Homeostasis of the retinal micro-environment: I. Magnesium,potassium and calcium distributions in the avian eye

The concentrations of Mg²⁺, K⁺ and Ca²⁺ in the intraocular fluids (IOFs) and blood plasma of chickens and pigeons were determined by atomic absorption spectrophotometry. The Mg²⁺ concentration in the IOFs of both species was greatest in the liquid vitreous adjacent to the retina followed by aqueous > blood plasma > plasma dialysate. In contrast the concentration of K⁺ in the IOFs of both chickens and pigeons was greater in the aqueous than in the liquid vitreous. The concentrations of Ca²⁺ in all IOF compartments of chicken eyes were virtually identical and were lower than that of blood plasma. The concentrations of Mg²⁺ in the IOFs of the chicken, especially in the liquid vitreous, was remarkably stable; experimentally lowering or raising the plasma Mg²⁺ concentration over a relatively wide range had little or no effect on the Mg²⁺ concentration in the IOFs of these animals. We can conclude that a high Mg²⁺ and low K⁺ concentration in the extracellular fluids of the retina is maintained in the avian eye, as in the mammalian eye, by active transport processes across the blood-retinal barrier systems. Because the avian retina is completely avascular, the site of these homeostatic transport processes must be the epithelium of the retinal choroid and/or the pecten. These findings support the concept that the contribution of the vitreous to the homeostasis of the retinal micro-environment is inversely related in vertebrates to the degree of retinal vascularization.     

Vergleich der Durchmesserreaktion retinaler Arterien und Venen auf Flickerlicht

ZusammenfassungZiel In dieser Studie soll die durch Flickerlicht verursachte Durchmesserreaktion retinaler Arterien und Venen hinsichtlich Ausmaß und zeitlichem Ablauf verglichen werden.Methoden In die klinische Studie wurden 26 gesunde Probanden einbezogen. Der Durchmesser der retinalen Gefäße jeweils eines Auges wurde kontinuierlich mittels eines Retinal vessel analyzer gemessen. Jede Untersuchung bestand aus 100 s Baseline sowie 5 Perioden von 20 s Flickerlichtstimulation, gefolgt von 80 s Beobachtung.Ergebnisse Unmittelbar nach Flickerlicht dilatierten die Arterien um 6,9±2,8% (MW±STD) und die Venen um 6,5±2,8% (Unterschied nicht signifikant). Der Quotient aus arterieller und venöser Dilatation (AVDQ) betrug 1,25±0,69 (Spannweite 0,2 bis 2,8). Es konnte keine signifikante Altersabhängigkeit der arteriellen bzw. venösen Dilatation oder des AVDQ nachgewiesen werden. Die arterielle Dilatation ging nach 25,9±10,8 s in eine leichte Konstriktion von –2,7±1,4% über. Im Gegensatz dazu waren die Venen zum Zeitpunkt des individuellen Konstriktionsmaximums noch um 0,5±1,3% dilatiert (p<0,001).Schlussfolgerungen Die flickerlichtinduzierte Durchmesserreaktion retinaler Arterien und Venen unterscheidet sich bei Gesunden nicht in ihrem mittleren dilatativen Maximum, aber in Form und zeitlichem Verlauf des Abklingens der Dilatation.Unterstützung durch: BMBF 13N7999.Vortrag gehalten auf der 101. Jahrestagung der DOG, Berlin, September 2003.     

Acute Multifocal Placoid Pigment Epitheliopathy Associated with Cavernous Sinus Thrombosis

Acute multifocal placoid pigment epitheliopathy (AMPPE) has been associated with disease of the central nervous system. In this case report, we discuss a patient presenting with AMPPE in the setting of a new central nervous system association: cavernous sinus thrombosis.     

Dual nonlinearities regulate contrast sensitivity in pattern discrimination tasks

Many current psychophysical models propose that visual processing in cortex is hierarchical, with nonlinearities sandwiched between linear stages of processing. In earlier publications, we proposed a model of this type to account for masking effects found with spatial frequency and orientation discriminations. Our model includes two nonlinear mechanisms that regulate contrast sensitivity in early cortical mechanisms. The first is a local within-pathway nonlinearity that accelerates at low contrasts but is compressive at high. The second is a pooled nonlinear gain control process that operates over a broad range of neurons with different tuning characteristics. Here, we test predictions of the model for spatial frequency discriminations. The model predicts that at low contrasts, adding a grating mask oriented parallel to test gratings will improve discrimination performance via operation of the within-pathway nonlinearity, analogous to the "dipper effect" found with contrast discriminations. Adding an orthogonally oriented mask is predicted to have no effect at low contrasts, where pooled gain control processes contribute little to performance. At high contrasts, the model predicts that performance will asymptote and become independent of contrast with either parallel or orthogonal masks. The results confirm model predictions.     

Usher综合征患者血清离子浓度的变化

目的　探讨Usher综合征(Usher syndrome,USH)患者血清离子浓度的变化情况。方法　选取2015年9月至2018年9月北京同仁医院眼科中心的46例临床诊断为USH患者作为USH组；同时选取同期于北京同仁医院体检中心体检的90例正常人为对照组。检测各组受试者血清离子浓度。将USH组与对照组的各血清离子浓度进行比较。结果　USH组患者血清钙离子浓度为（2.364±0.101）mmol·L^-1，高于对照组的血清钙离子浓度（2.304±0.082）mmol·L^-1，差异有统计学意义（P=0.000）；USH组患者钾离子浓度为（4.124±0.360）mmol·L^-1，高于对照组的钾离子浓度（3.965±0.288）mmol·L^-1，差异有统计学意义(P=0.006)；两组间的钠离子、氯离子、无机磷离子浓度相比，差异均无统计学意义（均为P>0.05）。结论　USH患者的钙离子与钾离子浓度异常，这种异常可能与其发病有关。     

Serie de casos de afección ocular por dengue. Primeros casos publicados en Guatemala

Objective

Describe the ocular findings of a case series of 8 patients with a diagnosis of dengue.

Management Dilemmas of Atypical Ocular Toxoplasmosis Aided by Wide-Field Fluorescein Angiography

Purpose: To report an atypical presentation of ocular toxoplasmosis and to demonstrate the utility of wide-field angiography in delineating peripheral retinal pathology.

Methods: Case Report.

Results: A 17-year-old male presented with acute unilateral papillitis and retinochoroiditis. Laboratory testing supported reactivation of congenitally acquired Toxoplasma gondii infection. Wide-field fluorescein angiography showed extensive retinal vasculitis. The patient was treated with sulfamethoxazole/trimethoprim. Ocular inflammation resolved over a two-week period. There was no documented visual loss.

Conclusion: Wide-field fluorescein angiography details ocular pathology otherwise unnoticed on traditional posterior pole fluorescein angiography. Documentation of extensive vasculitis associated with ocular toxoplasmosis can assist with management decisions.     

The rates of photodestruction of tryptophan residues in human and bovine ocular lens proteins

The relative rates of photodestruction of tryptophan residues in α-, β-, and γ-crystallin fractions from both human and bovine lenses have been measured. The destruction of tryptophan was monitored by observing loss of tryptophan fluorescence, changes in the UV absorption spectra, and changes in the near-UV CD spectra. Photolysis experiments using monochromatic 290 nm radiation were performed on air-equilibrated and vacuum-degassed 1·0 mg/ml protein solutions at 25°C. Both neutral aqueous buffer solutions and the denaturing solvents 8m-urea and 5m-guanidine hydrochloride were used in the photolysis studies. The observed rates of destruction of tryptophan residues in all three human crystallins were the same. Denaturing the human crystallin fractions with urea or guanidine hydrochloride did not significantly alter the photolysis rates. The same photolysis rates, and the same lack of effect of denaturation, were also observed for the bovine proteins. Vacuum degassing the lens protein solutions, prior to UV irradiation, resulted in reduction in the photolysis rates by a factor of about one-half.     

Retinal ganglion cell neuroprotection in a rat model of glaucoma following brimonidine, latanoprost or combined treatments

The aim of the present study is to evaluate the neuroprotective effect of two antiglaucomatous substances, regardless of their hypotensive effect in the eye. Brimonidine, which does not reduce IOP when administered intraperitoneally, and latanoprost, which has a renowned hypotensive effect topically. We examined rat retinal ganglion cell (RGC) survival and size distribution in experimental glaucoma in response to different glaucomatous agents. IOP was elevated by episcleral vein cauterization (EVC) prior to the application of different treatments: (I) PBS application (control group), (II) intraperitoneal administration of brimonidine (a general hypotensive agent), (III) topical application of latanoprost (an ocular hypotensive agent), and (IV) latanoprost combined with brimonidine. After 12 weeks, RGCs were retrogradely labeled with fluorogold and RGC density was analyzed. EVC caused a significant increase (42%) in IOP in each group before drug treatment. After 12 weeks of EVC, RGC survival in control vs. EVC rats was 78.9 ± 3.2%. No IOP reduction was observed in brimonidine injected rats, but RGC survival at 12 weeks was total (103.7 ± 2.7%). In latanoprost treated rats, IOP dropped by around 22% and 94.7 ± 3.7% of the RGC population survived. Finally in the latanoprost + brimonidine combined group, IOP was significantly reduced by 25% and 94.4 ± 2.2% of RGCs survived. Surprisingly, whereas EVC led to a 6% increase in RGC soma size, brimonidine treatment was associated with a 9% reduction in the soma size of RGCs at 12 weeks. We conclude that brimonidine exerts a neuroprotective effect via a mechanism which is independent of IOP reduction. These findings indicate that cell survival in glaucoma may be enhanced by neuroprotective strategies which are independent of IOP reduction. No synergistic neuroprotective effect was observed when both treatments were applied simultaneously.     

调节性细胞死亡在糖尿病视网膜病变中的研究进展

调节性细胞死亡（RCD）是一种独特的细胞死亡方式,包括细胞凋亡等多种形式。RCD参与人类正常生理活动的诸多环节,更与多种疾病的发生发展密切相关。糖尿病视网膜病变（DR）是近年来发病率较高的一种致盲性眼病。研究表明,DR的发生与细胞凋亡、铁死亡、细胞焦亡、细胞自噬、依赖性细胞死亡等多种RCD的相关蛋白异常表达有关。本文将对DR发病过程中与RCD相关的机制作一综述,以期为DR的靶向治疗提供思路。     

MNU诱导视网膜外层退行变性的细胞电生理和超微结构特征

目的：观察N-甲基-N-亚硝基脲（MNU）诱导的小鼠视网膜外层变性损伤的细胞电生理特征和超微结构变化。方法：实验研究。通过腹腔注射PBS和MNU,将C57/BL小鼠60 只随机分为对照组和MNU造模组。运用膜片钳电生理技术,观察位于外丛状层的双极细胞的电生理活动。用透射电子显微镜观察视网膜的超微结构。结果：膜片钳结果显示,给MNU后7 d,ON型双极细胞（ON-BC）对药物氨基（环丙基）（ 4-膦酰苯基）乙酸电生理反应完全消失,而OFF型双极细胞（OFF-BC）对药物α-氨基-3-羟基-5-甲基-4-异恶唑丙酸的刺激仍有电生理反应。给MNU后2 d,位于光感受器细胞外节（OS）的盘膜结构变薄。给MNU后5 d,OS消失,位于光感受器细胞内节（IS）的线粒体等细胞器严重肿胀。给MNU后10 d,IOS消失,光感受器细胞的核层变薄,核呈不同程度的浓染。下游的双极细胞核周间隙增宽,在双极细胞胞浆中有大量的自噬体。结论：MNU对ON型信号通路的损伤,比对OFF型信号通路的损伤要严重一些。MNU导致的视网膜损伤主要位于外侧（包括外核层和外丛状层）。MNU致光感受器细胞损伤的机制是凋亡。