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Biomedical subjects

H Wirt

Publications and source records attributed to H Wirt.

18 recordsLinked to original sources
PubMed2002

[In vivo measurement of temperature during phacoemulsification].

BACKGROUND: Based on our experience of in vitro measurements of temperature in the anterior chamber in 1994 we designed a new spatula with an integrated probe that enabled us to measure temperature continuously during phacoemulsification without any surgical effort. METHODS: We measured the temperature in the anterior chamber during 50 cases of phacoemulsification. Depending on the indications, we used different energy modes (0-100%) and pulse modes ranging from 3 to 10 pulses per second or continuous ultrasonic output. Different viscoelastic substances were also used. RESULTS: The average temperature in the anterior chamber was 30 degrees C and adapted to the temperature of the irrigation fluid within seconds as soon as irrigation was started. During phacoemulsification each ultrasonic output causes an increase of temperature. In the case of continuous mode, the maximum rise in temperature was 3.5 degrees C. When the pulse mode was used the temperature increased up to 1.7 degrees C. It is important to note that one single pulse may increase the temperature by 0.8 degree C close to the phacotip. The rise of temperature correlated with the viscosity of the viscoelastic substance used. CONCLUSIONS: The new probe proved to be a practical device to monitor temperature in the anterior chamber during phacoemulsification. Up to now we did not encounter any critical degrees of temperature but it should be pointed out that a functional irrigation unit, the use of pulse mode or permanent ultrasonic output and in particular the type of viscoelastic material used are all important parameters influencing the rise of temperature during phacoemulsification. Further experience and results obtained with the new probe will be reported in the future.

Anterior Chamber↗
PubMed2000

[Long-term results of combined glaucoma and cataract surgery. Intraocular pressure and visual acuity follow-up].

BACKGROUND: The aim of this investigation was to ascertain the long-term results of intraocular pressure and visual acuity after combined glaucoma and cataract surgery. PATIENTS AND METHODS: Between 1994 and 1997, 65 eyes underwent Pham's sclerectomy and at the same time 65 eyes underwent Elliot's trephination with scleral flap. Both procedures were combined with phacoemulsification and implantation of a posterior chamber lens. The mean follow-up was 21.9 +/- 11.0 months. RESULTS: The IOP of eyes that underwent Pham's sclerectomy decreased from 21.4 +/- 3.3 mmHg to 14.9 +/- 2.7 mmHg and of eyes that underwent Elliot's trephination from 24.6 +/- 7.3 mmHg to 15.8 +/- 2.6 mmHg. Thirty percent of the eyes with Pham's sclerectomy and 25% with Elliot's trephination required an additional medication. In both procedures the overall visual acuity increased by three lines. CONCLUSIONS: These results of combined glaucoma and cataract surgery confirm their efficiency. From the economical aspect, combined glaucoma and cataract surgery has gained increasing significance.

Aged↗
PubMed1995

[Experimental study of the temperature during phacoemulsification].

UNLABELLED: Reports on thermal burns during phacoemulsification motivated us to perform an experimental study on the temperature gradient [2,7]. A special measurement technique was developed that enable us to record temperatures in 0.1 s and to document these measurements and interpret them. The experiments were conducted in enucleated pig eyes, as well as in a constructed model of the anterior chamber. Using 500 such measurements, we discuss and demonstrate the influence of the volume of the anterior chamber, the adjustment of the phacoemulsification, the presence of viscoelastic material, the reflection of ultrasonic power on the lens, and insufficient or interrupted irrigation and/or aspiration. RESULTS: An analysis of the measurements showed that within 8 s extremely high temperatures developed. At the phacosleeve, temperatures of more than 100 degrees C were recorded. Measurements around the phacotip also showed high temperatures resulting in tissue degeneration, especially with simultaneous application of viscoelastic material and/ or the presence of a hard nucleus. When pulse modulation is applied or power reduced, temperatures drop to less than 50%. CONCLUSIONS: The main factor behind the development of high temperatures is the breakdown of irrigation. The danger of phacoburns increases by application of viscoelastic material, reduced volume of the anterior chamber when there is a hard nucleus and high ultrasonic power with no pulse.

Animals↗
PubMed1992

[New aspects of surgical treatment of glaucoma. Comparison of viscoelastic substances in chamber angle surgery].

The development of new viscoelastic substances opens up new perspectives for chamber angle surgery under direct view. The success of "Cyclodialysis ab interno" treating children with glaucoma is often reduced by scar formation of the cleft. Therefore four different viscoelastic substances were instilled during an animal experimental study into the cleft and compared in their effect. We used hyaluronic acid with different molecular weight (Healon and Healon GV) and cross-linked forms of hyaluronan as a fluid and a gel (Hylan fluid and Hylan gel). A cyclodialysis ab interno was performed on 14 eyes of cynomolgus monkeys. The functional results (tonometry, outflow facility, autoradiography) and the morphological findings will be presented and their consequences for an extended indication of the cyclodialysis ab interno will be discussed.

Animals↗
PubMed1990

[Clinical value of new tonometers].

In a clinical study four different tonometers [a hand-held applanation tonometer (HAT), a tonometer that works according to the principle of Mackay-Marg and two noncontact tonometers (NCT A und NCT B)] were compared with respect to accuracy and precision. In a randomized sequence, two physicians took six measurements of both eyes of 99 patients using the four different instruments. The interval between the two measurements in one eye was 3 min. The correlations of repetitive measurements for one tonometer in one eye showed good results for HAT (r = 0.985, SD = 1.66 mmHg), but significantly worse values for the other three tonometers (Mackay-Marg type: r = 0.85, SD = 3.5 mmHg; NCT A and NCT B: r = 0.91, SD = 2.93 mmHg). To establish the accuracy, the pressure values of the Mackay-Marg type and NCT A and NCT B were compared with those of the well-established HAT. The results were as follows: Mackay-Marg type: r = 0.84, SD = 3.78 mmHg; NCT A: r = 0.86, SD = 4.55 mmHg; NCT B: r = 0.89, SD = 3.26 mmHg). We conclude that the three tonometers tested (one based on the Mackay-Marg principle and the other two on the non-contact principle) are not suitable for clinical and scientific use.

Adolescent↗
PubMed1989

[Clinical and experimental evaluation of the so-called Tono-Pen tonometer].

The measuring accuracy and reliability of the new Tono-Pen tonometer, which works on the Mackay-Marg principle, were tested on isolated human and pigs' bulbi and on 24 patients. On isolated pigs' bulbi the Tono-Pen indicated the true pressure, whereas the pressures measured on isolated human bulbi were too high and the range of scatter was wider. On patients' eyes the values obtained with the Tono-Pen correlated well with those measured with the hand applanation tonometer (r = 0.92), although the values measured with the Tono-Pen again higher (mean 4.5 mm Hg). As indicated by autocorrelation of repeated measurements, the Tono-Pen appears to be mainly responsible for the difference between the two instruments. The standard deviation of the autocorrelation of the Tono-Pen values was 4.5 mm Hg, that of the hand applanation tonometer only 1.2 mm Hg. The considerable standard deviation of the Tono-Pen measurements may be due to the structure of the human cornea, and in particular Bowman's membrane. The reproducibility of Tono-Pen measurements is too low for it to be recommended for ophthalmological diagnosis.

Animals↗
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↗
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

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↗
PubMed1985

[Experimental studies on the correction of presbyopia].

As a consequence of the changing population structure the number of older, i.e., presbyopic people in work will increase in the future. At the same time the demands made on vision at work will also increase, as new technologies are introduced. Both of these factors will have to be taken into account by ophthalmologists and the optical industry. As accommodation deteriorates, special glasses become necessary which are suited to requirements for highly qualified work. With this in mind the authors conducted a joint investigation at a precision assembly workplace together with the manufacturing technology laboratory of Duisburg University. The results show that if bifocal or respectively trifocal glasses are prescribed at the right time efficiency can be improved both quantitatively and qualitatively. The specific requirements with regard to spectacles worn at such workplaces result in particular from the fact that, for ergonomic and technical reasons, operating devices and controls are being mounted ever more frequently above the horizontal line of gaze. Therefore, when prescribing the glasses, it is important that not only the correction for close and mid-range vision, but also the size and location of this portion of the lens should be taken into consideration. This is illustrated with a number of examples.

Adult↗
PubMed1985

Interindividual differences of corneal sensitivity. Genetic aspects.

By means of an electronic optical esthesiometer corneal sensitivity was examined in 91 volunteers of different age groups. Additionally, the anesthetic duration of the local anesthetic benoxinate was investigated. Corneal sensitivity decreases with advancing age. Comparing male and female subjects, we can suppose that there are age and sex specific differences of corneal sensitivity. There might be additional genetic factors. There are great interindividual differences in the anesthetic duration of benoxinate. It can be assumed that benoxinate is metabolized by pseudocholinesterase. One possible explanation for the great differences in the anesthetic duration of benoxinate can be seen in the genetically determined variants of pseudocholinesterase.

Adult↗
PubMed1984

[Long-term results following goniotomy in congenital glaucoma].

Between 1961 and 1983, 544 goniotomies were performed at the Department of Ophthalmology of the University of Hamburg and Bremen General Hospital. Of these 227 were performed in 130 eyes with congenital glaucoma between 1961 and 1983. Pressure regulation was achieved in 72% of the eyes examined 3-22 years postoperatively. The prognosis is not related to the preoperative corneal diameter or IOP, but the patient's age at the first goniotomy is of prognostic importance. Very poor results are achieved in cases of manifestation during the first 2 months of life. Of the regulated eyes, 56% achieved a visual acuity of over 0.4. If only one eye is affected, visual acuity attained is poorer. Results of surgical techniques and methods of goniotomy are compared and discussed.

Child, Preschool↗
PubMed1983

Visco elastic glaucoma surgery.

Hyaluronic acid facilitates and maintains separation of dissected structures in glaucoma microsurgery, thus preventing complications during surgery and in the immediate postoperative phase. Goniotomy is more easily controlled and is safer. Hyaluronic acid can therefore be used in glaucoma microsurgery to keep prepared layers of tissue separated for longer and can enlarge newly created space and almost eliminate the adhesive forces between the layers. Using hyaluronic acid the safety of glaucoma microsurgery is enhanced and the complication rate reduced. High elastic viscous substances offer better technical possibilities in microsurgery. Further experience is necessary before a final judgement can be made on the advantages.

Glaucoma↗
PubMed1982

[Long-term results after goniotomy (author's transl)].

Between 1961 and 1968 140 goniotomies were performed at the Department of Ophthalmology, University of Hamburg. The condition of 72 eyes was evaluated and 41 eyes were re-examined. The average intraocular pressure was 33 mmHg preoperativly and only 20 mmHg 13 to 20 years after the goniotomy procedure. Patients from this group with buphthalmus had an even lower pressure of only 17.6 mmHg. Pressure regulation was achieved in 85% of the evaluated eyes by one or more operations, in conjunction with drug therapy in some instances. In 18 of the 41 eyes a satisfactory result was achieved after a single goniotomy procedure. In 15 of the 41 eyes visual acuity was 0.3 or better with normal pressure. The risk of postoperative amblyopia is mentioned.

Adolescent↗