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Biomedical subjects

G C Brown

Publications and source records attributed to G C Brown.

At least 145 records · Page 8Linked to original sources
PubMed1993

Surgical management of complications associated with X-linked retinoschisis.

OBJECTIVE: To evaluate the role of surgical intervention in cases with severe, vision-threatening complications of X-linked retinoschisis. DESIGN: A retrospective survey of consecutive patients with X-linked retinoschisis who underwent surgery at our institution during a 16-year period. SETTING: A tertiary-care eye hospital. PATIENTS: Six eyes of four patients were identified. The mean age of the patients at the time of the first surgical procedure was 4.9 years (range, 18 months to 9 years). INTERVENTION: Scleral buckling procedure or pars plana vitrectomy. MAIN OUTCOME MEASURE: Surgical indications and long-term anatomic and visual outcome. RESULTS: Patients were initially operated on for rhegmatogenous retinal detachment (three eyes), exudative retinal detachment (one eye), and vitreous hemorrhage (two eyes). The surgical approach was scleral buckling for retinal detachment and vitrectomy for vitreous hemorrhage or proliferative vitreoretinopathy. Anatomic success and ambulatory vision (20/400 or better) was achieved in five of the six eyes with a mean follow-up of 3.8 years (range, 1 to 6 1/2 years). An average of 1.8 procedures per eye were performed. Two of the four eyes approached by primary scleral buckling eventually required vitrectomy. Proliferative vitreoretinopathy with retinal detachment was the major reason for reoperation. CONCLUSIONS: Surgery for X-linked retinoschisis-associated retinal detachment and vitreous hemorrhage can yield favorable anatomic and functional results. Multiple operations and the use of advanced vitreoretinal techniques to manage proliferative vitreoretinopathy-related complications, however, were necessary for ultimate success in certain cases.

Child↗
PubMed1993

Combined central retinal artery-central vein obstruction.

The cases of 23 patients with unilateral combined central retinal artery-central retinal vein obstruction are described. Criteria for the abnormality included: a history of relatively sudden visual loss; superficial retinal whitening in the posterior pole in combination with a cherry spot; and intraretinal blood, generally associated with dilated and/or tortuous retinal veins. In five instances (22%) the obstructions developed after retrobulbar injection. Among the 21 patients with followup for at least 6 months, or until the onset of neovascularization of the iris, 17 (81%) developed rubeosis iridis. Late histopathology was obtained in two eyes. Hemorrhagic necrosis of the retina was observed in some areas of the posterior pole and attenuation of the inner retinal layers, similar to that seen with late central retinal artery obstruction, was noted elsewhere. Periphlebitis of the central retinal vein within the optic nerve was found in each case.

Adult↗
PubMed1993

Behavioral toxicity of anticholinesterases in primates: chronic physostigmine and soman interactions.

Dose rates for continuous infusion of physostigmine salicylate required to inhibit 30 and 60% of normal serum cholinesterase activity in rhesus monkeys were determined. The effects of continuous physostigmine infusion at these dose rates on the behavioral toxicity of daily repeated low-dose soman were determined not to be deleterious; in fact, they were slightly (and variably) protective.

Animals↗
PubMed1993

Successful scleral buckling procedures decrease central retinal artery blood flow velocity.

BACKGROUND: Limited data suggest that scleral buckling procedures may decrease posterior segment blood flow. How this may affect functional outcome remains unknown. METHODS: In a prospective, controlled study, color Doppler imaging was used to measure blood flow velocities in the central retinal and ophthalmic arteries of both eyes in patients with unilateral rhegmatogenous retinal detachments before and after primary scleral buckle repair. Encircling elements were used in all patients. Fellow eyes served as controls. RESULTS: Data from six consecutive patients did not show significant preoperative circulatory abnormalities in either artery compared with the controls. There was a statistically significant reduction in mean central retinal artery blood flow velocities of up to 53% in the immediate postoperative period. Ophthalmic artery blood flow velocities, however, did not significantly change after the procedure. Successful retinal reattachment with the expected visual improvement was achieved in all patients with this primary surgery. CONCLUSIONS: Scleral buckling procedures with encircling elements decrease blood flow velocities in the central retinal artery but leave the ophthalmic artery unaffected. Good anatomic and functional results still can be achieved despite these hemodynamic changes.

Adult↗
PubMed1993

Extracapsular cataract extraction with placement of a posterior chamber lens in patients with diabetic retinopathy.

PURPOSE: The authors evaluated factors that might influence the outcome of extracapsular cataract extraction with placement of a posterior chamber lens in patients with diabetic retinopathy. The factors included patient age and sex, severity of the retinopathy, preoperative laser photocoagulation, vitrectomy, and posterior capsulotomy. METHODS: The records of 109 patients who had been examined by the authors before cataract surgery were retrospectively reviewed. RESULTS: The final visual acuity in only 48% of the eyes was 20/40 or better, and 28% had 20/200 or worse visual acuity. Only 65% had an improvement in visual acuity of two or more Snellen lines. Eyes with preoperative macular edema had a poorer visual outcome than eyes without. Macular edema and ischemia accounted for 70% of the eyes with a final visual acuity of 20/50 or worse. The authors found that age was a strong predictor of final visual acuity and chances of improvement. In patients 63 years of age and younger, 58% had 20/40 or better and 81% had improved visual acuity. In patients 64 years of age and older, only 38% had 20/40 or better and only 54% were improved. Supplementary panretinal photocoagulation was required in 37% of patients who had received it preoperatively. Neovascularization of the iris developed in 6% of patients. Posterior capsulotomy did not cause an increased incidence of neovascularization of the iris or in the development or progression of proliferative retinopathy or macular edema. CONCLUSION: The prognosis of patients with diabetic retinopathy about to undergo cataract surgery, even extracapsular cataract extraction with placement of a posterior chamber lens, is guarded.

Adult↗
PubMed1993

Effect of indomethacin on cerebral oxidized cytochrome oxidase in preterm infants.

To determine the effect of i.v. indomethacin on cerebral intracellular oxygenation, as judged by changes in the concentration of oxidized cytochrome oxidase, studies were performed using near-infrared spectroscopy on 15 infants of 23 to 29 wk gestation, aged 8 to 30 d, who required the drug for closure of a patent ductus arteriosus. Indomethacin caused significant (p < 0.01) falls in cerebral blood flow, oxygen delivery, and blood volume and its reactivity to changes in arterial carbon dioxide tension, as previously reported. In 11 of the 15 infants, significant (p < 0.01) falls of 0.18 to 0.92 mumol.L-1 in the concentration of oxidized cytochrome oxidase were observed. Parallel experiments on synaptosomes derived from rat brain showed that indomethacin was most unlikely to have had a direct effect on mitochondrial respiration. These results are consistent with the hypothesis that the observed falls in the concentration of oxidized cytochrome oxidase resulted from hemodynamic perturbations that reduced cerebral intracellular oxygenation.

Animals↗
PubMed1992

Sudden retinal manifestations of intranasal cocaine and methamphetamine abuse.

We examined two patients who had sudden decrease in vision after intranasal cocaine or methamphetamine abuse. A 38-year-old woman with a history of systemic arterial hypertension developed a central retinal artery occlusion four hours after intranasal use of cocaine. A 26-year-old woman had blurred vision and intraretinal hemorrhages shortly after using methamphetamine nasally. The adrenomimetic response and sudden increase in blood pressure associated with the intranasal use of these drugs may have contributed to the retinal vascular manifestations observed in these patients.

Cocaine↗
PubMed1992

Control of respiration and ATP synthesis in mammalian mitochondria and cells.

We have seen that there is no simple answer to the question 'what controls respiration?' The answer varies with (a) the size of the system examined (mitochondria, cell or organ), (b) the conditions (rate of ATP use, level of hormonal stimulation), and (c) the particular organ examined. Of the various theories of control of respiration outlined in the introduction the ideas of Chance & Williams (1955, 1956) give the basic mechanism of how respiration is regulated. Increased ATP usage can cause increased respiration and ATP synthesis by mass action in all the main tissues. Superimposed on this basic mechanism is calcium control of matrix dehydrogenases (at least in heart and liver), and possibly also of the respiratory chain (at least in liver) and ATP synthase (at least in heart). In many tissues calcium also stimulates ATP usage directly; thus calcium may stimulate energy metabolism at (at least) four possible sites, the importance of each regulation varying with tissue. Regulation of multiple sites may occur (from a teleological point of view) because: (a) energy metabolism is branched and thus proportionate regulation of branches is required in order to maintain constant fluxes to branches (e.g. to proton leak or different ATP uses); and/or (b) control over fluxes is shared by a number of reactions, so that large increases in flux requires stimulation at multiple sites because each site has relatively little control. Control may be distributed throughout energy metabolism, possibly due to the necessity of minimizing cell protein levels (see Brown, 1991). The idea that energy metabolism is regulated by energy charge (as proposed by Atkinson, 1968, 1977) is misleading in mammals. Neither mitochondrial ATP synthesis nor cellular ATP usage is a unique function of energy charge as AMP is not a significant regulator (see for example Erecinska et al., 1977). The near-equilibrium hypothesis of Klingenberg (1961) and Erecinska & Wilson (1982) is partially correct in that oxidative phosphorylation is often close to equilibrium (apart from cytochrome oxidase) and as a consequence respiration and ATP synthesis are mainly regulated by (a) the phosphorylation potential, and (b) the NADH/NAD+ ratio. However, oxidative phosphorylation is not always close to equilibrium, at least in isolated mitochondria, and relative proximity to equilibrium does not prevent the respiratory chain, the proton leak, the ATP synthase and ANC having significant control over the fluxes. Thus in some conditions respiration rate correlates better with [ADP] than with phosphorylation potential, and may be relatively insensitive to mitochondrial NADH/NAD+ ratio.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphate↗
PubMed1992

Reoperation following diabetic vitrectomy.

A review of 484 consecutive eyes that were undergoing an initial pars plana vitrectomy for the sequelae of proliferative diabetic retinopathy disclosed that 41 eyes (8.5%) required one or more additional vitrectomy operations. The primary causes for reoperation included rhegmatogenous retinal detachment in 18 (44%) of the 41 eyes, recurrent vitreous hemorrhage in 21 eyes (51%), and glaucoma in two eyes (5%). The visual prognosis was worse in the group with rhegmatogenous retinal detachment, with 10 (56%) of 18 eyes progressing to no light perception (P = .003). Severe preretinal and subretinal fibrous proliferation, as demonstrated histopathologically, accounted in large part for the poor result. The preretinal membrane formation appeared to occur secondary to a combination of diabetic extraretinal vascular growth and proliferative vitreoretinopathy. Among the total group of 41 eyes that required subsequent surgery, the retina eventually remained detached in 18 eyes (44%), and phthisis bulbi occurred in 13 eyes (32%). Rubeosis iridis developed in 17 (94%) of 18 eyes in which the retina remained detached.

Adult↗
PubMed1992

Visual symptoms associated with choroidal neovascularization. Photopsias and the Charles Bonnet syndrome.

One hundred consecutive patients with macular choroidal neovascularization were studied in a cross-sectional fashion. Evidence of bilateral choroidal neovascularization was present in 31 patients. Among the 100 subjects, 59% related a history of seeing flickering or flashing lights (photopsias) in the affected eye or eyes. The colors varied, but in 59% of instances the lights were white. Twelve subjects experienced formed hallucinations (Charles Bonnet syndrome); in nine (75%) of these patients, the sequelae of choroidal neovascularization were bilateral. Symptoms that are commonly attributed to vitreoretinal tractional phenomena as well as neurologic and/or psychiatric disease are also frequently encountered in patients with macular degeneration associated with choroidal neovascularization.

Adult↗
PubMed1992

Diode laser photocoagulation for retinopathy of prematurity. Preliminary results.

In a prospective, randomized clinical trial comparing transscleral cryotherapy with laser photocoagulation in the treatment of "threshold" stage 3+ retinopathy of prematurity, 32 infants were treated with diode laser photocoagulation in one eye. Twenty-eight infants have been followed up for at least 3 months, and seven have been followed up for at least 1 year. Twenty-five of 28 eyes treated with diode laser photocoagulation and followed up for at least 3 months have undergone regression. Of 24 fellow eyes treated with cryotherapy and followed up for at least 3 months, 20 have undergone regression. All seven eyes treated with diode laser photocoagulation and followed up for at least 1 year have undergone regression. Of seven fellow eyes treated with cryotherapy and followed up for at least 1 year, all have undergone regression. Our results suggest that diode laser photocoagulation is as effective as cryotherapy in the treatment of retinopathy of prematurity.

Cryosurgery↗
PubMed1992

Color Doppler imaging of the ocular ischemic syndrome.

PURPOSE: This study describes hemodynamic characteristics of the ophthalmic, central retinal, and posterior ciliary arteries in 16 eyes of 11 patients with the ocular ischemic syndrome. Understanding the hemodynamic characteristics of the retrobulbar circulation may elucidate the natural history and pathophysiology of the ocular ischemic syndrome and perhaps form the basis for rational treatment of this condition. METHODS: Color Doppler imaging, a procedure that permits rapid noninvasive imaging of the ophthalmic, central retinal, and posterior ciliary arteries, was used to quantitate peak systolic blood flow velocities and vascular resistance (pulsatility index) within these vessels in study group eyes and in an age-matched control population. RESULTS: We demonstrated markedly reduced ocular ischemic syndrome central retinal and posterior ciliary artery peak systolic velocities compared with control group eyes. Central retinal and posterior ciliary artery vascular resistance (pulsatility index) was greater in ocular ischemic eyes versus control group eyes. Reversal of ophthalmic artery blood flow was detected in 12 of 16 ocular ischemic syndrome eyes. Study group eyes with poor vision had no detectable posterior ciliary arterial blood flow. CONCLUSION: Color Doppler imaging quantitates hemodynamic characteristics of the retrobulbar circulation in the ocular ischemic syndrome. There is markedly reduced peak systolic velocity and increased vascular resistance in ocular end arteries such as the central retinal and posterior ciliary arteries. Ophthalmic artery reversal of flow seems to represent collateral blood flow to lower resistance vascular beds. Posterior ciliary artery hypoperfusion may correlate with poor vision in the ocular ischemic syndrome.

Aged↗
PubMed1992

Pseudophakic retinal detachments. Anatomic and visual results.

Retinal reattachment rates and visual results were analyzed in 227 consecutive primary pseudophakic rhegmatogenous retinal detachments. The overall anatomic reattachment rate was 90%, with no significant difference between the anterior chamber (AC) and posterior chamber intraocular lens groups. Visual results were significantly worse in the AC lens group (P less than 0.05). Negative prognostic indicators for reattachment included age greater than 65 years, poorer preoperative vision, larger extent of the retinal detachment, inability to identify a retinal break, longer duration of symptoms before presentation, and grades C or D proliferative vitreoretinopathy (P less than 0.05). In addition to the above factors, eyes with AC reaction, AC lenses, and macular detachment had a poorer visual prognosis.

Adult↗
PubMed1992

The leaks and slips of bioenergetic membranes.

Bioenergetic membranes use proton gradients to transduce energy. However, when the proton gradient is large 1) there is a passive leak of protons (and other ions) across these membranes, and 2) some proton pumps may fail to pump protons (a phenomenon known as slip). Leaks and slips may be an unavoidable consequence of membrane structure and cause significant wastage of free energy, but they may also have functional roles beneficial to the organism.

Animals↗
PubMed1992

Distribution of the posterior ciliary arteries revealed after vascular occlusions. A case report.

Recognized posterior ciliary artery occlusion combined with central retinal artery occlusion is relatively uncommon. Clinical and experimental evidence of combined occlusions appear to support a nasal and temporal distribution for the posterior ciliary arteries in most cases. A case involving a patient in whom the posterior ciliary arteries divided superiorly and inferiorly to supply the region of the macula is reported. Some of the more common variations in the distribution of the posterior ciliary arteries are discussed. Clinicians should be aware that the territorial divisions of the choroidal perfusion in the macula may be horizontally based.

Arterial Occlusive Diseases↗
PubMed1992

Purtscher's retinopathy preceding acute pancreatitis.

A patient with a long history of alcohol abuse had diminished vision. The clinical and angiographic findings were consistent with Purtscher's retinopathy. Subsequently, the patient was hospitalized for acute pancreatitis. To our knowledge, this is the first reported case of pancreatic retinopathy preceding the systemic findings of acute pancreatitis.

Acute Disease↗