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John Loewenstein

Publications and source records attributed to John Loewenstein.

10 recordsLinked to original sources
PubMed2006

Predictors of visual outcome and choroidal neovascular membrane formation after traumatic choroidal rupture.

OBJECTIVE: To determine predictors of choroidal neovascularization (CNV) and visual outcome after traumatic choroidal rupture. METHODS: A retrospective review of patients with traumatic choroidal rupture diagnosed in the Retina Service, Massachusetts Eye and Ear Infirmary, Boston, between January 1993 and August 2001 was performed. Parametric and nonparametric statistical methods were used to evaluate visual prognosis, CNV, and retinal detachment after traumatic choroidal rupture. RESULTS: One hundred eleven cases were identified and reviewed. Visual acuity (VA) changes were recorded in all of the cases. Thirty-eight (34%) of the 111 patients recovered driving vision (VA > or =20/40). Rupture location was recorded in 107 cases. Recovery of driving vision was seen in 20 (59%) of 34 eyes with peripheral choroidal ruptures, 17 (22%) of 73 eyes with macular choroidal ruptures, 38 (38%) of 99 eyes without CNV, 1 (8%) of 12 eyes with CNV, 38 (40%) of 96 eyes without retinal detachment, and 1 (7%) of 15 eyes with retinal detachment. Older age and location of rupture within the arcades were positively associated with CNV formation (P = .04 and .03, respectively). Foveal location of rupture, multiple ruptures, and poor baseline VA were associated with failure to recover driving vision in univariate regression analyses. In multivariate analysis, rupture location and baseline VA were independently associated with visual outcome. Of 12 patients diagnosed with CNV, 5 were not treated, 4 were treated with argon laser photocoagulation, 1 was treated with surgery, 1 was treated with argon laser photocoagulation followed by surgery, and 1 was treated with verteporfin photodynamic therapy. CONCLUSIONS: Most patients with traumatic choroidal rupture do not achieve final VA of 20/40 or better. Poor visual outcome was most highly associated with a macular rupture and baseline VA of less than 20/40. The formation of CNV was most strongly associated with older age and macular choroidal rupture.

Adolescent↗
PubMed2006

Biocompatibility of materials implanted into the subretinal space of Yucatan pigs.

PURPOSE: To assess the biocompatibility of materials for possible use in subretinal prostheses. METHODS: Strips (0.5 x 5 mm; 10-microm thick) of either plain poly(imide) or poly(imide) coated with amorphous aluminum oxide (AAO), amorphous carbon (AC), parylene, poly(vinyl pyrrolidone) (PVP), or poly(ethylene glycol) (PEG) were each implanted into the subretinal space of four Yucatan miniature pigs. Two types of control surgery without implantation were performed in four other animals. Electroretinograms (ERGs) were performed before and after surgery. All animals were euthanatized 3 months after surgery, and histologic slides of the retina were assessed for 15 criteria. Paired, two-tailed Student's t-tests were used for statistical analyses. RESULTS: Across all animals, the mean amplitude of the ERG b-wave did not differ from baseline after 3 months. In implanted animals, the histologic analyses revealed that (1) all the implanted materials produced abnormalities that were significantly greater than in the control subjects; (2) overall, PEG, parylene, and PVP produced less histologic disruption than the other three materials; (3) parylene and PEG did not differ significantly from the control in disturbing retinal anatomy; (4) only PI and AAO produced RPE alterations that were significantly greater than in control subjects; and (5) AAO and PI produced a significantly greater degree of peri-implant cellular responses than did the other materials. CONCLUSIONS: All implants produced some alteration of the retina, but there were clear differences among the materials in the degree to which their presence disturbed the normal anatomy of the retina or RPE or incited tissue reactions around the implant.

Animals↗
PubMed2005

Cone damage in patients receiving high-dose irofulven treatment.

OBJECTIVES: To describe the clinical, perimetric, and electroretinographic (ERG) results of 4 patients with cone dysfunction following irofulven treatment including the histopathologic and immunocytochemical features of one patient's retinas. DESIGN: Observational case series. METHODS: The patients were examined clinically, including perimetric and ERG evaluations. Eyes from patient 1 and healthy postmortem eyes were processed for histopathologic and immunocytochemistry studies with antibodies specific for cones, rods, and reactive Müller cells. MAIN OUTCOME MEASURES: Clinical signs and symptoms, perimetry, ERG, retinal histopathologic and immunocytochemistry study results. RESULTS: All 4 patients had ERG changes consistent with abnormal cone responses and relatively normal rod responses. Compared with control eyes, the retina of patient 1 had approximately half the normal numbers of macular cones and fewer peripheral cones. The number of rods were normal but all rod and cone outer segments were shortened. CONCLUSION: High-dose irofulven treatment causes cone-specific damage with relative sparing of rods.

Adult↗
PubMed2004

Attrition from ophthalmology residency programs.

PURPOSE: To investigate the incidence of and reasons for voluntary resident attrition from ophthalmology training programs. DESIGN: Retrospective survey. METHODS: A survey was mailed to residency program directors of the 121 Accreditation Council for Graduate Medical Education-accredited ophthalmology residency programs asking them to report the number of residents who withdrew from training during 2001 to 2002 and the reasons for withdrawal. RESULTS: Of 102 responding programs, 13 (12.7%) had one resident withdraw from training in the academic year 2001 to 2002. These 13 residents represented 1.1% of all ophthalmology residents in training at the responding institutions during that academic year. The most frequent reason for withdrawing was to enter another medical specialty. CONCLUSIONS: Voluntary resident attrition from ophthalmology training programs is uncommon. The 1.1% attrition rate in this study is the lowest among published reports of attrition from other specialties.

Career Choice↗
PubMed2003

Perceptual efficacy of electrical stimulation of human retina with a microelectrode array during short-term surgical trials.

PURPOSE: This work is part of a feasibility assessment of a retinal prosthesis as a means to restore vision to patients with blindness caused by retinitis pigmentosa. The primary goal was to assess the concordance of the form of induced perception and the pattern of electrical stimulation of the retina, and the reproducibility of the responses. METHODS: Five volunteers with severe retinitis pigmentosa and one with normal vision were studied. A companion paper in this issue provides details on demographics, visual function, surgical methods, general stimulation strategy, and data analysis. Volunteers were awake during surgery while a 10-microm-thick, microfabricated electrode array was placed on the retina. The array was connected to extraocular current sources that delivered charges to 50-, 100-, and 400-microm-diameter electrodes. Negative control trials were randomly included. Perceptual quality was judged by the similarity between the form of stimulation and perception (i.e., accuracy) and the reproducibility of responses. RESULTS: Only 1 of 40 control tests yielded a false-positive result. On average, volunteers 3, 5, and 6 reported percepts that matched the stimulation pattern 48% and 32% of the time for single- and multiple-electrode trials, respectively. Two-point discrimination in the best cases may have been achieved in two blind subjects using (center-to-center) electrode separation of 600 and 1960 microm. Reproducibility was achieved 66% of the time in the blind subjects. By comparison, in the normal-sighted subject, perceptual form was reported accurately 57% of the time, with 82% reproducibility, and two-point discrimination may have been achieved in one trial with 620-microm electrode spacing and in two trials each with 1860- and 2480-microm electrode spacing. In subjects 5 and 6, perceptual size was inconsistently related to the charge, although relatively large differences in charge (median: 0.55 microcoulombs [microC]) between two trials produced differently sized percepts. Longer stimuli did not produce rounder percepts. CONCLUSIONS: Single percepts induced by single-electrode stimulation were relatively small, but the form of percepts, especially after multielectrode stimulation, often did not match the stimulation pattern, even in a normal-sighted volunteer. Reproducible percepts were more easily generated than those that matched the stimulation pattern.

Adult↗
PubMed2003

Methods and perceptual thresholds for short-term electrical stimulation of human retina with microelectrode arrays.

PURPOSE: To report methods for performing epiretinal electrical stimulation with microfabricated electrode arrays and determining perceptual thresholds on awake human volunteers during acute surgical trials. METHODS: Four hypotheses were tested: (1) epiretinal stimulation can be performed during acute experiments without obviously damaging the retina or degrading vision or the health of the eye; (2) perception can be obtained 50% of the time in blind patients with charge densities below published safety limits; (3) the minimal charge needed to induce perception would be higher in patients with more severe retinal degeneration; and (4) threshold charge would be lower at shorter stimulus durations. Five subjects with severe blindness from retinitis pigmentosa and one with normal vision (who underwent enucleation of the eye because of orbital cancer) were studied. Electrical stimulation of the retina was performed on awake volunteers by placing a single 250-microm diameter handheld needle electrode or a 10-microm thick microfabricated array of iridium oxide electrodes (400-, 100-, or 50-microm diameter) on the retina. Current sources outside the eye delivered charge to the electrodes. Assessment of damage was made by observing the clinical appearance of the eyes, comparing pre- and postoperative visual acuity, obtaining retinal histology in one case, and comparing perceptual thresholds with published safety limits. RESULTS: No clinically visible damage to the eye or loss of vision occurred. Even at sites removed from stimulation, histology revealed swollen photoreceptor inner and outer segments, which were believed to be nonspecific findings. Percepts could not be reliably elicited with 50-microm diameter electrodes using safe charges in one blind patient. With the two larger electrodes, only the normal-sighted patient had thresholds at charge densities below 0.25 and 1.0 millicoulombs (mC)/cm(2) for 400- and 100-microm diameter electrodes, respectively, which is one seemingly reasonable estimate of safety derived from the product of charge per phase and charge density per phase. In blind patients, thresholds always exceeded these levels, although most were close to these limits in patient 6. The range of charge density thresholds with the 400- microm electrode in blind patients was 0.28 to 2.8 mC/cm(2). The normal-sighted patient had a threshold of 0.08 mC/cm(2) with a 400-microm electrode, roughly one quarter of the lowest threshold in the blind patients. Strength-duration curves obtained in two blind patients revealed the lowest threshold charge at the 0.25- or 1.0-ms stimulus duration. CONCLUSIONS: Threshold charge densities in severely blind patients were substantially higher than that in a normal-sighted patient. Charge densities in blind patients always exceeded one seemingly reasonable estimate of safe stimulation. The potential adversity of long-term stimulation of the retina by a prosthesis has yet to be determined.

Adult↗
PubMed2002

Electroretinograms as an indicator of disease activity in birdshot retinochoroidopathy.

PURPOSE: To determine whether electroretinogram results can help predict the success in tapering of immunosuppressive medication in patients with birdshot retinochoroidopathy. METHODS: Fifteen patients with birdshot retinochoroidopathy who had at least three serial electroretinograms (ERG) during the course of their disease were included in the study. Charts of patients seen at the Immunology and Uveitis Service at the Massachusetts Eye and Ear Infirmary, Boston, Massachusetts were retrospectively reviewed. Seven parameters of the ERGs were examined: dim scotopic amplitude, bright scotopic amplitude, bright scotopic implicit time, single-flash photopic amplitude, single-flash photopic implicit time, 30 Hz flicker amplitudes, and 30 Hz flicker implicit times. For each parameter the patients were divided into two groups, those with normal and those with abnormal responses at the time their immunosuppressive medication taper was initiated. The percentage of patients in each group who were able to successfully taper their immunosuppressive medication was calculated. A successful taper of medication was defined as no recurrence of disease signs or symptoms for at least 1 year after the medication was terminated. RESULTS: Abnormalities in the bright scotopic response amplitudes and 30 Hz flicker implicit times were associated with recurrence of inflammation as immunosuppressive therapy was tapered. CONCLUSION: ERG can serve as a useful adjunct in helping determine when to initiate tapering of immunosuppressive therapy in patients with birdshot retinochoroidopathy.

Adult↗