[Visual recovery as the target for glaucoma]. / Visuelle Regeneration als Ziel für das Glaukom.

BACKGROUND: Visual recovery is an established but poorly studied phenomenon in glaucoma. OBJECTIVE: To provide insights into functional recovery of retinal ganglion cells (RGCs) with a view to providing information on the development of forms of treatment that improve RGC function after injury. METHOD: A model of recoverable RGC function in the mouse eye, induced by short-term elevation of intraocular pressure (IOP). RESULTS: The RGCs manifest near complete functional recovery after a prolonged period of dysfunction following acute IOP elevation. Increasing age and a high fat diet were subsequently found to impair recovery, whereas exercise substantially improved recovery such that older mice recovered in a similar way to young mice. CONCLUSION: Injured RGCs have the capacity to restore function after periods of functional impairment. Therapies that specifically target injured RGCs and enhance their capacity to recover function may provide a new approach for treating glaucoma.

[Autoimmunity and glaucoma]. / Autoimmunität und Glaukom.

In addition to the clinically most relevant risk factor for glaucoma, i.e., elevated intraocular pressure (IOP), there are other factors with high relevance for the disease. Changes in the autoimmune component of the immune system are of particular importance. Clinical studies have demonstrated alterations in different autoantibodies in glaucoma patients compared to healthy controls, some of which increase in abundance/have a raised titer, but also some which have a reduced titer. These changes have a distinct potential-not only as a tool for early glaucoma detection, but also as a therapeutic option due to the documented neuroprotective effects of some of these antibodies. Several antibodies displaying lower abundance in glaucoma patients, e.g., antibodies against 14-3-3 proteins, γ­/α-synuclein, or also against glial fibrillary acidic protein (GFAP), show neuroprotective effects on retinal ganglion cells in vivo and in vitro. To assess the relevance of changes detected in the immune system of glaucoma patients, "­omics-based" analyses of different ocular tissues are of particular importance alongside cell culture studies. In this manner, not only samples derived from experimental studies but also samples derived from glaucoma patients in even very small amounts (e. g., tears, aqueous humor, serum, or post-mortem retina) can be analyzed in detail in terms of protein and, in particular, antibody changes. Modern mass spectrometric proteomic characterization of relevant samples will deliver valuable information concerning the understanding of molecular disease mechanisms in the coming years, thus also improving diagnosis and treatment of glaucoma.

Peripapillary fluorescence lifetime reveals age-dependent changes using fluorescence lifetime imaging ophthalmoscopy in rats.

Many fundus diseases accompany fundus autofluorescence change. Fluorescence lifetime imaging ophthalmoscope (FLIO) is a latest technique in imaging fundus autofluorescence. With FLIO, the fundus fluorescence lifetime (FLT) is recorded topographically, assisting to diagnose and monitor multiple fundus diseases. The purpose of this study was to evaluate the repeatability of FLT using FLIO on adult rats and to analyze the age-dependency of the peripapillary FLT of the fundus in a short spectral channel (498-560 nm) and a long spectral channel (560-720 nm). Sprague Dawley rats (n of eyes = 10) were used for repeatability experiments. Age-dependent changes were investigated in young (two months old, n of eyes = 20) and old (eight months old, n of eyes = 10) rats. Repeatability experiments showed highly corresponding data for all segments in both spectral channel, with higher repeatability in the short spectral channel. FLT decreased significantly in all areas in the short (young: 991 ±â€¯29 ps; old: 547 ±â€¯42 ps) and long (young: 382 ±â€¯28 ps; old: 261 ±â€¯16 ps) spectral channels, indicating an overall metabolic change of the fundus in old animals. FLT of veins increased in the short spectral channel (young: 385 ±â€¯43 ps; old: 424 ±â€¯25 ps) and no change was observed in the long spectral channel (young: 274 ±â€¯9 ps; old: 269 ±â€¯24 ps). FLIO represents a highly repeatable and sensitive method to detect changes of the FLT in aged eyes for monitoring the degeneration of the rodent retinae.

Decelerated neurodegeneration after intravitreal injection of α-synuclein antibodies in a glaucoma animal model.

Although elevated intraocular pressure (IOP) remains the major risk factor in glaucoma, neurodegenerative processes continue despite effective IOP lowering. Altered α-synuclein antibody (Abs) levels have been reported to play a crucial role. This study aimed at identifying whether α-synuclein Abs are capable to decelerate neuronal decay while providing insights into proteomic changes. Four groups of Sprague Dawley rats received episcleral vein occlusion: (1) CTRL, no intravitreal injection, n = 6, (2) CTRL IgG, intravitreal injection of unspecific IgG, n = 5, (3) Buffer, intravitreal injection of buffer, n = 6, (4), α-synuclein Ab, intravitreal injection of α-synuclein Ab, n = 5. IOP and retinal nerve fiber layer thickness (RNFLT) were monitored and immunohistochemistry, microarray and proteomic analysis were performed. RNFLT was reduced in CTRL, CTRL IgG and Buffer group (all p < 0.01) and α-synuclein Ab group (p = 0.17). Axon and RGC density showed an increased neurodegeneration in CTRL, CTRL IgG and Buffer group (all p < 0.01) and increased neuronal survival in α-synuclein Ab group (p = 0.38 and 0.06, respectively) compared with fellow eyes. Proteomic analysis revealed alterations of cofilin 1 and superoxide dismutase 1 expression. This data indicate that α-synuclein Ab might indirectly modulate the actin cytoskeleton organization and negatively regulate apoptotic processes via cofilin 1 and superoxide dismutase 1.

Revision of encapsulated blebs after trabeculectomy: Long-term comparison of standard bleb needling and modified needling procedure combined with transconjunctival scleral flap sutures.

PURPOSE: To compare two surgical approaches for treating encapsulated blebs after trabeculectomy with mitomycin C, in terms of the development of intraocular pressure and progression of glaucoma in a long-term follow up: 1. bleb needling alone vs. 2. a combined approach of needling with additional transconjunctival scleral flap sutures, to prevent early ocular hypotony. METHODS: Forty-six patients with failing blebs after trabeculectomy with mitomycin C were enrolled in this study. Patients received either needling revision alone (group 1; n = 23) or a combined needling with additional transconjuctival flap sutures, if intraoperatively the intraocular pressure was estimated to be low (group 2; n = 23). Intraocular pressure (IOP), visual acuity, visual fields, and optic nerve head configuration by means of Heidelberg Retina Tomograph (HRT®) were analysed over time. Results from both groups were compared using Mann-Whitney U-test for single timepoints. RESULTS: IOP did not differ significantly between the two groups during follow-up at three months (P = 0.13), six months (P = 0.12), one year (P = 0.92) and two years (P = 0.57) after surgery. Furthermore, there was no significant difference in the course of glaucoma concerning the optic nerve anatomy between the two groups (Rim Area Change in the Moorfields Regression Analysis of HRT®) till two years after surgery (P = 0.289). No functional impairment in visual acuity and visual fields was found in the groups of the study. CONCLUSIONS: Single needling procedure is a standard successful method for restoring the function of encapsulated blebs. Postoperative hypotony represents a possible hazard, which can be minimized by additional transconjunctival flap sutures. Long-term results suggest that this modification is equally effective in lowering the IOP and preventing the progression of glaucoma as the standard needling procedure. To our knowledge this is the first study to investigate the long-term effect of tranconjunctival sutures for the prevention of hypotony.

Biomarkers for glaucoma: from the lab to the clinic.

Glaucoma, a leading cause of irreversible blindness worldwide, is often not diagnosed until many years after disease onset. Early and objective diagnostic measures are yet missing. Besides the main risk factor, an elevated intraocular pressure (IOP), age, sex, and ethnicity are known to affect disease progression and severity. Furthermore, oxidative stress, elevated glutamate concentrations, and an autoimmune component are considered possible risk factors. We could identify several potential proteomic biomarkers in glaucoma and examine distinct changes in the glaucomatous human retina proteome. Using an experimental autoimmune glaucoma animal (EAG) model we could demonstrate an IOP-independent loss of retinal ganglion cells (RGC), which is accompanied by antibody depositions and increased levels of microglia. In a different animal model we showed that intermittent IOP elevations provoke neurodegeneration in the optic nerve and the retina and elicit changes of IgG autoantibody reactivities. The correlation between neuronal damage and changes in autoantibody reactivity suggests that autoantibody profiling could be a useful biomarker for glaucoma. In vivo studies on neuroretinal cells and porcine retinal explants demonstrated a protective effect of antibodies (eg, anti-GFAP) on RGC, which seems to be the result of reduced stress levels in the retina. We conclude that the absence of some autoantibodies in glaucoma patients reflects a loss of the protective potential of natural autoimmunity and may thus encourage neurodegenerative processes. Concluding, autoantibody profiles resemble useful biomarkers for diagnosis, progression and severity of glaucoma. Future longitudinal studies will help to improve early detection and enable better monitoring of disease progression.

Proteomics of Orbital Tissue in Thyroid-Associated Orbitopathy.

CONTEXT: A potentially altered protein expression profile in orbital tissue from patients with thyroid-associated orbitopathy (TAO) is suspected. OBJECTIVE: To detect for the first time changes in proteomic patterns of orbital connective tissue in TAO and compare these with control tissue using mass spectrometry. DESIGN: Proteomics cross-sectional, comparative study. SETTING: Two academic endocrine institutions. SAMPLES: A total of 64 orbital and peripheral adipose tissue samples were collected from 39 patients with TAO and 25 control subjects. METHODS: Samples were analyzed and identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry technology. MAIN OUTCOME MEASURES: Mean intensity values of all identified peptides per protein. RESULTS: Thirty-one proteins were identified, of which 16 differentiated between controls and patients with TAO. Different protein patterns between orbital and peripheral adipose tissue were observed. Compared to controls, 10 proteins were markedly up-regulated (≥ 2-fold) in the orbital tissue of untreated patients: beta IV spectrin (6.2-fold), GTP binding G protein 2 (5.6-fold), POTE ankyrin domain family member F (5.4-fold), xylulokinase (4.1-fold), kinesin family member 1A and lipocalin 1 (both 3.6-fold), semicarbazide-sensitive metalloproteinase amine oxidase 3 and polymerase I transcript release factor (both 3.4-fold), cell-cycle protein elongin A binding protein 1 (3.3-fold), annexin A2 and cavin (both 3-fold), protein pointing to cell proliferation histone H4 (2.8-fold), and ADAM metallopeptidase with thrombospondin type 1 motif 14 (2.7-fold). The highest protein up-regulations were noted in the orbital tissue of medically untreated patients. Steroid therapy markedly reduced up-regulation of these proteins, foremost in nonsmokers. CONCLUSIONS: Proteins involved in tissue inflammation, adipose tissue differentiation, lipid metabolism, and tissue remodeling were up-regulated in orbital tissue of untreated patients with TAO. Steroids decreased the expression of these proteins, whereas smoking attenuated such effect.

[Basic biochemical processes in glaucoma progression]. / Biochemische Grundlagenprozesse im Verlauf der Glaukomerkrankung.

The term glaucoma summarizes a group of eye diseases that are accompanied by impairments of the optic nerve and related visual field deficits. An early diagnosis of glaucoma is currently not possible due to a lack of diagnostic tests; therefore, in most cases the disease is diagnosed many years after onset, which prevents an early therapy. The known risk factors for the development and progression of glaucomatous optic neuropathy comprise elevated intraocular pressure and a broad range of pressure fluctuations as well as lipometabolic disorders, genetic factor and diabetes. The consequences include the induction of anti-inflammatory proteins, elevated levels of oxidative stress and the destruction of retinal ganglion cells. Changes in the autoantibody repertoire have also been observed in the course of the disease. Basic ophthalmological research therefore focuses on the investigation of basic biochemical processes in the course of the disease. A better understanding of physiological and biochemical events is sought in order to develop new and more sensitive diagnostic options and to allow more targeted therapeutic measures. The understanding of biochemical processes allows a better insight into glaucoma progression to be gained, which will lead to improvements in diagnosis and therapy.

[Pharmacokinetics of the anterior eye]. / Pharmakokinetik am vorderen Augenabschnitt.

The pharmacokinetics of the anterior eye comprises the application, resorption, bioavailability, metabolization and elimination of topically administered drugs. In addition to the necessity of the penetration of the substance through the naturally occurring barriers of the eye in the form of the tear film, cornea, conjunctiva and sclera, the correct technique for administration is necessary for an optimal effect of the drug. Several new application devices have been described in the literature but most are still in an experimental phase. The main aims are to increase drug exposure time to the anterior surface of the eye and decrease problems in administration. Furthermore, new preservative agents are in use in order to produce less toxic side effects.

[Autoimmunity and glaucoma]. / Immunreaktionen beim Glaukom.

Glaucoma is one of the most common causes of irreversible blindness worldwide. The pathogenesis of the disease is not fully understood. Elevated intraocular pressure is still considered to be one of the most important risk factors, but cannot explain all cases of glaucoma disease. The involvement of autoimmune mechanisms may play an important role in the pathogenesis of glaucoma. Evidence to support this theory has been shown by our group in previous studies: glaucoma patients were found to develop antibody alterations against specific retina and optic nerve proteins. In the experimental autoimmune glaucoma model, we demonstrated that an immunisation with these proteins causes retinal ganglion cell loss in an autoimmune context. In spite of these results, it is still unclear whether the changes in antibody patterns have a causal connection with glaucoma development or are merely an epiphenomena of the disease. However, these changes in the natural autoimmunity offer a new approach to gain deeper insight into glaucoma pathophysiology and to develop a diagnostic approach for early diagnosis.

Repeated intraocular pressure measurement in awake Lewis rats does not bias retinal ganglion cell survival.

PURPOSE: The TonoPen applanation tonometry is an established method for intraocular pressure (IOP) measurement. The IOP is one of the main variables affecting retinal ganglion cell (RGC) loss in experimental animal models in ophthalmology and the main risk factor for human glaucoma. In this study, we examined if IOP measurements with the TonoPen itself lead to retinal ganglion cell loss or any other possible retina damages, such as intraocular bleedings or ablation, in Lewis rats. METHODS: Three groups of rats (n = 5 each) were formed. IOP monitoring, using a TonoPen XL, was performed on groups 1 and 3. Animals in groups 1 and 2 received funduscopies before and after one and two weeks of the study, in order to detect possible abnormalities. After two weeks, retinal flatmounts were stained to detect ganglion cells. RGCs were manually counted in eight predefined areas to compare mean RGC densities between groups 1 and 2 (IOP readings vs. no readings), using student t-test. RESULTS: No significant difference in RGC density between animals that underwent IOP readings and controls could be observed (p = 0.8). As expected, no IOP alterations were monitored in groups 1 and 3 throughout the study. No retinal abnormalities, such as bleeding or retina ablation, were detectable. CONCLUSION: We could detect no effects on retinal ganglion cell survival in Lewis rats or any other damages to the retina caused by IOP measurements using a TonoPen XL. This study proposes that repeated applanation tonometry does not affect RGC numbers, one of the main monitored variables in most glaucoma model studies. Therefore, the use of a TonoPen XL for repeated IOP monitoring in Lewis rats can be considered harmless.

Enhanced characterization of serum autoantibody reactivity following HSP 60 immunization in a rat model of experimental autoimmune glaucoma.

PURPOSE: Antibodies against heat shock proteins have been identified in sera of human glaucoma patients in several studies and immunization with heat shock protein 60 (HSP 60) causes retinal ganglion cell (RGC) loss in an animal model of experimental autoimmune glaucoma. The aim of this study was to observe the time course of increased anti-retina antibody appearance in the serum and characterize the identification of prominent autoantibodies that accompany HSP 60 immunization in a rat model of experimental autoimmune glaucoma. METHODS: Eight weeks after immunization with HSP 60 retinal flatmounts were prepared and RGCs were counted in eight predefined areas and compared to controls. Serum collected before, as well as four and eight weeks after, immunization was used to detect antibody patterns against bovine retinal antigens using Western blotting techniques. These patterns were analyzed by multivariate statistical methods. Autoantibodies that were prominently increased were further identified through mass spectrometry. Intraocular pressure was measured throughout the study. RESULTS: After eight weeks, animals immunized with HSP 60 showed significant RGC loss of retinal flatmounts (P = 0.02), which was intraocular pressure independent. Early changes in antibody profiles, many of them significant upregulations, were detected. Antigens with significantly upregulated antibody reactivity after four weeks were identified as histone H2B type 1, S-arrestin, glial fibrillary acidic protein, vimentin, and heat shock protein 60. These upregulated autoantibodies returned to normal levels four weeks following their initial upregulation. Antibodies against retinaldehyde binding protein 1 on the other hand became upregulated after eight weeks. CONCLUSION: This is the first study to identify the appearance and disappearance of retinal autoantibodies in the serum of rats at several time-points following their initial upregulation in response to HSP 60 immunization in a model of experimental autoimmune glaucoma.

[Relationship between oxidatve stress and autoimmunity in glaucoma]. / Zusammenhang zwischen oxidativem Stress und immunologischen Störungen beim Glaukom.

Elevated intraocular pressure does not explain glaucoma in all patients, but there is information that autoimmune mechanisms may be involved in this disorder. We have demonstrated in several studies that glaucoma patients reveal changes in their immune reactivities against ocular antigens. The mechanisms of these reactivities are still widely unknown, but oxidative pathways could play a major role. There is evidence that free radicals are able to alter the ability of glial cells to be recognized as antigens. Furthermore, one can assume that during the aging process posttranslational changes, e. g., oxidation of ocular antigens increase with age. It is feasible that these changed antigens may trigger such changes. in an autoimmune glaucoma animal model we have shown that immunological processes after immunisation can lead to a loss of retinal ganglion cells. Considering that these changes in natural autoimmunity can be found consistently amongst different study populations, it might be a promising new tool for glaucoma diagnosis and new therapeutic immunomodulating options.

Proteomics in autoimmune thyroid eye disease.

Ocular and systemic autoimmune diseases impair the proteome patterns of tear fluid. To learn more about the complex pathological processes in autoimmune thyroid eye disease (TED) it is essential to get detailed information on these proteins. Therefore, the purpose of this prospective and controlled study was to detect and evaluate possible changes in the proteomic patterns in tear fluid of patients with TED. Tear samples from TED patients with various disease severity and activity, and healthy controls were analyzed with the SELDI-TOF-MS-technology using arrays with different chromatographic surfaces (CM10 cation exchange, H50 reversed-phase). Data were analyzed by multivariate statistical techniques and artificial neural networks. The discriminate analysis revealed significant changes (p<0.05) in the protein profiles of TED patients compared to controls. We obtained a set of protein biomarkers that allowed us to clearly discriminate between patients and controls with a very high sensitivity and specificity (ROC curve, r=0.99). All possible biomarkers found in this study had a molecular weight between 3000 and 20,000 Da. The majority of the proteins was downregulated in the patient group, with only few proteins overexpressed in comparison to healthy controls. The SELDI-TOF-MS is an accurate method for proteome analysis in tear fluid of TED patients. These proteins may serve as biomarkers for diagnosis and follow-up during treatment.

Transthyretin and complex protein pattern in aqueous humor of patients with primary open-angle glaucoma.

PURPOSE: To analyze protein patterns in the aqueous humor of glaucoma patients in comparison to control subject using two different methods. METHODS: Aqueous humor was collected from 52 patients with primary open-angle glaucoma (POAG) and from 55 control subjects (CO). Twenty-two POAG samples and 24 CO samples were used for protein profiling through surface enhanced laser desorption/ionization-time of flight-mass spectrometry (SELDI-TOF-MS) ProteinChip arrays. The data were analyzed by multivariate statistical methods and artificial neural networks. One highly significant biomarker was identified through matrix assisted laser desorption/ionisation time of flight-mass spectrometry (MALDI-TOF). Thirty samples from patients with POAG and 31 control samples were analyzed through two-dimensional electrophoresis. Subsequently, the protein spots of all gels were detected, and the two groups were compared. One spot group exhibiting clear differential abundance was identified by mass spectrometry (electrospray ionization mass spectrometry). RESULTS: In the samples analyzed by SELDI-TOF-MS, about 250 protein peaks could be consistently clustered in both groups. The analyses revealed eight biomarkers, which discriminated glaucoma from non-glaucoma controls with a sensitivity of 90% and a specificity of 87%. These biomarkers were purified further, and one marker, which was upregulated in glaucoma patients (p=0.006), was identified as transthyretin. The upregulation of transthyretin in POAG patients was also confirmed by enzyme linked immunosorbent assay (ELISA; p=0.03). In all samples analyzed by two-dimensional electrophoresis, complex protein patterns were detected in a total of 177 spot groups. The aqueous humor of all glaucoma patients revealed some regions that were clearly different from the controls. Several spots were significantly increased in the aqueous humor of glaucoma patients. One of the proteins that is highly abundant in the aqueous of glaucoma patients was identified as transthyretin. CONCLUSIONS: The aqueous humor of glaucoma patients revealed characteristic differences in protein/peptide profiles from control patients using two different analytical methods, SELDI-TOF-MS and two-dimensional electrophoresis. Interestingly, we could detect elevated transthyretin concentrations in glaucoma samples. Transthyretin might play a role in the onset of glaucoma since it has been shown to form amyloid deposits. These particles could cause outflow obstructions thereby increasing intraocular pressure as a possible onset mechanism.

[Legal regulations to produce serum eye drops : when is it necessary, and how can it be obtained?]. / Arzneimittelrechtliche Erlaubnis bei der Herstellung von Serum-Augentropfen : Wann ist sie erforderlich und wie kann sie umgesetzt werden?*

According to European Union and German legislation, the production of medicines such as eye drops from autologous serum requires a license from an appropriate authority. However, an exemption is granted to medical doctors who produce and apply medications under their immediate responsibility. If doctors do not actually produce such medications themselves, they must select appropriate personnel to do so. These individuals have to be sufficiently qualified and reliable and must be carefully instructed on the standard quality and manufacturing procedures, although the doctors are responsible for controlling the production and quality of the final product. The treating physicians are also responsible for the appropriate application of the produced medications. To dispense medication to patients without an appropriate license is considered a criminal offense. We describe how two German hospitals have established the production of serum eye drops in full compliance with legal regulations.

Immunological mechanisms in glaucoma.

Glaucoma is one of the most frequent causes of blindness worldwide. The elevated intraocular pressure does not explain glaucoma in all patients but can be considered as a risk factor of the disease. There are some evidences that autoimmune mechanisms may be involved in this disorder. This review attempts to demonstrate the findings about autoimmune mechanisms in glaucoma patients. Consistent up- and down-regulations in the autoantibody profiles against ocular antigens are present in glaucoma patients. These changes in natural autoimmunity could be found in independent study populations and might be a promising tool for glaucoma detection.

Glaucoma detection using the GDx nerve fiber analyzer and the retinal thickness analyzer (RTA).

PURPOSE: To compare the ability of the nerve fiber analyzer (GDx) and the retinal thickness analyzer (RTA) to discriminate between glaucomatous and healthy eyes. METHODS: Thirty-seven glaucoma patients (early to moderate severity) and 34 healthy controls were included. Glaucoma patients were defined as those with two repeatable abnormal visual fields by automated perimetry within 1 year. All subjects were examined with a GDx scanning laser polarimeter and RTA. Twelve GDx retinal nerve fiber layer parameters and 12 RTA optic disk topography parameters were obtained. GDx and RTA measurements were compared between both experimental groups using t-tests. Areas under the receiver operating characteristic curves (AUROC) for discriminating between healthy and glaucomatous eyes using GDx and RTA parameters were calculated and compared, and sensitivities at >or=80% and >or=95% specificity were reported. RESULTS: Statistically significant differences between glaucomatous and healthy eyes were found for most GDx and RTA parameters. For GDx, the parameter with the largest AUROC for discriminating between healthy and glaucomatous eyes was the number (AUROC = 0.91, sensitivity = 85% at specificity = 84%, sensitivity = 73% at specificity = 95%). For RTA, the parameter with the largest AUROC was mean cup depth (AUROC = 0.79, sensitivity = 61% at specificity = 82%, sensitivity = 33% at specificity = 95%). The AUROC for the GDx number was significantly larger than the AUROC for RTA mean cup depth (p<0.05). CONCLUSIONS: GDx showed better discrimination and better sensitivities at fixed specificities than RTA. The currently available RTA optic disk analysis software likely cannot replace GDx RNFL analysis software for successful glaucoma diagnosis.

[Goldmann applanation tonometry and dynamic contour tonometry. Comparison of intraocular pressure measurements in the course of product certification according to EN ISO 8612:2001]. / Goldmann-Applanationstonometrie und dynamische Konturtonometrie. Vergleich der intraokularen Druckmessung im Rahmen einer Typprüfung nach EN ISO 8612:2001.

BACKGROUND: The aim of the study was to compare intraocular pressure (IOP) measurements between Goldmann applanation tonometry (GAT) and dynamic contour tonometry (DCT) during product certification according to the international requirements for ophthalmic instruments (tonometers, ISO 8612:2001). METHODS: The study included 160 eyes of 80 subjects. IOP measurements were performed four times consecutively on each instrument in randomized order. The difference of mean IOP measurements between GAT and DCT was analyzed. Furthermore, Bland and Altman analysis was performed to assess agreement between the instruments. RESULTS: The mean difference between DCT and GAT IOP measurements was 0.30+/-2.18 mmHg. At low to normal IOP values of 7-16 mmHg and higher IOP values of > or =23 mmHg, the difference between DCT IOP measurements and GAT IOP measurements increased in the opposite direction (1.44+/-1.59 mmHg and -1.47+/-2.57 mmHg). The Bland and Altman analysis revealed a fixed bias of -0.4+/-2.0 mmHg. CONCLUSIONS: The test tonometer DCT exceeds the requirements for the international standard for tonometers ISO 8612:2001. The results are valid for a central corneal thickness of 540+/-40 microm.