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Biomedical subjects

R F Steinert

Publications and source records attributed to R F Steinert.

87 records · Page 5Linked to original sources
PubMed1983

Plasma formation and shielding by three ophthalmic neodymium-YAG lasers.

Because microplasma formation may provide an energy-absorbing shield that protects the retina from inadvertent injury during neodymium-YAG laser surgery, we studied plasma formation and shielding by three ophthalmic neodymium-YAG lasers (the Q-switched American Medical Optics YAG-100, the mode-locked Meditec OPL-3, and the Q-switched LASAG Sirius Microruptor 2) with three model targets (physiologic saline, 1% sodium hyaluronate, and a cellophane membrane). Plasma formation produced a linear reduction in the transmission of light energy along the beam path in a qualitatively differences. Plasma shielding was similar in both saline and sodium hyaluronate; enhancement of the shield effect occurred only with the cellophane membrane target. Operating the lasers at energy levels far above threshold did not reduce total light transmission significantly. Clinical use should be guided by the principle of employing the minimum energy necessary to cut the target tissue.

Lasers↗
PubMed1983

Plasma shielding by Q-switched and mode-locked Nd-YAG lasers.

Q-switched and mode-locked Nd-YAG lasers depend on beam divergence and plasma formation to reduce energy transmission below the retinal damage threshold. In a model system of physiologic saline, we investigated plasma "shielding" and found that plasma formation markedly reduces further energy transmission along the beam path once plasma formation occurs. The protective effect of plasma shielding appears similar for a Q-switched pulse and a train of mode-locked pulses in a physiologic saline medium.

Humans↗
PubMed1983

Laser surgery of the lens. Experimental studies.

The authors used high peak power nanosecond (Q-switched) and picosecond (mode-locked) pulses from the neodymium-YAG laser to perform experimental anterior and posterior capsulotomy in rabbits. The morphology of laser anterior capsulotomy was studied using scanning electron microscopy. Ultrastructural studies revealed no evidence of morphologic abnormality in the corneal endothelium in eyes in which laser capsulotomy had been performed. The critical factors for the prevention of inadvertent retinal injury during laser surgery in the anterior segment of the eye were identified as pulse energy and cone angle of incident laser radiation. Using wide angle fundus photography and fluorescein angiography, intentional retinal injury during laser surgery of the lens was experimentally documented when retinal radiant energy exposure exceeded injury threshold.

Animals↗
PubMed1981

Long-term drift and continued efficacy after multiyear timolol therapy.

The clinical courses of 41 patients who received timolol maleate for experimental protocols were reviewed. We reevaluated the conditions of 17 patients with the elevated pressures of primary open angle glaucoma who had received timolol alone or in combination with other glaucoma medications for a maximum of 35 months (average, 26 months). Withdrawal of timolol led to an average intraocular pressure rise of 5 mm Hg. Eight patients treated with timolol alone showed a progressive, significant, 3-mm Hg upward rise, or "long-term drift" in IOP during the follow-up period. Pressure rise after timolol withdrawal, however, was not significantly less than pressure reduction when timolol was initiated. At least two weeks are required for "washout" or disappearance of timolol effect after timolol is withdrawn, and re-treatment for one week restores IOP to prewithdrawal levels.

Acetazolamide↗
PubMed1980

Small unilateral foveal hemorrhages in young adults.

We studied nine cases of single, small, intraretinal foveal hemorrhages in one eye each of nine young adults during the last five years. The patients ranged in age from 18 to 47 years and were otherwise healthy. Four patients gave a history of strenuous exercise, most often weight lifting. The visual acuities ranged from 6/6 (20/20) to 6/60 (20/200) and most patients complained of a small central or paracentral scotoma. Fluorescein angiography did not show any retinal or choroidal vascular abnormalities and recovery of visual acuity was excellent in all patients available for follow-up examination during a period of two weeks to six months.

Adolescent↗
PubMed1978

Clinical trial comparing timolol ophthalmic solution to pilocarpine in open-angle glaucoma.

A ten-week, double-masked, randomized, clinical trial compared timolol ophthalmic solution and pilocarpine in the therapy of open-angle glaucoma. Timolol decreased the intraocular pressure at least as much as pilocarpine and did not induce miosis, accommodative spasm, or other annoying side effects. The pulse was slowed by timolol, but blood pressure was unaffected. Significant decreases in intraocular pressure were still present after ten weeks of maintenance therapy with the same concentration of drug.

Adult↗
PubMed1978

Long-term experience with timolol ophthalmic solution in patients with open-angle glaucoma.

Timolol was used by 37 glaucoma patients from 1 to 18 months. Of those 37 patients, 31 used timolol for three months or longer and 7 used timolol for over one year. Timolol produced sustained reductions in intraocular pressure with continuous administration and did not induce miosis, accommodative spasm, or other annoying side effects. Systemic absorption produced a mild slowing of resting pulse rate. In some patients, timolol's ocular hypotensive effects are additive to miotics and carbonic anhydrase inhibitors.

Adult↗
PubMed1975

Continuous measurement of O2 consumption and CO2 elimination during a wakeful hypometabolic state.

A previous investigation has demonstrated that the practice of a meditational technique elicits a wakeful, hypometabolic state. Measurement of O2 consumption and CO2 elimination was made by sampling techniques; mean values of these parameters were calculated from 6-10 minute samples. The present study extends this investigation, using a recently developed method of continuous measurement of O2 consumption and CO2 elimination. Continuous measurement of these parameters permitted the determination of mean values for the entire experimental periods as well as for selected intervals and permitted the examination of the sequence of respiratory changes. The present study reports statistically significant decreases in O2 consumption of 5 per cent and CO2 elimination of 6 percent for the entire 20 minutes of the mediation period. These are lower than the sample values of 16 percent and 15 percent reported in the previous study. However, when selected intervals of the mediation period are examined, decreases in O2 consumption and CO2 elimination are comparable to those previously reported. The results are consistent with the difference between the discontinuous sampling measurement method originally employed and the continuous measurement method of the present investigation.

Adult↗
PubMedDate not supplied

Timolol in the therapy of "ocular hypertension".

Timolol has been shown to be at least as effective as pilocarpine and epinephrine in the therapy of open angle glaucoma. To date there appear to have been few serious side effects from timolol when it has been used in patients without cardiac or pulmonary disease. The decision whether and when to treat a patient with elevated intraocular pressure depends upon a weighing of risk of glaucoma damage versus the side effects of the drugs used in therapy. The use of the beta blocking agents, particularly timolol, in the therapy of ocular hypertension is considered. Reports on the efficacy and safety of timolol are cited, and the author's reevaluation of their own series of patients treated with timolol for 17-36 months is discussed.

Adrenergic beta-Antagonists↗
PubMedDate not supplied

Laser interactions with the cornea.

Principles of laser-tissue interactions in the eye are reviewed. Corneal structure and function are summarized, with particular regard for features related to laser treatment. A summary of argon and carbon dioxide laser techniques in the cornea is presented, followed by a review of studies on corneal response to ultraviolet radiation. A detailed description is then given of the characteristics of excimer laser tissue ablation. Potential applications of this process in corneal and keratorefractive surgery are reviewed.

Argon↗
PubMedDate not supplied

Reduction of hyperopia associated with manual excision of Salzmann's nodular degeneration.

PURPOSE: Removing central corneal pathology often leads to a hyperopic shift secondary to corneal flattening. A myopic shift, or reduction in hyperopia, would be expected after removal of peripheral corneal pathology with central corneal steepening. This case illustrates the refractive changes induced by Salzmann's nodular degeneration and the myopic shift associated with their excision. METHODS: A 53-year-old female presented with a slowly progressive increase in hyperopia. Vision in the right eye was 20/40 with a refraction of +10.00 -4.00 x 90 degrees. Vision in the left eye was 20/30 with a refraction of +5.75 -2.00 x 105 degrees. Both corneas exhibited nodular subepithelial opacities in the mid-periphery. A superficial keratectomy was performed on each eye, 1 year apart. RESULTS: Twelve days postoperatively, uncorrected visual acuity in the right eye was 20/25, and 20/20 with a refraction of -0.75 -0.50 x 31 degrees, 6 months later. Six days postoperatively, uncorrected visual acuity in the left eye was 20/40, and 20/30 with a refraction of -1.25 D, 1 month later. CONCLUSION: Superficial keratectomy provides a means of restoring the original corneal contour, especially when the pathology is easily dissected from Bowman's layer. The surgeon should investigate the refractive status prior to the development of the nodules and be aware of the possible refractive change upon removal of the pathology.

Corneal Dystrophies, Hereditary↗
PubMedDate not supplied

Clinical strategies for excimer laser therapeutic keratectomy.

BACKGROUND: Surgical therapy for superficial corneal scars, dystrophies, or surface irregularities with the 193 nm excimer laser shows great promise. Depending upon the character of the pathology to be treated, different surgical strategies are required. METHODS: Treatment strategies for three patients with diverse corneal pathology are presented. Focal surface irregularities are treated with small laser spot sizes leaving the epithelium intact. Smooth, uniformly distributed subepithelial anterior stromal pathology is best removed with a large spot size through intact epithelium. When scattered scarring of variable thickness is present, selective epithelial debridement permits improved exposure of irregularities in Bowman's layer and the anterior stroma. RESULTS: Guidelines for selective debridement of epithelium and protection of adjacent and underlying stroma with moderate viscosity solutions enhances the surgeons's ability to obtain a smooth and clear surface while minimizing corneal thinning. Even with these strategies and use of plano disc ablation, net hyperopic shift generally occurs with broad large area therapeutic ablation. CONCLUSIONS: Superficial corneal opacities and irregularities can be surgically treated with the excimer laser as an alternative to the more invasive procedure of lamellar keratoplasty. Treatment failures can then go on to lamellar keratoplasty while successfully treated patients are more rapidly rehabilitated at lower total cost than a lamellar graft. Refinement of treatment strategies to minimize the hyperopic shift and facilitate masking around irregularities will further improve the results.

Adult↗
PubMedDate not supplied

Photorefractive keratectomy for myopia using a 4.5-millimeter ablation zone.

BACKGROUND: Argon fluoride (193 nm) excimer laser photorefractive keratectomy for myopia is under evaluation by the United States Food and Drug Administration. METHODS: We report a consecutive prospective series of 100 patients (one eye per patient) treated as part of the Phase IIB FDA-approved protocol, with 80 patients followed for 1 year. Patients' ages ranged from 21 to 62 years (mean, 35 years). The Summit Technology, Inc ExciMed UV200LA with a 4.5-mm diameter ablation was used. RESULTS: Baseline spherical equivalent refraction ranged from -2.00 to -6.90 diopters (D) (mean -4.60 D). Ninety-five percent of eyes reepithelialized by 72 hours. At 1 year, the difference between attempted and achieved correction was +/- 0.50 D for 42 eyes (53%) and +/- 1.00 D for 60 eyes (75%). During the first 6 months, there was a trend toward overcorrection and the majority of eyes showed some loss of initial refractive correction; 10 eyes (14%) changed by 1.00 D or more between 6 and 12 months. An uncorrected visual acuity of 20/25 or better was achieved by 50 eyes (63%) and 20/40 or better by 61 eyes (77%). Of the 10 eyes (12%) that lost two or more Snellen lines of spectacle-corrected or glare visual acuity, two had visual acuity of worse than 20/25. Central subepithelial corneal haze was absent to mild in 77 (96%) eyes at 12 months. CONCLUSIONS: Excimer laser photorefractive keratectomy as performed in this study was generally effective and safe in reducing simple spherical myopia. Further studies of the effect of a larger diameter ablation zone, smoother transitional corneal contours, and the effect of postoperative topical corticosteroids may lead to further improvements in outcome.

Adult↗