[Corneal Cross-Linking with Riboflavin and UVA in Keratoconus]. / Hornhautvernetzung mit Riboflavin und UV-A-Licht bei Keratokonus.

Changes in the biomechanical properties of the human cornea play an important role in the pathogenesis of corneal ectatic diseases. Many different pathological conditions in the cornea may reduce its biomechanical resistance. Corneal collagen cross-linking (CXL) has emerged as a promising technique to slow or even to stop the progression of ectasia. In this procedure, riboflavin (vitamin B2) is administered in conjunction with ultraviolet A light (UVA, 365 nm). This interaction causes the formation of reactive oxygen species, leading to additional covalent bonds between collagen molecules, with consequent biomechanical stiffening of the cornea. Although this method is not yet accepted as an evidence-based treatment of corneal ectasia, the results of prospective, randomised studies of CXL used in the treatment of this pathological entity show significant changes in the properties of corneal tissue. This procedure is currently the only aetiopathogenetic treatment of ectatic eyes that can delay or stop the process of cornea destabilisation, reducing the necessity for keratoplasty. Despite promising results, CXL is associated with issues that include long-term safety and duration of the stabilising effect.

[Cross-Linking in Keratoconus: "Epi-off" or "Epi-on"?]. / Hornhautvernetzung beim Keratokonus: "Epi-off" oder "Epi-on"?

Corneal cross-linking can halt the progression of keratoconus, but what is the best approach for treatment? There are a number of treatment options for keratoconus, but only corneal cross-linking (CXL) appears to halt the progression of the disease. To guarantee effective cross-linking, CXL treatment involves removal of the corneal epithelium prior to riboflavin application and ultraviolet light illumination - "epi-off" CXL. Several methods of "epi-on" (transepithelial) CXL have been proposed, such as keeping the corneal epithelium intact which should be less painful and help avoid other CXL-associated adverse events. The evidence so far is that epi-off CXL remains the most effective method of strengthening the cornea and slowing keratoconus progression - but transepithelial methods are gaining ground.

[Collagen cross-linking with riboflavin and UVA light]. / Kollagenvernetzung mit Riboflavin und UVA-Licht.

PURPOSE: Since 1998 collagen cross-linking is used for patients with progressive keratoconus. Today it can almost be considered as the standard therapy. METHODS: Patients with progressive keratoconus and minimal corneal thickness of 400 µm have been cross-linked within a study - (EK 310 499) approved by the ethical committee since 1998. An increase of the maximum K-value by ≥ 1 D within the last year, patient's statement of deteriorating visual acuity or the necessity of new contact len fitting more than once in 2 years were considered as progression. RESULTS: The analysis includes 153 eyes of 111 patients with a minimal follow-up of 12 months and a maximum follow-up of 6 years. The keratectasia significantly decreased in the 1 (st) year by 2.28 D. The visual acuity improved significantly by at least one line or, respectively, remained stable (i. e., no line loss) in the 1st year in 73 %. The results remained stable over the next two years. Despite the low number of patients with a follow-up longer than 3 years and therefore limited statistical statement power, our results still indicate a long-term stabilisation or, respectively, improvement after collagen cross-linking. We saw no severe side-effects. Three patients with an exacerbated neurodermitis showed continuous progression of keratoconus and were cross-linked again. CONCLUSIONS: To date there have been numerous promising publications on collagen cross-linking for keratoconus. The results of this study indicate that collagen cross-linking appears to be an effective therapeutic option for progressing keratoconus. Besides the clinical there are enormous economical and psychosocial benefits. Cross-linking is an out-patient, minimally-invasive, cost-effective treatment with minimal strain for the persons concerned.

[Statistical analysis of correlated measurement data in ophthalmology : Tutorial for the application of the linear mixed model in SPSS and R using corneal biomechanical parameters]. / Statistische Auswertung korrelierter Messdaten in der Augenheilkunde : Tutorial zur Verwendung des linear gemischten Modells in SPSS und R anhand biomechanischer Parameter der Hornhaut.

BACKGROUND: In ophthalmology data from both eyes of a person are frequently included in statistical analyses. As correlated data are used this procedure contradicts the independency principle for classical statistical tests, such as Student's t­test and analysis of variance (ANOVA). In this tutorial a new possibility is presented in which data from both eyes can be used for statistical analysis. OBJECTIVE: The statistical approach of linear mixed models (LMM) was used to take correlated data of both eyes of patients into account. METHODS: The LMM is available in several statistical software packages, e.g. SPSS and R, and allows the inclusion of measurement data from both eyes of a person in the statistical analysis. The application was tested on data from a biomechanical characterization of the cornea from healthy participants assessed with the dynamic Scheimpflug analyzer (Corvis ST; Oculus, Wetzlar, Germany). RESULTS: A total of 158 eyes from 79 healthy participants were included. A strong correlation between the right and left eyes of the participants could be observed with respect to the analyzed parameters. Comparison of the biomechanical parameters between the different age groups showed that P-values were increased when using the LMM compared to the ANOVA. Older participants (56-79 years) showed a significantly shorter time to the second applanation (P = 0.002), a significantly increased eyeball movement during the deformation (P = 0.001) and a significantly higher stiffness at the first applanation (P = 0.006) compared to younger participants (18-35 years). CONCLUSION: The analysis of measurement data from both eyes using classical statistical tests, without the consideration of the correlation, leads to an overestimation of the statistical power. This can be avoided by implementation of the LMM.

[Dynamic Scheimpflug Analyzer (Corvis ST) for measurement of corneal biomechanical parameters : A praxis-related overview]. / Dynamischer Scheimpflug-Analyzer (Corvis ST) zur Bestimmung kornealer biomechanischer Parameter : Ein praxisbezogener Überblick.

BACKGROUND: Topographic and tomographic parameters alone are often not sufficient for early detection of corneal changes. Pathological alterations in the microstructure of the cornea occur before changes in topography and tomography can be detected. Biomechanical parameters show a strong correlation with microscopic structural changes. OBJECTIVE: The aim of the study was to gain information about the microscopic structure and consistency of the cornea by measuring biomechanical parameters. MATERIALS AND METHODS: The deformation behavior of the cornea was analyzed with the Dynamic Scheimpflug Analyzer (Corvis ST; OCULUS, Wetzlar, Germany). Deformation parameters and biomechanical indices were derived from the deformation response of the cornea. RESULTS: Deformation parameters and indices in keratoconus patients differ significantly from healthy subjects. Alterations of the cornea can be detected before topographic and tomographic changes occur. The repeatability and reproducibility of relevant deformation parameters is good to very good. In glaucoma patients a modified deformation behavior of the cornea can be observed, which might be related to structural changes. CONCLUSION: The Corvis ST allows a reliable characterization of the tissue structure and consistency of the cornea.

[Intraocular pressure measurement during the day and night for glaucoma patients and normal controls using Goldmann and Perkins applanation tonometry]. / Augeninnendruckmessungen im Tages- und Nachtverlauf bei Glaukompatienten und Normalprobanden mittels Goldmann- und Perkins-Applanationstonometrie.

OBJECTIVE: Our aim was to evaluate intraocular pressure (IOP) levels in primary open angle glaucoma (POAG) patients and healthy controls during both the day and night while measuring in an upright as well as in a supine position. METHODS: In a prospective clinical trial, 30 glaucoma patients on topical treatment and 50 healthy controls received IOP measurements every 4 h for a 24 h period starting at 8 am. Additionally, blood pressure and heart rate were measured and perfusion pressures were calculated. At 12 am IOP was initially measured in a sitting position and then, after 20 min, in a supine position. At midnight this was carried out conversely. At 4 am IOP was measured in a supine position; all other measurements were performed in a sitting position. Measurements in the sitting position were performed by Goldmann and Perkins tonometry and in a supine position by Perkins tonometry. RESULTS: IOP was 1 mmHg lower in Perkins tonometry measurements compared to Goldmann tonometry. There was no difference between the two patient groups. In a supine position, IOP measured by Perkins tonometry was higher than in an upright position. At 12 am the difference was 1.8 mmHg+/-2.7 mmHg (p=0.001) in healthy subjects and 1.3+/-2.7 mmHg (p=0.013) in the POAG patients. At 12 pm the increase of IOP in the supine position was even more pronounced with 2.4+/-3.4 mmHg in healthy subjects and 5.6+/-3.2 mmHg in the POAG patients (p=0.001). The blood pressure and the perfusion pressure were lowest during night measurements. CONCLUSIONS: During diurnal IOP measurements in an upright position there were no statistically significant differences in IOP changes between groups. However, in a supine position IOP was significantly higher than in a sitting position and increased more in the glaucoma patients than in healthy controls. This observation might be due to a faulty regulation of the fluid shift in glaucoma patients and could cause progression of glaucomatous damage.

[Combined cryocoagulation of ciliary body and retina in neovascular glaucoma. Initial experience]. / Kombinierte Kryokoagulation von Ziliarkörper und Retina bei Neovaskularisationsglaukom. Erste Erfahrungen.

UNLABELLED: Therapeutic success in neovascular glaucoma with conservative and surgical methods is sadly inadequate. Based on the encouraging results we have obtained with transconjunctival cyclocryothermy in primary glaucoma and with peripheral cryopexy (transconjunctival cryotherapy), we applied these two methods in combination to treat neovascular glaucoma. PATIENTS: A total of 25 eyes in 23 patients were treated with the above method. The average preoperative bulbar pressure was 43 mmHg. RESULTS: The highest average reduction of pressure was obtained in weeks 2-4 after treatment (20 mmHg); 40% of the eyes were still compensated after 4 months (below 22 mmHg), 35% showed bulbar pressures between 26-28 mmHg, and 25% showed bulbar pressures about 35 mmHg. These patients had no troublesome symptoms. In all cases, a good improvement of rubeosis iridis was observed. The combined cryotherapeutic method of treating neovascular glaucoma is efficient in controlling the internal bulbar pressure.

[Treatment of keratoconus by collagen cross linking]. / Behandlung von Keratokonus durch Kollagenvernetzung.

BACKGROUND: We were able to show a significant increase in corneal stiffness of rabbit and porcine eyes after combined riboflavin/UVA-induced collagen cross-linking. In this study,we tried to treat keratoconus patients with this method to stop the progression of corneal ectasia. PATIENTS AND METHODS: We treated 16 eyes of 15 patients with progressive keratoconus and mostly moderate keratectasia (48-56 dpt). After removal of the epithelium (7 mm X), riboflavin solution was applied on the cornea, which was irradiated with UVA (370 nm,3 mW/cm(2)) at a distance of 1 cm for 30 min.Post-operative follow-up controls were conducted every 3 months in the first year and then every 6 months, always including visual acuity testing, corneal topography and measurements of endothelial cell density. The follow-up time was between 1 and 3 years. RESULTS: Progression of keratectasia was stopped in all patients. Best corrected visual acuity and the maximal keratometry values improved slightly in about 50% of the cases. In all patients corneal transparency, the degree of keratectasia registered by corneal topography and the density of endothelial cells remained unchanged within the follow-up time. No negative side-effects were observed. CONCLUSIONS: Our results show that collagen cross linking might be a useful conservative treatment modality to stop the progression of keratoconus. By this means the need for keratoplasty might be significantly reduced. Given the simplicity of the technique and minimal costs of the treatment it might also be well suited for developing countries.Further studies are envisaged to exclude long-term side effects and to evaluate the long term durability of the mechanical stiffness effect.

[Increased rigidity of the cornea caused by intrastromal cross-linking]. / Erhöhung der Festigkeit der Hornhaut durch Vernetzung.

PURPOSE: To increase the stability of the cornea by artificial cross-linking (radiation or chemical agents) and to investigate a future therapy for keratoconus. MATERIALS AND METHODS: The epithelium of enucleated porcine eyes was removed. Ten eyes in each of eight test groups were treated with UV light (lambda = 254 nm), 0.5% riboflavin and UV light (365 nm), blue light (436 nm) and sunlight, and the chemical agents glutaraldehyde (1% and 0.1%, 10 min) and Karnovsky's solution (0.1%, 10 min). Strips of 5 mm in width and 9 mm in length were cut from each cornea and the stress-strain behaviour of the strips was measured. For comparison, eight groups of ten untreated corneas each were measured by the same method. RESULTS: Compared to untreated corneas riboflavin and UV irradiation as well as glutaraldehyde and Karnovsky's solution treatment resulted in significantly increased stiffness of the cornea (p < 0.05). CONCLUSIONS: The biomechanical behaviour of the cornea can be altered by low-concentration glutaraldehyde, Karnovsky's solution, and by riboflavin and UV irradiation, which offers potential conservative treatment of keratoconus. To optimize this effect further investigation is necessary regarding the dose-effect relation and the in-vivo conditions.

[Laser-induced pressure waves in the eye. Propagation characteristics]. / Laserinduzierte Druckwellen am Auge. Ausbreitungscharakteristik.

BACKGROUND: The characteristics of shock waves during photoablation were investigated for an IR and a UV laser. These stress waves may be harmful to ocular structures. MATERIAL AND METHODS: The amplitude of shock waves was measured by a needle-shaped hydrophone in enucleated porcine eyes during excimer laser (193 nm, 23 ns, diameter of ablation 1.5-7.5 mm) and Er:YAG laser photoablation (2.94 microns, 200 microseconds, 1.2 mJ/cm2, diameter of ablation 4 mm). RESULTS: With the excimer laser at ablation zones larger than 4.5 mm, a pressure focus occurs at a distance of 4-6 mm behind the cornea. The pressure amplitudes are smaller than 80 bar for a fluence of 180 mJ/cm2 and decrease steadily to values below 10 bar towards the retinal level. Higher fluences produce higher pressure values; in the range of 60 to 220 mJ/cm2 the relation is linear. For the Er:YAG laser, pressure amplitudes are smaller than 0.5 bar. CONCLUSIONS: Mechanical damage of the retina is unlikely during excimer-or Er:YAG-laser ablation. The existence of a pressure focus may result in mechanical damages of the posterior lens or anterior vitreous at large ablation diameters. During Er:YAG laser ablation, shock waves could not be detected with our measurements. Theoretical estimations yield values of less than 700 mbar at a fluence of 1.2 J/cm2. The pressure load of the endothelium is independent of diameter but dependent on fluence.

[Studies on the stabilization of the cornea in rabbits]. / Untersuchungen zur Verfestigung der Hornhaut am Kaninchen.

BACKGROUND: The mechanical stabilization of the cornea in keratoconus may delay progression of this disease. The cross-linking techniques optimized in corneas of enucleated porcine eyes were investigated under in vivo conditions in rabbits to estimate the biocompatibility and duration of the stiffening effect. METHODS: Twenty-eight rabbits were treated monocularly, the fellow eye serving as control. The epithelium was mechanically removed and 19 eyes were treated with riboflavin plus ultraviolet irradiation (365 nm, 2 mW/cm2) for 45 min and 9 eyes with 0.075% glutaraldehyde for 20 min. After treatment, the eyelids were sutured for 3 days. The healing process was controlled by slit-lamp examination and photographically documented. After 1 month, 20 animals and after 3 months 8 animals were sacrificed, the eyes enucleated, and the stress-strain relation of the corneas measured and compared to the fellow eye. RESULTS: The epithelium was closed after 4-5 days. The transparency of the corneas remained clear during follow-up, and there were no signs of inflammatory reaction. Stress for a strain of 6% was higher in the treated corneas by a factor of 1.3 +/- 0.66 (P = 0.319) in the glutaraldehyde group and by a factor of 1.6 +/- 0.75 (P = 0.0408) in the riboflavin group at 1 month, and by 1.3 +/- 0.48 (P = 0.07) at 3 months after treatment. CONCLUSIONS: The cross-linking technique using riboflavin plus UV irradiation is suitable for at least temporarily stiffening the cornea in vivo and seems to be a promising method for conservative treatment of keratectasia.

[Cryotherapy of malignant eyelid tumors]. / Kryotherapie von malignen Lidtumoren.

The treatment of tumors of the eyelids must extend not only to complete removal or destruction of the neoplasm, but also to the maintenance of physiology functions. In addition, cosmetic aspects should be taken into consideration. In a prospective study, 278 cryosurgical operations performed for lid tumors in the years from 1980 to 1985 were followed up for 5 years to decide whether cryotherapy fulfilled these demands. We used spray freezing with liquid nitrogen, because the low temperatures and high freezing rates required for cell destruction are achieved only by this technique. The 5-year recurrence rate was 3.5%. The liquid nitrogen therapy is especially suitable when the eye lids are operated on, because the lacrimal system remains functional. Gas expansion cryotherapy should not be used in in the treatment of tumors, as it may lead to stimulation of growth.

[Influence of corneal biomechanical properties on myopic regression after laser in situ keratomileusis]. / Einfluss der kornealen Biomechanik auf die Myopieregression nach Laser-in-situ-Keratomileusis.

BACKGROUND: Laser in situ keratomileusis is a safe and accepted method for correcting myopia. The operational results in terms of accuracy as well as the subjective acceptance of patients for corrections to - 8 D are now considered to be promising (Seiler, Refraktive Chirurgie der Hornhaut, 2000); however, postoperative results show individual patient problems in long-term stability. It is believed that the preoperative condition of the cornea (e.g. thickness, biomechanical properties) could have an influence on postoperative problems such as myopic regression. METHOD: This study included a total of 46 eyes from 25 patients. At 3 months postoperatively, 15 patients (19 eyes) showed a SEQ of -0.50 D or more. Within this group, 11 patients (15 eyes) developed a regression (regression group) within the first 3 postoperative months. The remainder of the total group did not show any regression (stability group). The subjects of this study were on average 33 ± 8 years (stability group) and 31 ± 7 years old (regression group). The corneal thickness was tested and refractive error, visual acuity (BCVA/UCVA) and intraocular pressure was measured. In addition, the corneal hysteresis (CH) and corneal resistance factor (CRF) were determined. RESULTS: The mean preoperative spherical equivalent refraction was -3.14 D ± 1.41 D (SE) in the stability group and - 6.47 D ± 1.40 D (p = 0.001)in the regression group. Also, the postoperative spherical equivalents were statistically significant different (p < 0.05). In contrast, the mean preoperative corneal thickness showed no differences in both groups (p = 0.96) (stability group 563 ± 36 µm and regression group 563 ± 28 µm). CONCLUSIONS: The aim of the study to detect a possible causal relationship between myopia regression after LASIK and the biomechanical properties of the cornea and corneal thickness could not be clearly identified.

Interlamellar cohesion after corneal crosslinking using riboflavin and ultraviolet A light.

AIMS: Collagen crosslinking treatment of progressive keratoconus using the photosensitiser riboflavin and ultraviolet A light of 370 nm wavelength has been shown to increase significantly the tensile strength of corneal collagen by about 300%. In keratoconus, interlamellar and interfibrillar slippage have been proposed as pathogenetic mechanisms. Therefore, the aim of this study was to assess the impact of collagen crosslinking on the interlamellar cohesive force. METHODS: 72 post mortem porcine eyes were divided into six different treatment groups: the untreated control group, the standard crosslinking group, the hypo-osmolar crosslinking group, the stromal swelling group, the formaldehyde group and the α-amylase group. An anterior 9×4 mm strip of 400 µm thickness was prepared using a lamellar rotating microkeratome. For interlamellar cohesive force measurements a splitting plane was created at 50% depth. Force-distance profiles were recorded using a microcomputer-controlled biomaterial testing machine. RESULTS: The mean interlamellar cohesive force was 0.24 N/mm in the untreated control group, 0.26 N/mm in the standard crosslinking group, 0.25 N/mm in the hypo-osmolar crosslinking group, 0.23 N/mm in hydrated corneas, 0.27 N/mm in the formaldehyde group without statistically significant difference. Only the values of the α-amylase group were statistically significantly lowered by 31.5% to 0.16 N/mm. CONCLUSIONS: Surprisingly, corneal crosslinking does not increase the interlamellar cohesive force. In the α-amylase group the cohesive force was mainly decreased because of the digestion of proteoglycans. Crosslinking seems to stabilise only inter- and intrafibrillar, but not interlamellar cohesion.

[Corneal scar development after cross-linking in keratoconus]. / Narbenbildung nach Hornhautvernetzung beim Keratokonus.

BACKGROUND: Corneal scar development after riboflavin-UVA-induced corneal collagen cross-linking (CXL) was retrospectively evaluated. PATIENTS AND METHODS: A total of 163 CXL-treated eyes in 127 patients with stage 1-3 keratoconus according to Krumeich's classification were included in this retrospective analysis. The follow-up period was 1 year. At the first and at all follow-up examinations uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), biomicroscopic findings, corneal topography and corneal thickness were recorded. RESULTS: At 1 year following CXL, 149 eyes (91.4%) of 114 patients had a clear cornea without corneal scar (control group), while 14 eyes (8.6%) of 13 patients developed clinically significant corneal scar (scar group). Preoperatively, the mean K value of the apex was 62.1 ± 13.8 D in the control group and 71.1 ± 13.2 D in the scar group (P=.02). The mean value of corneal thickness before the procedure was 478.1 ± 52.4 µm in the control group and 420.0 ± 33.9 µm in the scar group (P=.001). The UCVA and BCVA, which were preoperatively similar between groups (P=.59, P=.75 respectively), were postoperatively improved in the control group (P=.023, P=.001 respectively), but reduced in the scar group (P=.012, P=.004 respectively). CONCLUSION: K-values and corneal thickness could be considered as predictive factors for the possible development of corneal scarring after riboflavin-UVA-induced CXL. Advanced keratoconus appears to be associated with a higher risk of corneal scar development due to lower corneal thickness, greater curvature and intrinsic tissue characteristics.

[Collagen cross-linking with riboflavin and UVA light in keratoconus. Results from Dresden]. / Kollagenvernetzung mit Riboflavin und UVA-Licht bei Keratokonus. Dresdner Ergebnisse.

PURPOSE: The aim of this long-term retrospective study was to prove a long-term halting effect of riboflavin and UVA-induced collagen cross-linking in progressive keratoconus. METHODS: Since 1998, within an ethics-committee-approved study (EK 310 499), patients with progressive keratoconus and a minimal corneal thickness of 400 microm have received cross-linking treatment. An increase of the maximum K-value by > or =1 D within the previous year, a patient's statement of deteriorating visual acuity, or the need for a new contact lens fitting more than once in 2 years was considered progression. The maximum follow-up time was 7.5 years. At the first examination and all follow-up examinations, refraction, best corrected visual acuity, corneal topography, and ultrasound pachymetry were recorded. RESULTS: The analysis included 153 eyes of 111 patients, with a minimal follow-up of 12 months. Keratectasia significantly decreased in the 1st year by 2.29 D, in the 2nd year by 3.27 D, and in the 3rd year by 4.34 D. Visual acuity improved significantly in at least one line or remained stable (i.e., no line loss) in the 1st year in 48.9% and 23.8%, respectively; in the 2nd year in 50.7% and 29.6%, respectively; and in the 3rd year in 60.6% and 36.4%, respectively. We saw no severe side effects. Three patients showed continuous progression of keratoconus and received cross-linking treatment again. Despite the small number of patients with a follow-up longer than 3 years, therefore limiting the statistical assertions, our results indicate long-term stabilization or improvement after collagen cross-linking. CONCLUSION: With regard to the size of our cohort and the follow-up time, no comparable data have been published in the literature. The results of this study indicate that collagen cross-linking appears to be an effective therapeutic option for progressing keratoconus. Besides the clinical benefit, there are enormous economic and psychosocial benefits. Cross-linking is an outpatient, minimally invasive, cost-effective treatment involving minimal effort for the persons concerned.

[Measurement of the disc area by indirect ophthalmoscopy]. / Flächenbestimmung der Papille mittels indirekter Ophthalmoskopie.

PURPOSE: The aim of this study was to assess the accuracy of measuring the optic disc area by indirect ophthalmoscopy. PATIENTS AND METHODS: In a prospective clinical trial, 57 eyes of 29 subjects (age 57.3+/-12.1 years) were examined. The refractive error was -0.67+/-2.69D (+3.75D to -8D).The vertical and horizontal disc diameters (DD) were measured using a Haag-Streit slit lamp and 60D-, 78D-, 90D-, and Super Field lenses (Volk Optical, Mentor, USA). Afterwards the disc area was calculated by an ellipse formula (horizontal DD x vertical DD x pi/4). The magnification factor given by the manufacturer was taken into account for each lens: 1.15x (60D lens), 0.93x (78D lens), 0.76x (90D lens), and 0.76x (Super Field lens), respectively. As reference for the disc size, the same eyes were examined by HRT II (Heidelberg Engineering, Heidelberg, Germany). Bland-Altman plots were used to assess the agreement between measurements obtained by indirect ophthalmoscopy and HRT. RESULTS: The results of the disc estimate compared with the HRT measurements were as follows: 0.119+/-0.51 mm(2) (60D lens), 0.224+/-0.57 mm(2) (78D lens), 0.10+/-0.51 mm(2) (90D lens), and -0.07 s+/-0.47 mm(2) (Super Field lens). Differences were not statistically significant for the 60D (p=0.083), 90D (p=0.147), or Super Field lenses (p=0.257). However, the difference between the 78D lens and HRT was statistically significant (Student's t-test; P=0.004). CONCLUSION: Measuring the disc size by indirect ophthalmoscopy is possible. The 90D lens showed the smallest and the 78D lens the largest deviation.

[Biomechanical condition of the cornea as a new indicator for pathological and structural changes]. / Biomechanische Zustand der Hornhaut als neuer Indikator für pathologische und strukturelle Veränderungen.

AIM: Several methods permit the measurement of geometric parameters of the cornea, but until now biomechanical conditions of the cornea have been ignored (e.g. in refractive corneal surgery). Besides the geometric condition, biomechanical properties of the cornea have been shown to influence applanation measurement of intra-ocular pressure (IOP) and epidemiological studies have identified corneal thickness as an independent risk factor for the development and progression of glaucoma. The aim of this investigation was to characterize the biomechanical properties of the cornea using the ocular response analyzer (ORA). METHODS: The ocular response analyzer (ORA) is a new method available for non-contact measurement of the biomechanical properties of the cornea. We evaluated the reproducibility of measurements, the difference between static and dynamic factors and the impact of independent factors (e.g. IOP, age, CCT, swelling of the cornea) on 2,500 measurements of corneal hysteresis (CH) and corneal resistance factor (CRF). RESULTS: In a large sample size we observed changes in CH and CRF after refractive surgery procedures (LASIK, UV-A cross-linking, keratoplasty) and in other corneal disorders (keratoconus, corneal dystrophies). CONCLUSIONS: CRF and CH changes may reflect structural changes of the cornea. Thus, the ORA provides valuable information for a better understanding and characterization of the biomechanical condition of the cornea, especially with regard to diseases such as keratoconus and glaucoma.

[Biophysical principles of collagen cross-linking]. / Biophysikalische Grundlagen der Kollagenvernetzung.

BACKGROUND: The reduced mechanical stability of the cornea in keratoconus or in keratectasia after Lasik may be increased by photooxidative cross-linking of corneal collagen. The biophysical principles are compiled for the safe and effective application of this new treatment method. METHODS: The setting of the therapy parameters should be elucidated from the absorption behaviour of the cornea. The safety of the method for the endothelium cells and the lens will be discussed. The induced cross-links are shown to be the result of changes in the physico-chemical properties of the cornea. RESULTS: To reach a high absorption of the irradiation energy in the cornea, riboflavin of a concentration of 0.1% and UV light of a wavelength of 370 nm, corresponding to the relative maximum of absorption of riboflavin, were used. An irradiance of 3 mW/cm(2) and an irradiation time of 30 min lead to an increase of the mechanical stiffness. The endothelium cells will be protected due to the high absorption within the cornea, that means the damaging threshold of the endothelium cells will not be reached in a 400 microm thick stroma. As evidence for cross-links we can consider the increase of the biomechanical stiffness, the increased resistance against enzymatic degradation, a higher shrinkage temperature, a lower swelling rate and an increased diameter of collagen fibres. CONCLUSIONS: The therapy parameters were tested experimentally and have been proven clinically in the corneal collagen cross-linking. These parameters should be respected to reach a safe cross-linking effect without damage of the adjacent tissues.

[Statistical methods for comparison of two measuring procedures and for calibration: analysis of concordance, correlation and regression in the case of measuring intraocular pressure]. / Statistische Verfahren zum Vergleich zweier Messmethoden und zur Kalibrierung: Konkordanz-, Korrelations- und Regressionsanalyse am Beispiel der Augeninnendruckmessung.

BACKGROUND: The comparison of two or more quantitative measurement procedures applied to the same patient is often carried out by unsuitable statistical methods. An orientation for the choice of methods has been given for such problems. METHODS: Graphical methods, the concordance correlation coefficient and some regression straight lines are presented for the judgement of concordance of measurement values, and they are exemplary explained for the measurement of the intraocular pressure with lid tonometry and the ocular blood flow system (OBF). RESULTS: The t-test for paired samples and tests of equivalence are invalid in this context. The Pearson correlation coefficient measures to what degree two variables are associated over a linear relation with reference to the population. It ignores location shift as well as scale shift, and it says nothing about the intraindividual concordance. A suitable procedure is the concordance correlation coefficient which can decomposed into precision, location shift, and scale shift. CONCLUSIONS: An assessment of concordance of intraindividual measurement values should include an x-y-graphic of the measured points, a Bland-Altman plot, and the concordance correlation coefficient.