Laser-Induced Ocular Hypertension in a Mouse Model of Glaucoma.

Glaucoma is a neurodegenerative disease that leads to the loss of retinal ganglion cells (RGC) and thus to blindness. There are numerous experimental models used for the study of this pathology. Among the different models, episcleral vein photocoagulation is one of the most widely used. In this model there is a transient increase in intraocular pressure that returns to normal values about 7 days after induction of ocular hypertension (OHT). In addition, typical glaucoma changes, such as loss of RGC, thinning of the optic nerve fiber layer, and glial activation, occur in this model. All these changes have been described in detail over time after OHT induction. In this chapter, we describe the detailed method of OHT induction in Swiss albino mice by diode laser photocoagulation of limbal and episcleral veins.

Idiopathic elevated episcleral venous pressure in a teenager.

PURPOSE: To report a case of unilateral idiopathic elevated episcleral venous pressure (IEEVP) in a 15-year-old patient. We reviewed and summarized published case reports of IEEVP to determine how to manage this challenging and rare condition. OBSERVATIONS: A 15-year-old Caucasian male presented with elevated intraocular pressures (IOP), blood in Schlemm canal in the left eye, and asymmetric cupping with corresponding glaucomatous findings on testing. We diagnosed the patient with IEEVP and describe successful surgical intervention with deep sclerectomy and viscocanalostomy. CONCLUSIONS AND IMPORTANCE: IEEVP is a diagnosis of exclusion and based on clinical findings of dilated episcleral veins, blood in Schlemm canal and glaucomatous changes. If glaucomatous progression occurs with medication, filtration surgery is usually required, and most patients have good results in the literature. Care should be taken to prevent post-operative hypotony and serous choroidal detachment.

[Comparison of two experimental models of glaucoma in rabbits] / Comparación de dos modelos experimentales de glaucoma en conejos.

Objective: to compare two models of experimental glaucoma by induction of ocular hypertension in rabbits. Materials and methods: Sixteen New Zealand female rabbits, 2-3 kg were used. Model A (n=6): cauterization of episcleral and perilimbar veins of the right eye (RE) with surgical electrocautery. Model B (n=10): Injection of ?-chymotrypsin in posterior chamber of RE. Intraocular pressure (IOP) was measured before and after the induction of ocular hypertension (OHT), once a week at the same time of day for 40 days, with a manual tonometer. The animals were euthanized by CO2 inhalation. In both models the control was the IOP of the left eye (LE). The mean and standard error (SE) values of IOP, expressed in mmHg, were compared statistically by applying Student's t-test with a significance level of p<0.05. Results: The IOP in LE (control) of model A: was 12.9±1.05 and in model B: 12.9±1.09. There were no significant differences between the models. Model A: The IOP increase in RE was 14.7% (14.8±1.4) with respect to LE. A significant increase in IOP was observed within the first 24 hours: 23.5±1.9 (p<0.05) compared to the control eye. There were no significant differences with subsequent controls. Model B: The increase in IOP in RE was 129.1% (29.6±3.4) with respect to LE. In all cases an increase was observed from Day 1 (p<0.05). The IOP peak in RE was evidenced on Day 25: 35±3.4 (p<0.05). The increase in IOP induced by model B was significantly higher (p<0.01) than in model A. There was loss of ganglion cells of the retina in both models, but the following anatomo-pathological changes were observed only in model B: buphthalmos, subluxation of the lens and increased excavation of the papilla. Conclusion: This study indicates that model B is the most appropriate method to induce a rapid, controlled increase of IOP in rabbits and, more importantly, that this increase may be sustained over extended periods of time. This model could be useful for evaluating the efficacy of new ocular drug delivery systems and for further studies of the physiopathology of glaucoma.

Objetivo: comparar dos modelos de glaucoma experimental por inducción de hipertensión ocular en conejos y describir cambios anatomo-patológicos. Materiales y métodos: Se utilizaron 16 conejos New Zealand, hembras, de 2-3 kg. Modelo A (n=6): cauterización de venas epiesclerales y perilimbares en ojo derecho (OD) con cauterio eléctrico quirúrgico. Modelo B (n=10): inyección intracamerular en OD de ?-quimotripsina. Se midió la presión intraocular (PIO) antes y después de la inducción de la hipertensión ocular (HTO), una vez por semana, a la misma hora del día, durante 40 días, con tonómetro manual. Los animales fueron sacrificados por inhalación de CO2. En ambos modelos la PIO del ojo izquierdo (OI).fue tomado como valor control. La media y error estándar (EE) de los valores de la PIO, expresada en mmHg, fueron evaluadas y comparadas estadísticamente aplicando Test T de Student considerando un nivel de significación de p < 0.05. Resultados: La PIO en OI (control) del modelo A: fue 12,9±1,05 y en el modelo B: 12,9±1,09. No se observaron diferencias significativas entre ambas. Modelo A: el aumento de la PIO en OD fue 14,7% (14,8±1,4) con respecto a OI. Se observó un incremento significativo de la PIO dentro de las primeras 24 hs: 23,5±1,9 (p<0,05) comparado con el valor del ojo control. No hubo diferencias significativas con los controles posteriores. Modelo B: el aumento de la PIO en OD fue 129,1% (29,6±3,4) con respecto al OI. En todos los casos se observó un incremento desde el día 1 (p<0,05). El pico de PIO en OD se evidenció el día 25: 35±3,4 (p<0,05). El incremento de la PIO inducida en el modelo B fue significativamente mayor (p<0,01) que en el modelo A. En ambos modelos hubo pérdida de células ganglionares de la retina, pero sólo en el modelo B se observaron los siguientes cambios anatomo-patológicos: buftalmus, subluxación del cristalino y aumento de la excavación de la papila. Conclusión: De acuerdo a este estudio, el modelo B aparece como el método más apropiado a los fines de inducir un incremento rápido y controlado de la IOP en conejos y más importante, este incremento sería capaz de mantenerse alto a lo largo de periodos de tiempos extendidos. Este modelo podría ser de gran utilidad para evaluar la eficacia de nuevos sistemas oculares de liberación de fármacos y realizar futuros estudios de la fisiopatología del glaucoma Conclusión: De acuerdo a este estudio, el modelo B aparece como el método más apropiado a los fines de inducir un incremento rápido y controlado de la IOP en conejos y más importante, este incremento sería capaz de mantenerse alto a lo largo de periodos de tiempos extendidos. Este modelo podría ser de gran utilidad para evaluar la eficacia de nuevos sistemas oculares de liberación de fármacos y realizar futuros estudios de la fisiopatología del glaucoma

Hypertonic Saline Injection Model of Experimental Glaucoma in Rats.

A reliable method of creating chronic elevation of intraocular pressure (IOP) in rodents is an important tool in reproducing and studying the mechanisms of optic nerve injury that occur in glaucoma. In addition, such a model could provide a valuable method for testing potential neuroprotective treatments. This paper outlines the basic methods for producing obstruction of aqueous humor outflow and IOP elevation by injecting hypertonic saline (a sclerosant) into the aqueous outflow pathway. This is one of several rodent glaucoma models in use today. In this method, a plastic ring is placed around the equator of the eye to restrict injected saline to the limbus. By inserting a small glass microneedle in an aqueous outflow vein in the episclera and injecting hypertonic saline toward the limbus, the saline is forced into Schlemm's canal and across the trabecular meshwork. The resultant inflammation and scarring of the anterior chamber angle occurs gradually, resulting in a rise in IOP after approximately 1 week. This article will describe the equipment necessary for producing this model and the steps of the technique itself.

Ocular Hypertension/Glaucoma in Minipigs: Episcleral Veins Cauterization and Microbead Occlusion Methods.

Two methods to induce elevation of the intraocular pressure (experimental glaucoma) are described in the present chapter. The first method is based on increasing the post-trabecular resistance to aqueous outflow by cauterizing the episcleral veins (EVC). This method allows the observation of ultrastructural changes in the trabecular meshwork (TM) without interfering with any structure within the eye such as TM, ciliary body, and/or the Retina. The second method is the multiple injection of microbeads into the anterior chamber, as a pre and intra-trabecular method that induce secondary effects on the TM cells. Both methods lead to an increase in IOP.

Variations in active outflow along the trabecular outflow pathway.

Previous tracer studies have shown segmental outflow in the trabecular meshwork (TM) and along the inner wall (IW) of Schlemm's canal (SC). Whether segmental outflow is conserved distal to SC has not yet been investigated. This study aims to investigate whether the segmented pattern of outflow is conserved in distal outflow pathways by using a newly developed global imaging method and to evaluate variations of active outflow in three distinct regions along trabecular outflow pathway. Six normal whole globe human eyes were first perfused at 15 mmHg to establish a stable baseline outflow facility. The anterior chamber was then exchanged (5 mL) and perfused with fluorescent microspheres (0.002% v/v, 200 µL) to label areas of active outflow. All eyes were perfusion fixed and dissected into anterior segments. The TM and scleral surface were en face imaged globally. Effective filtration area (EFA) and fluorescent tracer distribution and intensity were analyzed in global images for both the TM and episcleral veins (EPVs). Anterior segments were further dissected into a minimum of 16 radial wedges, from which frontal sections were cut, stained, and imaged, using confocal microscopy. EFA from all three locations along the trabecular outflow pathway were measured and compared. Additionally, TM thickness, SC height, and total number of collector channels (CC) were analyzed and compared between active and inactive areas of outflow. Statistical analysis was performed using Student's t-tests and Wilcoxon signed-rank test with a required significance of p ≤ 0.05. All three locations showed a segmental outflow pattern. The TM had a significantly higher mean EFA (86.3 ± 3.5%) compared to both the IW (34.7 ± 2.9%; p ≤ 0.01) and EPVs (41.1 ± 3.8%; p ≤ 0.01). No significant difference in mean EFA was found between IW and EPVs. Preferential active outflow was observed in the nasal and inferior quadrants. TM thickness was significantly larger in areas of active outflow (103.3 ± 4.0 µm; p ≤ 0.01) compared to areas of inactive outflow (78.5 ± 6.5 µm), but there was no significant difference in SC height between active and inactive outflow areas. Among all eyes, a total of 80 CCs were counted with 63 associated with active outflow and 17 associated with inactive outflow. A higher number of CCs associated with areas of active outflow were found in the nasal (26 of 63) and inferior (20 of 63) quadrants compared to the temporal (9 of 63) and superior (8 of 63) quadrants. A segmental nature of outflow is conserved along the trabecular outflow pathway with variations in three distinct locations (TM, IW, and EPVs). IW and EPVs showed a similar mean EFA. Preferential active outflow was observed in the nasal and inferior quadrants of the eye, which are associated with more expanded TM and higher number of CCs. Normal outflow patterns and its variations along the outflow pathway reported in this study will provide the basis for future studies of the outflow changes in eyes with glaucoma.