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M Kohlhaas

Publications and source records attributed to M Kohlhaas.

At least 37 records · Page 2Linked to original sources
PubMed1996

[Clinical calibration and in vitro evaluation of the validity of 2 microprocessor controlled tonometers].

In a randomised clinical study two new microprocessor-controlled tonometers working according to the Mackay-Marg principle (Tono-Pen and ProTon, two samples of each) and two established applanation tonometers [hand-held applanation tonometer, Draeger (HAT) and Goldmann tonometer] were compared with respect to accuracy, precision, examiner dependence and internal measurement differences (Tono-Pen I vs II, ProTon I vs II). The four tonometers were used by two examiners six times on each of 193 eyes of 100 patients of the university eye department. The same measuring procedure was performed on four cadaver eyes in situ, using a manometer system. The correlation coefficient between Tono-Pen and HAT and between ProTon and HAT was 0.9, with a high standard deviation, about +/- 3.1 mmHg. HAT gave the best results in repetitive measurements in the same eye (precision: r = 0.92, SD = +/- 1.41 mmHg). In applanation tonometers but not in Mackay-Marg tonometers measurement values depended significantly on the physician. There was a significantly higher standard deviation between Tono-Pen I and II than between ProTon I and II. Concerning in vitro calibration series on human bulbs (manometry), accuracy was high with each tonometer. The regression line of HAT is similar to that of ProTon. Tono-Pen overestimates the manometrically determined intraocular pressure. Because of their lack of precision the two new tonometers are not suitable for clinical use.

Calibration↗
PubMed1996

[Biomechanical study of corneal stability after radial keratotomy].

BACKGROUND: Radial Keratotomy is one of the most frequent refractive surgical procedures performed worldwide. It results in considerable alterations of the corneal structure. What does this mean for the mechanical properties of the cornea? METHODS: Intraocular pressure was increased via a 180 degrees tilt. Before and during this procedure, corneal topography was measured by photokeratoscopy. We examined 36 patients after RK and 25 controls who had not undergone any surgical procedure. RESULTS: The corneal center flattened by 0.523 +/- 0.054 dpt (p < 0.01) in the RK patients and by 0.187 +/- 0.045 dpt (p < 0.05) in the control group. CONCLUSION: Even several years after radial keratotomy, corneal stability is still decreased.

Adult↗
PubMed1995

[Corneal reinnervation after keratomileusis in situ and keratomileusis myopica--a comparison].

BACKGROUND: In a retrospective study corneal sensitivity after keratomileusis in situ and keratomileusis myopica was measured. METHOD: 5 points on the cornea were measured with the Draeger aesthesiometer at 18 eyes after keratomileusis myopica and at 66 eyes after keratomileusis in situ. RESULTS: The ingrowth of corneal nerve fibres is delayed after keratomileusis myopica compared to keratomileusis in situ because of delayed stromal repopulation of keratocytes and disturbances of stromal metabolism due to toxic effects of the cryopreservation solution.

Adolescent↗
PubMed1995

[Effect of corneal hydration and dehydration of donor tissue on the precision of the thickness in lamellar refractive keratoplasty].

The influence of corneal hydration on the precision of plano lamellas and on the precision of lenticles modified with a "non-freeze" technique was studied in pig eyes. Ten pig eyes were dissected with a rotating lamellar microkeratome, and the discs were measured with a mechanical pachymeter. The hydration of the discs was measured in BSS and in dextran solution. A total of 160 corneal discs with different degrees of hydration were modified with a "non-freeze" technique on concave anf convex vacuum cylinders and measured with a photokeratoscope TMS. The discs increased in thickness within 3 h becoming 1.7 times as thick in BSS and 1.2 times as thick in dextran. After refractive dissection minor modifications were achieved with higher precision than were larger corrections. However, we achieved an undercorrection after all refractive dissections. Plano-discs for refractive modification should be taken from dehydrated corneoscleral discs or from intact eyes. Owing to mechanical factors during cutting and tissue hydration undercorrection of the intended change was observed.

Animals↗
PubMed1995

[Corneal reinnervation after lamellar refractive corneal surgery].

In a retrospective study corneal sensitivity after refractive autokeratoplasty for correction of myopia was measured. Thirty-eight patients operated on for keratomileusis in situ and 18 patients for keratomileusis myopica were examined with the Draeger esthesiometer between 1 and 23 months after surgery. Three measurements points were on the refractive disc, two others on the untouched cornea. After keratomileusis myopica, the corneal reinnervation is significantly delayed compared to keratomileusis in situ. In the first group sensitivity is normal after 2 years and in the second group after 1 year. Even refraction and visual acuity depend on metabolism and reorganization of the tissue after surgery. Besides retarded cell repopulation and disturbed stromal metabolism--caused by toxic and cryopreservation effects--the dissection depth of the refractive ablation is responsible for these phenomena.

Adolescent↗
PubMed1995

[Keratomileusis with a lamellar microkeratome and the excimer laser].

In a combined prospective study with E. Arnott's department, intrastromal excimer keratomileusis on the lenticle stroma was performed in 15 eyes of 15 patients (follow-up 6 months). The primary keratectomy was performed using the lamellar automatic rotating microkeratome, followed by refractive modification by the excimer laser on the excised corneal discs. For the laser ablation, a repetition rate of 10 Hz and a fluence on the corneal plane of 180 mJ/cm2 was used. Following surgery, all treated eyes were subjected to guttae of Maxitrol q.i.d. for 12 weeks. Excimer laser intrastromal keratomileusis effectively combines corneal microsurgery and photoablation. The predictability of the refractive correction is better than with the other surgical keratomileusis techniques.

Adult↗
PubMed1995

[Cyclocryocoagulation in treatment of special types of glaucoma].

In this retrospective study, we examine the efficiency of cyclocryocoagulation in eyes with secondary and congenital glaucoma. We studied 137 eyes with advanced, inadequately controlled glaucoma, which were operated from 1984 to 1993. Besides the intraocular pressure (IOP), we assessed the effect on the visual acuity and the optic nerve. We also compared the efficiency of two different cryomethods (CO2/N2 cyclocryocoagulation). Fifty eyes were cyclocryocoagulated with CO2 and 87 with N2. After a period of 6 months, 90 eyes were regulated (IOP between 7 and 21 mm Hg). At this time the mean IOP was 16 mmHg, whereas it had been 40 mm Hg before the cyclocryocoagulation. Serious complications like a phthisis bulbi were seen in only 18 eyes. Five eyes became blind despite therapy because of an absolute glaucoma. Concerning the different types of glaucoma, the neovascular glaucoma was the most difficult type to regulate. We obtained better and more lasting results with N2 cyclocryocoagulation (68% regulation) than with CO2 cyclocryocoagulation (62% regulation). Thus, cyclocryocoagulation represents a good method for the treatment of advanced, inadequately controlled glaucoma eyes when other methods have failed.

Adult↗
PubMed1994

[Physical and aerodynamic airflow relations of the air stream of the Micro-Air aesthesiometer].

BACKGROUND: In an experimental study we examined the aerodynamical airstreamprofile of a new airstream aesthesiometer. With this instrument it is possible to measure corneal sensitivity without touching the cornea. METHOD: A constant hotwire-anemometer was used to measure the 0.5 s air impulse in different distances. The corneal topographic sensitivity was measured at 45 probands, age 20 to 80. RESULTS: The investigations show that the laminar air stream within the 0.2 mm wide nozzle changes after withdrawal, in regards to stream profile, jet width and speed. The parabolashaped stream profile passes over through the air matrix and changes into a bell-shaped profile. The stream properties of the circular free system imply that the air stream in a 4 mm distance is nearly half as wide and double as high or fast in comparison to an 8 mm distance. The corneal sensitivity measured with the CMA showed in comparison to the Draeger aesthesiometer a lower sensitivity than in the periphery. CONCLUSION: A clinical use for measuring corneal sensitivity with the CMA can not be recommended.

Adult↗
PubMed1994

[Corneal reinnervation after lamellar keratoplasty in comparison with epikeratophakia and photorefractive keratectomy].

Corneal sensitivity was examined with the Draeger aesthesiometer in 8 patients after lamellar keratoplasty, 7 patients after epikeratophakia and 82 patients after photorefractive keratectomy. We examined 9 different points in each cornea. The corneal sensitivity of patients after lamellar keratoplasty was normal 1 year after operation. A correlation with the depth of the lamellar dissection was demonstrated. Patients with lamellar keratoplasty with pterygium showed a sensitivity decrease in the nasal parts of the lenticule even after one year. Three years after epikeratophakia the corneal center was still not sensitive. After photorefractive keratectomy of more than 10 D, corneal hyposensitivity was shown even 2 years after operation.

Adult↗
PubMed1994

[Measuring corneal sensitivity with the air aesthesiometer in comparison with the Draeger electromagnetic air aesthesiometer].

A new air aesthesiometer developed by S. Weinstein was tested with an anemometer device. It could be shown that the air stream is not linear. The normal sensitivity threshold pattern was measured in 271 probands varying in age from 10 to 98 years. In a comparative study we measured the corneal sensitivity of 20 patients after penetrating keratoplasty with the air aesthesiometer and the Draeger electromechanical aesthesiometer. Because of the aerodynamic broadening of the airstream it was not possible to measure corneal sensitivity at the transplant periphery or host cornea with the new device, while we could demonstrate corneal nerve fibre degeneration at the host cornea or regeneration of the transplant with the electromechanical aesthesiometer.

Adolescent↗
PubMed1993

[Pressure-induced change in corneal curvature in patients with refractive surgery and unoperated probands].

Helmholtz suspected there was a connection between intraocuclar pressure and lateration of corneal curvature. With a view to potential changes in corneal stability following different refractive procedures, we tried to demonstrate these side effects by increasing the intraocular pressure. A tilting-table was used to induce a rapid pressure increase via the fluid shift. Corneal curvature was measured by photokeratoscopy before and after pressure changes. The results were different in corneas subjected to radial and photorefractive keratotomy than in intact corneas. We suggest a physical model that might provide an explanation.

Adolescent↗
PubMed1992

[Technical problems in microsurgical processing of preserved donor tissue].

The microsurgical processing of longterm preserved tissue is still a problem for lamellar and perforating keratoplasties. Advantages of donor tissue cut with rotortrephines versus manual trephines are presented. Optimal possibilities of examination and storage of donor tissue are explained. A lamellar microkeratome, an artificial anterior chamber for corneoscleral discs and a refractive workbench for non-freeze modification are shown.

Corneal Transplantation↗
PubMed1992

[Prerequisites for the use of preserved donor tissue in perforating and lamellar keratoplasty].

The longterm tissue culture is performed at the University Eye-Hospital of Hamburg since 1985 with a standardized procedure. The number of donor material and operations in the first 7 months of 1991 are reported. Preparation, storing and HLA-typing of the tissue are considered. The technical working up of the stored tissue for penetrating and lamellar keratoplasties will be explained.

Corneal Transplantation↗
PubMed1992

[Aesthesiometry of the cornea after refractive corneal surgery].

The corneal sensibility was examined with the aesthesiometer of Draeger in 41 patients after refractive corneal surgery, 31 patients after radial keratotomy, 5 after epikeratophakia, 5 after excimer laser ablation. It could be shown that after radial corneal incisions the sensibility remains normal. After epikeratophakia the corneal sensibility is asensible even 3 years after operation. The lenticle periphery shows an increase of sensibility after 6 months. Excimer patients with "haze" showed a significant hyposensibility in the centre. The central sensibility showed normal values after a normal corneal wound healing.

Adult↗
PubMed1992

[Precision of lenticular thickness in relation to full stroma corneal thickness. Experimental results with the lamellar microkeratome].

In this study 150 pig corneas and 20 human corneas were dissected with an automatic rotating microkeratome for lamellar grafting. The cornea thickness varied between 0.507 mm and 0.829 with an average 0.66 mm. The aim of this investigation was to show the influence of corneal thickness, the chosen diameter and spacing on the precision of cutting lenticles. We did ten series: the pig corneas were dissected at three different intervals of 0.15, 0.25, 0.35 mm and diameters of 9 and 6mm. The human corneas were cut at intervals of 0.4 mm and 0.25 mm and with diameter of 9 and 7 mm. Although the pig corneas were fresh, the intraocular pressure was too low. It was raised with an injection of physiological salt solution to a predefined level. The rotating speed of the trephine blade, the speed of blade advancement and lubrication fluid were kept constant. Ultrasound pachymetry was performed on the center of the corneas before cutting had on the lenticles afterward. We showed that a thick corneal diameter had a negative influence, i.e., the greater the diameter, the lesser the precision; the same was true for the corneal thickness. On the other hand, the intervals had just the opposite effect: the closer they were, the better the correlation. The human eye results were different in quantity but not in tendency, with less striking effects. The average variation for pig corneas was 22% and for human eyes 8%. The best results were received with a large interval, a small diameter, and a normal corneal thickness in human eyes.

Animals↗
PubMed1990

[Precision of lamellar refractive corneal lenticules].

We studied the changes in central lenticular thickness in 40 porcine corneal specimens subjected to refractive modification on the "Hamburg Refractive Bench." The changes in thickness attempted were +0.1 mm (group 1), +0.2 mm (group 2), -0.15 mm (group 3), and -0.25 mm (group 4). The lenticular thickness was determined by ultrasound in nine positions. When the intended changes in central corneal thickness were compared with the actual changes, the findings were +0.1047 in group 1, +0.169 in group 2, -0.1047 in group 3, and -0.2185 in group 4. We conclude that minor modifications in lenticular thickness can be achieved with high precision, but for large corrections in the hyperopic direction, only 85% of the desired changes can be accomplished.

Animals↗
PubMed1989

Vacuum fixation of corneal lenticules for refractive surgery.

Using the rotating lamellar keratome, a simplified method for nonfreeze shaping of corneal tissue was developed. A set of refractive molding forms was designed for a standardized lenticule diameter. The fixation of the lenticule was achieved by a system of suction holes. A mechanical fixation ring was not required, as the total shearing force exerted by the rotating blade is neutralized even by a low suction setting. Different surface properties (polished, matt, rough) were compared, showing an influence of the surface structure on friction and thus lenticule fixation. With our optimized molding form, the lenticule is safely retained at a suction of 2.5 m H2O.

Cornea↗