BACKGROUNDElevated intraocular pressure (IOP) is primarily due to increased aqueous outflow resistance, but how aqueous outflow resistance is generated and regulated are still not fully understood. The aim of this study is to determine whether changes in outflow facility, outflow pattern, and morphology following acute IOP elevation were reversible when the IOP was returned to a normal level in bovine eyes using a two-color tracer technique to label outflow patterns within the same eye.

METHODSTwelve fresh enucleated bovine eyes were perfused with Dulbecco's phosphate buffer saline (PBS) containing 5.5 mmol/L glucose (DBG) at 30 mmHg first to establish the baseline outflow facility followed by a fixed volume of red fluorescent microspheres (0.5 µm, 0.002% v/v). After the red tracer being replaced with DBG in the anterior chamber, perfusion was continued at 7 mmHg with the same volume of green tracer, followed by a fixative. In two control groups, the eyes were constantly perfused at either 30 mmHg (n = 6) or 7 mmHg (n = 6) using the same methods. The outflow facility (C, µl × min × (-1)mmHg(-1)), was continuously recorded. Confocal images were taken along the inner wall (IW) of the aqueous plexus (AP) in frontal sections. The percent of the effective filtration length (PEFL, PEFL = IW length exhibiting tracer labeling/total length of IW) was measured. Sections with AP were processed and examined by light microscopy. The total length of IW and the length exhibiting separation (SL) in the juxtacanalicular connective tissue (JCT) were measured. A minimum of eight collector channel (CC) ostia per eye were analyzed for herniations.

RESULTSIn the experimental (30 - 7 mmHg) group, the outflow facility was significantly higher at 7 mmHg ((4.81 - 1.33) µl × min × (-1)mmHg(-1)) than that at 30 mmHg ((0.99 ± 0.15) µl × min × (-1)mmHg(-1), P = 0.002), corresponding to a significant increase in the PEFL (P = 0.0003). The percent of CC ostia exhibiting herniations in the experimental group ((67.40 ± 8.90) µl × min × (-1)mmHg(-1)) decreased significantly compared to that in the control at 30 mmHg ((94.44 ± 3.33) µl × min × (-1)mmHg(-1), P = 0.03), but higher than that in the control at 7 mmHg ((29.43 ± 4.60) µl × min × (-1)mmHg(-1), P = 0.01). Washout-associated separation between the IW and JCT was found by light microscopy and percent separation length (PSL, PSL = SL/total length of IW) was decreased in the control at 30 mmHg compared to that in the experimental group and control at 7 mmHg.

CONCLUSIONSThe pressure-induced morphological and hydrodynamic changes were reversible. Changes (collapse of AP, separation between the JCT and IW, and herniation into CC ostia) influence the effective filtration area that regulates outflow facility.

Animals ; Aqueous Humor ; physiology ; Cattle ; Hydrodynamics ; Intraocular Pressure ; physiology ; Microscopy, Confocal

BACKGROUNDAhmed Glaucoma Valve implantation (AGVI) is used to treat refractory glaucoma. Breakdown of the blood-aqueous barrier (BAB) has been noted after some surgical techniques. The current study was designed to assess BAB disruption after AGVI.

METHODSAnterior chamber protein content was measured by the laser flare cell photometry in 22 eyes of 22 patients with refractory glaucoma before AGVI and at each postoperative visit up to 1 month.

RESULTSBefore AGVI the mean aqueous flare values in all eyes were (15.17 ± 9.84) photon counts/ms. After AGVI, the values significantly increased at day 1, day 3, and week 1 compared to those before AGVI (all P < 0.05) with a peak at day 3. They returned to pre-operative levels at week 2, and were lower than preoperative level at month 1. Eyes with previous intraocular surgery history had greater aqueous flare values than those without previous intraocular surgery history, but there were no significant differences at all time points postoperatively (all P > 0.05). Furthermore, eyes with shallow anterior chambers had greater aqueous flare values at day 3 and week 1 (all P < 0.05). When comparing eyes with other refractory glaucoma conditions, neovascular glaucoma combined with intravitreal bevacizumab injection resulted in lower aqueous flare values after AGVI, but no significant differences were observed at all time points, postoperatively (all P > 0.05).

CONCLUSIONSThe BAB was impaired and inflammation was present in the anterior chamber in refractory glaucomatous eyes following AGVI. However, such conditions were resolved within 1 month postoperatively. Intravitreal bevacizumab treatment in neovascular glaucoma eyes before AGVI may prevent BAB breakdown.

Adult ; Aqueous Humor ; physiology ; Blood-Aqueous Barrier ; pathology ; Female ; Glaucoma Drainage Implants ; adverse effects ; Humans ; Male ; Middle Aged ; Prospective Studies

The measurement of the rate of flow of aqueous humor is very important for the investigation of the physiology in the aqueous humor and maintenance of the intraocular pressure. Argon laser trabeculoplasty apears to be effective in lowering intraocular pressure with much advantage over standard filtering operation but despite the, widespread use of argon laser traheculoplasty in medically unresponsive open angle glaucoma, the exact mechanism by which it reduce outflow resistance remains unknown and so the study of the mechanism and the most suitable site are required due to the associated complication and less effectiveness during long term evaluation. We studied the changes in the rate of constant, the rate of flow for 2 weeks, intraocular pressure and C-value for 4 weeks, histopathologic changes for 36 days after argon laser trabeculoplasty in 25 rabbits(21 white and 4 black). The normal control group of 20 rabbits was also measured for intraocular pressure and C-value and the rate of constant, the rate of flow. In trabeculoplasty, we used the Britt 900 argon laser photocoagulator(pulse wave) with 50~60 burns at a setting of 700~800 mW, 0.2 seconds duration, 50 micro beam diameter in 360 degrees portion at the site between scleral spur and trabecularmeshwork. The results were as follows; 1) In control group of 20 rabbits. 1. The mean normal intraocular pressure was 18.5 +/- 2.0mmHg. 2. The mean normal C-value was 0.385 +/- 0.072 cumm/min/mmHg. 3. The mean normal rate of constant was 0.0114 +/- 0.0021min(-1). 4. The mean normal rate of flow was 3.980 +/- 0.735 micro l/min. 5. The relationship between rate of flow and C-value was high. 2) In rabbits after argon laser trabeculoplasty. 1. The white and black rabbits showed a statistically significant decrease of intraocular pressure for 4 weeks and elevation of rate of flow for 2 weeks after argon laser trabeculoplasty (p<0.001). 2. The changes of post-laser intraocular pressure was related with changes of C-value after argon laser trabeculoplasty for 4 weeks. 3. The changes of the mean IOP and C-value for post-laser 4 weeks showed no significant differences between white group and black group. 4. In histopathologic changes for 36 days, inflammtory change was not seen for post-laser period, fibrosis and edema in trabecular meshwork was more prominent at the 8th day, edema and fibrosis was regressed as normal at the post-laser 27th day.
Aqueous Humor* ; Argon* ; Burns ; Edema ; Fibrosis ; Glaucoma, Open-Angle ; Intraocular Pressure ; Physiology ; Rabbits* ; Trabecular Meshwork ; Trabeculectomy*

BACKGROUNDElevation of intraocular pressure is usually associated with primary open angle glaucoma and caused by increased outflow resistance. A two-color fluorescent tracer technique was developed to investigate the hydrodynamics of aqueous humor outflow with changing intraocular pressure within the same eye, to better understand the relationship between outflow facility and effective filtration area.

METHODSEighteen enucleated bovine eyes were first perfused at 30 mmHg with Dulbecco's phosphate-buffered saline containing 5.5 mmol/L D-glucose. After a stable baseline facility, red fluorescent microspheres (0.5 microm, 0.002% v/v) were exchanged and perfused. Eyes in the one-color control group (n = 6) were immediately perfused with fixative. In the experimental group (n = 6), eyes were perfused with green tracer after intraocular pressure reduced to 7 mmHg, while in the two-color control group (n = 6), eyes were perfused with green tracer with intraocular pressure remaining at 30 mmHg. All 12 eyes were then perfusion-fixed. Outflow facility was continuously recorded in all eyes. Confocal images were taken along the inner wall of the aqueous plexus and the percent of the effective filtration length (PEFL; length of inner wall exhibiting tracer labeling/total length of inner wall) was measured. The relationships between outflow facility and PEFL were analyzed statistically.

RESULTSNo significant differences were found in baseline facilities (microl x min(-1) x mmHg(-1)) among the three groups (the experimental group: 0.93 +/- 0.12; the two-color control group: 0.90 +/- 0.19; the one-color control group: 0.98 +/- 0.13). In the experimental group, the outflow facility was significantly higher at 7 mmHg (4.29 +/- 1.01) than that at 30 mmHg (1.90 +/- 0.67, P < 0.001), which corresponded to a significant increase in the PEFL at 7 mmHg (54.70 +/- 8.42) from that at 30 mmHg ((11.76 +/- 4.56)%, P < 0.001). The PEFL labeled by red fluorescent microspheres in the experimental group ((11.76 +/- 4.56)%) showed no significant difference from that of the one-color control group ((13.39 +/- 2.19)%, P = 0.473) or the two-color control group ((11.49 +/- 4.95)%, P = 0.930). The PEFL labeled by green fluorescent microspheres in the experimental group ((54.70 +/- 8.42)%) was significantly higher than that of the two color control group ((37.34 +/- 8.17)%, P = 0.010). A positive correlation was found between outflow facility and PEFL (r = 0.897, R(2) = 0.804) in the experimental group.

CONCLUSIONSChanges in aqueous humor outflow patterns before and after a change in intraocular pressure can be successfully distinguished within the same eye using our newly developed two-color tracer perfusion technique. The PEFL showed positive correlation with the outflow facility.

Animals ; Aqueous Humor ; physiology ; Cattle ; Intraocular Pressure ; Luminescent Proteins ; metabolism ; Microscopy, Confocal ; Microspheres ; Perfusion ; methods

It is very difficult to measure the human eye properties directly, such as the accommodation mechanism, intraocular pressure distribution, the dynamics of aqueous humor flow and the bio-heat transfer in human eyes. Modeling and simulation may, therefore, play an increasingly important role in the ophthalmologic investigation. The major computer modeling methods, including geometric modeling, physical modeling and mathematical modeling, are introduced in this paper. Modeling and simulation anatomy properties and physiological properties of eye tissues, such as the cornea, aqueous humor and crystalline lens, vitreous, optic nerve head, sclera, are analyzed in the order from global to local, from front to back, from outside to inside. Finally, the problems of computer modeling in ophthalmologic investigation are discussed, and the development trends of the future are pointed out.
Aqueous Humor ; physiology ; Computer Simulation ; Cornea ; physiology ; Eye ; anatomy & histology ; Humans ; Lens, Crystalline ; physiology ; Ophthalmology ; trends ; Sclera ; physiology

A three-dimensional (3D) model of human anterior chamber is reconstructed to explore the effect of different corneal temperatures on the heat transfer in the chamber. Based on the optical coherence tomography imaging of the volunteers with normal anterior chamber, a 3D anterior chamber model was reconstructed by the method of UG parametric design. Numerical simulation of heat transfer and aqueous humor flow in the whole anterior chamber were analyzed by the finite volume methods at different corneal temperatures. The results showed that different corneal temperatures had obvious influence on the temperature distribution and the aqueous flow in the anterior chamber. The temperature distribution is linear and axial symmetrical around the pupillary axis. As the temperature difference increases, the symmetry becomes poorer. Aqueous floated along the warm side and sank along the cool side which forms a vortexing flow. Its velocity increased with the addition of temperature difference. Heat fluxes of cornea, lens and iris were mainly affected by the aqueous velocity. The higher the velocity, the bigger more absolute value of the above-mentioned heat fluxes became. It is practicable to perform the numerical simulation of anterior chamber by the optical coherence tomography imaging. The results are useful for studying the important effect of corneal temperature on the heat transfer and aqueous humor dynamics in the anterior chamber.
Anterior Chamber ; physiology ; Aqueous Humor ; physiology ; Cornea ; physiology ; Humans ; Iris ; Lens, Crystalline ; Models, Biological ; Temperature ; Tomography, Optical Coherence

Preoperative aqueous humor, known to inhibit the growth of fibroblasts in tissue culture assay, was used as an adjunct to filtering surgery in rabbits to determine its effect in vivo on the outcome of filtering surgery. Fifteen rabbits underwent a posterior-lip sclerectomy in both eyes. In experimental eyes 1.4 ml preoperative aqueous humor and in fellow eyes 1.4 ml balanced salt solution were injected intracamerally. Gross and histopathological differences of bleb were observed. In this animal experiment, although there was no statistical significance or late postoperative effect, the rabbit eyes refilled with preoperative aqueous humor intracamerally just after filtering surgery, had a larger bleb and less fibroconnective tissue on the bleb than the control eyes in the early postoperative period.
Animals ; Anterior Chamber/*pathology ; Aqueous Humor/*physiology ; Connective Tissue/pathology ; Fibroblasts/pathology ; Isotonic Solutions ; Rabbits ; Sclera/surgery

The changes in intraocular pressure (IOP) following peritomy and wet-field coagulation of 10 rabbit eyes and 7 human cataractous eyes were investigated. The IOP difference before and after 180-degree and 360-degree wet-field coagulation on rabbit eyes showed an average increase of 11.0 +/- 5.8 mmHg and 25.8 +/- 7.1 mmHg(mean +/- SD), respectively (p < 0.05, p < 0.01). The IOP of both groups in rabbit eyes were elevated for 2 to 3 days postoperatively and then became normal by the 7th postoperative day. The IOP difference before and after 180-degree peritomy and wet-field coagulation in human cataractous eyes showed an average increase of 8.4 +/- 5.8 mmHg(mean +/- SD)(p < 0.05). The outflow facility was poor immediately following wet-field coagulation but then improved gradually by means of tonography and concentration changes of anterior chamber neutral-red. Histologically, there was endothelial cell damage, congestion, and red blood cell extravasation of the episcleral and intrascleral vessels at one day after wet-field coagulation in the light microscopic findings. Recanalization of the episcleral and intrascleral capillaries was noted 3 days after wet-field coagulation and was completed 3 weeks after wet-field coagulation. There was poor plastic infusion through the trabecular spaces in the one-day postoperative group compared to the control group by scanning electron micrograph. In conclusion, we have to bear in mind the possibility of an IOP rise after wet-field coagulation following peritomy for cataract and retinal surgery.
Animals ; Aqueous Humor/physiology ; Cataract Extraction ; Conjunctiva/*surgery/ultrastructure ; Humans ; *Intraocular Pressure ; *Light Coagulation ; Microscopy, Electron, Scanning ; Rabbits ; Surgical Flaps ; Tonometry, Ocular ; Trabecular Meshwork/ultrastructure

BACKGROUNDNuclear factor-kappa B (NF-kappaB) is elevated in regulating transcription of many cytokines and inflammatory mediators. The purpose of this study was to investigate the activation and the significance NF-kappaB in lipopolysaccharide (LPS) induced keratitis.

METHODSLPS induced keratitis model was based on Wistar rats. At 0.5, 1, 3, 6, 12, 24 or 72 hours after LPS treatment, the rat corneas were observed with a slit lamp microscope, then the rats were sacrificed and their corneas were excised for routine histological analysis. The expression of NF-kappaB was detected with immunohistochemical staining. The change of tumour necrosis factors-alpha (TNF-alpha) mRNA expression was identified by reverse transcriptase polymerase chain reaction (RT-PCR).

RESULTSHistological findings demonstrated that LPS treated corneas showed significant changes in corneal structure. Corneal edema, pronounced inflammatory cells infiltration and inordinate collagen fibres were observed. Immunohistochemical results showed that the expression of NF-kappaB and its activation obviously increased after LPS treatment compared with the normal group and control group. Positive cells could be observed at 0.5 hour and peak expression of NF-kappaB was observed between 3 hours and 12 hours after infection, but returned to or approached normal level by 72 hours. RT-PCR showed that the level of TNF-alpha mRNA began to increase 0.5 hour after LPS treatment, peaked at 6 hours and then subsided by 72 hours. NF-kappaB had a positive correlation with the expression of TNF-alpha mRNA (r = 0.964, P < 0.01), both NF-kappaB and TNF-alpha had a strong positive correlation with the degree of inflammatory response in LPS treated corneas (r = 0.929, P < 0.01; r = 0.587, P < 0.05, respectively).

CONCLUSIONSThe activation of NF-kappaB was increased in LPS treated corneas and was elevated in LPS induced keratitis by promoting overexpression of TNF-alpha mRNA. NF-kappaB may play an important role in the pathogenesis of LPS-associated keratitis in rats.

Animals ; Aqueous Humor ; cytology ; Epithelium, Corneal ; physiology ; Immunohistochemistry ; Keratitis ; chemically induced ; pathology ; Lipopolysaccharides ; toxicity ; NF-kappa B ; analysis ; physiology ; RNA, Messenger ; analysis ; Rats ; Rats, Wistar ; Tumor Necrosis Factor-alpha ; genetics ; physiology

PURPOSE: To compare oxidative stress status in the aqueous humor of highly myopic eyes and control eyes. METHODS: Aqueous humor samples were collected from 15 highly myopic eyes (high myopia group) and 23 cataractous eyes (control group) during cataract surgery. Central corneal thickness, corneal endothelial cell density, hexagonality of corneal endothelial cells, and cell area of corneal endothelial cells were measured using specular microscopy. Axial length was measured using ultrasound biometry. 8-Hydroxydeoxyguanosine (8-OHdG) and malondialdehyde levels were measured using enzyme-linked immunosorbent assay. RESULTS: 8-OHdG level was lower in the aqueous humor of myopic patients than in that of control group (p = 0.014) and was positively correlated with central corneal thickness and negatively correlated with axial length (r = 0.511, p = 0.02; r = -0.382, p < 0.001). There was no correlation between 8-OHdG level and corneal endothelial cell density, hexagonality, or cell area. Malondialdehyde level did not show any correlation with any parameters evaluated. CONCLUSIONS: 8-OHdG might be a sensitive biomarker for evaluating oxidative stress status in the eye. Oxidative stress level was lower in the aqueous humor of highly myopic eyes compared to that in control eyes, which indicates lower metabolic activity in these eyes.
Aged ; Aqueous Humor/*metabolism ; Deoxyguanosine/*analogs & derivatives/metabolism ; Enzyme-Linked Immunosorbent Assay ; Female ; Humans ; Male ; Malondialdehyde/*metabolism ; Middle Aged ; Myopia/*metabolism/physiopathology ; *Oxidative Stress ; Refraction, Ocular/*physiology ; Severity of Illness Index