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H M Lambert

Publications and source records attributed to H M Lambert.

At least 19 recordsLinked to original sources
PubMed2005

Photodissociation channels for N2O near 130 nm studied by product imaging.

The photodissociation of N(2)O at wavelengths near 130 nm has been investigated by velocity-mapped product imaging. In all, five dissociation channels have been detected, leading to the following products: O((1)S)+N(2)(X (1)Sigma), N((2)D)+NO(X (2)Pi), N((2)P)+NO(X (2)Pi), O((3)P) + N(2)(A (3)Sigma(+) (u)), and O((3)P) + N(2)(B (3)Pi(g)). The most significant channel is to the products O((1)S) + N(2)(X(1)Sigma), with strong vibrational excitation in the N(2). The O((3)P) + N(2)(A,B):N((2)D,(2)P) + NO branching ratio is measured to be 1.4 +/- 0.5, while the N(2)(A) + O((3)P(J)):N(2)(B) + O((3)P(J)) branching ratio is determined to be 0.84+/-0.09. The spin-orbit distributions for the O((3)P(J)), N((2)P(J)), and N((2)D(J)) products were also determined. The angular distributions of the products are in qualitative agreement with excitation to the N(2)O(D (1)Sigma(+)) state, with participation as well by the (3)Pi(v) state.

Computer Simulation↗
PubMed2004

Quantum yields for product formation in the 120-133 nm photodissociation of O2.

The photodissociation of O(2) in the region from 120-133 nm has been investigated using product imaging. The spectrum in this region is dominated by transitions from the ground state to the first three vibrational levels of the E (3)Sigma(u) (-) state. The O((1)D)+O((3)P) channel is the only product channel observed by product imaging for dissociation at either 124.4 nm or 120.4 nm. The O((1)D(2)) product is aligned in the molecular frame in such a way that its J vector is perpendicular to the relative velocity vector between the O((1)D) and the O((3)P). The variation in the anisotropy of dissociation is approximately predicted by considering transitions on individual lines and then taking into account the coherent excitation of overlapping resonances. At 132.7 nm, both the O((1)D)+O((3)P) and the O((3)P)+O((3)P) channels are observed with branching ratios of 0.40+/-0.08 and 0.60+/-0.09, respectively. At 130.2 nm, the quantum yield for production of O((1)D) is 0.76+/-0.28.

Computer Simulation↗
PubMed2001

Massive suprachoroidal hemorrhage during pars plana vitrectomy associated with Valsalva maneuver.

PURPOSE: To report the intraoperative occurrence of massive intraocular suprachoroidal hemorrhage associated with Valsalva maneuver. METHODS: Retrospective, multicenter study of patients who developed massive choroidal hemorrhage associated with Valsalva maneuver during vitrectomy. RESULTS: Massive intraoperative suprachoroidal hemorrhage in seven patients (seven eyes) involved three men and four women with a median age of 52 years (range, 26 to 82 years). General anesthesia was used in six of seven cases. Coughing or "bucking" on the endotracheal tube during general anesthesia or severe coughing during the one vitrectomy performed under local anesthesia was associated with massive suprachoroidal hemorrhage. In five of seven eyes, this occurred near the end of surgery, after air-fluid exchange but before sclerotomy closure. Scleral plugs were immediately placed, and sclerotomy closure was performed exigently. Immediate posterior sclerotomy was performed on five of seven eyes; an additional patient underwent posterior sclerotomy postoperatively. After median follow-up of 18 months (range, 3 to 36 months), final visual acuity was no light perception in four eyes, light perception in one eye, 20/250 in one eye, and 20/20 in one eye. Four eyes became phthisical. CONCLUSIONS: Valsalva maneuver during pars plana vitrectomy may result in massive suprachoroidal hemorrhage with disastrous visual consequences. Precautionary measures to prevent coughing or "bucking" on the endotracheal tube during general anesthesia, or a prolonged episode of coughing during local anesthesia, may prevent this potentially devastating complication.

Adult↗
PubMed2000

Characteristics after cataract extraction or secondary lens implantation among patients screened for the Endophthalmitis Vitrectomy Study.

PURPOSE: This report describes the presenting clinical ophthalmic features and historical findings in patients with a clinical diagnosis of endophthalmitis after cataract extraction or secondary lens implant surgery screened for enrollment in the Endophthalmitis Vitrectomy Study (EVS). DESIGN: Clinic-based, cross-sectional study. PARTICIPANTS: Eight hundred fifty-four patients suspected to have endophthalmitis after cataract extraction or secondary lens implantation. METHODS: As part of the screening process for the study, an eye examination, a medical history, and demographic data were recorded in standardized form for all patients with endophthalmitis after cataract extraction or secondary lens implant surgery referred to the clinical centers, regardless of whether the patient met entry criteria. MAIN OUTCOME MEASURES: Demographics, presenting signs, and symptoms. RESULTS: The median age of individuals presenting with suspected bacterial endophthalmitis was 75 years (range, 9-100 years). Most of those screened (57.7%) were women. Seventy-nine percent of patients sought treatment within 6 weeks of surgery. Blurred vision, conjunctival injection, pain, and lid swelling were the predominant presenting symptoms in order of prevalence. Ocular pain and hypopyon, widely regarded as diagnostic of endophthalmitis, were each absent in 25% of patients. The median hypopyon height, when present, was 1.5 mm. CONCLUSIONS: The classic presentation of postoperative endophthalmitis includes reduced vision, conjunctival hyperemia, pain, hypopyon, and lid swelling within days after cataract surgery or secondary lens implantation. These were the prominent clinical findings in the EVS as well. Because pain and hypopyon, although common, were not always present, clinicians must be vigilant in postsurgical monitoring of patients.

Adolescent↗
PubMed2000

The management of subfoveal choroidal neovascular membranes and hemorrhage.

At the beginning of the past decade (1990), the Macular Photocoagulation Studies (MPS) were underway evaluating the efficacy of the treatment of subfoveal choroidal neovascularization (CNV) with conventional lasers. When this proved to limit the loss of vision and give little chance for improving vision, vitreoretinal surgeons turned to surgical approaches to treating these lesions. The surgical excision of subfoveal CNV has been under study for the remainder of the decade with the recent addition of macular/retinal translocation to attempt vision improvement for these patients. Other modalities including interferon therapy and external beam irradiation have proven ineffective, but new laser studies may offer promise with photosensitizing chemicals. Despite much study a single therapy that can reliably return sight to the majority of patients has not been developed. This article reviews the various therapies of the 1990s and renders some thoughts for the future.

Choroid Hemorrhage↗
PubMed1999

Surgical removal of subfoveal choroidal neovascularization in age-related macular degeneration.

OBJECTIVE: To assess the results of surgical excision of subfoveal choroidal neovascularization (CNV) in patients with age-related macular degeneration (AMD). DESIGN: Retrospective, interventional, noncomparative case series. PARTICIPANTS AND INTERVENTION: Sixty-four consecutive patients undergoing surgical removal of AMD-related subfoveal CNV were studied. The surgical method included a small retinotomy, subretinal tissue plasminogen activator (t-PA), perfluoro-n-octane, and air-fluid exchange. MAIN OUTCOME MEASURES: Final visual acuity was the main outcome measure; surgical complications and recurrence rates were also assessed. RESULTS: Preoperative visual acuity ranged from 20/100 to 1/200, with a mean of 20/400. Average follow-up was 19 months. The best acuity achieved after surgery ranged from 20/20 to hand motions, with a mean of 20/200. Final visual acuity ranged from 20/50 to light perception, with a mean of 20/400. Final acuity was improved 3 or more lines in 19 eyes (30%) (median, 5 lines), stable in 27 eyes (42%), and 3 or more lines worse in 18 eyes (28%) (median, 4 lines). Factors associated with greater visual improvement included poorer initial acuity, larger CNV size, and smaller subretinal hemorrhage. Analysis of groups similar to Macular Photocoagulation Study subgroups A through D showed an average improvement of 1 line for group C (visual acuity, 20/200 or worse; CNV larger than 2 disc areas). Other preoperative, intraoperative, and postoperative factors, including recurrence and retinal detachment, did not have a significant effect on final visual outcome. CONCLUSIONS: After surgical excision of AMD-related subfoveal CNV, vision improved or stabilized in the majority of patients. Surgery may be of greatest value for patients with poorer vision, larger subfoveal CNV, and minimal hemorrhage. Further evaluation of this technique should be accomplished via completion of a controlled, randomized multicenter study.

Aged↗
PubMed1998

Optimal imaging protocol after intraocular silicone oil tamponade.

PURPOSE: Our purpose was to define the optimal protocol for imaging of the orbits after vitreous humor replacement with silicone oil. METHODS: Eleven eyes in 10 patients with tractional and/or rhegmatogenous retinal detachment were studied. Five CT scans and 18 high-field (1.5 T) MR images were obtained. Standard T1-weighted, T1-weighted with fat and silicone saturation, fast spin density-weighted, and T2-weighted orbital MR sequences were performed. Unique pulse sequences included fast spin density-weighted and T2-weighted imaging with and without fat saturation or silicone saturation, gradient-echo imaging, and short-tau inversion recovery imaging. RESULTS: The T1-weighted MR and CT studies were comparable in displaying the silicone. However, the fat- or silicone-saturated fast T2-weighted sequences always showed the fibrous bands and subretinal fluid to best advantage. In one case, the eye also contained inadvertently retained perfluorocarbon liquid, which blended with silicone oil on both saturated images, requiring companion T1-weighted sequences without saturation to demonstrate its presence. CONCLUSION: Simple, commonly available fat-saturated fast T2-weighted MR images supplemented by standard T1-weighted images are all that are needed to evaluate the eye efficiently after vitrectomy and tamponade.

Adult↗
PubMed1997

Combined subretinal and sub-retinal pigment epithelium neovascular membranes in age-related macular degeneration: a clinicopathologic study of six cases.

BACKGROUND AND OBJECTIVE: Subfoveal neovascular membranes are usually located either in the subsensory retinal space or below the retinal pigment epithelium (RPE). This article describes the clinical and histopathologic features of subfoveal membranes with both subretinal and sub-RPE components (combined membranes). PATIENTS AND METHODS: Six surgically excised subfoveal neovascular membranes from six patients were examined histopathologically. Preoperative and postoperative clinical information was obtained from each patient. RESULTS: Clinically, the combined membranes had no special characteristic features. The most common fluorescein angiographic finding postoperatively was a window defect of the RPE. Visual acuity improved in three patients and became worse in the other three patients. CONCLUSIONS: All patients with combined subfoveal neovascular membranes had age-related macular degeneration. In this disease, a single subfoveal membrane may extend into both the subretinal and the sub-RPE spaces. Patients may benefit from surgical removal of the membrane.

Aged↗
PubMed1996

Transdifferentiated retinal pigment epithelial cells are immunoreactive for vascular endothelial growth factor in surgically excised age-related macular degeneration-related choroidal neovascular membranes.

PURPOSE: To determine the cellular origin and the vascular endothelial growth factor (VEGF) immunoreactivity of the nonvascular stromal cells in surgically excised age-related macular degeneration (ARMD)-associated choroidal neovascular membranes (CNVMs). METHODS: Immunohistochemical analysis was performed on frozen sections of eight surgically excised ARMD-related CNVMs. RESULTS: Cytokeratin-positive, smooth muscle actin-positive polygonal or fibroblastic (transdifferentiated RPE) cells were the principal nonvascular stromal cells detected. The polygonal cells were more commonly found in active (highly vascularized) regions and were strongly immunoreactive for VEGF. The fibroblastic cells were predominantly found in fibrotic (hypovascular) regions and were minimally immunoreactive for VEGF. CONCLUSIONS: Transdifferentiated RPE cells are the principal nonvascular stromal cells of both vascular and fibrotic ARMD-related CNVMs. Preferential localization of VEGF immunoreactivity with the cytoplasm of the polygonal transdifferentiated RPE cells in the highly vascularized regions of the surgically excised CNVMs suggests an important angiogenic role of these cells and this growth factor in the progression of ARMD-related choroidal neovascularization.

Actins↗
PubMed1996

Use of perfluorocarbon liquid in the repair of retinoschisis retinal detachments.

BACKGROUND AND OBJECTIVES: To determine the effectiveness of perfluorocarbon liquid in the repair of retinoschisis-associated retinal detachments. PATIENTS AND METHODS: Four patients with either degenerative or juvenile X-linked retinoschisis had rhegmatogenous retinal detachments that were repaired with the use of perfluorocarbon liquid during vitrectomy. The patients' ages ranged from 17 to 78 years and the postoperative follow-up was at least 6 months. RESULTS: All of the patients had complete anatomic repair of the retinoschisis-associated retinal detachments. The postoperative visual acuity was 20/200 or better in all of the patients and 20/40 or better in half of the patients. CONCLUSIONS: The use of perfluorocarbon liquid is an effective adjunct in the management of rhegmatogenous retinal detachments associated with degenerative and juvenile X-linked retinoschisis.

Adolescent↗
PubMed1995

Current management of proliferative vitreoretinopathy.

The recognition of APVR and its dissection, along with the use of perfluorocarbon liquids, has greatly improved the success rate in surgery for severe PVR. In reviewing our first 71 cases using these techniques, 75% were attached with one operation and 90% were attached with one or more operations. These techniques have greatly improved our operative results and have obviated the use of retinal tacks and suturing, retinotomy (in most cases), and the need for very high scleral buckles. (We rarely alter an in-place scleral buckle.)

Fluorocarbons↗
PubMed1994

Clinicopathologic features of surgically excised choroidal neovascular membranes.

PURPOSE: The purpose of this study is a descriptive correlation of the clinical, fluorescein angiographic, and pathologic features in a large series of patients who underwent surgical removal of choroidal neovascular membranes. METHODS: The patients' clinical data were recorded for each surgically removed choroidal neovascular membrane received in the authors' laboratory. Fluorescein angiographic characteristics of the membranes, including well-demarcated versus poorly demarcated preoperative appearance, postoperative choroidal atrophy, and membrane recurrence, were recorded whenever possible. The pathologic features of the membranes, including cellular and extracellular constituents, were determined on light and electron microscopic examination. RESULTS: A total of 123 membranes were studied. Underlying diseases in decreasing order of frequency were age-related macular degeneration, ocular histoplasmosis syndrome, myopia, idiopathic and pattern dystrophy. The cellular and extracellular constituents of the membranes were similar, regardless of underlying disease, with the exception of basal laminar deposit, seen almost exclusively in age-related macular degeneration. Well-demarcated membrane components were localized with a central subretinal pigment epithelium fibrovascular core. Poorly demarcated membranes were represented by a subneurosensory retinal (breakthrough) component, although most of these membranes had associated retinal pigment epithelium. Fragments of Bruch's membrane were common in specimens from patients with postoperative choroidal atrophy, and there was generally a lack of vascular channels in membranes that led to recurrence. CONCLUSIONS: This study suggests that choroidal neovascular membranes represent a stereotypic, nonspecific response, regardless of underlying disease. Most membranes are subretinal pigment epithelium, and what is recognized angiographically as a subneurosensory retinal component contains associated retinal pigment epithelium in most instances. Fragments of Bruch's membrane in the specimen correlate with postoperative choroidal atrophy. Lack of vascular channels in the surgical specimen may correlate with a risk for postoperative membrane recurrence.

Adult↗
PubMed1993

Diode-laser photocoagulation for zone 1 threshold retinopathy of prematurity.

We used the diode-laser indirect ophthalmoscope in the treatment of 17 (30 eyes) infants with zone 1 (a circle centered on the optic disk with a radius of twice the distance from the disk to the fovea) threshold retinopathy of prematurity (at least five continuous or eight cumulative 30-degree sectors [clock hours] of ridge with extraretinal fibrovascular proliferation in the presence of plus disease). Mean follow-up was 31.2 weeks. Two eyes (6.7%) required retreatment of missed areas that had persistent plus disease (enlarged posterior veins and tortuous arterioles). A favorable outcome was attained in 25 eyes (83.3%). Five eyes (16.7%) developed retinal detachments, three of which remained stable at Stage 4A (extrafoveal retinal detachment) and two of which ultimately progressed to Stage 5 (total retinal detachment). Both eyes that went on to Stage 5 had severe posterior pole hemorrhages at the time of treatment. Two eyes that developed retinal detachments (one, stage 4A and one, stage 5) had rhegmatogenous components. Among 14 infants followed up for more than three months, four developed nystagmus, and six developed strabismus. In contrast to cryoablation, diode-laser photoablation of the peripheral retina was found to be an effective treatment for threshold retinopathy of prematurity located in zone 1. Portability and ease of use of the laser system, precision of treatment, and minimal postprocedural adnexal inflammation are further advantages of this therapeutic modality.

Female↗
PubMed1993

Pneumococcal endophthalmitis associated with nasolacrimal obstruction.

Pneumococcal endophthalmitis can be a devastating postoperative infection after cataract extraction or penetrating keratoplasty. Streptococcus pneumoniae was isolated as the causative agent in three of the 124 patients (2%) who were treated for endophthalmitis at our institution between 1984 and 1990. Two of the three patients lost light perception in the affected eye. All three patients had previously unrecognized or untreated chronic nasolacrimal obstruction of varying causes. We studied the role of pneumococcal lacrimal conjunctivitis in the pathogenesis of the postoperative pneumococcal endophthalmitis in these patients.

Aged↗
PubMed1993

Ultrastructural features of surgically excised subretinal neovascular membranes in the ocular histoplasmosis syndrome.

We evaluated the ultrastructural features of seven surgically excised submacular neovascular membranes from seven patients with the ocular histoplasmosis syndrome. Excised neovascular membranes were composed of fibrovascular tissue interposed between Bruch's membrane and the retinal pigment epithelium. Cellular components present in the membranes included, in decreasing order of frequency, retinal pigment epithelium, vascular endothelium, photoreceptor cells, macrophages, erythrocytes, ghost erythrocytes, fibrocytes, myofibroblasts, glial cells, smooth-muscle cells, and lymphocytes. Extracellular constituents of the neovascular membranes included 20 to 25-nm collagen fibrils, fibrin, 10-nm collagen fibrils, and fragments of Bruch's membrane and choroid. Our findings are consistent with the concept that subretinal neovascular membranes in the ocular histoplasmosis syndrome represent a nonspecific healing response to a local stimulus or injury.

Adolescent↗