Physiological Intraocular Pressure Research Articles

Effects of intramuscular alfaxalone and dexmedetomidine alone and combined on ocular, electroretinographic, and cardiorespiratory parameters in normal cats.

This study aimed to determine the effects of intramuscular (IM) administration of alfaxalone with or without dexmedetomidine on short electroretinography (ERG), ocular parameters and cardiorespiratory in healthy cats. Eight healthy female spayed cats were treated with three sedation protocols: IM administration of 5 μg/kg dexmedetomidine (DEX), 5 mg/kg alfaxalone (ALF), and 5 μg/kg dexmedetomidine plus 5 mg/kg alfaxalone (DEX + ALF). The washout period after each treatment was 2 weeks. Physiological parameters, time metrics, intraocular pressure (IOP), Schirmer tear test 1 (STT-1) and a short ERG protocol were recorded. For age data, weight data, time metrics and ERG data, one-way ANOVA with Bonferroni posterior comparisons were performed. For physiological parameters, IOP and STT-1 data, two-way repeated measures ANOVA with Bonferroni posterior comparisons were performed. Statistical significance was set at a p-value <0.05. IOPs were increased in all three groups compared to baseline and showed no significant differences among three groups at any time point. STT-1 values were decreased significantly during the process. Significant differences were noticed between a-wave amplitude in the dark-adapted response between DEX and ALF, and a-wave amplitude in light-adapted response between ALF and DEX + ALF. This study demonstrates the feasibility of three sedation protocols for short ERG recording in cats. All these treatments resulted in increased IOP values and reduced STT-1 values. But baseline data of ERG was not obtained as a blank control in cats.

Phacoemulsification using an Active Fluidics System at Physiologic versus High IOP: Impact on Anterior and Posterior Segment Physiology.

Evaluate the impact of high vs low intraoperative IOP during phacoemulsification on anterior and posterior physiology. Private practice in Des Moines, Iowa. Prospective, randomized, paired-eye clinical trial of patients anticipating bilateral cataract surgery. Twenty-seven subjects randomized at the time of their first cataract surgery to either low intraocular pressure (IOP) or high IOP group. The subsequent cataract surgery was done under the alternate condition. During phacoemulsification and cortex removal, IOP was maintained either at low (≤28 mmHg) or at high (≥55-60 mmHg) levels. The primary outcome was fluid usage, with secondary outcomes of central corneal thickness, FAZ (foveal avascular zone) area, foveal and macular thickness, endothelial cell density and post-operative inflammation. Surgery with low IOP settings used less fluid (40.0cc v 55.6 cc, p<0.0001). Corneal thickness changes were smaller in low IOP eyes at 1 day and 1 week (3.0% v 8.1%, p=0.01; 3.1% v 4.4%, p=0.01) but were similar by 1 and 3 months. Endothelial cell density (ECD) dropped less in low IOP eyes at 1 and 3 months (-1.7%v-12.3%, p=0.001, 2.1% vs -8.9%, p=0.0003.) IOP remained a significant predictor of ECD change when relationship was controlled for fluid use and phaco energy. Retinal parameters did not vary among all eyes or when compared by IOP setting. Visual acuity was similar at all time points. Low IOP settings resulted in less inflammation and less corneal trauma, as evidenced by a smaller drop in endothelial cell density and less postop corneal edema, when compared to high IOP settings. Retinal parameters did not change significantly. The different outcomes did not result in a difference in visual acuity.

Comparative study of recording intraocular pressure in adults by three different tonometers Goldmann applanation tonometer, noncontact tonometer, and tonopen

Purpose To compare and correlate the intraocular pressure (IOP) measurement obtained by Goldmann applanation tonometer (GAT), noncontact tonometer (NCT), and tonopen in normal and glaucomatous patients. Patients and methods A cross-sectional, observational, and comparative study was carried out. Two hundred eyes of 100 patients were screened, detailed history was taken, and thorough ocular examination was done. IOP was recorded using NCT (Keeler Pulsair), Tonopen (Tonopen XL), and GAT. Gonioscopy, optic disc examination, central corneal thickness, and visual field testing were done. Results The mean age of the study group was 53.25 years. Mean IOP by NCT was 19.20 mmHg, by GAT was 22.44 mmHg, and by tonopen was 19.33 mmHg. There was statistically significant difference between mean IOP with respect to method used (P&lt;0.001). Forty-eight percent of eyes, 40% eyes, and 49% eyes had IOP less than 18 mmHg by NCT, GAT, and tonopen, respectively. In total, 35.5% eyes, 19.5% eyes, and 35.5% eyes had IOP ranging between 18 and 25 mmHg by NCT, GAT, and tonopen, respectively. In total, 16.5% eyes, 40.5% eyes, and 15.5% eyes had IOP more than 25 mmHg by NCT, GAT, and tonopen, respectively. Conclusion NCT and tonopen readings correlate well with GAT readings in physiologic IOP range up to 20 mmHg, but at higher IOP range they tend to underestimate IOP readings as compared with GAT. However, NCT and tonopen can be used for screening purpose as they are portable and easy to use.

Effect of Anterior Chamber Air on Central Corneal Thickness in Human Donor Eyes.

The purpose of this study was to describe the effects of intracameral air on corneal edema. A laboratory investigation was performed on human donor corneas. Baseline pachymetry measurements through anterior segment optical coherence tomography and endothelial cell density were obtained for all corneas. Each pair of corneas was separated and randomly assigned to undergo air injection or Optisol-GS into a BIONIKO artificial anterior chamber for 5 minutes at physiologic intraocular pressure confirmed by digital palpation. Photographs were obtained immediately on connection of the cornea to the artificial anterior chamber and on completion of the 5 minutes of treatment, with anterior chamber air being exchanged for Optisol-GS. Pretreatment and posttreatment photographs were obtained. Immediately after treatment, pachymetry was again obtained on all corneas. Pachymetry data underwent statistical analysis. Corneal pachymetry improved from 690.5 ± 126.6 to 576.1 ± 87.2 μm, yielding a 114.4 ± 50.4 μm improvement of pachymetry in the group with air injected into the anterior chamber. This was a significant improvement of pachymetry when compared with the group with Optisol-GS injected into the anterior chamber, which showed an improvement from 662.3 ± 126.5 to 613.5 ± 108.0 μm, yielding an improvement of 48.8 ± 34.3 μm. Injection of air into the anterior chamber leads to a significant decrease in corneal pachymetry. We thereby propose that injecting air intracamerally is an effective intraoperative intervention when visualization is negatively affected by corneal edema.

Biomechanical Study of the Eye with Keratoconus-Type Corneal Ectasia Using a 3D Geometric Model

Keratoconus is an eye disease that distorts the shape of the cornea. This study aimed to analyze the effect of an increase in intraocular pressure applied to eyes with different severity of keratoconus disease using patient-specific models. Finite element models of the normal eye, eye with keratoconus, and eye with keratoglobus were constructed. The loading conditions considered the intraocular pressure increment as well as their physiological intraocular pressure. The analysis was performed with distinct materials for normal and keratoconic eyes. The finite element analysis revealed differences in the three models in terms of their deformation and maximum principal stress, and differences were observed in corneal curvature and thickness. These findings could enhance research in the biomechanical area, leading to more successful treatment options and a more individualized approach in the field of practical ophthalmology. Further investigation with larger sample sizes and more precise data on eye material would allow us to evaluate whether these disparities could inform the diagnosis of keratoconus.

A predictive model of UV-A-riboflavin crosslinking treatment on porcine corneas

The crosslinking technique (CXL) is an effective low-risk therapeutic treatment of keratoconus and other ectatic disorders of the human cornea. The effect of corneal CXL is to increase the stiffness of the stroma to prevent the progression of the cornea distortion. Several clinical and experimental studies have shown that the stiffening effects predominantly localize on the anterior portion of the stroma and that the in-depth stiffening distribution is highly dependent on the duration of treatment. Yet, how the stiffening effects distribute through the cornea thickness as a function of the treatment duration is an open question. Here, we propose an analytical model of the stiffening profile due to CXL treatment as a function of the irradiation time. We consider linear and nonlinear variations of the crosslinking effects across the thickness and implement them into a finite element model of the porcine cornea. We present a time-dependent in-depth stiffening profile that allows us to predict the post-operative cornea response to physiological intraocular pressure for different irradiation times. We anticipate that this predictive model will support the development of patient specific three-dimensional models that will allow clinicians to design customized CXL treatment, thus enhancing treatment outcomes.

Comparison of INTREPID® balanced and hybrid tips on anterior capsule rupture in ex vivo porcine eyes.

Phacoemulsification has emerged as the global standard for cataract surgery, and various novel methods, tools, and agents have promoted surgical efficiency and reduced complications. Conventionally, the phaco tip, which cleaves and aspirates the cataractous lens, has been mainly constructed of metal. In this study, the risk of anterior capsule rupture was evaluated under conditions of different power modes, longitudinal (Mode-L), torsional (Mode-T), or both (Mode-LT), and different aspiration powers (0 or 200 mmHg), using a traditional metal phaco tip (Group-M) or a new phaco tip with a high-strength polymer overmold on the needle edge (Group-P), which was developed to reduce the risk of capsule rupture. One hundred twenty porcine eyes were used for experiments within a setting of typical human physiological intraocular pressure. We found that Group-M showed capsule rupture with a smaller ultrasound power than did Group-P, regardless of power mode or aspiration power. In Group-M, there was no significant difference in risk of capsule rupture among power modes, however in Group-P, capsule rupture was least likely to occur with Mode-T. These results provide useful information for inexperienced ophthalmologists to improve surgical safety.

Who bears the load? IOP-induced collagen fiber recruitment over the corneoscleral shell

Collagen is the main load-bearing component of cornea and sclera. When stretched, both of these tissues exhibit a behavior known as collagen fiber recruitment. In recruitment, as the tissues stretch the constitutive collagen fibers lose their natural waviness, progressively straightening. Recruited, straight, fibers bear substantially more mechanical load than non-recruited, wavy, fibers. As such, the process of recruitment underlies the well-established nonlinear macroscopic behavior of the corneoscleral shell. Recruitment has an interesting implication: when recruitment is incomplete, only a fraction of the collagen fibers is actually contributing to bear the loads, with the rest remaining “in reserve”. In other words, at a given intraocular pressure (IOP), it is possible that not all the collagen fibers of the cornea and sclera are actually contributing to bear the loads.To the best of our knowledge, the fraction of corneoscleral shell fibers recruited and contributing to bear the load of IOP has not been reported. Our goal was to obtain regionally-resolved estimates of the fraction of corneoscleral collagen fibers recruited and in reserve. We developed a fiber-based microstructural constitutive model that could account for collagen fiber undulations or crimp via their tortuosity. We used experimentally-measured collagen fiber crimp tortuosity distributions in human eyes to derive region-specific nonlinear hyperelastic mechanical properties. We then built a three-dimensional axisymmetric model of the globe, assigning region-specific mechanical properties and regional anisotropy. The model was used to simulate the IOP-induced shell deformation. The model-predicted tissue stretch was then used to quantify collagen recruitment within each shell region. The calculations showed that, at low IOPs, collagen fibers in the posterior equator were recruited the fastest, such that at a physiologic IOP of 15 mmHg, over 90% of fibers were recruited, compared with only a third in the cornea and the peripapillary sclera. The differences in recruitment between regions, in turn, mean that at a physiologic IOP the posterior equator had a fiber reserve of only 10%, whereas the cornea and peripapillary sclera had two thirds. At an elevated IOP of 50 mmHg, collagen fibers in the limbus and the anterior/posterior equator were almost fully recruited, compared with 90% in the cornea and the posterior sclera, and 70% in the peripapillary sclera and the equator. That even at such an elevated IOP not all the fibers were recruited suggests that there are likely other conditions that challenge the corneoscleral tissues even more than IOP. The fraction of fibers recruited may have other potential implications. For example, fibers that are not bearing loads may be more susceptible to enzymatic digestion or remodeling. Similarly, it may be possible to control tissue stiffness through the fraction of recruited fibers without the need to add or remove collagen.

The Effect of Intraocular Pressure Load Boundary on the Biomechanics of the Human Conventional Aqueous Outflow Pathway.

Aqueous humor outflow resistance in the trabecular meshwork (TM), juxtacanalicular connective tissue (JCT), and Schlemm's canal (SC) endothelium of the conventional outflow pathway actively contribute to intraocular pressure (IOP) regulation. Outflow resistance is actively affected by the dynamic outflow pressure gradient across the TM, JCT, and SC inner wall tissues. The resistance effect implies the presence of a fluid-structure interaction (FSI) coupling between the outflow tissues and the aqueous humor. However, the biomechanical interactions between viscoelastic outflow tissues and aqueous humor dynamics are largely unknown. A 3D microstructural finite element (FE) model of a healthy human eye TM/JCT/SC complex was constructed with elastic and viscoelastic material properties for the bulk extracellular matrix and embedded elastic cable elements. The FE models were subjected to both idealized and a physiologic IOP load boundary using the FSI method. The elastic material model for both the idealized and physiologic IOP load boundary at equal IOPs showed similar stresses and strains in the outflow tissues as well as pressure in the aqueous humor. However, outflow tissues with viscoelastic material properties were sensitive to the IOP load rate, resulting in different mechanical and hydrodynamic responses in the tissues and aqueous humor. Transient IOP fluctuations may cause a relatively large IOP difference of ~20 mmHg in a very short time frame of ~0.1 s, resulting in a rate stiffening in the outflow tissues. Rate stiffening reduces strains and causes a rate-dependent pressure gradient across the outflow tissues. Thus, the results suggest it is necessary to use a viscoelastic material model in outflow tissues that includes the important role of IOP load rate.

Changes in Intraocular Pressure following Narcosis With Medetomidine, Midazolam, and Fentanyl in Association With Initial Intraocular Pressure in Mice

Purpose This article describes the development of decreased intraocular pressure (IOP) under general anesthesia with medetomidine, midazolam, and fentanyl in mice with normal and elevated IOP. Methods IOP was measured using the iCare Tonolab rebound tonometer. Twelve 3–4 months-old male and female C57BL/6J mice were randomized to a control group with physiological IOP and a high IOP group with experimentally induced ocular hypertension using tarsal injections of dexamethasone-21-acetate. For anesthesia, medetomidine and midazolam were used, subgroups additionally received fentanyl. IOP was measured every 2.5 min for 30 min. Results Control group differed with 14.89 mmHg (SEM: 0.58) significantly (p = 0.0002) from the high IOP group with initial 20.44 mmHg (SEM: 0.75). All groups showed a significant (p < 0.05) decrease in IOP under general anesthesia. There was no significant difference in IOP development and decrease between the group additionally receiving fentanyl and the group without fentanyl. The decrease in IOP was highly dependent on the initial value, with the high IOP group showing a greater decrease. After 10 min, no significant difference in IOP could be detected between the high IOP and control group. Conclusions In mice, general anesthesia with medetomidine and midazolam leads to a declining IOP over time. Adding fentanyl to the anesthesia did not alter these effects. The decline is time-dependent and IOP-dependent

Neovascular Glaucoma from Ocular Ischemic Syndrome Treated with Serial Monthly Intravitreal Bevacizumab and Panretinal Photocoagulation: A Case Report

Purpose To describe a case of open-angle neovascular glaucoma (NVG) secondary to ocular ischemic syndrome (OIS) treated with a planned series of 6 monthly anti-VEGF injections with interspersed panretinal photocoagulation (PRP) sessions. We term this treatment protocol the Salvaging Conventional Outflow Pathway in Neovascular Glaucoma (SCOPING) Protocol, and this is our (MQ and DS) standard of care for all NVG patients presenting with partially or completely open angles. Case A 66-year-old man's right eye had a visual acuity of 20/50, intraocular pressure (IOP) of 42 mmHg on 0 IOP-lowering medications, and neovascularization of the iris and angle with no peripheral anterior synechiae. Fundoscopy revealed midperipheral dot-blot hemorrhages without diabetic retinopathy or vein occlusion. Fluorescein angiography revealed peripheral retinal nonperfusion in both eyes. The patient was diagnosed with open-angle NVG secondary to OIS and treated with 6 serial monthly anti-VEGF injections interspersed with 4 PRP sessions, after which his anterior segment neovascularization regressed and IOP normalized on 0 medications. Ten weeks after the last injection, the anterior segment neovascularization and elevated IOP recurred, so he underwent 4 more monthly anti-VEGF injections and 4 PRP sessions, after which his anterior segment neovascularization regressed and his IOP normalized on 0 medications. However, 6 weeks after the last injection, the anterior segment neovascularization and elevated IOP again recurred, so he was resumed on a third course of lifetime monthly anti-VEGF injections, which may be continued in perpetuity. Conclusion The patient's NVG was quiescent while under the protection of serial anti-VEGF injections with interspersed PRP; however, the disease recurred each time injections were stopped. Therefore, in patients with open-angle NVG secondary to OIS, serial monthly anti-VEGF injections may be necessary combined with PRP to suppress underlying neovascular drive and regress anterior segment neovascularization, maintain physiologic IOP, and prevent synechial angle closure.

Intracorneal Ring Segment Implantation Results in Corneal Mechanical Strengthening Visualized With Optical Coherence Elastography.

To quantify the mechanical impact of intracorneal ring segment (ICRS) implantation of different dimensions in an ex vivo eye model. A total of 30 enucleated porcine eyes were assigned to ICRS implantation (thickness: 300 µm, angle: 120°, 210°, or 325°), tunnel creation only, or virgin control groups. For mechanical evaluation, each globe was mounted on a customized holder and intraocular pressure (IOP) was increased in steps of 0.5 mm Hg from 15 to 17 mm Hg, simulating physiologic diurnal IOP fluctuations. At each step, an optical coherence tomography volume scan was recorded. Deformations between subsequent scans and the locally induced axial strains were analyzed using a vector-based phase difference method. The effective E-modulus was derived from the overall induced strain as a measure of global mechanical impact. ICRS implantation increased the effective E-modulus from 146 and 163 kPa in virgin and tunnel-only eyes to 149, 192, and 330 kPa in eyes that received a 5-mm optical zone ICRS with 120°, 210°, and 325° arc length, respectively; and to 209 kPa in a 6-mm optical zone ICRS with 325° arc length. The most consistent effect was a shift toward positive strains in the posterior stroma by 0.1% to 0.46% (factor 1.15 to 2.15) after ICRS surgery. ICRS implantation reduces the overall tissue strain under the load of the IOP and provokes posterior tissue relaxation. This effect is more prominent the longer the arc length and the smaller the optical zone of the ICRS is. ICRS have not only a geometrical, but also a mechanical impact on corneal tissue. This behavior might have clinical implications when ICRS implantation is performed in biomechanically weakened keratoconic corneas. [J Refract Surg. 2022;38(7):459-464.].

Development and validation of methods to visualize conventional aqueous outflow pathways in canine primary angle closure glaucoma.

Angle closure glaucoma (PACG) is highly prevalent in dogs and is often refractory to medical therapy. We hypothesized that pathology affecting the post-trabecular conventional aqueous outflow pathway contributes to persistent intraocular pressure (IOP) elevation in dogs with PACG. The goal of this study was to determine the potential for aqueous angiography (AA) and optical coherence tomography (OCT) to identify abnormalities in post-trabecular aqueous outflow pathways in canine PACG. AA and anterior segment OCT (Spectralis HRA+OCT) were performed ex vivo in 19 enucleated canine eyes (10 normal eyes and 9 irreversibly blind eyes from canine patients enucleated for management of refractory PACG). Eyes were cannulated and maintained at physiologic IOP (10-20mmHg) prior to intracameral infusion of fluorescent tracer. OCT scleral line scans were acquired in regions of high and low perilimbal AA signal. Eyes were then perfusion fixed and cryosections prepared from 10/10 normal and 7/9 PACG eyes and immunolabeled for a vascular endothelial marker. Normal canine eyes showed segmental, circumferential limbal AA signal, whereas PACG eyes showed minimal or no AA signal. AA signal correlated with scleral lumens on OCT in normal dogs, but lumens were generally absent or flattened in PACG eyes. Collapsed vascular profiles were identified in tissue sections from PACG eyes, including those in which no lumens were identified on AA and OCT. In canine eyes with PACG, distal aqueous outflow channels are not identifiable by AA, despite normalization of their IOP, and intra-scleral vascular profiles are collapsed on OCT and histopathology.

Anterior Segment Organ Culture Platform for Tracking Open Globe Injuries and Therapeutic Performance.

Open globe injuries have poor visual outcomes, often resulting in permanent loss of vision. This is partly due to an extended delay between injury and medical intervention in rural environments and military medicine applications where ophthalmic care is not readily available. Untreated injuries are susceptible to infection after the eye has lost its watertight seal, as well as loss of tissue viability due to intraocular hypotension. Therapeutics to temporarily seal open globe injuries, if properly developed, may be able to restore intraocular pressure and prevent infection until proper ophthalmic care is possible. To facilitate product development, detailed here is the use of an anterior segment organ culture open globe injury platform for tracking therapeutic performance for at least 72 h post-injury. Porcine anterior segment tissue can be maintained in custom-designed organ culture dishes and held at physiological intraocular pressure. Puncture injuries can be created with a pneumatic-powered system capable of generating injury sizes up to 4.5 mm in diameter, similar to military-relevant injury sizes. Loss of intraocular pressure can be observed for 72 h post-injury confirming proper injury induction and loss of the eye's watertight seal. Therapeutic performance can be tracked by application to the eye after injury induction and then tracking intraocular pressure for multiple days. Further, the anterior segment injury model is applicable to widely used methods for functionally and biologically tracking anterior segment physiology, such as assessing transparency, ocular mechanics, corneal epithelium health, and tissue viability. Overall, the method described here is a necessary next step toward developing biomaterial therapeutics for temporarily sealing open globe injuries when ophthalmic care is not readily available.

Assessment of Commercial Off-the-Shelf Tissue Adhesives for Sealing Military-Relevant Corneal Perforation Injuries.

Open-globe ocular injuries have increased in frequency in recent combat operations due to increased use of explosive weaponry. Unfortunately, open-globe injuries have one of the worst visual outcomes for the injured warfighter, often resulting in permanent loss of vision. To improve visual recovery, injuries need to be stabilized quickly following trauma, in order to restore intraocular pressure and create a watertight seal. Here, we assess four off-the-shelf (OTS), commercially available tissue adhesives for their ability to seal military-relevant corneal perforation injuries (CPIs). Adhesives were assessed using an anterior segment inflation platform and a previously developed high-speed benchtop corneal puncture model, to create injuries in porcine eyes. After injury, adhesives were applied and injury stabilization was assessed by measuring outflow rate, ocular compliance, and burst pressure, followed by histological analysis. Tegaderm dressings and Dermabond skin adhesive most successfully sealed injuries in preliminary testing. Across a range of injury sizes and shapes, Tegaderm performed well in smaller injury sizes, less than 2 mm in diameter, but inadequately sealed large or complex injuries. Dermabond created a watertight seal capable of maintaining ocular tissue at physiological intraocular pressure for almost all injury shapes and sizes. However, application of the adhesive was inconsistent. Histologically, after removal of the Dermabond skin adhesive, the corneal epithelium was removed and oftentimes the epithelium surface penetrated into the wound and was adhered to inner stromal tissue. Dermabond can stabilize a wide range of CPIs; however, application is variable, which may adversely impact the corneal tissue. Without addressing these limitations, no OTS adhesive tested herein can be directly translated to CPIs. This highlights the need for development of a biomaterial product to stabilize these injuries without causing ocular damage upon removal, thus improving the poor vision prognosis for the injured warfighter.

Characterization of an anterior segment organ culture model for open globe injuries

Open-globe injuries have poor visual outcomes and have increased in frequency. The current standard of care is inadequate, and a therapeutic is needed to stabilize the injury until an ophthalmic specialist is reached. Unfortunately, current models or test platforms for open-globe injuries are insufficient. Here, we develop and characterize an open-globe injury model using an anterior segment organ-culture platform that allows therapeutic assessment for up to 72 h post-injury. Anterior segments maintained in organ culture were kept at physiological intraocular pressure throughout, and puncture injuries were created using a novel pneumatic-powered system. This system can create high-speed, military-relevant injuries up to 4.5 mm in diameter through the cornea. From intraocular pressure readings, we confirmed a loss of pressure across the 72 h after open-globe injury. Proof-of-concept studies with a Dermabond tissue adhesive were performed to show how this model system could track therapeutic performance for 72 h. Overall, the organ-culture platform was found to be a suitable next step towards modeling open-globe injuries and assessing wound closure over the critical 72 h post-injury. With improved models such as this, novel biomaterial therapeutics development can be accelerated, improving care, and, thus, improving the prognosis for the patients.

Comparison of the influx of bacterial-sized particles in single plane versus multiplane femtosecond laser incisions

Purpose: To present ingress of dye particles that are of size of bacteria though single and multi-planar corneal incision created by femtosecond laser in donor eyes. Setting: A tertiary eye Hospital, Central Saudi Arabia. Design: Ex vivo experimental study. Methods: This ”as ex vivo experimental study. Eyes acquired from an eye-bank that ”ere deemed unsuitable for corneal transplant ”ere used to create single as ”ell as multi-planar corneal incision using LenSx femtosecond laser. Each eye received single plane (SP) and one of the multiplanes either default multi-planar (DMP) or a right-angled multi-planar (RAMP) incision. After maintaining intraocular pressure (IOP), India ink ”as placed on the ”ound. Length and ”idth of ingress dye ”ere photographed and measured for different types of ”ound. Results: A total of 10 eyes ”ere used for this experiment. At physiologic IOP, the median and 25% quartile of length”ise invasion ”as 0.29 mm for the SP group (10 eyes), 0.23 mm for the DMP group (5 eyes), and 0.22 mm for the RAMP group (5 eyes). The difference of ingress bet”een the SP and RAMP groups as ”ell as SP and DMP group ”ere statistically significant (P = 0.005). The difference in length”ise and area ”ise invasion bet”een the DMP and RAMP groups ”as not statistically significant (P = 0.5). Conclusion: Bacteria size particle ingress seems to be more likely through SP incision compared to multi-plane corneal incisions created ”ith a femtosecond laser.

Use of the corneal bioreactor to assess deswelling efficacy of hyperosmotic eye drops

AbstractPurposeThe preclinical testing of the efficacy and safety of hyperosmotic anti‐edematous eye drops is complicated by the lack of a simple in vivo and ex vivo animal model. Our patented corneal bioreactor (BR) allows prolonged preservation of the human cornea by restoring physiological intraocular pressure and renewing the culture medium. Under certain experimental conditions, the corneas preserved in BR are nevertheless thicker than normal (684 ± 52 um, A J Transplantation 2019).AimTo use this characteristic of corneas stored in the BR to test the efficacy of new hyperosmotic eye drops prototypes.MethodsHuman corneas (n = 4) discarded by our eye banks were used whatever their endothelial status. They were first stored for 2 weeks into the BR filled with CorneaMax (Eurobio, France), with 21 mmHg in the endothelial chamber to allow regeneration of a normal epithelium as previously shown. Using a specific BR lid allowing sterile instillation in front of corneal center, each cornea was treated topically with 3 drops, every 2 hr, repeated 3 times. The epithelial chamber was emptied just before instillation and filled again with CorneaMax 2 min after instillation. Three corneas were treated with a commercial eyedrop containing 5% NaCl and 0.15% sodium hyaluronate and one cornea with Balanced Salt Solution (BSS) as a control. Central corneal volume (on an 8mm disc, CCV8 in mm3) was measured with OCT (Casia, Tomey) immediately before and after each instillation. The decrease in CCV was calculated for each instillation and before the first and the third instillation.ResultsFor corneas treated with NACl 5%, CCV decreased by (mean ± SD) 1.0 ± 0.4, 0.7 ± 0.1 and 0.6 ± 0.2 mm3, respectively, for the first, the second and the third instillation, and globally by 2.4 ± 1.1 mm3. The cornea treated with BSS remained unchanged.ConclusionsThe BR is an efficient tool to quantify the efficacy of hyperosmotic eye drops designed to deswell human cornea.

Generation of a Matrix Gla (Mgp) floxed mouse, followed by conditional knockout, uncovers a new Mgp function in the eye

The ability to ablate a gene in a given tissue by generating a conditional knockout (cKO) is crucial for determining its function in the targeted tissue. Such tissue-specific ablation is even more critical when the gene’s conventional knockout (KO) is lethal, which precludes studying the consequences of its deletion in other tissues. Therefore, here we describe a successful strategy that generated a Matrix Gla floxed mouse (Mgp.floxed) by the CRISPR/Cas9 system, that subsequently allowed the generation of cKOs by local viral delivery of the Cre-recombinase enzyme. MGP is a well-established inhibitor of calcification gene, highly expressed in arteries’ smooth muscle cells and chondrocytes. MGP is also one of the most abundant genes in the trabecular meshwork, the eye tissue responsible for maintenance of intraocular pressure (IOP) and development of Glaucoma. Our strategy entailed one-step injection of two gRNAs, Cas9 protein and a long-single-stranded-circular DNA donor vector (lsscDNA, 6.7 kb) containing two loxP sites in cis and 900–700 bp 5′/3′ homology arms. Ocular intracameral injection of Mgp.floxed mice with a Cre-adenovirus, led to an Mgp.TMcKO mouse which developed elevated IOP. Our study discovered a new role for the Mgp gene as a keeper of physiological IOP in the eye.

Developing a multiscale in silico cornea for understanding the role of cell mechanics in corneal pathologies

Multiscale in silico modeling of the cell-tissue-organ units is an emerging area of research with the potential to improve our understanding of various disease pathogenesis. Using a multiscale modeling approach, we developed a computational model of the human cornea to investigate how the application of macroscale loads may alter the micro-mechanical environment of the cells. We then utilized the multiscale model to study the effect of physiological and non-physiological mechanical loading conditions such as intraocular pressure (IOP) loading, IOP spike, and eye-poking on the corneal cells. On comparing the results obtained under increased IOP and eye-poking loading, we observed large differences in the averaged principal stress magnitudes in the immediate vicinity of the cell through the thickness of the cornea. On the other hand, our model predicted that under physiological IOP loading, the average principal strain magnitudes in the immediate vicinity of the cell remained almost constant irrespective of the cell location in the stroma. To our knowledge, this is the first study that investigates the effect of mechanical loading on the corneal cells through a multiscale modeling framework. Our computational multiscale cornea model provides a platform to perform virtual experiments and test hypotheses to further our understanding of the potential mechanical cause of multiple diseases in the cornea.