8 mm from the limbus. [J Pediatr Ophthalmol Strabismus. 2021;58(1):62-65.].

The impact of limbus detection, arcus lipoides and limbal vessels on the primary patency of clear cornea incisions in femtosecond laser-assisted cataract surgery.

PURPOSE: To analyse the factors influencing the primary patency of clear corneal incisions in femtosecond laser-assisted cataract surgery (FLACS). METHODS: In this prospective single-centre study, the graphical user interfaces of 159 patients undergoing femtosecond laser-assisted cataract surgery were documented by video. Subsequently, the quality of limbus detection along with the incidence of vessels and an arcus lipoides were assessed by a grading system and analysed in relation to the primary patency of the incisions. In particular, the differences between a superior and a temporal main incision were analysed. RESULTS: The designed grading system could be applied in all cases without any problems. Limbus detection was highly inhomogeneous but had no influence on the patency of the incisions (46.3% poor, 18.4% moderate, 35.1% good). The characteristics of the arcus lipoides had little influence on the patency of the main incisions. Pronounced vascular ingrowth caused more tissue bridges but did not reduce the patency of the incisions. Temporal access was generally easier to open than a superior one (97.1% versus 88.9%). CONCLUSION: We showed a patency rate of superior FLACS incisions of over 97% with the Femto LDV Z8 in our study. Temporal main incision is preferable to superior main incision in more difficult situations. The new grading system is suitable for further studies to provide information on the quality of the incision.

Serial anterior segment optical coherence tomography post autologous simple limbal epithelial transplantation.

A 24-year-old young man presented to us with total limbal stem cell deficiency (LSCD) in the right eye 1 year post ocular chemical burn. The patient subsequently underwent limbal biopsy in the healthy contralateral eye and autologous simple limbal epithelial transplantation in the right eye. The patient was followed up with sequential imaging of the cornea with high-resolution anterior segment optical coherence tomography (HR-ASOCT) for 3 years. The serial HR-ASOCT imaging in the operated eye showed regeneration of the epithelium from the limbal transplant over the human amniotic membrane (hAM) with integration of the transplant within the cornea with subepithelial retention of the hAM. Over the long-term follow-up, thinning of the hAM and thickening of the epithelium was noted. At 3 years, the cornea maintained an intact epithelium with no signs of recurrence of LSCD.

Collector Channels: Role and Evaluation in Schlemm's Canal Surgery.

OBJECTIVES: 1) To elucidate the role of collector channels in the aqueous humor outflow pathway 2) To suggest anatomic and functional methods of imaging collector channels in-vitro and in-vivo and 3) To discuss the role of such imaging modalities in the surgical management of glaucoma. METHODS: A thorough literature search was conducted on databases for studies published in English regarding the available methods to determine the role of collecting channels in normal and glaucomatous patients and to assess their patency. RESULTS: Intraocular pressure (IOP) exists as a balance between aqueous humor production and aqueous humor outflow. Collector channels are an essential anatomical constituent of the distal portion of the conventional aqueous humor outflow pathway. There are different surgical options for glaucoma management and with the recent advances in Schlemm's canal-based surgeries, collector channel's patency became a key factor in determining the optimum management for the glaucomatous eye. The advent of anatomic imaging methods has improved the ability to visualize collector channel morphology in-vitro, including swept-source optical coherence tomography (SS-OCT), spectral domain optical coherence tomography (SD-OCT), micro-computed tomography (micro CT), new immunohistochemistry techniques and scanning electron microscopy. The recent advent of real-time assessment of collector channel patency (including evaluation of episcleral venous outflow, observation of episcleral venous fluid wave, and tracer studies utilizing fluorescein, indocyanine green, and trypan blue) has been validated by the aforementioned anatomic imaging modalities. CONCLUSIONS: New modalities of in-vitro and in-vivo studies of collector channels provide promise to aid in the assessment of collector channel patency and individualization of surgical management for glaucoma patients.

Microarchitecture of Schlemm Canal Before and After Cataract Extraction Surgery.

PRECIS: Schlemm canal (SC) expands after cataract extraction (CE), both in the area and in volume by 25% as was measured using enhanced-depth imaging optical coherent tomography (EDI-OCT) in patients before and 1 week after CE. PURPOSE: This study aims to characterize the structural and volume changes on the microstructure of SC in patients before and after uneventful phacoemulsification CE by using EDI-OCT. MATERIALS AND METHODS: Forty-one serial horizontal EDI-OCT B-scans (interval between B-scans, 69 µm) were obtained in the nasal corneoscleral limbus before and 1 week after CE. The structure of aqueous channels, conjunctival blood vessels and iris anatomy in each scan were used as landmarks to select for overlapping scans taken before and following CE. The SC cross-section area was measured in each of the selected scans and SC volume was determined following a 3-dimensional reconstruction. RESULTS: Eleven eyes (6 females and 5 males) were imaged successfully before and after CE. Mean age was 70.54±11.38 years. The mean axial length was 23.10±0.87 mm. After CE, the mean best-corrected visual acuity in logMAR improved from 0.4±0.13 to 0.2±0.13 (P=0.028). There was no significant change in the mean intraocular pressure before and after CE (15.09±1.33 to 15.0±2.16 mm Hg; P=0.39). The mean SC cross-section area increased by 25%, from 4744±376 to 5941±1048 µm (P<0.001). SC volume in the analyzed region increased by 25% from 6,641,473±585,954 to 8,317,909±1,328,809 µm (P<0.001). CONCLUSION: CE expands SC dimensions in healthy eyes. EDI-OCT imaging of SC may prove useful in the evaluation of the SC dimensions in vivo before and after CE.

[Panorama of limbal alterations (French translation of the article)]. / Panorama des altérations limbiques cornéennes.

The corneal limbus is a privileged region on the border between two quite different microenvironments, where corneal epithelial stem cells, numerous melanocytes, and antigen-presenting cells are all concentrated within a richly vascularized and innervated stroma. This situation within the ocular surface confers on it the key functions of barrier, epithelial renewal and defense of the cornea. As an immunological crossroads and since the corneoscleral limbus is directly exposed to external insults such as caustic agents, ultraviolet radiation, microbial agents, and allergens, it is the potential site of many tumoral, degenerative or inflammatory pathologies and may progress under certain conditions to limbal stem cell deficiency.

Panorama of limbal changes.

The corneal limbus is a privileged region on the border between two quite different microenvironments, where corneal epithelial stem cells, numerous melanocytes, and antigen-presenting cells are all concentrated within a richly vascularized and innervated stroma. This situation within the ocular surface confers on it the key functions of barrier, epithelial renewal and defense of the cornea. As an immunological crossroads and since the corneoscleral limbus is directly exposed to external insults such as caustic agents, ultraviolet radiation, microbial agents, and allergens, it is the potential site of many tumoral, degenerative or inflammatory pathologies and may progress under certain conditions to limbal stem cell deficiency.

Limbal ischemia: Reliability of clinical assessment and implications in the management of ocular burns.

PURPOSE: Limbal ischemia is an important prognostic factor in the management of ocular burns. In this study, we evaluated the reliability of clinically assessing limbal ischemia among ophthalmic professionals. METHODS: This study included 111 ophthalmic professionals who were shown 12 diffuse illumination color slit-lamp photographs of eyes with recent chemical injuries. Respondents were asked whether the photos were assessable and if yes, then to indicate the presence, location, and grade of limbal ischemia in each case. The responses were collected using a standard data collection sheet and the inter-observer agreement was calculated. RESULTS: All participants responded to every question. Of the 1,332 responses, images were deemed assessable in 1,222 (91.7%) instances. The overall agreement (Fleiss' kappa) for the presence of limbal ischemia and severity of limbal ischemia was 0.106 and 0.139, respectively (P < 0.012). Among the four groups of observers, practicing cornea specialists displayed significantly (P < 0.003) higher kappa values (0.201-0.203) when compared to residents (0.131-0.185), fellows (0.086-0.127), and optometrists (0.077-0.102). All indicated a poor level of inter-rater consistency. CONCLUSION: The results indicate that clinical assessment of limbal ischemia is highly subjective and there is lack of reliability even among cornea specialists who regularly manage patients with ocular burns. A non-invasive, standardized, objective, accurate, and reliable modality for ocular surface angiography is desperately needed for proper assessment and prognostication of ocular burns.

Horizontal Extraocular Muscle and Scleral Anatomy in Children: A Swept-Source Anterior Segment Optical Coherence Tomography Study.

PURPOSE: To evaluate the efficacy of anterior segment swept-source optical coherence tomography (SS-OCT) for examining horizontal extraocular muscle thickness, distance from the corneal limbus to the insertion of the horizontal extraocular muscle (limbus to insertion distance), and scleral thickness in Korean pediatric strabismus patients. METHODS: This study included pediatric strabismus patients between 5 and 10 years of age. Children with any ocular disease other than strabismus or a history of ocular surgery were excluded. SS-OCT was used to measure horizontal extraocular muscle thickness, limbus to insertion distance, and scleral thickness. Eyes were classified into subgroups by sex, spherical equivalent of the refractive error (measured with cycloplegic refraction), and fixating/deviating eye. RESULTS: One patient initially included in this study was excluded due to poor cooperation. Of the remaining 35 eyes of 20 patients, 19 eyes (54.3%) were from male patients and 16 eyes (45.7%) were from female patients. The mean patient age was 7.86 ± 1.38 years. Lateral scleral thickness was greater in male eyes than in female eyes (p = 0.048). No other differences were noted between male and female children. Additionally, there were no statistically significant differences between fixating and deviating eyes or among spherical equivalent groups for any parameter examined. CONCLUSIONS: Anterior segment SS-OCT can successfully and comfortably measure horizontal extraocular muscle and scleral anatomy in children. These measurements may be helpful for treatment and follow-up of pediatric strabismus patients.

Characterizing Anterior Segment OCT Angle Landmarks of the Trabecular Meshwork Complex.

PURPOSE: To identify the presence or absence of 3 identifiable landmarks: trabecular meshwork (TM), Schlemm's canal (SC), and a novel landmark termed the band of extracanalicular limbal lamina (BELL), which is a landmark adjacent to SC visible on anterior segment (AS) OCT. These landmarks also were analyzed pathologically to identify all 3 landmarks. DESIGN: Retrospective review. PARTICIPANTS: One eye per participant from prior institutional review board-approved studies in which AS OCT imaging was performed. METHODS: Horizontal images from 2-dimensional angle analysis scans using a CASIA SS-1000 (Tomey, Nagoya, Japan) AS OCT were evaluated by masked readers. Logistic regression was used to analyze the potential factors of age, gender, race, intraocular pressure, gonioscopy grade, angle location, and history or presence of surgery on the visibility of these structures. Pathologic correlation on 5 previously enucleated eyes also was performed. MAIN OUTCOME MEASURES: Presence or absence of angle landmarks-TM, SC, and BELL-using Anterior Chamber Analysis and Interpretation software (ACAI, Houston, TX). RESULTS: Three hundred three angles of 153 horizontal images were included in this study. The mean age was 51.5±16.0 years, with 98 women (64%) and 100 white persons (66%). The outer border of the BELL was observed in 288 angles (95%), TM was found in 220 angles (73%), and SC was seen in 120 angles (40%). The outer border of the BELL was more visible in white persons (P = 0.02) than Asians and in eyes with a Spaeth gonioscopy grade of E than those with a grade of A (P = 0.02). Both TM (P = 0.001) and SC (P = 0.001) were more visible in temporal angles (81% for TM, 49% for SC) than in nasal angles (64% for TM, 30% for SC). Additionally, SC was more visible in open angles (43%) than in narrow angles (27%; P = 0.02). These 3 structures were verified in a pathologic study. CONCLUSIONS: We identified a novel AS OCT landmark adjacent to SC. This structure also was identified on pathologic samples from enucleated eyes. Further study is needed to determine the pathophysiologic relevance of these findings.

The accuracy of wide-field ultrasound biomicroscopy in localizing extraocular rectus muscle insertions in strabismus reoperations.

PURPOSE: To compare the accuracy of widefield ultrasound biomicroscopy (UBM) with mechanical intraoperative measurements of the distance between rectus muscle insertions and the corneal limbus in strabismus reoperations. METHODS: Subjects with a history of horizontal rectus muscle surgery who required further surgery on horizontal rectus muscle(s) were recruited prospectively. All widefield UBM measurements were carried out under topical anesthesia using a 50 MHz linear probe without immersion cup and external caliper. The insertion angle distance was measured using the caliper tool of the UBM device; the actual muscle insertion distance from the limbus was considered to be the measured distance plus 1 mm. The distance from muscle insertion to the limbus was also measured intraoperatively. The results of UBM and surgical measurements were compared. RESULTS: A total of 28 subjects were recruited, and 53 horizontal muscles (30 medial rectus, and 23 lateral rectus muscles) were included. The longest distance of the muscle insertion from limbus detectable on UBM was 13 mm for the medial rectus muscle and 15 mm for the lateral rectus muscle. In 38 muscles (71.7%) UBM and surgical measurements were within 1 mm of each other. Only in 1 muscle (1.9%) was the difference between measurements >2 mm (2.3 mm). The intraclass correlation coefficient was 0.87, demonstrating excellent agreement between measurements. Limit of agreement analysis demonstrated better agreement between measurements of medial rectus muscles and in consecutive exotropia cases. CONCLUSIONS: This study demonstrated good agreement between intraoperative and widefield UBM measurements of the muscle insertion-limbus distance in our patient cohort.

Imaging collector channel entrance with a new intraocular micro-probe swept-source optical coherence tomography.

PURPOSE: To describe the use of a newly developed side-viewing catheter probe to provide the cross-sectional images of collector channel entrance (CCE), achieved by swept-source optical coherence tomography (SS-OCT). METHODS: A side-viewing SS-OCT catheter probe was developed that has a core probe diameter of 0.15 mm and an outer diameter of 0.25 mm, for the purpose of imaging CCEs within eye globe. Cadaver eyes harvested from swine and human were used to demonstrate its feasibility. For porcine eyes, the probe imaged the CCE by accessing the region of the aqueous plexus (AP) as well as along the inner wall (IW) of the trabecular meshwork (TM). For human eyes, the CCE images were captured by placing the probe within the lumen of the Schlemm's canal (SC) and along its IW. RESULTS: With the optical coherence tomography (OCT) catheter probe, the CCE is well delineated as optically empty areas within the highly scattering sclera. In porcine eyes, images captured in the region of the AP demonstrate a large cavity with delicate tissue strands around the probe. The CCE can be identified at the outer margin of the AP. When imaged along the IW, the TM is discernable but difficult to be distinguished from the AP. In the human limbal regions, when placed within the lumen of the SC, the catheter probe fully occupies the potential space. TM is highly compact. The CCE can be identified at the outer wall of the SC. When imaged along the IW of TM, the SC and CCE can be identified. CONCLUSION: The intraocular SS-OCT catheter probe is feasible to provide the CCE images, indicating useful clinical applications to assist glaucoma surgery.

A method for quantifying limbal stem cell niches using OCT imaging.

AIMS: To evaluate the efficacy of Fourier domain-optical coherence tomography (FD-OCT) in imaging and quantifying the limbal palisades of Vogt and to correlate these images with histological findings. METHODS: The superior and inferior limbal region of both eyes of 50 healthy volunteers were imaged by FD-OCT. Images were processed and analysed using Matlab software. In vitro immunofluorescent staining of a cadaveric donor limbus was analysed to correlate the presence of stem cells in the visualised structures. RESULTS: FD-OCT could successfully visualise limbal crypts and the palisades of Vogt in the limbus region. Fluorescent labelling confirmed the presence of stem cells in these structures. The mean palisade ridge width (ΔPR) and the mean interpalisade epithelial rete peg width (ΔERP) were both of the order of 72 µm, leading to a palisade density (PD) of about 7.4 palisades/mm. A significant difference in ΔPR, ΔERP and PD was seen between the inferior and superior sides of the right eye and the superior sides of the left and right eye(p<0.05.). A significant influence of iris colour on parameters ΔPR, ΔERP and PD was found, and of age on PD and ΔERP (p<0.05). CONCLUSIONS: In vivo OCT imaging is a safe and effective modality to image the limbus and can be used to visualise the palisades of Vogt. Image processing using Matlab software enabled quantification and density calculation of imaged limbal palisades of Vogt. This technique may enhance targeted limbal biopsies for transplantation.

Microarchitecture of Schlemm Canal Before and After Selective Laser Trabeculoplasty in Enhanced Depth Imaging Optical Coherence Tomography.

PURPOSE: To characterize the in vivo effect of selective laser trabeculoplasty (SLT) on the Schlemm canal (SC) in eyes with primary open-angle glaucoma (POAG). MATERIALS AND METHODS: Eighty-one serial horizontal enhanced depth imaging optical coherence tomograph B-scans (interval between B-scans, ∼35 µm) of the nasal corneoscleral limbus were obtained before and 4 weeks after SLT. Fifty B-scans in the overlapping regions before and after SLT were selected for analysis based on the structures of aqueous and blood vessels as landmarks. The SC cross-sectional area (CSA) was measured in each selected B-scan and averaged to generate the mean SC CSA of the eye. SC volume in the overlapping region was calculated using commercially available 3-dimensional reconstruction software. The mean SC CSA and SC volume were compared between pre-SLT and post-SLT B-scans. Correlation analysis was performed between SC CSA changes and intraocular pressure (IOP) changes. RESULTS: Thirteen POAG eyes (13 patients) were included for analysis (mean age, 68.2±9.2 y). After SLT, the mean IOP was reduced from 19.8±7.6 to 14.4±3.8 mm Hg (P=0.003); the mean SC CSA increased by 8%, from 2478±550 to 2682±598 µm (P=0.029); and the mean SC volume increased from 4,304,592±954,777 to 4,658,250±1,039,956 µm (P=0.029). Increase in SC CSA had a significant positive correlation with IOP reduction after SLT (P=0.023, R=0.622). CONCLUSIONS: SLT expands SC in POAG patients and even more so with greater IOP reduction after SLT. Post-SLT expansion of SC may be due to increased trabecular aqueous outflow, IOP decrease, or structural changes in trabecular meshwork resulting from SLT.

Prospective observation of filtration blebs in high-risk eyes with limbal-based conjunctival flap.

OBJECTIVE: To evaluate time-dependent changes in filtering bleb parameters using 3-dimensional anterior segment optical coherence tomography (3-D AS-OCT) in high-risk eyes after a limbal-based trabeculectomy procedure. DESIGN: Prospective, observational study. PARTICIPANTS: Twenty-three patients who underwent uncombined limbal-based trabeculectomy surgery and who also had a history of prior intraocular surgery. METHODS: Of 23 eyes, 15 eyes were followed for 1 year without additional glaucoma surgeries, and their bleb parameters were measured 0.5, 3, 6, and 12 months after the trabeculectomy using 3-dimensional anterior segment optical coherence tomography. The correlations of these parameters to other clinical data were investigated. RESULTS: Statistical analysis showed significant changes in the bleb wall thickness (0.7 ± 0.4 mm vs 0.4 ± 0.2 mm; p = 0.007) and fluid cavity height (0.3 ± 0.2 mm vs 0.7 ± 0.4 mm; p = 0.005) between 0.5 and 3 months only. The width of the filtration openings at 0.5 months after trabeculectomy (2.1 ± 1.0 mm) was significantly associated with the intraocular pressure at 12 months (15.1 ± 5.7 mm Hg; R2 = 0.37, t = -2.65, and p = 0.021). CONCLUSIONS: The width of the filtration opening in the early stage may be a prognostic factor for long-term intraocular pressure control.