Biomedical subjects

M M Kus

Publications and source records attributed to M M Kus.

42 records · Page 3Linked to original sources

PubMed1996

[Regularity of corneal topography after penetrating keratoplasty--comparison between non-mechanical (excimer laser 193 nm) and mechanical trepanation].

BACKGROUND: "Vertical tilt" of the graft caused by incongruent cut angles, "horizontal torsion" caused by a asymmetric suturing and decentration of the wound seem to be the most important reasons for high and/or irregular postoperative astigmatism and deterioration of visual outcome after penetrating keratoplasty. We studied the time course of qualitative and quantitative topographic criteria after nonmechanical and mechanical trephination in correlation with visual outcome. PATIENTS AND METHODS: Fifty patients each (30 keratconus, 20 Fuchs' dystrophies) underwent nonmechanical trephination (excimer laser MEL60, Aesculap-Meditec, Heroldsberg) and mechanical motor-trephination in penetrating keratoplasty. All procedures (7.5 mm trephination diameter in Fuchs, 8.0 mm in keratoconus, double-running 10-0 nylon suture) were done by one surgeon. Pre-, intra- and postoperative treatment were identical. At the follow-up examinations, the keratometric astigmatism, qualitative and quantitative criteria of the automatic videokeratography, visual acuity and refraction were assessed. In addition, vector-corrected astigmatism (Jaffe-model) was evaluated in the postoperative time course, particularly after suture removal. RESULTS: After a mean follow-up of 1.1 +/- 0.8 years, keratometric net astigmatism was 4.0 and 4.2 diopters after nonmechanical and mechanical trephination. Corneal topography analysis showed a higher orthogonality of the bowtie shape and less asymmetry between opposite hemimeridians. Vector-corrected changes of corneal astigmatism were less after complete suture removal in nonmechanical trephination. After nonmechanical trephination, visual acuity was 2 decimal lines better. DISCUSSION: Nonmechanical trephination with the excimer laser 193 nm has the potential to improve the visual outcome by creating smooth and congruent cut edges parallel to the optical axis and the application of "orientation teeth". Since corneal net astigmatism does not differ significantly, a higher regularity of corneal topography after excimer laser trephination is supposed to be a main reason for this finding.

Adolescent↗

PubMed1995

[Endothelial keratopathy in pseudoexfoliation syndrome: quantitative and qualitative morphometry using automated video image analysis].

UNLABELLED: This prospective study intended to quantify and classify morphological changes of the corneal endothelium in pseudoexfoliation syndrome (PSX) after having tested reproducibility and validity of a new automated technique for analysing corneal endothelium. PATIENTS AND METHODS: We used a contact specular microscope combined with a video camera (Tomey EM-1000) and a computer (IBM compatible PC, 486DX33) with suitable software (Tomey EM-1100, version 0.94). Video images of corneal endothelium (area: 0.312 mm2) are passed directly into the computer input by means of a frame grabber and are automatically processed. Missing or falsely recognized cell borders are corrected using the mouse. We examined 85 eyes with PSX and 33 healthy control eyes. At first, retest-stability and validity of the cell density measurements were assessed in the PSX-eyes. A qualitative analysis of the corneal endothelium followed. RESULTS: The cell density measurements showed a high retest-stability (reliability coefficient r = 0.974). The values of the automated method (2040 +/- 285 cells/mm2) and those of manual cell counting (2041 +/- 275 cells/mm2) did not differ significantly (p = 0.441). The mean difference was 3.1 +/- 2.4%. Comparing the 85 PSX-eyes (2052 +/- 264 cells/mm2) to the 33 control eyes (2372 +/- 276 cells/mm2), there was a significant reduction of cell density (p < 0.001). The cell density of the 69 PSX-eyes with glaucoma (2014 +/- 254 cells/mm2) was significantly lower than that of the 16 PSX-eyes without glaucoma (2214 +/- 251 cells/mm2) (p = 0.008). Eighty-five percent of the 85 PSX-eyes showed polymegalism, 77% pleomorphism; 68% had white deposits and 42% guttae. White deposits and guttae were significantly more frequent and more intensive in PSX-eyes than in control eyes. PSX-eyes with and those without glaucoma showed no significant differences concerning the four qualitative parameters. CONCLUSION: The automated method for analysing corneal endothelium quickly provides reproducible and valid results using the correction mode of the software. Semiquantitative analysis of qualitative parameters permits a more differentiated assessment of keratopathy in pseudoexfoliation syndrome than does mere consideration of endothelial cell density. Both evaluations are recommended to assess the risk of a diffuse endothelial decompensation before intraocular surgery.

Aged↗

PubMed1993

[193 excimer laser trepanation in perforating keratoplasty. Report of 70 patients].

BACKGROUND: In penetrating keratoplasty, trephination with the 193 nm excimer laser may help avoid the differences in the deformation of the donor and recipient wound margins which occur with the conventional procedure. By varying the shape of the "open metal mask", other cut configurations can be achieved besides circular. Thus, "vertical tilt" and "horizontal torsion", both potential reasons for persistent long-term astigmatism after PK, may be minimized. Following experimental studies, the authors present the results obtained in their first 70 consecutive patients. PATIENTS AND METHODS: 38 women and 32 men were treated (mean age 60.6 years, range 17 to 89 years). Indications were corneal processes without vascularization: Fuchs' dystrophy (n = 32), other stromal dystrophies (n = 5), secondary corneal endothelial decompensation (n = 6), keratoconus (n = 15), nonvascularized corneal scars (n = 4) and miscellaneous (n = 8 ). We used elliptical metal masks with/without orientation teeth and circular masks with four and eight orientation teeth, respectively. The HeNe aiming beam was manually controlled by a micromanipulator ("joystick"). The technical data of the laser were as follows: spot mode, 1.5 x 1.5 mm; repetition rate 30/sec and 25/sec, respectively; pulse energy 15-25 mJ; mean number of pulses 6407 (recipient) and 9150 (donor). With an elliptical outline, wound closure was usually achieved with single sutures. With a circular outline with orientation teeth, wound closure was most commonly achieved with a double running suture. Patients were prospectively documented using modified Erlangen record sheets. Follow-up ranged from 3 months to 3.4 years (mean 11.4 months). RESULTS: With two exceptions, penetration of the anterior chamber with the 193 nm excimer laser was accomplished without deformation of the cut edges. The elliptical outline facilitated fitting of the graft into the recipient wound bed, and the orientation teeth made fitting even easier. Initial intraoperative complications due to excessive laser energy densities included minor thermally induced corneal alterations caused by the heat of the metal mask and in a few cases minimal iris bleeding during corneal penetration. The median duration of re-epithelialization was two days. Wound healing was without complications. In particular, no primary graft insufficiency and no unexpected effects in donor or recipient corneas, iris, lens or posterior segments were observed. Postoperative complications were one corneal ulcer caused by premature fitting of an extended-wear contact lens and two immunologic graft reactions (3%). Mean astigmatism after suture removal was 4.6 D with an elliptical outline, and 3.9 D after trephination with orientation teeth and with the sutures in situ. CONCLUSION: Non-mechanical, "non-thermal" trephination with elliptical and circular metal masks with orientation teeth represents a viable alternative to knife trephination in penetrating keratoplasty. No unexpected complications such as disturbances of wound healing were seen. Further studies are needed to determine the effect on residual long-term astigmatism after suture removal.

Adolescent↗

PubMedDate not supplied

Design of computer-generated hologram with ring focus for nonmechanical corneal trephination with Er:YAG laser in penetrating keratoplasty.

PURPOSE: To calculate a beam-shaping optical element for homogeneous intensity distribution within a focal ring to be used in nonmechanical trephination with the Er:YAG laser in penetrating keratoplasty instead of a spot guiding device. METHODS: The phase distribution behind a holographic optical element (HOE) k psi(u) can be described by the addition of the hologram phase phiH(u) to the beam phase phiE(u): k psi(u) = phiH(u) + phiE(u), k = 2pi/lambda, where u denotes the coordinates inside the hologram aperture, k an integer, and lambda the laser wavelength. To avoid discontinuous wavefronts leading to speckle noise, a smooth phase function is necessary. After transforming the hologram aperture coordinates into the focal plane x in a focal distance f, psi can be retrieved from the slope equation: inverted delta psi(u) = x(u) - u/f. RESULTS: Creating a ring focus can be reduced to an essentially one-dimensional problem by separation of variables due to the symmetry condition. We calculated a computer-generated eight-level phase-only HOE with 4096 x 4096 pixels from a Gaussian-distributed 2.94 Er:YAG laser spot with a beam diameter of 10 mm and a focal distance of 100 mm. Thereby, a ring focus with an inner/outer radius of 7/8 mm can be created. To avoid Poisson's spo, the symmetry of the problem was broken by circular modulation of the phase leading to a spiral-like structure. The calculated efficiency of the HOE relating the energy within the ring to the total energy was 91%. CONCLUSION: With an HOE it is possible to redistribute the energy along the desired focal ring. The HOE design can be adapted to the intensity distribution of the impinging laser beam with its characteristic aperture shape. A circular homogeneous corneal trephination depth is possible, because the energy fluctuation from pulse to pulse does not locally affect the ablation process. A ring focus for the Er:YAG laser has the potential to render superfluous a manual beam control via micromanipulator and to allow a more rapid and more regular corneal trephination along aperture masks.

Cornea↗

PubMedDate not supplied

Evaluation of corneal flap dimensions and cut quality using a manually guided microkeratome.

BACKGROUND: To evaluate reproducibility of corneal flap dimensions and cut quality with repeated blade use with a manually guided microkeratome in pig eyes. METHODS: Corneal flaps were created using a manually guided microkeratome (Model One, Moria) with an intended 130-microns cut depth in 130 enucleated pig eyes. Flap thickness was calculated by pachymetry and diameter was estimated by means of applanation lenses compared to planimetry. Histology and scanning electron microscopy of samples and blades were performed to evaluate the keratectomy surface and blade cutting edge after repeated use of the blades. RESULTS: Mean flap central thickness was 135 microns (SD, 37 microns). The mean diameter of 8.4 mm (SD, 0.4 mm) correlated significantly (P < .001) to the intended diameter (r = .79). Mean difference from the intended diameter was 0.8 mm (SD, 0.3 mm; range, 0.04 to 1.4 mm). Scanning electron microscopy showed even and smooth cuts with chatter lines at the keratectomy edge using new blades. After repeated blade use, increasing cut irregularity, folds, and tissue remnants on the corneal bed surface, and nicks and tissue remnants at the cutting edge of the blades were observed. CONCLUSION: Reproducible flap dimensions were obtained using the Moria One microkeratome on pig eyes. The cut surface was regular and smooth with a new blade, but surface quality deteriorated considerably after repeated use of the same blade.

Animals↗

PubMedDate not supplied

Evaluation of corneal flap dimensions and cut quality using the Automated Corneal Shaper microkeratome.

PURPOSE: To evaluate flap dimensions and cut deterioration with repeated blade use in an automated microkeratome. METHODS: The Automated Corneal Shaper (Chiron-Adatomed, Munich, Germany), 160-microm plate attached, was used to make a corneal flap in 90 pig cadaver eyes, reusing blades up to five times. Flap diameter was measured by planimetry and thickness was calculated by ultrasound pachymetry. Scanning electron microscopy of stromal beds and blade cutting edges was performed to assess cut deterioration after repeated blade use. RESULTS: Mean flap central thickness was 125 +/- 32 microm. Mean vertical flap diameter was 7.6 +/- 0.4 mm. No correlation was found between thickness and diameter (r = 0.15, P = .45). Progressive thinning of the flap was observed in the direction of the flap hinge. Smooth cuts (using new blades) with periodic chatter lines at the keratectomy edge and in the stromal bed were observed with scanning electron microscopy. Increasing tissue remnants on the stromal bed and decreasing cut quality occurred with repeated blade use. Blades showed larger tissue remnants, nicks, and even folds on the cutting edge proportional to the number of times blades were used. CONCLUSION: Satisfactory cut quality and reproducibility were obtained after a single use of stainless steel blades in the Automated Corneal Shaper microkeratome. Cut quality was degraded dramatically by repeated use of blades.

Animals↗