[Chromatic Swept-Source Laser Scanning - Concept for a Cell-Resolving Confocal Laser Slit Lamp?] / Chromatic Swept-Source Laser Scanning ­ Konzept für eine zellauflösende konfokale Laserspaltlampe?

BACKGROUND: The in vivo characterisation of corneal epithelial tissue morphology is of considerable importance for diagnosis, disease prognosis, and the development of a treatment strategy for ocular surface diseases. In contrast to many alternative methods, in vivo corneal confocal microscopy (CCM) not only provides a macroscopic description of the corneal tissue but also allows its visualisation with cellular resolution. However, the translation of CCM from research to clinical practice is significantly limited by the complex and still largely manual operation of available CCM systems. In addition, for cross-sectional images, and analogously to conventional slit lamp microscopy, volume data must be acquired in time-consuming depth scans due to the frontal orientation of the image field in CCM, from which depth slices can subsequently be calculated. The pure acquisition time is already in the range of seconds, and additionally, motion artefacts have to be corrected in a sophisticated way. MATERIALS AND METHODS: This paper presents the concept and optics simulation of a new imaging technique based on a swept-source laser in combination with special chromatic optics. Here, the laser periodically changes its wavelength and is focused at different depths due to the wavelength-dependent aberration of the chromatic optics. RESULTS: The optics simulation results promise good optical resolution at a total imaging depth of 145 µm. CONCLUSION: The long-term goal is cell-resolving in vivo corneal confocal microscopy in real time with differently oriented sectioning directions.

Techniques for In Vivo Assessment of Corneal Biomechanics: Brillouin Spectroscopy and Hydration State - Quo Vadis? / Technologien zur In-vivo-Untersuchung der Biomechanik der Hornhaut: Brillouin-Spektroskopie und Hydratationszustand ­ quo vadis?

To assess the structural integrity of the cornea, non-invasive methods are needed for the local measurement of its mechanical properties. Among a number of established techniques and their associated advantages and disadvantages, Brillouin spectroscopy is still a relatively new technique, capable of determining the compressive modulus of biological tissue, specifically the cornea, in vivo. In the present paper, these various existing and developing technologies for corneal biomechanics are discussed and correlated.

Retinal and Choroidal Ultra-Widefield OCT - Technology, Insights, and Clinical Relevance. / Retinale und choroidale Ultra-Weitwinkel-OCT ­ Technologie, Einblicke und klinische Bedeutung.

As one of the most state-of-the-art procedures for retinal and choroidal imaging, ultra-widefield optical coherence tomography (UWF-OCT) offers significant gains in terms of information pertaining to peripheral retinal lesions and their differential diagnoses. In particular, it enables the presence of minimal accumulations of subretinal fluid to be assessed in detail and then documented. It also enables choroidal expansion of choroidal lesions to be precisely measured. Similar to conventional OCT, its only limitations relate to patient compliance and opacities of the ocular media. While the pupil width is somewhat less important here, the quality of the images is nevertheless better with the patient under medication-induced mydriasis. Used in combination with UWF fundus photography, UWF-OCT is a helpful tool for assessing and monitoring peripheral retinal and choroidal lesions.

The Rostock Method for Qualitative and Quantitative Evaluation of Intraocular Lenses. / Die Rostocker Methode zur qualitativen und quantitativen Bewertung von Intraokularlinsen.

BACKGROUND: For quantitative and qualitative evaluation of the imaging properties of IOLs, axial cross-sectional images can be obtained from the 3-dimensional light distribution by means of an optical bench, as is known from light sheet recordings in fluorescein baths. This paper presents a new image-processing algorithm to enhance the quality of generated axial cross-sectional images, and the two methods are then compared. MATERIAL AND METHODS: The 3-dimensional point spread function of a diffractive trifocal IOL (AT LISA tri 839MP, Carl Zeiss Meditec AG, Jena, Germany) was recorded on an optical bench developed in Rostock for different pupil diameters. A specially adapted image processing algorithm was then applied to the measurements, allowing through-focus curves to be generated. In addition, cross-sectional images of the IOLs studied were acquired using the light sheet method in a fluorescein bath. RESULTS: The study clearly shows the superiority of the newly developed method over the light sheet method in terms of image quality. In addition to the individual focal points, fine focal structures as well as halos can be made visible in the cross-sectional images obtained using the new method. In the generated through-focus curves, 3 intensity peaks can be identified, which represent the near, intermediate and far focus of the tested MIOL and cannot be represented by light sheet methods. CONCLUSION: The interaction of the optical bench with the developed image processing algorithm allows a more detailed understanding of the image formation and false light phenomena of IOLs, which was restricted by the technical limitations of the existing light sheet method. In addition, other quantities such as the through-focus curve can be derived quantitatively.

Optical Technologies, Digitally Assisted: Surgical Microscope - quo vadis? / Optische Technologien, digital unterstützt: Operationsmikroskop ­ quo vadis?

Adequate magnification and proper illumination are crucial for success in microsurgical interventions. Thus, surgical microscopes have long been an integral part of modern eye surgery and are at the heart of modern operating theatres. This paper first briefly reviews the history microscopes in ophthalmic surgery - from the initial developments in the mid 19th century to the current state of the art systems with powerful coaxial illumination and fibre-guided xenon or LED light sources. The discussion then turns to current developments, particularly in the area of workflow support and integration of complementary technologies such as intraoperative OCT, "augmented reality", and visual data feeds useful to the surgeon. The last part presents an outlook on future developments, with a particular focus on the digital image chain and intelligent automated assistance.

Cataract surgery in Kinshasa-Is there a place for "Monovision"?

OBJECTIVES: Monovision is a method of correcting presbyopia where one eye is focused for far and the other for near vision. It is a simple, cost-effective approach to overcome the loss of accommodation with age and to become spectacles independent. METHODOLOGY: About 50 patients, where bilateral cataract extraction was indicated, were included in this study performed at the St. Joseph's Eye Hospital in Kinshasa (DR Congo). Small incision cataract surgery technique (SICS) was applied with the implantation of 6 mm PMMA lenses in the capsular bag. IOL refractive power choice was made to achieve a post-operative refraction of -0.5 dpt for the eye selected for far vision. The second eye received an implant heading for a post-operative myopia of -1.5 dpt suitable for intermediated and near vision. According to the literature, monovision criteria have been regarded as fulfilled when (a) far vision was 0.5 (logMAR) or better and (b) near vision was P3 (0.40, Decimal 32 cm) or better. Spectacle dependence after bilateral cataract surgery heading for monovision was analysed using a dedicated questionnaire. RESULTS: Out of all 50 patients 22 (44%) fulfilled the above defined criteria of monovision in terms of post-operative refraction and visual acuity. About 19 out of these 22 (86.3%) patients were happy without glasses. Two of them used bifocal spectacles, whereas the remaining patient refused spectacles. About 28 patients did not fulfill monovision criteria. Out of these 28 patients, however, 9 (32.1%) of them are happy without glasses. CONCLUSION: In view of the described local circumstances aiming for monovision after bilateral cataract surgery is a suitable approach to optimise cataract surgical outcomes with no extra costs for surgery but considerable improvement of patient's visual performance in daily life.

In vivo Histology of the Cornea - from the "Rostock Cornea Module" to the "Rostock Electronic Slit Lamp" - a Clinical "Proof of Concept" Study. / In-vivo-Histologie der Hornhaut ­ vom "Rostocker Cornea Modul" zur "Rostocker Elektronischen Spaltlampe" ­ eine klinische "Proof-of-Concept"-Studie.

INTRODUCTION: Confocal in vivo microscopy is an established method in ophthalmology research. As it requires contact coupling and calibration of the instruments is suboptimal, this method has been only rarely used in clinical routine work. As a result of close collaboration between physicists, information scientists and ophthalmologists, confocal laser scanning microscopy (CLSM) of the eye has been developed in recent years and a prototype can now be used in patients. The present study evaluates possible clinical uses of this method. MATERIAL AND METHODS: The essential innovations in CLSM are (1) a newly designed coupling element with superficial adaptation to corneal curvature and (2) the use of a dual computerised piezo drive for rapid and precise focusing. In post-processing and after elastic imaging registration of the individual images parallel to the surface, it is also possible to produce sagittal sections resembling a split lamp and with resolution in the micrometer range. The concept was tested on enucleated pig bulbi and tested on normal volunteers and selected patients with diseases of the cornea. RESULTS: Simultaneous imaging in planes parallel to the surface and in sagittal planes provided additional information that can help us to understand the processes of wound healing in all substructures of the cornea and the role of immune competent cells. Possible clinical uses were demonstrated in a volunteer with healthy eyes and several groups of patients (keratoconus after CXL, recurrent keratitis, status after PRK). These show that this new approach can be used in morphological studies at cellular level in any desired and appropriate test plane. CONCLUSIONS: It could be shown that this new concept of CLSM can be used clinically. It can provide valuable and novel information to both preclinical researchers and to ophthalmologists interested in corneal disease, e.g. density of Langerhans cells and epithelial stratification in ocular surface diseases.

[Systems Biology in Ophthalmology - Innovative Drug Identification for the Specific Prevention of Postoperative Fibrosis]. / Systembiologie in der Ophthalmologie ­ innovative Wirkstoffidentifikation zur spezifischen Vermeidung postoperativer Fibrose.

BACKGROUND: The long-term success of fistulating therapies for the treatment of glaucoma is essentially limited by excessive scarring reactions (fibrosis). Cytostatic agents such as mitomycin C can prevent fibrosis, but are often associated with side effects. Specific antifibrotics are not currently in clinical use. Therefore, this study describes a systems biology approach using a dedicated bioinformatics technology platform, with which active substances can be identified and repositioned as antifibrotics. MATERIALS AND METHODS: Differential gene expression data of human Tenon fibroblasts (hTF) were collected from untreated hTF and from hTF stimulated with TGF-ß1 ("fibrotic fibroblasts") by next-generation sequencing (NGS) and were used as the basis for the drug identification process. These data were filtered with the bioinformatic tool "FocusHeuristics". In comparison with the Connectivity Map database, antifibrotic agents were identified. The evaluation of a potentially promising drug as an antifibrotic was performed at hTF by indirect immunofluorescence in vitro. RESULTS: The analysis of the gene expression data led to the identification of several interaction networks of genes or proteins involved in fibrotic processes. One of these networks contains the cytokine bone morphogenic protein 6 (BMP6), interleukin 6 (IL6) and fibroblast growth factor 1 (FGF1). Another relevant network has been identified around the cluster of differentiation 34 (CD34) gene. The comparison of these data with those of the Connectivity Map allowed the identification of an inhibitory drug. Its evaluation in the fibrotic cell culture model in vitro using indirect immunofluorescence led to a significant reduction in the expression of the fibrotic marker proteins fibronectin and alpha-smooth muscle actin (α-SMA), which confirmed the predicted antifibrotic effect. CONCLUSION: Systems biological approaches can be used for the identification of antifibrotic drug candidates for the prevention of postoperative fibrosis and should be transferable by the investigating differential gene expression data of further ocular cells or tissues to other ophthalmological fields of application.

[Digital Image Processing and Deep Neural Networks in Ophthalmology - Current Trends]. / Digitale Bildverarbeitung und Tiefe Neuronale Netze in der Augenheilkunde ­ aktuelle Trends.

The use of deep neural networks ("deep learning") creates new possibilities in digital image processing. This approach has been widely applied and successfully used for the evaluation of image data in ophthalmology. In this article, the methodological approach of deep learning is examined and compared to the classical approach for digital image processing. The differences between the approaches are discussed and the increasingly important role of training data for model generation is explained. Furthermore, the approach of transfer learning for deep learning is presented with a representative data set from the field of corneal confocal microscopy. In this context, the advantages of the method and the specific problems when dealing with medical microscope data will be discussed.

Millimeter spatial resolution in vivo sodium MRI of the human eye at 7 T using a dedicated radiofrequency transceiver array.

PURPOSE: The aim of this study was to achieve millimeter spatial resolution sodium in vivo MRI of the human eye at 7 T using a dedicated six-channel transceiver array. We present a detailed description of the radiofrequency coil design, along with electromagnetic field and specific absorption ratio simulations, data validation, and in vivo application. METHODS: Electromagnetic field and specific absorption ratio simulations were performed. Transmit field uniformity was optimized by using a multi-objective genetic algorithm. Transmit field mapping was conducted using a phase-sensitive method. An in vivo feasibility study was carried out with 3-dimensional density-adapted projection reconstruction imaging technique. RESULTS: Measured transmit field distribution agrees well with the one obtained from simulations. The specific absorption ratio simulations confirm that the radiofrequency coil is safe for clinical use. Our radiofrequency coil is light and conforms to an average human head. High spatial resolution (nominal 1.4 and 1.0 mm isotropic) sodium in vivo images of the human eye were acquired within scan times suitable for clinical applications (∼ 10 min). CONCLUSIONS: Three most important eye compartments in the context of sodium physiology were clearly delineated in all of the images: the vitreous humor, the aqueous humor, and the lens. Our results provide encouragement for further clinical studies. The implications for research into eye diseases including ocular melanoma, cataract, and glaucoma are discussed. Magn Reson Med 80:672-684, 2018. © 2018 International Society for Magnetic Resonance in Medicine.

Multiband diffusion-weighted MRI of the eye and orbit free of geometric distortions using a RARE-EPI hybrid.

Diffusion-weighted imaging (DWI) provides information on tissue microstructure. Single-shot echo planar imaging (EPI) is the most common technique for DWI applications in the brain, but is prone to geometric distortions and signal voids. Rapid acquisition with relaxation enhancement [RARE, also known as fast spin echo (FSE)] imaging presents a valuable alternative to DWI with high anatomical accuracy. This work proposes a multi-shot diffusion-weighted RARE-EPI hybrid pulse sequence, combining the anatomical integrity of RARE with the imaging speed and radiofrequency (RF) power deposition advantage of EPI. The anatomical integrity of RARE-EPI was demonstrated and quantified by center of gravity analysis for both morphological images and diffusion-weighted acquisitions in phantom and in vivo experiments at 3.0 T and 7.0 T. The results indicate that half of the RARE echoes in the echo train can be replaced by EPI echoes whilst maintaining anatomical accuracy. The reduced RF power deposition of RARE-EPI enabled multiband RF pulses facilitating simultaneous multi-slice imaging. This study shows that diffusion-weighted RARE-EPI has the capability to acquire high fidelity, distortion-free images of the eye and the orbit. It is shown that RARE-EPI maintains the immunity to B0 inhomogeneities reported for RARE imaging. This benefit can be exploited for the assessment of ocular masses and pathological changes of the eye and the orbit.

Role of Corneal Stromal Cells on Epithelial Cell Function during Wound Healing.

Following injury, corneal stromal keratocytes transform into repair-phenotype of activated stromal fibroblasts (SFs) and participate in wound repair. Simultaneously, ongoing bi-directional communications between corneal stromal-epithelial cells also play a vital role in mediating the process of wound healing. Factors produced by stromal cells are known to induce proliferation, differentiation, and motility of corneal epithelial cells, which are also subsequently the main processes that occur during wound healing. In this context, the present study aims to investigate the effect of SFs conditioned medium (SFCM) on corneal epithelial cell function along with substance P (SP). Antibody microarrays were employed to profile differentially expressed cell surface markers and cytokines in the presence of SFCM and SP. Antibody microarray data revealed enhanced expression of the ITGB1 in corneal epithelial cells following stimulation with SP whereas SFCM induced abundant expression of IL-8, ITGB1, PD1L1, PECA1, IL-15, BDNF, ICAM1, CD8A, CD44 and NTF4. All these proteins have either direct or indirect roles in epithelial cell growth, movement and adhesion related signaling cascades during tissue regeneration. We also observed activation of MAPK signaling pathway along with increased expression of focal adhesion kinase (FAK), paxillin, vimentin, ß-catenin and vasodilator-stimulated phosphoprotein (VASP) phosphorylation. Additionally, epithelial-to-mesenchymal transition (EMT) regulating transcription factors Slug and ZEB1 expression were enhanced in the presence of SFCM. SP enriched the expression of integrin subunits α4, α5, αV, ß1 and ß3 whereas SFCM increased α4, α5, αV, ß1 and ß5 integrin subunits. We also observed increased expression of Serpin E1 following SP and SFCM treatment. Wound healing scratch assay revealed enhanced migration of epithelial cells following the addition of SFCM. Taken together, we conclude that SFCM-mediated sustained activation of ZEB1, Slug in combination with upregulated migration-associated integrins and ERK (Extracellular signal-regulated kinase)-FAK-paxillin axis, may lead to induce type 2 EMT-like changes during corneal epithelial wound healing.

Role of Bone Morphogenetic Protein 7 (BMP7) in the Modulation of Corneal Stromal and Epithelial Cell Functions.

In the cornea, healing of the wounded avascular surface is an intricate process comprising the involvement of epithelial, stromal and neuronal cell interactions. These interactions result to the release of various growth factors that play prominent roles during corneal wound healing response. Bone morphogenetic proteins (BMPs) are unique multi-functional potent growth factors of the transforming growth factor-beta (TGF-β) superfamily. Treatment of corneal epithelial cells with substance P and nerve growth factor resulted to an increase in the expression of BMP7 mRNA. Since BMP7 is known to modulate the process of corneal wound healing, in this present study, we investigated the influence of exogenous rhBMP7 on human corneal epithelial cell and stromal cell (SFs) function. To obtain a high-fidelity expression profiling of activated biomarkers and pathways, transcriptome-wide gene-level expression profiling of epithelial cells in the presence of BMP7 was performed. Gene ontology analysis shows BMP7 stimulation activated TGF-β signaling and cell cycle pathways, whereas biological processes related to cell cycle, microtubule and intermediate filament cytoskeleton organization were significantly impacted in corneal epithelial cells. Scratch wound healing assay showed increased motility and migration of BMP7 treated epithelial cells. BMP7 stimulation studies show activation of MAPK cascade proteins in epithelial cells and SFs. Similarly, a difference in the expression of claudin, Zink finger E-box-binding homeobox 1 was observed along with phosphorylation levels of cofilin in epithelial cells. Stimulation of SFs with BMP7 activated them with increased expression of α-smooth muscle actin. In addition, an elevated phosphorylation of epidermal growth factor receptor following BMP7 stimulation was also observed both in corneal epithelial cells and SFs. Based on our transcriptome analysis data on epithelial cells and the results obtained in SFs, we conclude that BMP7 contributes to epithelial-to-mesenchymal transition-like responses and plays a role equivalent to TGF-β in the course of corneal wound healing.

[Pre-clinical Evaluation of Intraocular Lenses through Simulated Implantation]. / Präklinische Bewertung von Intraokularlinsen durch simulierte Implantation.

The development of new optical designs for intraocular lenses (IOL) is a major challenge for lens manufacturers, as postoperative patient satisfaction is difficult to assess a priori with new concepts. Until now, invasive clinical investigations were carried out for this purpose. In contrast, the simulated implantation of IOLs allows a risk-free determination of the achievable visual performance and a subjective evaluation of the visual impression of new optical concepts. For intraocular lens manufacturers, this offers, on the one hand, the possibility to take the subjective perception of test persons into account during the development and optimization of novel lens designs and, on the other hand, to carry out comparative performance tests with known products before the first implantation. By means of simulated implantation, subjectively optimized IOLs may lead to a better postoperative visual quality for the patients and minimize the risk of a cost-intensive development of products with clinically unacceptable visual perception achievements due to optical side effects. The application of the simulated implantation during the preoperative patient consultation may enable the determination of the patient's subjective visual preferences and result in a targeted IOL selection recommendation. In addition to an improved selection from an existing IOL portfolio, IOL manufacturers could also offer individualized multifocal IOLs that match the patient's previous preference pattern. This article explains the technical background and application scenarios of the simulated implantation and introduces current procedures and devices.

Magnetic resonance safety and compatibility of tantalum markers used in proton beam therapy for intraocular tumors: A 7.0 Tesla study.

PURPOSE: Proton radiation therapy (PRT) is a standard treatment of uveal melanoma. PRT patients undergo implantation of ocular tantalum markers (OTMs) for treatment planning. Ultra-high-field MRI is a promising technique for 3D tumor visualization and PRT planning. This work examines MR safety and compatibility of OTMs at 7.0 Tesla. METHODS: MR safety assessment included deflection angle measurements (DAMs), electromagnetic field (EMF) simulations for specific absorption rate (SAR) estimation, and temperature simulations for examining radiofrequency heating using a bow-tie dipole antenna for transmission. MR compatibility was assessed by susceptibility artifacts in agarose, ex vivo pig eyes, and in an ex vivo tumor eye using gradient echo and fast spin-echo imaging. RESULTS: DAM (α < 1 °) demonstrated no risk attributed to magnetically induced OTM deflection. EMF simulations showed that an OTM can be approximated by a disk, demonstrated the need for averaging masses of mave = 0.01 g to accommodate the OTM, and provided SAR0.01g,maximum = 2.64 W/kg (Pin = 1W) in OTM presence. A transfer function was derived, enabling SAR0.01g estimation for individual patient scenarios without the OTM being integrated. Thermal simulations revealed minor OTM-related temperature increase (δT < 15 mK). Susceptibility artifact size (<8 mm) and location suggest no restrictions for MRI of the nervus opticus. CONCLUSION: OTMs are not a per se contraindication for MRI. Magn Reson Med 78:1533-1546, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

[Measurement of the Strength of Human Musculus Orbicularis Oculi Using Video Analysis]. / Messaufbau zur videoanalysebasierten Bestimmung der Lidschlusskraft des humanen Musculus orbicularis oculi.

Introduction Current methods to measure the of strength of the musculus orbicularis oculi are limited by high proneness to examiner error or by their complex and impracticable set-ups. Our aim was to develop a simple and practicable method to measure eye lid power via video analysis. Methods 50 healthy subjects were included. A deformable single use lid speculum was used. Forced maximum lid closure was recorded via a video slit lamp. Analysis of the video data was performed with open source tracking software. The maximum and minimum distances of the inserted lid speculum were detected. The rigidity and mechanical characteristics of the lid speculum were tested separately. In this way, lid power could be determined by analysis of the maximum compression of the lid speculum. To explore the impact of age and sex on eye lid power, Pearson's correlation coefficient was evaluated. ICC (intra class correlation) was analysed as a measure of reliability. Results In three repeated measurements in 9 subjects, an ICC of α = 0.91 was detected. With 50 healthy subjects, the range of lid power was 0.62 - 4.72 N. No correlation was found between the age of the subjects and eyelid power (Pearson's correlation coefficient = 0.054). A weak correlation was found between the sex of the subjects and eyelid power. For female subjects, the mean power was 1.82 N and for male subjects 2.58 N (Pearson's correlation coefficient = 0.428). Discussion A test series of 50 healthy subjects exhibited a wide range of lid power. The wide range makes it difficult to distinguish between pathological and normal eyelid power. The major application field of the method may therefore be in inner-individual measurements of known eyelid pathologies, such as paresis of the facial nerve or ocular myasthenia.

[Visual Analysis of Retinal OCT Data]. / Visuelle Analyse von retinalen OCT-Daten.

Optical coherence tomography (OCT) enables noninvasive high-resolution 3D imaging of the human retina, and thus plays a fundamental role in ophthalmology. Via OCT examination, even subtle retinal changes can be captured, which occur in very early stages of different diseases (e.g., glaucoma, diabetes mellitus, or age-related macular degeneration). Yet, analyzing the resulting data is challenging. Conventionally, OCT data are strongly aggregated via automated methods. While this reduces the amount of information to be analyzed, it also makes it difficult, if not impossible, to identify small and localized retinal changes. This might lead to wrong diagnoses, since these methods do not account for patient-specific characteristics. We address this problem by providing new and efficient visual-interactive methods. Particularly, we introduce dedicated visualizations that show different aspects of the data. In addition, we support patient-specific selections of relevant data regions. Selected regions are emphasized, or separately visualized to inspect retinal substructures in detail. By visually comparing the regions to reference data, even very small retinal changes can be detected. We demonstrate the utility of our approach by applying it to data of a study with pediatric patients suffering from diabetes mellitus type 1. Our results show that visual-interactive methods indeed help to analyze subtle retinal changes and, thus, support the diagnosis of diseases in an early stage.

[Effect of the Age-Related Corneal Elasticity on Applanation Tonometry]. / Auswirkungen des altersbezogenen kornealen Elastizitätsmoduls auf die Applanationstonometrie.

Elevated intraocular pressure (IOP) is accepted to be one important criterion for glaucoma and is usually measured by applanation or rebound tonometry. The individual uncertainty due to central cornea thickness (CCT) is thereby corrected, while the error induced by age-related elastic modulus (EM) change of the cornea is ignored. To investigate its influence on IOP measurement, we derive a model including also the elastic modulus. Our approach is based on known equations from experimental physics and several assumptions being justified in this paper. Our correction values are in good agreement with the Dresden correction table for low CCT values up to 650 µm using a mean EM of 0.29 MPa. An EM variation from 0.2 to 0.5 MPa, which relates to ages from infancy to 90 years, results in an IOP error of up to 10 mmHg. A variation of the cornea curvature from 7.4 mm to 8.0 mm results in a total IOP change of about 3 mmHg, which is usually neglected. The derived model shows that established correction formulas can be insufficient for a reliable IOP determination. In many cases, the conventionally measured IOP may be precise enough, but the uncertainty in IOP determination due to CCT and EM influence are almost in the same range. Measuring the IOP using applanation methods with established correction formulas should not be overestimated without to respect the EM of the cornea.