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Biomedical subjects

J Draeger

Publications and source records attributed to J Draeger.

At least 109 records · Page 6Linked to original sources
PubMed1989

[Development of new fixing mechanisms and forms for the preparation of refractive corneal sections].

A method was developed for lathing corneal tissue without freezing. As a cutting instrument we used the rotating lamellar keratome, which was integrated in a mechanically adjustable microsurgical work bench. A set of refractive lathing forms was designed for a lenticule diameter of up to 9.5 mm. For fixation of the tissue, different kinds of suction holes were investigated. A mechanical fixation ring was not required, as the shearing force from the rotating blade does not loosen the lenticule even at a low suction setting. Different surface properties were compared. We found a rough surface to be the most suitable for retaining tissue. With our optimized molding form, the lenticule can be safely retained at a suction of 2.5 m H2O.

Animals↗
PubMed1989

[Bacterial contamination in corneal preservation: pathogens and their origin].

We compared the results of microbiological cultures of conjunctival swabs and organ culture samples of human corneoscleral tissue and found bacterial contimination of the conjunctiva in 54% of all eyes investigated post mortem. Donor age or time after death up to 60 h showed no influence on the rate of microbial growth. The bacterial flora in the conjunctiva was not responsible for microbial growth in the organ cultures, and none of the bacteria found in the cultures could be related to the conjunctival flora. A sterile conjunctival swab does not mean that the organ culture is sterile.

Bacteria↗
PubMed1989

[Comparative studies of the calibration of new electronic automatic tonometers].

Over the last years the number of newly developed automatic microprocessor controlled tonometers has been increasing. These devices follow totally different measurement principles. Therefore the physical methods for calibration of these tonometers differ widely. Described is the possibility of calibration of new microprocessor-controlled tonometers. First the Tonopen, which follows the Mackay-Marg principle was tested. Its accuracy in measuring the intraocular pressure and its independency of position was examined. Moreover, the non-contact tonometers were tested. Especially the airstream of non-contact tonometers (CT 10, Pulsair) was measured with a Constant Temperature Anemometer (CTA). The topspeed of the airstream was 335 km/h for the CT 10 and 249 km/h for the Pulsair tonometer. The profile of the airstream was paraboloid. The base measured about 5 mm in diameter. For detection of the effect of the airstream to the cornea, a camera was connected over a special interface with the CT 10 and triggered with a flashlight generator. The airstream produced at the moment of pressure measurement an exact applanation of the cornea with a diameter of about 4 mm. The results demonstrate the possibility of physical calibration, but this does not substitute biometrical measurements.

Calibration↗
PubMed1988

[New methods of refractive corneal surgery. Experimental studies].

In an experimental study the surface characteristics of two fundamentally different lamellar corneal dissection techniques were compared. Using porcine corneae, 9.5 mm lenticles were cut from the whole globe and evaluated by SEM. With an oscillating blade, a smooth cut surface was found in most cases with occasional irregularities. The rotating lamellar keratome had uniform cutting characteristics with a somewhat wavy surface structure, which has not so far been observed in human tissue. By increasing the speed of rotation and decreasing the rate of advance of the blade the surface structure was improved. The two cutting principles and their possible clinical applications are discussed.

Animals↗
PubMed1987

Ultrasonographic measurement of the posterior coats of the eye and their relation to axial length.

In 159 eyes with a spherical correction varying from +14.0 to -27.0 diopters, the axial length and thickness of posterior ocular coats were measured ultrasonographically. As proven in experimental studies, retina, choroid, and sclera were resolved in a considerable percentage of cases by combining A- and B-mode techniques of modern ultrasonographic equipment. The presumed close inverse correlation between the axial length of the eye and ocular coat dimensions was confirmed by statistical analysis. These values were used to calculate the approximative volume of the posterior half of the ocular coats. There was evidence for a constant tissue volume regardless of the difference in surface and axial length parameters between hyperopic and myopic eyes. Results are discussed and compared with theories of axial growth under physiological and pathological conditions.

Animals↗
PubMed1987

[Automatic measurement of intraocular pressure with an electronic sensor tonometer].

Applanation tonometry based on Imbert-Flick's law and calibrated by Goldmann for clinical application is generally performed today with a standard diameter of the applanation surface of 3.06 mm. This diameter is determined optically by the examiner; the force required for applanation is the measured variable. With electronic, nonoptical definition of the applanation area a reading which cannot be falsified by an error on the part of the examiner can be obtained automatically and considerably faster.

Animals↗
PubMed1987

[Cryopreservation of porcine corneas with chondroitin sulfate].

A new method for cryopreservation of porcine corneoscleral discs has been developed. Instead of the widely used cryoprotectant DMSO, chondroitin sulfate was applied as a cryoprotectant for the first time. Post-thawing evaluation was done after short-term tissue culture. Central cell counts showed a mean endothelial cell density of 2430 cells/mm2 (+/- 383) after freezing with a combination of 2% chondroitin sulfate and 20% fetal calf serum. Corneae which were cryopreserved with DMSO using the method established by Capella and Kaufman showed a mean endothelial cell density of 1672 cells/mm2 (+/- 617). These experiments demonstrated significant cryoprotective properties of chondroitin sulfate. In addition to its application in refrigerated corneal storage at 4 degrees C and organ culture at 32 degrees C, this substance may also be useful in cryopreservation.

Animals↗
PubMed1987

[Keratoplasty in children and adolescents].

In a retrospective study 37 penetrating keratoplasties performed on 33 eyes of 29 patients under age 12 were evaluated. One year postoperatively, 19 of 35 grafts were clear and 16 of 35 had failed. In the group aged under 3, most of whom had congenital anomalies, 4 of 14 had clear grafts and 10 of 14 failed grafts after one year. Two patients were not investigated one year after keratoplasty, but probably had cloudy grafts at that time. Loosening of the sutures and keratitis were the main complications in the postoperative course. Graft rejection was clinically diagnosed in 11 of 37 cases.

Adolescent↗
PubMed1987

Nonoptical definition of applanation surface.

Based on the Imbert-Fick law and the theoretical considerations of Goldmann, new applanation tonometers were designed, still using an applanation diameter of 3.06 mm to avoid a new biometric calibration. Three different electronic recording devices were used for the area assessment. An optical, a capacitance and a digital line sensor were tested in first calibration experiments.

Animals↗
PubMed1987

The corneal endothelium as a standard for the assessment of complications in microsurgery.

Endothelial cell morphology is an important parameter for the quality control of different surgical techniques, especially in the anterior segment. The minimizing effect of hyaluronic acid in implant surgery can be demonstrated by the decrease of endothelial cell loss as compared to standard techniques. Besides, we can show that the implantation of artificial lenses into the capsular bag is less traumatizing to the cornea than anterior chamber lenses. Other factors to control the surgical techniques are the keratoplastics, especially modified to different trephination techniques and last but not least YAG laser surgery of the cataract membranes. In the latter, there is a direct correlation between endothelial trauma and distance of focus and total energy. Even in isolated cases we can draw conclusions from endothelial morphology to intra-postoperative complications. New surgical techniques which could lead to damage of the cornea should be tested by endothelial cell analysis.

Cataract Extraction↗
PubMed1987

[Possibility of surface-independent tonography and tonometry].

A method of simultaneous measurement of intraocular pressure and volume displacement is reported. An electronic pressure sensor (diameter 3 mm) was positioned in the centre of the base of a transparent applanation body (diameter 9 mm). The corneal applanation area could be changed by different applanation forces and was measured photographically. In isolated human and porcine eyes, sensor signal and intraocularly measured pressure were related linearly and independently of the applanation area. In human eyes in situ, the rigidity coefficient decreased with increasing pressure. Adhesive forces and stiffness of the cornea obviously only falsify tonometry at the margin of the applanation area.

Biomechanical Phenomena↗