Thomas Hammer

Influence of melatonin and serotonin on glucose-stimulated insulin release from perifused rat pancreatic islets in vitro.

Peschke E, Peschke D, Hammer T, Csernus V. Influence of melatonin and serotonin on glucose‐stimulated insulin release from perifused rat pancreatic islets in vitro. J. Pineal Res. 1997; 23:156–163.

Dynamic insulin secretion from perifused rat pancreatic islets

Abstract. Insulin secretion from isolated pancreatic islets of 8- to 12-day-old rats was investigated in a dynamic in vitro (perifusion) system. The aims of the study were (i) to describe a carefully controlled in vitro method to study the mechanism of insulin secretion and to analyse the effects and dynamic interactions of bioactive compounds on isolated rat pancreatic islets, (ii) to validate the method by comparing fundamental data on the functions of the islets obtained with this method to those collected with other techniques; and (iii) to find novel features of the control of insulin secretion. The method was carefully designed to maintain the functional capacity of the explanted cells. A functional standardization system was elaborated consisting of (i) analysis of the changes in the basal hormone secretion of the cells; (ii) evaluating responses to a standard, specific stimuli (50 mM glucose for 3 min); (iii) determining the alteration of the momentary size of the hormone pool with responses to KCl; and (iv) direct determination of the total intracellular hormone content from the extract of the column. The technique provides accurate quantitative data on the dynamic responses to biologically active compounds that act directly on the pancreatic islets. The islets maintained their full responsiveness for up to 7 days, and responses as close as in 1-min intervals could be distinguished. A linear dose-response relationship was found on the glucose-induced insulin release in case of 3-min stimulation with 4 and 500 mM of glucose (lin-log graph). Utilizing this method, we showed that no desensitization to glucose-induced insulin release can be observed if the responsiveness of the cells is properly maintained and the parameters of the stimulation are carefully designed. Exposure of the explanted islets to 10 μM acetylcholine or 30 mM arginine (Arg) induced a transitory elevation of insulin release similar in shape to that experienced after glucose stimulation. Norepinephrine (NE), dopamine (DA) and somatostatin (SS) did not induce any detectable alteration on the basal insulin secretion of the islets. However, 100 nM SS given together with 50 mM glucose, 30 mM Arg or 10 μM acetylcholine significantly reduced the insulin-releasing effect of these substances (by 75.5, 71.5 and 72.5%, respectively). At the same time, SS did not alter the insulin response of the islets to 100 mM elevation of K+ concentration. SS also inhibited glucose-induced insulin release in a dose-dependent way (ED50 = 22 nM). A similar dose-dependent inhibitory effect on glucose-induced insulin release was found with NE (ED50 = 89 nM) and DA (ED50 = 2.2 μM). γ-Aminobutyric acid (GABA) did not influence insulin release under similar circumstances.

Evaluation of Four Microkeratome Models: Quality and Reproducibility of Cut Edge and Cut Surface as Determined by Scanning Electron Microscopy

PURPOSE To compare the quality and reproducibility of cuts produced by four automatic microkeratomes: Amadeus, Hansatome, Summit-Krumeich-Barraquer (SKBM), and Supratome. For the adjustable models (Amadeus and SKBM), the effects of oscillation frequency and blade feed rate were determined. METHODS Eight cuts (flap thickness 160 to 180 microm) were made with each microkeratome at each parameter setting and examined using a scanning electron microscope. Quality of the cut surface was scored for each flap according to four criteria, and results were averaged to give a maximum possible score of 64. Quality of the cut edges was scored from 1 (blurred indistinct edge) to 3 (sharp and clearly visible edge). RESULTS The four microkeratomes performed similarly on overall quality of the cut surface (range: 78% to 88% of theoretical maximum). The Hansatome scored highest (88%), followed by SKBM (86%; 1.0 mm/s blade feed and 7000 rpm oscillation), Amadeus (84%; 2.5 mm/s, 8000 rpm), Supratome (84%; 16.6 mm/s, 12,500 rpm), Amadeus (81%; 3.0 mm/s and 13,000 rpm), and SKBM (78%; 1.5 mm/s, 14,000 rpm). Performance differences were clearer for cut edge quality. The Amadeus produced cuts of the highest quality in 62.5% of cases (at both settings), compared with only 12.5% of cases with the Hansatome, 25% of cases with the Supratome and SKMB (1.0 mm/s, 7000 rpm), and in no cases with the SKBM at 1.5 mm/s and 14,000 rpm. CONCLUSIONS Overall, high frequency with low blade feed rate is desirable for reproducible sharp edges and cut area quality. However, at very high frequencies (e.g., 14,000 rpm with the SKBM) tissue is displaced, producing an uneven cut area. Oscillation/feed quotients of 2000 to 4000 (rpm/mm x s) are a good compromise. Sharp edges are believed to reduce the risk of comeal erosion, introduction of epithelial cells into the interfacial region, and scarring during wound healing.

Vergleich des Femtec Femtosekundenlasers und des Zyoptix XP Mikrokeratoms

OBJECTIVE To demonstrate the qualities and compare the typical features of cut surfaces and cut edges created by the Femtec femtosecond laser and the Zyoptix XP microkeratome, using scanning electron microscope (SEM) pictures. METHODS Lamellar keratotomies were performed using a femtosecond laser (40 kHz) or a microkeratome on freshly enucleated porcine eyes (n=16, eight each per technique). After special preparation, SEM images were taken to evaluate the qualities of the cut surfaces and cut edges. Therefore, special criteria were involved, including relief and homogeneity of the surface and sharpness of the cut edges. RESULTS Surfaces created by microkeratome cuts were very homogenous. Concerning surface relief, nearly no irregularities occurred. Cut edges showed a flat, serrated course from the epithelial layer to the stroma of the cornea. The edges were sharp and easily visible. After preparation using the femtolaser, the surface showed many rips in the tissue, leading to irregularities. Nevertheless, the cut edges were very sharp and entered the corneal layer straight at 90 degrees . CONCLUSIONS A comparison of the two systems shows that the microkeratome creates a more homogenous cut surface. The need for preparation after automated cutting with the femtosecond laser leads to irregularities on the cut surface. The cut edges of both systems tested here differ concerning their angles on entering the tissue. With regard to the sharpness of the cuts, the qualitative aspect is nearly similar, although the cut edges of the microkeratome are serrated. Because the microkeratome-cut edge has a flatter course, the wound area might be bigger. Cut edges with the steepness produced by the femtosecond laser could be an advantage for repositioning the flap after LASIK. If excimer laser ablation is performed later, the flap bed created by the femtosecond laser could be disadvantageous.

Scanning electron microscopic characteristics of lamellar keratotomies using the Femtec femtosecond laser and the Zyoptix XP microkeratome. A comparison of quality

OBJECTIVE To demonstrate the qualities and compare the typical features of cut surfaces and cut edges created by the Femtec femtosecond laser and the Zyoptix XP microkeratome, using scanning electron microscope (SEM) pictures. METHODS Lamellar keratotomies were performed using a femtosecond laser (40 kHz) or a microkeratome on freshly enucleated porcine eyes (n=16, eight each per technique). After special preparation, SEM images were taken to evaluate the qualities of the cut surfaces and cut edges. Therefore, special criteria were involved, including relief and homogeneity of the surface and sharpness of the cut edges. RESULTS Surfaces created by microkeratome cuts were very homogenous. Concerning surface relief, nearly no irregularities occurred. Cut edges showed a flat, serrated course from the epithelial layer to the stroma of the cornea. The edges were sharp and easily visible. After preparation using the femtolaser, the surface showed many rips in the tissue, leading to irregularities. Nevertheless, the cut edges were very sharp and entered the corneal layer straight at 90 degrees . CONCLUSIONS A comparison of the two systems shows that the microkeratome creates a more homogenous cut surface. The need for preparation after automated cutting with the femtosecond laser leads to irregularities on the cut surface. The cut edges of both systems tested here differ concerning their angles on entering the tissue. With regard to the sharpness of the cuts, the qualitative aspect is nearly similar, although the cut edges of the microkeratome are serrated. Because the microkeratome-cut edge has a flatter course, the wound area might be bigger. Cut edges with the steepness produced by the femtosecond laser could be an advantage for repositioning the flap after LASIK. If excimer laser ablation is performed later, the flap bed created by the femtosecond laser could be disadvantageous.

[Results of wavefront-guided LASIK].

BACKGROUND Wavefront-guided LASIK procedures provide patients with customized corneal treatments. The computer ablation profiles correct both spherical and/or cylindrical errors of refraction and aberrations up to the fifth order. METHODS We performed wavefront-guided LASIK treatments on 62 patients using the Keracor 217 Z. The spherical equivalent was -6.11 +/-2.29 D on the average. Data collected for 3 months were evaluated to determine the predictability, efficacy, stability, and safety of the refractive procedure. RESULTS We found good predictability of the refractive result after correcting -1 to -6 D of myopia. Beyond -7 D there were over- and undercorrections of +/-2 D in 10% of the procedures. A UCVA of 0.8 or better was observed in 53% of the patients 3 months postoperatively, and 75% of the patients reached a BCVA of 0.8 or better. After 3 months 6% lost 2 lines, 22% lost 1 line, 22% of the patients gained 1-2 lines, and BCVA remained unchanged in 55%. The fluctuation of the refraction was about -0.23 D during the first 3 postoperative months. CONCLUSIONS The low and middle range of myopia can be corrected very accurately using the wavefront technology. Higher degrees of myopia face both under- and overcorrections. Postoperative refractions become stable very quickly. However, the visual acuity changes even 6 months postoperatively. From our point of view, wavefront correction by LASIK should be more reliable in terms of centration, accuracy, and standardization to get better results.

Influence of microkeratome parameters on the stromal bed and flap edge quality in laser in situ keratomileusis

Purpose Femtosecond lasers have become the standard for laser-assisted in situ keratomileusis (LASIK) flap creation, but advanced mechanical microkeratomes are still an alternative, more cost-effective way to create the flap. The SCHWIND Carriazo-Pendular microkeratome is one of the most commonly used microkeratomes. The influence of different cutting parameters (head-advance speeds, cutting heads) on morphology of LASIK cuts was investigated. Setting Experimental study performed at the University Eye Hospital of the Martin Luther University Halle/Wittenberg, Halle (Saale), Germany. Methods The Carriazo-Pendular microkeratome was used on freshly enucleated porcine eyes for lamellar keratotomy. After flap removal, the cutting edge and stromal bed were evaluated from scanning electron micrographs using an individualized scoring system. Four different settings of microkeratome parameters were compared. For each setting, eight cuts were evaluated (n=32). Results Different oscillation frequencies and head-advance speeds did not influence the cutting qualities. A higher oscillation/feed rate ratio seemed to be advantageous for a smoother interface. Concerning different cuttings heads, a deeper keratotomy led to sharper cutting edges. The thinner the flap, the more irregularities in the stromal bed appeared. Complications did not occur. Conclusion The Carriazo-Pendular microkeratome is a safe tool with which to create a LASIK flap and is a good alternative to a costly femtosecond laser. Deeper keratotomies, as well as the use of a higher oscillation/feed rate quotient, improve the cutting quality.

Methods of fixation of intraocular lenses according to the anatomical structures in trauma eyes

Ocular trauma can lead to severe visual impairment and morbidity, depending on the anatomical structures affected. The main causes of ocular trauma include foreign bodies, impact by an object, falls, and chemicals. Most ocular traumas occur in children or young male adults. A meticulous slit lamp examination is crucial for assessing all anatomical structures. Trauma to the crystalline lens can result in dislocation, an intralenticular foreign body, cataract, fragmentation, and capsular breach. An intraocular lens (IOL) can endure subluxation or luxation under the conjunctiva, into the anterior chamber or the vitreous, or can be extruded. The surgical approach depends on the condition and morphology of the lens and the anatomical structures surrounding it. If there is capsular bag support, a secondary IOL can be placed in the sulcus using remnants of the damaged capsule. If there is no capsular bag support, a secondary IOL can be fixated to the anterior chamber angle, to the iris, or to the sclera. A detailed history of injury cannot always be obtained in trauma settings. Proper education, supervision, and certified safety eye protectors could prevent up to 90% of ocular injuries. Lens trauma can be treated with various surgical procedures and fixation techniques, which nevertheless require advanced surgical skills owing to the fine anatomical structure of the anterior segment. A careful surgical strategy should be established for a globe reconstruction after trauma with secondary lens implantation. Clin. Anat. 31:6–15, 2018.

Anatomic landmarks in lacrimal surgery from an ophthalmologist's point of view

Epiphora is a common clinical symptom of nasolacrimal duct obstruction. However, it is present in several pathologies and can lead to decreased quality of life for patients. A careful clinical examination including a detailed patients history and diagnostic tests such as the fluorescein dye disappearance test and diagnostic syringing of the lacrimal duct are essential. Depending on the time of presentation (congenital, primary, or secondary acquired), grade (subtotal or total) and location of the stenosis, different surgical approaches can be considered. These are subdivided into minimally invasive (transcanalicular) and anastomosing (dacryocystorhinostomy) procedures. Furthermore, the anatomical landmarks and the site of surgical intervention differentiate the surgical techniques into endoscopic or transcutaneous. Modern intubation techniques offer a large spectrum of therapeutic possibilities enabling patient care to be customized and individualized. Knowledge of the topographical anatomy is crucial for achieving greater success and a lower complication rate. Clin. Anat. 30:1034–1042, 2017.

Ergebnisse der wellenfrontgestützten LASIK

BACKGROUND Wavefront-guided LASIK procedures provide patients with customized corneal treatments. The computer ablation profiles correct both spherical and/or cylindrical errors of refraction and aberrations up to the fifth order. METHODS We performed wavefront-guided LASIK treatments on 62 patients using the Keracor 217 Z. The spherical equivalent was -6.11 +/-2.29 D on the average. Data collected for 3 months were evaluated to determine the predictability, efficacy, stability, and safety of the refractive procedure. RESULTS We found good predictability of the refractive result after correcting -1 to -6 D of myopia. Beyond -7 D there were over- and undercorrections of +/-2 D in 10% of the procedures. A UCVA of 0.8 or better was observed in 53% of the patients 3 months postoperatively, and 75% of the patients reached a BCVA of 0.8 or better. After 3 months 6% lost 2 lines, 22% lost 1 line, 22% of the patients gained 1-2 lines, and BCVA remained unchanged in 55%. The fluctuation of the refraction was about -0.23 D during the first 3 postoperative months. CONCLUSIONS The low and middle range of myopia can be corrected very accurately using the wavefront technology. Higher degrees of myopia face both under- and overcorrections. Postoperative refractions become stable very quickly. However, the visual acuity changes even 6 months postoperatively. From our point of view, wavefront correction by LASIK should be more reliable in terms of centration, accuracy, and standardization to get better results.