Histopathologic Results of Retinal Diode Laser Photocoagulation in Rabbit Eyes

• Diode laser photocoagulation was applied to rabbit retina simulating scatter treatment using an endolaser probe and in a manner simulating treatment of peripheral retinal breaks using a transscleral retinopexy probe. Clinically appearing mild, moderate, and severe burns were created by altering the burn duration in one eye and by altering the power setting in the fellow eye. Histopathologic results demonstrated the clinically evident dose-response effect with sparing of inner retinal cellular elements with mild burns and full-thickness retinal cell loss with severe burns. Bruch's membrane ruptures were seen in three of 42 endophotocoagulation severe spots placed with high power, but in none of the 42 severe spots placed with long burn duration. Thus, longer burn duration appeared to be a safer way to produce a severe burn than higher power. Burns characteristically bloomed during the several seconds following laser application by both modalities, possibly indicating a deep source of energy absorption. Scleral effects, seen only when high energy levels were used to treat atrophic areas, were mild

Histopathologic Characteristics of Diode Laser-Induced Chorioretinal Adhesions for Experimental Retinal Detachment in Rabbit Eyes

• A retinal break and localized retinal detachment were induced in 10 rabbit eyes. The retinal break was treated within regions of detached retina using diode laser transscleral retinopexy (four eyes), diode laser indirect ophthalmoscopy (two eyes), or retinocryopexy (two eyes). Two eyes were left as untreated controls. The clinical and histopathologic effects were studied 1 day and 3 weeks after initial treatment. Suitable chorioretinal adhesions were induced with all treatment modalities. The extent of tissue effects was greater in cryopexy and smaller in laser treatment. The histopathologic characteristics of the lesions induced by diode laser indirect ophthalmoscopy were similar to those seen with transscleral diode treatment and were more focal than those seen with cryopexy. Transscleral and transpupillary diode laser photocoagulation were effective in inducing chorioretinal adhesions in detached retina in this experimental model in rabbits

Phosphatidylserine-Containing Liposomes Promote Maximal Survival of Retinal Neurons after Ischemic Injury

We investigated the systemic effect of liposomes bearing apoptotic signals on the level of inflammation and neuronal death induced by ischemia–reperfusion (IR). Using a model of retinal ischemia, we showed that treatment with phosphatidylserine (PS) and phosphatidylcholine (PC) liposomes significantly reduced the expression of proinflammatory genes, including that of Il1b, Il6, Ccl2, Ccl5, Cxcl10, and Icam1, 24 h after reperfusion. Phosphatidylserine liposome treatment was the most efficient and correlated with significantly reduced neuronal death in the retina 7 days after reperfusion. The results of our study indicate that therapeutic strategy based on mimicking a systemic increase in apoptotic signaling can significantly reduce central nervous system damage induced by IR and improve neurologic outcome

Toll-like receptor 4 contributes to retinal ischemia/reperfusion injury

PURPOSE: We investigated whether retinal ischemia and inflammation produced by raising the intraocular pressure above normal systolic levels differs in mice that lack a functional toll-like receptor 4 (Tlr4) signaling pathway. METHODS: In this work we used the murine strain B6.B10ScN-Tlr4(lps-del)/JthJ, which does not express functional Tlr4. C57BL/6J was considered as the control. We induced retinal ischemia by unilateral elevation of intraocular pressure for 1 h by direct corneal cannulation. The changes in expression of proinflammatory genes 24 h postreperfusion were assessed by quantitative PCR. Corresponding changes in protein abundances were analyzed by western blot and immunohistochemistry. Cell death was evaluated by direct counting of neurons in the ganglion cell layer of flat-mounted retinas seven days postreperfusion. RESULTS: We showed that Tlr4-deficient mice display significantly reduced expression of proinflammatory genes, including RelA, tumor necrosis factor (Thf), interleukin 6 (Il6), chemokine (C-C motif) ligand 2 (Ccl2), chemokine (C-C motif) ligand 5 (Ccl5), chemokine (C-X-C motif) ligand 10 (Cxcl10), Cybb, nitric oxide synthase 2 (Nos2), and intercellular adhesion molecule 1 (Icam1) 24 h after reperfusion. The mice that lacked Tlr4 showed significantly increased survival of neurons in the ganglion cell layer following ischemic injury, as compared to wild-type controls. CONCLUSIONS: Our results indicate that Tlr4 signaling is involved in retinal damage and inflammation triggered by ischemic injury

Biodegradable Mechanical Retinal Fixation: A Pilot Study

• Mechanical retinal fixation is a useful tool in the armamentarium of vitreoretinal surgeons. Unfortunately, the use of metallic retinal tacks on a permanent basic mandates a retained intraocular foreign body that poses some potential for longrange toxic effects. Herein, we report the results of our initial experience with a temporary, biodegradable mechanical retinal fixation device ("biopin") in rabbits. When compared with metallic tacks, the biopins appeared to be well tolerated intraocularly, with minimal damage detectable at the light microscopic level. Disinsertion of the biopins occurred in 46% of the eyes within two weeks and in all eyes by four weeks. Initial signs of degradation of the biopins were observed at six weeks (median) in the lensectomized/vitrectomized eyes and at 12 weeks (median) in the nonvitrectomized eyes. Differences were found in the occurrence of retinal detachment between animals that underwent lensectomy/vitrectomy with insertion of two metallic tacks and animals that underwent insertion of one biopin without vitrectomy. The biopin has a potential as a vehicle for sustained release of pharmacologic agents to inhibit directly the development of vitreoretinal proliferation, thereby retarding or preventing subsequent retinal traction and detachment

Neuronal NAD(P)H oxidases contribute to ROS production and mediate RGC death after ischemia

To study the role of neuronal nicotinamide adenine dinucleotide phosphate [NAD(P)H] oxidase-dependent reactive oxygen species (ROS) production in retinal ganglion cell (RGC) death after ischemia. Ischemic injury was induced by unilateral elevation of intraocular pressure via direct corneal cannulation. For in vitro experiments, RGCs isolated by immunopanning from retinas were exposed to oxygen and glucose deprivation (OGD). The expression levels of NAD(P)H oxidase subunits were evaluated by quantitative PCR, immunocytochemistry, and immunohistochemistry. The level of ROS generated was assayed by dihydroethidium. The NAD(P)H oxidase inhibitors were then tested to determine if inhibition of NAD(P)H oxidase altered the production of ROS within the RGCs and promoted cell survival. It was reported that RGCs express catalytic Nox1, Nox2, Nox4, Duox1, as well as regulatory Ncf1/p47phox, Ncf2/p67phox, Cyba/p22phox, Noxo1, and Noxa1 subunits of NAD(P)H oxidases under normal conditions and after ischemia. However, whereas RGCs express only low levels of catalytic Nox2, Nox4, and Duox1, and regulatory Ncf1/p47, Ncf2/p67 subunits, they exhibit significantly higher levels of catalytic subunit Nox1 and the subunits required for optimal activity of Nox1. It was observed that the nonselective NAD(P)H oxidase inhibitors VAS-2870, AEBSF, and the Nox1 NAD(P)H oxidase-specific inhibitor ML-090 decreased the ROS burst stimulated by OGD, which was associated with a decreased level of RGC death. The findings suggest that NAD(P)H oxidase activity in RGCs renders them vulnerable to ischemic death. Importantly, high levels of Nox1 NAD(P)H oxidase subunits in RGCs suggest that this enzyme could be a major source of ROS in RGCs produced by NAD(P)H oxidases

Spectral domain optical coherence tomography in a murine retinal detachment model

Spectral domain optical coherence tomography (SD-OCT) was used to image retinal detachments in vivo, in a murine model of retinal detachment (RD). Subretinal injections of hyaluronic acid (Healon) were delivered to the right eye of seventeen 10–20 week-old C57Bl6 mice. Evaluation of the fundus with an operating microscope and fundus photography were performed. In vivo, non-contact, ultra high resolution SD-OCT imaging was performed on day 0, day 1–2, day 5–6 and day 15–16. The retinal morphology at the edge and in the area of maximal RD was evaluated. Eyes were enucleated for histologic analysis. The retinal detachment was confirmed by microscopy in all mice. The extent of the retinal detachment was evaluated by measuring the height of the retinal detachment. The retinal layers, including the photoreceptor layer, were evaluated. Retinal layers appeared indistinct soon after RD (day 1, 5), particularly over areas of maximal detachment. By day 5 and 15 the external limiting membrane was no longer visible and there was increased reflectivity of the photoreceptor layer and undulation of the outer retina in areas of RD on both SD-OCT and histology. The thickness of the outer nuclear layer and photoreceptor outer segments decreased on day 5 and 15. SD-OCT is a promising technology to follow retinal detachment and outer retinal abnormalities in a murine model

Succinylcholine-stimulated muscle tensions following botulinum injection in the domestic cat

Succinylcholine (SCh) selectively stimulates, and can therefore selectively assay, the multiple innervated (MI) fiber system of the extraocular muscles. Since botulinum-A toxin has been observed to induce changes in eye position in humans. SCh was used to assess the effect of botulinum-A on the SCh-sensitive MI fibers of extraocular muscles. Intravenous SCh infusion (40 μg −1 kg −1 min −1) was performed in the anesthetized domestic cat. Thirty-eight infusions were performed in 19 normal controls, measuring the peak tensions generated in the four horizontal and four vertical rectus muscles. Succinylcholine-stimulated muscle tensions (SSMT) were then repeated in nine animals, 4 weeks and 10 weeks following injection of botulinum-A toxin into both medial rectus muscles. Mean peak SSMTs were unchanged at 4 and 10 weeks following botulinum injection when compared to controls. We propose that botulinum chemo-denervation has no acute or chronic effect on the MI SCh-sensitive muscle fibers of the medial recti of the domestic cat. This lack of effect on the postsynaptic MI fibers indirectly supports light and electron microscopic studies which show changes predominantly in the singly innervated (SI), rather than the MI fibers following botulinum injection. Mean peak SSMTs were also greater for medial and superior rectus muscles compared to lateral and inferior recti respectively, suggesting a greater number or proportion of MI fibers in medial and superior recti