Casein kinase-2 inhibition promotes retinal ganglion cell survival after acute intraocular pressure elevation

Intraocular pressure elevation can induce retinal ganglion cell death and is a clinically reversible risk factor for glaucoma, the leading cause of irreversible blindness. We previously demonstrated that casein kinase-2 inhibition can promote retinal ganglion cell survival and axonal regeneration in rats after optic nerve injury. To investigate the underlying mechanism, in the current study we increased the intraocular pressure of adult rats to 75 mmHg for 2 hours and then administered a casein kinase-2 inhibitor (4,5,6,7-tetrabromo-2-azabenzimidazole or 2-dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole) by intravitreal injection. We found that intravitreal injection of 4,5,6,7-tetrabromo-2-azabenzimidazole or 2-dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole promoted retinal ganglion cell survival and reduced the number of infiltrating macrophages. Transcriptomic analysis showed that the mitogen activated protein kinase signaling pathway was involved in the response to intraocular pressure elevation but was not modulated by the casein kinase-2 inhibitors. Furthermore, casein kinase-2 inhibition downregulated the expression of genes (Cck, Htrsa, Nef1, Htrlb, Prph, Chat, Slc18a3, Slc5a7, Scn1b, Crybb2, Tsga10ip, and Vstm21) involved in intraocular pressure elevation. Our data indicate that inhibition of casein kinase-2 can enhance retinal ganglion cell survival in rats after acute intraocular pressure elevation via macrophage inactivation.

A multi-scale/multi-physics model for the theoretical study of the vascular configuration of retinal capillary plexuses based on OCTA data

The retinal tissue is highly metabolically active and is responsible for translating the visual stimuli into electrical signals to be delivered to the brain. A complex vascular structure ensures an adequate supply of blood and oxygen, which is essential for the function and survival of the retinal tissue. To date, a complete understanding of the configuration of the retinal vascular structures is still lacking. Optical coherence tomography angiography has made available a huge amount of imaging data regarding the main retinal capillary plexuses, namely the superficial capillary plexuses (SCP), intermediate capillary plexuses (ICP) and deep capillary plexuses (DCP). However, the interpretation of these data is still controversial. In particular, the question of whether the three capillary plexuses are connected in series or in parallel remains a matter of debate. In this work, we address this question by utilizing a multi-scale/multi-physics mathematical model to quantify the impact of the two hypothesized vascular configurations on retinal hemodynamics and oxygenation. The response to central retinal vein occlusion (CRVO) and intraocular pressure (IOP) elevation is also simulated depending on whether the capillary plexuses are connected in series or in parallel. The simulation results show the following: (i) in the in series configuration, the plexuses exhibit a differential response, with DCP and ICP experiencing larger pressure drops than SCP; and (ii) in the in parallel configuration, the blood flow redistributes uniformly in the three plexuses. The different vascular configurations show different responses also in terms of oxygen profiles: (i) in the in series configuration, the outer nuclear layer, outer plexiform layer and inner nuclear layer (INL) are those most affected by CRVO and IOP elevation; and (ii) in the in parallel configuration the INL and ganglion cell layer are those most affected. The in series results are consistent with studies on paracentral acute middle maculopathy, secondary to CRVO and with studies on IOP elevation, in which DCP and ICP and the retinal tissues surrounding them are those most affected by ischemia. These findings seem to suggest that the in series configuration better describes the physiology of the vascular retinal capillary network in health and disease.

A Dietary Combination of Forskolin with Homotaurine, Spearmint and B Vitamins Protects Injured Retinal Ganglion Cells in a Rodent Model of Hypertensive Glaucoma

There is indication that nutritional supplements protect retinal cells from degeneration. In a previous study, we demonstrated that dietary supplementation with an association of forskolin, homotaurine, spearmint extract and B vitamins efficiently counteracts retinal dysfunction associated with retinal ganglion cell (RGC) death caused by optic nerve crush. We extended our investigation on the efficacy of dietary supplementation with the use of a mouse model in which RGC degeneration depends as closely as possible on intraocular pressure (IOP) elevation. In this model, injecting the anterior chamber of the eye with methylcellulose (MCE) causes IOP elevation leading to RGC dysfunction. The MCE model was characterized in terms of IOP elevation, retinal dysfunction as determined by electrophysiological recordings, RGC loss as determined by brain-specific homeobox/POU domain protein 3A immunoreactivity and dysregulated levels of inflammatory and apoptotic markers. Except for IOP elevation, dysfunctional retinal parameters were all recovered by dietary supplementation indicating the involvement of non-IOP-related neuroprotective mechanisms of action. Our hypothesis is that the diet supplement may be used to counteract the inflammatory processes triggered by glial cell activation, thus leading to spared RGC loss and the preservation of visual dysfunction. In this respect, the present compound may be viewed as a potential remedy to be added to the currently approved drug therapies for improving RGC protection.

Provocative intraocular pressure challenge preferentially decreases venous oxygen saturation despite no reduction in blood flow

PURPOSE

Ocular disease can both alter the retina's oxygen requirements, and decrease its ability to cope with changes in metabolic demand. We examined the influence of a moderate intraocular pressure (IOP) elevation on three outcome measures: arterial and venous oxygen saturation, blood flow, and the pattern electroretinogram (PERG).

METHODS

We increased IOP to ˜30 mmHg in 23 healthy participants (22-39 years) using a mechanical probe applied to the eyelid, thereby lowering ocular perfusion pressure (OPP) by ~30%. The Oxymap retinal oximeter was used to measure oxygen saturation for arteries and veins. Blood flow, volume and velocity were measured using the Heidelberg retinal flowmeter and steady-state PERG waveforms (8.34 Hz) were recorded bilaterally (200 sweeps). For each outcome measure, data was obtained three times: at baseline, 1 min into sustained IOP elevation, and 1 min after the probe was removed.

RESULTS

During IOP elevation, changes in oxygen saturation of retinal arteries failed to reach statistical significance [F(1,30) = 3.69, p = 0.05], whereas venous oxygen saturation was significantly reduced [F(1,21) = 27.43, p < 0.01]. Blood flow increased slightly [F(2,40) = 6.28, p < 0.0001], PERG amplitude significantly reduced [F(2,44) = 24.24, p < 0.0001] and PERG phase was significantly delayed [F(2,44) = 17.00, p < 0.0001]. Contralateral eyes were unchanged. OPP reduction correlated little with PERG amplitude, PERG phase or venous oxygen saturation.

CONCLUSIONS

Mild, acute IOP elevation increases arterio-venous oxygen saturation differences primarily through lowering venous oxygen saturation, suggesting increased oxygen consumption by healthy neurons when physiologically stressed.

Ultrasound biomicroscopy of hyperpressurized eyes following pars plana vitrectomy

Early elevated intraocular pressure (IOP) following pars plana vitrectomy is a common complication of vitreoretinal surgery and severe pressure elevation may result in visual loss. To investigate the mechanism of IOP elevation following pars plana vitrectomy, a retrospective review of 119 patients (132 eyes) who had undergone vitreoretinal surgery was performed. Ultrasound biomicroscopy (UBM) was used to observe the changes in the structure of the anterior segment following vitrectomy and to compare various parameters pre- and postsurgery. The UBM examination revealed inflammation within the anterior chamber and hyphema with increased IOP. In certain patients, the iris had adhered to the trabecular meshwork and the anterior chamber angle was closed. Cyclodialysis involving the pars plicata and iris was also observed. Furthermore, silicone oil emulsification in the anterior chamber angle and posterior chamber presurgery were noted in certain cases. Edema and forward rotation of the ciliary body resulted in the closure of the anterior chamber angle. The measured parameters indicated that the anterior chamber became shallower and that the anterior chamber angle was narrowed in phakic eyes with elevated IOP. Eyes with elevated IOP and intraocular lenses were not observed to be different from phakic eyes with elevated IOP. This may be due to the fact that an eye with an intraocular lens is thinner than a phakic eye. This study suggests that UBM examination is useful for investigating the pathogenesis of elevated IOP following vitrectomy, and provides a theoretical basis.

Glaucoma associated with the management of rhegmatogenous retinal detachment

Transient or permanent elevation of intraocular pressure (IOP) is a common complication following vitreoretinal surgery. Usually secondary glaucoma, which develops after scleral buckling procedures, or pars plana vitrectomy for repair of rhegmatogenous retinal detachment, is of multifactorial origin. It is essential, for appropriate management, to detect the cause of outflow obstruction. An exacerbation of preexisting open-angle glaucoma or a steroid-induced elevation of IOP should also be considered. Scleral buckling may be complicated by congestion and anterior rotation of the ciliary body resulting in secondary angle closure, which can usually resolve with medical therapy. The use of intravitreal gases may also induce secondary angle-closure with or without pupillary block. Aspiration of a quantity of the intraocular gas may be indicated. Secondary glaucoma can also develop after intravitreal injection of silicone oil due to pupillary block, inflammation, synechial angle closure, or migration of emulsified silicone oil in the anterior chamber and obstruction of the aqueous outflow pathway. In most eyes medical therapy is successful in controlling IOP; however, silicone oil removal with or without concurrent glaucoma surgery may also be required. Diode laser transscleral cyclophotocoagulation and glaucoma drainage devices constitute useful treatment modalities for long-term IOP control. Cooperation between vitreoretinal and glaucoma specialists is necessary to achieve successful management.

Intravitreal triamcinolone acetonide: Pattern of secondary intraocular pressure rise and possible risk factors

Purpose

To determine the pattern of increase in intraocular pressure (IOP) following intravitreal triamcinolone acetonide (IVTA) and identify possible risk factors associated with this rise in IOP.

Methods

We carried out a retrospective review of records for 185 patients (226 eyes) who received 4 mg of IVTA at the American University of Beirut Medical Center and Hotel Dieu de France eye clinics between 2003 and 2005

Results

Mean follow-up was 8.17 months (range 6 to 24 months). The mean number of IVTA injections per eye was 1.31 ± 0.69. The mean IOP increased after the first IVTA injection from 15.04 ± 3.18 mmHg at baseline to a mean maximum of 17.20 ± 5.75 mmHg (p < 0.0001, paired t-test) at month 3 of follow-up with a return to mean baseline IOP (15.49 ± 4.79 mmHg) at month 12. Fifty nine of 226 eyes showed IOP higher than 21 mmHg during follow-up. Nine eyes started to have IOP greater than 21 mmHg, 6 to 12 months after a single injection. Intraocular pressure lowering medications were started when IOP exceeded 25 mmHg in 15 of the 226 eyes studied. No risk factors have been found to predict this IOP rise

Conclusions

IOP elevation can occur in a significant number of eyes receiving 4 mg of IVTA. This phenomenon seems to be transient and a small number of eyes required treatment during this period. Eyes that received IVTA need to be monitored for IOP changes especially during the first 3 months, but the IOP may still rise 6 months and even 12 months after a single injection. This study did not show any risk factor that may predict this IOP rise