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Biomedical subjects

T Seiler

Publications and source records attributed to T Seiler.

At least 109 records · Page 6Linked to original sources
PubMed1991

[Excimer laser keratomileusis for myopia correction. Results and complications].

Results of excimer laser keratomileusis in 26 myopic sighted eyes are presented. The follow-up was at least 9 months. The base-line refraction was -4.48 +/- 1.81 D (range: -1.4 to -9.25 D). After 3 months 85% were within +/- 1 D from the intended refraction. The such defined success rate after 6 months was 87.5%, after 9 months 88%, and after 12 months 92%. One month after surgery we found an overcorrection of +1.45 +/- 1.22 D decreasing to +0.27 +/- 0.94 D at three months, becoming an undercorrection of -0.24 +/- 0.76 D after six, and -0.32 +/- 0.69 D after nine months, and of -0.36 +/- 0.6 D after one year. Stability within the measurement error (+/- 0.25 D) appeared in 79% of the treated eyes six months after treatment. Three patients have been excluded from the study group because they did not follow the protocol. Subepithelial haze occurred in all patients, becoming most intense after 3 months, gradually clearing over the next months. With appropriate steroid medication, the refractive effect may be modulated. Complications as steroid glaucoma, recurrent erosion, loss of acuity, or extensive corneal scarring seem to be very rare.

Adult↗
PubMed1991

[Wound healing of the cornea of New World monkeys after surface keratectomy: Er:YAG-excimer laser].

Corneal wound healing was studied after photoablation with an excimer laser (193 nm, 43 pulses at 180 mJ/cm2 [symbol: see text] 11 microns ablation depth, optical zone 2.0 mm) and with an erbium-YAG laser (2.94 microns, 5 pulses at 2.5 J/cm2 [symbol: see text] 50 microns ablation depth, optical zone 1.6 mm). The corneas of marmosets (Callithrix jacchus) were prepared 5 and 10 days and 4 and 25 weeks after photoablation. The sections were investigated by conventional light microscopy or exposed to antibodies against collagen types I, III, IV, VII and laminin and stained by indirect immunofluorescence. Macroscopically, the time-course of wound healing was comparable to that seen, after laser keratomileusis for correction of myopia in humans (epithelium closure after 24-48 h, subepithelial haze: erbium-YAG less than or equal to excimer). Histologically the time-course of wound healing could be schematically divided into three phases: (1) epithelial hyperplasia, inhomogeneous new synthesis of collagen fibrils subepithelially; (2) reorganization of the epithelium, hyperplasia of keratocytes, incipient reorganization of the collagen fibrils, increase in subepithelial haze; (3) reorganization of the collagen fibrils, decrease in subepithelial haze. The distribution of collagen type VII during the corneal wound healing suggests that the subepithelial haze observed during the healing process after laser keratomileusis for correction of myopia is based on the anchoring fibrils of the basement membrane.

Animals↗
PubMed1991

[Laser coagulation of the cornea with a holmium:YAG laser for correction of hyperopia].

We present a new technique of hyperopic correction similar to radial thermokeratoplasty. A pulsed Ho: YAG laser was used that emitted radiation at 2.06 microns and was guided by a quartz fiber and a focusing hand piece. The penetration depth of this light in the cornea is about 400 microns. Eight or 16 concentric point coagulations result in steepening in the central cornea. This refractive change is inverse related to the distance to the cornea center, and it increases linearly with increasing laser pulse energy. In four blind eyes it was demonstrated that the parameters evaluated in cadaver eyes can be transferred to living eyes. Surprisingly, the refractive change so created of up to 5 dpt is stable within a period of 4 months. Immediately after surgery, concentric descemet folds can be detected, which gradually decrease within the period reported.

Cornea↗
PubMed1991

[Photoablation with the Er:YAG laser in ocular tissues].

Photoablation of ocular tissues is not restricted to the excimer laser. Alternative tools are erbium lasers. As there is maximum absorption in ocular tissue at about 3 microns, two types of erbium lasers are capable of photoablation. One is the Er:YAG laser working at a wavelength of 2.94 micron; the other is the Er:YSGG laser emitting light with a wavelength of 2.79 microns. Both lasers produce higher ablation rates than the excimer laser. In comparison to the excimer laser (thermal damage of less than 1 micron), there is more thermal damage in the remaining tissue (3 microns). The lower ablation rate of the Er:YSGG laser due to the greater distance of the wavelength from the absorption maximum can be compensated by a higher output energy and a higher repetition rate (25 Hz). Wound-healing studies in rabbit corneas show no significant differences between the excisions performed with the Er:YAG laser and 193 nm excimer laser.

Cornea↗
PubMed1990

[Emmetropization. A statistical study].

The relations between bulb length and the refractive power of the cornea were investigated in 3358 eyes of nonselected patients. There was a negative correlation between corneal refraction and bulb length in the range 19 to 29 mm. However, the data do not support the recently advanced hypothesis that corneal curvature and bulb length are regulated by means of optimal retinal contrast. The mean bulb length in males was 23.83 mm, in females 23.25 mm.

Cataract Extraction↗
PubMed1990

[Laser surgery of the cornea].

Photoablation is a new type of laser-tissue interaction that allows the removal of corneal tissue with submicron precision. To date, three potential applications have been developed: (1) peripheral keratectomies; (2) reprofiling of the central cornea; (3) corneal smoothing. Mimicking conventional incision techniques, excimer laser keratectomies indirectly influence the central cornea by mechanically relaxing the peripheral part. The most important clinical application is the correction of astigmatism. By irradiating the central cornea directly, small lenticules of tissue can be removed by making the curvature of the cornea flatter. Complications can arise from repair mechanisms leading to glare or reduction in the initial amount of optical correction. Corneal smoothing using an immersion fluid can be used after lamellar keratoplasty or to remove superficial pathological structures such as band keratopathy and superficial scars.

Astigmatism↗
PubMed1990

[Basic considerations on the use of the Excimer laser in dentistry].

SEM studies showed that irradiation in the energy density range of 4-6 J/cm2 resulted in the removal of hard tooth structure without causing thermal alterations of the tissues. In this process (photoablation) the natural structures of the tissues are "exposed". The surface structure thus produced in dentin depends on whether the dentin tubules are hit transversally or longitudinally and varies accordingly. The surface structure of enamel, as well, is determined by the alignment of the prisms. When the laser beam was optimally adjusted (energy densities of 4-6 J/cm2 and peripheral fading), no structural changes could be demonstrated in the depth of the tissue.

Dental Cavity Preparation↗
PubMed1990

[Laser keratomileusis for correction of myopia].

Laser keratomileusis with the excimer laser (193 nm) is a new method of refractive surgery. With this procedure a thin lenticule is ablated from the central cornea with submicron precision. The refraction changes achieved in 13 eyes ranged from 1.5 to 7.5 dpt. With this correction 92% of the treated eyes were within 1.0 dpt either way at 3 months after surgery, but after 6 months this proportion decreased to 77%. The best-corrected visual acuity recovers within 1 months to preoperative values. In all patients a slight subepithelial haze was detected with the slit-lamp in the early postoperative phase, but cleared within 4-6 months to a clinically non-significant level.

Adult↗
PubMed1990

[The ablation behavior of various corneal layers].

The difference in structure of the corneal layers leads to an inhomogeneous reaction to photoablation with 193 nm excimer laser light. This is important for the calculation of photorefractive keratectomy (PRK) where only a thin layer (10-50 microns) of the cornea must be removed. Therefore, the ablation rate for the Bowman zone is 2.5 times lower than that for corneal stroma; the same value is found in Descemet membrane. In contrast, the ablation rate of the epithelium is 1.5 times higher. Based on these data it will be possible to achieve high precision with PRK.

Astigmatism↗
PubMed1989

[Magnetic resonance tomography in ophthalmology. II. Manifestations of edema of the optic nerve].

MRI findings specific for lesions of the optic nerve are reported in the present paper for the first time: a dilated subarachnoidal space during the acute phase and scars in the neural tissue several months later. For imaging, the authors used special pulse sequences and surface coils. Twenty of 37 patients presenting with these symptoms were suffering from retrobulbar neuritis. In at least 12 (60%) of them the neuritis was associated with multiple sclerosis. Patients with tumors of the sella region usually have bilateral edema in the subarachnoidal spaces of both nerves. The edema is always located distal to the nerve lesion. The subarachnoidal edema is only of limited significance as a sign of optic neuritis. On the other hand, the authors failed to find a single case of neuritis without such edema.

Adult↗
PubMed1989

[Partial external trabeculectomy].

The authors show that with the Excimer laser partial trabeculectomy can be performed, a procedure in which the juxtacanalicular meshwork is removed while the other layers remain untouched. It was proved in experiments on ten enucleated human eyes that at most 3% of the outflow resistance is localized in the uveal and sclerocorneal meshwork. The clinical applicability of partial trabeculectomy was demonstrated on five eyes.

Choroid Neoplasms↗
PubMed1989

[Amelanotic melanoma and nuclear magnetic resonance tomography--case report].

In MRI choroidal melanoma shows a very short relaxation time (T2), shorter than that of any other intraocular tumor. This short T2 time is referred to the high concentration of paramagnetic melanine in this tumor. Therefore, it is of interest to measure the relaxation time in an amelanotic melanoma and compare it with the histological analysis. The duration of T2 for the amelanotic melanoma examined ranged from 130 to 160 ms. The small concentration of melanine is not a sufficient explanation, but it is possible that there are some precursors of melanine with paramagnetic characteristics.

Adult↗
PubMed1989

[Superficial ablation of the cornea using the excimer laser (193 nm)].

The final result of corneal surgery such as resection of the pterygium or lamellar keratoplasty is a rough corneal surface. Scanning electron microscopy shows that it is possible to obtain a smoother surface by using the 193 nm excimer laser, as it shows significantly better results than with conventional methods. This procedure was tested on eight patients and documented photographically.

Animals↗