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Biomedical subjects

A Loewenstein

Publications and source records attributed to A Loewenstein.

At least 37 records · Page 2Linked to original sources
PubMed1999

Manipulations of ACHE gene expression suggest non-catalytic involvement of acetylcholinesterase in the functioning of mammalian photoreceptors but not in retinal degeneration.

To explore role(s) of acetylcholinesterase (AChE) in functioning and diseased photoreceptors, we studied normal (rd/+) and degenerating (rd/rd) murine retinas. All retinal neurons, expressed AChEmRNA throughout fetal development. AChE and c-Fos mRNAs peaked at post-natal days 10-12, when apoptosis of rd/rd photoreceptors begins. Moreover, c-Fos and AChEmRNA were co-overexpressed in rd/rd mice producing transgenic human (h), and host (m) AChE, but not in rd/+ mice. However, mAChE overexpression also occurred in transgenics expressing human serum albumin. Drastic variations in AChE catalytic activity were ineffective during development. Neither transgenic excess nor diisopropylfluorophosphonate (DFP) inhibition (80%) affected the rd phenotype; nor did DFP exposure induce photoreceptor degeneration or affect other key cholinergic proteins in rd/+ mice, unlike reports of adult mice and despite massive induction under DFP of c-Fos70 years). Therefore, the extreme retinal sensitivity to AChE modulation may reflect non-catalytic function(s) of AChE in adult photoreceptors. These findings exclude AChE as causing the rd phenotype, suggest that its primary function(s) in mammalian retinal development are non-catalytic ones and indicate special role(s) for the AChE protein in adult photoreceptors.

Acetylcholinesterase↗
PubMed1999

Retinal vein occlusion associated with methylenetetrahydrofolate reductase mutation.

OBJECTIVE: To report on the occurrence of methylenetetrahydrofolate reductase (MTHFR) deficiency in patients with retinal vein occlusion (RVO). DESIGN: Prospective case series PARTICIPANTS: Fifty-nine consecutive patients with newly diagnosed RVO seen at the Retina Unit in the Tel Aviv Medical Center during 1997. METHODS/TESTING: Interviews and multiple blood analyses were done. Data were compared to the reported incidence of MTHFR deficiency in the Israeli population at large. RESULTS: Twenty-six patients (44.1%) were heterozygotes and 11 (18.6%) were homozygotes for 677C-T mutation in MTHFR. The MTHFR 677C-T homozygosity was documented as being present in 10.4% of healthy individuals in the Israeli population. The difference in homozygosity was found to be statistically significant (P = 0.038). CONCLUSIONS: Retinal vein occlusion may be associated with a mutation in MTHFR.

Adult↗
PubMed1999

Macular ring in a patient with Terson's syndrome.

PURPOSE: To report on a pigmented finding in the macula that is unique to Terson's syndrome, and was previously described only once. METHOD: A 49-year-old man underwent vitrectomy for vitreous hemorrhage due to Terson's syndrome. During surgery the retina was exposed, and a pigmentation was noticed around the macula. Follow-up of the macular finding is presented. RESULTS: At surgery a pigmented "ring" encircling the macula was revealed. Two and six months later, the pigmented line was still noticed, and an epiretinal membrane appeared in the temporal macula. CONCLUSION: Terson's syndrome may be associated with a pigmented "ring" encircling the macula, a finding that may be a result of a detachment of the internal limiting membrane (ILM). The epiretinal membrane that was later noticed, might also be related to the damage to the ILM.

Cerebral Hemorrhage↗
PubMed1999

Cilioretinal artery occlusion during coronary catheterization.

PURPOSE: To report on a patient with cilioretinal artery occlusion during cardiac catheterization. METHODS: A 51-year-old man complained of blurred vision in the left eye immediately following cardiac catheterization. Visual acuity was 6/12 and the eye had a dense central scotoma. RESULTS: Mild retinal whitening of the posterior pole and segmented filling of the cilio-retinal artery established the diagnosis of cilioretinal artery occlusion. Immediate paracentesis was performed. Two weeks later, a tiny central scotoma could be observed and visual acuity was 6/6. CONCLUSIONS: Cardiac catheterization may result in retinal infarction. Awareness to any visual symptoms, immediate diagnosis and prompt intervention may prevent permanent visual impairment.

Cardiac Catheterization↗
PubMed1998

Low-frequency submicron fluctuations of red blood cells in diabetic retinopathy.

OBJECTIVE: To characterize cell membrane mechanical fluctuations of red blood cells (RBCs) in patients with diabetic retinopathy. METHODS: Point dark-field microscopy-based recordings of these local displacements of the cell membrane in human erythrocytes were compared between patients with severe proliferative diabetic retinopathy and healthy controls. The study was performed on discoid RBCs. RESULTS: The average of the maximal displacement amplitude in the diabetic patients was 13.9% +/- 1.7% (236 +/- 29 nm) compared with 18.7% +/- 1.75% (318 +/- 30 nm) for the controls (P<.001). The decrease of the RBCs' average displacement amplitude was not correlated with the variation in negative curvature of the central area of discoid cells. CONCLUSIONS: Microdisplacements of the cell membrane, which reflect the bending deformability of the RBCs, are directly connected with its efficiency in passing through capillaries narrower than its own diameter. These microdisplacements were significantly reduced in patients with severe diabetic retinopathy because of an increase in viscoelasticity of the cell membrane. Such reduced cell membrane microdisplacements, which reflect lower bending deformability of the RBC, reduce the ability of the cell to enter and pass through small capillaries, increasing tissue ischemia and consequently contributing to the development of diabetic retinopathy.

Diabetic Retinopathy↗
PubMed1998

The effect of intraocular pressure on the absorption of air from the vitreous cavity.

BACKGROUND: The duration of an intraocular gas bubble used in vitreoretinal surgery is an important determinant of the safety and effectiveness of intraocular gas use. Considerable variability impedes the clinical determination of this parameter. The aim of the study was to study experimentally the relationship between intraocular pressure (i.o.p.) and the absorption of an intravitreal air bubble. METHODS: We compared the rate of absorption of an intravitreal air bubble in rabbit eyes that had been treated with cyclocryotherapy (n = 17) to the absorption of air bubbles in untreated fellow eyes (n = 17). RESULTS: Intravitreal air bubble persisted longer in the cyclocryotherapy-treated rabbit eye (mean +/- SD 78 +/- 16 h) than in the control fellow eyes (43 +/- 15 h). This difference was statistically significant (P < 0.001). The length of time an air bubble persisted could be predicted from the IOP. CONCLUSIONS: The reason for the increased length of time an air bubble remained in cyclocryotherapy-treated eyes is probably the result of several factors, including primarily reduced aqueous flow and reduced IOP. Our results show that the duration of air injected into the vitreous cavity correlated to IOP. In addition to other known factors, the IOP should be considered in predicting intravitreal gas persistence.

Absorption↗
PubMed1998

Scanning laser ophthalmoscope fundus perimetry after surgery for choroidal neovascularization.

PURPOSE: Submacular surgery is under investigation for the treatment of subfoveal choroidal neovascularization secondary to age-related macular degeneration, ocular histoplasmosis syndrome, and other causes. The aims of this study were to determine whether the macular area from which choroidal neovascularization was removed surgically remained functional and whether there was any qualitative difference between eyes with different disease conditions or between eyes of younger and older patients. METHODS: Our study included 19 patients (19 eyes) with choroidal neovascularization, seven cases caused by age-related macular degeneration and 12 caused by ocular histoplasmosis syndrome, pathologic myopia, or idiopathic causes. All tests were performed at least 6 months after surgical removal of choroidal neovascularization. All patients underwent fundus perimetry with the scanning laser ophthalmoscope for evaluation of dense and relative scotomas and fixation site. RESULTS: After submacular surgery in 19 patients, 10 patients (one with age-related macular degeneration and nine with pathologic myopia, ocular histoplasmosis syndrome, or an idiopathic cause of choroidal neovascularization) fixated within an area that ophthalmoscopically and angiographically was an area of retinal pigment epithelial disturbance occupied by choroidal neovascularization preoperatively. Of 12 patients without age-related macular degeneration, seven of eight patients younger than 50 years of age compared with two of four patients 50 years or older fixated within the area of retinal pigment epithelial disturbance. CONCLUSIONS: Our data suggest that in patients without age-related macular degeneration who undergo submacular surgery, the surgically disturbed area previously occupied by choroidal neovascularization can remain functional postoperatively. Furthermore, occasionally a patient with age-related macular degeneration undergoing submacular surgery still can fixate in the area from which the choroidal neovascularization was removed.

Adolescent↗
PubMed1998

Translocation of the retina for management of subfoveal choroidal neovascularization II: a preliminary report in humans.

PURPOSE: To report a surgical method for translocation of the foveal retina in eyes with subfoveal choroidal neovascularization. METHODS: In three eyes of three patients, a crescent-shaped, partial-thickness scleral resection was performed near the equator at either the superotemporal or the inferotemporal quadrant. A near-total retinal detachment was created; then the edges of the resected sclera were sutured, causing shortening of the sclera with subsequent reattachment of the retina, resulting in translocation of the fovea to an area overlying nonfoveal retinal pigment epithelium and choroid. RESULTS: In three eyes of three patients, the fovea was surgically translocated to overlie retinal pigment epithelium that preoperatively was not underlying the fovea. In two patients, laser photocoagulation was applied to the choroidal neovascularization that, after translocation of the fovea, was no longer subfoveal, so that the photocoagulation was not associated with immediate visual loss. After a follow-up of 4 to 6 months, the visual acuity had improved in all patients (from 20/126 preoperatively to 20/70 in one patient, from 20/200 preoperatively to 20/70 in the second, and from 20/160 to 20/30 in the third). The patients noted distortion or tilting of the images, which improved over time. CONCLUSIONS: Limited foveal translocation may offer a therapeutic modality to preserve or improve vision in cases of subfoveal choroidal neovascularization. Additional follow-up is needed to assess the impact of potential complications associated with the surgical procedure, such as retinal detachment, proliferative vitreoretinopathy, and cataract, as well as the possibility of recurrent choroidal neovascularization.

Adult↗
PubMed1998

Translocation of the retina for management of subfoveal choroidal neovascularization I: experimental studies in the rabbit eye.

PURPOSE: To report a surgical method for retinal translocation as a potential treatment for eyes with subfoveal choroidal neovascularization. METHODS: Thirty right eyes of 30 pigmented rabbits were used for this study. The first 15 were used to develop the technique. The complete surgical technique for retinal translocation was performed in the last consecutive 15 rabbits. Intravitreal injection of sulfur hexafluoride was performed to compress and liquefy the vitreous. Two weeks later, we used transscleral subretinal hydrodissection to create a retinal detachment. A scleral resection was then performed near the equator in the superotemporal quadrant. Fundus photographs were taken to record the retinal status before, immediately after, and 1, 3, and 7 days after surgery. Electroretinography was performed in three rabbits 3, 7, and 14 days after retinal translocation. Histologic studies were performed in one rabbit 7 days after retinal translocation. RESULTS: Our results are based on experiments performed in the last consecutive 15 rabbits. One day after surgery, retinal reattachment was observed in 14 of the 15 animals. The remaining animal developed endophthalmitis. A predictable retinal translocation of about 1,000 microm was achieved. Retinal tears were noted on the retinal folds in four cases after 1 week. Electroretinographic studies showed transient reduction in retinal function. Mild morphologic damage to the outer retinal layers was seen histologically. Retinal detachment or proliferative vitreoretinopathy did not develop in any rabbit in the 14 days of follow-up. CONCLUSIONS: Limited retinal translocation with repositioning of the central retina was accomplished in rabbits.

Animals↗
PubMed1998

Effect of scleral indentation on diode laser transscleral retinal photocoagulation.

BACKGROUND AND OBJECTIVE: To evaluate the effect of the degree of scleral indentation with a modified AlGaAs diode laser for transscleral retinopexy in the rabbit. MATERIALS AND METHODS: Transscleral diode laser photocoagulation was performed on the eyes of Dutch-belted rabbits using a modified AlGaAs diode laser with a wider base and various prism protrusions. RESULTS: The transscleral photocoagulation generally became more efficient with an increasing amount of scleral indentation. Effectiveness increased up to a prism protrusion of 1.5 mm. CONCLUSION: This study shows that a wide-based AlGaAs diode laser with a 1.5-mm protrusion provides a more easily oriented probe for creating more efficient chorioretinal burns.

Animals↗
PubMed1997

Echographic diagnosis of scleral fold in hypotony.

PURPOSE: To report the echographic appearance of a scleral fold in hypotony. METHOD: We performed ultrasonography on a patient who, after trabeculectomy with mitomycin C, had an intraocular pressure of 1 mm Hg, an opaque cataract, and suspected hypotonous maculopathy in the left eye. RESULTS: An area of dome-shaped eyewall thickening was noted near the tendon of the lateral rectus muscle in primary gaze. This thickening increased substantially in lateral gaze, mimicking a foreign body or a tumor. CONCLUSION: Recognizing this abnormality is important to avoid erroneous diagnosis of an intraocular foreign body or a tumor in hypotonous eyes.

Cataract↗