Search PubMed⌕ Search

Biomedical subjects

A Loewenstein

Publications and source records attributed to A Loewenstein.

At least 19 recordsLinked to original sources
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↗
PubMed1997

Bilateral retinal vein occlusion associated with 5,10-methylenetetrahydrofolate reductase mutation.

PURPOSE: To report on the occurrence of 5,10-methylenetetrahydrofolate reductase (MTHFR) deficiency, known to cause mild to moderate hyperhomocystinemia and increased risk of vascular occlusive disease, in a young patient with bilateral central retinal vein occlusion. METHODS: A 25-year-old man was initially examined with central retinal vein occlusion in the right eye, followed 4 months later by a central retinal vein occlusion in the left eye. Studies for risk factors predisposing to thrombosis were performed. RESULTS: Hematologic studies failed to detect any pathology. However, the patient was found to be homozygous for 677C-T mutation in MTHFR enzyme. CONCLUSION: Central retinal vein occlusion may be associated with a mutation in MTHFR.

5,10-Methylenetetrahydrofolate Reductase (FADH2)↗
PubMed1997

Late onset corneal haze after photorefractive keratectomy for moderate and high myopia.

BACKGROUND: Corneal haze after photorefractive keratectomy (PRK) usually appears within 4 weeks after the procedure. A new type of corneal haze, starting relatively late after PRK, is reported. METHODS: The authors reviewed the files of their first 1000 consecutive patients who completed a follow-up of 12 months or more and identified all those who had clear corneas for at least 4 months, after which corneal haze appeared. The clinical course in these patients was evaluated. RESULTS: Late onset corneal haze (LOCH) had occurred in 18 eyes of 17 patients (incidence, 1.8%), appearing 4 to 12 months after PRK and resulting in decreased visual acuity and regression. Treatment with topical steroids or reoperation resulted in partial reversibility of haze and regression. CONCLUSIONS: A new entity of LOCH is described. The appearance of LOCH suggests that corneal healing and remodeling continue for at least 1 year after PRK.

Administration, Topical↗
PubMed1997

Delay of corneal wound healing in patients treated with colchicine.

BACKGROUND: Colchicine has a known adverse effect on wound healing through its inhibitory effect on tubulin-dependent cell functions and through collagenase activation. In the cornea, it has been shown in animal and in vitro studies to inhibit epithelium mitosis, fibroblast mitosis and migration, as well as to reduce collagen deposition. The authors report on two patients with corneal ulcers refractory to conventional treatment while the patients were undergoing oral colchicine therapy. CASE REPORTS: The first patient was an 86-year-old woman who had been treated with oral colchicine because of rheumatoid arthritis. She was admitted to the authors' department with a deep corneal ulcer in the right eye for which she had been treated for 3 weeks with local antibiotics without any improvement. The second patient, a 60-year-old woman, was hospitalized because of a corneal ulcer in her left eye. She had been receiving oral colchicine therapy for mixed connective tissue disease. Treatment with local antibiotics was initiated but the condition of the eye worsened, ultimately resulting in corneal perforation. RESULTS: Withdrawal of oral colchicine therapy was followed by rapid corneal wound healing in both patients. CONCLUSION: The findings in these two patients suggest that colchicine may delay corneal wound healing. The authors suggest that in patients with corneal ulcers refractory to conventional treatment who are receiving colchicine, cessation of colchicine therapy should be considered.

Aged↗
PubMed1997

Macular hemorrhage after excimer laser photorefractive keratectomy.

We describe three patients with high myopia, 13.0 to 20.0 diopters (D), who had typical myopic macular hemorrhages 1 to 6 months after photorefractive keratectomy (PRK). The hemorrhages eventually resolved, with resultant permanent decrease in vision and pigmentary and atrophic changes in the macula. Highly myopic eyes are predisposed to bleeding in areas of lacquer cracks and to myopic choroidal neovascularization formation. Awareness of potential retinal pathology in patients having PRK and follow-up retinal examinations are warranted.

Adult↗
PubMed1997

Complications of excimer laser photorefractive keratectomy for myopia.

PURPOSE: To evaluate the safety and complication rates of excimer laser photorefractive keratectomy (PRK). SETTING: Assutah Laser Center, Tel-Aviv, Israel. METHODS: This retrospective study evaluated the complication rate after PRK in 825 consecutive patients who had PRK for myopia and had a follow-up of at least 12 months. RESULTS: At 12 months postoperatively, 4.0% of patients suffered from overcorrection and 8.6% from undercorrection. Induced astigmatism developed in 1.4% of all operated eyes. Three percent of the patients had haze, and 3.6% reported glare or halos. Twenty-three eyes (2.7%) lost one line or more of best corrected visual acuity (BCVA). Ptosis developed in 0.4% of the eyes, and 3.5% had a significant increase in intraocular pressure resulting from corticosteroid treatment. There were no complications in 678 eyes (82.5%). CONCLUSION: Eighty-two percent of eyes having PRK did not develop complications. In 18.0% one or more complication, mainly undercorrection, overcorrection, or loss of BCVA, occurred.

Administration, Topical↗
PubMed1997

Excimer laser reablation.

BACKGROUND AND OBJECTIVE: To evaluate the outcome of repeated excimer laser keratectomy after photorefractive keratectomy (PRK). PATIENTS AND METHODS: A retrospective study of 32 of 1000 consecutive patients who had a follow-up of at least 12 months and who underwent repeated PRK in the Assutah Laser Center. RESULTS: The mean spherical equivalent (SE) declined significantly as a result of the repeated treatment. As opposed to zero eyes before re-treatment, 19 of 29 eyes (66%) achieved SE of within +/-1 D 6 months after re-treatment. Before re-treatment, 20 of 32 eyes (62%) had medium or severe haze, whereas after re-treatment only 1 of 29 eyes (3%) had medium haze, and none of the eyes had severe haze. At 6 months after reoperation, visual acuity had improved to 20/36, a significant improvement to the mean log MAR equivalent of 20/40 before re-treatment, yet still significantly worse than the log MAR equivalent before initial ablation which was 20/30. CONCLUSION: Repeated excimer laser PRK has the potential for successful treatment of undercorrection, regression, and haze occurring after an initial PRK.

Corneal Opacity↗
PubMed1997

An intraocular telescopic lens for macular degeneration.

Age-related macular degeneration is a leading cause of visual loss in adults older than 60 years of age. Once vision has been seriously compromised, the only means of improving visual function are optical devices that produce magnification of images. These devices fall into three categories: (1) high-plus lenses, (2) external telescopes, and (3) a high-minus center intraocular lens combined with external high-plus glasses. The authors designed a new intraocular lens with an entire telescope in its center. In vitro tests were performed to evaluate modulation transfer function, visual field, and optical aberrations. Implantation in cadaver eyes was performed to test the surgical technique and safety. Test results showed that satisfactory modulation transfer function and optic aberration were achieved, and implantation in cadaver eyes was proven to be feasible and safe. It was concluded that a fully implanted intraocular telescopic lens is an effective optical solution for age-related macular degeneration.

Adult↗