Achim Langenbucher

Nonmechanical corneal trephination with the excimer laser improves outcome after penetrating keratoplasty1

OBJECTIVE To assess the impact of nonmechanical trephination on the outcome after penetrating keratoplasty (PK). DESIGN Prospective, randomized, cross-sectional, clinical, single-center study. PATIENTS A total of 179 eyes of 76 females and 103 males, mean age at the time of surgery 50.6 +/- 18.5 (range, 15-83) years. Inclusion criteria were (1) time interval from October 1992 to December 1997; (2) one surgeon (GOHN); (3) primary central PK; (4) Fuchs dystrophy (diameter, 7.5 mm) or keratoconus (diameter, 8.0 mm); (5) graft oversize, 0.1 mm; (6) no previous intraocular surgery; and (7) 16-bite double-running diagonal suture. INTERVENTION In a randomized fashion, eyes were assigned either to trephination with the 193-nm Meditec excimer laser (manually guided beam in patients, automated rotation device of artificial anterior chamber in donors) along metal masks with eight orientation teeth/notches (EXCIMER: 53 keratoconus, 35 Fuchs dystrophy; mean follow-up, 37 +/- 16 months) or with a hand-held motor trephine (Microkeratron; Geuder) ( CONTROL 53 keratoconus, 38 Fuchs dystrophy; mean follow-up, 38 +/- 14 months). Subjective refractometry (trial glasses), standard keratometry (Zeiss), and corneal topography analysis (TMS-1; Tomey) were performed before surgery, before removal of the first suture (15.2 +/- 4.2 months), and after removal of the second suture (21.4 +/- 5.6 months). MAIN OUTCOME MEASURES Keratometric and topographic net astigmatism as well as refractive cylinder; keratometric and topographic central power; best-corrected visual acuity (VA); surface regularity index (SRI), surface asymmetry index (SAI), and potential visual acuity (PVA) of the TMS-1. RESULTS Before suture removal, mean refractive/keratometric/topographic astigmatism did not differ significantly between EXCIMER (2.5 +/- 1.8 diopters [D]/3.4 +/- 2.8 D/4.7 +/- 3.1 D) and CONTROL groups (3.0 +/- 1.8 D/3.7 +/- 2.4 D/4.3 +/- 2.1 D). After suture removal, respective values were significantly lower in the EXCIMER group (2.8 +/- 2.0 D/3.0 +/- 2.1 D/3.8 +/- 2.6 D) than in the CONTROL group (4.2 +/- 2.4 D/6.1 +/- 2.7 D/6.7 +/- 3.1 D) (P < 0.0009). In the EXCIMER versus CONTROL group, mean VA increased from 20/100 versus 20/111 (P > 0.05) before surgery, to 20/31 versus 20/38 before (P = 0.001) and to 20/28 versus 20/39 (P < 0.00001) after suture removal. Mean spherical equivalent was significantly less myopic in the EXCIMER group before (-0.9 +/- 3.6 D vs. -2.6 +/- 3.4 D) (P = 0.01) and after suture removal (-1.4 +/- 3.1 D vs. -2.4 +/- 3.5 D) (P = 0.02). Mean SRI (P = 0.04) and PVA (P = 0.007) were significantly more favorable in the EXCIMER versus CONTROL group after suture removal (0.91 +/- 0.45 and 0.82 +/- 0.15 vs. 1.05 +/- 0.46 and 0.73 +/- 0.18). CONCLUSIONS Postkeratoplasty results seem to be superior using nonmechanical excimer laser trephination. Thus, this methodology is recommended as the procedure of first choice in avascular corneal pathologies requiring PK.

SCANNING-SLIT AND SPECULAR MICROSCOPIC PACHYMETRY IN COMPARISON WITH ULTRASONIC DETERMINATION OF CORNEAL THICKNESS

Purpose. To determine the central corneal thickness values in healthy eyes with the recently developed Orbscan scanning-slit system, contact and noncontact specular microscopic pachymetry and compare the results to conventional ultrasonic pachymetry. Methods. In the following sequence, Orbscan, Topcon SP-2000P noncontact specular microscope, AL-1000 ultrasound, and Tomey contact specular microscope were used to record thickness values. Thirty-four healthy right corneas of 34 healthy subjects were investigated. Results. Orbscan pachymetry correlated significantly with ultrasound (r = 0.64, p < 0.001), contact (r = 0.45, p < 0.001), and noncontact specular microscopy (r = 0.72, p < 0.001). Likewise, the Topcon SP-2000P noncontact specular microscopy pachymetry disclosed similar statistical results compared with ultrasound (r = 0.88, p < 0.001), and contact specular microscopy pachymetry (r = 0.76, p < 0.001). The mean central corneal thickness results were significantly higher (p ≤ 0.01) than ultrasonic values (580 ± 43 &mgr;m) using the contact specular microscope (640 ± 43 &mgr;m) or Orbscan system (602 ± 59 &mgr;m) but were significantly lower (p < 0.001) using the noncontact specular microscope (547 ± 49 &mgr;m). Conclusions. The results indicate that the devices tested cannot be simply used interchangeably. For long-term patient follow-up, one specific instrument is recommended. Recently developed pachymetry machines are especially helpful when additional corneal data such as thickness profile, elevation maps, anterior chamber depth, and endothelial morphology are required.

Nonmechanical posterior lamellar keratoplasty using the femtosecond laser (femto-plak) for corneal endothelial decompensation☆

PURPOSE To assess the potential of a short pulsed laser to cut a posterior graft and bed for posterior lamellar keratoplasty (PLAK). DESIGN Experimental study. METHODS Using the laser FEMTEC (20/10 Perfect Vision, Heidelberg, Germany), posterior lamellar dissections (wave length approximately 1 microm, pulse energy < 10 microJ, spot size <10 microm, repetition rate 12.5 kHz, 6-mm-7 mm diameter, 31 s and 90 s) were performed in 18 freshly enucleated porcine eyes and 10 human donor corneas starting from the anterior chamber and ending with the lamellar bed. RESULTS Before removal, 50 microm to 500 microm-thick flaps were delineated by partly confluent gas bubbles (maximum 2-mm long) with minute tissue bridges (typically 5- to 10 microm) in between. Scanning electron microscopy displayed smooth cut surfaces and rectangular corners with minor remaining tissue bridges (approximately 5 microm). By transmission electron microscopy, the cut edges were lined by a delicate, electron-dense layer (5 nm-10 nm in width) and essentially normal adjacent collagen fibers. CONCLUSIONS Femtosecond laser technology seems to offer a promising approach to minimally invasive posterior lamellar keratoplasty (femto-PLAK) through small tunnel incisions in corneal endothelial diseases.

Effect of decentration and tilt on the image quality of aspheric intraocular lens designs in a model eye

PURPOSE: To determine the impact of decentration and tilt on the imaging quality of aspheric intraocular lens (IOL) designs in a schematic model eye. SETTING: Institute of Medical Physics, University of Erlangen‐Nuremberg, Erlangen, Germany. METHOD: A model eye was used to calculate the impact of misalignment on the imaging quality of 6 IOL designs. The crystalline lens in the model eye was replaced with IOL designs with 22.0 diopters nominal refractive power, and the anterior chamber depth (ACD) was set to the estimated ACD value provided by the manufacturer. The retinal position was optimized for the best image quality. The IOLs were decentered up to ±1.0 mm and tilted up to ±5 degrees relative to the line of sight. At each position, the modulation transfer function was recorded with 3.0 mm and 4.5 mm pupil diameters. The results between the IOL designs and those of the phakic model eye were then compared. RESULTS: Aberration‐correcting IOLs were very sensitive to decentration and tilt. However, the impact of misalignment depended on IOL design. Aberration‐free IOLs showed less sensitivity within a wide range of displacement but provided better results than the spherical IOL. CONCLUSIONS: Overall, modern aspheric IOLs provided better imaging quality than conventional spherical IOL designs. Aberration‐free IOLs were less sensitive to decentration and tilt than aberration‐correcting IOLs but provided better image quality than spherical IOLs. Aberration‐correcting IOLs have the potential to provide diffraction‐limited imaging quality when perfectly aligned.

Evaluating the eye's rotational stability during standard photography: effect on determining the axial orientation of toric intraocular lenses.

Purpose: To evaluate the rotational stability of the eye during standard photography and determine its effect on the measurement of toric intraocular lens (IOL) orientation. Setting: Department of Ophthalmology, University Erlangen‐Nuremberg, Erlangen, Germany. Methods: The rotational stability of the eye was evaluated using standard photographs taken with a telecentric fundus camera (Zeiss). Two sets of fundus images were taken at least 6 months apart in 400 eyes of 200 patients. The axial position of the eye was determined using 2 characteristic markers of the fundus. The angle between the 2 images (autorotation angle) was measured in each eye. Results: The mean absolute autorotation was 2.3 degrees ± 1.7 (SD) (range 0 to 11.5 degrees). Nine percent of eyes did not rotate. The rotation was less than 3 degrees in 55% of eyes and was 3 degrees or greater in 36% of eyes. Eyes of patients younger than 50 years rotated less than eyes in older patients (mean 2.2 ± 1.5 degrees and 2.5 ± 1.8 degrees, respectively) (P = .04). A visual acuity of 20/20 or better (P = .02) and a refractive cylinder of less than 1.75 diopters (P = .01) were correlated with smaller amounts of autorotation. Potential causes of artificial eye rotation induced by the photographic technique included camera adaptation (3‐degree intrinsic error), slide mounting (<1 degree), slide projection (<0.5 degree), marking of characteristic fundus details (<1 degree), and head inclination. Conclusions: Cyclorotation of the eye during standard photography may lead to overestimation or underestimation of the presumed spontaneous rotation of an implanted toric IOL. Results show that 11.5 degrees of toric IOL rotation would lead to residual astigmatism that is 40% of the initial astigmatic power and 3 degrees, 10% of the initial power. Digital imaging may reduce the intrinsic errors of standard photography.

Evaluation of normal corneas using the scanning-slit topography/pachymetry system

Purpose To obtain anterior and posterior corneal shape, curvature, and thickness of normal human corneas. To provide a semiquantitative analysis of normal topography patterns of the anterior and posterior corneal surfaces. Methods Eighty-eight healthy corneas of 44 normal subjects were analyzed using the scanning-slit topography/pachymetry system. Anterior and posterior elevation and mean power (central and steepest spherical and cylindrical) values and pachymetry data were determined. Right eye values were submitted for primary analysis; however, a comparison between right and left eyes was made in addition to test the possible reliability of the system. Results There was no significant difference between right and left corneas in 28 evaluated parameters, except for anterior central cylindrical (P = 0.005) and steepest cylindrical (P = 0.017) mean power. The anterior central spherical mean power correlated inversely with the posterior central spherical mean power (r = −0.27, P = 0.04), and the anterior steepest spherical mean power value showed inverse correlation with the mean posterior steepest spherical value (r = −0.44, P = 0.001). The mean central thickness of the cornea was 593.7 ± 54.19 μm at the center and was 578 ± 50.53 μm at the thinnest point, which was localized in 41% (n = 18) of the cases in the inferotemporal quadrant. An oval-shaped pattern was the most characteristic feature of the anterior and posterior elevation, mean power, and pachymetry maps. Conclusion Orbscan scanning-slit topography seems to be a reliable technique for the evaluation of normal corneas not only for anterior shape and curvature but also for a real pachymetry gradient recording.

[The penetrating keratoplasty. A 100-year success story].

ZusammenfassungBei der perforierenden Keratoplastik werden zehn Vorkehrungen zur Astigmatismusprophylaxe empfohlen:1.Die Spendertopographie sollte angestrebt werden, um zurückliegende refraktive Chirurgie, einen Keratokonus oder einen hohen Astigmatismus auszuschließen, und um die „Harmonisierung“ der Spender-Empfänger-Topographie zu ermöglichen.2.Spender- und Empfängertrepanation sollten einheitlich von der epithelialen Seite mit dem gleichen Trepansystem erfolgen. Das ist die Voraussetzung für kongruente Schnittflächen und -winkel beim Spender und Empfänger. Typischerweise wird heute für die Spendertrepanation eine künstliche Vorderkammer benutzt.3.Orientierungsstrukturen beim Spender und Empfänger erleichtern die korrekte Platzierung der ersten vier bzw. acht Situationsnähte und tragen somit dazu bei, die „horizontale Torsion“ zu vermeiden.4.Eine messbare Verbesserung scheint durch das geführte Trepansystem (GTS) nach Krumeich, durch die zweite Generation des Hanna-Trepans mit Einführung der künstlichen Vorderkammer und die Erlanger Technik der nichtmechanischen Trepanation mit dem Excimerlaser möglich.5.Die horizontale Positionierung von Kopf- und Limbusebene sind unabdingbare Voraussetzungen für die Vermeidung von Dezentrierung, „vertikaler Verkippung“ und „horizontaler Torsion“.6.Die Transplantatgröße sollte individuell an die Hornhautgröße angepasst werden („so groß wie möglich, so klein wie nötig“).7.Im Zweifel sollte der Limbuszentrierung der Vorzug über die Pupillenzentrierung gegeben werden (insbesondere beim Keratokonus muss die optische Verlagerung der Pupille bedacht werden).8.Exzessive Über- und Unterdimensionierung des Transplantats im Vergleich zum Empfängerbett sollen vermieden werden, um einer Streckung oder Stauchung des peripheren Spendergewebes vorzubeugen.9.Bei intakter Bowman-Lamelle sollte der doppelt fortlaufenden Kreuzstichnaht nach Hoffmann der Vorzug gegeben werden, weil sie mit einer höheren topographischen Regularität, einer früheren visuellen Rehabilitation und einer geringeren Fadenlockerungsrate einhergeht.10.Die intraoperative Keratoskopie sollte angewendet werden, nachdem Lidsperrer und Haltefäden entfernt worden sind.AbstractTen precautions for prophylaxis of astigmatism in penetrating keratoplasty are recommended:1.The attempt should be made to determine donor topography for exclusion of previous refractive surgery, keratoconus/high astigmatism, and to allow for “harmonization” of donor and recipient topography.2.Donor and recipient trephination should be performed from the epithelial side with the same system, which is the prerequisite for congruent cut surfaces and angles in donor and recipient. For this purpose an artificial anterior chamber is used for donor trephination.3.Orientation structures in donor and host facilitate the correct placement of the first four or eight cardinal sutures to avoid horizontal torsion.4.A measurable improvement seems to be possible, using the Krumeich guided trephine system (GTS), the second generation Hanna trephine, and the Erlangen technique of nonmechanical trephination with the excimer laser.5.Horizontal positioning of the head and limbal plane are indispensable for state-of-the-art PKP surgery in order to avoid decentration, vertical tilt, and horizontal torsion.6.Graft size should be adjusted individually (“as large as possible, as small as necessary”).7.Limbal centration should be preferred over pupil centration (especially in keratoconus).8.Excessive graft over- or undersize should be avoided to prevent stretching or compression of peripheral donor tissue.9.As long as Bowman’s layer is intact a double running cross-stitch suture (according to Hoffmann) is preferred since it results in higher topographic regularity, earlier visual rehabilitation, and less suture loosening requiring only rarely suture replacement.10.Intraoperative keratoscopy should be applied after removal of lid specula and fixation sutures.

Corneal endothelial cell density and pachymetry measured by contact and noncontact specular microscopy.

Purpose: To determine the endothelial cell density and thickness of normal human and postkeratoplasty corneas with contact specular microscopy and to compare these measurements with those obtained by noncontact specular microscopy. Setting: Department of Ophthalmology, University of Erlangen‐Nürnberg, Erlangen, Germany. Methods: The central corneal endothelial cell density and thickness were determined in 65 healthy eyes of 39 patients with a mean age of 71 years ± 12 (SD) and in 50 corneal grafts of 41 patients with a mean age 53 ± 17 years using noncontact (Topcon SP‐2000P, Topcon Corp.) and contact (EM‐1000, Tomey) specular microscopes. Appropriate conversion factors were used for accurate cell count comparison. Results: The mean cell count of the normal corneas was 2445 ± 425 cells/mm2 measured by noncontact specular microscopy and 2471 ± 393 cells/mm2 measured by contact specular microscopy (P = .70). After penetrating keratoplasty, the mean cell density was 1610 ± 499 cells/mm2 and 1584 ± 469 cells/mm2, respectively (P = .88). Significantly lower thickness was measured with the noncontact specular microscope than by contact pachymetry in normal eyes (543 ± 46 &mgr;m and 642 ± 42 &mgr;m, respectively) and postkeratoplasty eyes (538 ± 61 &mgr;m and 627 ± 48 &mgr;m, respectively) (P < .0001). Conclusions: To determine endothelial cell density, contact and noncontact specular microscopy may be used interchangeably. However, for the combined measurement of endothelial cell density and pachymetry, the use of the same specular microscope is recommended for long‐term patient follow‐up.

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.

Die perforierende Keratoplastik

ZusammenfassungBei der perforierenden Keratoplastik werden zehn Vorkehrungen zur Astigmatismusprophylaxe empfohlen:1.Die Spendertopographie sollte angestrebt werden, um zurückliegende refraktive Chirurgie, einen Keratokonus oder einen hohen Astigmatismus auszuschließen, und um die „Harmonisierung“ der Spender-Empfänger-Topographie zu ermöglichen.2.Spender- und Empfängertrepanation sollten einheitlich von der epithelialen Seite mit dem gleichen Trepansystem erfolgen. Das ist die Voraussetzung für kongruente Schnittflächen und -winkel beim Spender und Empfänger. Typischerweise wird heute für die Spendertrepanation eine künstliche Vorderkammer benutzt.3.Orientierungsstrukturen beim Spender und Empfänger erleichtern die korrekte Platzierung der ersten vier bzw. acht Situationsnähte und tragen somit dazu bei, die „horizontale Torsion“ zu vermeiden.4.Eine messbare Verbesserung scheint durch das geführte Trepansystem (GTS) nach Krumeich, durch die zweite Generation des Hanna-Trepans mit Einführung der künstlichen Vorderkammer und die Erlanger Technik der nichtmechanischen Trepanation mit dem Excimerlaser möglich.5.Die horizontale Positionierung von Kopf- und Limbusebene sind unabdingbare Voraussetzungen für die Vermeidung von Dezentrierung, „vertikaler Verkippung“ und „horizontaler Torsion“.6.Die Transplantatgröße sollte individuell an die Hornhautgröße angepasst werden („so groß wie möglich, so klein wie nötig“).7.Im Zweifel sollte der Limbuszentrierung der Vorzug über die Pupillenzentrierung gegeben werden (insbesondere beim Keratokonus muss die optische Verlagerung der Pupille bedacht werden).8.Exzessive Über- und Unterdimensionierung des Transplantats im Vergleich zum Empfängerbett sollen vermieden werden, um einer Streckung oder Stauchung des peripheren Spendergewebes vorzubeugen.9.Bei intakter Bowman-Lamelle sollte der doppelt fortlaufenden Kreuzstichnaht nach Hoffmann der Vorzug gegeben werden, weil sie mit einer höheren topographischen Regularität, einer früheren visuellen Rehabilitation und einer geringeren Fadenlockerungsrate einhergeht.10.Die intraoperative Keratoskopie sollte angewendet werden, nachdem Lidsperrer und Haltefäden entfernt worden sind.AbstractTen precautions for prophylaxis of astigmatism in penetrating keratoplasty are recommended:1.The attempt should be made to determine donor topography for exclusion of previous refractive surgery, keratoconus/high astigmatism, and to allow for “harmonization” of donor and recipient topography.2.Donor and recipient trephination should be performed from the epithelial side with the same system, which is the prerequisite for congruent cut surfaces and angles in donor and recipient. For this purpose an artificial anterior chamber is used for donor trephination.3.Orientation structures in donor and host facilitate the correct placement of the first four or eight cardinal sutures to avoid horizontal torsion.4.A measurable improvement seems to be possible, using the Krumeich guided trephine system (GTS), the second generation Hanna trephine, and the Erlangen technique of nonmechanical trephination with the excimer laser.5.Horizontal positioning of the head and limbal plane are indispensable for state-of-the-art PKP surgery in order to avoid decentration, vertical tilt, and horizontal torsion.6.Graft size should be adjusted individually (“as large as possible, as small as necessary”).7.Limbal centration should be preferred over pupil centration (especially in keratoconus).8.Excessive graft over- or undersize should be avoided to prevent stretching or compression of peripheral donor tissue.9.As long as Bowman’s layer is intact a double running cross-stitch suture (according to Hoffmann) is preferred since it results in higher topographic regularity, earlier visual rehabilitation, and less suture loosening requiring only rarely suture replacement.10.Intraoperative keratoscopy should be applied after removal of lid specula and fixation sutures.