Dynamics of retinal photocoagulation and rupture.

In laser retinal photocoagulation, short (<20 ms) pulses have been found to reduce thermal damage to the inner retina, decrease treatment time, and minimize pain. However, the safe therapeutic window (defined as the ratio of power for producing a rupture to that of mild coagulation) decreases with shorter exposures. To quantify the extent of retinal heating and maximize the therapeutic window, a computational model of millisecond retinal photocoagulation and rupture was developed. Optical attenuation of 532-nm laser light in ocular tissues was measured, including retinal pigment epithelial (RPE) pigmentation and cell-size variability. Threshold powers for vaporization and RPE damage were measured with pulse durations ranging from 1 to 200 ms. A finite element model of retinal heating inferred that vaporization (rupture) takes place at 180-190 degrees C. RPE damage was accurately described by the Arrhenius model with activation energy of 340 kJ/mol. Computed photocoagulation lesion width increased logarithmically with pulse duration, in agreement with histological findings. The model will allow for the optimization of beam parameters to increase the width of the therapeutic window for short exposures.

Effect of pulse duration on size and character of the lesion in retinal photocoagulation.

OBJECTIVE: To systematically evaluate the effects of laser beam size, power, and pulse duration of 1 to 100 milliseconds on the characteristics of ophthalmoscopically visible retinal coagulation lesions. METHODS: A 532-nm Nd:YAG laser was used to irradiate 36 retinas in Dutch Belt rabbits with retinal beam sizes of 66, 132, and 330 mum. Lesions were clinically graded 1 minute after placement, their size measured by digital imaging, and their depth assessed histologically at different time points. RESULTS: Retinal lesion size increased linearly with laser power and logarithmically with pulse duration. The width of the therapeutic window, defined by the ratio of the threshold power for producing a rupture to that of a mild coagulation, decreased with decreasing pulse durations. For 132- and 330-mum retinal beam sizes, the therapeutic window declined from 3.9 to 3.0 and 5.4 to 3.7, respectively, as pulse duration decreased from 100 to 20 ms. At pulse durations of 1 millisecond, the therapeutic window decreased to unity, at which point rupture and a mild lesion were equally likely to occur. CONCLUSIONS: At shorter pulse durations, the width and axial extent of the retinal lesions are smaller and less dependent on variations in laser power than at longer durations. The width of the therapeutic window, a measure of relative safety, increases with the beam size. CLINICAL RELEVANCE: Pulse durations of approximately 20 milliseconds represent an optimal compromise between the favorable impact of speed, higher spatial localization, and reduced collateral damage on one hand, and sufficient width of the therapeutic window (> 3) on the other.

Male infertility, impaired spermatogenesis, and azoospermia in mice deficient for the pseudophosphatase Sbf1.

Pseudophosphatases display extensive sequence similarities to phosphatases but harbor amino acid alterations in their active-site consensus motifs that render them catalytically inactive. A potential role in substrate trapping or docking has been proposed, but the specific requirements for pseudophosphatases during development and differentiation are unknown. We demonstrate here that Sbf1, a pseudophosphatase of the myotubularin family, is expressed at high levels in seminiferous tubules of the testis, specifically in Sertoli's cells, spermatogonia, and pachytene spermatocytes, but not in postmeiotic round spermatids. Mice that are nullizygous for Sbf1 exhibit male infertility characterized by azoospermia. The onset of the spermatogenic defect occurs in the first wave of spermatogenesis at 17 days after birth during the synchronized progression of pachytene spermatocytes to haploid spermatids. Vacuolation of the Sertoli's cells is the earliest observed phenotype and is followed by reduced formation of spermatids and eventual depletion of the germ cell compartment in older mice. The nullizygous phenotype in conjunction with high-level expression of Sbf1 in premeiotic germ cells and Sertoli's cells is consistent with a crucial role for Sbf1 in transition from diploid to haploid spermatocytes. These studies demonstrate an essential role for a pseudophosphatase and implicate signaling pathways regulated by myotubularin family proteins in spermatogenesis and germ cell differentiation.

Implantation of Modular Photovoltaic Subretinal Prosthesis.

BACKGROUND AND OBJECTIVE: Establish the surgical procedure for subretinal implantation of multiple photovoltaic arrays for the restoration of sight. MATERIALS AND METHODS: Multiple silicon photovoltaic arrays of 1 mm in diameter and 30 µm in thickness were implanted subretinally via single retinotomy in rabbits. Ophthalmoscopic imaging and optical coherence tomography (OCT) were used to validate the implants' placement. RESULTS: Vitrectomy, followed by subretinal fluid injection for retinal detachment and retinotomy, allowed accurate placement of seven modules in the bleb, covering approximately a 3.5-mm diameter area on the retina via a single 1.5-mm retinotomy. OCT confirmed complete reattachment of the retina over the implants. CONCLUSION: Subretinal implantation of multiple photovoltaic arrays via a single retinotomy, followed by their tiling, minimizes the scleral and retinal incisions and provides better fit to the spherical shape of the eye ball, compared to a single, larger module. Such minimally traumatic procedure can be performed with 20-gauge intraocular instruments.

Design of a high-resolution optoelectronic retinal prosthesis.

It has been demonstrated that electrical stimulation of the retina can produce visual percepts in blind patients suffering from macular degeneration and retinitis pigmentosa. However, current retinal implants provide very low resolution (just a few electrodes), whereas at least several thousand pixels would be required for functional restoration of sight. This paper presents the design of an optoelectronic retinal prosthetic system with a stimulating pixel density of up to 2500 pix mm(-2) (corresponding geometrically to a maximum visual acuity of 20/80). Requirements on proximity of neural cells to the stimulation electrodes are described as a function of the desired resolution. Two basic geometries of sub-retinal implants providing required proximity are presented: perforated membranes and protruding electrode arrays. To provide for natural eye scanning of the scene, rather than scanning with a head-mounted camera, the system operates similar to 'virtual reality' devices. An image from a video camera is projected by a goggle-mounted collimated infrared LED-LCD display onto the retina, activating an array of powered photodiodes in the retinal implant. The goggles are transparent to visible light, thus allowing for the simultaneous use of remaining natural vision along with prosthetic stimulation. Optical delivery of visual information to the implant allows for real-time image processing adjustable to retinal architecture, as well as flexible control of image processing algorithms and stimulation parameters.

The role of the TH1 and TH2 immune responses in loosening and osteolysis of cemented total hip replacements.

The mechanisms underlying the development of osteolysis and aseptic loosening have an impact on the longevity of total hip replacements (THRs). This study examines the specific roles of lymphocytes in the TH1 and TH2 subsets in osteolysis and aseptic loosening of THR. Tissue from periprosthetic regions from patients with loose, cemented acetabular components were used to determine the TH1 and TH2 cytokine profile. Twelve tissue specimens from patients with radiographic signs of osteolysis, and nine tissue specimens from patients with no signs of osteolysis were harvested during revision surgery. Immunohistochemistry using primary antibodies against CD3, interferon (IFN)-gamma, interleukin (IL)-2, IL-4, and IL-10 was performed on frozen sections to determine the percentage of positive cells for each of the sections. No statistically significant differences in the percentage of positive cells expressing cytokines characteristic of the TH1 pathway (IFN-gamma, IL-2) or TH2 pathway (IL-4, IL-10) were found when comparing osteolytic and non-osteolytic tissues. However, significant numbers of T cells (averaging about 10% of the total cells) and TH1 and TH2 immune cytokines (averaging 3-5% of cells) implicate a possible role for immune processes at the prosthetic interface.

Expression of nitric oxide, peroxynitrite, and apoptosis in loose total hip replacements.

Nitric oxide (NO) is an effector molecule associated with inflammation, immune function, bone metabolism, and the induction of apoptosis. This study examined the role of NO, peroxynitrite (ONOO(-)), and apoptosis in cases of revision total hip replacements (THRs). We hypothesized that apoptosis and excess production of NO contribute to the inflammatory reaction to orthopedic biomaterial wear debris that is associated with loosening and osteolysis. Periprosthetic membranous specimens were collected from revised cemented acetabular components with simple loosening and ballooning osteolysis. Synovial samples from patients undergoing primary THR were used as controls. The presence of macrophages (CD68(+)) and levels of inducible nitric oxide synthase (INOS), endothelial nitric oxide synthase (EcNOS), ONOO(-) (Nitro, assayed by the amount of nitrated tyrosine residues), and apoptosis (TUNEL staining) were examined using immunohistochemistry. Increased expression for INOS, EcNOS, and ONOO(-) in both the loose/osteolytic and the loose/non-osteolytic groups was observed when compared to the synovium group. There were no significant differences between the loose/osteolytic group and loose/non-osteolytic group for these biologic markers. TUNEL staining showed a significant increase in apoptosis in the loose/osteolytic group compared to the loose/non-osteolytic group and synovial tissues. These findings suggest that NO and NO-derived molecules, such as ONOO(-), may be involved in sustaining the foreign-body reaction to wear debris. NO and ONOO(-) may prove to be useful markers of prosthetic loosening whereas apoptosis may be a marker distinguishing ballooning from simple osteolysis.

Vasoconstriction by electrical stimulation: new approach to control of non-compressible hemorrhage.

Non-compressible hemorrhage is the most common preventable cause of death on battlefield and in civilian traumatic injuries. We report the use of microsecond pulses of electric current to induce rapid constriction in femoral and mesenteric arteries and veins in rats. Electrically-induced vasoconstriction could be induced in seconds while blood vessels dilated back to their original size within minutes after stimulation. At higher settings, a blood clotting formed, leading to complete and permanent occlusion of the vessels. The latter regime dramatically decreased the bleeding rate in the injured femoral and mesenteric arteries, with a complete hemorrhage arrest achieved within seconds. The average blood loss from the treated femoral artery during the first minute after injury was about 7 times less than that of a non-treated control. This new treatment modality offers a promising approach to non-damaging control of bleeding during surgery, and to efficient hemorrhage arrest in trauma patients.

Hepatocyte growth factor receptor in acute tubular necrosis.

In acute tubular necrosis, there are early transient increases in circulating and local bioactive hepatocyte growth factor (HGF) levels and renal HGF receptor (c-MET) gene expression. It has therefore been suggested that endogenous HGF may play a role in initiating renal repair. To test this hypothesis, changes in the levels, activity, and anatomic distribution of c-MET protein were characterized in relation to the onset and localization of DNA synthesis in kidneys of rats with ischemia-induced acute tubular necrosis. Whole-kidney c-MET protein levels were significantly increased in the injured kidneys 12 h after injury and rose to a maximum after 1 d, exceeding the control values by sevenfold. Eight days after injury, c-MET levels, although decreasing, were still elevated above control values. An increase in the levels of activated c-MET, i.e., tyrosine-phosphorylated c-MET, was also evident as early as 12 h after injury. Histologic analyses demonstrated that the increase in c-MET immunoreactivity was most marked in the most severely damaged nephron segments in the outer medulla. In injured proximal tubules, the receptor was redistributed from an apical location to an intracellular location. DNA synthesis was increased in the injured kidneys, especially in the outer medulla, where the increase in c-MET protein levels was most prominent. The increase in DNA synthesis was first detected 12 h after the initial increase in activated c-MET levels. It is concluded that the early increases in the levels of c-MET protein and activated receptor support the hypothesis that HGF participates in the initiation of renal regeneration. In addition, the persistent elevation of c-Met protein levels suggests that prolonged and even late treatment with HGF may be of therapeutic value