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Biomedical subjects

D Gaasterland

Publications and source records attributed to D Gaasterland.

At least 19 recordsLinked to original sources
PubMed1997

A multicenter comparison study of the Humphrey Field Analyzer I and the Humphrey Field Analyzer II.

PURPOSE: The purpose of the study is to determine the comparability of the 30-2 full-threshold program in the original Humphrey Field Analyzer (HFA) I to the same test procedure in the new Humphrey Field Analyzer II. METHODS: At each of five clinical centers, one eye of patients with ocular hypertension and normal visual fields, patients with early glaucomatous visual field loss, and patients with more advanced visual field loss were tested with the two instruments plus a retest on a separate HFA I. All participants had undergone at least one prior visual field examination. To minimize the influence of any residual learning or fatigue effects, the order of testing for the three visual field examinations was counterbalanced across subjects. A total of 250 patients were tested (81 patients with ocular hypertension, 81 patients with early glaucomatous visual field loss, and 88 patients with more advanced glaucomatous visual field loss). RESULTS: No statistically significant differences were observed between thresholds, visual field indices, or reliability indices obtained with the HFA I and the HFA II. The small differences between the two instruments were equivalent to the variation observed for test-retest measures using only the HFA I. These results were consistent across the range of visual field characteristics shown by the ocular hypertensive, early glaucoma, and moderate glaucoma patient groups. CONCLUSIONS: The authors' results indicate that there are no differences in the visual field results obtained with the HFA I and the HFA II. These findings suggest that with careful attention to test protocols, the HFA I and HFA II may be used interchangeably to observe patients, even within the context of multicenter clinical trials.

False Negative Reactions↗
PubMed1996

Translating research into practice: controlled clinical trials and their influence on glaucoma management.

Historically, management strategies for glaucoma have stressed reduction of IOP as the primary goal. Yet, if we question this principle, we find a deficiency of information to support it as the optimal strategy for managing glaucoma patients and those at risk of developing glaucoma. Thus, the practice of lowering IOP in glaucoma management was placed on trial by the 1987 Eddy and Billings report (D. M. Eddy and J. Billings, 1987). Although generally denounced by clinicians, this report nonetheless alerted the ophthalmologic community that success of glaucoma treatment must be measured by endpoints unrelated to IOP and that a controlled trial to demonstrate glaucoma treatment efficacy was necessary. A clinical trial is an experiment. As such, it is the best study design for inferring causality between an exposure (e.g., IOP) and an outcome (e.g., glaucoma), and it is the best methodology for demonstrating treatment efficacy. However, it is important to understand that efficacy is not the same as effectiveness. Whereas "efficacy" is the extent to which a specific intervention produces a beneficial result under ideal conditions, "effectiveness" is the extent to which a specific intervention, when deployed in the field, does what it is intended to do. The influence of study results on the practice of medicine is more a function of demonstrated effectiveness than efficacy of an intervention. All of the completed glaucoma clinica trials reviewed were well performed, and many have had a substantial influence on the philosophy and practice of glaucoma management. The glaucoma clinical trials currently being performed represent the highest standards of clinical trial methodology. This is an exciting time for clinical research on glaucoma. Well accepted dogmas are being challenged, and the ophthalmic community is aggressively addressing difficult issues. Questions being asked are of fundamental importance and addressing them is essential. Particularly exciting in these trials is the fact that IOP is not being considered as an endpoint and that consideration is being given to the previously ignored but extremely important issue of overall patient well-being. Only with time will the ultimate impact of these trials on the philosophy and practice of glaucoma management become evident.

Controlled Clinical Trials as Topic↗
PubMed1990

Trans-scleral application of a semiconductor diode laser.

We used a diode laser with an output power of 1 W through a fiberoptic light pipe (200 microns diameter) to deliver laser energy through the sclera of pigmented rabbits. Ciliary body destruction occurred with energy levels of 300-400 mW and exposure time of 0.5 sec. Retinal photocoagulation was achieved with energy levels of 200-500 mW in 0.5 sec. Histologic examination of acute lesions demonstrated thermal destruction of ciliary body processes and retina. Chorioretinal scar formation was observed clinically and histologically within 2-3 weeks. Our data indicate that the transscleral diode laser may be used for destruction of the ciliary body processes or peripheral retinal coagulation in pigmented eyes.

Animals↗
PubMed1986

The flow of aqueous humor through micro-porous filters.

Flow resistance was measured as bovine and primate aqueous humor was passed through Nuclepore polycarbonate filters having flow dimensions similar to those found within the juxtacanalicular meshwork of the aqueous outflow network. The results indicate that aqueous humor has a greater flow resistance than isotonic saline; this greater resistance is attributable to proteins or glycoproteins in aqueous humor that obstruct the filters. If the same phenomenon is operative in the aqueous outflow network, it would help to explain discrepancies between calculated and measured aqueous outflow resistance.

Animals↗
PubMed1984

The effect of isoproterenol on aqueous humor formation in humans.

Isoproterenol was applied topically to one eye of each of 20 normal human volunteers. The rate of aqueous humor flow was measured with fluorophotometry. Intraocular pressure fell slightly in the treated eye, but the rate of aqueous humor flow was unaltered. Even when applied to the cornea in high concentrations, this beta-adrenergic agonist appeared to have no measurable effect on the flow of aqueous humor through the anterior chamber in the human eye.

Anterior Chamber↗
PubMed1978

Axoplasmic flow during chronic experimental glaucoma. 1. Light and electron microscopic studies of the monkey optic nervehead during development of glaucomatous cupping.

The anterior optic nerve and the macular region of the retina of glaucomatous eyes of five rhesus monkeys (Macaca mulatta) have been examined by light and electron microscopy. The experimental glaucoma had been induced by argon laser treatment of the anterior chamber angle. The eyes were examined 3 to 11 weeks after the onset of sustained elevation of intraocular pressure above 20 mm Hg. Severe degenerative changes were seen in eyes with higher intraocular pressure and longer duration of glaucoma. Eyes with a lesser elevation of intraocular pressure and shorter duration of glaucoma showed changes sharply localized to the axon bundles in the scleral lamina cribrosa. Accumulation of mitochondria and dense bodies occurred anterior and posterior to collagenous septae. The location of these changes is in agreement with the localization of block of axoplasmic transport identified by autoradiographic studies. It is speculated that these cytologic changes reflect blockage of axoplasmic flow in the optic nerve of eyes with glaucoma.

Animals↗
PubMed1977

Management of a patient with orbital varices, visual loss, and ipsilateral glaucoma.

A man with congenital orbital varices developed progressive ipsilateral visual loss beginning at age 62. Work-up demonstrated elevated intraocular pressure, decreased outflow facility, and mildly elevated episcleral venous pressure in the affected eye. Initiation of adequate glaucoma treatment was associated with interruption of declining visual acuity and with expansion of the constricted visual field. Medical control of coexisting glaucoma should be attempted prior to consideration of surgical intervention in any patient with visual loss and an ipsilateral orbital varix.

Epinephrine↗
PubMed1976

Studies of aqueous humor dynamics in man. V. Effects of acetazolamide and isoproterenol in young and old normal volunteers.

Young and old volunteers received acetazolamide systemically or isoproterenol topically. Although the responses of the two groups of volunteers were quite similar for acetazolamide, they differed significantly for isoproterenol. It is suggested that a normal aging change is altered responsiveness of the site of aqueous production and of the outflow pathways to topical isoproterenol. The site of aqueous production becomes less responsive; the outflow pathways become more responsive.

Acetazolamide↗
PubMed1975

Studies of aqueous humor dynamics in man. IV. Effects of pilocarpine upon measurements in young normal volunteers.

The acute effects of topical pilocarpine 4 per cent, administered to one eye, have been studied in replicate experiments in young volunteers. One hour after medication administration the intraocular pressure was significantly lower. The magnitude of the reduction exceeded that predicated from the significant increase of true facility of outflow. This is explained by the observation of a significant reduction of calculated aqueous humor flow. Pilocarpine caused a significant increase of pseudofacility, a clinically useful drug effect not previously reported. One hour after medication administration, measured episcleral venous pressure was not different from the pretreatment level.

Administration, Topical↗