Biomedical subjects

T Seiler

Publications and source records attributed to T Seiler.

At least 91 records · Page 5Linked to original sources

PubMed1993

[Effect of pulse duration of the Er:YAG laser on photoablation in ocular tissue (cornea and sclera)].

After photoablation in corneal and scleral tissue with the Er:YAG laser, two zones of thermal damage can be detected: The first zone (about 3 microns thick) consists of thermally denatured debris. The second zone (about 30 microns thick) shows a slightly more intense staining (H&E) compared to the non-influenced tissue. Variation of laser pulse duration between 100 microseconds and 1300 microseconds does not influence the extension of these two thermal damage zones. Furthermore, ablation rate and ablation volume remain nearly constant within this range of pulse durations. These data were obtained by histology (H&E staining) and with a recently published silicon cast replica method. All experiments have been performed on corneas and sclera of pig eyes.

Animals↗

PubMed1993

[Mathematical presentation of postoperative regular corneal astigmatism].

BACKGROUND: There are several contradictory approaches to describe a change in corneal astigmatism induced by operations. METHODS: Assuming a rotational ellipsoid for the outer surface of the cornea we derived formulas that represent the change in astigmatism. Also, the change of the corneal power in the axis of the intervention (e.g. operation) has been determined. RESULTS: The exact derivation yield formulas for the absolute value of the astigmatism change identical to those of Naylor and Jaffe but includes, in addition, algorithms for "with-the-rule" and "against-the-rule" components. The spherical change of the cornea is also obtained. The models of Cravy and Naeser are mathematically inconsistent and should be avoided. CONCLUSION: The presentation of the change in astigmatism should depend on the primary question. In many cases, the complicated non-linear vector calculation is not necessary since the actual changes in corneal shape may be demonstrated by simpler formulas. The results of these formulas are much easier to interpret.

Astigmatism↗

PubMed1993

Results of a prospective evaluation of photorefractive keratectomy at 1 year after surgery.

The 1-year results obtained in 193 eyes of 146 patients who were enrolled in a prospective study investigating photorefractive keratectomy for myopia correction with the excimer laser are reported. Because of lost follow-up (17 eyes) and reoperations (15 eyes), a complete 1-year follow-up was available in 161 eyes of 115 patients that were included in the analysis. At 12 months after surgery, the percentage of eyes showing refractions within +/- 1.0 D of the attempted refraction was 97.6% in the lower group (up to -3.0 D), 91.8% in the middle group (-3.1 to -6.0 D), 44.4% in the higher group (-6.1 to -9.0 D), and 25% in the high-myopia group (more than -9.0 D). Best spectacle-corrected visual acuity was unchanged in 95% of the eyes, two eyes (1.2%) lost two lines, and six eyes (3.7%) gained two lines. Visual acuity under glare conditions was reduced from 0.71 at baseline to 0.625 at 1 year after surgery (P < 0.001). The incidence of manifest corneal scars was significantly related to the attempted refractive change (P < 0.0001). Complications were rare and not severe. These data suggest that photorefractive keratectomy is an effective and relatively safe procedure for the correction of myopia of up to -6.0 D, once long-term stability is proven. However, in eyes involving an attempted correction of more than 6.0 D (52 eyes), we found high rates of scarring in 8 eyes (15.4%) and undercorrection in 27 eyes (52%), and reoperations were needed because of scarring or undercorrection in 14 eyes (25%).

Adult↗

PubMed1993

Central corneal iron deposit after photorefractive keratectomy.

Iron lines in the corneal epithelium are well-documented clinical signs in various circumstances. After photorefractive keratectomy, a new type of iron deposit can be found: a central round spot that occurred in more than 80% of cases of 1 year after surgery. It can be recognized at the slitlamp 6 months after surgery, and its incidence is related to the amount of attempted refractive change. In otherwise clear corneas, the central iron spot is the only clinical sign of a previously performed photorefractive keratectomy.

Adult↗

PubMed1993

[Silicone impression procedure. Principles for determining ablation and healing parameters in vitro and in vivo].

Topometry and measurement of photoablation patterns are key questions for keratorefractive photoablation. So far, ablation rates have been determined either by tissue perforation or histological micrometry. A cast of irradiated cornea was made by using a 2-component silicon that polymerizes within minutes, thus preserving the corneal topography immediately after photoablation. The silicon surface is extremely smooth and the accuracy of the cast better than 1 micron. Reproducibility and long-term stability were proven for casts of photoablated PMMA. Thus ablation rates and profile, volumetry and topometry can be determined at any time. The method was applied for 193 nm excimer and 2.94 microns Er:YAG laser in vitro irradiation of the human cornea. Ablation rates in Bowman's layer and stroma were observed for various radiant energies and distinct pulse numbers. The average ablation rates are in agreement with published data. It could be demonstrated that there was an incubation effect for the first pulses. The method feasibility for in vivo measurement was also proven in an animal model. After excimer photoablation in rabbit eyes (beam diameter 3.5 mm, radiant energy 185 mJ/cm3, ablation rate 0.3 micron/pulse), wound healing was recorded: for the right eye silicon casts were molded at three different moments. For the left eye only photographs were taken. There was no difference in the time course of wound healing, so the silicon does not seem to interfere with repair mechanisms of the corneal epithelium. No side effects were observed.

Animals↗

PubMed1992

Repeated excimer laser treatment after photorefractive keratectomy.

Scarring or undercorrection occurs in a small percentage of patients after myopic photorefractive keratectomy. Scarring occurred in 1.8% of 298 patients with a baseline myopia of 6.0 diopters or less, increasing to 8.8% in those with corrections of more than 6.0 D. Undercorrection of more than 1 D occurred in 2.7% of the eyes with a baseline myopia of up to -6.0 D. A much greater incidence of undercorrection (30% to 40%) was found after corrections of more than 6.0 D. Thirty eyes in 30 patients were reoperated because of scarring (11 eyes) and/or undercorrection (27 eyes) and were observed for 6 to 18 months (average, 7.8 months). Only one of the eyes has shown mild scar formation after this second laser treatment. Sixty-three percent of these patients had a manifest refraction between -1.0 D and +1.0 D six months after reoperation. Repeated phototablation seems to be a valuable technique for treatment of undercorrection and/or scarring after photorefractive keratectomy.

Adult↗

PubMed1992

[Complications of laser keratomileusis with the excimer laser (193 nm)].

Complications of photorefractive keratectomy (PRK) for myopia correction are presented based on 615 procedures with a follow-up of up to 2 years. Intraoperative complications with experienced surgeons are extremely rare. The used laser system worked without technical failures for the last 18 months. Gross eccentricities of the ablative zone (1.0 mm to 1.5 mm) occurred in two eyes (0.3%). Also, epithelial disorders are very rare. Recurrent erosions did not occur. Increased intraocular pressure due to the postoperative steroid medication (dexamethasone 0.1% or prednisolone 1%) was manifest in about 30% in patients with a baseline myopia of up to -9.0 D. In myopia over -9.0 D the incidence of steroid glaucoma was about 50%. Steroid responders reveal an increased risk of overcorrection. Subepithelial haze is a common symptom after PRK. Scarring interfering with vision correlates with the amount of attempted correction: up to 6.0 D the incidence of scars is about 0.5% and increases to more than 10% in corrections of more than 10 D. Also, undercorrections of more than 1 D depend strongly on the attempted correction. The most severe complication was a noninfectious corneal ulcer in a patient with systemic lupus erythematosus. Therefore, autoimmune and connective-tissue diseases represent an absolute contraindication for PRK. Corrections of more than 6.0 to 7.0 D should be considered as a relative contraindication for PRK at this time.

Adult↗

PubMed1992

Recent developments in refractive corneal surgery.

The 4- and 5-year results of the Prospective Evaluation of Radial Keratotomy Study reveal a hyperopic shift of more than 1.0 D within the follow-up time in 22% and 24%, respectively, of the eyes that underwent radial keratotomy. The number of eyes with this complication increased progressively from 6 months to 4 years. Attempts to correct this progressive hyperopia are discussed. Results of clinical studies of myopic photorefractive keratectomy performed with the excimer laser are reviewed. Regarding safety and short-term efficacy, photorefractive keratectomy is a promising technique. In the past, corneal topography has been interpreted qualitatively. Ray-tracing analysis now allows quantitative estimation of the influence of aspheric corneas on the degradation of the retinal image. Three approaches to correct hyperopia, radial thermokeratoplasty, laser thermokeratoplasty, and hexagonal keratotomy are reviewed and discussed. Additional concave intraocular lenses for correction of high myopia are still undergoing clinical evaluation. Endothelial damage is the most dangerous short-term complication of implantation with these lenses.

Cornea↗

PubMed1992

[Space-occupying lesions of the orbit: modern imaging diagnosis].

The paper summarises imaging of orbital diseases by CT and MRI. As localisation is an important clue to differential diagnosis in orbital tumours, the different pathologies are described according to sites of prevalent occurrence. Morphological criteria of orbital pathology are described, and the more frequent entities are illustrated.

Diagnosis, Differential↗

PubMed1992

Diurnal variation in refraction after excimer laser photorefractive keratectomy.

Diurnal fluctuations in vision are common after radial keratotomy (RK), associated with a myopic change in refraction and keratometric power mostly in the morning. After photorefractive keratectomy (PRK), only a small percentage of patients report fluctuations of vision. We tested ten such patients who had undergone excimer laser PRK with regard to refraction, keratometry, and visual acuity 5 to 20 months after surgery. Patients were examined five times during one day from 8:00 a.m. to 8:00 p.m. Ten volunteers serving as a control group were examined following the same protocol. None of the patients showed an increase in minus spherical power of the manifest refraction between morning and evening. The change in manifest refraction from morning to evening was +0.3 D +/- 0.3 D, which was not significantly different from the control group. The change in refraction did not correlate with keratometric power, follow-up time of age of the patients.

Adult↗

PubMed1992

Pseudoexfoliation syndrome and glaucoma. Does glaucoma capsulare exist?

Pseudoexfoliation syndrome (PES) is seen in patients with a characteristic deposition of material on the anterior preequatorial region of the lens and on a variety of surfaces throughout the anterior segments of the eye. A high frequency of associated glaucoma has also been reported. In spite of numerous clinical and histological investigations, the mechanisms for the glaucoma are unclear. In a series of 5154 patients referred to our hospital for cataract extraction we found a prevalence of 6.1% (n = 314). In 51 of these patients (16.2%) glaucoma was diagnosed in contrast to 33 patients (10.9%) in an age-matched control group. The prevalence of glaucoma in PES patients and the control group was not statistically different, so our findings in cataract patients do not support the interpretation that there is a clinical entity called "glaucoma capsulare."

Aged↗

PubMed1992

[Analysis of photo-ablation products of excimer and erbium:YAG laser treated human corneas. Combined gas chromatography/mass spectroscopy].

The photoablation products from human cadaver corneas treated with an excimer laser (192 nm) or an erbium: YAG laser (2.94 microns) were qualitatively analyzed using a combined gas chromatography mass spectrometry (GC/MS) system. GC/MS is the most sensitive analyzing system in use today for molecules with a relative molecular mass of 40 to 400. More than 20 different types of molecules were detected; most of them were identified as alkanes. Comparison of the two types of laser showed larger fragments and fewer different types of molecules after excimer laser treatment than after erbium: YAG photoablation. We postulate that the smaller molecules after erbium: YAG treatment indicate a greater heat during photoablation than with excimer laser treatment.

Alkanes↗

PubMed1992

Pterygium excision using 193-nm excimer laser smoothing and topical mitomycin C.

A total of 31 eyes with primary pterygium and 24 eyes with recurrent pterygium underwent surgical treatment and were followed for at least 1 year. The surgery involved a conventional bare-sclera technique combined with excimer laser smoothing of the wound bed. Postoperatively, the eyes were medically treated with topical mitomycin C (0.02%) for 4 days and with steroids for several weeks. No recurrence was noted within the 1st year in the primary pterygium group, whereas recurrence was observed in 3/24 eyes that had been treated for recurrent pterygium, equivalent to a recurrence rate of 12.5% in this subgroup. Nine eyes (16.4%) had gained 2 lines or more in visual acuity by 1 year after surgery. Granuloma developed in 3 eyes, and dellen formation was detected in 1 eye after surgery. The combination of surgical management with local mitomycin therapy may be considered to be a safe and effective technique for the removal of pterygium. Although the visual results were good, the role of excimer laser smoothing in the treatment of this disorder needs further investigation.

Female↗

PubMed1992

[Dye laser coagulation of diabetic maculopathy].

Eighty eyes of 48 patients were followed after laser photocoagulation (615 nm) of the macula because of diabetic macular edema. The follow-up time was at least 6 months (average 10.2 months). The morphological status improved in more than 60% of eyes with focal edema but in only 40% of eyes with diffuse macula edema. Improvement of distance visual acuity was obtained in 35% of the eyes, mostly in those with good baseline acuity (greater than or equal to 0.7). The fraction with improved visual acuity decreased to 13% in eyes with a baseline acuity of 0.6 or less. Similar results were found for near visual acuity. The discrepancies between morphological and functional improvement are still unclear.

Adult↗

PubMed1992

[The Excimer laser. An instrument for corneal surgery].

Photoablation of the cornea using excimer lasers (193 nm) results in keratectomies with very precise edges and minimal damage to the adjacent tissue. Deep keratectomies for relaxation incisions (astigmatic correction) and for trephination (lamellar or penetrating keratoplasty) are possible, but have not been applied routinely. Superficial keratectomies can induce corneal flattening--a promising approach for correction of myopia. This unique keratorefractive technique, called photorefractive keratectomy (PRK), has been studied worldwide with a follow-up time of up to 2 years. The success rate (+/- 1 D from the refraction aimed at) is approximately 90%, and vision-threatening complications are extremely rare. However, this is true only in corrections of up to -6.0 D. Corrections of more than this result in a significant decrease in the refractive success and a tremendous increase in complications. Therefore, we believe that corrections of more than -6.0 D are clinically not acceptable. Long-term stability is not yet proven, and consequently PRK must be used with strict indications. Superficial scars, corneal dystrophies, and degenerations of the outer cornea can be removed with the excimer laser much more gently than with conventional techniques.

Adult↗

PubMed1992

Gas chromatographic and mass spectroscopic analysis of excimer and erbium: yttrium aluminum garnet laser-ablated human cornea.

The photoablative products from human cadaver corneas treated with lasers were investigated using gas chromatography and mass spectroscopy. The photoablations were done separately with an excimer laser (193 nm) and with an erbium: yttrium aluminum garnet (Er:YAG) laser (2.94 microns). More than 20 different types of molecules with a molecular weight of 40-400 mass units could be identified, most of which were found to be alkanes. The comparison of the two types of laser ablations showed larger fragments and fewer types of molecules present after excimer laser treatment than after Er:YAG photoablation.

Cornea↗

PubMed1991

[Refractive surgery of the cornea. Corneal surgery--an alternative to optical aids?].

Errors of refraction of the eye can be corrected not only by means of spectacles, contact lenses or intra-ocular lenses, but also by operative procedures on the cornea. At present, correction of myopia is accomplished with radial keratotomy (RK), a procedure that achieves the best results in the range up to - 6.0 diopters. However, on account of its side effects, in particular poor predictability, the method is no true alternative to the use of optical aids. Epikeratoplasty done to correct hyperopia and aphakia, is even more imprecise, and should only be employed in exceptional cases. Laser surgery of the cornea is still undergoing clinical testing, but has already produced promising results.

Astigmatism↗

PubMed1991

Myopic photorefractive keratectomy with the excimer laser. One-year follow-up.

To evaluate the efficacy, predictability, and stability of myopic photorefractive keratectomy (PRK), the authors completed a 1-year follow-up study on a consecutive series of 26 sighted eyes undergoing this procedure. The results of this follow-up are presented. In addition, side effects and complications in another 255 sighted eyes with a follow-up of 3 months to 1 year are reported to judge the safety of the procedure. Twenty-four of 26 eyes (92%) were within +/- 1.0 diopter (D) of the intended final refraction (baseline, -1.4 to -9.25 D). Fifty-eight percent of the eyes were stable within +/- 0.25 D between 6 and 12 months. One year after surgery, none of the patients lost or gained more than one line of best corrected (spectacle) visual acuity. Uncorrected visual acuity improved to 20/40 or better in 96% of the eyes and to 20/20 or better in 48% of the eyes (not including the eyes that were intentionally undercorrected). However, visual acuity with glare decreased from 20/27 preoperatively to 20/31 after 1 year. Scarring occurred in 2.8% of the treated corneas. Risk factors for scarring include noncompliance with postoperative steroid medication, high myopic corrections, and high steroid responders (3.1%). Collagen vascular and other autoimmune diseases are a contraindication for PRK.

Adult↗