Search PubMed⌕ Search

Biomedical subjects

H Lewis

Publications and source records attributed to H Lewis.

At least 55 records · Page 3Linked to original sources
PubMed1999

Macular translocation for subfoveal choroidal neovascularization in age-related macular degeneration: a prospective study.

PURPOSE: To conduct a prospective study of macular translocation in patients with subfoveal choroidal neovascularization secondary to age-related macular degeneration. METHODS: In 10 eyes of 10 patients with subfoveal choroidal neovascularization and best-corrected visual acuity ranging from 20/50 to 20/800 (median, 20/111), the fovea was relocated by means of scleral imbrication, intentional retinal detachment with small posterior retinotomies, and partial fluid-air exchange. In two eyes, the choroidal neovascular membranes were removed at the time of macular translocation; in seven eyes they were photocoagulated in the postoperative period; and in one eye the membrane was removed during reoperation to unfold a macular fold. RESULTS: All 10 eyes were followed up for 6 months. The median postoperative foveal displacement was 1286 microm (range, 114 to 1,919 microm). In three eyes (30%), a foveal fold formed postoperatively requiring reoperation, with one of these eyes requiring a second reoperation for a rhegmatogenous retinal detachment. Best-corrected visual acuity improved in four eyes (median, 10.5 letters) and decreased in six eyes (median, 14.5 letters). The median change in visual acuity was a decrease of 5 letters. The final best-corrected visual acuity was 20/80 in two eyes, 20/126 in one eye, 20/160 in four eyes, 20/200 in one eye, 20/250 in one eye, and 20/640 in one eye. CONCLUSIONS: Our initial experience with limited macular translocation suggests that this surgical technique is unpredictable. However, in patients with subfoveal choroidal neovascularization from age-related macular degeneration, it offers the potential for improving visual function and may be associated with less loss of vision than the disease itself, if allowed to progress. Further refinements in surgical indications and technique are needed to make this procedure safer, more predictable, and more beneficial.

Aged↗
PubMed1999

A study of the ability of tissue plasminogen activator to diffuse into the subretinal space after intravitreal injection in rabbits.

PURPOSE: Intravitreal injections of tissue plasminogen activator have been used to lyse fibrin from blood in the subretinal space, despite the lack of proof that tissue plasminogen activator can diffuse across the retina. We tested whether tissue plasminogen activator injected into the vitreous could penetrate the neural retina and enter the subretinal space. METHODS: We injected a mixture of 50 microg of tissue plasminogen activator (70 kD) labeled with fluorescein isothiocyanate and rhodamine B isothiocyanate-labeled dextran, which has a lower molecular weight (20 kD), into the midvitreous cavity of one eye in each of 18 rabbits. The eyes were enucleated after 3, 6, and 24 hours, and cryosections were examined with epifluorescent microscopy to determine the distribution of the labeled molecules. We also evaluated tissue plasminogen activator pharmacokinetics in one eye each of 18 rabbits in which a subretinal clot was induced by injecting autologous blood (50 microL) into the subretinal space through the sclera. Fluorescein isothiocyanate-labeled tissue plasminogen activator was injected into the vitreous 2 days after induction of the subretinal clot. RESULTS: Fluorescein isothiocyanate-labeled tissue plasminogen activator was present at the vitreal surface of the retina in a linear array in all 36 eyes studied, whereas the rhodamine B isothiocyanate-labeled dextran had diffused throughout the neural retina in the same sections. No fluorescein isothiocyanate signal was observed in the neural retina or in the subretinal clot. Vitreous hemorrhage caused by retinal perforation was observed in all eyes with intraretinal hemorrhage in which fluorescein isothiocyanate fluorescence was seen in the neural retina and inside the clot. CONCLUSION: Intravitreal tissue plasminogen activator did not diffuse through the intact neural retina to reach a subretinal clot. This study demonstrates no scientific rationale for the intravitreal tissue plasminogen activator treatment of submacular hemorrhage without vitreous hemorrhage presumably caused by an overlying retinal break.

Animals↗
PubMed1999

Surgical management of subfoveal neovascularization in children.

OBJECTIVE: To report the authors' clinical experience with submacular surgery for subfoveal membranes in children and to evaluate the histopathologic findings of membranes in children with various etiologies of choroidal neovascularization. DESIGN: Retrospective, noncomparative, interventional case series. PARTICIPANTS: Twelve eyes of 12 consecutive children with subfoveal choroidal neovascularization treated by vitrectomy and excision of the choroidal neovascular complex. INTERVENTION: Vitrectomy, excision of the choroidal neovascular complex, and air-fluid exchange. MAIN OUTCOME MEASURES: Visual acuity and recurrence of choroidal neovascular membrane. RESULTS: Preoperative visual acuities ranged from 20/60 to 20/800 (median, 20/300). Postoperative visual acuities ranged from 20/25 to 20/400 (median, 20/80) after an average follow-up of 20 months (range, 7-62 months). Ten of 12 eyes improved from immediate preoperative visual acuity, and four eyes developed recurrence of neovascular membranes over a mean follow-up of 18 months. Histopathologic examination of six excised membranes showed that the most common components of the membranes were retinal pigment epithelium, fibrocytes, vascular endothelium, and collagen. CONCLUSION: Selected eyes of children with subfoveal neovascular membranes and no evidence of membrane regression may benefit from submacular surgery. The histopathologic findings were similar to adult choroidal neovascularization not associated with age-related macular degeneration.

Adolescent↗
PubMed1999

Kupffer cell blockade, tumour necrosis factor secretion and survival following endotoxin challenge in experimental biliary obstruction.

BACKGROUND: Gram-negative sepsis and its sequelae frequently complicate invasive procedures in patients with obstructive jaundice. In response to endotoxin, Kupffer cells secrete tumour necrosis factor (TNF), a pivotal early mediator of sepsis. An investigation was carried out into the specific role of Kupffer cell TNF secretion following endotoxin challenge in obstructive jaundice. METHODS: Survival following intraperitoneal administration of endotoxin (2.0, 0.02 and 0.0002 mg per 100 g) was determined in rats following bile duct ligation (BDL) or sham operation. Plasma TNF concentration was quantified following endotoxin administration (0.0002 mg per 100 g) at 1, 2 and 6 h. Subsequently, the effect of Kupffer cell blockade by gadolinium chloride on survival and plasma TNF concentration was assessed. RESULTS: Jaundiced animals showed a significantly increased mortality rate following intraperitoneal injection of endotoxin 2.0 mg per 100 g (BDL 100 per cent versus sham 0 per cent) and 0.02 mg per 100 g (BDL 70 per cent versus sham 0 per cent; P = 0. 002, Fisher's exact test). Median plasma TNF concentration was significantly greater in jaundiced animals 1 h after endotoxin administration (BDL 943 (interquartile range (i.q.r.) 211-3900) pg/ml versus sham 64 (i.q.r. 47-127) pg/ml; P = 0.002, Mann-Whitney U test). Kupffer cell blockade with gadolinium chloride increased the survival rate following endotoxin administration in BDL animals (BDL-GdCl3 100 per cent versus BDL-saline 40 per cent; P = 0.0003, Fisher's exact test) and decreased median plasma levels of TNF (BDL-GdCl3 88 (i.q.r. 0-1065) pg/ml versus BDL-saline 16 550 (1255-29 360) pg/ml; P = 0.002, Mann-Whitney U test). CONCLUSION: Kupffer cell blockade improved survival and suppressed systemic TNF activity after endotoxin challenge. In obstructive jaundice, hypersecretion of TNF by Kupffer cells may supplement systemic cytokine production and be responsible for significant complications.

Animals↗
PubMed1999

Subclinical depletion of primordial follicular reserve in mice treated with cyclophosphamide: clinical importance and proposed accurate investigative tool.

Studies have shown that ovarian failure is a common side-effect of chemotherapy treatment; however, continuation of regular menses post-treatment does not necessarily imply that the ovaries have escaped damage. This animal study measures directly the primordial follicle (PMF) loss following exposure to chemotherapy and evaluates reproductive outcome following significant destruction of the PMF population. Inbred Balb/c mice aged 5-6 weeks were administered different doses of an alkylating agent, cyclophosphamide, and the total number of PMF remaining in both ovaries was counted. Results show that cyclophosphamide causes PMF destruction in proportion to increasing dose (P = 0.0001). Reproductive performance was assessed after exposure to 75 mg/kg cyclophosphamide, a dose which destroys approximately 50% of PMF reserve, by evaluation of ovulation, mating and pregnancy rates. Reproductive potential of treated mice was not affected compared with controls despite the significant loss of PMF. Our results indicate that reproductive performance is not an accurate parameter for assessing ovarian injury. Rather, histological counting of PMF number more directly reflects the damage caused by chemotherapy to the ovary. This method can be used as a sensitive, inexpensive tool to gauge the damage to fertility caused by new chemotherapy agents or protocols.

Animals↗
PubMed1998

Development of a multiple-drug delivery implant for intraocular management of proliferative vitreoretinopathy.

A prototype multiple-drug delivery implant has been developed for the intraocular management of proliferative vitreoretinopathy (PVR). Because of the recurrent nature of the disease, PVR causes blindness in approximately 7% of patients who have undergone retinal re-attachment surgery. The poly(dl-lactide-co-glycolide) 50/50 (PLGA) implant consists of three cylindrical segments, each of which contains one of the following drugs: 5-fluorouridine (5FUrd, an antimetabolite), triamcinolone (Triam, a corticosteroid), and human recombinant tissue plasminogen activator (t-PA, a thrombolytic agent). The device can be inserted through a 20-gauge syringe needle into the vitreous body of the eye. The implant also possesses a PLGA coating over the t-PA-containing terminal segment, which creates a lag-time to deliver t-PA when most needed and to decrease the risk of postoperative bleeding. Two methods of cylinder fabrication were investigated: heat and solvent extrusion. The release behavior of several drugs was examined as a function of the processing variables including: extrusion method, drug loading, polymer molecular weight, and drug particle size. The presence of either the organic solvent (acetone) during processing or a highly water-soluble drug (5FUrd) in the formulation increased the polymer porosity, which in turn, increased the drug release-rate. Drug loading effects were consistent with percolation concepts, and a low-molecular-weight PLGA (e.g., Mw=42000 for inherent viscosity=0.58 dl/g) was desirable to produce controlled release close to one month. Based on pharmacological and pharmacokinetic data of these compounds and our clinical experience with this disease, several design criteria for a combined implant were devised. Optimal cylindrical segments from the formulation studies were selected and combined in series to form a contiguous implant. After successful combination and coating procedures were developed, prototype implants were prepared. From the 3-drug prototype, 5FUrd and Triam were released approximately 1 microgram/day for over 4 weeks and 10-190 microgram/day over 2 weeks, respectively. The solvent-extrusion procedure did not significantly alter the stability of the encapsulated t-PA (>94+/-5% serine protease activity after preparation). After a lag-time of approximately 2 days, t-PA was released active at a rate of approximately 0.2-0.5 microgram/day in approximately 2 weeks. The release characteristics from the combined implant largely met our initial design criteria. Hence, controlled-release implants of this kind may have potential use for intraocular treatment of PVR.

Chromatography, High Pressure Liquid↗
PubMed1998

Management of submacular hemorrhage associated with retinal arterial macroaneurysms.

PURPOSE: Experience is reported with intraoperative pharmacologic lysis of recent submacular hemorrhage with tissue plasminogen activator followed by surgical drainage of the unclotted blood in patients with retinal arterial macroaneurysms. METHODS: Nine eyes (nine patients) with a recent (< or = 7 days old) submacular hemorrhage involving the center of the fovea secondary to retinal arterial macroaneurysm that were managed with recombinant tissue plasminogen activator-assisted subretinal hemorrhage evacuation, including subretinal injection of tissue plasminogen activator and removal of the liquefied blood. Patients were followed for a mean 18 +/- 7 months (range, 7 to 30 months). RESULTS: All nine eyes had improved final corrected visual acuity after surgery, and eight eyes (89%) attained a corrected visual acuity of 20/60 or better (mean, 20/40; range, 20/20 to 20/200). Final corrected visual acuity was limited to 20/200 in one eye. Two eyes developed a cataract that required surgery. CONCLUSIONS: Submacular surgery with tissue plasminogen activator-assisted thrombolysis achieved improved best-corrected visual acuity in eyes with recent submacular hemorrhage involving the center of the fovea associated with retinal arterial macroaneurysm.

Aged↗
PubMed1998

Understanding binge drinking among young people: an application of the Theory of Planned Behaviour.

Binge drinking (i.e. consuming half the recommended weekly consumption of alcohol in a single session) is a common activity among young people. Using the Theory of Planned Behaviour as its theoretical framework, this paper reports a study exploring the motivational and attitudinal factors underlying binge drinking in a sample of undergraduate students. Questionnaires were completed by 136 undergraduates which focused on their drinking behaviour and their beliefs about binge drinking. Binge drinking was found to be more prevalent among male respondents, and a number of significant differences in the beliefs of male and female respondents were found which supported this difference in drinking behaviour. A regression analysis identified two key predictors of the frequency of binge drinking; these being positive control beliefs and perceived behavioural control. Frequent binge drinkers were more likely to recognize the influence of a range of factors which may serve to encourage binge drinking (e.g. celebrating an event) and less likely to believe that the decision to engage in binge drinking is under their control. The results are discussed in relation to measures which may help to reduce the incidence of binge drinking through changes in the social environment.

Adolescent↗
PubMed1998

Use of commercially available hemoglobin standards to quantitatively calibrate a high performance liquid chromatography method.

High performance liquid chromatography (HPLC) has proven to be an extremely useful analytical technique to separate and identify different types of hemoglobins, particularly A, C, F and S in blood samples, and compute their relative percentages. Such data provide useful information in the diagnosis of hemoglobinopathies including sickle cell anemia, beta-thalassemia, hemoglobin C disease,etc. In the present investigation, we have explored the determination of absolute concentrations of individual hemoglobins in g/dL and recommend it as an additional parameter which could be included as part of clinical data. Possible correlations between g/dL hemoglobin and the severity of a specific hemoglobinopathy could be established and aid in the diagnosis and/or treatment of such diseases. Several commercially available hemoglobin standards were analyzed and evaluated for use in creating g/dL calibration graphs for the HPLC. Appropriate calibration procedures have been developed and are presented. Also, linear regression graphs and sample chromatograms are included. Preliminary results obtained demonstrate the feasibility of using commercially available hemoglobin standards to calibrate an HPLC method for the estimation of absolute hemoglobin concentrations.

Calibration↗
PubMed1997

Vitreoretinal surgery for complications of congenital retinoschisis.

PURPOSE: To report the results of vitreoretinal surgery for the management of complications associated with congenital retinoschisis in children. METHODS: We conducted a review of consecutive children with complications of congenital retinoschisis treated with advanced vitreoretinal techniques. Nine eyes of seven patients with congenital retinoschisis had vitreoretinal surgery for one of the following complications of congenital retinoschisis: hemorrhage within a large schisis cavity with a dense vitreous hemorrhage; rapid progression of schisis threatening the macula; obscuration of the macula by the overhanging inner wall of a schisis cavity; a combined schisistraction retinal detachment; or a combined schisis-rhegmatogenous retinal detachment. Vitreoretinal surgery consisted of vitrectomy, inner schisis wall retinectomy, fluid-gas exchange, endolaser treatment, and perfluoropropane gas injection. After vitreoretinal surgery, patients were followed up for a mean of 26 months (range, 9 to 67 months). Retinal reattachment, visual acuity, and visual fields were used as outcome measures. RESULTS: Eight of nine eyes had successful retinal reattachment. Six eyes postoperatively had improved visual acuity or visual field, or both. One eye had stabilization of visual acuity, and two eyes had a decrease in visual acuity. CONCLUSION: In children with complications of congenital retinoschisis, vitreoretinal surgery with excision of the inner wall of the peripheral schisis cavity may be effective in achieving retinal reattachment, thereby improving visual acuity or visual field size.

Adolescent↗
PubMed1997

Leukocoria caused by occult penetrating trauma in a child.

PURPOSE: To report a child with leukocoria caused by occult penetrating trauma. METHODS: Case report. The clinical findings and surgical repair of acquired leukocoria of the right eye in a 2-year-old boy are presented. RESULTS: In the right eye, slit-lamp examination disclosed a retrolenticular cyclitic membrane and moderately severe (3+) cells and flare anterior chamber reaction. The eye was hypotonous, and B scan showed that the membrane was associated with a retinal detachment. Surgery was performed to repair the retinal detachment and to remove the retrolenticular membrane. Two months before initial examination, the patient had been attacked by a rooster. CONCLUSION: Occult penetrating trauma should be considered in the differential diagnosis of pediatric leukocoria.

Animals↗
PubMed1997

Tissue plasminogen activator-assisted surgical excision of subfoveal choroidal neovascularization in age-related macular degeneration: a randomized, double-masked trial.

OBJECTIVE: To determine whether lysing subretinal fibrin with tissue plasminogen activator (t-PA) before excising subfoveal choroidal neovascularization improves visual acuity in patients with age-related macular degeneration. DESIGN: Randomized, double-masked trial. PARTICIPANTS: Eighty eyes of 80 patients with subfoveal choroidal neovascularization secondary to age-related macular degeneration were studied. INTERVENTION: Each eye underwent pars plana vitrectomy and received a subretinal injection of t-PA or balanced salt solution (BSS) before the neovascular membrane was excised. Preoperative and postoperative protocol refraction, ophthalmic examination, color photography, and fluorescein angiography were performed in all 80 eyes. MAIN OUTCOME MEASURES: Visual acuity and fluorescein angiographic evidence of leakage after 1 year. RESULTS: Visual acuity did not differ between the t-PA group (n = 40) and the BSS group (n = 40), and median best-corrected visual acuity was 20/320 for both groups (P = 0.38). Changes in visual acuity from baseline were also equal, with a median loss of 1 line in each group (P = 0.78). Patients whose initial visual acuity was 20/250 or less were more likely to improve by 2 or more lines (P = 0.01) and less likely to lose 2 or more lines (P < 0.001). Patients with choroidal neovascularization of at least 4 disc areas were more likely to improve by 2 or more lines (P = 0.02) and less likely to lose 2 or more lines (P < 0.001). After 1 year, choroidal neovascularization was present in seven of the t-PA eyes and in eight of the BSS eyes (P = 0.78). CONCLUSIONS: With current surgical techniques, the use of t-PA before surgical excision of subfoveal choroidal neovascularization is of no visual or anatomic benefit to patients with age-related macular degeneration.

Aged↗
PubMed1996

Surgical treatment for chronic hypotony and anterior proliferative vitreoretinopathy.

PURPOSE: To determine whether vitreoretinal surgery to release anterior traction in eyes with chronic hypotony and attached posterior retinas increases the intraocular pressure and prevents atrophia bulbi. METHODS: In this prospective study, we operated on and followed-up postoperatively 17 eyes of 17 consecutive patients with previous vitreoretinal surgeries for retinal detachments and severe proliferative vitreoretinopathy. These eyes had developed chronic hypotony (intraocular pressure < or = 5 mm Hg for at least one month) and anterior proliferative vitreoretinopathy. RESULTS: After a minimum of six months of postoperative follow-up (mean, 10.6 months), mean intraocular pressure had increased significantly after surgery from 1.7 to 7.2 mm Hg (P < .001), and ten (59%) of the 17 eyes had a final intraocular pressure greater than 5 mm Hg. Visual acuity did not change significantly after surgery (P = .25). In 13 (76%) of the 17 eyes, visual acuity improved or remained the same. Factors associated with higher postoperative intraocular pressure included hypotony of less than three months' duration (P = .007), preoperative visual acuity of 2/200 or more (P = .02), extent of anterior proliferative vitreoretinopathy of less than 90 degrees (P = .003), absence of tissue over the pars plicata (P = .001), and no anterior reproliferation after surgery (P = .04). CONCLUSIONS: Early surgery to release traction over the anterior retina and uveal tissue in eyes with chronic hypotony and anterior proliferative vitreoretinopathy can increase intraocular pressure and stabilize visual acuity.

Adult↗
PubMed1996

Anterior proliferative vitreoretinopathy in the silicone study. Silicone Study Report Number 10.

BACKGROUND: As part of the design of the Silicone Study, a new classification of proliferative vitreoretinopathy (PVR) was developed that distinguishes the different types of contraction found in PVR. In contrast to the original Retina Society system that emphasized the post-equatorial retinal pathology (posterior PVR), the Silicone Study classification system included the characteristic types of contraction found in both the equatorial region and the pre-equatorial retina and vitreous base (anterior PVR). METHODS: The authors contrast (1) preoperative and intraoperative findings and (2) vision and anatomic outcomes in the cohort of anterior PVR eyes with the cohort of posterior-only PVR eyes. For the cohort of eyes randomized to perfluoropropane gas (C3F8) or silicone oil, the authors carry out univariate and multivariate analyses to assess the predictive value of baseline and intraoperative parameters on vision and anatomic outcome. RESULTS: Anterior PVR was present in 321 eyes (79%) and was more prevalent in eyes that had undergone an unsuccessful vitrectomy before study entry than in eyes that underwent a primary vitrectomy for PVR (88% versus 73%; P < 0.001). Compared with eyes that had posterior PVR at the preoperative examination, eyes that had anterior PVR tended to (1) be graded (Retina Society classification system) as D-1 or worse (86% versus 49%; P < 0.0001), (2) have worse (< 2/200) visual acuity (93% versus 86%; P = 0.003), (3) have more hypotony (24% versus 11%; P = 0.03), more edema (8% versus 2%; P = 0.04), more aqueous flare (P = 0.02), more macular pucker (69% versus 52%; P = 0.005), and more intravitreal contraction (21% versus 6%; P = 0.002). When compared with eyes that had anterior PVR, eyes with posterior PVR had a better outcome at the 6-month postoperative examination: complete attachment of the retina (76% versus 62%; P = 0.04), visual acuity of 5/200 or better (64% versus 45%; P = 0.006), and normal intraocular pressure (86% versus 71%; P = 0.04). For eyes with anterior PVR, significant predictors of poor (< 5/200) visual acuity were a preoperative PVR grade D-1 or worse and the use of C3F8 gas as the intraocular tamponade. CONCLUSION: The Silicone Study classification of anterior PVR permits greater specificity in characterizing PVR and is prognostic of anatomic and vision outcome. Eyes with anterior PVR and clinically significant posterior PVR changes had a better visual prognosis if silicone oil was used. With the current understanding of the pathoanatomy of anterior PVR and the recent development of new surgical techniques, the incidence of anterior PVR in eyes that previously underwent vitrectomy may decline, and the prognosis in eyes with anterior PVR may improve.

Adult↗
PubMed1996

Vitrectomy in eyes with peripheral retinal angioma associated with traction macular detachment.

PURPOSE: Peripheral angiomas have been associated with epiretinal membranes and traction retinal detachment. The authors investigated the timing, results, and complications of vitreous surgery to remove the retinal traction and treat the peripheral vascular tumor. METHODS: The authors reviewed the results of ten eyes that had undergone vitrectomy for macular pucker and/or traction retinal detachment. These eyes had either preoperative or intraoperative treatment of the peripheral tumor. RESULTS: Patients were followed 4 to 95 months. Six eyes had nonfamilial peripheral acquired retinal hemangioma, three had von Hippel angiomas, and one had multiple large peripheral retinal angiomas associated with extensive retinal telangiectasis. Four eyes received cryotherapy and/or laser photocoagulation 2 to 3 months before surgery. In the remaining six eyes, initial treatment to the peripheral angioma was performed at the time of vitreous surgery. At final follow-up, all eyes were attached without retinal traction. Vision improved in all eyes; six (60%) achieved 20/50 or better visual acuity. Complications included recurrent epiretinal membrane (n=3); nonregressed angiomas (n=3); increased nuclear sclerosis (n=2); and retinal detachment (n=1). CONCLUSION: Vitreous surgery, when applied to epiretinal membranes or traction retinal detachments associated with peripheral vascular tumors, has a good chance of improving vision. Treatment of the hemangioma, before or during vitrectomy, usually results in tumor regression.

Adult↗