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Biomedical subjects

S L Trokel

Publications and source records attributed to S L Trokel.

At least 19 recordsLinked to original sources
PubMed1992

In situ collagen gel mold as an aid in excimer laser superficial keratectomy.

PURPOSE: The aim of this study is to evaluate the potential use of bovine type I collagen as an adjuvant to excimer laser keratectomy. METHOD: A suspension of collagen with the capability to polymerize into a gel was applied to the anterior corneal surface of freshly enucleated porcine eyes, using 35.0 diopter (D), 45.5 D, or 52.0 D contact lenses as molds. Keratometry, photokeratoscopy, slit-lamp photography, scanning electron microscopy, and light microscopy were performed on the new surfaces. Furthermore, an irregular corneal surface was created and a suspension of collagen was applied to mask protruding irregularities, therefore creating a smooth surface that was subjected to excimer laser keratectomy. Ablation rates for both collagen and cornea were measured. RESULTS: Collagen suspension placed on a cornea and molded with contact lenses created a smooth-surfaced gel that conformed to the shape of the contact lens and adhered to the anterior cornea; it was optically smooth and regular as shown by photokeratoscopy, keratometry, and scanning electron microscopy. The corneal curvature was altered in accordance with the base curvature of the contact lens used. Results of keratometry showed resolution of pre-existing astigmatism without induction of new astigmatism. The ablation rate of the gel was not measurably different than that of cornea; hence, when applied to an irregular corneal surface, a smooth surface was created after excimer laser ablation. CONCLUSION: This study supports the potential value of collagen gel as an adjuvant to excimer laser keratectomy for removal of corneal irregularities as well as for correction of myopia or hyperopia with or without astigmatism.

Animals↗
PubMed1992

Pupil diameter and the principal ray.

Placement of the surgical zone is critical in refractive procedures that alter a portion of the corneal curve. An improperly centered optical zone may produce glare, decrease best corrected visual acuity, and decrease contrast sensitivity. For proper placement, the new surface should be centered around the line of sight, which is the principal ray from the object of regard that passes through the image of the patient's pupil as projected on the cornea. This point is not necessarily at the geometric center of the cornea and is found by locating the center of the pupil while the patient is maintaining fixation coaxially with the surgeon. However, the pupil does not dilate concentrically and its geometric center moves as the pupil diameter changes. We have found a shift up to 0.7 mm in the geometric center of the pupil as it dilates. Therefore, centration of an ablated or a radial keratotomy zone is most efficiently done when the diameter of the modified corneal optical zone is centered around the line of sight and is superimposed upon the entrance pupil. This will minimize extension of the edge of the large pupil beyond the ablated zone and reduce unwanted secondary optical effects from degrading vision.

Adult↗
PubMed1992

Soft tissue effects of the THC:YAG laser on canine vocal cords.

Recently, a laser based on a thulium-holmium-chromium (THC) doped Yttrium-aluminum-garnet (YAG) rod has been developed that produces light of 2.15 microns wavelength and can be transmitted through a low OH- silica fiberoptic cable. This wavelength falls on one of the peaks of the energy absorption spectrum of water. Thus, the THC:YAG laser eliminates the disadvantage of a cumbersome delivery system found in the CO2 laser while still providing precise cutting and minimal tissue injury inherent in lasers emitting light absorbed by water. We evaluated the soft tissue effects of this laser on canine vocal cords. Ablative lesions were produced by the THC:YAG laser and histologically examined on postoperative days 1, 7, and 28. Results indicate that the depth of tissue penetration is easily controlled and the healing response to tissue injury is comparable to that of the CO2 laser. The THC:YAG laser should prove to be a superior laser for use in otorhinolaryngology, especially when adapted to a flexible endoscope.

Aluminum Silicates↗
PubMed1991

Alternative lasers for endoscopic surgery: comparison of pulsed thulium-holmium-chromium:YAG with continuous-wave neodymium:YAG laser for ablation of colonic mucosa.

Precise and controllable tissue vaporization is essential for minimizing risk in removal of sessile polyps from the lumen of thin walled gastrointestinal organs such as the colon. We compared the ablative efficiency on canine colonic mucosa of the THC:YAG laser with the clinically employed cw Nd:YAG laser. Fresh canine colon was treated with a progressive dose schedule using each laser at several energy/power densities. Ablation depth was measured on fresh tissue and thermal (non-ablation or coagulative) damage examined histologically. The THC:YAG ablation rates were 13.7 +/- 0.8 and 10.2 +/- 0.4 microns/J at 55 and 85 J/cm2, respectively. The Nd:YAG laser generated 3.7 +/- 0.3, 2.8 +/- 0.1, and 3.6 +/- 0.2 microns/J at 4,460, 5,095, and 5,730 W/cm2, respectively. There was a significant (P less than 0.001) difference among the THC:YAG ablation rates and between the THC:YAG and Nd:YAG ablation rates (ANOVA). The THC:YAG laser craters had significantly less collateral thermal damage than Nd:YAG. The pulsed THC:YAG laser should have an important clinical role since its use could reduce the risk of perforation in endoscopic laser procedures such as the removal of sessile polyps.

Aluminum Silicates↗
PubMed1991

Evidence of genotoxic damage in human cataractous lenses.

Lens epithelial fragments (tags) recovered from individuals during routine cataract extraction have been assessed for cellular changes reflective of genotoxic damage. A high percentage of tags exhibited a population of micronucleated and polyploid cells. The presence and number of micronuclei (MN) in the epithelia of cataract patients appears to be independent of age and sex. However, a large number of MN in the epithelial cells of some individuals strongly suggests a history of compromised genomic integrity. While the study was not designed to define the role of DNA damage in the development of cataracts or to monitor human populations at risk of exposure to exogenous mutagens/cataractogens, the potential of the methodology to address each is demonstrated.

Adult↗
PubMed1991

Photokeratitis from 193 nm argon-fluoride laser radiation.

The threshold for photokeratitis at 193 nm was obtained for the rabbit cornea using an ArF excimer laser. Because ablation occurs at a level below that for photokeratitis, it was necessary to expose the cornea to a lengthy series of low-energy exposures. It is concluded that the 193 nm photons have such a shallow penetration depth, being limited to the outermost epithelial cells, that classical photokeratitis occurs from the fluorescence emitted at the corneal epithelial absorption site. An intact tear film may help to protect the cornea from low-level, scattered 193 nm laser radiation.

Animals↗
PubMed1991

Laser radiation at various wavelengths for decompression of intervertebral disk. Experimental observations on human autopsy specimens.

The interaction of laser radiation with the nucleus pulposus from autopsy specimens of human intervertebral disks was evaluated at different wavelengths (193 nm, 488 nm & 514 nm, 1064 nm, 1318 nm, 2150 nm, 2940 nm, and 10600 nm). A significant correlation of linear least squares fit of the mass ablated as a function of incident energy was found for all lasers used except the Excimer at 193 nm. The 2940-nm Erbium:YAG laser was most efficient in terms of mass of disk ablated per joule in the limited lower range where this wavelength was observed. At higher energy levels, the CO2 laser in the pulsed mode was most efficient. However, the Nd:YAG 1064-nm and 1318-nm lasers are currently best suited for percutaneous laser disk decompression because of the availability of usable waveguides. Carbonization of tissue with the more penetrating Nd:YAG 1064-nm laser increases the efficiency of tissue ablation and makes it comparable to the Nd:YAG 1318-nm laser.

Autopsy↗
PubMed1990

Effects of a 2.15-micron laser on human atherosclerotic xenografts in vivo.

The thulium-holmium-chromium:yttrium-aluminum-garnet (THC:YAG) laser has a tissue effect similar to that of the CO2 laser, with the advantage of transmissibility through flexible fibers. The authors used a human-rabbit xenograft model to evaluate the thrombotic and healing responses of atherosclerotic vessels subjected to laser energy. Occluded atherosclerotic human coronary artery segments were recanalized in vitro by use of the THC:YAG laser. Destruction of plaque by the laser was achieved with minimal collateral thermal damage. These vascular segments were then transplanted into the rabbit abdominal aorta. The authors observed that the luminal surface of the lased vessels was more thrombogenic than that of the nonlased control vessels. However, occlusion of the lased vessels did not occur. Repair of laser-treated tissue progressed until a mature, nonthrombogenic fibrin-platelet aggregate was adherent to the luminal wall. Overall, the lased vessels behaved in a fashion similar to the nonlased control vessels. On the basis of these results, the authors believe that the THC:YAG laser may have use in human angioplasty.

Angioplasty, Laser↗
PubMed1989

Corneal healing following laser refractive keratectomy.

A 193-nm excimer laser system was used to ablate 4.5-mm optically contoured zones in the corneal stroma of rabbits to achieve optical flattening of 2, 4, 8, and 16 diopters. We studied the effect of edge profile and wound depth on reepithelialization and stromal remodeling using dichlorotriazinyl aminofluorescein, a vital dye that covalently binds to the stromal bed and delineates the boundaries of new collagen synthesis. All the corneas reepithelialized; no subsequent recurrent erosions occurred. All seven corneas that received an ablation of less than 50 microns were clear centrally at 8 weeks. At an ablation depth of approximately 100 microns, opacification and scarring were observed biomicroscopically and histopathologically in two specimens. No evidence of new collagen formation or epithelial hyperplasia was found in any of the seven corneas that remained clear. Stromal remodeling was observed in the two corneas that exhibited scarring.

Animals↗
PubMed1989

A fiberoptic compatible midinfrared laser with CO2 laser-like effect: application to atherosclerosis.

In theory, pulses of laser light in the 2-microns range should ablate tissue in a manner similar to that of the 10.6-microns CO2 laser with the added advantage of efficient transmission through flexible quartz fibers. Using 200-microseconds pulses of 2.15-microns thulium-holmium-chromium:YAG (THC:YAG) laser light, we were able to create 700-microns-diameter holes through calcific atherosclerosis in vitro. In vivo evaluation of thrombogenicity and healing was accomplished by exposing the luminal surface of rabbit aortas to the THC:YAG laser. Serial histologic examinations of laser-treated rabbit aortae revealed a time course of resolution of the lesions which was very similar to that observed with like-sized lesions created with the same amount of continuous wave CO2 energy. No significant differences in thrombogenicity nor healing response were noted. The excellent in vivo response observed is due in part to the pulsed nature of the THC:YAG laser output as well as to the efficient tissue absorption at the 2.15-microns wavelength. We feel that excellent ablative effects with minimal collateral thermal damage can be obtained through fiberoptic delivery systems by taking advantage of laser wavelengths corresponding to the infrared absorption peak of water in the 2-microns region and pulsed delivery of the laser energy.

Animals↗
PubMed1979

Recognition and differential diagnosis of enlarged extraocular muscles in computed tomography.

We found enlargement of the extraocular muscles in 70 patients out of 603 orbit studies, of whom 310 had exophthalmos. The majority (46 of 70) had the eye signs of Graves' disease. Arteriovenous malformations and carotid cavernous fistulas can cause enlargement of the extraocular muscles by a diffuse increase in orbital venous pressure, Acute orbital myositis can be distinguished from other forms of pseudotumor by the presence of a single enlarge extraocular muscle with associated inflammatory findings which responds to corticosteroid therapy. Neoplasms may invade extraocular muscles or compress their venous drainage causing secondary muscle enlargement. In all these patients the presence of a mass was correctly identified. The ability of the computed tomography scanner to recognize abnormalities of the extraocular muscles represents a significant advance in classification and diagnosis of the causes of exophthalmos.

Adult↗
PubMed1978

Pulsating metastatic tumor of the orbit.

A 47-year-old white man in apparent good health had diplopia and swelling of the right upper eyelid. Ocular examination showed proptosis of the right eye, together with a large, pulsatile, collapsible mass simulating a vascular neoplasm and involving the right temple as well as the right upper outer quadrant of the orbit. Biopsy of the orbital tumor disclosed a clear-cell carcinoma compatible with a renal primary tumor; subsequent laboratory examination revealed the offending tumor in the left kidney. Renal carcinomas may metastasize to the globe or to the orbit before the primary tumor is recognized. Pulsatile exophthalmos acquired in middle life associated with significant bone destruction represents a constellation of findings most consistent with a metastatic tumor, probably renal carcinoma, caused by the exceedingly rich vascularization of these metastatic deposits.

Adenocarcinoma↗
PubMedDate not supplied

Photokeratitis from subablative 193-nanometer excimer laser radiation.

BACKGROUND: Photokeratitis is a side effect of UV light exposure whereby the corneal epithelium is photochemically injured in a time delayed fashion. UV light exposure in the far ultraviolet wavelength range has not previously been observed. This study addresses the concern of photokeratitis from subablative 193-nanometer excimer laser light. METHODS: Dutch belted rabbit corneas were irradiated with subablative 193-nanometer excimer laser light over a wide range of total energy exposures, and examined by slit lamp biomicroscope for signs of photokeratitis. Photokeratitis was identified by epithelial haze and stippling, and rose bengal and fluorescein staining at varied time intervals between 1/2 to 26 hours post exposure. RESULTS: At threshold energy exposures of 1.0 to 1.5 J/cm2, an immediate superficial epithelial haze was seen which disappeared within several hours. At higher energy exposures of 10 J/cm2, a delayed photokeratitis with deep rose bengal and even fluorescein staining was seen. This latter delayed photokeratitis resembles that of longer UV wavelengths and is due to excimer laser fluorescence, whereas the former is a direct response of the 193-nanometer light. The percentage of excimer laser light undergoing fluorescence is calculated as less than 1%. CONCLUSIONS: The potential side effects and hazards of scattered 193-nanometer radiation during excimer laser surgery are extremely limited because of the shorter penetration depth of direct excimer radiation and the minimal fluorescent emission of longer UV wavelengths for energy exposures within the realm of clinical use.

Animals↗