Lloyd-model generalization: Conductance fluctuations in one-dimensional disordered systems.

We perform a detailed numerical study of the conductance G through one-dimensional (1D) tight-binding wires with on-site disorder. The random configurations of the on-site energies ε of the tight-binding Hamiltonian are characterized by long-tailed distributions: For large ε, P(ε)∼1/ε^{1+α} with α∈(0,2). Our model serves as a generalization of the 1D Lloyd model, which corresponds to α=1. First, we verify that the ensemble average 〈-lnG〉 is proportional to the length of the wire L for all values of α, providing the localization length ξ from 〈-lnG〉=2L/ξ. Then, we show that the probability distribution function P(G) is fully determined by the exponent α and 〈-lnG〉. In contrast to 1D wires with standard white-noise disorder, our wire model exhibits bimodal distributions of the conductance with peaks at G=0 and 1. In addition, we show that P(lnG) is proportional to G^{ß}, for G→0, with ß≤α/2, in agreement with previous studies.

Universality in the spectral and eigenfunction properties of random networks.

By the use of extensive numerical simulations, we show that the nearest-neighbor energy-level spacing distribution P(s) and the entropic eigenfunction localization length of the adjacency matrices of Erdos-Rényi (ER) fully random networks are universal for fixed average degree ξ≡αN (α and N being the average network connectivity and the network size, respectively). We also demonstrate that the Brody distribution characterizes well P(s) in the transition from α=0, when the vertices in the network are isolated, to α=1, when the network is fully connected. Moreover, we explore the validity of our findings when relaxing the randomness of our network model and show that, in contrast to standard ER networks, ER networks with diagonal disorder also show universality. Finally, we also discuss the spectral and eigenfunction properties of small-world networks.

[Intravitreal triamcinolone combined with grid laser photocoagulation for patients with cystoid macular edema and advanced diabetic retinopathy: pilot study]. / Triamcinolona intravítrea combinada con fotocoagulación láser en rejilla en pacientes con edema macular quístico y retinopatía diabética avanzada: estudio piloto.

BACKGROUND: To determine if primary intravitreal injection of triamcinolone acetonide (TA) plus grid laser photocoagulation (GLP) is effective in treating cystoid diabetic macular edema (DME). METHODS: Prospective comparative non-randomized clinical trial. Fourteen eyes (14 patients) diagnosed with cystoid DME were treated with GLP according to the Early Treatment Diabetic Retinopathy Study (ETDRS) guidelines, plus an intravitreal injection of 4 mg of TA. A matched control group (16 eyes [16 patients]) treated with GLP was selected retrospectively from our medical records. Best-corrected visual acuity (BCVA), and quantitative change in optical coherence tomography (OCT) macular thickness were assessed. RESULTS: Mean follow up was 14.9 months (12 to 19 months). In 3 (21.4%) eyes BCVA increased > 2 ETDRS lines, in 5 (35.7%) eyes BCVA remained the same, and BCVA decreased >2 ETDRS lines in 6 (42.8%) eyes. Central macular thickness, as measured by OCT, decreased a mean of 106.2 µm (30.2%). The difference with the control group was not statistically significant (P = .2). Four (28.5%) eyes developed an increased in intraocular pressure in our study group. CONCLUSIONS: Although all of our patients showed an improvement of cystoid DME by means of OCT and fluorescein angiography, 42.8% (6 eyes) lost 2 or more lines in BCVA with primary intravitreal injection of TA plus GLP. Primary intravitreal injection of TA plus GLP may not be effective for cystoid DME at 12-months.

Scattering and transport properties of tight-binding random networks.

We study numerically scattering and transport statistical properties of tight-binding random networks characterized by the number of nodes N and the average connectivity α. We use a scattering approach to electronic transport and concentrate on the case of a small number of single-channel attached leads. We observe a smooth crossover from insulating to metallic behavior in the average scattering matrix elements <|S(mn)|(2)>, the conductance probability distribution w(T), the average conductance , the shot noise power P, and the elastic enhancement factor F by varying α from small (α→0) to large (α→1) values. We also show that all these quantities are invariant for fixed ξ=αN. Moreover, we proposes a heuristic and universal relation between <|S(mn)|(2)>, , and P and the disorder parameter ξ.

[Decompression retinopathy after intraocular surgery]. / Retinopatía por descompresión después de cirugía intraocular.

OBJECTIVE: To report 10 instances of decompression retinopathy (DCR) developing after intraocular surgery. METHODS: This was a case series of 9 patients (10 eyes). Decompression retinopathy occurred after trabeculectomy (4 eyes), phacomulsification (3 eyes), Ahmed valve placement (1 eye), silicone oil removal (1 eye) and vitrectomy (1 eye). Fundus evaluation and fluorescein angiography were performed in all instances. RESULTS: Superficial, subhyaloidal, and deep retinal hemorrhages were noted in the posterior pole and peripheral retina; some of these had a white center. Nine (90%) of 10 eyes had a previous diagnosis of glaucoma, 6 having primary open-angle glaucoma, 2 neovascular glaucoma and 1 secondary glaucoma associated with intravitreal silicone oil. The patient without glaucoma had a history of cataract surgery and a vitrectomy to close a macular hole. The mean preoperative intraocular pressure (IOP) was 36.6 mm Hg (range: 15 to 58 mm Hg) despite maximal medical therapy in those patients with glaucoma. Fluorescein angiography demonstrated hypofluorescence throughout the study associated with superficial, and deep retinal hemorrhages. On the first post-operative day, visual acuity (VA) decreased more than 2 ETDRS lines in all cases. A pars plana vitrectomy (PPV) was performed in 5 eyes. All patients improved more than 2 ETDRS lines at a mean of 9 months after DCR. CONCLUSIONS: A gradual decrease of IOP pre-operatively and intra-operatively is recommended in order to avoid this complication. Early vitrectomy represents a useful treatment in many cases. A previous history of glaucoma seems to be an important risk factor for the development of DCR.

High-dose (5000-microg) intravitreal ganciclovir combined with highly active antiretroviral therapy for cytomegalovirus retinitis in HIV-infected patients in Venezuela.

PURPOSE: To describe the use of high doses of intravitreal ganciclovir combined with highly active antiretroviral therapy (HAART) for the treatment of cytomegalovirus (CMV) retinitis in human immunodeficiency virus (HIV)-infected patients. METHODS: Thirteen HIV-infected patients (18 eyes) with active CMV retinitis (83.3% in zone 1 and 38.4% resistant) participated in this prospective interventional case series. Patients were treated with high dose intravitreal ganciclovir (5.0 mg/0.1 mL once a week) in combination with HAART therapy. Intravitreal injections were discontinued once CMV retinitis healed if there was a significant increase in CD4+ count (any increase of > or 50 cells/microL to levels over 100 cells/microL sustained for at least 3 months). Mean follow-up was 15.6 months. Main outcome measures included assessment of visual acuity and retinal inflammation (CMV retinitis activity). A matched historical control group of 20 eyes (15 patients) with CMV retinitis treated with systemic ganciclovir (intravenous [induction] and oral [maintenance]) was included. RESULTS: Complete regression of the retinitis was obtained with high doses of intravitreal ganciclovir in 88.8% of eyes (two patients died during follow-up) at a mean of 4.5 weeks (2 to 8 weeks). Visual acuity improved two or more lines in 61.1% of eyes. No ganciclovir retinal toxicity was identified. Three eyes presented CMV retinitis reactivation at a mean of 25.6 days after their last injection. Complications (33.3%) included retinal detachment (RD; 3 eyes), immune recovery uveitis (IRU; 2 eyes), and endophthalmitis (1 eye). In our control group complete regression of the retinitis was obtained in 100% of eyes at a mean of 4 weeks (3 to 7 weeks). However, 12 eyes (60%) presented with CMV retinitis relapse at a mean of 29 days (21 to 32 days) after initiating oral ganciclovir (maintenance). Complications included RD (7 eyes, 35%) and IRU (3 eyes, 15%). Severe neutropenia occurred in 2 patients (13%). CONCLUSIONS: High doses of intravitreal ganciclovir (5.0 mg) once a week in combination with HAART therapy is effective to control CMV retinitis, and may be discontinued after CMV retinitis has healed if immune reconstitution with a significant increase in CD4+ count has occurred.