Growth, characterization, and transport properties of ternary (Bi1-x Sb x )2Te3 topological insulator layers.

Ternary (Bi1-x Sb x )2Te3 films with an Sb content between 0 and 100% were deposited on a Si(1 1 1) substrate by means of molecular beam epitaxy. X-ray diffraction measurements confirm single crystal growth in all cases. The Sb content is determined by x-ray photoelectron spectroscopy. Consistent values of the Sb content are obtained from Raman spectroscopy. Scanning Raman spectroscopy reveals that the (Bi1-x Sb x )2Te3 layers with an intermediate Sb content show spatial composition inhomogeneities. The observed spectra broadening in angular-resolved photoemission spectroscopy (ARPES) is also attributed to this phenomena. Upon increasing the Sb content from x = 0 to 1 the ARPES measurements show a shift of the Fermi level from the conduction band to the valence band. This shift is also confirmed by corresponding magnetotransport measurements where the conductance changes from n- to p-type. In this transition region, an increase of the resistivity is found, indicating a location of the Fermi level within the band gap region. More detailed measurements in the transition region reveals that the transport takes place in two independent channels. By means of a gate electrode the transport can be changed from n- to p-type, thus allowing a tuning of the Fermi level within the topologically protected surface states.

Coherent ultrafast spin-dynamics probed in three dimensional topological insulators.

Topological insulators are candidates to open up a novel route in spin based electronics. Different to traditional ferromagnetic materials, where the carrier spin-polarization and magnetization are based on the exchange interaction, the spin properties in topological insulators are based on the coupling of spin- and orbit interaction connected to its momentum. Specific ways to control the spin-polarization with light have been demonstrated: the energy momentum landscape of the Dirac cone provides spin-momentum locking of the charge current and its spin. We investigate a spin-related signal present only during the laser excitation studying real and imaginary part of the complex Kerr angle by disentangling spin and lattice contributions. This coherent signal is only present at the time of the pump-pulses' light field and can be described in terms of a Raman coherence time. The Raman transition involves states at the bottom edge of the conduction band. We demonstrate a coherent femtosecond control of spin-polarization for electronic states at around the Dirac cone.

Room-temperature high-frequency transport of dirac fermions in epitaxially grown Sb2Te3- and Bi2Te3-based topological insulators.

We report on the observation of photogalvanic effects in epitaxially grown Sb2Te3 and Bi2Te3 three-dimensional (3D) topological insulators (TI). We show that asymmetric scattering of Dirac fermions driven back and forth by the terahertz electric field results in a dc electric current. Because of the "symmetry filtration" the dc current is generated by the surface electrons only and provides an optoelectronic access to probe the electron transport in TI, surface domains orientation, and details of electron scattering in 3D TI even at room temperature.

[Adoption of OSCE Examination Procedures in Ophthalmology]. / Etablierung der OSCE-Prüfungsmethode in der Ophthalmologie.

BACKGROUND: The department of ophthalmology at the medical faculty of the University of Ulm provides additionally for interested students in clinical semesters an optional activity. In small groups the students deepen their theoretical knowledge and learn more about ophthalmological diagnostic standard procedures. The "objective structured clinical examination" (OSCE) is known as a useful tool in the assessment of clinical skills. The OSCE is a well-established and valid examination method, but also time-consuming and costly. In form of a trial the OSCE was launched during the optional activity "Look into my eyes, baby"; in the summer semester 2009. METHODS: By means of four examination areas established diagnostic methods in ophthalmology were tested. During the tests two simulation patients as well as two phantom heads for ophthalmological examinations were assessed. The preparation of the examination materials occurred in close collaboration with the department of ophthalmology and the division exam development of our university. In the assessment of the examinations a high value was set on good communication skills between students and simulation patients as well as on the professional handling of the student tasks. After the examinations the acceptance of the test methods was evaluated using a focused group interview between the students of the optional activity and the participating examiners. RESULTS: We performed two OSCEs involving three students each in the last two semesters. The OSCE was to a great extent time- and resource-consuming, due to the intensive pre- and post-reviewing and the time students needed to pass the various examination areas. Students and examiners as well confirmed the validity of the assessment and acknowledged a positive effect on the students learning behaviour. CONCLUSIONS: The teaching staff members are willing to accept the OSCE, especially when the assessment procedures are thoroughly planned and well structured. The acceptance of the students can be achieved by providing valid assessment and reviewed teaching conditions. The high input in personnel and instrumental resources for the assessment and the student's individual supervision should be critically discussed in the light of the efficacy of the additional ongoing hospital and outpatient services and the personnel-relevant education budget assigned to the department of ophthalmology of a university.

[Potentials of monocular augmented reality technology in automobile production]. / Eignung monokularer "Augmented Reality" - Technologien in der Automobilproduktion.

INTRODUCTION: Augmented reality (AR) technologies can enrich the real environment with visual data, which has potential benefits for optimising the operator's working process. It offers the possibility to provide context-sensitive information independently of the user's location and position. Data are presented to the dominant eye on a semi-transparent mirror using a head-mounted display (HMD) unit that works with retinal laser technology. In this study the potential benefits and drawbacks of this new AR technology were evaluated. MATERIALS AND METHODS: 45 participants without any visual impairment were randomly assigned to 3 groups and completed a variety of tasks during a simulated working day. Group 1 received conventional working aids (paper-based documents) to support the task processing. Group 2 additionally wore an HMD unit that was switched off. Group 3 wore a functioning HMD without any additional aids. Evaluation was carried out by means of a standardised questionnaire (BMS) and a concentration test ("d2 Aufmerksamkeits-Belastungs-Test"). RESULTS: No significant differences between the 3 groups were found in terms of mental strain, concentration-test performance and physical or mental complaints reported in a follow-up interview. Around 20 % of the subjects noticed a higher pressure and blurred vision in both eyes as well as headaches. Half of the participants complained about deficiencies concerning the ergonomic hardware design of the AR system. DISCUSSION: Changes in objective ophthalmological investigation parameters were not observed. Subjects reported reduced acceptance of the HMD based on non-ophthalmological reasons, for example, the weight of the unit or the length of the cable. However, for some specific working tasks, advantages in process optimisation and operator support were observed.

[Comparison of Preferential Hyperacuity Perimeter (PHP) test and Amsler grid test in the diagnosis of different stages of age-related macular degeneration]. / Vergleich des Preferential-Hyperacuity-Perimeter (PHP)-Tests mit dem Amsler-Netz-Test bei der Diagnose verschiedener Stadien der altersbezogenen Makuladegeneration.

BACKGROUND: Age-related macular degeneration (ARMD) is the leading cause of blindness in people over 65 years of age. A rapid loss of vision occurs especially in cases with choroidal neovascularisation. Early detection of ARMD and timely treatment are mandatory. We have prospectively studied the results of two diagnostic self tests for the early detection of metamorphopsia and scotoma, the PHP test and the Amsler grid test, in different stages of ARMD. PATIENTS AND METHODS: Patients with ARMD and best corrected visual acuity of 6/30 or better (Snellen charts) were examined with a standardised protocol, including supervised Amsler grid examination and PHP, a new device for metamorphopsia or scotoma measurement, based on the hyperacuity phenomenon in the central 14 degrees of the visual field. The stages of ARMD were independently graded in a masked fashion by stereoscopic ophthalmoscopy, stereoscopic fundus colour photographs, fluorescein angiography, and OCT. The patients were subdivided into 3 non-neovascular groups [early, late (RPE atrophy > 175 microm) and geographic atrophy], a neovascular group (classic and occult CNV) and an age-matched control group (healthy volunteers). RESULTS: 140 patients, with ages ranging from 50 to 90 years (median 68 years), were included in the study. Best corrected visual acuity ranged from 6/30 to 6/6 with a median of 6/12. 95 patients were diagnosed as non-neovascular ARMD. Thirty eyes had early ARMD (9 were tested positive by the PHP test and 9 by the Amsler grid test), and 50 late ARMD (positive: PHP test 23, Amsler grid test 26). The group with geographic atrophy consisted of 15 eyes (positive: PHP test 13, Amsler grid test 10). Forty-five patients presented with neovascular ARMD (positive: PHP test 38, Amsler grid test 36), 34 volunteers served as control group (positive: PHP test 1, Amsler grid test 5). CONCLUSIONS: The PHP and Amsler grid tests revealed comparable results detecting metamorphopsia and scotoma in early ARMD (30 vs. 30 %) and late ARMD (46 vs. 52 %). However, the PHP test more often revealed disease-related functional changes in the groups of geographic atrophy (87 vs. 67 %) and neovascular ARMD (84 vs. 80 %). This implies that the PHP and Amsler grid self tests are useful tools for detection of ARMD and that the PHP test has a greater sensitivity in the groups of geographic atrophy and neovascular AMD.

[In-vitro comparison of morphology of current microkeratomes for LASIK]. / Morphologische In-vitro-Vergleichsanalyse aktueller Mikrokeratome zur LASIK.

BACKGROUND: We have performed an in-vitro examination of the morphology of flap thickness and stromal bed after LASIK in porcine eyes. MATERIALS AND METHODS: Freshly enucleated porcine eyes and synthetic eye models were used for cutting flaps with the microkeratomes Hansatome-Excellus (Bausch&Lomb), M2 single use (Moria), Amadeus (AMO), MK-2000 (Nidek) and Carriazo-Pendular (Schwind). The flap thickness of porcine eyes was determined using a non-contact, confocal optical distance measuring device (CHR 150N, Jurca), in the eye models a mechanical thickness measuring device (Käfler) was used. The morphology of the stromal bed was examined by photography, histology, scanning electron microscopy and confocal optical distance measurements. RESULTS: The optical/mechanical flap thickness measurements showed an average difference compared to the adjusted thickness of - 3/+ 90 microm (Hansatome-Excellus), + 7/+ 100 microm (M2 single use), - 35/+ 40 microm (Amadeus), - 4/+ 80 microm (MK-2000) and + 11/+ 0 microm (Carriazo-Pendular). Histology showed no mechanical damage and smooth, slightly undulating surfaces with all microkeratomes. In the scanning electron microscopic examination, the stromal surface was found to be homogeneous and smooth for all of the microkeratomes. Average roughness of the ablation surface was 0.27 microm (Hansatome-Excellus), 0.23 microm (M2 single use), 0.21 microm (Amadeus), 0.23 microm (MK-2000) and 0.29 microm (Carriazo-Pendular). CONCLUSION: The stromal bed showed in all cases only a slightly roughness, which seems to be acceptable for the clinical outcome. However, the more critical point is the large variations in flap thickness compared to the intended thickness.

[Comparative results of keratometry with three different keratometers after LASIK]. / Vergleichende Ergebnisse der Hornhautbrechkraftbestimmung dreier Messgeräte nach LASIK.

BACKGROUND: Postoperative hyperopia is a frequent result of cataract surgery in eyes after previous myopic kerato-refractive surgery. One reason for the underestimation of intraocular lens (IOL) power is the wrong corneal refractive power measurement obtained by keratometers and corneal topography systems after LASIK. The aim of this study was to compare the precision of measurements of three different keratometers after LASIK. METHOD: We studied 58 eyes of 34 refractive patients aged between 20 and 51 years. The preoperative measurements and the measurements one month after LASIK were performed with the Keratometer (Zeiss), the corneal topograph (EyeSys Technologies) and the IOL-Master (Zeiss). We compared our postoperative measurement results obtained with the three keratometers with the results obtained by using the clinical history method (chm). RESULTS: The smallest mean deviation was achieved with the IOL-Master (measured mean +/- SD: 38.94 +/- 1.88 D, vs. chm: 38.35 +/- 2.13 D). The Keratometer (Zeiss) showed a larger deviation (measured: 39.12 +/- 1.76 D, chm 38.34 +/- 2.07 D) and the largest deviation was shown with the corneal topograph (measured: 39.84 +/- 1.85 D, chm: 38.86 +/- 2.10 D), which measured in mean one diopter higher than what was obtained utilizing the chm. A positive correlation between corrected myopia and the postoperative difference between the measured and calculated value for each keratometer was found. CONCLUSION: This study demonstrates that with common keratometers central corneal power is measured too high after LASIK. For IOL calculation in patients after LASIK, the wrongly positive deviation from measured central corneal power has to be taken into account.

[Comparison of the optical coherence method (Zeiss IOL-Master) with two ultrasonographic biometric methods for the calculation of posterior chamber intraocular lenses after phacoemulsification as part of clinical routine]. / Vergleich der optischen Kohärenzmethode (Zeiss IOL-Master) mit zwei ultrasonographischen Biometrieverfahren zur Kunstlinsenkalkulation nach Phakoemulsifikation im klinischen Alltag.

BACKGROUND: The aim of this work was to investigate the accuracy of prediction of three different biometric methods for the calculation of posterior chamber intraocular lenses. METHODS: In 59 consecutive patients who underwent extracapsular cataract-extraction with posterior chamber intraocular lens implantation, we compared the refractive results at the first day (D1) and 6 weeks (W6) after surgery with the calculated refraction of three biometric methods: the Carl Zeiss "IOL-Master 99" (IOLM), the Biovision "Echograph Class 1 - Type B" (BIOV) and the Allergan Humphrey "Ultrasonic Biometer Mod. 820" (AHUB). For statistical calculation box-plots, the Wilcoxon signed-rank test and linear regression analysis were used. RESULTS: In all patients the mean of the postoperative refraction was - 0.07 D (SD: 1.41) at day 1 and 0.12 D (SD: 1.18) at week 6. Compared to the postoperative refraction at week 6, the calculated refractive values were higher in all three measuring devices: IOLM: + 0.28 D (SD: 0.67), BIOV: + 0.60 D (SD: 0.88), AHUB: + 0.26 D (SD: 0.92). There were no statistically significant differences between IOLM and BIOV, or respectively, AHUB and BIOV (p < 0.0001), but a significant difference was found between IOLM and AHUB, (p = 0.906). To adjust for systematic differences of the agreement, one can calculate the postoperative refraction at week 6 (REF6) from IOLM by using the linear regression formula: REF6 = 1.1 x IOLM + 0.3. CONCLUSION: A comparison between the three biometric methods and the refractive results at day 1 and week 6 after cataract surgery with implantation of a posterior chamber intraocular lens showed that the calculated mean values obtained from the three biometric methods are higher than the real postoperative refraction. Calculations using the Zeiss IOL-Master and the Allergan Humphrey Ultrasonic Biometer are closer to the patient's postoperative refraction than calculations using the Biovision Echograph.

[Comparison of different methods for pupillometry for mesopic and scotopic conditions]. / Vergleich verschiedener Pupillometrieverfahren unter mesopischen und skotopischen Bedingungen.

BACKGROUND: The aim of the study was to compare different methods for pupillometry, namely the Goldmann perimeter (gp), the Colvard pupillometer (cp) and the Procyon Video pupillometer (pvp). For the pvp three different illuminations were available: mesopic high, mesopic low, and scotopic. PATIENTS: The size of the pupil was measured in 100 eyes (50 healthy subjects) with the three different methods. We examined 29 females (58 %) and 21 males (42 %) with an average age of 25.16 years, ranging from 18 to 30 years. RESULTS: For the Goldmann perimeter, a mean pupil diameter of 4.39 mm +/- 0.62 mm was found under mesopic conditions (1.40 lux). For the Colvard pupillometer for scotopic conditions (0 lux), a mean pupil diameter of 6.80 mm +/- 0.81 mm was found. For pvp the pupil diameter ranged from 7.06 mm +/- 0.71 mm for scotopic (0.04 lux), over 6.24 mm +/- 0.80 mm for mesopic low (0.40 lux) to 4.65 mm +/- 0.73 mm for mesopic high conditions (4.00 lux). CONCLUSION: The comparison of the results showed a high correlation between the Goldmann perimeter and the Procyon Video Pupillometer for mesopic high with a minimum difference of 0.25 +/- 0.69 mm. By addition of 2.67 mm to the mesopic measurement of the Goldmann perimeter, the results for the Procyon Video pupillometer at the scotopic level, by addition of 2.4 mm the scotopic measurement of the Colvard pupillometer could be achieved.

[Prospective comparison of the new indentation tonometer TGdC-01, the non-contact tonometer PT100 and the conventional Goldmann applanation tonometer]. / Prospektiver Vergleich des neuen Impressionstonometers TGDc-01 und des Non-Kontakt-Tonometers PT 100 mit der etablierten Goldmann-Applanationstonometrie.

BACKGROUND: This study aimed to compare the results of newer tonometric techniques with standard tonometry for the examples of the Goldmann applanation tonometry (GAT), the indentation tonometer "TGDc-01" and the non-contact tonometer "PT 100". PATIENTS: The study was conducted on a total of 52 healthy subjects. The IOP was measured in each subject on both eyes with all three methods. There were 27 males (51.9 %), 25 females (48.1 %) with an average age of 28.5 years, with a minimum of 13 and a maximum of 79 years. RESULTS: There was no statistically significant difference between the non-contact and the Goldmann applanation tonometry. The measurements were 0.4 mmHg lower, no difference for the left or right side was seen. For IOP higher than 15 mmHg - 0.88 mmHg lower and for IOP lower 15 mmHg - 0.15 mmHg. The results for the "TGDc01" were 0.82 mmHg lower than GAT, the standard deviation was a little higher with 2.9 mmHg compared to 2.67 mmHg for GAT. For IOP higher than 15 mmHg they rose up to - 2.28 mmHg, for IOP lower than 15 mmHg the results for "TGDc-01" were only - 0.2 mmHg lower. There was also an effect with respect to the side, on the right eye the difference was significant with 3.03 mmHg (p = 0.006), in contrast to the left eye with 2.69 mmHg (p = 0.235). For "TGDc01" the standard deviation was higher with 2.9 mmHg compared to 2.6 mmHg for "PT 100". CONCLUSIONS: The non-contact tonometer showed no clinical relevant difference compared with GAT for measuring IOP. The indentation tonometer showed differences for precision, for higher tension IOP the measurement was lower compared with GAT. There was also a significant side difference using the "TGDc-01".

[Effect of growth factors on the differentiation of porcine lens epithelial cells]. / Einfluss von Wachstumsfaktoren auf die Differenzierung von porcinen Linsenepithelzellen.

BACKGROUND: Besides cell proliferation, transdifferentiation of lens epithelial cells (LECs) to myofibroblasts is one of the mechanisms of secondary cataract formation. This process is characterized by increased expression of alpha-smooth muscle actin (alpha-SMA). This study investigated the influence of bFGF, TGF-beta2, EGF and IGF-1 on the expression of alpha-SMA in porcine LECs. MATERIALS AND METHODS: Porcine LECs were cultured for 7 days in serum-free medium without or with 1 to 50 ng/ml bFGF, TGF-beta2, EGF or IGF-I. Alpha-SMA was detected immunocytochemically with a mouse monoclonal antibody, and the relative numbers of alpha-SMA-positive cells were calculated. Statistical analysis was performed using Student's unpaired t-test. RESULTS: The ratio of alpha-SMA-positive cells cultured for 7 days in serum-free medium was 36 +/- 11.9 % (mean +/- SD). BFGF significantly reduced this ratio in a dose-dependent manner to 11.2 +/- 7.3 % at a concentration of 50 ng/ml (p < 0.0001). EGF reduced the ratio significantly to 25.1 +/- 15.7 % (p = 0.05) when 50 ng/ml were applied. IGF-1 (10 ng/ml) reduced the relative numbers of transdifferentiated cells to 16.8 +/- 5.8 %, but the reduction was not statistically significant (p = 0.0787). TGF-beta2 (50 ng/ml) slightly increased the relative number of alpha-SMA-positive cells to 44.2 +/- 13.8 %. However, this increase was not significant (p = 0.1202) during a culture period of 7 days. CONCLUSIONS: BFGF and EGF significantly reduced the expression of alpha-SMA by LECs while TGF-beta and IGF-1 had no statistically significant effect. These results suggest that bFGF and EGF do not primarily induce secondary cataract formation by the mechanism of cell transdifferentiation.

Octreotide prevents growth factor-induced proliferation of bovine retinal endothelial cells under hypoxia.

Ocular diseases such as proliferative diabetic retinopathy are the major cause of blindness in industrialized countries. The main pathologic features of these diseases are hypoxia and overproduction of growth factors resulting in pathologic proliferation of endothelial cells and new vessel formation. Particularly, hypoxia and growth factors, such as VEGF, IGF-1, bFGF and TGF beta(2), show a complex interaction in the onset and progression of the diseases. Therefore, to date, most therapeutic strategies for proliferative retinopathies have targeted proliferation of endothelial cells evoked by growth factors. Recently, a synthetic analog of somatostatin, octreotide, has been shown to inhibit the proliferation of various cells in vitro, including endothelial cells. In this study, we have investigated the proliferative response of bovine retinal endothelial cells (BREC) to growth factors under hypoxic conditions and the modulation by octreotide. We found a dose-dependent increase of cell proliferation with VEGF, IGF-1 and bFGF, and inhibition of hypoxia-induced cell proliferation with TGF beta(2). Moreover, growth factor-induced, but not hypoxia-induced, cell proliferation was attenuated in the presence of octreotide. In contrast, TGF beta(2) abolished hypoxia-induced BREC proliferation. Similar to octreotide BIM23027, a somatastatin receptor subtype 2 (SSTR2) receptor agonist was able to attenuate the growth factor-induced proliferation of BREC expressing mRNA and protein for SSTR2. Therefore, we postulate that octreotide exerts its effects mainly through binding to the SSTR2. Taken together, our findings point to octreotide as a promising candidate for the treatment of eye disorders involving growth factor-dependent proliferation of endothelial cells.

[Intracanalicular trabeculostomy with the Er:YAG laser]. / Intrakanaläre Trabekulostomie mit dem Er:YAG-Laser.

PURPOSE: To develop a new ab externo technique for glaucoma trabecular surgery using the infrared Er:YAG laser radiation (2.9 micrometer) guided into Schlemm's canal by an optical fiber. MATERIAL AND METHODS: In order to create a drainage canal to the anterior chamber, a quartz fiber (core diameter: 100 micrometer) coupled to an Er:YAG laser was shielded by a metal canula (diameter: 280 micrometer) bent in conformance to the curvature of Schlemm's canal. A 45 degrees -mirror enabled the laser radiation to exit the canula perpendicular to the fiber axis. The complete surgery device was tested on agar medium and enucleated human eyes. RESULTS: Using the unshielded quartz fiber, eight pulses of 8 mJ (frequency: 7 Hz, pulse duration: 150 microseconds) were sufficient to perforate the trabecular meshwork of the human eye. Histology showed a rippled canal with 50 micrometer average diameter and a surrounding necrosis zone of 15-35 micrometer. The complete device could be easily inserted into Schlemm's canal similar to the classic trabeculostomy probe and a conical-shaped canal with a length of 2-3 mm could be created in agar medium within a few seconds. CONCLUSIONS: Initial experience in an experimental set-up show the ab externo creation of a draining canal between Schlemm's canal and the anterior chamber with only minimal irritation of the surrounding tissue. Further refinements of the laser parameters and the biomechanical set-up resulted in a new hand-held device with improved function. The Er:YAG laser intracanalicular trabeculostomy could become a new ab externo technique for minimal invasive therapy of open angle glaucoma.

[Prospective randomized comparative study of frequency doubling perimetry vs standard automated perimetry in patients with glaucoma]. / Prospektive, randomisierte Vergleichsstudie von frequenzverdoppelnder Perimetrie und standardisierter automatischer Perimetrie bei Patienten mit Glaukom.

AIM: To compare frequency doubling perimetry (FDP) versus standard automated perimetry in glaucoma. To evaluate the reproducibility of both methods. PATIENTS AND METHODS: All the patients were tested (full threshold test) twice with both FDP (N-30) and Humphrey Field Analyzer II model 750 (HFA) (30-2 procedures) in random sequence, within one day. The parameters mean deviation (MD), pattern standard deviation (PSD) and measured thresholds per quadrant and center areas were evaluated for FDP/HFA comparison in 45 glaucoma patients. The same parameters were used for testing the reproducibility of FDP (n = 46) and HFA (N = 39). Additionally, the center and each quadrant area were checked for any deviation in the total deviation probability plots. For statistical analysis Kappa coefficients and Bland/Altman plots were used. RESULTS: An average MD (FDP vs HFA) of -7.3 +/- 5.8 dB vs -8.9 +/- 7.6 dB and PSD of 6.9 +/- 2.4 dB vs 6.5 +/- 3.6 dB were found. Kappa coefficients denote marginal accordance (kappa: 0.11-0.38) for area deviations. In a total of 225 areas HFA detected 191 deviations and FDP 165. HFA measured more negative deviation compared with FDP in the case of MD < -15 dB. The reproducibility was 0.98 (MD) and 0.92 (PSD) for FDP and 0.98 (MD) and 0.95 (PSD) for HFA (95% confidence interval). CONCLUSIONS: There was great conformity between FDP and HFA in glaucoma patients. HFA detected more deviations in the total deviation probability plots than FDP. There was a high reproducibility of both methods. FDP is an appropriate tool for detecting visual field loss in glaucoma patients.

The effectiveness of a topical antibiotic irrigating solution in a model of staphylococcal keratitis after lamellar keratectomy.

PURPOSE: To create a model of Staphylococcus aureus keratitis after lamellar keratectomy; to assess the toxicity of an antibiotic irrigating solution on the corneal stromal bed; and to test the chemotherapeutic effectiveness of a topical antibiotic, both alone and with an antibiotic-containing irrigating solution in preventing S. aureus keratitis after lamellar keratectomy. METHODS: The right eye of each of 38 rabbits were used in this study. In 18 eyes, a lamellar flap was created with a microkeratome, and an inoculum of S. aureus (either 1,000, 5,000, or 50,000 CFUs) was instilled under each flap; the eyes were examined for signs of infection and inflammation at 24 and 48 hours. In another five eyes, a lamellar flap was created in the same manner and the stromal bed was irrigated with 0.3% ofloxacin; the eyes were assessed for ocular inflammatory changes and evidence of crystalline deposits. Finally, in each of 15 additional eyes, 1,000 CFUs of S. aureus were instilled under a lamellar flap to create experimental infectious keratitis. The keratitis was treated according to three regimens: irrigation of the stromal bed with sterile balanced salt solution; irrigation of the stromal bed with 0.3% ofloxacin, followed by application of topical ofloxacin four times a day; application of topical ofloxacin only, four times a day. Eyes were examined for infection and ocular inflammatory changes at 24 and 48 hours. RESULTS: Staphylococcus aureus keratitis can consistently be produced under the stromal flap by inoculation of relatively few organisms. Irrigation of the stromal bed with commercial-strength topical ofloxacin does not appear to be toxic to the stromal bed, with no evidence of crystalline precipitates of the antibiotic. In our model of infectious keratitis after lamellar keratectomy, both topical ofloxacin alone and the combination of topical ofloxacin and irrigation of the stromal bed with 0.3% ofloxacin were effective at preventing S. aureus keratitis. However, the combined treatment of antibiotic irrigation plus topical antibiotic was more effective at preventing inflammation than topical ofloxacin alone. CONCLUSIONS: In this model of S. aureus keratitis after lamellar keratectomy, irrigation of the stromal bed with antibiotic plus topical antibiotic appears to be both safe and effective for preventing infection.

Thermal and biomechanical parameters of porcine cornea.

PURPOSE: New methods in refractive surgery require a considerable understanding of the material "cornea" and are often studied by theoretical modeling in order to gain insight into the procedure and an optimized approach to the technique. The quality of these models is highly dependent on the preciseness of its input parameters. Porcine cornea often is used as a model in preclinical studies because of its similarity to man and its availability. METHODS: The important physical parameters for biomechanical deformation, heat conduction, and collagen denaturation kinetics have been determined for porcine cornea. Experimental methods include densitometry, calorimetry, turbidimetry, tensile tests, stress relaxation, and hydrothermal isometric tension measurements. RESULTS: The density of porcine cornea was measured as p = 1062+/-5 kg/m3, the heat capacity gave c = 3.74+/-0.05 J/gK. The stress-strain relation for corneal strips is represented by a third order approximation where the secant modulus yields about Esec approximately equal to 0.4 MPa for small strains less than 2%. The normalized stress relaxation is described by an exponential fit over time. The denaturation process of cornea is characterized by specific temperatures which can be related to the change of the mechanical properties. Denaturation kinetics are described according to the model of Arrhenius yielding the activation energy deltaEa = 106 kJ/mol and the phase transition entropy deltaS = 39 J/(mol x K). CONCLUSIONS: The established set of parameters characterizes the porcine cornea in a reliable way that creates a basis for corneal models. It furthermore gives direct hints of how to treat cornea in certain refractive techniques.

Corneal morphology in vitro after superficial keratectomy with q-switched Er:YSGG and free-running Er:YAG lasers.

PURPOSE: Examination of morphology in corneal ablation induced by a q-switched Er:YSGG (2.79 microm) laser and a free-running Er:YAG laser (2.94 microm). METHODS: Defined ablation of 6-mm diameter and 15, 30, 55, 90, and 120-microm depth was performed on freshly enucleated swine eyes. Er:YSGG laser parameters: fluence 1.6 J/cm2, frequency 6 Hz, spot-size 465 microm FWHM, scanning-mode, pulse number 1520 to 6210. Er:YAG laser parameters: fluence 3 J/cm2, frequency 1.5 Hz, spotsize 6 mm, wide area ablation, pulse number 2 to 13. Corneal morphology was analyzed by gross photography, histology, scanning electron microscopy, and scanning nearfield acoustic microscopy. RESULTS: Histology showed thermal damage of 5 to 15 microm in depth caused by the Er:YSGG laser in comparison with 10 to 20 microm by the Er:YAG laser. Average roughness of the ablated surface measured with scanning nearfield acoustic microscopy was 20 to 40 microm for the Er:YSGG laser and 5 to 15 microm for the Er:YAG laser. These data confirm the subjective impression of images created by scanning electron microscopy and gross photography. CONCLUSIONS: Although the Er:YAG laser system appeared to demonstrate a smoother corneal surface than the q-switched Er:YSGG laser, the thermal damage in either case poses a potential limitation for clinical use in lamellar refractive surgery.

Influence of temperature and time on thermally induced forces in corneal collagen and the effect on laser thermokeratoplasty.

PURPOSE: To investigate thermomechanical aspects of corneal collagen denaturation as a function of temperature and time and the effect of the induced forces on refractive changes with laser thermokeratoplasty (LTK). SETTING: Medical Laser Center Lübeck, Lübeck, Germany. METHODS: In a material-test setup, porcine corneal strips were denatured in paraffin oil at various constant temperatures for 10 and 500 seconds, and the temporal course of the contractive forces was studied under isometric conditions. Typical LTK lesions were performed in porcine eyes in vitro with a continuous-wave infrared laser diode at a wavelength of 1.87 microm for 10 and 60 seconds. The laser power was chosen to achieve comparable denatured volumes at both irradiation times. The refractive changes were measured and analyzed by histologic evaluations and temperature calculations. RESULTS: The time course of the induced forces was characterized by a maximal force, which increased almost linearly with temperature, and a residual lower force. After 500 seconds of heating, the highest force was achieved with a temperature of 75 degrees C. With a limited heating period of only 10 seconds, the forces steadily increased with temperature over the entire observation period. Laser thermokeratoplasty produced less refractive change after 10 seconds of irradiation than after 60 seconds, although the laser power was 25% higher in the short heating period. Polarization light microscopy of LTK lesions revealed different stages of thermal damage. CONCLUSION: The course of the contractive forces during and after heating is a complicated function of the spatial time/temperature profile. Laser thermokeratoplasty lesions produced with 2 irradiation times showed different stages of denaturation and induced refractive change.