Anterior Segment Optical Coherence Tomography Angiography Imaging of Conjunctiva and Intrasclera in Treated Primary Open-Angle Glaucoma

Visualization of porcine and human aqueous humor outflow tract anatomies with transparency enhancement

PURPOSE

There is no established method for visualizing the three-dimensional (3D) structure of the aqueous humor outflow tract. This study attempted to visualize the 3D structures of porcine and human ocular tissues, particularly the aqueous humor outflow tract using a transparency reagent composed of 2, 2-thiodiethanol.

STUDY DESIGN

Clinical and experimental.

METHODS

The porcine eyes were collected in Japan, and the human eyes were imported from the United States. The human eyes were obtained from a 64-year-old Caucasian woman, arriving 7 days after her death. The specimens were formalin-fixed upon arrival, fluorescently labeled, optically cleared using a transparency-enhancing reagent, and visualized using a confocal microscope.

RESULTS

Both porcine and human eyes were visualized to the extent that the choroidal vessels were observed on gross examination. The aqueous humor outflow tract was clearly observed as a luminal structure in the porcine eye, mainly depicted by autofluorescence, and in the human eyes as a luminal structure continuing from the trabecular meshwork without fluorescence.

CONCLUSION

Observations using transparency-enhancing technology enabled us to obtain 3D images useful for visualizing ocular tissues, especially the aqueous humor outflow tract.

Anterior Segment Optical Coherence Tomography Angiography: A Review of Applications for the Cornea and Ocular Surface

Dye-based angiography is the main imaging modality in evaluating the vasculature of the eye. Although most commonly used to assess retinal vasculature, it can also delineate normal and abnormal blood vessels in the anterior segment diseases-but is limited due to its invasive, time-consuming methods. Thus, anterior segment optical coherence tomography angiography (AS-OCTA) is a useful non-invasive modality capable of producing high-resolution images to evaluate the cornea and ocular surface vasculature. AS-OCTA has demonstrated the potential to detect and delineate blood vessels in the anterior segment with quality images comparable to dye-based angiography. AS-OCTA has a diverse range of applications for the cornea and ocular surface, such as objective assessment of corneal neovascularization and response to various treatments; diagnosis and evaluation of ocular surface squamous neoplasia; and evaluation of ocular surface disease including limbal stem cell deficiency and ischemia. Our review aims to summarize the new developments and clinical applications of AS-OCTA for the cornea and ocular surface.

Impact of scleral cautery on limbal vasculature after cataract surgery assessed using optical coherence tomography angiography

We investigate the influence of scleral cautery during cataract surgery on limbal vascular density and remodeling using anterior segment optical coherence tomography angiography (AS-OCTA). Twenty eyes of 20 patients who underwent cataract surgery with a sclerocorneal incision were included. Patients were divided into two groups: non-cautery (n = 10) and cautery (n = 10). The area around the incision site was scanned using AS-OCTA before surgery and at 1, 3, 5, 7, 14, 21, 28, and 90 days postoperatively. Images were analyzed to depict conjunctival vasculature (surface to a depth of 200 μm) and intrascleral vasculature (depth of 200 to 1000 μm). Vascular density was evaluated using ImageJ software. In the non-cautery group, intrascleral vascular density significantly increased during the wound-healing period up to 21 days postoperatively. Cautery application completely diminished this effect, resulting in significantly reduced intrascleral vascular density in the cautery group compared to the non-cautery group until 5 days after surgery. On the seventh day and later, intrascleral vascular density in the cautery group recovered, but the vascular pattern did not return to its preoperative state even at 90 days after surgery. Conjunctival flap vascular density was reduced for 28 days after surgery, with cautery application further decreasing conjunctival vascular density. AS-OCTA enabled separate observation of conjunctival and intrascleral vasculature. Intrascleral blood flow significantly increased after cataract surgery, but scleral cauterization markedly blocked this effect. The vascular reconstruction process following cataract surgery continued for almost a month, with cautery application leading to prolonged vascular disruption and altered vascular patterns.

Blood flow alterations in cavernous sinus dural arteriovenous fistula: Optical coherence tomography angiography findings

Purpose

This case report details the diagnostic process for a patient with an initial diagnosis of scleritis who was unresponsive to typical treatment modalities, culminating in the identification of a cavernous sinus dural arteriovenous fistula (CS-DAVF). The case highlights the role of anterior segment optical coherence tomography angiography (OCTA) in the diagnosis of this vascular anomaly and in monitoring the response to treatment.

Observations

A 45-year-old man with persistently elevated intraocular pressure (IOP) and ocular congestion in the left eye was unresponsive to treatment for scleritis. The persistent ocular symptoms and new-onset tinnitus prompted further investigation. Anterior segment OCTA revealed vascular anomalies, and magnetic resonance imaging confirmed a CS-DAVF. The patient underwent endovascular treatment for the CS-DAVF. This intervention led to a significant reduction in IOP in the left eye and the resolution of ocular congestion.

Conclusions and importance

This case highlights the diagnostic complexities of ophthalmic symptoms that mimic those of other conditions. Furthermore, it demonstrates the essential role of anterior segment OCTA in the accurate diagnosis and effective management of CS-DAVF and highlights the need for comprehensive diagnostic approaches in ophthalmology.

Current clinical applications of anterior segment optical coherence tomography angiography: a review

Optical coherence tomography (OCT) is a revolutionary in vivo imaging technology that presents real-time information on ocular structures. Angiography based on OCT, known as optical coherence tomography angiography (OCTA), is a noninvasive and time-saving technique originally utilized for visualizing retinal vasculature. As devices and built-in systems have evolved, high-resolution images with depth-resolved analysis have assisted ophthalmologists in accurately localizing pathology and monitoring disease progression. With the aforementioned advantages, application of OCTA has extended from the posterior to anterior segment. This nascent adaptation showed good delineation of the vasculature in the cornea, conjunctiva, sclera, and iris. Thus, neovascularization of the avascular cornea and hyperemia or ischemic changes involving the conjunctiva, sclera, and iris has become prospective applications for AS-OCTA. Although traditional dye-based angiography is regarded as the gold standard in demonstrating vasculature in the anterior segment, AS-OCTA is expected to be a comparable but more patient-friendly alternative. In its initial stage, AS-OCTA has exhibited great potential in pathology diagnosis, therapeutic evaluation, presurgical planning, and prognosis assessments in anterior segment disorders. In this review of AS-OCTA, we aim to summarize scanning protocols, relevant parameters, and clinical applications as well as limitations and future directions. We are sanguine about its wide application in the future with the development of technology and refinement in built-in systems.

Characteristic Assessment of Angiographies at Different Depths with AS-OCTA: Implication for Functions of Post-Trabeculectomy Filtering Bleb

This study aimed to analyze the quantitative vascular biomarkers of filtering bleb function at different depths using anterior segment optical coherence tomography angiography (AS-OCTA). This cross-sectional study is registered on Clinicaltrails.gov (NCT 04515017). Forty-six eyes with primary open-angle glaucoma that had undergone trabeculectomy with mitomycin-C for more than six months were included. Vessel density (VD) and vessel diameter index (VDI) in the superficial layer (SL), Tenon’s layer (TL), and deep layer (DL) of the bleb were obtained. The VD and VDI were higher in the failure group (both p = 0.000). Significant correlations were found between the SL, TL, DL’s VDI, and IOP in the success group (p = 0.013, 0.016, 0.031, respectively). The VD of the TL and DL were related to IOP in the failure group (p = 0.012, 0.009). Tenon’s VD (TVD) and Tenon’s VDI (TVDI) correlated with IOP adjusting for TVD, TVDI, and the Indiana Bleb Appearance Grading Scale (IBAGS) (p = 0.009, 0.043) or Kenfeld grading system (KGS) (p = 0.011, 0.016). The area under curve (AUC) of the TVD, TVDI, IBAGS, and KGS to predict surgery failure were 0.960, 0.925, 0.770, and 0.850. AS-OCTA realized the quantitative evaluation of vessels, especially the invisible vascularity beneath the conjunctiva. TVD and TVDI as detected by AS-OCTA better reflected bleb function than conventional grading systems.

Anterior Segment Optical Coherence Tomography Angiography Following Trabecular Bypass Minimally Invasive Glaucoma Surgery

Objective

To assess anterior segment optical coherence tomography angiography (AS-OCTA) imaging of the episcleral vessels before and after trabecular bypass minimally invasive glaucoma surgery (MIGS).

Design

A prospective, clinical, single-centre, single-arm pilot feasibility study conducted at National University Hospital, Singapore.

Subjects

Patients with primary glaucomatous optic neuropathy undergoing Hydrus Microstent (Ivantis Inc., Irvine, CA, USA) implantation, who require at least one intra-ocular pressure-lowering medication. One or two eyes per patient may be enrolled.

Methods

We performed AS-OCTA (Nidek RS-3000 Advance 2, Gamagori, Japan) pre- and up to 6 months post-MIGS implantation using a standard protocol in all cornealimbal quadrants, to derive episcleral vessel densities (VD) using a previously described technique.

Main Outcome Measures

Episcleral VD pre- and post-surgery, in sectors with and without the implant.

Results

We obtained serial AS-OCTA images in 25 eyes undergoing MIGS implantation (23 subjects, mean age 70.3 ± 1.5, 61% female) with mean preoperative intraocular pressure (IOP) of 15.5 mmHg ± 4.0. We observed reductions in postoperative episcleral VD compared to preoperative VD at month 1 (mean difference −3.2, p = 0.001), month 3 (mean difference −2.94, p = 0.004) and month 6 (mean difference −2.19, p = 0.039) in sectors with implants (overall 6 month follow-up, p = 0.011). No significant changes were detected in episcleral VD in the sectors without implants (p = 0.910).

Conclusion

In our pilot study, AS-OCTA was able to detect changes in the episcleral VD following trabecular bypass MIGS, which may be a useful modality to evaluate surgical outcomes if validated in future studies.

Preparing the ocular surface for glaucoma filtration surgery: an unmet clinical need

The mutual relationship among medical therapy, ocular surface (OS) and filtration surgery (FS) represents one of the most crucial issues in glaucoma management. As the long-term use of intraocular pressure-lowering medications significantly affect the OS health, patients with an uncontrolled disease frequently undergo glaucoma surgery in less-than-ideal conditions. As we known, OS changes strongly affect the post-operative bleb filtration capability. Therefore, improving the OS conditions before proceeding with FS is needed. Currently, given the rapid diffusion of new surgical procedures, this need is even more perceived. Nevertheless, despite surgeons retain the OS preparation of primary importance, and recognize the OS disease (OSD) as the only modifiable risk factor for filtration failure, there is no agreement on which strategies should be preferred to prepare patients. This is largely due to the lack of validated guidelines, which forces clinicians to adopt personal approaches based on evidence derived from low-quality studies. In this review, we provided an overview of risk factors involved in the FS failure, with particular attention to those depending on OS changes, and how OSD negatively affects the aqueous humor resorption after surgery. Moreover, we reported the most exploited measures to mitigate the OSD before surgery, the possible reasons underlying the absence of shared approaches, and the upcoming area of intervention to preserve the OS health during glaucoma management. Finally, based on the current evidence, we proposed a pre-operative outline reporting the main risk factors that should be considered before surgery, and the therapeutical options available to improve the OS.

Advances and Current Clinical Applications of Anterior Segment Optical Coherence Tomography Angiography

Optical coherence tomography angiography (OCTA) is the most relevant evolution based on optical coherence tomography (OCT). OCTA can present ocular vasculature, show detailed morphology for assessment, and quantify vessel parameters without intravenous dye agent. Research on the anterior segment OCTA (AS-OCTA) is only in its initial phase, and its advances in clinical diagnosis and treatment efficacy evaluations require a detailed comparison to traditional imaging methods. In this review of AS-OCTA, we summarize its technical features, imaging advances, current clinical applications in various eye diseases, as well as its limitations and potential future directions. AS-OCTA offers potential advantages in ophthalmic imaging, and with further development it could become a common tool in the near future.

Longitudinal changes in complete avascular area assessed using anterior segmental optical coherence tomography angiography in filtering trabeculectomy bleb

Optical coherence tomography angiography (OCTA) is a new technique for non-invasive imaging of blood vessels, allowing combined evaluation of both deep and surface vessels. The purpose of this study was to evaluate the post-trabeculectomy longitudinal changes in complete avascular area (CAA) of filtering blebs using anterior segment (AS-) OCTA and their association with surgical outcomes. This study included 57 eyes of 53 patients who had undergone trabeculectomy with mitomycin C. AS-OCTA images of filtering bleb were acquired at 3 and 6 months after trabeculectomy, and at 1 month in possible cases. CAAs, regions where complete blood flow was not depicted in AS-OCTA images, were evaluated for their presence, extent, and change over time. CAAs were detected in 37 eyes (65%) and 33 eyes (58%) at 3 and 6 months postoperatively, respectively. The extent of CAAs reduced over time after surgery in most cases. No parameters related to CAAs were significantly associated with surgical success (i.e., intraocular pressure (IOP) ≤ 12 mmHg and IOP reduction > 20% without medication). In conclusion, although it is difficult to predict surgical success by CAA itself, AS-OCTA may be useful for the objective evaluation of the vascularity of filtering blebs.

Prediction of trabecular meshwork-targeted micro-invasive glaucoma surgery outcomes using anterior segment OCT angiography

We performed a prospective, longitudinal study to investigate the association between the preoperative intrascleral vasculature assessed using anterior segment (AS)-optical coherence tomography angiography (OCTA) and surgical outcomes of trabecular meshwork-targeted micro- or minimally invasive glaucoma surgery (MIGS). We included 37 patients with primary open-angle glaucoma. Preoperative AS-OCTA images of the sclero-conjunctiva of the nasal corneal limbus were acquired in the superficial (conjunctival) and deep (intrascleral) layers. The vessel densities (VDs) of each layer were measured separately in the entire area, limbal side, and fornix area. Surgical success was determined by postoperative intraocular pressure (IOP) and IOP reduction. Twenty-three and 14 eyes were classified as having successful and unsuccessful outcomes, respectively. The deep VDs of the entire area and fornix area were significantly lower in the successful group (P = 0.031 and P = 0.009). The success rate was significantly higher for eyes with a lower deep VD than for eyes with a higher deep VD. A greater IOP reduction was significantly associated with lower deep VD in the fornix area (P = 0.022) and higher preoperative IOP (P < 0.001). These results indicate that intrascleral vasculature assessed using preoperative AS-OCTA was negatively correlated with surgical success and IOP reduction resulting from trabecular meshwork-targeted MIGS. AS-OCTA images might help predict MIGS outcomes.

Anwendungsmöglichkeiten der optischen Kohärenztomographie beim trockenen Auge

Durch die stetige Weiterentwicklung und Verbesserung der Technik hat die optische Kohärenztomographie (OCT) in den letzten Jahren neue Möglichkeiten zur Beurteilung der Strukturen des vorderen Augenabschnittes eröffnet. Aufgrund der Darstellung kleinster Strukturen, wie beispielsweise des Tränenfilms, nimmt die OCT in der Diagnostik und Verlaufsbeurteilung des trockenen Auges eine immer wichtigere Rolle ein. Der vorliegende Beitrag gibt einen Überblick über die derzeitigen Einsatzmöglichkeiten der OCT beim trockenen Auge.

Short-Term Effects of Different Types of Anti-Glaucoma Eyedrop on the Sclero-Conjunctival Vasculature Assessed Using Anterior Segment OCTA in Normal Human Eyes: A Pilot Study

BACKGROUND

To investigate the short-term effects of different types of anti-glaucoma eyedrop on sclero-conjunctival vasculatures and their associations with intraocular pressure (IOP) reduction.

METHODS

This was a prospective study including 20 healthy subjects. A single instillation of ripasudil or bimatoprost was introduced into the right eyes of the participants. The superficial (conjunctival) and deep (intrascleral) vasculatures of the corneal limbus using anterior-segment optical coherence tomography angiography (OCTA) and IOP were examined in both eyes at baseline and 15 min and 2 h after instillation.

RESULTS

In the ripasudil group, the vessel density (VD) (median) at baseline (deep, 13.1%; superficial, 28.5%) significantly increased in both layers at 15 min (deep, 19.9%; superficial, 37.3%) and the deep layer at 2 h (deep, 14.8%; superficial, 31.6%). In the bimatoprost group, the superficial VD significantly changed over time, but the deep VD did not. The greater effect of ripasudil on IOP reduction was significantly associated with a lower baseline VD in the deep layer (at 15 min, p = 0.004; at 2 h, p = 0.018).

CONCLUSIONS

Differences in the timing, depth, and extent of the effects on vasculature after instillations, could be detected using OCTA. The IOP-lowering effects of ripasudil might be associated with the deep vasculature.

Optical Coherence Tomography Angiography of Perilimbal Vasculature in Port-Wine Stain and Sturge-Weber Syndrome Patients

Purpose

To evaluate episcleral vasculature in corneal limbus with optical coherence tomography angiography (OCTA) in normal controls, port-wine stain (PWS) patients, and Sturge-Weber syndrome (SWS) patients.

Methods

Unilateral eyes from 18 normal controls (25.41 ± 4.00 years), 16 PWS patients (21.35 ± 11.05 years), and 8 SWS patients with ipsilateral late-onset glaucoma (22.13 ± 7.82 years). Each subject underwent slit-lamp examination, applanation tonometry, and OCTA. All OCTA scans were performed using an OCTA system operating at a wavelength of 1050-nm in four quadrants (superior, inferior, nasal, and temporal). The scans were delineated into conjunctival and episcleral layers using IMAGEnet6 for analysis.

Results

Slit-lamp and OCTA images demonstrated dense dilated episcleral vessels in PWS and SWS patients, particularly in the SWS group. The mean limbal involvements of episcleral vascular anomalies under slit lamp were respectively 0.00 ± 0.00, 5.44 ± 2.92, and 8.88 ± 2.70 clock hours in the control, PWS, and SWS groups (F = 58.46, P < 0.01). Quantitative analysis of OCTA scans showed that the episcleral vessel density in controls, PWS, and SWS groups were 25.03% ± 1.47%, 28.28% ± 1.96%, and 33.59% ± 3.00%, respectively (F = 18.17, P < 0.01). We also observed higher episcleral vessel diameter index in the SWS and PWS groups in comparison with the controls, particularly in the SWS group (P < 0.01). The vessel measurements, including density and diameter, were significantly correlated with the increased IOP and cup-to-disc (C/D) in SWS patients (P < 0.01).

Conclusions

To our knowledge, this is the first demonstration of OCTA in PWS and SWS patients and represents direct pathoanatomic evidence for episcleral alterations in SWS patients. The episcleral vessel measurements correlated with the increased IOP and C/D in SWS patients, indicating the episcleral vascular hypertrophy may be a risk factor for glaucoma in adult SWS patients.

Vascular Density of the Anterior Segment of the Eye Determined by Optical Coherence Tomography Angiography and Slit-Lamp Photography

<b><i>Objective:</i></b> To determine the vascular density of the anterior segment (AS) of the eye from optical coherence tomography angiography (OCTA) images and slit-lamp photographs. <b><i>Methods:</i></b> A swept-source OCTA (Plex Elite 9000; Carl Zeiss) device modified with a +10-diopter lens was used to record the vasculature of the AS. Twenty eyes, including 4 eyes of 4 healthy subjects and 16 eyes of 12 patients scheduled for cataract surgery or combined vitrectomy and cataract surgery, were studied. The slit-lamp photographs of the AS were acquired concurrently with the AS-OCTA images. The vascular density was measured preoperatively and postoperatively in the nasal, temporal, superior, and inferior quadrants after binarization with ImageJ software. <b><i>Results:</i></b> Acceptable AS-OCTA images were obtained of 65% (superior), 80% (nasal), 70% (inferior), and 80% (temporal) of the eyes. The percentage of acceptable images was significantly lower in the superior quadrant among the AS-OCTA images than among the AS photographs (100%; <i>p</i> = 0.004). The vascular density determined by AS-OCTA was higher than that determined in the AS photographs in all quadrants (<i>p</i> = 0.011 to &#x3c;0.001). The AS-OCTA B-mode images showed that vascular flow was identified mainly between the conjunctiva and sclera but not in the ciliary body. The vascular density increased significantly after cataract surgery in the superior quadrant, which was significantly correlated with the location of the surgical incision (<i>p</i> = 0.03). <b><i>Conclusion:</i></b> AS-OCTA can obtain images with higher vascular density of the conjunctiva and sclera than slit-lamp photographs, and AS-OCTA images can show a postoperative increase in vascular density.