Aqueous Humor Volume Research Articles

In vivo quantification of anterior and posterior chamber volumes in mice: implications for aqueous humor dynamics.

Aqueous humor inflow rate, a key parameter influencing aqueous humor dynamics, is typically measured by fluorophotometery. Analyzing fluorophotometric data depends, inter alia, on the volume of aqueous humor in the anterior, but not the posterior, chamber. Previous fluorophotometric studies of aqueous inflow rate in mice have assumed the ratio of anterior:posterior volumes in mice to be similar to those in humans. Our goal was to measure anterior and posterior chamber volumes in mice to facilitate better estimates of aqueous inflow rates. We used standard near-infrared optical coherence tomography (OCT) and robotic visible-light OCT (vis-OCT) to visualize, reconstruct and quantify the volumes of the anterior and posterior chambers of the mouse eye in vivo. We used histology and micro-CT scans to validate relevant landmarks from ex vivo tissues to facilitate in vivo measurement. Posterior chamber volume is 1.1 times the anterior chamber volume in BALB/cAnNCrl mice, i.e. the anterior chamber constitutes about 47% of the total aqueous humor volume, which is very dissimilar to the situation in humans. Anterior chamber volumes in 2-month-old BALB/cAnNCrl and 7-month-old C57BL6/J mice were 1.55 ± 0.36 μL (n=10) and 2.41 ± 0.29 μL (n=8), respectively. This implies that previous studies likely over-estimated aqueous inflow rate by approximately two-fold. It is necessary to reassess previously reported estimates of aqueous inflow rates, and thus aqueous humor dynamics in the mouse. For example, we now estimate that only 0-15% of aqueous humor drains via the pressure-independent (unconventional) route, similar to that seen in humans and monkeys.

Intracameral Injection in Rats with Low Risk of Adverse Effects.

Intracameral injection is a standard administration routine in ophthalmology. The application of intracameral injection in rodents for research is challenging due to the limiting dimensions and anatomy of the eye, including the small aqueous humor volume, the lens curvature, and lens thickness. Potential damage during intracameral injections introduces adverse effects and experimental variability. This protocol describes a procedure for intracameral injection in rats, allowing precision and reproducibility. Sprague-Dawley rats were used as experimental models. Since the lens position in rats protrudes into the anterior chamber, injecting from the periphery, as done in humans, is unfavorable. Therefore, an incision is created in the central corneal region using a 31 gauge 0.8 mm stiletto blade to form a self-sealing tunnel into the anterior chamber. An incision atan angle close to the flat allows to create a long tunnel, which minimizes the loss of aqueous humor and shallowing of the anterior chamber. A 34 gauge nanoneedle is inserted into the tunnel for injection. This enables penetration with minimal friction resistance and avoids touching the lens. Injection of trypan-blue allowsvisualizationby slit microscopy the presence of the dye in the anterior chamber and exclude leakage. Bioavailability to the corneal endothelial layer is demonstrated by injection of Hoechst dye, which stained the nuclei of corneal endothelial cells after injection. In conclusion, this protocol implements a procedure for accurate intracameral injection in rats. This procedure may be used for intracameral delivery of various drugs and compounds in experimental rat models, increasing the efficiency and reproducibility of ophthalmic research.

Mechanosensor channels of the lens and ciliary body: patch clamp studies

Epithelia from the lens and the ciliary body possess mechanosensors, including Piezo1 and transient receptor potential (TRP) channels, that may partake in the regulation of lens and aqueous humor volume. Although these mechanosensor channels commonly allow calcium entry, the outcomes of elevated intracellular calcium vary with the type of channel activated. For instance, separate activation of TRPV4 and TRPV1 increases Na-K-ATPase and Na/K/2Cl cotransporter activities, respectively. To further understand the role of mechanosensitivity in lens and ciliary body, we are currently using patch clamp techniques to characterize the response of primary cultured cells to chemical agonists and antagonists, as well as direct mechanical stimulation. Previously, we found that in mouse lens epithelial cells (mLEC), TRPV4 activation by agonist GSK1016790A (GSK) is followed by disappearance of a fast, transient K+-like outward current (Ipeak), decrease of a steady state outward current (Iss), fast depolarization of resting membrane potential (RMP) values from near -50 mV to near 0 mV, increase of Cx43 hemichannel-like events, and increase of overall membrane conductance ( gm) at holding potential (HP) = -50mV. More recently, we found that in mLEC, shear stress (streaming of external solution from a pipette tip over the cell membrane) reduced Ipeak but did not cause large RMP changes. Porcine non-pigmented epithelial cells (pNPE) in normal conditions display no Ipeak, small Iss, small RMP near -20 mV and spontaneous Cx43 hemichannel-like event activity. Nevertheless, GSK caused further depolarization of pNPE cells, and while no gm changes were seen when GSK was applied while holding cells at -50 mV, gm did increase when GSK exposure occurred during repeated ±80 mV pulses. Preliminary experiments show that activation of TRPM3 by its agonist pregnenolone causes a minimal hyperpolarization in mLEC. In comparison, in a line of human LEC (HLE B3) expressing TRPM3 channels, and which appear generally depolarized, pregnenolone caused a proportionally larger shift toward more negative RMP values; more intriguing, GSK has no measurable effect on the gm of HLE B3 cells. Taken together, and apart from considerations of cell- and species-specific differences, the data suggest that mechanosensor channels have different and/or opposite effects on the regulation of membrane ion channel activity, and thus on cell function. R01EY029171 and R01EY009532. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Adaptation of the AbsoluteIDQ p180 kit to the analysis of metabolites in the human aqueous humor

The aim of this study was to use the commercial kit AbsoluteIDQ p180 (Biocrates) for the quantification of metabolites in aqueous humor (AH), as well as to determine the optimal volume of AH that is necessary to obtain reliable and reproducible results. Different volumes of AH (10 µl, 20 µl, and 30 µl) were tested. Of the 188 metabolites measurable with the Biocrates kit, 69 were detected in AH. Depending on the volume used, 41, 51, and 63 metabolites were measured using 10 µl, 20 µl, and 30 µl of AH, respectively. The repeatability of the measurements improved with increasing AH volume. Considering only those metabolites that were obtained with a CV < 15%, 34 metabolites at 10 µl, 41 at 20 µl, and 44 at 30 µl AH were received. On this basis, it can be concluded that the tested method can be successfully applied to analyze metabolites in the human AH. To achieve the most comprehensive detection range and highest repeatability of measurements, it is recommended to use 30 µl AH.

Pharmacokinetic-pharmacodynamic model to predict drug concentrations and intraocular pressure lowering effect for a bimatoprost six-month slow-release system.

Ophthalmic drug product development and dosing regimen selection depend on animal eye drug concentration-effect relationships since human eye tissues cannot be sampled for drug quantification. This study hypothesized that a pharmacokinetic-pharmacodynamic (PK-PD) mathematical model developed based on dog studies can be applied to the human eye of different ages, based on physiological parameter adjustment, to predict drug concentrations and effects in response to a new 6-month slow-release, intracameral, intraocular pressure (IOP) lowering, anti-glaucoma bimatoprost implant. Using previously reported dog concentration-effect relationship data at various doses, and the physiological parameters of dog eye, a PK-PD model was designed to predict dog aqueous humor drug concentrations and IOP lowering effects simultaneously for a given dose. After validating the model using the dog IOP data, it was applied to the human eye. Using a drug release rate constant of 0.0002 h-1, the model predicted the dog IOP lowering effect with an error less than 6% or less at various doses (Observed = 0.91*Predicted + 2.35; R2 = 0.98). Considering literature reported aqueous humor volumes and flow rates in old (over 60 years) and young (20 to 30 years) humans, aqueous humor elimination rate constant was estimated to be 0.9 and 0.68 h-1, respectively. The model when modified using the older human eye parameters, predicted the IOP lowering effects reported in a clinical trial with 63-year-old adults, with an error of 6.2% or less. The model, when used for young adult eye not previously tested in clinical trials, predicted lower drug concentrations and effects, possibly due to 54% higher aqueous humor volume relative to older adults. The model predicted an IOP reduction of 26.3 and 30.6%, at 10 and 15 microgram doses, respectively, in young adults. The PK-PD model developed is useful for product design and patient dosing by predicting eye drug concentration and effect time-courses in response to implant administration at various doses, frequencies, and release rates.

Iris Color Matters-A Contractility Analysis With Dynamic Volume-Rendered Optical Coherence Tomography Pupillometry.

To analyze natural variability in pupillary contractility with dynamic volume-rendered optical coherence tomography (OCT) pupillometry regarding iris color, age, and sex in healthy Caucasian participants. The intrapupillary spaces (IPSs) derived from anterior segment swept-source OCT of 71 healthy eyes were retrospectively analyzed. Baseline scotopic and photopic volumes and the functional parameters of pupillary ejection fraction (PEF), three-dimensional (3D) contractility, and relative light response (RLR) were measured on the swept-source OCT volumes. The effect on these parameters of iris color (brown, green, and blue), age, and sex was assessed. More pigmented irises were more contractile than less pigmented irises. Iris color significantly affected scotopic baseline IPSs (brown, 10.39 ± 4.86 mm3; green, 9.68 ± 3.31 mm3; blue, 6.75 ± 4.27 mm3; P = 0.018), PEF (brown, 90.8% ± 2.7%; green, 89.1% ± 2.5%; blue, 85.0% ± 9.3%; P = 0.010), 3D contractility (brown, 9.52 ± 4.59 mm3; green, 8.66 ± 3.07 mm3; blue, 6.44 ± 4.87 mm3; P = 0.016), and RLR (brown, 11.90 ± 4.03; green, 9.75 ± 2.73; blue, 8.52 ± 3.88; P = 0.026). Absolute scotopic volume (P = 0.022) and 3D contractility (P = 0.024) decreased with age. Sex showed no correlations. The natural variability of pupillary contractility can be analyzed with dynamic OCT pupillometry. Iris color and age can impact pupillary response with this method. Iris contractility parameters can be measured using a commercially available OCT system, allowing for quantification of the aqueous humor volume inside the pupil.

Analysis of aqueous humor total antioxidant capacity and its correlation with corneal endothelial health.

Corneal endothelial decompensation is a serious condition that frequently requires treatment via corneal transplantation which contributes to a global shortage in donor corneas. Therefore, the purpose of this study was to analyze the influence of aqueous humor total antioxidant capacity (TAC) on corneal endothelial health. There is an urgent need for discovering protective factors to combat corneal endothelial cell (CEC) loss. For methods, we developed a cupric ion‐based TAC (CuTAC) assay to analyze TAC level in a small volume of aqueous humor, that is, 10 μL per test, and examined the influences of ascorbic acid (AA) and antioxidant proteins on aqueous humor TAC. To broaden the investigation, we conducted a case–control study with patients classified into two groups, an insufficient endothelial cell density (ECD < 2100 cells/mm2) group, and a control group. These groups were formed based on baseline ECD values and were used to evaluate the influence of aqueous humor TAC and AA on overall corneal endothelial health. A CuTAC assay was used to accurately measure aqueous humor TAC without the need for sample dilution. After analyzing a total of 164 human aqueous humor samples, we found that AA was the major contributor to aqueous humor TAC (73.2%). In addition, TAC and AA levels in the IECD and control groups were both found to be significantly different (1.168 vs. 1.592 mM, p = 0.009 and 0.856 vs. 1.178 mM, p = 0.016). TAC and AA were considered independent protective factors against IECD with adjusted odds ratios of 0.02 (p = 0.017) and 0.023 (p = 0.033), respectively. In conclusion, aqueous humor TAC and AA contribute to the maintenance of sufficient corneal ECD, and our CuTAC assay can be a useful tool for analyzing TAC using only a small aqueous humor sample volume.

Features of the Eye Hydrodynamics on the Background of Thyroid Dysfunctions

Purpose: to study the features of eye hydrodynamics in patients with thyroid dysfunctions.Patients and methods. The material for this study was the results of a survey of 43 patients (86 eyes) with thyroid dysfunctions: 23 people (46 eyes) with primary untreated hypothyroidism (PGT) and 20 people (40 eyes) with primary untreated thyrotoxicosis (PTT). There weren’t ophthalmic hypertension and glaucoma There weren’t signs of ophthalmic hypertension and glaucoma in the patients included in this study at the stage of primary ophthalmologic diagnostics.Results. Correlation analysis revealed a causal relationship between the ratio of T4 / TSH hormones, on the one hand, and indicators of secretion of aqueous humor per unit of time and ease of outflow, on the other hand. In the group of patients with hypothyroidism, a weak linear inverse correlation was found between the ratio of free thyroxine and thyroid stimulating hormone and the minute volume of aqueous humor: according to the regression model, an increase in the ratio of T4 / TSH hormones by 1 was accompanied by a decrease in the minute volume of aqueous humor by 3 units. In patients with thyrotoxicosis, a statistically significant inverse linear correlation was found between the ratio of the T4 / TSH hormones and the coefficient of ease of outflow. According to the regression model, with an increase in the ratio of hormones T4 / TSH by 1, the coefficient of lightness of outflow decreases by 5 units. The presence of thyroid receptors in the cytoplasm and nuclei of the endothelium cells of the trabecular apparatus, the nuclei of fibroblasts forming the stroma of the trabeculae, as well as in the nuclei of the pigment and non-pigment epithelium of the processes of the ciliary body substantiates the molecular basis of the causal connection of thyroid dysfunctions with hydrodynamic disorders The conducted studies confirm the modern concept that the control of regulation of the tissue and organ homeostasis is carried out by the coordinated interaction of 3 systems: nervous, endocrine, and immune. Regression modeling clearly shows a pronounced causal relationship between thyroid dysfunctions and hydrodynamic processes in the eye.Conclusion. The results of clinical studies demonstrate the fact of controlling regulation by hydrodynamic processes at the eye level by the endocrine system, explain the possible mechanism on a morphological basis, and reveal the potential of a new therapeutic strategy.

Testing a Novel Disposable Aqueous Humor Collector: An Approach to Improve Safety, Accuracy, and Efficiency.

Aqueous humor (AH) is a useful biofluid for differential diagnosis and disease monitoring in a variety of ophthalmologic conditions. There are no commercially available medical devices specially designed for AH sampling. To improve the safety, accuracy, efficiency, and convenience of anterior chamber (AC) paracentesis, a novel vacuum-based disposable AH collector with a draw volume of 50 μL was designed. The safety and performance of this novel medical device was tested in New Zealand white rabbits. A commonly used 25G 1 mL syringe was used as the control device with target AH collection volume also intentionally set at 50 μL. The 36 eyes included in the study (18 rabbits) were divided into collector (R), collector (L), syringe (R), and syringe (L) subgroups, and each included 9 eyes (R/L indicates the paracentesis was performed by right/left hand). The mean AH volume collected by the collector (R), collector (L), syringe (R), and syringe (L) subgroups were 46.66 ± 3.37 (range: 39.20-50.40), 48.71 ± 2.88 (range: 45.00-53.60), 85.11 ± 18.70 (range: 64.00-123.50), and 80.68 ± 20.87 (range: 36.8-115.8) μL, respectively. The mean absolute deviation from the target volume and mean operation time of the collector subgroups were significantly lower than the syringe subgroups. Seidel tests revealed no AH leakage in any of the tested eyes. This study revealed that this novel AH collector facilitates one-handed AC paracentesis and accurate AH sampling, and appeared to be safer and more efficient than the traditional syringe-based techniques.

Roles of the ocular pressure, pressure-sensitive ion channel, and elasticity in pressure-induced retinal diseases.

The intraocular pressure inside the human eye maintains 10–21 mmHg above the atmospheric pressure. Elevation of intraocular pressure is highly correlated with the retinopathy in glaucoma, and changes in the exterior pressure during mountain hiking, air traveling, and diving may also induce vision decline and retinopathy. The pathophysiological mechanism of these pressure-induced retinal disorders has not been completely clear. Retinal neurons express pressure-sensitive channels intrinsically sensitive to pressure and membrane stretch, such as the transient receptor potential channel (TRP) family permeable to Ca2+ and Na+ and the two-pore domain K channel family. Recent data have shown that pressure excites the primate retinal bipolar cell by opening TRP vanilloid 4 to mediate transient depolarizing currents, and TRP vanilloid 4 agonists enhance the membrane excitability of primate retinal ganglion cells. The eyeball wall is constructed primarily by the sclera and cornea of low elasticity, and the flow rate of the aqueous humor and intraocular pressure both fluctuate, but the mathematical relationship between the ocular elasticity, aqueous humor volume, and intraocular pressure has not been established. This review will briefly review recent literature on the pressure-related retinal pathophysiology in glaucoma and other pressure-induced retinal disorders, the elasticity of ocular tissues, and pressure-sensitive cation channels in retinal neurons. Emerging data support the global volume and the elasticity and thickness of the sclera and cornea as variables to affect the intraocular pressure level like the volume of the aqueous humor. Recent results also suggest some potential routes for TRPs to mediate retinal ganglion cell dysfunction: TRP opening upon intraocular pressure elevation and membrane stretch, enhancing glutamate release from bipolar cells, increasing intracellular Na+, Ca2+ concentration in retinal ganglion cells and extracellular glutamate concentration, inactivating voltage-gated Na+ channels, and causing excitotoxicity and dysfunction of retinal ganglion cells. Further studies on these routes likely identify novel targets and therapeutic strategies for the treatment of pressure-induced retinal disorders.

Reply.

Arshinoff and Modabber5 call into question two assumptions of our mathematical model describing the residence times of moxifloxacin in the anterior segment with two different intracameral injection strategies.1 The authors of the letter agree with us on the underlying principle of our publication but disagree on the volume of the anterior chamber (AC) and the half-life of antibiotics. We selected two representative mean pseudophakic AC volumes (0.19 mL and 0.33 mL), substantiated by the literature,2,3 to demonstrate the principle that injecting the same dose of antibiotics (eg, 500 μg) into ACs with varying volumes produces varying concentrations of antibiotics within the total aqueous humor volume. The larger volume of 0.33 mL of Matsuura was derived from aqueous humor sampling immediately after intracameral injection in humans, before any possible fibrosis of the capsule. Libre and Mathews4 also agree with this volume. Arshinoff and Modabber's5 estimation of 0.5 mL is based on a mean phakic AC volume in the human eye of 0.25 mL; however, measurements of the AC volume in the elderly phakic eye average only 0.15 mL.6,7 With this experimentally derived volume, Arshinoff's estimation of the mean pseudophakic aqueous volume would be 0.4 mL, close to Matsuura and Libre's reported value of 0.33 mL. The AC size is known to vary from patient to patient, which cataract surgeons recognize when operating on smaller eyes and myopic eyes with longer axial lengths and larger chambers. Therefore, attempting to replace the aqueous contents with an antibiotic solution of known concentration will achieve the more consistent final concentration of drug, irrespective of the patient's pseudophakic AC volume. This same principle would have been demonstrated had we chosen two different AC volumes. There is a wide variation in the reported half-life elimination of antibiotics in the AC. Generally speaking, interdrug variation in elimination times, especially in the eye, may be due to factors such as differences in the drug molecular size, tissue binding, active pump mechanisms, and obstructions or reductions to outflow and drug elimination. Asena obtained antibiotic half-lives between 1.2 hours and 13 hours in rabbits, depending on which time points were used8; Lipnitzki et al.9 found between 0.64 hours and 1.8 hours in rabbits. Matsuura et al.3,10 demonstrated a half-life in rabbits and humans that averaged 1.2 hours over most time points. We chose 1.2 hours as it agrees with the 1% per minute aqueous turnover rate noted by Goel et al.11 The varied measures of the intradrug half-life elimination time of moxifloxacin and other antibiotics in the AC may be due to imprecision in injection and sampling techniques, pharmacokinetics that are not single compartment, and variations in individual subject anatomy and physiology. We would caution against the speculation of postantibiotic effects in regard to half-life because efficacy should be related to the target microorganism.12 Furthermore, principles that apply to the multidose administration of antibiotics in the treatment of systemic infections should not be presumptively applied to the scenario of single-dose intraocular injection without empirical evidence. Our study used two different and substantiated aqueous volumes and demonstrated that injecting small volumes of an agent can result in unequal final drug concentrations in the AC. Given the patient-to-patient variations, the “flushing” or large-volume injection technique should offer some degree of standardization and assurance of a more uniform final drug concentration in the pseudophakic AC as compared with smaller-volume–injected aliquots, thereby minimizing the interpatient variable of AC volume differences during cataract surgery.

A novel multiplex detection array revealed systemic complement activation in oral squamous cell carcinoma.

Oral squamous cell carcinoma (OSCC) is one of the most common tumors within the oral cavity. Early diagnosis and prognosis tools are urgently needed. This study aimed to investigate the activation of the complement system in OSCC patients as potential biomarker. Therefore, an innovative complement activation array was developed.Characterized antibodies detecting the complement activation specific epitopes C3a, C5a and sC5b-9 along with control antibodies were implemented into a suspension bead array. Human serum from a healthy (n = 46) and OSCC patient (n = 57) cohort were used to investigate the role of complement activation in oral tumor progression. The novel multiplex assay detected C3a, C5a and sC5b-9 from a minimal sample volume of human tears, aqueous humor and blood samples. Limits of detection were 0.04 ng/mL for C3a, 0.03 ng/mL for C5a and 18.9 ng/mL for sC5b-9, respectively. Biological cut-off levels guaranteed specific detections from serum. The mean serum concentration of a healthy control cohort was 680 ng/mL C3a, 70 ng/mL C5a and 2247 ng/mL sC5b-9, respectively. The assay showed an intra-assay precision of 2.9–6.4% and an inter-assay precision of 9.2–18.2%.Increased systemic C5a (p < 0.0001) and sC5b-9 (p = 0.01) concentrations in OSCC patients were determined using the validated multiplex complement assay. Higher C5a concentrations correlated with tumor differentiation and OSCC extension state. Systemic sC5b-9 determination provided a novel biomarker for infiltrating tumor growth and C3a levels were associated with local tumor spreading.Our study suggests that systemic complement activation levels in OSCC patients may be useful to assess disease progression.

Quantification of MicroRNAs in human aqueous humor by miRFLP assay

MiRNAs are expressed in a tissue-specific fashion in the eyes and changes in miRNAs levels in aqueous humor (AH) may reflect the function of the eye and eye disease. Due to the low concentration of total miRNA in human aqueous humor, high volume of sample is required for RNA extraction prior to routine quantification such as RT-qPCR. However, limited volume of AH could be collected through surgery because of the characteristic of the eye. In addition, inefficiency of RNA-extraction kits could affect target miRNA quantification dramatically. AH-direct miRFLP assay was developed for quantification of target miRNAs in human aqueous humor samples. For the first time, accurate miRNA quantification in human AH was achieved with microliter scale sample loading. Higher copy numbers of target miRNAs were obtained in direct detection than in RNA-extraction solution. It indicates that AH-direct miRFLP assay was able to quantify target miRNAs more accurately with no requirement for RNA-extraction to avoid sampling variability.

LC-MS-Based Metabolic Fingerprinting of Aqueous Humor.

Aqueous humor (AH) is a transparent fluid which fills the anterior and posterior chambers of the eye. It supplies nutrients and removes metabolic waste from avascular tissues in the eye. Proper homeostasis of AH is required to maintain adequate intraocular pressure as well as optical and refractive properties of the eye. Application of metabolomics to study human AH may improve knowledge about the molecular mechanisms of eye diseases. Until now, global analysis of metabolites in AH has been mainly performed using NMR. Among the analytical platforms used in metabolomics, LC-MS allows for the highest metabolome coverage. The aim of this study was to develop a method for extraction and analysis of AH metabolites by LC-QTOF-MS. Different protocols for AH preparation were tested. The best results were obtained when one volume of AH was mixed with one volume of methanol : ethanol (1 : 1). In the final method, 2 µL of extracted sample was analyzed by LC-QTOF-MS. The method allowed for reproducible measurement of over 1000 metabolic features. Almost 250 metabolites were identified in AH and assigned to 47 metabolic pathways. This method is suitable to study the potential role of amino acids, lipids, oxidative stress, or microbial metabolites in development of ocular diseases.

Computational Study of Aqueous Humor Dynamics Assessing the Vault and the Pupil Diameter in Two Posterior-Chamber Phakic Lenses.

To compare the behavior of aqueous humor (AH) and analyze flow differences by comparing the volume and velocity of the flow after two different models of implantable collamer lens (ICL) placement. Computational fluid dynamics with numerical simulation using Ansys Fluent software was performed to compare the AH flow through a peripheral iridotomy (PI), which is typically performed after implantation of a V4b lens to the central hole of a V4c lens. The volume and flow rate in 24 scenarios were compared according to the type of lens, pupil diameter (PD) (3.5 or 5.5 mm), the vault (100, 350, and 800 μm) and the PI (single or double, 180 or 360 μm). With a standard vault (350 μm) and a PD of 3.5 mm, the volume of AH that flows from the posterior to the anterior chamber through the PI (V4b lens: 73.4% in 360 μm and 17.3% in 180 μm) and for the central hole (V4c lens: 75.7%) is larger than in the case of a PD of 5.5 mm (13.9%, 0.91%, and 15.3% respectively). When the vault is low (100; PD 3.5 mm), the volume of AH that reaches the central hole of the V4c lens is diminished (52.0%), being 5.1% if the pupil is enlarged. AH flow varies depending on the type of ICL implanted, whether it is implanted with an iridotomy or a central hole on the lens, the PD, and the vault.

Patients With Intravitreal Gas Bubbles at Risk of High Intraocular Pressure Without Exceeding Elevation of Surgery: Theoretical Analysis

The purpose of this study was to show the mechanism responsible for high peak IOP in patients with intravitreal gas bubbles resulting from a descent to low elevation and a return ascent, without exceeding the surgical elevation. A computational model reconstructed four clinical cases, using published elevations, ascent rates, and initial bubble sizes. In each case, patients first underwent surgery (790 m), then went home (790 m, 790 m, 325 m, 240 m). When returning for follow-up visits, patients descended to a low elevation (20 m, 0 m, 25 m, -310 m), then ascended to surgical elevation (790 m). The computational model output bubble size, aqueous humor volume, and IOP during the patients' travels. A parametric study was conducted to investigate the role of each modeling parameter. All four simulated cases showed increased peak IOP (34-50 mm Hg). Intraocular pressure returned to a normal value (15 mm Hg) after prolonged exposure to the surgical elevation. Over the course of the entire path, the gas bubble volume changed approximately 5%, decreasing in size during descent and then increasing during ascent. In our simulations the change of bubble size outpaced the change of aqueous humor volume resulting in a 2-fold risk to patients. First, the bubble size reduction at the low elevation may increase the risk of ocular hypotony and postsurgical retinal detachment. Second, the combined increasing bubble size and accumulated aqueous humor puts patients at risk of high peak IOP after ascent even without exceeding the surgical elevation. The risks are primarily dependent on rates of elevation change and duration spent at the different elevations.

Effect of Posture in Intraocular Pressure, Comparison between Normal and Glaucomatous Subjects

Introduction: Intraocular pressure (IOP) increases when changing from sitting to supine position with an average difference of 0.3 to 6.0mm of Hg. These postural changes of IOP have been found in normal persons, patients with ocular hypertension and normal tension glaucoma. The eye is relatively non-distensible, even small changes in the volume of aqueous humor may significantly change IOP. The increase in resistance in aqueous flow is thought to be the reason for higher IOP in supine compared to sitting position. The aim of this study was to analyze the effects of posture in intraocular pressure in normal and primary open angle glaucoma subjects. Methods: It was a prospective cross sectional study done in Armed Forces Medical College, Pune, between May, 2007 to May, 2009 with sample sized of 60 people (30 controls and 30 Primary open angle glaucoma). Patients underwent complete ocular examination. Two drops of Topical 4% lignocaine were instilled. IOP measurements were taken by Rebound tonometer in sitting and supine positions at 10 min and 30 min interval respectively. Results: Control group (40-76 yrs) and POAG group (40-78 yrs) were found to have a mean rise of IOP of 1.65 and 2 mm of Hg respectively from sitting to lying for 10min, and a mean rise of 2.52 and 5.36 mm of Hg respectively from sitting to lying for 30min. Conclusions: The rise in IOP due to change of posture from sitting to supine positions was significantly higher in glaucomatous patients.Medical Journal of Shree Birendra Hospital; July-December 2012/vol.11/Issue2/21-23 DOI: http://dx.doi.org/10.3126/mjsbh.v11i2.7904

Sampling Aqueous Humor: Anterior Segment Anatomy, Anesthetic and Surgical Technique, and Rates of Yield

Purpose: To evaluate anterior segment anatomy and anesthetic and surgical techniques with respect to the amount of aqueous humor (AH) that can be sampled out of the anterior chamber (AC) at the beginning of standard cataract removal procedures (phacoemulsification). Methods: In a prospective survey, volumes of sampled AH from 123 eyes (110 patients) were analyzed in regard to AC anatomy (anterior chamber depth, ACD) and different anesthetic techniques (local and general anesthesia). Results: 107 eyes (87%) were included into our analysis, and 16 eyes (13%) had to be excluded due to failure of AH collection. We found a significant positive association between ACD and obtained AH volume (p = 0.007). In general anesthesia, a strong trend to acquire more AH in comparison to local anesthesia was apparent, but statistical significance failed (p = 0.167). Different anesthetic techniques seem to have no significant influence on ACD (p = 0.169). No training curve for the individual surgeon was obtained. No complications were observed. Conclusion: When AH sampling is performed in eyes with a deep AC and when the procedure is performed under general anesthesia, more AH can be aspirated.

Evaluation of the analgesic effect of intracameral lidocaine hydrochloride injection on intraoperative and postoperative pain in healthy dogs undergoing phacoemulsification

To evaluate the intraoperative and postoperative analgesic effects of intracameral lidocaine hydrochloride injection in dogs undergoing phacoemulsification. 12 healthy Beagles with healthy eyes. Dogs were randomly assigned to receive 1 of 2 intracameral injections: 2% lidocaine hydrochloride solution (0.3 mL) or an equivalent amount of balanced salt solution (BSS). All dogs were treated with acepromazine (0.05 mg/kg, i.v.) and cefazolin (30 mg/kg, i.v.), and tropicamide drops were topically applied to the eyes. Anesthesia was induced with propofol and maintained with isoflurane. The initial end-tidal isoflurane concentration was maintained at 1.2%. Heart rate, respiratory rate, arterial blood pressure, esophageal temperature, inspired and end-tidal isoflurane concentrations, and oxygen saturation were recorded every 5 minutes. The allocated agent was injected intracamerally after aspiration of the same volume of aqueous humor. Ten minutes after injection, phacoemulsification was performed. After surgery began, the isoflurane concentration was adjusted according to heart rate and mean arterial blood pressure. Pain scores were recorded before surgery and at 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 6, 8, 16, and 24 hours after extubation. Isoflurane requirements were significantly higher in the BSS group than in the lidocaine group. Mean +/- SD time to administration of supplementary analgesia was significantly shorter in the BSS group (1.4 +/- 1.2 hours) than in the lidocaine group (4.9 +/- 1.2 hours). Intracameral lidocaine injection had significant analgesic effects in dogs undergoing cataract surgery. Results of this study suggest the value of intracameral lidocaine injection as an analgesic for intraocular surgery in dogs.

Evaluation of the mydriatic effect of intracameral lidocaine hydrochloride injection in eyes of clinically normal dogs

OBJECTIVE-To evaluate the mydriatic effect of intracameral injection of preservative-free 1% and 2% lidocaine hydrochloride solutions and determine the onset and duration of mydriasis according to the concentration and volume of lidocaine administered in healthy dogs. ANIMALS-5 healthy adult Beagles weighing 7 to 10 kg, with no apparent ocular disease. PROCEDURES-A double-blind randomized 9-session crossover trial was designed. Both eyes were assigned to 9 treatments with a minimum 7-day washout period between treatments: 0.1, 0.2, and 0.3 mL of 2% lidocaine solution; 0.1, 0.2, and 0.3 mL of 1% lidocaine solution; and 0.1, 0.2, and 0.3 mL of balanced salt solution. Dogs were anesthetized, and the allocated treatment was injected intracamerally after aspiration of the same volume of aqueous humor from the anterior chamber of each eye. Two perpendicular pupil diameters were measured. Intraocular pressure, heart rate, respiratory rate, ECG readings, and end-tidal partial pressure of CO(2) were monitored. RESULTS-Intracameral injection of 1% or 2% lidocaine solutions in volumes of 0.1 to 0.3 mL induced a significant degree of mydriasis, and the effect was maintained for 74 to 142 minutes. Lidocaine injection had no significant effect on intraocular pressure, heart rate, respiratory rate, ECG readings, or end-tidal partial pressure of CO(2). CONCLUSIONS AND CLINICAL RELEVANCE-Intracameral lidocaine injection in healthy dogs induced mydriasis, the timing of which was affected by concentration and volume of lidocaine. This technique could serve as an alternative to topically administered mydriatics for intraocular surgery in dogs.