Search PubMed⌕ Search

Biomedical subjects

J W McMeel

Publications and source records attributed to J W McMeel.

At least 19 recordsLinked to original sources
PubMed2001

Erosion and intrusion of silicone rubber scleral buckle. Presentation and management.

OBJECTIVE: To describe the clinical presentation and management of erosion and intrusion of silicone rubber implants that are used in scleral buckling procedures for the treatment of retinal detachment. METHODS: The authors identified four patients from their practices during the last 20 years (1978-1998) who had erosion or intrusion of silicone rubber scleral buckles that were used to manage retinal detachment. Approximately 4400 scleral buckling procedures were performed during this period. A retrospective review of the medical records of all patients was performed. Factors that influenced management decisions concerning the intruding buckle are emphasized. RESULTS: All four patients had myopia. The interval between placement of the scleral buckle and development of intrusion ranged from 1 to 20 years. The buckles were intrascleral in three cases and episcleral in one. Recurrent detachment and vitreous hemorrhage were indications for surgical intervention in three cases. After the surgical removal of buckling elements, visual acuity stabilized in all patients and the retina remained attached in all cases. CONCLUSIONS: Erosion and intrusion of scleral buckle are rare complications of scleral buckling procedures. The intruding buckle may be left intact unless there is significant threat to the integrity of ocular structures, recurrent detachment, or hemorrhage. Manipulation of the encircling band or buckle does not necessarily alter the visual acuity or the status of the retina.

Adult↗
PubMed2000

Vascular endothelial growth factor and hepatocyte growth factor levels are differentially elevated in patients with advanced retinopathy of prematurity.

Although the roles of vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) in angiogenesis are well described, the putative roles of these factors in retinopathy of prematurity (ROP) remain unknown. We evaluated VEGF and HGF protein levels in subretinal fluid of eyes with ROP, and expression of their corresponding receptors in retrolental membranes associated with stage 5 ROP. We examined subretinal fluid samples from eyes using rhegmatogenous retinal detachment as a control. VEGF and HGF were differentially elevated in eyes with ROP. In Stage 5 ROP (n = 22), the mean VEGF and HGF levels were 14.77 +/- 14.01 ng/ml and 16.56 +/- 9.62 ng/ml, respectively. Interestingly, in patients with active stage 4 ROP, mean VEGF levels were highly elevated (44.16 +/- 18.72 ng/ml), whereas mean HGF levels remained very low (4.77 +/- 2.50 ng/ml). Next, we investigated in vivo expression of VEGF receptor-2 and HGF receptor in retrolental membranes from 16 patients with stage 5 ROP. Both VEGF receptor-2 and HGF receptor proteins were detected mainly in posterior portions of the membrane as well as in vessel walls and along the retinal interface where angiogenesis was active. These findings together suggest that VEGF and HGF play important roles in the pathogenesis of ROP.

Adult↗
PubMed1999

Diabetic macular edema: risk factors and concomitants.

PURPOSE: To investigate the systemic and ocular factors associated with diffuse macular edema in patients with diabetic retinopathy (DR) and compare with patients with focal or no macular edema. METHODS: From 160 consecutive patients with DR, we obtained medical and ocular histories, blood pressure and visual acuity. Macular edema was determined by biomicroscopy and stereoscopic fundus photography. Fluorescein angiography was used in the characterization of its leakage, and the vitreoretinal relationship was performed by preset lens biomicroscopy. RESULTS: Among adult-onset diabetes mellitus (DM) patients, 55% had diffuse, 23.5% had focal and 21.5% had no macular edema (p=0.01). The risk of developing diffuse macular edema was 3.2 times greater in patients with high blood pressure (HBP) (95% confidence interval (CI), 1.5 to 6.9). Patients with cardiovascular disease (CVD) had a higher prevalence of diffuse (58.0%) than focal (26.0%) or no maculopathy (16.0%) (p=0.01). The odds for development of diffuse macular edema was 3.4 times greater in patients with vitreomacular adhesion (95% CI, 1.15 to 13.30) than in those with complete posterior vitreoretinal attachment or vitreoretinal separation. The odds for development of diffuse macular edema were 6.2 (95% CI, 1.83 to 21.04) and 7.7 times greater (95% CI, 3.12 to 19.12) in patients with PPDR and PDR, respectively, in comparison with those with NPDR. CONCLUSIONS: In this study, adult-onset DM, HBP, CVD, vitreomacular adhesion and advanced retinopathy were associated with increased risk of development of diffuse diabetic macular edema.

Blood Pressure↗
PubMed1996

Retinal blood flow increases following short-term aspirin usage in type I diabetics with no or minimal retinopathy.

In a double-masked, randomized, placebo-controlled, two-period crossover study, we measured the effect of aspirin on retinal blood flow in 8 type I diabetic patients, 5 with no observable retinopathy, and 3 with 1-10 observable microaneurysms and no other signs of retinopathy. Each patient ingested 1 capsule/day of either aspirin (650 mg) or placebo for 14 days. Following a 1-month washout period, the treatment was reversed. The bidirectional laser Doppler technique and monochromatic photography were used to measure the blood flow rate in a major temporal retinal artery in 1 eye of each patient at baseline and on the 14th day of each treatment period. Retinal blood flow increased following aspirin in 7 of the 8 patients. Using a standard crossover analysis we found a mean aspirin-placebo treatment difference of 21 +/- 17% (mean +/- 95% CI), which was statistically significant (p = 0.03). Retinal blood flow increased following aspirin by 44 +/- 10% (mean +/- SEM) in the 5 patients with no retinopathy (p = 0.04), but only by 8 +/- 10% (n.s.) in the 3 patients with minimal retinopathy.

Adult↗
PubMed1996

Retinal hemodynamics in middle-aged normal subjects.

The laser Doppler technique and monochromatic photography were used to measure the total retinal blood flow, temporal/nasal differences in blood flow and the relationship between blood flow and vessel diameter in 5 healthy subjects, aged 54-58 years. Systemic blood pressure (BP) and intraocular pressure were also measured, and the retinal perfusion pressure was calculated. The measurements were compared to those previously obtained from a younger group of 7 healthy subjects, aged 25-38 years. Total retinal blood flow was 73 +/- 13 microliters/min in the middle-aged subjects and was not significantly different from the value measured in young subjects (80 +/- 12 microliters/min). Retinal perfusion pressure was significantly higher in the older subjects, primarily due to elevated systemic BP. The similarity in total flow between the two groups, even though the retinal perfusion pressures were higher in the older group, is an indication of an increased vascular resistance to flow. The increase may be an aging phenomenon or an indication of a well-functioning autoregulatory capacity in the retinal vasculature of the older subjects.

Adult↗
PubMed1996

[The new laser Doppler velocimetry for the measurement of retinal circulation and its clinical application].

We developed a new laser Doppler instrument to measure retinal blood flow. This instrument is equipped with an eye tracking system, which maintains the laser beam on the retinal vessel, thus enabling the measurement of patients with poor visual acuity and poor fixation. In diabetic patients even those without retinopathy, the retinal blood flow decreased compared to the control subjects. This was mainly the result of decreased retinal blood speed and no significant change in the arterial diameter. In diabetic patients requiring panretinal photocoagulation, we studied the regional changes in retinal blood flow following superior or inferior half fundus argon laser treatment, which produced a significant retinal blood flow decrease only in the treated area. We also studied the retinal circulatory changes in retinal branch vessel occlusion. In retinal branch view occlusion, the blood flow in arteries supplying the affected lesion showed 80-90% decrease compared to the arteries supplying the unaffected region. In retinal branch artery occlusion, the retinal blood flow in occluded arteries showed 40-50% decrease compared to the non-occluded arteries. In one patient with retinal branch vein occlusion in whom we measured the retinal blood flow over 18 months, the blood flow increased with the development of collateral vessels. The results showed that retinal circulatory abnormalities can be also evaluated quantitatively during the course of retinal vascular occlusive disease by our newly developed laser Doppler instrument, which proved that this instrument is a clinically very useful tool.

Adult↗
PubMed1994

Prognostic value of initial electroretinogram in central retinal vein obstruction.

We retrospectively studied the correlation between the initial electroretinogram (ERG) recordings and the final visual acuities (VA) of 47 patients with central retinal vein obstruction (CRVO) after follow-up of more than 1 year. The a- and b-wave amplitudes and the b/a ratio with white flash were significantly larger in patients with good vision (VA > 20/200) than in those with poor vision (VA < or = 20/200). The b/a ratio and b-wave amplitude with white flash showed sensitivity and specificity of more than 78% for visual prognosis. The latest VA was < or = 20/200 in all 20 patients with a subnormal b-wave amplitude and in all 15 with b/a ratio < 1.05. These results suggest that the ERG recorded soon after (CRVO) onset correlates strongly with visual prognosis.

Adult↗
PubMed1994

Quantitative circulatory measurements in branch retinal vessel occlusion.

We used the laser Doppler technique to quantify retinal circulatory abnormalities in three patients with branch retinal artery occlusion and in two patients with branch retinal vein occlusion, each of whom had shown delayed filling on fluorescein angiography. Blood flow in occluded arteries was 40-50% lower than in non-occluded arteries of the same branching order. In the patients with branch retinal vein occlusion blood flow in arteries supplying the affected regions was 80-90% lower than in arteries supplying the unaffected regions. One vein occlusion patient was measured serially over 18 months. Blood flow increased from 4 to 12 microliters/min in the artery supplying the affected region in this patient. The results demonstrate that retinal circulatory abnormalities can be evaluated quantitatively during the course of retinal vascular occlusive disease, and suggest that the efficacy of therapy can be monitored using our techniques.

Aged↗
PubMed1994

Regional retinal blood flow reduction following half fundus photocoagulation treatment.

Regional changes in retinal blood flow following inferior and subsequent superior argon laser half fundus photocoagulation treatment were measured in six diabetic patients with advanced retinopathy. Centreline blood velocity, vessel diameter, and blood flow in major inferior and superior temporal retinal arteries were measured at baseline and following each treatment using the bidirectional laser Doppler technique and monochromatic fundus photography. Inferior fundus laser treatment produced a significant blood flow decrease in inferior temporal arteries ranging from 60% to 78%. Blood flow changes in superior temporal arteries were not significant, ranging from -7% to +14%. Subsequent superior fundus laser treatment produced a significant blood flow decrease in superior temporal arteries ranging from 50% to 66%. Subsequent blood flow changes in inferior temporal arteries were not significant, ranging from -19% to +21%. The results indicate that regional laser treatment produces a regional reduction in retinal blood flow, consistent with measurements of preretinal and intraretinal oxygen tension which have indicated increases in oxygen over photocoagulated regions.

Adult↗
PubMed1993

Proton magnetic resonance spectroscopy of vitreal changes in experimental streptococcal endophthalmitis.

We used magnetic resonance spectroscopy to examine endophthalmitis in rabbits inoculated with a virulent strain of Streptococcus pneumoniae. On different days after infection, the animals were sacrificed and the vitreous isolated and examined with water-suppressed proton magnetic resonance spectroscopy. A broad resonance corresponding to the methyl envelope of lipoprotein lipids appeared 2 days after infection and persisted until the eyes developed phthisis (around 10 days postinfection). This resonance was absent in the control eye and the bacterial culture; it could be used as the marker of breakdown of blood-vitreous barrier and onset of endophthalmitis-induced changes.

Animals↗
PubMed1992

Magnetic resonance microscopy of rabbit eyes.

Magnetic resonance (MR) micro-imaging was performed on enucleated eyes from rabbits previously injected with perfluoropropane gas (C3F8), with or without the surgical creation of retinal detachment. Condensed vitreous, which exhibited shortened longitudinal relaxation time (T1), could be differentiated with proton-density and T1-weighted imaging. Gradient-echo imaging could in addition detect vitreo-retinal tractions. The detached retina itself was also seen. Further, proton-density but not T1-weighted imaging showed lens opacities appearing as high-intensity regions. MR microscopy is a convenient method for gross morphological examination of intact eyes.

Animals↗
PubMed1992

Retinal detachment after cataract surgery. Surgical results.

The authors studied the results obtained by the Retina Associates in 376 eyes of 361 patients operated on for retinal detachment associated with aphakia or pseudophakia with a postoperative follow-up of at least 6 months. All eyes underwent scleral buckling. The series included 103 eyes with aphakia, 17 eyes with iris-fixated intraocular lens, 111 eyes with anterior chamber (AC) IOL, and 145 eyes with posterior chamber (PC) IOL. The overall success rate for retinal detachment was 93%, without significant difference among the different groups. The aphakia and PC IOL groups had significantly higher prevalence (63% and 60%, respectively) of visual acuity equal to or better than 20/40 compared with the AC IOL group (33%). The prevalence of postoperative corneal edema in the AC IOL group was significantly higher than in the aphakia and PC IOL groups. Preoperative vitreous hemorrhage, large retinal breaks, posterior retinal breaks, total retinal detachment, proliferative vitreoretinopathy, and the need for performing a closed vitrectomy were significant factors in predicting ultimate failure.

Aged↗
PubMed1992

Retinal detachment after cataract surgery. Predisposing factors.

The authors studied the characteristics of 376 eyes of 361 patients with primary retinal detachment (RD) and surgical aphakia (103 eyes) or pseudophakia (273 eyes). Of the pseudophakic eyes, 17 had an iris-fixated intraocular lens (IOL), 111 had an anterior chamber (AC) IOL, and 145 had a posterior chamber (PC) IOL. Of the PC IOL cases, 48 (33%) had undergone YAG capsulotomy, and 46% of them developed RD within 6 months after capsulotomy. The frequency of no breaks found in pseudophakic RD (15%) was significantly higher than in RD with simple aphakia (5%). The most frequent reasons were incomplete fundus view due to a small pupil in the iris-fixated (83%) and the AC (44%) groups, and cloudiness of capsular remnants in the PC group (78%). In pseudophakic RD, sizable single tears, located more posteriorly than in RD with simple aphakia, were frequent. The authors speculate that in pseudophakic RD the retinal breaks may resemble those noted in phakic RD.

Aged↗
PubMed1992

Retinal blood flow alterations associated with scleral buckling and encircling procedures.

The bidirectional laser Doppler technique and monochromatic photography were used to measure the absolute blood flow rate in the major temporal retinal arteries in seven patients following unilateral scleral buckling and encircling procedures, and in two patients before and after removal of scleral buckling elements. In the seven patients who had undergone uncomplicated scleral buckling procedures the arterial flow rates were on average 50% lower (p = 0.01) in the surgically treated eyes than in the contralateral eyes. Removal of scleral buckling elements in two patients produced increases of 73% and 44% in arterial blood flow rates.

Adult↗
PubMed1992

Comparison between B-scan ultrasound and MRI in the detection of diabetic vitreous hemorrhage.

The efficacy of proton magnetic resonance imaging (MRI) was evaluated and compared with that of B-scan ultrasound in the detection and differentiation of diabetic vitreous hemorrhage. Although conventional spin-echo MRI could not locate vitreous hemorrhages, gradient-recalled-echo (GRE) MRI readily did so. The aberrant signals appeared to originate from the interfacing between hemorrhages and the vitreous, and possibly also from the paramagnetic effect of the ferrous ion. The information provided by boundary/susceptibility detection, unique to the GRE sequence, is useful in delineating the extent of vitreous hemorrhage and hemolysis. However, for the diagnosis and follow up of diabetic vitreous hemorrhages, MRI appears no more informative than B-scan ultrasonography.

Aged↗
PubMed1992

[Retinal blood flow changes in eyes with rhegmatogenous retinal detachment and scleral buckling procedures].

Bidirectional laser Doppler technique and monochromatic photography was used to measure the absolute blood flow rate (F) in the major superior or inferior temporal retinal arteries in 3 patients with rhegmatogenous retinal detachment, in 4 patients following unilateral scleral buckling procedures, and in one patient before and after removal of scleral buckling elements. In 2 of the eyes with retinal detachment, F in arteries supplying the detached portion of the retina was approximately 30% lower than in arteries supplying the attached portion. On average, F measured in the arteries supplying the detached portion of the retina in 2 patients was 8.9 +/- 1.3 microliters/min, 67% lower than normal controls. F measured in the arteries supplying the attached portion of the retina in 3 patients was 15.2 +/- 3.9 microliters/min, on average, 43% lower than in normal controls. In 4 patients who had undergone uncomplicated, unilateral scleral buckling procedures, F in an artery of the affected eye was compared with F in the corresponding artery of the fellow eye. F in the artery of the affected eyes was 8.7 +/- 3.2 microliters/min, on average, 59% lower than that of the fellow eyes (p less than 0.05), and 68% lower than in normal controls (p less than 0.0001). Removal of scleral buckling elements in one patient produced a 79% increase in F in the measured artery. Then, F returned to normal levels after removal of scleral buckling elements.

Adult↗