M. Kohlhaas

Mechanical stability of the cornea after radial keratotomy and photorefractive keratectomy

BACKGROUND Corneal refractive surgical procedures alter the shape and structure of the tissue, possibly compromising its mechanical stability. METHODS One or both eyes of 87 subjects were studied: 26 of these 87 had been treated for myopia by excimer laser ablation and 36 by radial keratotomy; 25 without previous corneal surgery functioned as controls. Corneal topography was evaluated by TMS-1 videophotokeratography before and after 180 degrees tilting of the patient, and the pressure-induced ring-wise changes in spherical equivalent power (axial power) were calculated. Changes in corneal shape also were evaluated by computing the instantaneous radius of curvature. The intraocular pressure was measured before and after tilting by a hand-held applanation tonometer. RESULTS The mean intraocular pressure increased from 13.9 +/- 2.3 mm Hg before tilting to 30.0 +/- 3.8 mm Hg during tilting. In the control eyes, the mean power of the central cornea during tilting decreased 0.187 +/- 0.045 diopters (D) (p < .05); in the excimer-laser-ablated eyes, 0.038 +/- 0.056 D (not statistically significant); and in those treated with radial keratotomy, 0.523 +/- 0.054 D (p < .01). After radial keratotomy, the cornea steepened outside the clear zone in response to pressure loading, whereas it did not change significantly in the laser-ablated or control eyes. CONCLUSIONS Pressure-induced deformation of normal and excimer laser-ablated human cornea is small, whereas radially incised corneas have significantly decreased mechanical stability.

Enzymatischer Nachweis der Tiefenabhängigkeit der Vernetzungswirkung von Riboflavin/UVA an der Hornhaut

PURPOSE It has been shown that the treatment of keratoconus with riboflavin/ultraviolet A (UVA) causes significant stiffening of the cornea due to cross-linking. The aim of this study was to evaluate how deep the mechanical stabilization after collagen cross-linking could be shown biochemically. METHOD Ten out of 20 enucleated porcine eyes were treated with riboflavin as a photosensitizer and UVA (370 nm, 3 mW/cm2, 30 min). The other 10 eyes served as controls. With a Microkeratom device, two flaps with a thickness of 200 microm and a diameter of 8 mm were cut off from each eye and put in a collagenase solution (NaCl plus collagenase A, 1:1). The surfaces of the flaps were measured digitally every day to characterize the dissolving behavior. RESULTS The resistance (regarding corneal collagen against enzymatic digestion) of the treated superficial flaps was considerably higher (p=0.001) compared to those that were cut secondarily and to the control flaps. But even the flaps from deeper layers showed a significant increase in resistance (p=0.02) compared with the untreated flaps. The half-life of the surfaces of the treated superficial flaps was 220 h; of those cut secondarily, it was 80 h. Both untreated flaps had a half-life of 50 h. CONCLUSIONS The biochemical study showed that the treatment of the cornea with riboflavin/UVA leads to significant collagen cross-linking not only in the anterior slice of 200 microm but also in the following 200 microm. This locally limited cross-linking effect may be explained by the absorption behavior for UVA of the riboflavin-treated cornea; 65% of UVA irradiation is absorbed in the first 200 microm and only 25-30% in the next 200 microm. Therefore, deeper-lying structures and especially the endothelium are not affected.

[Enzymatic evidence of the depth dependence of stiffening on riboflavin/UVA treated corneas].

PURPOSE It has been shown that the treatment of keratoconus with riboflavin/ultraviolet A (UVA) causes significant stiffening of the cornea due to cross-linking. The aim of this study was to evaluate how deep the mechanical stabilization after collagen cross-linking could be shown biochemically. METHOD Ten out of 20 enucleated porcine eyes were treated with riboflavin as a photosensitizer and UVA (370 nm, 3 mW/cm2, 30 min). The other 10 eyes served as controls. With a Microkeratom device, two flaps with a thickness of 200 microm and a diameter of 8 mm were cut off from each eye and put in a collagenase solution (NaCl plus collagenase A, 1:1). The surfaces of the flaps were measured digitally every day to characterize the dissolving behavior. RESULTS The resistance (regarding corneal collagen against enzymatic digestion) of the treated superficial flaps was considerably higher (p=0.001) compared to those that were cut secondarily and to the control flaps. But even the flaps from deeper layers showed a significant increase in resistance (p=0.02) compared with the untreated flaps. The half-life of the surfaces of the treated superficial flaps was 220 h; of those cut secondarily, it was 80 h. Both untreated flaps had a half-life of 50 h. CONCLUSIONS The biochemical study showed that the treatment of the cornea with riboflavin/UVA leads to significant collagen cross-linking not only in the anterior slice of 200 microm but also in the following 200 microm. This locally limited cross-linking effect may be explained by the absorption behavior for UVA of the riboflavin-treated cornea; 65% of UVA irradiation is absorbed in the first 200 microm and only 25-30% in the next 200 microm. Therefore, deeper-lying structures and especially the endothelium are not affected.

Aesthesiometry after Cryo-keratomileusis and in situ Keratomileusis

Objective: Evaluation of corneal reinnervation after cryo-keratomileusis and keratomileusis. Study Design: Retrospective evaluation of corneal sensitivity after cryo-keratomileusis and in situ keratomileusis. The measurements were performed with the Draeger electromechanical optical-controlled aesthesiometer, which is very precise and independent of external changes in temperature and humidity. Three measuring points were on the lenticle and 2 at approximately 1 mm distance from the limbus. Setting: Instituto Barraquer, Bogota, Columbia (South America). Patients: Twelve patients after cryo-keratomileusis and 38 patients after in situ keratomileusis. Results: It was shown that the recovery of corneal sensitivity after cryo-keratomileusis is delayed due to the depth of the keratectomy and freezing procedure compared to in situ keratomileusis.

Ultraschallbiomikroskopie bei Pigmentglaukom

ZusammenfassungHintergrund: Bei Patienten mit Pigmentglaukom und Pigmentdispersionssyndrom wurde gehäuft eine Anlagerung des Irispigmentblattes an die Zonulafasern beobachtet. Dieser anatomischen Besonderheit wird eine pathogenetische Bedeutung bei der Entstehung der Pigmentfreisetzung zugesprochen. Ein Druckausgleich zwischen Vorderkammer und Hinterkammer durch eine Iridotomie oder Iridektomie soll den Zonulakontakt der Iris aufheben und somit eine Pigmentfreisetzung verhindern. Patienten und Methoden: Es wurden 28 Patienten mit Pigmentglaukom (20 Männer, 8 Frauen, Durchschnittsalter 43,4 Jahre, 25 der 28 Patienten waren myop) in eine prospektive, klinische Studie eingeschlossen. Der mittlere unbehandelte Augeninnendruck betrug 24,3 mmHg, alle Patienten wiesen glaukomatöse Gesichtsfelddefekte und glaukomatöse Papillenveränderungen auf. Es wurde eine Ultraschallbiomikroskopie (UBM, Humphrey-Heiss, 50 MHZ Schallkopf, Auflösung 50 mm) vor und nach YAG-Laser-Iridotomie unter standardisierten Bedingungen durchgeführt. Der Verlauf des Augeninnendruckes wurde dokumentiert und die mittlere Nachbeobachtungszeit beträgt 9 Monate. Die statistische Auswertung erfolgte mit dem Wilcoxon-Test. Ergebnisse: Bei 10 der 28 Patienten ließen sich ein irido-zonularer Kontakt und eine Konkavität der mittelperipheren Iris nachweisen. Bei diesen Patienten zeigte sich ein statistisch signifikanter Abfall (p<0,05) des Augeninnendruckes von 24,6±2,1 mmHg auf 18,3±2,0 mmHg nach der Iridotomie. Der Augeninnendruck der Patienten, die keinen iridozonularen Kontakt aufwiesen, sank statistisch nicht signifikant um 8% von 23,1±2,3 mmHg auf 23,1±2,1 mmHg. Schlussfolgerung: Aus diesen Ergebnissen lässt sich ableiten, dass die Durchführung einer YAG-Laser-Iridotomie beim Pigmentglaukom nur dann sinnvoll erscheint, falls ein iridozonularer Kontakt mit der Ultraschallbiomikroskopie nachweisbar ist.SummaryPurpose: To evaluate the anatomical relationships of the iris in pigmentary glaucoma before and after laser iridotomy and to evaluate the effect on intraocular pressure. Methods: Ultrasound biomicroscopy (UBM, Humphrey-Zeiss) of the anterior segment was performed in 28 eyes of 28 patients (20 male, 8 female, mean age 43 years, mean untreated IOP 24,3 mmHg) with pigmentary glaucoma before and after laser iridotomy. The slope of intraocular pressure was documented. Mean follow-up was 9 months. For statistical analysis the Wilcoxon test was used. Results: Ten out of 28 eyes showed iridozonular contact and concavity of the midperipheral iris. Laser iridotomy resulted in a significant pressure drop (P<0.05) in these 10 eyes (24.6 mmHg to 18.3 mmHg). Eighteen eyes, however, did not show iridozonular contact and intraocular pressure did not drop sufficiently (P>0.05; 25.1 mmHg to 23.1 mmHg) after laser iridotomy. Conclusion: The results show that iridozonular contact does not exist in every patient with pigmentary glaucoma. Therefore, it seems possible that more than one pathogenic mechanism is involved in pigmentary glaucoma. In patients with iridozonular contact, however, laser iridotomy significantly reduces intraocular pressure.

Biomechanische Untersuchung der Hornhautstabilität nach photorefraktiver Keratektomie

Hintergrund: Die PRK ist der heute am häufigsten durchgeführte refraktivchirurgische Eingriff. Um die Brechkraft der Hornhaut zu verändern, werden die vorderen Stromaanteile einschließlich der Bowman-Membran mit einem Laserstrahl verdampft. Diese Operation stellt einen erheblichen Eingriff in die Struktur der Hornhaut dar. Wie verändern sich die biomechanischen Eigenschaften einer so veränderten Hornhaut?Material und Methode: Wir untersuchten 26 Patienten nach photorefraktiver Keratektomie und 25 unoperierte Probanden als Kontrollgruppe mit der von uns entwickelten druckinduzierten Hornhautstabilitätsmessung. Bei dieser Meßmethode werden die Probanden auf einer Kippliege um 180° gedreht, wodurch es zu einem intraokularen Druckanstieg von ca. 16 mmHg kommt. Vor und während des Kippmanövers wird der Hornhautkrümmungsradius mit dem Photokeratoskop bestimmt. Die Änderung des Hornhautkrümmungsradius unter Druckbelastung ist der Parameter für die Beurteilung der Hornhautstabilität.Ergebnisse: Die zentrale Hornhaut flachte bei den PRK-Patienten um 0,038 ± 0,056 dpt (nicht signifikant) und bei den unoperierten Probanden um 0,187 ± 0,045 dpt (p < 0,05) ab. Bei Aufteilung der PRK-Patienten nach der Länge der postoperativen Zeit, zeigten die vor weniger als 1 Jahr operierten Hornhäute zentral eine geringe Versteilerung, wohingegen die vor 1 oder mehr Jahren operierten Hornhäute ein den unoperierten Hornhäuten ähnliches Verhalten im Druckversuche zeigten (p < 0,05).Schlußfolgerung: Nach photorefraktiver Keratektomie ist die Stabilität der Hornhaut im Vergleich zu unoperierten Hornhäuten post-operativ verändert. Nach etwa 1 Jahr scheint es im Rahmen von stromalen Umbauvorgängen zu einer Normalisierung der Hornhautstabilität zu kommen.Background: Photorefraktive keratectomy (PRK) is the most frequent refractive surgical procedure worldwide. The central corneal thickness is reduced due to removal of the anterior stroma, including Bowmans layer, with a laser beam. This procedure 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° tilt. Before and during this procedure, corneal topography was measured by photokeratoscopy. We examined 26 patients after PRK and 25 controls who had not undergone any surgical procedure.Results: The corneal center flattened by 0.038 ± 0.05 dpt (P > 0.05) in the PRK patients and by 0.187 ± 0.045 dpt (P < 0.05) in the control group. PRK patients within 1 year after operation showed a minimal central corneal steepening, whereas PRK patients after more than 1 year showed a reaction similar to that in normal corneas (P < 0.05).Conclusion: Corneal stability is altered after PRK. After 1 year corneal stability seems to normalize due to stromal remodelling.

Primary orbital implant luxation. A retrospective study

SummaryBackground: To compensate the orbital volume deficit after enucleation orbital implants are used. Method: Between 1986 and 1996, 449 enucleations were performed. One hundred and fifty-five orbital implants were used: 96 hydroxylapatite-ceramic-silicon (HAK-silicon), 29 hydroxylapatite-ceramic (HAK), 26 Kiel bone chips, 3 Walser and 1 Bangerter implant. Results: Ten orbital implants (6.45 %) had to be explanted. Seven of the 96 HAK-silicon implants were explanted: four could be changed, two of them with a smaller and two with a same diameter. We observed a complication rate of 7.29 % and a rate of total loss of 3.13 %. One luxated HAK-implant could be refixated (3.45 %), and one implant (3.85 %) of the Kiel bone chip implants was explanted. Conclusion: Using different types of orbital implants after enucleation, we observed a complication rate of 7 %. However, to avoid the post-enucleation-syndrome and to achieve better motility of the prosthesis, orbital implants should be used.ZusammenfassungHintergrund: Zur Kompensation des Orbitavolumendefizits, zur Vermeidung des Post-Enukleations-Syndroms, sowie der Verbesserung der Prothesenmotilität werden nach durchgeführter Enukleation Orbitaimplantate verwendet. Patienten und Methode:Über einen Zeitraum von 10 Jahren wurden von 1986–1996 in der Universitäts-Augenklinik Hamburg bei 449 Enukleationen insgesamt 155 Orbitaimplantate eingesetzt, davon 96 × ein Hydroxyl-Apatit-Keramik-Silikon-, 29 × ein Hydroxyl-Apatit-Keramik- (HAK), 26 × ein Kieler Knochenspan-, 3 × ein Walser-, sowie 1 × ein Bangerter-Implantat. Ergebnisse: Insgesamt mußten 10 Orbitaimplantate (6,45 %) wieder entfernt werden. Ausgehend von 96 HAK-Silikon-Implantaten wurden 7 Implantate entfernt, davon konnten 4 durch ein gleichartiges Implantat mit 2 × kleinerem und 2 × gleichem Durchmesser ersetzt werden, was einer Komplikationsrate von 7,29 % und einer Verlustrate von 3,13 % entspricht. Von den 29 HAK-Implantaten konnte 1 luxiertes (3,45 %) neu fixiert werden, während von 26 Kieler Knochenspan-Implantaten 1 Implantat (3,85 %) ohne Ersatz entfernt werden mußte. Ein verwendetes Bangerter-Implantat wurde durch ein Kieler Knochenspan-Implantat ersetzt. Schlußfolgerung: Trotz Komplikationsraten von durchschnittlich ca. 7 % stellt eine Orbitaplombenimplantation aufgrund der niedrigen Infektionsgefahr, der Vermeidung des Post-Enukleations-Syndroms, der verbesserten Motilität der Augenprothese und der guten, für den Patienten so entscheidenden Kosmetik, bei möglicherweise eingeschränktem Patientengut und verbesserter Wundadaption, die momentan beste Alternative dar.

Aspergillus-Endophthalmitis nach Lebertransplantation bei einem Säugling

Immunosuppressed patients and transplant patients bear an increased risk for invasive aspergillosis and Aspergillus endophthalmitis. An 8-month-old boy developed severe unilateral panuveitis after liver transplantation. Bronchopulmonary infiltrates were present, but a pulmonary Aspergillus infection was not confirmed. An enucleation was performed in order to prevent a life-threatening disseminated Aspergillus infection.

Enzymatischer Nachweis der Tiefenabhängigkeit der Vernetzungswirkung von Riboflavin/UVA an der Hornhaut@@@Enzymatic evidence of the depth dependence of stiffening on riboflavin/UVA treated corneas

PURPOSE It has been shown that the treatment of keratoconus with riboflavin/ultraviolet A (UVA) causes significant stiffening of the cornea due to cross-linking. The aim of this study was to evaluate how deep the mechanical stabilization after collagen cross-linking could be shown biochemically. METHOD Ten out of 20 enucleated porcine eyes were treated with riboflavin as a photosensitizer and UVA (370 nm, 3 mW/cm2, 30 min). The other 10 eyes served as controls. With a Microkeratom device, two flaps with a thickness of 200 microm and a diameter of 8 mm were cut off from each eye and put in a collagenase solution (NaCl plus collagenase A, 1:1). The surfaces of the flaps were measured digitally every day to characterize the dissolving behavior. RESULTS The resistance (regarding corneal collagen against enzymatic digestion) of the treated superficial flaps was considerably higher (p=0.001) compared to those that were cut secondarily and to the control flaps. But even the flaps from deeper layers showed a significant increase in resistance (p=0.02) compared with the untreated flaps. The half-life of the surfaces of the treated superficial flaps was 220 h; of those cut secondarily, it was 80 h. Both untreated flaps had a half-life of 50 h. CONCLUSIONS The biochemical study showed that the treatment of the cornea with riboflavin/UVA leads to significant collagen cross-linking not only in the anterior slice of 200 microm but also in the following 200 microm. This locally limited cross-linking effect may be explained by the absorption behavior for UVA of the riboflavin-treated cornea; 65% of UVA irradiation is absorbed in the first 200 microm and only 25-30% in the next 200 microm. Therefore, deeper-lying structures and especially the endothelium are not affected.

[Severe Aspergillus endophthalmitis occurring after liver transplantation in an 8-month-old baby].

Immunosuppressed patients and transplant patients bear an increased risk for invasive aspergillosis and Aspergillus endophthalmitis. An 8-month-old boy developed severe unilateral panuveitis after liver transplantation. Bronchopulmonary infiltrates were present, but a pulmonary Aspergillus infection was not confirmed. An enucleation was performed in order to prevent a life-threatening disseminated Aspergillus infection.