Progression of nuclear sclerosis based on changes in refractive values after lens-sparing vitrectomy in proliferative diabetic retinopathy.

BACKGROUND: Nuclear sclerosis (NS) based on the Emery-Little classification and refractive values after lens-sparing vitrectomy was compared between proliferative diabetic retinopathy (DR) patients and nondiabetic patients. METHODS: Progression of NS based on the Emery-Little classification and changes in refractive values were compared between 13 proliferative DR patients (14 eyes, DR group) and 14 nondiabetic patients (14 eyes, non-DR group) who underwent lens-sparing vitrectomy. All patients revealed grade I NS based on the Emery-Little classification. Mean patient age and refractive value just after surgery were 56.07 years and -0.33 diopters (D) in the DR group, and 57.06 years and -0.96 D in the non-DR group. RESULTS: The Emery-Little classification in the DR group at 6 and 24 months postoperative were grade I (13 eyes)/grade II (one eye) and grade I (eleven eyes)/grade II (three eyes), respectively. Mean refractive values in the DR group at 6, 12, and 24 months postoperative were +0.28 D, +0.27 D, and +0.37 D, respectively. The Emery-Little classification in the non-DR group at 6 and 24 months (or preoperative for patients undergoing cataract surgery) were grade I (five eyes)/grade II (eight eyes) and grade I (zero eyes)/grade II (eight eyes)/grade III (five eyes), respectively. The mean refractive value in the non-DR group at 6 months postoperative was -3.20 D. All eyes exhibited myopic changes and progression of NS. CONCLUSION: The findings of this study show that the progression of NS postvitrectomy is mild, even for DR patients 50 years of age or older, thus suggesting the need to reconsider the indications for simultaneous cataract surgery with vitrectomy.

[Case of unilateral impairment of short-wavelength sensitive cone with sudden onset].

BACKGROUND: Compare to either the middle or the long cones, short cones (S-cone) are easily damaged. CASE: A 62 year-old men complained of acute tritan OS. The corrected visual acuity was 1.2 OU. Routine ocular examinations showed no remarkable abnormalities, but we detected impaired responses using S-cone ERG and blue-on-yellow perimetry OS. We diagnosed this case as acute damage of the blue cone. CONCLUSION: S-cone damage can be determined by electro-physiological and psychophysical examinations in cases of unilateral color abnormality.

Diabetes-induced inhibition of voltage-dependent calcium channels in the retinal microvasculature: role of spermine.

PURPOSE: Although decentralized control of blood flow is particularly important in the retina, knowledge of the functional organization of the retinal microvasculature is limited. Here, the authors characterized the distribution and regulation of L-type voltage-dependent calcium channels (VDCCs) within the most decentralized operational complex of the retinal vasculature--the feeder vessel/capillary unit--which consists of a capillary network plus the vessel linking it with a myocyte-encircled arteriole. METHODS: Perforated-patch recordings, calcium-imaging, and time-lapse photography were used to assess VDCC-dependent changes in ionic currents, intracellular calcium, abluminal cell contractility, and lumen diameter, in microvascular complexes freshly isolated from the rat retina. RESULTS: Topographical heterogeneity was found in the distribution of functional VDCCs; VDCC activity was markedly greater in feeder vessels than in capillaries. Experiments showed that this topographical distribution occurs, in large part, because of the inhibition of capillary VDCCs by a mechanism dependent on the endogenous polyamine spermine. An operational consequence of functional VDCCs predominantly located in the feeder vessels is that voltage-driven vasomotor responses are generated chiefly in this portion of the feeder vessel/capillary unit. However, early in the course of diabetes, this ability to generate voltage-driven vasomotor responses becomes profoundly impaired because of the inhibition of feeder vessel VDCCs by a spermine-dependent mechanism. CONCLUSIONS: The regulation of VDCCs by endogenous spermine not only plays a critical role in establishing the physiological organization of the feeder vessel/capillary unit, but also may contribute to dysfunction of this decentralized operational unit in the diabetic retina.

High infusion pressure in conjunction with vitreous surgery alters the morphology and function of the retina of rabbits.

PURPOSE: To investigate the effects of high infusion pressure in conjunction with pars plana vitrectomy (PPV) on retinal morphology and function in rabbits. METHODS: Pars plana vitrectomy was performed under urethane (0.8 mg/kg) anaesthesia in the right eye of albino rabbits following phacoemulsification and aspiration (PEA). The left eyes were not touched. After PEA, the animals were divided into two groups. In six eyes, intraocular pressure (IOP) was increased to 80 mmHg for 30 mins (high-pressure group) and in five eyes IOP was maintained at 40 mmHg for 30 mins (low-pressure group). The IOPs were regulated by the height of the bottle of balanced salt solution (BSS) and monitored with a pressure transducer. After the pressure elevation, vitreous fluid was collected to measure the glutamate concentration. Then, PPV was performed for 15 mins in both groups under an infusion pressure of 40 mmHg. In five additional rabbits, PEA alone was performed in the right eye, and vitreous fluid was collected (PEA group). Functional alterations were assessed by recording visual evoked potentials (VEPs) and electroretinograms (ERGs). Ten days after the IOP changes, the animals were killed with intravenous pentobarbital sodium and the eyes were prepared for histological analysis. Damage to retinal ganglion cells (RGCs) was quantified by counting the number of cells in the ganglion cell layer (GCL). The contralateral eyes in the high-pressure group served as controls (n = 6). RESULTS: The mean implicit time (IT) of the VEPs in the high-pressure group was significantly longer than that before the IOP elevation, by 114-124% (p < 0.05, paired t-test), and also than that of control eyes (p < 0.05, anova followed by t-test). No significant changes in the VEPs were detected in either the low-pressure group or the PEA group. There were significantly fewer cells in the GCL in the high-pressure group (24.7/mm) than in the control animals (41.4/mm; p < 0.05, Dunnett's test). The number of cells in the GCL in the low-pressure and PEA groups did not significantly differ to that in the controls. The amplitudes of the ERG a- and b-waves were not significantly changed (p > 0.05, paired t-test). CONCLUSIONS: These results suggest that high infusion pressure in conjunction with PPV leads to morphological and functional changes in the retina. The absence of ERG changes and presence of VEP changes suggest that these changes were due to damage to RGCs, which supports the morphological observations.

Senior-loken syndrome complicated with severe coats disease-like exudative retinopathy.

BACKGROUND: Senior-Loken syndrome is a rare disorder that combines juvenile nephronophthisis with retinitis pigmentosa. METHODS: Case report. RESULTS: A 9-year-old Japanese girl diagnosed with Senior-Loken syndrome subsequently developed severe Coats disease-like exudative retinopathy. Although retinal coagulation, pars plana lensectomy, and vitrectomy were performed, she lost light perception in both eyes. CONCLUSION: Faulty vascular morphogenesis and its dysfunction might contribute to the development of Coats disease-like exudative retinopathy in Senior-Loken syndrome.

Characterization of heme-regulated eIF2alpha kinase: roles of the N-terminal domain in the oligomeric state, heme binding, catalysis, and inhibition.

Heme-regulated eIF2alpha kinase [heme-regulated inhibitor (HRI)] plays a critical role in the regulation of protein synthesis by heme iron. The kinase active site is located in the C-terminal domain, whereas the N-terminal domain is suggested to regulate catalysis in response to heme binding. Here, we found that the rate of dissociation for Fe(III)-protoporphyrin IX was much higher for full-length HRI (1.5 x 10(-)(3) s(-)(1)) than for myoglobin (8.4 x 10(-)(7) s(-)(1)) or the alpha-subunit of hemoglobin (7.1 x 10(-)(6) s(-)(1)), demonstrating the heme-sensing character of HRI. Because the role of the N-terminal domain in the structure and catalysis of HRI has not been clear, we generated N-terminal truncated mutants of HRI and examined their oligomeric state, heme binding, axial ligands, substrate interactions, and inhibition by heme derivatives. Multiangle light scattering indicated that the full-length enzyme is a hexamer, whereas truncated mutants (truncations of residues 1-127 and 1-145) are mainly trimers. In addition, we found that one molecule of heme is bound to the full-length and truncated mutant proteins. Optical absorption and electron spin resonance spectra suggested that Cys and water/OH(-) are the heme axial ligands in the N-terminal domain-truncated mutant complex. We also found that HRI has a moderate affinity for heme, allowing it to sense the heme concentration in the cell. Study of the kinetics showed that the HRI kinase reaction follows classical Michaelis-Menten kinetics with respect to ATP but sigmoidal kinetics and positive cooperativity between subunits with respect to the protein substrate (eIF2alpha). Removal of the N-terminal domain decreased this cooperativity between subunits and affected the other kinetic parameters including inhibition by Fe(III)-protoporphyrin IX, Fe(II)-protoporphyrin IX, and protoporphyrin IX. Finally, we found that HRI is inhibited by bilirubin at physiological/pathological levels (IC(50) = 20 microM). The roles of the N-terminal domain and the binding of heme in the structural and functional properties of HRI are discussed.

Electrotonic transmission within pericyte-containing retinal microvessels.

OBJECTIVE: Little is known about the electrotonic architecture of the pericyte-containing retinal microvasculature. Here, the authors focus on the cell-to-cell transmission of hyperpolarization, which can induce abluminal pericytes to relax and lumens to dilate. METHODS: With perforated-patch pipettes, the authors monitored the membrane potentials and ionic currents of pairs of pericytes located on freshly isolated rat retinal microvessels. Voltage changes were induced by administering electrical stimuli into pericytes, miniperfusing the KATP channel opener pinacidil, or using oxotremorine to activate chloride channels. RESULTS: Suggestive of extensive cell-to-cell communication, spontaneous voltage changes were strikingly similar in widely separated pericytes. In addition, injection of current into one of a pair of sampled pericytes always elicited a voltage response in the other sampled pericyte; the gap junction uncoupler, heptanol, blocked this transmission. In the dual recordings, hyperpolarization spreading from a current-injected pericyte decayed approximately 40% within 100 microm. In contrast, pinacidil-induced hyperpolarizations diminished by only approximately 2% in 100 microm. Depolarizations also appeared to spread with similar transmission efficacies. CONCLUSIONS: Based on the experiments, the authors propose that key features of the electrotonic architecture of retinal microvessels include highly efficient cell-to-cell communication within the endothelium and relatively inefficient transmission at pericyte/endothelial junctions. Thus, the endothelium is likely to provide an efficient pathway that functionally links contractile pericytes and thereby, serves to coordinate the vasomotor response of a retinal capillary.

Effects of angiotensin II on the pericyte-containing microvasculature of the rat retina.

The aim of this study was to identify the mechanisms by which angiotensin II alters the physiology of the pericyte-containing microvasculature of the retina. Despite evidence that this vasoactive signal regulates capillary perfusion by inducing abluminal pericytes to contract and thereby microvascular lumens to constrict, little is known about the events linking angiotensin exposure with pericyte contraction. Here, using microvessels freshly isolated from the adult rat retina, we monitored pericyte currents via perforated-patch pipettes, measured pericyte calcium levels with fura-2 and visualized pericyte contractions and lumen constrictions by time-lapse photography. We found that angiotensin activates nonspecific cation (NSC) and calcium-activated chloride channels; the opening of these channels induces a depolarization that is sufficient to activate the voltage-dependent calcium channels (VDCCs) expressed in the retinal microvasculature. Associated with these changes in ion channel activity, intracellular calcium levels rise, pericytes contract and microvascular lumens narrow. Our experiments revealed that an influx of calcium through the NSC channels is an essential step linking the activation of AT(1) angiotensin receptors with pericyte contraction. Although not required in order for angiotensin to induce pericytes to contract, calcium entry via VDCCs serves to enhance the contractile response of these cells. In addition to activating nonspecific cation, calcium-activated chloride and voltage-dependent calcium channels, angiotensin II also causes the functional uncoupling of pericytes from their microvascular neighbours. This inhibition of gap junction-mediated intercellular communication suggests a previously unappreciated complexity in the spatiotemporal dynamics of the microvascular response to angiotensin II.