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Biomedical subjects

R F Steinert

Publications and source records attributed to R F Steinert.

At least 73 records · Page 4Linked to original sources
PubMed1986

Vitreous changes after neodymium-YAG laser photodisruption.

We investigated physicochemical changes in the vitreous body after photodisruption with a Q-switched neodymium-YAG laser. In vivo proton nuclear magnetic resonance imaging techniques were employed to assess alterations in the vitreous of irradiated rabbit eyes. Measurements of proton relaxation times (T1 and T2), viscosity, and chromatographic spectra were made in vitro on irradiated bovine and rabbit vitreous, and circular dichroism measurements were used to study changes in an irradiated sodium hyaluronate solution. Statistically significant changes in T1, were observed immediately after irradiation, but the small magnitude and reversibility of those changes, combined with the fact that the other measurements detected no changes, suggest that neodymium-YAG laser photodisruption does not have a direct deleterious effect on the structural integrity of the normal vitreous body.

Animals↗
PubMed1986

Corneal endothelial injury in rabbits following excimer laser ablation at 193 and 248 nm.

We performed a morphologic investigation of the corneal endothelium following in vivo excimer laser ablation at 193 and 248 nm in rabbit eyes. Control experiments were performed in eyes with incisions of similar depth made with a diamond surgical knife, and normal control eyes were studied in parallel. We found that 193-nm excimer laser incision to 90% of corneal depth produces endothelial alterations similar to those seen underlying diamond knife incisions of similar depth. Scanning electron microscopy revealed an incisional ridge and endothelial cellular edema; endothelial cell loss was not observed. In contrast, 248-nm ablations of similar depth and energy density revealed loss of underlying endothelial cells and a surrounding zone of severe cellular damage.

Animals↗
PubMed1985

Prevention of intraocular pressure elevation following neodymium-YAG laser posterior capsulotomy.

Thirty-two eyes of 32 patients were treated with 0.5% timolol, 2% pilocarpine, or normal saline five and 30 minutes following neodymium-YAG laser posterior capsulotomy in a randomized, double-masked study. Mean maximum intraocular pressure (IOP) elevation was 8 +/- 2 mm Hg following treatment with normal saline, 5 +/- 3 mm Hg following treatment with 2% pilocarpine, and 1 +/- 2 mm Hg following treatment with 0.5% timolol. Fewer patients treated with 0.5% timolol developed an IOP elevation of 5 mm Hg or more than control patients. On aphakic patient treated with 0.5% timolol developed a maximum IOP greater than or equal to 40 mm Hg. We found that treatment with 0.5% timolol after neodymium-YAG laser posterior capsulotomy provides partial protection from IOP elevation.

Aged↗
PubMed1985

Cutting efficiency of single shot and burst mode neodymium:YAG lasers.

The efficiency of cutting by single pulses and bursts of two, four, and eight pulses from a Q-switched Nd:YAG laser was determined in a model of a heavy membrane and a loosely floating target. The burst modes cut the targets somewhat more quickly than single shots, but required a marked increase in total energy delivered. Anterior movement of the breakdown zone and posterior displacement of the target explain the energy inefficiency of burst-mode photodisruption.

Humans↗
PubMed1985

Neodymium:YAG laser cutting of intraocular lens haptics.

Neodymium:YAG laser cutting of polymethylmethacrylate and polypropylene anterior chamber and posterior chamber intraocular lens haptics was studied in terms of ease of transection and physical structure of the cut areas as seen by scanning electron microscopy. A marked difference was discovered, with the polymethylmethacrylate cutting easily along transverse planes, whereas the polypropylene resisted cutting along longitudinal fibers. Clinical guidelines are presented.

Aged↗
PubMed1985

Neodymium: YAG laser trabeculopuncture in open-angle glaucoma.

Ten eyes of eight patients with open-angle glaucoma (OAG) had neodymium (Nd):YAG trabeculopuncture performed in an investigational protocol as an alternative to surgical intervention. In each, at four to six sites in the mid-trabecular meshwork, three to six superimposed applications were made (2 to 6 mJ). In four of six patients with adult OAG, a small decrease in intraocular pressure (IOP) was noted (from a mean of 25.5 to 20.0 mmHg after 3-4 weeks in the treated eyes, compared to no change at 21 mmHg in the fellow eyes). There appeared to be further attenuation of this IOP effect over the subsequent 2 to 11 months, and all patients demonstrated gonioscopic closure of all the puncture sites with time. One patient demonstrated an acute IOP elevation to 58 mmHg after the procedure, necessitating emergency filtration surgery. In contrast, in four eyes of two patients with juvenile open angle glaucoma, a dramatic lowering of IOP and improvement in tonographic outflow facility was demonstrated, although the effects were only temporary in one patient. YAG laser treatment to the trabecular meshwork may have its greatest potential usefulness when abnormalities in the uveal meshwork are involved, such as in certain cases of juvenile or congenital glaucoma, and may help identify the need for a surgical goniotomy. With more usual forms of OAG, however, widespread use of this technique should be avoided until greater efficacy can be achieved.

Adolescent↗
PubMed1985

Excimer laser ablation of the cornea and lens. Experimental studies.

The pulsed ultraviolet excimer laser has been used to produce tissue ablation with a high degree of precision and with minimal thermal damage to adjacent structures. In comparative studies of excimer laser ablation of the cornea and crystalline lens using 193 nm and 248 nm radiation, threshold fluence for corneal and lens ablation was higher at 248 nm than at 193 nm. Ablation of corneal stroma at 193 nm produced the most precise cuts. When examined by transmission electron microscopy, a narrow zone of damaged tissue (0.1 to 0.3 micron) was seen immediately adjacent to the tissue removed by the laser. Ablation with 248 nm radiation produced incisions with ragged edges and with a wider and more severe zone of damage in adjacent stroma. Ultraviolet spectral transmission studies of the corneal stroma showed that absorption is 10 times greater at 193 nm than at 248 nm. The excimer laser was effective in producing well controlled ablation of the crystalline lens in vitro, with effects parallel to those seen in the cornea.

Animals↗
PubMed1985

Intraocular pressure elevation following Nd:YAG laser posterior capsulotomy.

Intraocular pressures (IOP) and tonographic outflow facilities were measured following neodymium (Nd): YAG laser posterior capsulotomy in 13 pseudophakic and 8 aphakic eyes. Mean intraocular pressure (IOP) peaked by three hours with a mean increase of 13 mmHg, remained elevated by 5 mmHg at 24 hours but returned to baseline by one week. Fourteen eyes (67%) had greater than or equal to 10 mmHg elevation and eight (38%) had greater than or equal to 40 mmHg maximum IOP. All the patients who eventually demonstrated a greater than or equal to 10 mmHg elevation within six hours of the capsulotomy initially had an IOP elevation greater than or equal to 5 mmHg at one hour. The mean outflow facility was reduced from 0.18 microl/min/mmHg before capsulotomy to 0.08 microl/min/mmHg (55%, P less than 0.0001) at four hours and was still decreased at 0.13 microl/min/mmHg (27%, P less than 0.05) at one week. Seventy-five percent of aphakic and 15% of pseudophakic patients had maximum IOP greater than or equal to 40 mmHg (P less than 0.01). Measurements should be performed one hour postlaser in all patients for IOP and three to four hours in aphakic patients, glaucomatous patients, patients receiving greater than or equal to 200 mjoules total laser energy, and patients with greater than or equal to 5 mmHg elevation at one hour in order to detect and treat significant IOP elevations.

Cataract Extraction↗
PubMed1985

Time-resolved studies of Nd:YAG laser-induced breakdown. Plasma formation, acoustic wave generation, and cavitation.

The use of high intensity ultrashort pulsed laser radiation to produce optical breakdown is an important approach for the surgical treatment of intraocular structures. We have investigated the transient properties of Nd:YAG laser induced breakdown in a saline model using time-resolved spectroscopic techniques. Spatially resolved pump and probe techniques are applied to study the dynamic behavior of the plasma formation, acoustic wave generation, and cavitation processes which accompany the optical breakdown. Measurements of plasma shielding and luminescence indicate that the laser induced plasma forms on a subnanosecond time scale and has a lifetime of several nanoseconds. An acoustic transient is generated at the breakdown site and propagates spherically outward with an initial hypersonic velocity, then loses energy and propagates at sound velocity. Transient heating following the plasma formation produces a liquid-gas phase change and gives rise to cavitation or gas bubble formation. This gas bubble expands rapidly for several microseconds, then slows to reach its maximum size and finally collapses.

Eye↗
PubMed1984

Neodymium-YAG laser therapy to the anterior hyaloid in aphakic malignant (ciliovitreal block) glaucoma.

In three aphakic eyes and two eyes with intraocular lens implants (five patients, four women and one man, ranging in age from 65 to 76 years) persistent shallow or flat anterior chamber was observed despite multiple patent laser or surgical iridectomies. In each case direct application of the neodymium-YAG laser (3 to 11 mJ) to the anterior hyaloid face resulted in immediate deepening of the anterior chamber. This deepening was sustained in four of the cases. These results confirm previous observations suggesting that the anterior hyaloid can be the locus of abnormality in aphakic malignant (ciliovitreal block) glaucoma. Neodymium-YAG "hyaloidotomy" may be better than penetrating surgery in such cases.

Aged↗
PubMed1984

Neodymium-YAG laser surgery on experimental vitreous membranes.

A Q-switched neodymium-YAG laser was used to cut experimental vitreous membranes in rabbit eyes. We were able to cut vitreous membranes up to 4 mm from the retinal surface using single pulse energies of up to 4 mJ without fluorescein angiographic evidence of retinal injury. When cutting membranes between 1.5 and 3 mm from the retinal surface, injury was documented in five of seven cases. The most frequently observed fundus injury was choroidal hemorrhage. The neodymium-YAG laser may be useful in cutting avascular membranes in the posterior segment of the eye.

Animals↗
PubMed1984

Long-term follow-up of Nd:YAG laser posterior capsulotomy.

A Nd:YAG laser developed for ophthalmic surgery was studied for safety and efficacy in secondary discission of the posterior capsule in aphakic and pseudophakic subjects. The study involves 6,800 subjects, 526 of whom had completed the six-month postoperative course by the time the data base was closed for analysis. Of the 526 subjects who were treated with the laser, 87.8% had improved vision, with 82.9% achieving a visual acuity of 20/40 or better. This result compares favorably with results for the surgically treated population in which only 68.4% experienced improved vision, with 80.2% achieving a visual acuity of 20/40 or better. Approximately four times more surgically treated subjects than laser-treated subjects experienced diminished vision (14.8%). Cumulative complication rates in the laser-treated population were very low (CME 2.3%, secondary glaucoma 3.6%, retinal detachment 0.4%, overall rate 4.8%). Persistent complications (present at the six-month postoperative period) were present at an overall incidence of 2.3%, comprised primarily of CME, 0.2%, retinal detachment, 0.2%, and secondary glaucoma, 0.8%. Only 5.7% of subjects experienced an intraocular pressure (IOP) rise to 30 mm Hg or greater. Return to the preoperative IOP level occurred in 89% of subjects in the first 24 hours to one week. Predictors of IOP rise to 30 mm Hg or greater were determined to be preoperative glaucoma and/or preoperative IOP of greater than 20 mm Hg.

Aged↗
PubMed1984

Pre-keratoplasty potential acuity evaluation. Laser interferometer and potential acuity meter.

Twenty-three patients who underwent penetrating keratoplasty were evaluated preoperatively for potential retinal acuity utilizing the Randwal Laser Interferometer and the Mentor Potential Acuity Meter. When compared with Snellen visual acuity during the early postoperative period (1-6 months), both instruments were useful as qualitative predictors of macular function when used in the presence of mild to moderate corneal edema. The laser interferometer was somewhat more accurate in the severe cases of corneal edema.

Cataract Extraction↗
PubMed1984

Endothelial guttata and facility of aqueous outflow.

Thirty-eight eyes of 22 patients with corneal endothelial guttata were examined by slit lamp, tonometry, tonography, and wide-field specular microscopy. The mean value for facility of outflow (C55) was 0.23, and it was not statistically different from reported values for a normal population. Also, there was no correlation between extent of guttata as seen with wide-field specular microscopy and facility of outflow. Thus, contrary to a previous report, endothelial guttata does not seem to predispose to impaired facility of outflow.

Aqueous Humor↗