320 research outputs found
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Measurements of atmospheric electricity aloft
Measurements of the electrical characteristics of the atmosphere above the surface have been made for over 200 years, from a variety of different platforms, including kites, balloons, rockets and aircraft. From these measurements, a great deal of information about the electrical characteristics of the atmosphere has been gained, assisting our understanding of the global atmospheric electric circuit, thunderstorm electrification and lightning generation mechanisms, discovery of transient luminous events above thunderstorms, and many other electrical phenomena. This paper surveys the history of atmospheric electrical measurements aloft, from the earliest manned balloon ascents to current day observations with free balloons and aircraft. Measurements of atmospheric electrical parameters in a range of meteorological conditions are described, including clear air conditions, polluted conditions, non-thunderstorm clouds, and thunderstorm clouds, spanning a range of atmospheric conditions, from fair weather, to the most electrically active
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Intraocular lens insertion during vitrectomy
Vitrectomy was performed in 10 patients in combination with posterior chamber intraocular lens (IOL) insertion. Indications for vitrectomy included traumatically dislocated cataract, choroidal hemorrhage, epiretinal membrane, lens involving intraocular foreign body, vitreous hemorrhage, and extruded anterior chamber IOL. Postoperative visual acuity improved in each case. The main advantages of simultaneous IOL insertion, in selected cases, are reduced cost and inconvenience, and more rapid visual rehabilitation
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Nutritional amblyopia. A histopathologic study with retrospective clinical correlation
During a 10-year period ending in 1985, we observed atrophy of the maculopapillary bundle in both eyes of 25 cases examined post mortem. We retrospectively examined the clinical history and general autopsy findings for evidence of malnutrition. An adequate clinical history was obtained in 24 patients, and an autopsy was performed on 21 patients. Our review disclosed that all 25 patients had marked nutritional deprivation, most commonly from alcohol abuse (20 patients), advanced carcinoma (8 patients, 7 of whom were also alcohol abusers), and other malnutritional and disabling conditions (4 patients). A history of heavy smoking was documented in 11 patients. Our findings support the contention that dietary deficiency plays a role in the pathogenesis of the condition that in the past has been referred to as tobacco-alcohol amblyopia and more recently has been called nutritional amblyopia
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Idiopathic macular hole following vitrectomy: implications for pathogenesis
Attention to the pathogenesis and clinical features of macular hole formation has increased with the advent of therapy. The purpose of this study is to present three cases that occurred in atypical settings that may have important pathogenic implications.
The authors conducted a retrospective study of three patients who presented with macular holes that developed 10 months to 5.5 years after previous vitrectomy. In each case, the cortical vitreous layer was absent in the region of the macula at the time of operation for the macular hole.
The macular hole was successfully sealed and the visual acuity improved in all patients. All three cases in this report lacked an operculum, occurred long after vitreous removal, and had no evidence of any residual cortical vitreous.
Macular hole formation in the absence of cortical vitreous suggests the possibility that the etiology of macular holes may involve a spontaneous umbo dehiscence rather than vitreous-induced surface traction. A mechanism involving a cystic degenerative process is proposed as the cause of atypical and typical macular hole formation
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Posterior chamber IOL implantation with suboptimal posterior capsular support
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Pathogenesis of macular holes and therapeutic implications
To review the literature and identify consistencies and inconsistencies in existing theories of pathogenesis and to consider some of their possible therapeutic implications.
Presentation of clinical case material with a synthesis of ideas on macular holes.
The literature of macular hole surgery is reviewed pertinent to pathogenic theories. Clinical examples of evolving macular holes shown on ocular coherence tomography are presented to illustrate issues.
The history of pathogenesis and macular holes is interesting in that, in many ways pathogenic theory has come full cycle. Initially, anteroposterior traction was thought to cause direct formation of a macular hole. Subsequently, degenerative and then tangential tractional etiologies were proposed. Current imaging studies have greatly advanced our understanding of anatomic features of full-thickness holes and early full-thickness hole conditions. These are most consistent with a focal anteroposterior traction mechanism, but some inconsistences in clinical cases suggest a role for degeneration of the inner retinal layers.
Degeneration of the inner retinal layers at the central fovea may predispose the eye to macular hole formation. What may otherwise be incidental tractional forces appear to initiate the hole. These tractional elements are oriented perpendicularly to the retinal surface, rather than tangentially. Further observations, especially with sequential observations from ocular coherence tomography, may yield further insights into the pathogenesis of macular holes as well as implications regarding the best repair techniques
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