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Biomedical subjects

J W McMeel

Publications and source records attributed to J W McMeel.

At least 19 recordsLinked to original sources
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↗
PubMed1991

Comparative study of vitreoretinal relationships using biomicroscopy and ultrasound.

We prospectively studied 29 consecutive eyes with proliferative diabetic retinopathy that showed media clear enough to enable characterization of vitreoretinal relationships by biomicroscopy. Vitreoretinal relationships were also determined by contact B-scan ultrasound. With both techniques, these relationships were documented by photographs and drawings. Biomicroscopy showed complete posterior vitreous detachment (PVD) in 4 eyes (14%), partial PVD in 18 (62%), and no PVD in 7 (24%). Ultrasound examination revealed complete PVD in 4 eyes (14%), partial PVD in 19 (66%), and no PVD in 6 (21%). The results we obtained using ultrasound agreed significantly with those obtained by biomicroscopy [Cohen's kappa = 0.93, 95% confidence interval = (0.80, 1.06)]. Ultrasound detected vitreous changes more easily than biomicroscopy when mild media opacities were present and when the equatorial areas of the globe were examined. Results suggest that ultrasound is adequate to determine vitreoretinal relationships in eyes with clear media and that it is a good alternative to biomicroscopy in eyes with significant media opacities.

Adolescent↗
PubMed1991

Effect of timolol on human retinal, choroidal and optic nerve head circulation.

In a double-masked, randomized, placebo-controlled study, we evaluated the effect of topical timolol maleate 0.5% on the retinal, choroidal, and optic nerve head circulation in 5 healthy volunteer subjects. Changes in the pulsatile component of choroidal blood flow (PCBF) were determined from measurements of the ocular pulse wave. Changes in the retinal arterial blood flow rate (RBF) and optic nerve head capillary blood speed (CBS) were determined by laser Doppler velocimetry and monochromatic photography. In timolol-treated eyes, PCBF decreased by 32 +/- 12% (p = 0.0007). Changes in RBF and CBS were not statistically significant. In the contralateral placebo-treated eyes, PCBF decreased by 15 +/- 8% (p = 0.006) and RBF increased by 18 +/- 10% (p = 0.002). The change in CBS was not statistically significant.

Administration, Topical↗
PubMed1991

Magnetic resonance imaging of intraocular tamponades.

The efficacy of proton magnetic resonance imaging in differentiating vitreous from C3F8 gas and silicone oil tamponades, and in detecting fresh hemorrhages and condensed vitreous was tested in rabbits in vivo. The results suggest that this imaging method could provide a useful alternative to ultrasonography, especially in eyes with opaque media.

Animals↗
PubMed1979

Conjunctival capillary fragility: a preliminary study.

Conjunctival capillary fragility (CCF) and skin capillary fragility (SCF) were studied by a negative-pressure suction cup method in 25 normal subjects and 38 diabetic patients with diabetic retinopathy. The CCF was significantly higher (P less than .001) in patients with diabetic retinopathy than in normal subjects; there was no significant difference in the SCF.

Adult↗
PubMed1979

Diabetic traction detachment.

One hundred thirty-six of 124 patients with diabetic traction detachment (TD) were observed for an average of 4.6 years (range, 3.0 to 9.4 years) with no surgical intervention. Visual acuity was maintained or improved in 51 of these eyes; 71 continued to be 20/200 or better. Diabetic TDs remained stable for long periods, those of more severe grade being more stable. At final examination, 60% (81/136) were graded at the same anatomic level (36/136) or an improved level (45/136). Spontaneous reattachment occurred in 20% (27/136); 78% (21/27) of these eyes had small detachments (TD1). The status of the vitreous and the vitreoretinal adhesion determined both the degree of detachment and the incidence of spontaneous reattachment.

Diabetic Retinopathy↗
PubMed1978

Severe adolescent-onset proliferative diabetic retinopathy: the effect of pituitary ablation.

Proliferative diabetic retinopathy (PDR) is uncommon in patients younger than the age of 20 and has been rarely reported. Since 1969, 14 adolescents with severe PDR have been seen, the youngest of whom was 16 years old and the oldest, 19 years old. The shortest duration of diabetes mellitus prior to diagnosis of PDR was eight years. Ten patients had a positive family history of diabetes. Thirteen patients had suboptimal metabolic control. Ten patients had some degree of azotemia, seven were hypertensive, and six had proteinuria. Ophthalmic findings included advanced neovascular and fibrous proliferation on initial classification, and rapid progression to blindness-which was most frequently secondary to traction retinal detachment. In a small retrospective study, pituitary ablation may have offered greater preservation of vision than that observed in untreated patients.

Adolescent↗
PubMed1977

Glaucoma occurring after closed vitrectomy.

Six of 20 eyes developed postoperative glaucoma within two to ten days after closed vitrectomy for vitreous hemorrhage. Intraocular pressure was greater than 40mm Hg in all six eyes, and three developed pressure greater than 60 mm Hg. Intraocular pressure in four eyes was controlled with medical antiglaucoma therapy and two eyes required anterior chamber irrigation. Six months postoperatively three of the eyes had normal pressures, one was hypotonous, and two developed increased intraocular pressure secondary to angle neovascularization. Three of the 14 eyes that did not develop glaucoma developed a cellular accumulation in the anterior chamber. The glaucoma was caused mainly by obstruction of the trabecular meshwork by degenerated red blood cells known as ghost cells. The cells may be identified by phase-contrast examination of anterior chamber aspirates. Glaucoma can be prevented through irrigation of the vitreous cavity at the time of vitrectomy ensuring that no cells and debris are left behind to migrate into the anterior chamber and obstruct the trabecular meshwork. This type of glaucoma is caused mainly by ghost cells, whereas hemolytic glaucoma is caused mainly by macrophages and red blood cell debris.

Eye Diseases↗
PubMed1977

Argon laser treatment in supine position.

When using an argon laser photocoagulator it is often advantageous and sometimes indispensable to treat the patient in a supine position. Stabilization of the laser beam requires the use of a microscope equipped with a beam manipulator (joystick) that maintains the orientation of the laser beam wherever it is placed, without the operator having to hold the joystick. A low-vacuum contact lens or a three-mirror lens, and a microscope suspended from a floor stand are used. The patient is placed in the supine position on a stretcher of adjustable height with his head in a foam rubber conformer. Local anesthesia may not be necessary, but if indicated, the patient should not be treated in an upright position. A lid block is rarely required. General anesthesia is used with patients who cannot cooperate. There are 4 main indications for treatment in the supine position: (1) cases in which great accuracy is needed, such as treatment near the macula; (2) all cases in which retrobulbar anesthesia is necessary, with or without a lid block; (3) cases in which the patient is unable to cooperate; and (4) cases that require prolonged photocoagulation.

Adult↗
PubMed1976

Chorioretinal anastomoses after argon laser photocoagulation.

Communication between the retinal and the choroidal circulation occurred in one case of proliferative diabetic retinopathy and one case of Leber's disease (multiple miliary aneurysms) after argon laser photocoagulation treatment to eliminate abnormal retinal vasculature. In both instances rapid-sequence fluorescein angiography documented the choroidal origin of the anastomoses. Such anastomoses developed in areas where an excessively dense laser beam aimed at occluding retinal vessels presumably destroyed the underlying Bruch's membrane and permitted invasion of the retina by fibrovascular growth from the choriod. The occurrence of such growths is a potential complication of argon laser photocoagulation directly related to the power density used.

Adult↗
PubMed1976

Effect of the ocular media on the main wavelengths of argon laser emission.

(1) In owl monkeys, where no yellow staining of the media is present, there are clear-cut ophthalmoscopic and histologic differences in the lesions produced by equal amounts of argon green and blue light. (2) The yellow staining of the macula causes differences in lesion intensity and depth when different wavelengths are used for photocoagulation. (3) In humans the influence of age on this difference is apparent.

Adult↗