Rescue of exposed scleral buckles with cadaveric pericardial patch grafts.

PURPOSE: To describe a new method for salvaging externally exposed silicone scleral exoplants (buckles) to avoid removal and the consequent risk of retinal redetachment. DESIGN: A retrospective, noncomparative, interventional case series. PARTICIPANTS: Four patients with exposed, clinically uninfected scleral buckles after initial surgery for the treatment of rhegmatogenous retinal detachment. INTERVENTION: Processed human donor pericardium patch grafts (Tutoplast; Innovative Ophthalmic Products, INC:, Costa Mesa, CA) were used to cover exposed areas of scleral buckles in concert with conjunctivoplasty. MAIN OUTCOME MEASURES: Scleral buckle preservation was the goal of this new treatment strategy. RESULTS: In four eyes treated with pericardial patch grafts to cover segments of exposed scleral buckles, three (75%) were managed successfully with one surgery. One eye (25%) had this treatment method fail and required scleral buckle removal. CONCLUSIONS: Processed human donor pericardium patch grafting is one useful way to avoid removing exposed scleral buckles, and consequently, sparing patients the risk of recurrent retinal detachment.

Niacin maculopathy.

Three patients with niacin-induced visual symptoms had cystoid maculopathy without leakage on fluorescein angiography, and a fourth patient with no fundus abnormality experienced cessation of visual symptoms upon discontinuation of niacin. All four patients had been taking high doses of niacin (3.0-4.5 g daily) before the onset of symptoms. An additional 15 asymptomatic patients who were receiving high doses of oral niacin (1.0-6.0 g daily) for the treatment of hypercholesterolemia were evaluated for evidence of subclinical macular disease. None of these patients had cystic or other significant macular changes. Niacin causes a reversible toxic cystoid maculopathy that occurs in approximately 0.67% of patients taking high doses of the drug. The authors conclude that among patients taking high doses of oral niacin only those who experience visual symptoms need to be ophthalmologically evaluated.

Maculopathy associated with combination chemotherapy and osmotic opening of the blood-brain barrier.

Eleven patients with intracranial malignant neoplasms underwent hyperosmotic opening of the blood-brain barrier by rapid mannitol infusion via the internal carotid or vertebral artery. Cyclophosphamide was administered intravenously preceding the mannitol infusion and methotrexate was infused after the mannitol via the same artery. Both the mannitol and methotrexate delivered via the carotid artery have direct access to the ipsilateral choroidal and retinal circulations. In these patients, retinal pigment epithelial changes eventually developed ipsilateral to the carotid infusions. The changes probably represent the toxicity of intraarterial methotrexate possibly potentiated by mannitol-induced opening of the blood-retinal barrier. Functional visual loss was minimal and was not a limiting factor with this therapeutic modality.

Ophthalmologic and systemic manifestations of Alström's disease.

Alström's syndrome consists of pigmentary retinopathy, diabetes, obesity, normal mental capacity, and sensorineural deafness. The early retinal findings are optic atrophy, salt-and-pepper pigment epithelial abnormalities, and marked vascular attenuation. Later in the disease process, diffuse areas of chorioretinal atrophy and large clumps of pigment develop. Severe visual loss in the first decade is characteristic and is an important point in the differential diagnosis. Clinically evident renal disease is a variable age-related phenomenon, and is probably the most frequent cause of death.

Abnormal glucose metabolism and parafoveal telangiectasia.

Parafoveal telangiectasia is a microvascular abnormality of the macula that may be developmental or acquired. Twenty-eight patients with this condition and normal fasting blood glucose levels underwent ophthalmologic evaluation and glucose tolerance testing. Bilateral telangiectasia was more frequently associated with laboratory evidence of abnormal glucose metabolism than unilateral disease (five of eight cases vs six of 17 cases). In five of our patients, results of glucose tolerance testing were consistent with diabetes even though fasting blood glucose levels were normal. Right-angle venules, which have been reported to be an important sign of bilateral disease, were also found in unilateral telangiectasia. Unilateral telangiectasia occurs in females as well as males. Glucose tolerance testing should be performed in all patients who have bilateral parafoveal telangiectasia.

The reduced nicotinamide adenine nucleotide-activated phosphoenolpyruvate carboxylase from Pseudomonas MA. Further studies on regulatory properties.

Phosphoenolpyruvate carboxylase from Pseudomonas MA grown on methylamine as a sole carbon source is an allosteric enzyme activated by NADH. Activation is accompanied by a change in the sedimentation value of the enzyme from 12 S to 9 S. In this paper ADP is shown to be an inhibitor of the enzyme. ADP has its most potent effect on the NADH-activated enzyme. Kinetics of ADP inhibition in the presence of NADH and of NADH activation in the presence of ADP are allosteric. The presence of ADP prevents the decrease in sedimentation value in the presence of NADH. Cross-linking studies indicate that the 12 S form of the enzyme is a tetramer of identically sized subunits and that the 9 S form corresponds to a dimer. The cross-linked enzyme is active and is activated by NADH and inhibited by ADP. It is proposed that NADH and ADP are a regulatory pair for this enzyme and reflect the energy status of the organism, allowing the carboxylase to control the flow of carbon into anabolic or catabolic pathways.

The reduced nicotinamide adenine dinucleotide-activated phosphoenolpyruvate carboxylase from Pseudomonas MA. Correlation of allosteric properties with changes in the sedimentation behavior.

Phosphoenolpyruvate carboxylase from Pseudomonas MA, grown on methylamine as a sole carbon source, has been studied with respect to some of its regulatory properties. The enzyme shows both negative and positive cooperativity with respect to the substrate phosphoenolpyruvate (Hill coefficients of 0.5 and 1.75). The enzyme requires a divalent cation for activity. Either magnesium or manganous ion is effective. While magnesium shows normal kinetics, manganous ion shows positive cooperativity with a Hill coefficient of 1.4. The enzyme is activated 50-fold by 0.2 mM NADH at 1 mM phosphoenolpyruvate. This activation is hysteretic, showing a lag of 2 to 3 min. Both NADH and Mn2+ induce a change in the sedimentation coefficient of the enzyme from 12.4 to 8.5 as measured by sucrose density gradient centrifugation. High concentrations of phosphate or sulfate are capable of producing this effect on sedimentation, but neither will activate more than 3-fold. Thus, if NADH is an indicator of the total energy level of the cell, the enzyme appears to be susceptible to control by factors which reflect this total energy level. The importance of this control with respect to hypothetical pathways of carbon utilization in the organism is discussed.