PubMed Health⌕ Search

Biomedical subjects

A Langenbucher

Publications and source records attributed to A Langenbucher.

89 records · Page 5Linked to original sources
PubMed1998

The regularity of laser keratectomy depth in nonmechanical trephination for penetrating keratoplasty.

BACKGROUND AND OBJECTIVES: To study the regularity of laser keratectomy depth in nonmechanical trephination for penetrating keratoplasty (PK) and to assess its implications on astigmatism and visual acuity (VA). PATIENTS AND METHODS: In this retrospective clinicopathologic study, the authors enrolled 26 women and 32 men (mean age 54 +/- 20 years) with either keratoconus (n = 27) or Fuchs' dystrophy (n = 31), who underwent excimer laser (193 nm) trephination using a manually guided beam. Donor cornea trephination was performed using an artificial anterior chamber and either an automated rotation device (n = 27) or a manually guided beam (n = 31). The minimum residual corneal thickness (MRCT) and the random residual corneal thickness (RRCT), requiring division with scissors in excised patient buttons or corneoscleral donor rims, were assessed in a masked fashion using histologic sections. The postkeratoplasty keratometric net astigmatism, the subjective cylinder, and the VA were evaluated before and after suture removal. RESULTS: In patients with keratoconus, the mean MRCT (13% +/- 14%) and RRCT (38% +/- 20%) were significantly higher than in the patients with Fuchs' dystrophy (7% +/- 11% and 26% +/- 15%, respectively) (P < .01). When an automated rotation device for trephination of the donor cornea was used, the mean MRCT (2% +/- 4%) and RRCT (14% +/- 11%) were significantly smaller than when a manually guided laser beam was employed (15% +/- 12% and 38% +/- 15%, respectively) (P < .001). After suture removal, the VA increased significantly with automated trephination (P = .04), but not with manually guided trephination of the donor cornea (P = .24). However, after a mean follow-up of 30 +/- 8 months, the differences in the mean keratometric astigmatism, refractive cylinder, and VA after automated trephination (3.0 D, 2.6 D, 20/29, respectively) compared with those after manually guided trephination of the donor cornea (4.3 D, 3.9 D, 20/33, respectively) did not reach statistical significance. CONCLUSIONS: The regularity of donor trephination depth can be significantly improved by using an automated rotation device instead of a manually guided beam. Although residual postkeratoplasty astigmatism was not directly related to trephination depth, the improvement of the functional results after suture removal seems to be promoted by automated trephination.

Astigmatism↗
PubMed1998

Graft decentration in penetrating keratoplasty: nonmechanical trephination with the excimer laser (193 nm) versus the motor trephine.

BACKGROUND AND OBJECTIVE: Graft decentration is an obvious cause of postkeratoplasty astigmatism. The purpose of this study was to compare graft decentration after nonmechanical trephination with the excimer laser (193 nm) with that after mechanical motor-trephination in 50 consecutive patients with Fuchs' dystrophy and 50 patients with keratoconus. PATIENTS AND METHODS: To determine decentration in absolute values and clock hours, a postoperative slide was projected with a fixed magnification onto a pattern with circles corresponding to the trephination margin. Using a second transparent and movable pattern with concentric circles and ellipses, the authors measured the amount and direction of decentration relative to the limbus and to the pupil. In addition, the keratometric astigmatism and the refractive cylinder were assessed. In this prospective study, the patients were assigned randomly to either method of trephination. RESULTS: The decentration was significantly lower (P < .002) with excimer laser trephination (0.23 +/- 0.26 mm, relative to the limbus; 0.33 +/- 0.26 mm, relative to the pupil) than with mechanical trephination (0.58 +/- 0.23 mm, relative to the limbus [P < .01]; 0.64 +/- 0.24 mm, relative to the pupil [P < .005]). There was no significant difference between the results obtained in patients with Fuchs' dystrophy and those of patients with keratoconus. The preferred direction of decentration relative to the pupil was the lower quadrants. There was a mild correlation between net astigmatism and the absolute value of decentration. However, with sutures in place, there were no significant differences in the keratometric net astigmatism between mechanical and nonmechanical trephination (P = .16) or between Fuchs' dystrophy and keratoconus (P = .18). CONCLUSIONS: The results indicate that the amount of decentration can be reduced by specific techniques associated with nonmechanical trephination. This might have a favorable impact on the residual astigmatism after suture removal.

Adolescent↗
PubMed1998

Ellipsoidal fitting of corneal topography data after arcuate keratotomies with compression sutures.

BACKGROUND AND OBJECTIVE: After paired arcuate keratotomies and compression sutures (AK) for treatment of high postkeratoplasty astigmatism, corneal topography tends to be irregular. The purpose of this study was to demonstrate a mathematical method for approximation of discrete corneal topography power data with an ellipsoid for better appreciation of the clinical outcome after AK. PATIENTS AND METHODS: Thirty-one eyes of 28 consecutive patient who underwent AK for excessive postkeratoplasty astigmatism were studied. Regular keratometry, corneal topography (TMS-1), subjective refraction, and best-corrected visual acuity (VA) were assessed preoperatively and at 1 week and 1 year postoperatively. A simplex algorithm was applied for fitting an ellipsoidal surface to raw corneal topography power data. A set of parameters (meridional power, axis, and asphericity) were calculated. The cylinder of subjective refraction was correlated with the keratometric readings, the simulated keratometry (SimK) of the topography system, and the respective parameters of the model surface. RESULTS: Keratometric astigmatism and the cylinder of the model surface decreased from 8.1 +/- 3.2 and 7.9 +/- 2.9 D preoperatively to 4.5 +/- 2.1 and 5.3 +/- 2.0 D after 1 year, respectively. The asphericity in both meridional cross sections changed from a prolate ellipse preoperatively to an ablate ellipse at the early postoperative follow-up stage. Regarding the cylinder axis, there was a significant correlation of the model surface with the refractive cylinder at all examinations (P < .05), whereas there was no significant correlation of the SimK axis and the refractive cylinder axis. CONCLUSION: The approximation of corneal topography power data with an ellipsoidal model surface renders reconstruction of clinically relevant corneal topography parameters, including corneal asphericity with a marked data compression. Even in markedly irregular corneal surfaces, such as after AK, the correlation of amount/axis of refractive cylinder with the model surface parameters is more accurate than it is with respective SimK values of corneal topography analysis.

Adult↗
PubMed1997

[Reproducibility and validity of a new automatic method of specular microscopy analysis of corneal endothelium].

PURPOSE: This prospective study was designed to test the reproducibility of a new automated technique for analyzing the corneal endothelium and to assess the validity of the technique by comparing it with a standard method. SUBJECTS 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 the corneal endothelium (area: 0.312 mm2) were passed directly into the computer input by means of a frame grabber and were automatically processed. The area to be analyzed could be varied by location and size (5580-135,150 microns2), depending on the quality of the image. Healthy corneas of 67 volunteers (age: 30.9 +/- 8.6 years) were examined. One examiner measured cell density three times in each of 42 eyes (retest-stability); three different examiners made one measurement in each of 25 eyes (objectivity). We evaluated the cell density determined by the computer after automated analysis and assessed the corrected cell density. This second result was obtained after the examiner had corrected the processed image by drawing in cell boundaries that the computer had not recognized or erasing cell boundaries the computer had sketched in by mistake. Additionally, a photograph of the corneal endothelium (specular microscope Bio Optics LSM 2000 A) was obtained from 40 volunteers to be used for manual cell counting applying a "fixed-frame" technique (validity). RESULTS: The corrected values showed a high retest-stability (reliability coefficient r = 0.943) and a high objectivity (r = 0.904). The values obtained by the automated method (2415 +/- 214 cells/mm2) did not differ significantly from those obtained by manual cell counting (2431 +/- 228 cells/mm2) (P = 0.898). The uncorrected values (2252 +/- 190 cells/mm2) were on average 7.2 +/- 2.6% lower than the corrected ones (177 +/- 69 cells/mm2). Retest-stability (r = 0.856) and objectivity (r = 0.737) of the uncorrected values were satisfactory. The uncorrected value was significantly lower than the value of manual cell counting (P < 0.001). The size of the analyzed area (range 12,750-84,708 microns2; average 31,438 +/- 10,655 microns2) had no significant effect on cell density (Spearman's correlation coefficient k = -0.150, P = 0.093). CONCLUSION: The automated method for analyzing the corneal endothelium quickly produces valid, reproducible results in normal corneas, provided that the correction mode of the software is applied.

Endothelium, Corneal↗
PubMed1997

[Fourier analysis as a mathematical model for evaluating and presenting postoperative corneal topography data after non-mechanical perforating keratoplasty].

BACKGROUND: Videokeratography has given the possibility to obtain information in curvature from a much larger region of the cornea than that covered by keratometry. Fourier analysis as a mathematical model can be used to represent real physical attributes of the cornea and to divide corneal topography in its basic components: the zero-frequency component as the mean ring power, the one-cycle component as a representation of decentration and the two-cycle component as a representation of regular corneal toricity. The purpose of this study was the reconstruction of the corneal refraction after penetrating keratoplasty with a small number of characteristic parameters and the evaluation of the time course of the fourier coefficients as indices for a regular astigmatic cornea in the postkeratoplasty period including suture removal. PATIENTS AND METHODS: Fourty patients (group 1: 20 primary dystrophies, group 2: 20 keratoconus) underwent nonmechanical trephination (excimer laser MEL60, Aesculap-Meditec, Heroldsberg, Germany) in penetrating keratoplasty. All procedures (7.5 mm in dystrophies, 8.0 mm in keratoconus, 8 orientation teeth, double-running 10-0 nylon suture) were performed by one surgeon. At a postoperative gate of 6 weeks, 6 months, before partial suture removal and after complete suture removal, corneal topography (TMS1, Tomey, Tennenlohe, Germany), keratometry, visual acuity and subjective refraction were assessed. Radial approximation with a 5th order polynomial fit of the refractive data on 25 non-centric rings of the TMS, within 256 hemimeridians was performed to get data at equally spaced concentric rings. Fast Fourier transformation of the data sets in the mid periphery (1.4-1.8 mm apical distance) was done to get DC-, one-cycle and two-cycle component. Fourier coefficients were correlated with keratometric readings, subjective refractive values and visual acuity. RESULTS: Spherical equivalent was fairly constant in the postoperative interval before suture removal. After suture removal, a corneal flattening of about 3 diopters occurred. The one-cycle component before suture removal tended to be higher in group 1 compared to group 2 before suture removal. This difference was statistically significant (p = 0.01) after suture removal. Comparing keratometry, calculated meridians by the Tomey software, two-cycle component of the fourier decomposition and subjective refraction, the best correlation (p = 0.02) was observed between two-cycle-component and the refractive cylinder in amplitude and axis after suture removal. Best corrected visual acuity was inversely correlated with the amount of energy of higher harmonics compared to the whole energy before (p = 0.04) and after (p = 0.01) suture removal. CONCLUSIONS: Fourier transformation renders reconstruction of corneal topography data with a marked data reduction and a small error. From fourier coefficients conclusions may be drawn concerning potential best-corrected visual acuity and amplitude/axis of subjective cylinder, even in corneas with severe local irregularities.

Adult↗
PubMed1997

[Limbus-parallel keratotomies with compression sutures in treatment of high astigmatism after perforating keratoplasty: a vector analysis and topographic study].

BACKGROUND: Visual acuity following penetrating keratoplasty is frequently limited by excessive astigmatism which cannot be compensated for with spectacles or contact lenses. The purpose of the study was to determine the effects of arcuate keratotomies and compression sutures on the amount and regularity of corneal astigmatism and on the visual acuity. PATIENTS AND METHODS: Between June 1989 and August 1995, 56 eyes from 56 patients (30 women, 26 men, average age 53 +/- 16 years) with excessive post-penetrating keratoplasty astigmatism were treated with paired arcuate cuts and compression sutures 4.8 +/- 3.5 years after suture removal (45% keratoconus, 30% scars, 20% dystrophies). The incisions were made along the meridian of maximum dioptric power in a sector extending for 60 +/- 15 degrees (6 mm diameter). Incision depth was standardized at 450 microns. Compression sutures were placed 90 degrees away in the flat meridian. Eight patients required more than one procedure to obtain the desired effect. Best corrected visual acuity (VA), keratometric readings and topographic power maps were analyzed pre- and postoperatively. We categorized the topographic maps into six groups: from group 1 (regular) to group 6 (irregular). For description of the astigmatic change after surgery, the formulas by Naylor and Jaffe (vector-corrected astigmatism) were applied. RESULTS: The mean preoperative astigmatism was 10.8 +/- 3.1 (4.2 to 19.2) diopters (D). After a mean follow-up of 1.1 years, the mean net astigmatism was 5.8 +/- 3.2 (0 to 16) D. The mean preoperative visual acuity (VA) was 0.38 +/- 0.31 (from 0.03 to 1.0). At the end of follow-up, the mean VA was 0.43 +/- 0.25. Non-refractive reasons for poor visual acuity included amblyopia (n = 5), macular degeneration (n = 4), glaucoma (n = 4), cataract (n = 2), and others (n = 5). Twenty-seven percent of the preoperative topographic maps were categorized into groups 1 and 2 and only 10% into groups 5 and 6. At the end of the follow-up, none of the 53 available topographic maps was categorized into group 1, 7.5% into group 2 and 30% into groups 5 and 6. The mean astigmatic change (vector-corrected astigmatism) was 12.3 +/- 5.2 (1.0 to 29.8) D with a turn of the axes ranging from -39 to 44 degrees. CONCLUSIONS: Arcuate incisions with compression sutures are easily performed and hold a low complication rate in comparison with other refractive operations. Definition of successful surgery is even broader when a significant reduction of astigmatism that usually allows the use of spectacles or contact lenses is considered. A disadvantage is that each particular case is unpredictable because of the tendency of the topography to irregularity and possible regression of the effect.

Adult↗
PubMed1997

Corneal topography.

In the review period, limitations of individual Placido disk-based topography systems have been studied and new principles, such as raster photogrammetry, pancorneal slit topography, laser holographic interferometry, and confocal laser scanning topography, have been introduced for laboratory or clinical work. Both Fourier analysis and Zernike decomposition of topographic height data seem to be powerful new tools for cross-sectional analysis of complex topographic corneal images, such as after cataract surgery, penetrating keratoplasty, and refractive surgery, as well as for longitudinal studies of corneal changes, such as in schoolchildren. Subdividing into rational optical components may improve consistency and standardization of topography data from different systems. Topography-based flying-spot-mode excimer laser photoablation after Zernike decomposition of topography height data has been proposed for correction of irregular corneal astigmatism. Topography-based central power measurements are of increasing value for intraocular lens power calculation before cataract surgery in eyes with irregular corneal surfaces, such as in keratoconus or after refractive surgery procedures. Quantitative and qualitative classification of corneal topography maps after corneal transplantation following conventional mechanical and nonmechanical trephination or after refractive surgery may lead to a better understanding of impaired visual acuity despite a clear graft or despite significantly reduced ametropia or corneal astigmatism.

Cornea↗
PubMed1996

Thermal effects in excimer laser trephination of the cornea.

BACKGROUND: Excimer laser trephination, as an alternative to mechanical trephination of the cornea in penetrating keratoplasty, is expected to reduce long-term postkeratoplasty astigmatism. Trephination with high energy densities may induce thermal epithelial alterations when metal aperture masks are used. METHODS: Ninety porcine eyes fixed in an artificial anterior chamber (20 mmHg) were trephined with a 193-nm excimer laser in order to study the effect of the temperature on the cornea and the aperture mask during and after termination of the laser exposure. Energy levels tested were in the range used in patients. A pyroelectric infrared sensor connected to a PC via an analog-digital converter was used. With a high-speed sampling routine written in C+2 it was possible to monitor on line the temperature in a focus 0.8 mm in diameter. RESULTS: In donor trephination the maximum temperature increase of the metal mask was 11 K (donor tissue 6.1 K, repetition rate 30/s). During recipient trephination the maximum temperature increase of the mask was 9.4 K (7.5 K on the cornea). An increase in the repetition rate and a decrease in the rotation speed resulted in greater temperature increase of the exposed cornea or metal mask. CONCLUSIONS: Online monitoring of cornea and mask surface temperatures during excimer laser trephination is possible using high-speed sampling equipment. Appropriate adjustment of repetition rate and rotation speed may reduce thermal effects, especially in donor trephination.

Animals↗
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

Impact of increased intraocular pressure on long-term corneal endothelial cell density after penetrating keratoplasty.

PURPOSE: Besides immunological graft rejection, persistently increased intraocular pressure (IOP) is among the most important causes for graft failure after penetrating keratoplasty (PK). The purpose of this study was to assess the longitudinal development of IOP after PK and to investigate possible correlations with corneal endothelial cell density. METHODS: This longitudinal prospective study included 209 eyes after PK with a complete follow-up at 3 months, 6 months, before first suture removal (16 +/- 5 months) and after complete suture removal (21 +/- 5 months). At each examination, IOP was measured by Goldmann applanation tonometry. Endothelial cell density was assessed by specular microscopy (EM 1100, Tomey). The indications for PK were 48% keratoconus, 34% Fuchs' dystrophy, 5.4% stromal dystrophies, 8.6% secondary bullous keratopathy and 4% corneal scars. An iridotomy was performed routinely during PK. The postoperative treatment with topical steroids was standardized. RESULTS: Preoperatively, the mean IOP was 13.6 +/- 2.9 mm Hg with increased IOP (>21 mm Hg) in 2.0% of eyes. After 3 months, the incidence of increased IOP (24.5 +/- 4.6 mm Hg) was highest (6.7%) and decreased thereafter to 3.0% after complete suture removal. No patients showed IOP higher than 30 mm Hg. A persistently increased IOP for more than 3 months was seen in 2% of patients. At 3 months postoperatively, the mean endothelial cell density was 1,977 +/- 496/mm(2) and did not decrease significantly (p > 0.05) until 6 months (1,771 +/- 507 cells/mm(2)). At the end of the follow-up period, the mean endothelial cell density was significantly reduced (1,347 +/- 501 cells/mm(2)). There was no significant correlation between IOP and mean endothelial cell density at any postoperative examination stage (p > 0.24). Patients with persistently increased IOP for more than 3 months did not have significantly different endothelial cell densities in comparison with those without increased IOP. CONCLUSION: From 6 months after PK, the incidence of increased IOP was not higher than the preoperative level. Mild to moderate temporary IOP elevations after PK do not seem to affect the endothelial cell density of the graft until complete suture removal. Further long-term studies are necessary to assess the clinical relevance of these observations.

Cell Count↗
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↗
PubMedDate not supplied

Intraocular lens power calculation in eyes after corneal refractive surgery.

PURPOSE: The purpose of this review article is to discuss the major reasons for postoperative hyperopia after cataract surgery following radial keratotomy (RK) and photorefractive keratectomy (PRK) and to illustrate potential methods for improvement of intraocular lens (IOL) power prediction after keratorefractive surgery based on exemplary model calculations. METHODS: We previously performed model calculations in eyes after PRK for myopia (-1.50 to -8.00 D, mean -5.40 +/- 1.90 D) using keratometry readings as measured by the Zeiss keratometer and the TMS-1 topography unit and as calculated using the "clinical history method" (spherical equivalent refraction change) and change in anterior surface keratometry readings. RESULTS: We found that after PRK, mean measured keratometry readings were significantly greater than respective calculated values considering the preoperative to postoperative change of anterior corneal surface (P < .001), which itself was significantly greater than calculated keratometry readings considering the preoperative to postoperative change of spherical equivalent refraction (P < .001). IOL power underestimation correlated significantly with the difference between preoperative and postoperative spherical equivalent refraction (P = .001). CONCLUSIONS: For correct assessment of keratometric readings to be entered into more than one modern third-generation IOL power calculation formula (but not a regression formula), the clinical history method should be applied whenever refraction and keratometric diopters before the keratorefractive procedure are available to the cataract surgeon. If preoperative keratometric diopters and refraction are not known, average central power on the postoperative videokeratograph may be used after RK, but refined calculation of keratometric diopters from radius of anterior and posterior corneal surface should be used after PRK and/or LASIK.

Cataract Extraction↗