Scleral structure, organisation and disease. A review

Assessment of conjunctival, episcleral and scleral thickness in healthy individuals using anterior segment optical coherence tomography

PURPOSE

To determine the thickness of the conjunctiva, episclera and sclera in healthy individuals using anterior segment optical coherence tomography (AS-OCT).

METHODS

We prospectively included 107 healthy individuals of different age groups (18-39 years, 40-54 years, 55-69 years and ≥70 years). For each eye, AS-OCT scans of four quadrants (temporal, nasal, superior and inferior) were acquired. The thickness of the conjunctiva, episclera and sclera was measured for each scan. In addition, the axial length of both eyes was measured, and general characteristics, including smoking, allergies and contact lens use, were collected.

RESULTS

The mean conjunctival thickness was significantly different between the nasal and superior quadrants (87 ± 30 μm vs. 77 ± 16 μm; p < 0.001), as well as the superior and inferior quadrants (77 ± 16 μm vs. 86 ± 19 μm; p = 0.001). The mean episcleral thickness was larger in the superior (174 ± 54 μm) and inferior (141 ± 43 μm) quadrants, compared to the nasal (83 ± 38 μm) and temporal quadrants (90 ± 44 μm). The mean scleral thickness of the inferior quadrant was the largest (596 ± 64 μm), followed by the nasal (567 ± 76 μm), temporal (516 ± 67 μm) and superior (467 ± 52 μm) quadrants (all p < 0.001). The averaged scleral thickness increased 0.96 μm per age year (0.41-1.47 μm, p < 0.001).

CONCLUSIONS

This study provides an assessment of the thickness of scleral and adjacent superficial layers in healthy individuals determined on AS-OCT, which could enable future research into the use of AS-OCT in diseases affecting the anterior eye wall.

CHANGES IN SCLERAL THICKNESS IN THE ACUTE PHASE OF VOGT-KOYANAGI-HARADA DISEASE

PURPOSE

To evaluate changes in scleral thickness in Vogt-Koyanagi-Harada (VKH) disease.

METHODS

This study included 34 eyes of 17 treatment-naïve patients with acute-phase VKH disease. Scleral thickness and the presence of ciliochoroidal effusion were examined using anterior segment optical coherence tomography at baseline and 1 week, 2 weeks, and 12 weeks after the start of corticosteroid treatment. Scleral thickness was measured 6 mm posterior to the scleral spur in four directions.

RESULTS

Twenty-eight eyes (82.4%) initially had ciliochoroidal effusion, but this rapidly decreased to nine eyes (26.5%) after 1 week. The sclera with ciliochoroidal effusion became thinner from baseline to 1 week at the superior (400.2 ± 46.9-353.5 ± 47.9 µm), temporal (428.4 ± 53.6-387.8 ± 56.1 µm), inferior (451.5 ± 71.0-400.5 ± 50.5 µm), and nasal (452.4 ± 78.0-407.6 ± 62.9 µm) points (P < 0.01 for all), and no further changes were observed. The sclera without ciliochoroidal effusion remained unchanged.

CONCLUSION

In VKH disease, eyes with ciliochoroidal effusion exhibited the maximum scleral thickness during the acute phase. This thickening responded rapidly to treatment and became thinner within 1 week. Inflammation in VKH disease may affect not only the choroid but also the sclera.

The Evolving Surgical Paradigm of Scleral Allograft Bio-Tissue Use in Ophthalmic Surgery: Techniques and Clinical Indications for Ab-Externo and Ab-Interno Scleral Reinforcement

To review the latest surgical advances and evolving clinical use of scleral bio-tissue for reinforcement in the eye and review the published literature on novel surgical applications of scleral allograft bio-tissue. Conventional surgical procedures for scleral reinforcement using homologous scleral allograft have been traditionally ab-externo interventions comprising of anterior or posterior reinforcement of the sclera for clinical indications such as trauma, scleromalacia, glaucoma drainage device coverage, scleral perforation, buckle repair as well as posterior reinforcement for pathologic myopia and staphyloma. There have been a few novel ab-interno uses of scleral bio-tissue for reinforcement in both retina and glaucoma. Over the last decade, there has been an increase in peer-reviewed publications on scleral reinforcement, reflecting more interest in its clinical applications. With favorable biological and biomechanical properties, scleral allograft may be an ideal substrate for an array of new applications and surgical uses.

RAD21 deficiency drives corneal to scleral differentiation fate switching via upregulating WNT9B

The cornea and sclera are distinct adjacent tissues, yet their stromal cells originate from common neural crest cells (NCCs). Sclerocornea is a disease characterized by an indistinguishable boundary between the cornea and sclera. Previously, we identified a RAD21 mutation in a sclerocornea pedigree. Here, we investigated the impacts of RAD21 on NCC activities during eye development. RAD21 deficiency caused upregulation of PCDHGC3. Both RAD21 knockdown and PCDHGC3 upregulation disrupted the migration of NCCs. Transcriptome analysis indicated that WNT9B had 190.9-fold higher expression in scleral stroma than in corneal stroma. WNT9B was also significantly upregulated by both RAD21 knockdown and PCDHGC3 overexpression, and knock down of WNT9B rescued the differentiation and migration of NCCs with RAD21 deficiency. Consistently, overexpressing wnt9b in Xenopus tropicalis led to ocular developmental abnormalities. In summary, WNT9B is a determinant factor during NCC differentiation into corneal keratocytes or scleral stromal cells and is affected by RAD21 expression.

The structure and function of the human choroid

In this manuscript, the structure of the human choroid is reviewed with emphasis of the macro- and microscopic anatomy including Bruch's membrane, choriocapillaris, Sattler's and Haller's layer, and the suprachoroid. We here discuss the development of the choroid, as well as the question of choroidal lymphatics, and further the neuronal control of this tissue, as well as the pathologic angiogenesis. Wherever possible, functional aspects of the various structures are included and reviewed.

Prognostic factors for surgical treatment of radiation-induced scleral necrosis after brachytherapy for uveal melanoma

PURPOSE

Radiation-induced scleral necrosis (RISN) is a less frequent complication of brachytherapy for uveal melanoma, and may require surgical treatment in selected cases. We aimed to identify the prognostic factors for RISN treatment.

METHODS

All patients with brachytherapy for uveal melanoma treated at our institution between 01/1999 and 12/2016 who developed RISN were followed until 02/2021. Various parameters were evaluated through univariable and multivariable Cox regression analysis. The surgical intervention due to RISN was the principal outcome event of this study.

RESULTS

Of 115 patients in the final cohort, 51 individuals (44%) underwent RISN treatment (conjunctival revision [n = 2], patching [n = 46] or enucleation [n = 3]) at median 1.80 months after RISN occurrence. Significant RISN characteristics were summarized into a novel RISN severity scale - Grade I: largest diameter ≤ 5 mm and no progression; Grade II: largest diameter > 5 mm or any progression during the follow-up; Grade III: presence of uveal prolapse; and Grade IV: leakage through open eyewall perforation. In the multivariable analysis, the RISN severity scale (aHR = 2.37 per grade increase, p = 0.01) and the time between brachytherapy and RISN occurrence (<15 months, aHR = 6.33, p < 0.0001) were independently associated with the study endpoint. The RISN severity scale showed high diagnostic accuracy for prediction of RISN treatment (AUC = 0.869).

CONCLUSIONS

In our series, about the half of RISN cases underwent surgical treatment. The presented novel severity scale for RISN might become a helpful tool for clinical management of individuals with RISN. We recommend external validation of the diagnostic accuracy of the presented scale.

The enigma of sclera-specific autoimmunity in scleritis

Scleritis is a severe and painful ophthalmic disorder, in which a pathogenic role for collagen-directed autoimmunity was repeatedly suggested. We evaluated the presence of sclera-specific antibodies in a large cohort of patients with non-infectious scleritis. Therefore, we prospectively collected serum samples from 121 patients with non-infectious scleritis in a multicenter cohort study in the Netherlands. In addition, healthy (n = 39) and uveitis controls (n = 48) were included. Serum samples were tested for anti-native human type II collagen antibodies using a validated enzyme-linked immunosorbent assay (ELISA). Further, sclera-specific antibodies were determined using indirect immunofluorescence (IIF) on primate retinal/scleral cryosections. Lastly, human leukocyte antigen (HLA) typing was performed in 111 patients with scleritis. Anti-type II collagen antibodies were found in 13% of scleritis patients, in 10% of healthy controls and in 11% of uveitis controls (p = 0.91). A specific reaction to scleral nerve tissue on IIF was observed in 33% of patients with scleritis, which was higher than in healthy controls (11%; p = 0.01), but similar to uveitis controls (25%; p = 0.36). Reactivity to the scleral nerve tissue was significantly associated with earlier onset of scleritis (48 versus 56 years; p < 0.001), bilateral involvement (65% versus 42%; p = 0.01), and less frequent development of scleral necrosis (5% versus 22%; p = 0.02). HLA-B27 was found to be twice as prevalent in patients with scleritis (15.3%) compared to a healthy population (7.2%). In conclusion, scleral nerve autoantibody reactivity was more common in scleritis and uveitis patients in contrast to healthy controls. Further research is needed to characterize these scleral-nerve directed antibodies and assess their clinical value.

Is Keratoconus More Than Just a Corneal Disease?

PURPOSE

The aims of this study were to compare the scleral thickness (ST), lamina cribrosa thickness (LCT), and lamina cribrosa curvature index between patients with keratoconus and healthy controls and to evaluate the relationship between these values and corneal parameters.

METHODS

This cross-sectional study included 41 eyes of 41 patients with keratoconus and 30 eyes of 30 age-matched, sex-matched, and axial length-matched controls. Nasal and temporal STs were measured vertically, 4 mm posterior to the scleral spur, using anterior segment optical coherence tomography. The LCT was measured on the radial scans of the optic nerve head. The lamina cribrosa curvature index (lamina cribrosa curvature depth/curvature width × 100) was calculated to determine the degree of posterior bowing of the lamina cribrosa.

RESULTS

The nasal ST and temporal ST were significantly lower in the keratoconus group than in the control group ( P = 0.016 and P = 0.023, respectively). The LCT was significantly lower in the keratoconus group compared with the control group ( P < 0.001). There was no significant difference between the groups for the lamina cribrosa curvature index ( P = 0.375). Correlation analysis revealed a significant correlation between the nasal and temporal STs and the central corneal thickness (r = 0.376, P < 0.001 and r = 0.387, P < 0.001, respectively). There was also a significant correlation between the temporal ST and the minimum corneal thickness in the keratoconus group (r = 0.332, P = 0.015). The LCT was significantly correlated with the central corneal thickness (r = 0.445, P < 0.001).

CONCLUSIONS

Structural features of the cornea, sclera, and lamina cribrosa with similar collagen content may be similarly affected in patients with keratoconus. Further histologic studies are needed to confirm our results.

Two-dimensional elastic distribution imaging of the sclera using acoustic radiation force optical coherence elastography

The scleral elasticity is closely related with many ocular diseases, but the relevant research is still insufficient. Here, we utilized optical coherence elastography to carefully study biomechanical properties of the sclera at different positions and under different intraocular pressures. Meanwhile, elastic wave velocity and Young's modulus of each position were obtained using a phase velocity algorithm. Accordingly, the two-dimensional elasticity distribution image was achieved by mapping the Young's modulus values to the corresponding structure based on the relationship between the position and its Young's modulus. Therefore, elastic information in regions-of-interest can be read and compared directly from the scleral structure, indicating that our method may be a very useful tool to evaluate the elasticity of sclera and provide intuitive and reliable proof for diagnosis and research.

Potential Biomarkers for Noninfectious Scleritis Identified by Serum and Tear Fluid Proteomics

Purpose

Scleritis is an extremely painful and potentially blinding inflammation of the sclera with unknown pathogenesis and unpredictable course. To gain insight in its disease process and identify biomarker candidates, we performed extensive proteomics in serum and tear fluid.

Design

Prospective multicenter cohort study.

Participants

A total of 121 patients with noninfectious scleritis (of which 39 active cases), 30 healthy controls, and 23 disease controls (uveitis and rheumatoid arthritis) were enrolled in the Netherlands from 2020 to 2022.

Methods

Serum, tear fluid of both eyes, and clinical data were gathered. The level of 368 inflammatory proteins was measured using proximity extension assays. Results were validated in an independent cohort of 15 patients with scleritis, and using addressable laser bead immunoassay, or enzyme-linked immunoassays. In addition, we studied an extended panel of matrix metalloproteinases in tear fluid of necrotizing scleritis with addressable laser bead immunoassay.

Main Outcome Measures

Statistically significant differences in the level of inflammatory proteins between patients with scleritis and control groups.

Results

Proteomics revealed 18 significantly upregulated or downregulated serum proteins in active scleritis cases compared with all control groups in both the discovery cohort and the validation cohort. The most upregulated protein was nuclear migration protein nudC (NudC; P = 0.0032), a protein involved in neurogenesis. The other significant hits included proteins involved in T-cell activation, apoptosis, epithelial barrier maintenance, and angiogenesis. Our tear fluid analysis showed matrix metalloproteinase 9 (MMP9) to be upregulated in the tear fluid of patients with scleral necrosis.

Conclusions

The results of our proteomics analysis suggest a role for neurogenesis, T-cell activation, disruption of epithelial barrier, and angiogenesis in the pathogenesis of scleritis, and highlight MMP9 and NudC as biomarkers with potential clinical relevance.

Funding Disclosures

The authors have no proprietary or commercial interest in any materials discussed in this article.

2D or not 2D? Mapping the in-depth inclination of the collagen fibers of the corneoscleral shell

The collagen fibers of the corneoscleral shell play a central role in the eye mechanical behavior. Although it is well-known that these fibers form a complex three-dimensional interwoven structure, biomechanical and microstructural studies often assume that the fibers are aligned in-plane with the tissues. This is convenient as it removes the out-of-plane components and allows focusing on the 2D maps of in-plane fiber organization that are often quite complex. The simplification, however, risks missing potentially important aspects of the tissue architecture and mechanics. In the cornea, for instance, fibers with high in-depth inclination have been shown to be mechanically important. Outside the cornea, the in-depth fiber orientations have not been characterized, preventing a deeper understanding of their potential roles. Our goal was to characterize in-depth collagen fiber organization over the whole corneoscleral shell. Seven sheep whole-globe axial sections from eyes fixed at an IOP of 50 mmHg were imaged using polarized light microscopy to measure collagen fiber orientations and density. In-depth fiber orientation distributions and anisotropy (degree of fiber alignment) accounting for fiber density were quantified over the whole sclera and in 15 regions: central cornea, peripheral cornea, limbus, anterior equator, equator, posterior equator, posterior sclera and peripapillary sclera on both nasal and temporal sides. Orientation distributions were fitted using a combination of a uniform distribution and a sum of π-periodic von Mises distributions, each with three parameters: primary orientation μ, fiber concentration factor k, and weighting factor a. To study the features of fibers that are not in-plane, i.e., fiber inclination, we quantified the percentage of inclined fibers and the range of inclination angles (half width at half maximum of inclination angle distribution). Our measurements showed that the fibers were not uniformly in-plane but exhibited instead a wide range of in-depth orientations, with fibers significantly more aligned in-plane in the anterior parts of the globe. We found that fitting the orientation distributions required between one and three π-periodic von Mises distributions with different primary orientations and fiber concentration factors. Regions of the posterior globe, particularly on the temporal side, had a larger percentage of inclined fibers and a larger range of inclination angles than anterior and equatorial regions. Variations of orientation distributions and anisotropies may imply varying out-of-plane tissue mechanical properties around the eye globe. Out-of-plane fibers could indicate fiber interweaving, not necessarily long, inclined fibers. Effects of small-scale fiber undulations, or crimp, were minimized by using tissues from eyes at high IOPs. These fiber features also play a role in tissue stiffness and stability and are therefore also important experimental information.

Scleral changes in systemic lupus erythematosus patients using swept source optical coherence tomography

Purpose

This study aims to examine scleral thickness in patients with systemic lupus erythematosus (SLE) without clinically evident scleritis and episcleritis, utilizing swept-source optical coherence tomography (SS-OCT).

Methods

This cross-sectional single center study compared scleral thickness (Nasal scleral thickness 1mm, 2mm, 3mm, 6mm from scleral spur; Temporal scleral thickness 1mm, 2mm, 3mm, 6mm from scleral spur) in 73 SLE patients without clinically evident scleritis and episcleritis and 48 healthy volunteers with SS-OCT. Further, we investigated the correlation between scleral thickness in SLE patients and various parameters including laboratory markers, disease duration, disease activity, and organ involvement.

Results

Across all measured sites (nasal scleral thickness at distances of 1mm, 2mm, 3mm, and 6mm from the scleral spur, and temporal scleral thickness at the same distances), the scleral thickness in the SLE group was significantly greater than that in the control group (all p-values <0.001). SLE patients with a disease duration of 5 years or less exhibited a higher scleral thickness compared to those with a more prolonged disease duration. Patients with a higher erythrocyte sedimentation rate (ESR) had a thinner temporal scleral thickness. However, no significant associations were identified between scleral thickness and disease activity, organ involvement, or other laboratory markers.

Conclusion

Scleral thickness measured by SS-OCT was higher in SLE patients than healthy controls. Changes in scleral thickness in SLE patients are related to disease duration and ESR. SS-OCT can detect asymptomatic structural changes in SLE patients and may be a useful tool in the evaluation of early scleral abnormality.

[Biomechanics of the lamina cribrosa: A determining factor in glaucomatous neuropathy. A review of the literature]

Glaucoma is a chronic optic neuropathy characterized by progressive sclero-laminar remodeling. The main factor at the origin of these deformations is the intraocular pressure (IOP), the effect of which varies according to the biomechanical properties of the individual lamina cribrosa (LC). In this environment, the LC represents a malleable zone of weakness within a rigid corneoscleral shell. It is a dynamic structure whose movements play a key role in the pathogenesis of glaucoma: displacing it posteriorly, in addition to contributing to the characteristic appearance of glaucomatous cupping, would increase constriction on the nerve fibers and the laminar capillaries. Often incorrectly considered permanent in adults, these deformations have a certain degree of reversibility, which is currently better characterized thanks to progress in imaging techniques. The occurrence of anterior displacement and laminar thickening following a reduction in IOP could thus constitute a good prognostic factor by reducing mechanical stress on this region. These changes would tend to reduce laminar pore tortuosity and shear forces, which are probably key mechanisms of axonal loss in glaucoma.

Trends in Formulation Approaches for Sustained Drug Delivery to the Posterior Segment of the Eye

The eye, an intricate organ comprising physical and physiological barriers, poses a significant challenge for ophthalmic physicians seeking to treat serious ocular diseases affecting the posterior segment, such as age-related macular degeneration (AMD) and diabetic retinopathy (DR). Despite extensive efforts, the delivery of therapeutic drugs to the rear part of the eye remains an unresolved issue. This comprehensive review delves into conventional and innovative formulation strategies for drug delivery to the posterior segment of the eye. By utilizing alternative nanoformulation approaches such as liposomes, nanoparticles, and microneedle patches, researchers and clinicians can overcome the limitations of conventional eye drops and achieve more effective drug delivery to the posterior segment of the eye. These innovative strategies offer improved drug penetration, prolonged residence time, and controlled release, enhancing therapeutic outcomes for ocular diseases. Moreover, this article explores recently approved delivery systems that leverage diverse polymer technologies, such as chitosan and hyaluronic acid, to regulate drug-controlled release over an extended period. By offering a comprehensive understanding of the available formulation strategies, this review aims to empower researchers and clinicians in their pursuit of developing highly effective treatments for posterior-segment ocular diseases.

Birefringence-derived artifact in optical coherence tomography imaging of the lamina cribrosa in eyes with glaucoma

We investigated birefringence-derived artifacts that potentially mimic focal defects of the lamina cribrosa (focal LC defects) in optical coherence tomography (OCT) imaging of eyes with glaucoma. This study included 74 eyes of 48 patients with glaucoma. Five horizontal line B-scan images of the optic disc were obtained using commercial swept-source OCT. From a dataset of prototype swept-source polarization-diversity OCT, we calculated the following types of OCT images: polarization-dependent, polarization-dependent attenuation-coefficient, polarization-independent, and polarization-independent attenuation-coefficient. We assessed the commercial OCT images for the presence of birefringence-derived artifacts by comparison with the polarization-diversity OCT images. Commercial OCT showed suggestive findings of focal LC defects in 17 of 74 eyes. Reevaluation using polarization-independent OCT revealed that the focal LC defects in one of 17 eyes (5.9%) were actually birefringence-derived artifacts. This study demonstrated the existence of birefringence-derived artifacts mimicking focal LC defects in commercial OCT imaging and indicated that polarization-diversity OCT is an effective tool to evaluate the presence of these artifacts.

Hyperprolactinemia modifies extracellular matrix components associated with collagen fibrillogenesis in harderian glands of non- and pregnant female mice

The harderian gland (HG) is a gland located at the base of the nictating membrane and fills the inferomedial aspect of the orbit in rodents. It is under the influence of the hypothalamic-pituitary-gonadal axis and, because of its hormone receptors, it is a target tissue for prolactin (PRL) and sex steroid hormones (estrogen and progesterone). In humans and murine, the anterior surface of the eyes is protected by a tear film synthesized by glands associated with the eye. In order to understand the endocrine changes caused by hyperprolactinemia in the glands responsible for the formation of the tear film, we used an animal model with metoclopramide-induced hyperprolactinemia (HPRL). Given the evidences that HPRL can lead to a process of cell death and tissue fibrosis, the protein expression of small leucine-rich proteoglycans (SLRPs) was analyzed through immunohistochemistry in the HG of the non- and the pregnant female mice with hyperprolactinemia. The SRLPs are related to collagen fibrillogenesis and they participate in pro-apoptotic signals. Our data revealed that high prolactin levels and changes in steroid hormones (estrogen and progesterone) can lead to an alteration in the amount of collagen, and in the structure of type I and III collagen fibers through changes in the amounts of lumican and decorin, which are responsible for collagen fibrillogenesis. This fact can lead to the impaired functioning of the HG by excessive apoptosis in the HG of the non- and the pregnant female mice with HPRL and especially in the HG of pregnancy-associated hyperprolactinemia.

Delayed presentation of surgically induced scleral necrosis after I-BRITE procedure treated with immunosuppressive therapy

Surgically induced scleral necrosis (SISN) is an uncommon complication of ocular procedures. Cosmetic eye-whitening surgery involves conjunctival and Tenon's capsule dissection, cautery, and mitomycin C application. We report the case of a 36-year-old white woman referred to our clinic for severe pain, scleral inflammation, and necrosis in both eyes 9 years after I-BRITE, an elective eye-whitening procedure. An extensive workup yielded negative results. The patient improved with aggressive lubrication and topical and high-dose systemic prednisone (60 mg), with recurrence upon steroid tapering. Concomitant weekly methotrexate was added, resulting in inflammatory control and allowing discontinuance of topical and oral steroids.

Biomechanics of open-globe injury: a review

Open-globe injury is a common cause of blindness clinically caused by blunt trauma, sharp injury, or shock waves, characterised by rupture of the cornea or sclera and exposure of eye contents to the environment. It causes catastrophic damage to the globe, resulting in severe visual impairment and psychological trauma to the patient. Depending on the structure of the globe, the biomechanics causing ocular rupture can vary, and trauma to different parts of the globe can cause varying degrees of eye injury. The weak parts or parts of the eyeball in contact with foreign bodies rupture when biomechanics, such as external force, unit area impact energy, corneoscleral stress, and intraocular pressure exceed a certain value. Studying the biomechanics of open-globe injury and its influencing factors can provide a reference for eye-contact operations and the design of eye-protection devices. This review summarises the biomechanics of open-globe injury and the relevant factors.

High-frequency ultrasound point-of-care device to quantify myopia-induced microstructural changes in the anterior sclera

PURPOSE

To develop a point-of-care (POC) device using high-frequency ultrasound (US) for evaluating microstructural changes in the anterior sclera associated with myopia.

METHODS

The proposed POC device must satisfy four primary requirements for effective clinical use: the measurement component is handheld; the software must be simple and provide real-time feedback; patient safety and health data security requirements set forth by relevant governing bodies must be satisfied and the measurement data must have sufficient signal-to-noise ratio (SNR) and repeatability. Radiofrequency (RF) echo data acquired by the POC device will be processed using our quantitative US methods to characterise tissue microstructure and biomechanical properties.

RESULTS

All stated requirements have been met in the developed POC device. The high-frequency transducer is housed in a custom, 3D-printed, pen-like holder that allows for easy measurements of the anterior sclera. Custom software provides a simple interface for data acquisition, real-time data display and secure data storage. Exposimetry measurements of the US pressure field indicate device compliance with United States Food and Drug Administration limits for ophthalmic US. In vivo measurements on a volunteer suggest the RF data SNR and acquisition consistency are suitable for quantitative analysis.

CONCLUSIONS

A fully functioning POC device using high-frequency US has been created for evaluating the microstructure of the anterior sclera. Planned studies using the POC device to scan the eyes of myopia patients will help clarify how the anterior sclera microstructure may be affected by myopia. If effective, this portable, inexpensive and user-friendly system could be an important part of routine eye examinations.

Scleral thickness in normal Indian eyes measured using spectral domain anterior segment optical coherence tomography

Purpose

To establish normative data on anterior scleral thickness using the spectral domain anterior segment optical coherence tomography (AS-OCT).

Methods

In total, 200 eyes of 100 healthy subjects underwent AS-OCT scans in the temporal and nasal quadrants. The scleral + conjunctival complex thickness (SCT) was measured by a single examiner. Mean SCT was analyzed for differences across age groups, gender, and location (nasal versus temporal).

Results

Mean age was 46.4 ± 18.3 (21-84) years; male to female ratio was 54:46. Mean SCT (nasal + temporal) of the right eye (RE) was 682.3 ± 64.2 μm in males and 660.6 ± 57.1 μm in females. In the left eye (LE), it was 684.6 ± 64.9 μm in males and 661.8 ± 49.3 μm in females. These differences between male and female for both eyes were statistically significant (P = 0.006 and P = 0.002). The mean SCT of temporal and nasal quadrants in the RE was 678.54 ± 57.50 and 666 ± 66.2 μm, respectively. In the LE, the temporal mean SCT quadrant was 679.6 ± 55.8 μm, and the nasal was 668.6 ± 63.6 μm. Age had a negative correlation with SCT (-0.62 μm/year; P = 0.03), and males had a higher temporal SCT than females (22 μm higher; P = 0.03). After adjusting for age and gender in a multivariate analysis, temporal SCT was significantly (P < 0.001) higher than nasal SCT.

Conclusion

In our study, mean SCT decreased with age and males had a higher temporal SCT. This is the first study to evaluate scleral thickness in the Indian population, and the data can be used as a baseline for comparing variations in scleral thickness in disease.

Acoustic radiation force optical coherence elastography: A preliminary study on biomechanical properties of trabecular meshwork

Evaluating biomechanical properties of trabecular meshwork (TM) is of great significance for understanding the mechanism of aqueous humor circulation and its relationship to some eye diseases such as glaucoma; however, there is almost no relevant study due to the lack of clinical measurement tool. In this paper, an acoustic radiation force optical coherence elastography (ARF-OCE) system is developed with the advantages of noninvasive detection, high resolution, high sensitivity, and high-speed imaging, by which elastic modulus of the porcine and human TMs is accurately quantified. As the first OCE imaging of TM, our study demonstrates that ARF-OCE may be an effective approach to advance the research of diseases related to aqueous humor circulation.

Scleral Thickness as a Risk Factor for Central Serous Chorioretinopathy and Pachychoroid Neovasculopathy

In the pathophysiology of central serous chorioretinopathy (CSC), scleral changes inducing increased venous outflow resistance are hypothesized to be involved. This work aims to investigate anterior scleral thickness (AST) as a risk factor for pachychoroid disorders. A randomized prospective case-control study was performed at the Ludwig Maximilians University, Department of Ophthalmology. In patients with CSC or pachychoroid neovasculopathy (PNV) and in an age- and refraction-matched control group, swept source optical coherence tomography (SS-OCT) was used to measure anterior scleral thickness (AST). Subfoveal choroidal thickness (SFCT) was assessed using enhanced depth imaging OCT (EDI-OCT). In total, 46 eyes of 46 patients were included in this study, with 23 eyes in the CSC/PNV and 23 eyes in the control group. A significantly higher AST was found in the CSC/PNV compared with the control group (403.5 ± 68.6 (278 to 619) vs. 362.5 ± 62.6 (218 to 498) µm; p = 0.028). Moreover, the CSC/PNV group showed a higher SFCT (392.8 ± 92.8 (191-523) vs. 330.95 ± 116.5 (167-609) µm, p = 0.004). Compared with the age- and refraction-matched controls, patients with CSC and PNV showed a significantly thicker anterior sclera. Scleral thickness might contribute to the venous overload hypothesized to induce pachychoroid phenotypes.

Role of anterior segment optical coherence tomography in scleral diseases: A review

BACKGROUND

Scleritis and episcleritis are an overlapping spectrum of diseases and accurate diagnosis is of utmost importance as the treatment and prognosis are vastly different. Predominantly a clinical diagnosis, the challenge lies in those cases with equivocal clinical features. Furthermore, clinical grading of scleritis is subjective and hence is neither very reliable nor reproducible. Existing modalities such as slit lamp examination and clinical photographs in scleritis describe macroanatomy but do not provide details on the microanatomy of the sclera. A recent adjusted algorithm for anterior segment optical coherence tomography (AS-OCT) imaging has improved the ability of this device to aid in the diagnosis of all the major forms of scleritis.

PURPOSE

To highlight the role of AS-OCT in delineating various anatomical forms of episcleritis and scleritis and explore this tool in monitoring disease course and response to therapy.

METHODS

A comprehensive literature search was carried out in various medical databases using keywords AS-OCT and scleritis; AS-OCT and episcleritis; anterior segment imaging in scleritis; scleritis and episcleritis; Recent advances in anterior segment imaging. Original articles and novel reports describing the potential role of AS-OCT in the diagnosis and management of scleritis and episcleritis were included.

RESULTS

After a thorough assessment, it was clear that published literature lacks guidelines for uniform interpretation and also for classification and follow-up in scleritis. We describe a uniform protocol for AS-OCT image acquisition, interpretation of images and list the advantages and limitations.

CONCLUSIONS

AS-OCT can be used to localize the level of scleral inflammation thus helping in the diagnosis of scleral inflammatory disease. It can be a valuable tool in studying progression.

Recent Progress of Solid Lipid Nanoparticles and Nanostructured Lipid Carriers as Ocular Drug Delivery Platforms

Sufficient ocular bioavailability is often considered a challenge by the researchers, due to the complex structure of the eye and its protective physiological mechanisms. In addition, the low viscosity of the eye drops and the resulting short ocular residence time further contribute to the observed low drug concentration at the target site. Therefore, various drug delivery platforms are being developed to enhance ocular bioavailability, provide controlled and sustained drug release, reduce the number of applications, and maximize therapy outcomes. Solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) exhibit all these benefits, in addition to being biocompatible, biodegradable, and susceptible to sterilization and scale-up. Furthermore, their successive surface modification contributes to prolonged ocular residence time (by adding cationic compounds), enhanced penetration, and improved performance. The review highlights the salient characteristics of SLNs and NLCs concerning ocular drug delivery, and updates the research progress in this area.

Aging Effects on Optic Nerve Neurodegeneration

Common risk factors for many ocular pathologies involve non-pathologic, age-related damage to the optic nerve. Understanding the mechanisms of age-related changes can facilitate targeted treatments for ocular pathologies that arise at any point in life. In this review, we examine these age-related, neurodegenerative changes in the optic nerve, contextualize these changes from the anatomic to the molecular level, and appreciate their relationship with ocular pathophysiology. From simple structural and mechanical changes at the optic nerve head (ONH), to epigenetic and biochemical alterations of tissue and the environment, multiple age-dependent mechanisms drive extracellular matrix (ECM) remodeling, retinal ganglion cell (RGC) loss, and lowered regenerative ability of respective axons. In conjunction, aging decreases the ability of myelin to preserve maximal conductivity, even with "successfully" regenerated axons. Glial cells, however, regeneratively overcompensate and result in a microenvironment that promotes RGC axonal death. Better elucidating optic nerve neurodegeneration remains of interest, specifically investigating human ECM, RGCs, axons, oligodendrocytes, and astrocytes; clarifying the exact processes of aged ocular connective tissue alterations and their ultrastructural impacts; and developing novel technologies and pharmacotherapies that target known genetic, biochemical, matrisome, and neuroinflammatory markers. Management models should account for age-related changes when addressing glaucoma, diabetic retinopathy, and other blinding diseases.

Assessment of the Retinal Nerve Fibre Layer, Retina, and Choroid in Osteogenesis Imperfecta

BACKGROUND

Osteogenesis imperfecta (OI) is a genetic disorder in which there are problems in tissues containing type I collagen, predominantly the cornea and sclera in the eye. Although there are many studies on problems with the anterior segment of the eye in patients with OI, studies on posterior structures are limited. Involvement of the sclera may affect the retinal nerve fibre layer (RNFL), which is indirectly related to intraocular pressure. In addition, the retina and choroid containing type I collagen may be affected. The aim of the study was to compare the posterior segment structures of the eye, including the RNFL, retina, and choroid, in patients with OI to those of healthy control subjects.

METHODS

This cross-sectional study recruited 19 patients with OI, as well as 22 age- and gender-similar healthy control subjects. Measurements of the RNFL, retina, and choroid were obtained with optical coherence tomography (Spectralis SD-OCT, Heidelberg Engineering, Heidelberg, Germany).

RESULTS

Patients with OI (mean age 14.32 ± 5.08 years) and the control group (mean age 13.73 ± 3.56 years) had similar age, refractive error, and intraocular pressure values (p > 0.05). There was no difference between groups in terms of RNFL thickness, including the superonasal, nasal, inferonasal, inferotemporal, temporal, and superotemporal sectors, retinal thickness, and choroidal thickness from five different locations (p > 0.05, for all).

CONCLUSION

According to these results, OI does not clinically affect the RNFL, retina, and choroid in childhood.

Pediatric Scleritis: An Update

Posterior idiopathic scleritis is the most common type of scleritis observed in childhood. Nevertheless, anterior and even necrotizing inflammatory scleritis may occur as well. Although less frequently than in the adult population, scleral inflammation can be associated with systemic disorders, which should be promptly recognized and treated to avoid both ocular and systemic complications. Hence, a multidisciplinary diagnostic work-up should be performed to rule out primarily infectious and autoimmune causes, such as viral and bacterial infections, anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis, pediatric sarcoidosis, Behçet's disease and HLA-B27-associated diseases. Treatment of scleritis should aim to control ocular inflammation, relieve symptoms and prevent relapses, to avoid complications, preserve visual acuity and improve the child's quality of life. It should be tailored to the patient, considering the type and severity of scleritis, the possible identification of an infectious cause or the presence of an associated rheumatologic condition.

Management of scleral melt

Scleral melting, while rare, can lead to significant ocular morbidity. Several possible risk factors for scleral melt have been identified, such as infection, autoimmune disease, trauma, and post-surgical state, and these may act in combination with each other. Treatment should be tailored according to the etiology and severity of the scleral melt. Medical management may be indicated, especially in cases of autoimmune-related melt; however, surgical procedures are often necessary due to compromised ocular integrity and limited penetration of medications into the avascular sclera. An understanding of the surgical options available and their operative outcomes is particularly important when choosing the appropriate treatment protocol for each patient.

Characterization of nonpathological intrascleral cartilage in the domestic sheep (Ovis aries)

ABSTRACT: Birds, cartilaginous and teleost fish, reptiles, and some amphibians have intrascleral cartilage and/or bone; however, these are rarely reported in therian mammals. This study aimed to investigate and characterize a nonpathological formation of cartilage in the posterior sclera of sheep macroscopically, histologically, and by immunohistochemical exam (IHC). Ninety eyes from 45 domestic sheep were collected, underwent gross examination, fixed in formalin, and embedded in paraffin for the microscopical assessment. Sections with histological shreds of cartilage were selected to perform IHC to confirm the presence of cartilage. Intrascleral cartilage was detected in 60 eyeballs (66.66%) from 37 sheep (82.22%). A slight whitish thickening was grossly seen in the posterior sclera. The histologic exam revealed a few scattered, isolated chondrocytes to larger aggregates of cartilaginous islands in the posterior sclera. Eighteen (30%) of 60 eyeballs revealed marked anti-collagen type II immunolabeling. The development of cartilaginous structures in the eyes is considered rare in mammalian animals. The high occurrence of intrascleral cartilage in the examined sheep eyes suggests that this finding corresponds to an anatomical component of sheep sclera, despite the age, breed, or body condition.

Scleral melt and uveal prolapse following 23-gauge pars plana vitrectomy

Purpose

To report a case of uncontrolled juvenile open angle glaucoma (JOAG), with secondary high axial myopia who presented with scleral melting and uveal prolapse post pars plana-vitrectomy.

Observations

A 17-year-old male juvenile glaucoma patient, not known to have any systemic disease underwent a right eye 23-gauge-pars plana vitrectomy for retinal detachment repair. Three weeks following his surgery he presented complaining of tearing and photophobia in the operated eye in the absence of any ocular pain. Clinical exam revealed enlarged sclerotomy sites with localized conjunctival and episcleral injection, scleral thinning and uveal prolapse. Infectious and serologic work up were obtained to rule out an infectious etiology or underlying autoimmune disease. Patient was successfully managed with topical steroids and a donor scleral patch graft.

Conclusion and importance

This report addresses multiple risk factors for a devastating complication that may occur in predisposed patients, with primary or secondary axial myopia and a compromised sclera. This group of patients can be at risk of post-operative scleral melting and thinning and should be identified pre-operatively and monitored closely during their post-operative course.

Delayed reorganisation of F-actin cytoskeleton and reversible chromatin condensation in scleral fibroblasts under simulated pathological strain

Mechanical loading regulates the functional capabilities of the ocular system, particularly in the sclera (‘white of the eye’) – the principal load-bearing tissue of the ocular globe. Resident fibroblasts of the scleral eye wall are continuously subjected to fluctuating mechanical strains arising from eye movements, cerebrospinal fluid pressure and, most influentially, intra-ocular pressure (IOP). Whilst fibroblasts are hypothesised to actively participate in scleral biomechanics, to date limited information has been reported on how the macroscopic stresses and strains are transmitted via their cytoskeletal networks. In this study, the effect of applying either a ‘physiological load’ (simulating healthy IOP) or a ‘pathological load’ (simulating an elevated glaucomatous IOP) to bovine scleral fibroblasts, as a model of human glaucoma, was conducted to characterise cytoskeletal organisation, chromatin condensation and cell dimensions using immunofluorescence confocal microscopy. Quantification of cell parameters and cytoskeletal element anisotropy were subsequently performed using FibrilTool, and chromatin condensation parameter assessment through a bespoke MATLAB script. The novel findings suggest that physiological load-induced F-actin rearrangement is transient, whereas pathological load, recapitulating in vivo glaucomatous IOP levels, had a reversible and inhibitory influence on remodelling of the cytoskeletal architecture and, further, induction of chromatin condensation. Ultimately, this could compromise cell behaviour. These findings could provide valuable insight into the mechanism(s) used by scleral fibroblasts to mechanically adapt to support biomechanical tissue integrity, and how it could be potentially modified for therapeutic avenues targeting mechanically mediated ocular pathologies such as glaucoma.

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Physiological strain induced a transient F-actin rearrangement in scleral fibroblasts.

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In contrast, pathological strain reversibly delayed F-actin rearrangement.

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Vimentin and β-tubulin networks were largely unaffected by strain regimens.

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Pathological strain reversibly increased chromatin condensation parameter.

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Pathological strain may induce ‘inhibition delay’ to confer cytoprotection.

The adaptive significance of human scleral brightness: an experimental study

Homogeneously depigmented sclerae have long been proposed to be uniquely human-an adaptation to enable cooperative behaviour by facilitating interpersonal coordination through gaze following. However, recent evidence has shown that deeply pigmented sclerae also afford gaze following if surrounding a bright iris. Furthermore, while current scleral depigmentation is clearly adaptive in modern humans, it is less clear how the evolutionarily intermediate stages of scleral pigmentation may have been adaptive. In sum, it is unclear why scleral depigmentation became the norm in humans, while not so in sister species like chimpanzees, or why some extant species display intermediate degrees of pigmentation (as our ancestors presumably did at some point). We created realistic facial images of 20 individually distinct hominins with diverse facial morphologies, each face in the (i) humanlike bright sclera and (ii) generalised apelike dark sclera version. Participants in two online studies rated the bright-sclera hominins as younger, healthier, more attractive and trustworthy, but less aggressive than the dark-sclera hominins. Our results support the idea that the appearance of more depigmented sclerae promoted perceived traits that fostered trust, increasing fitness for those individuals and resulting in depigmentation as a fixed trait in extant humans.

Birefringence-derived scleral artifacts in optical coherence tomography images of eyes with pathologic myopia

We investigated birefringence-derived scleral artifacts in optical coherence tomography (OCT) images of eyes with pathologic myopia. This study included 76 eyes of 42 patients with pathologic myopia. Five sets of OCT B-scan images of the macula were obtained using commercial swept-source OCT. A dataset of prototype swept-source polarization-diversity OCT images was used to identify polarization-dependent OCT images (i.e., complex averaging of OCT signals from two polarization channels) and polarization-independent OCT images (i.e., intensity averaging of two OCT signals). Polarization-dependent OCT images and commercial OCT images were assessed for the presence of birefringence-derived artifacts by comparison with polarization-independent OCT images. Both polarization-dependent OCT images and commercial OCT images contained scleral vessel artifacts. Scleral vessel artifacts were present in 46 of 76 eyes (60.5%) imaged by polarization-dependent OCT and 17 of 76 eyes (22.4%) imaged by commercial OCT. The proportion of images that showed scleral vessel artifacts was significantly greater among polarization-dependent OCT images than among commercial OCT images (P < 0.001). Additionally, polarization-dependent OCT images showed low-intensity band artifacts. This study demonstrated the existence of birefringence-derived scleral artifacts in commercial OCT images and indicated that polarization-diversity OCT is an effective tool to evaluate the presence of these artifacts.

Activity-Dependent Neuroprotective Protein (ADNP): An Overview of Its Role in the Eye

Vision is one of the dominant senses in humans and eye health is essential to ensure a good quality of life. Therefore, there is an urgent necessity to identify effective therapeutic candidates to reverse the progression of different ocular pathologies. Activity-dependent neuroprotective protein (ADNP) is a protein involved in the physio-pathological processes of the eye. Noteworthy, is the small peptide derived from ADNP, known as NAP, which shows protective, antioxidant, and anti-apoptotic properties. Herein, we review the current state of knowledge concerning the role of ADNP in ocular pathologies, while providing an overview of eye anatomy.

The role of Tenonplasty in the management of limbal and scleral ischemia due to acute ocular chemical burns

Of the various manifestations of ocular chemical burns (OCBs), ischemia of the limbus and the peri-limbal sclera indicates poor prognosis and in severe cases threaten the integrity of the globe. Tenonplasty is a surgical procedure which involves advancing the Tenon’s capsule over the ischemic areas to provide a vascular supply and to enable migration of the conjunctival epithelium. This review aims to provide an overview of the diagnosis of limbal ischemia and its management with Tenonplasty. A literature review was conducted using the keywords “Tenonplasty,” “Tenon’s capsule,” “ocular chemical injury,” “ocular thermal injury,” “Tenon advancement,” “scleral ischemia,” and “limbal ischemia,” and outcomes were studied from seven selected articles. In addition to clinical evaluation, in vivo imaging techniques such as anterior segment optical coherence tomography angiography can provide an objective method of measuring and monitoring the ischemia and re-perfusion of the peri-limbal vasculature. Tenonplasty can be performed in eyes with acute OCBs with scleral or limbal ischemia by dissecting the Tenon’s layer from the orbit and securing it to the limbus. The indications, mechanism of action, peri-operative considerations, surgical technique, and post-operative care of Tenonplasty are discussed in detail. The average time for post-operative re-epithelization ranges from 1 to 6 months with the formation of a symblepharon being the most common complication. In conclusion, Tenonplasty is a globe-salvaging procedure in cases with severe limbal and scleral ischemia because of OCBs and has good anatomical outcomes priming the globe for subsequent re-constructive and vision-restoring surgeries.

Changes in Rat Scleral Collagen Structure Induced by UVA-Riboflavin Crosslinking at Various Tissue Depths in Whole Globe Versus Scleral Patch

Purpose

To investigate structural changes in scleral collagen fibers at various tissue depths before and after photosensitized crosslinking (CXL) both isolated scleral patch versus whole globe using second-harmonic generation (SHG) imaging.

Methods

Scleral tissues were harvested from Sprague-Dawley rats and separated into three groups: untreated sclera (control), full-thickness scleral patch for CXL (Free Scleral CXL group), and sclera in intact globe for CXL (Globe CXL group). The CXL groups were soaked in 0.1% riboflavin and irradiated with 365 nm ultraviolet-A light (power, 0.45 mW/cm2) for 30 minutes. SHG images were acquired every 5 µm between 10 and 60 µm from the outer scleral surface. Collagen fiber waviness was calculated as the ratio of the total length of a traced fiber and the length of a straight path between the fiber ends.

Results

In the Free Scleral CXL group, collagen waviness was significantly increased compared to the control group at 35 to 50 µm (P < 0.05). In the Globe CXL group, collagen waviness was decreased compared to control at all depths with statistical significance (P < 0.05) achieved from 10 to 45 µm.

Conclusions

Depending upon its initial state (i.e., free scleral patch versus mechanically loaded intact globe under pressure), collagen may experience different structural changes after CXL. In addition, the extent of the CXL effects may vary at different depths away from the surface.

Translational Relevance

Understanding the CXL effects on collagen structure may be important in optimizing the scleral crosslinking protocol for future clinical applications such as preventing myopic progression.

Anterior staphyloma repair following trauma and surgery - A retrospective review of techniques and outcomes over 25 years

Purpose

To review surgical options, techniques, and outcomes of anterior staphyloma repair done following trauma and surgery.

Methods

This was a retrospective case study of patients who underwent staphyloma repair with scleral or tibial periosteal patch grafts following trauma and surgery with a minimum follow-up of 3 months postoperatively. Preoperative risk factors, choice of graft materials, surgical details, and outcomes in terms of graft uptake and tectonic integrity were analyzed.

Results

Seventeen eyes of 17 patients underwent successful staphyloma repair (scleral 15, tibial periosteal two). Mean follow-up was 47.1 months (3-159 months). Postoperative intraocular pressure rise noted in four eyes was controlled medically or surgically. Three patients underwent successful repeat patch grafting (graft melt one and recurrent ectasia two). Tectonic integrity of the eyeball was restored and maintained in all patients at the final follow-up.

Conclusion

Comprehensive evaluation of the risk factors, control of ocular comorbid conditions, and early and meticulous surgery can optimize results.

A Novel Human Sex Difference: Male Sclera Are Redder and Yellower than Female Sclera

In a seminal study, Kobayashi and Kohshima (1997) found that the human sclera-the white of the eye-is unique among primates for its whitish color, and subsequent work has supported the notion that this coloration underlies the human ability to gaze follow. Kobayashi and Kohshima also claimed that there is no significant sex difference in sclera color, though no data were presented to support the claim. We investigated sclera color in a standardized sample of faces varying in age and sex, presenting the first data comparing male and female sclera color. Our data support the claim that indeed there is a sex difference in sclera color, with male sclera being yellower and redder than female sclera. We also replicated earlier findings that female sclera vary in color across the adult lifespan, with older sclera appearing yellower, redder, and slightly darker than younger sclera, and we extended these findings to male sclera. Finally, in two experiments we found evidence that people use sclera color as a cue for making judgements of facial femininity or masculinity. When sclera were manipulated to appear redder and yellower, faces were perceived as more masculine, but were perceived as more feminine when sclera were manipulated to appear less red and yellow. Though people are typically unaware of the sex difference in sclera color, these findings suggest that people nevertheless use the difference as a visual cue when perceiving sex-related traits from the face.

Cyclosporine-loaded micelles for ocular delivery: Investigating the penetration mechanisms

Cyclosporine is an immunomodulatory drug commonly used for the treatment of mild-to-severe dry eye syndrome as well as intermediate and posterior segment diseases as uveitis. The ocular administration is however hampered by its relatively high molecular weight and poor permeability across biological barriers. The aim of this work was to identify a micellar formulation with the ability to solubilize a considerable amount of cyclosporine and promote its transport across ocular barriers. Non-ionic amphiphilic polymers used for micelles preparation were tocopherol polyethylene glycol 1000 succinate (TPGS) and Solutol® HS15. Furthermore, the addition of alpha-linolenic acid was assessed. A second aim was to evaluate micelles fate in the ocular tissues (cornea and sclera) to shed light on penetration mechanisms. This was possible by extracting and quantifying both drug and polymer in the tissues, by studying TPGS hydrolysis in a bio-relevant environment and by following micelles penetration with two-photon microscopy. Furthermore, TPGS role as permeation enhancer on the cornea, with possible irreversible modifications of tissue permeability, was analyzed. Results showed that TPGS micelles (approx. 13 nm in size), loaded with 5 mg/ml of cyclosporine, promoted drug retention in both the cornea and the sclera. Data demonstrated that micelles behavior strictly depends on the tissue: micelles disruption occurs in contact with the cornea, while intact micelles diffuse in the interfibrillar pores of the sclera and form a reservoir that can sustain over time drug delivery to the deeper tissues. Finally, cornea quickly restore the barrier properties after TPGS removal from the tissue, demonstrating its potential good tolerability for ocular application.

Remodeling of the Lamina Cribrosa: Mechanisms and Potential Therapeutic Approaches for Glaucoma

Glaucomatous optic neuropathy is the leading cause of irreversible blindness in the world. The chronic disease is characterized by optic nerve degeneration and vision field loss. The reduction of intraocular pressure remains the only proven glaucoma treatment, but it does not prevent further neurodegeneration. There are three major classes of cells in the human optic nerve head (ONH): lamina cribrosa (LC) cells, glial cells, and scleral fibroblasts. These cells provide support for the LC which is essential to maintain healthy retinal ganglion cell (RGC) axons. All these cells demonstrate responses to glaucomatous conditions through extracellular matrix remodeling. Therefore, investigations into alternative therapies that alter the characteristic remodeling response of the ONH to enhance the survival of RGC axons are prevalent. Understanding major remodeling pathways in the ONH may be key to developing targeted therapies that reduce deleterious remodeling.

Postnatal eye size in mice is controlled by SREBP2-mediated transcriptional repression of Lrp2 and Bmp2

Eye size is a key parameter of visual function, but the precise mechanisms of eye size control remain poorly understood. Here, we discovered that the lipogenic transcription factor sterol regulatory element-binding protein 2 (SREBP2) has an unanticipated function in the retinal pigment epithelium (RPE) to promote eye size in postnatal mice. SREBP2 transcriptionally represses low density lipoprotein receptor-related protein 2 (Lrp2), which has been shown to restrict eye overgrowth. Bone morphogenetic protein 2 (BMP2) is the downstream effector of Srebp2 and Lrp2, and Bmp2 is suppressed by SREBP2 transcriptionally but activated by Lrp2. During postnatal development, SREBP2 protein expression in the RPE decreases whereas that of Lrp2 and Bmp2 increases as the eye growth rate reduces. Bmp2 is the key determinant of eye size such that its level in mouse RPE inversely correlates with eye size. Notably, RPE-specific Bmp2 overexpression by adeno-associated virus effectively prevents the phenotypes caused by Lrp2 knock out. Together, our study shows that rapid postnatal eye size increase is governed by an RPE-derived signaling pathway, which consists of both positive and negative regulators of eye growth.

Biomechanical changes in myopic sclera correlate with underlying changes in microstructure

Myopia alters the microstructural and biomechanical properties of the posterior sclera, which is characterized as a layered structure with potentially different inter-layer collagen fibril characteristics. Scanning acoustic microscopy (SAM) has been used to investigate how the micron-scale bulk mechanical properties of the posterior sclera are affected by myopia. Other investigators have employed second harmonic generation (SHG) imaging to characterize the collagen microstructure of tissues. In the present study, SAM and SHG imaging were used to investigate the existence of biomechanically-distinct scleral layers and identify relationships between mechanical properties and tissue microstructure in myopic guinea pig (GP) eyes. Diffusers were worn over the right eyes of six, 1-week-old GPs for one week to induce unilateral form-deprivation myopia. GPs were euthanized, enucleated, and eyes were cryosectioned. Twelve-micron-thick adjacent vertical cryosections were scanned with SAM or SHG. SAM maps of bulk modulus, mass density, and acoustic attenuation were estimated. A fiber-extraction algorithm applied to SHG images estimated collagen fiber length, width, straightness, alignment, and number density. Results revealed that the posterior sclera may exhibit biomechanically distinct layers that are affected differently in myopia. Specifically, a layered structure was observed in the mechanical-parameter maps of control eyes that was less apparent in myopic eyes. Collagen fibers in myopic eyes had smaller diameters and were more aligned. Myopia-associated biomechanical changes were most significant in the outermost and innermost scleral layers. SAM-measured mechanical parameters were correlated with collagen fiber microstructure, particularly fiber length, alignment, and number density, which may imply the biomechanical parameters estimated from SAM measurements are related to tissue microstructure. Interestingly, some changes were greatest in more-peripheral regions, suggesting interventions to strengthen the sclera may be effective away from the optic nerve and efficacy may be achieved best when intervention is applied to the outermost layer.

Polymer based sustained drug delivery to the ocular posterior segment: barriers and future opportunities for the treatment of neovascular pathologies

There is an increasing momentum in research and pharmaceutical industry communities to design sustained, non-invasive delivery systems to treat chronic neovascular ocular diseases that affect the posterior segment of the eye including age-related macular degeneration and diabetic retinopathy. Current treatments include VEGF blockers, which have revolutionized the standard of care for patients, but their maximum therapeutic benefit is hampered by the need for recurrent and invasive administration procedures. Currently approved delivery systems intended to address these limitations exploit polymer technology to regulate drug release in a sustained manner. Here, we critically review sustained drug delivery approaches for the treatment of chronic neovascular diseases affecting the ocular posterior segment, with a special emphasis on novel and polymeric technologies spanning the spectrum of preclinical and clinical investigation, and those approved for treatment. The mechanism by which each formulation imparts sustained release, the impact of formulation characteristics on release and foreign body reaction, and special considerations related to the translation of these systems are discussed.

The choroid-sclera interface: An ultrastructural study

Emmetropization is an active and visually guided process that involves the retina, choroid and sclera, and results in compensatory changes in eye growth. This guided growth is the result of visual cues and possibly mechanical interactions being translated into growth signals via molecular events from the retina into the choroid and sclera, through the choroidal scleral transition zone. If mechanical interactions were a part of the choroid-sclera signaling transduction cascade, specific morphological arrangements should be detectable in this region at the ultrastructural level. The goal of this study was to investigate the ultrastructural features of the choroidal scleral transition zone by comparing avian, non-human primate and human eyes, with the goal to confirm whether specific mechanical structures are present. Choroidal and scleral tissue from chicken, marmoset, and human eyes were imaged using transmission electron microscopy to document the choroid-sclera transition zone. In chicken eyes, fibroblast lamellae bordered the scleral matrix and formed thin end elongated processes that were undercut by scleral collagen fibrils. These processes back-looped into the scleral matrix, and displayed small club-like membrane protrusions. Differences in these arrangements in mature vs young chickens were not detected. The club-like membrane protrusions identified in chickens were rare in marmoset eyes, which instead exhibited two types of collagen fibrils discriminated by size, and were absent in the human eyes investigated. In marmoset and human eyes, elastic components were detected in the transition zone that were absent in chickens. In summary, cellular/membrane specializations indicating a mechanical interaction at the choroid-sclera transition zone were not detected in chicken, non-human primate or human eyes. If mechanotransduction is necessary for scleral growth, matrix integrity or development, alternative structural arrangements might be required.

Semilunar sign of cornea: A multimodal analysis of the posterior corneal opacity in non-infectious anterior scleritis

Purpose:

To analyze the morphological outcomes of the posterior corneal opacity or “semilunar sign” in noninfectious anterior scleritis using multimodal imaging.

Methods:

This was a prospective observational case series. Patients with anterior scleritis from January 2018 to January 2019 were included. Clinical and demographic data were collected. Posterior cornea was visualized using the digital slit lamp photography (Elite, mega digital vision), spectral domain optical coherence tomography (MS39), and specular count analyzer (EM-3000). “Semilunar sign” was defined by the (1) presence of posterior corneal opacity, (2) concave semilunar pattern, (3) absence of blood vessels, and (4) normal anterior cornea. Incidence, clinical characteristics and significance, correlation with Mantoux sensitivity, and role of multimodal valuation were assessed.

Results:

Overall 76 eyes of 72 patients were recruited with anterior scleritis. Fifteen eyes of 11 patients (15.3%) presented with semilunar sign. The scleritis was both nonnecrotizing (n = 8) and necrotizing (n = 7). The semilunar configuration appeared as isolated (n = 9) and continuous lesion (n = 6). The extent was directly related to the scleral disease extent (P = 0.002). The mean thickness measured 212.5 ± 129.3 mm. The mean central endothelial cell density (ECD) was 2540.8 ± 351.7 cells/mm², which was significantly higher than the involved peripheral cornea (P = 0.05). The mean surface area of the semilunar sign was 7.7 ± 5.2 mm². There was no significant correlation between the opacity thickness and the best-corrected visual acuity (P = 0.895, r = −0.39), ECD (P = 0.52, r = −0.188), and Mantoux (P = 0.696, r =− 0.142)

Conclusion:

Corneal semilunar sign of scleritis affected the peripheral cornea and caused no functional abnormality in early presentation. Multimodal analysis can aid in clinical assessment and severity.

Corneal transparency and scleral opacity arises from the nanoarchitecture of the constituent collagen fibrils

While human scleral and corneal tissues possess similar structural morphology of long parallel cylindrical collagen fibrils, their optical characteristics are markedly different. Using pseudospectral time-domain (PSTD) simulations of Maxwell's equations, we model light propagation through realistic representations of scleral and corneal nanoarchitecture and analyze the transmittance and spatial correlation in the near field. Our simulation results provide differing predictions for scleral opacity and corneal transparency across the vacuum ultraviolet to the mid-infrared spectral region in agreement with experimental data. The simulations reveal that the differences in optical transparency between these tissues arise through differences in light scattering emanating from the specific nanoscale arrangement and polydispersity of the constituent collagen fibrils.

Sustained Release Biodegradable Microneedles of Difluprednate for Delivery to Posterior Eye

Purpose: Difluprednate ophthalmic emulsion (Durezol^®) is currently used for the treatment of anterior uveitis; however, recent studies have shown that difluprednate can treat posterior eye conditions. Topical formulations limit the amount of drug capable of permeating to the posterior segment due to permeation barriers, lacrimation, and lymphatic clearance. Methods: Resomer^®-based microneedle patches were fabricated for difluprednate using poly(acrylic acid) (PAA) for the rapidly dissolvable backing. The patches were analyzed for microneedle uniformity and sharpness using scanning electron microscopy, and the penetration depth was analyzed by confocal microscopy. Failure force necessary to break the microneedles and force needed to penetrate the sclera were analyzed by the texture analyzer. Difluprednate release and trans-scleral permeation studies on microneedles were performed using Franz diffusion cells. Results: The microneedles were uniform, sharp, and penetrated to 500 μm depth on sclera. The microneedles have a failure force proportional to the molecular weight (MW) of the polymer used. There was no correlation between failure force and the penetration force of the microneedles. The PAA backing dissolved within 30-40 min, while release studies showed a matrix diffusion-controlled release over the 7-day study. The amount of drug permeation and retention in the sclera were decreased with an increase in the MW of the Resomer and failure force of each array. Conclusions: Resomer-based microneedles have a potential application for the sustained release of difluprednate for posterior segment conditions.

Ocular characteristics and complications in patients with osteogenesis imperfecta: a systematic review

PURPOSE

Osteogenesis imperfecta (OI) is a rare inherited heterogeneous connective tissue disorder characterized by bone fragility, low bone mineral density, skeletal deformity and blue sclera. The dominantly inherited forms of OI are predominantly caused by mutations in either the COL1A1 or COL1A2 gene. Collagen type I is one of the major structural proteins of the eyes and therefore is the eye theoretically prone to alterations in OI. The aim of this systematic review was to provide an overview of the known ocular problems reported in OI.

METHODS

A literature search (in PubMed, Embase and Scopus), which included articles from inception to August 2020, was performed in accordance with the PRISMA guidelines.

RESULTS

The results of this current review show that almost every component of the eye could be affected in OI. Decreased thickness of the cornea and sclera is an important factor causing eye problems in patients with OI such as blue sclera. Findings that stand out are ruptures, lacerations and other eye problems that occur after minor trauma, as well as complications from standard surgical procedures.

DISCUSSION

Alterations in collagen type I affect multiple structural components of the eye. It is recommended that OI patients wear protective glasses against accidental eye trauma. Furthermore, when surgery is required, it should be approached with caution. The prevalence of eye problems in different types of OI is still unknown. Additional research is required to obtain a better understanding of the ocular defects that may occur in OI patients and the underlying pathology.