Ralph Michael

Ralph Michael
Centro de Oftalmologia Barraquer

About

100
Publications
10,334
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2,334
Citations
Citations since 2016
28 Research Items
1247 Citations
2016201720182019202020212022050100150200
2016201720182019202020212022050100150200
2016201720182019202020212022050100150200
2016201720182019202020212022050100150200

Publications

Publications (100)
Article
Full-text available
Soemmerring’s rings consist of a ring of lens epithelial derived cells that grow along the periphery of an aphakic lens capsule, or around an intraocular lens. These rings when visualized frontally, appear opaque, however, in some cases the cells that compose these rings are organized in the same fashion as those in normal transparent adult lenses....
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Purpose: To evaluate ocular biometry in a large paediatric population as a function of age and sex in children of European descent. Methods: Children were examined as part of the LIFE Child Study (Leipzig Research Centre for Civilization Disease), a population-based study in Leipzig, Germany. Altogether, 1907 children, aged from 4 to 17 years, w...
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Purpose To identify the causes of failure of the different surgical corneal graft techniques: penetrating keratoplasty (PK), deep anterior lamellar keratoplasty (DALK), Descemet stripping automated endothelial keratoplasty (DSAEK) and Descemet membrane endothelial keratoplasty (DMEK). Methods This multicentric retrospective study enrolled a consec...
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PURPOSE: Human cortical opacities are most commonly accompanied by changes in lens fiber structure in the equatorial region at the lens nucleus-cortex interface. Cortex and nucleus have different elastic properties which change with age. We therefore subjected lenses ex vivo to simulated accommodation and studied the internal deformations to bette...
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Full-text available
Cell therapy approaches hold great potential for treating retinopathies, which are currently incurable. This study addresses the problem of inadequate migration and integration of transplanted cells into the host retina. To this end, we have identified the chemokines that were most upregulated during retinal degeneration and that could chemoattract...
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Correction for ‘Bacterial nanocellulose as a corneal bandage material: a comparison with amniotic membrane’ by Irene Anton-Sales et al. , Biomater. Sci. , 2020, 8 , 2921–2930, DOI: 10.1039/D0BM00083C.
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Corneal trauma and ulcerations are leading causes of corneal blindness around the world. These lesions require attentive medical monitoring since improper healing or infection has serious consequences in vision and quality of life. Amniotic membrane grafts represent the common solution to treat severe corneal wounds. However, amniotic membrane’s av...
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Regeneration of ocular tissues using stem cells is currently under investigation for the cornea and the retina. Some more recent studies focus also on the regeneration of the crystalline lens. The lens consists of only two cell types, epithelial cells, which can differentiate and act as progenitor cells to the other cell type, fiber cells. Lens epi...
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Purpose To compare bacterial nanocellulose (BNC) patches produced by K.xylinus, against the amniotic membrane (AM) as a bandage material for ocular surface disorders. Based on previous structural characterizations of our BNC patches, and detailed cytocompatibility tests of BNC with human dermal fibroblasts; we hypothesise that BNC is viable as a ba...
Article
In order to study the mechanisms involved in the development of posterior capsule opacification (PCO) we compared in vivo developed PCO with PCO formed in tissue culture with focus on the periphery of the lens capsule to evaluate lens regeneration potential. We studied 3 human tissue groups: Cultured lens capsules after mock cataract surgery (n = 6...
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Purpose: To evaluate the relationship between the presence of cortical cataract and accommodation effort, using refractive error as a proxy. Methods: Patients between 50 and 90 years, scheduled for cataract surgery, were selected with the help of a photographic database. Nuclear and cortical cataract were graded and patients grouped having no ca...
Article
Purpose: To compare anatomical and functional results between three types of keratoprosthesis (KPro) in chemical injury and autoimmune disease. Methods: 70 clinically comparable cases were included as follows: Boston KPro Type 1 25 eyes, osteo-odonto-keratoprosthesis (OOKP) 23 eyes, Tibial bone KPro 22 eyes. Survival times for anatomical and fun...
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The objective of our study was to define principal risk factors for graft failure in patients who underwent penetrating keratoplasty (PK).Retrospective data obtained from a cohort of 895 penetrating keratoplasties performed between 2001 and 2006 were analysed. Recipient related factors, graft characteristics, and surgical technique were assessed in...
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In order to determine whether posterior capsule opacification after cataract surgery, could be delayed or inhibited through the application of hydrogen peroxide (H2O2) or distilled water (H2Od),we extracted lens capsules from 25 human donor eye globes. Samples were treated for 5 min with either 30 mM H2O2 or H2Od or used as controls, and cultured f...
Article
Purpose: To compare the anatomical and the functional results between osteo-odonto-keratoprosthesis (OOKP) and keratoprosthesis using tibial bone autograft (Tibial bone KPro). Methods: We reviewed the charts of 258 patients; 145 had OOKP whereas 113 had Tibial bone KPro implanted. Functional success was defined as best corrected visual acuity ≥0...
Article
Experimental protocols have been developed to measure the spatial variation of the mechanical strains induced in the lens capsule during ex vivo lens stretching. The paper describes the application of these protocols to porcine lenses. The deformations and mechanical strains developed in the anterior capsule during each experiment were determined u...
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Neuritic plaques and neurofibrillary tangles are crucial morphological criteria for the definite diagnosis of Alzheimer’s disease. We evaluated 12 unstained frontal cortex and hippocampus samples from 3 brain donors with Alzheimer’s disease and 1 control with hyperspectral Raman microscopy on samples of 30 × 30 µm. Data matrices of 64 × 64 pixels w...
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Purpose To observe the reactions of lens epithelial cells (LECs) to a short exposure of an elevated oxidative stress. To help find future treatments for the prevention of posterior capsule opacification. Using cultured human lens capsules as an experimental model and hydrogen peroxide (H2O2) as the stress inducer. Methods Lens capsule‐ciliary body...
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Purpose: To evaluate a new nuclear cataract grading system which is intended as a surgical guidance system to predict lens hardness before cataract surgery. Methods: The new BCN 10 grading system consists of frontal and cross-sectional slit-lamp images of human eye lenses, ranging from a completely transparent lens nucleus to a totally black nuc...
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Equatorial wrinkles, or crenations, have been previously observed around the equator in coronal images of the human ocular lens. However, wrinkles are typically not apparent when the lens is viewed from saggital directions. In the current paper, the existence and geometry of these wrinkles is shown to be consistent with a mechanical model of the is...
Article
In previous publications, we found that human cortical and cuneiform opacities are accompanied by changes in fiber structure and architecture mainly in the equatorial border zone between the lens nucleus and cortex. Because the lens cortex and nucleus have different viscoelastic properties in young and old lenses, we hypothesized that external forc...
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Purpose of Review The purpose of this study is to explain the different types of keratoprosthesis depending on the material; biological or nonbiological, and in the mode of fixation; transcorneal, intracorneal, or epi-corneal fixation; to define the general indications depending on the characteristics of the ocular surface; if it is a wet blinking...
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Purpose: To analyze the anatomical and functional results of keratoprosthesis using tibial bone autograft. Methods: We reviewed 113 charts of patients who underwent tibial bone osteokeratoprothesis implantation at the Centro de Oftalmologia Barraquer. Kaplan-Meier survival curves with 95% confidence interval were calculated for functional succes...
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Purpose: To evaluate the corneal button of primary penetrating keratoplasty of patients diagnosed with congenital aniridia. The study took place at the Instituto Universitario Barraquer and the Centro de Oftalmología Barraquer. Methods: A retrospective analysis of cases diagnosed with congenital aniridia was carried out. We analyzed 13 corneal b...
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To evaluate the performance of a manual lens stretching device using clinical scanners to analyze variations in lens topography and cross sections.
Article
To explore alternative experimental protocols to investigate the biomechanical behavior of the crystalline lens and zonules using ex vivo stretching. Radial stretching tests were conducted on the anterior segment (consisting of lens, zonules, ciliary body, and sclera) of four pairs of presbyopic human donor eyes. A simple mechanical model is used t...
Article
A European project studying the prevalence of visual function impairment in European drivers (2422 subjects) showed that intraocular stray light correlates with cataract grading scores. Measured intraocular stray light increases continuously with cataract severity, as estimated by the mean of the LOCS score (average of nuclear colour, nuclear opaci...
Article
Commonly, lens opacities and cataract are considered protein aggregation disorders. Increased light scattering is attributed to larger high-molecular-weight fractions of proteins. The impact on transparency of fiber membranes and their age- and disease-related changes is addressed to a lesser extent in the literature. In the lens cortex of transpar...
Article
We will conclude our SIS with an overview of additional technologies to restore accommodation. This should open a short a discussion between our speakers and the audience about the most promising future approach to resolve presbyopia.
Article
Purpose: To analyse how primary diagnosis and complications affect the evolution of post-operative visual acuity (VA). Methods: We performed retrospective chart analysis on 59 eyes in 57 patients with various diagnoses, most of which were non-standard indications for Boston type 1 keratoprosthesis (Kpro) implantation. The follow-up period was at...
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Purpose To describe the outcome of patients with Boston type 1 keratoprosthesis, with regard to anatomical and visual success. Methods Retrospective case series of patients who underwent Boston type I keratoprosthesis surgery at the Centro de Oftalmología Barraquer in Barcelona and at the University Eye Clinic in Salzburg between May 2006 and Dece...
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We have compared the protein profiles in plaques and tangles in the hippocampus of post-mortem Alzheimer brains and in opaque and clear regions in the deep cortex of eye lenses of the same donors. From the 7 Alzheimer donors studied, 1 had pronounced bilateral cortical lens opacities, 1 moderate and 5 only minor or no cortical opacities. We focused...
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Purpose Eye lenses from human donors with and without Alzheimer's disease (AD) were studied to evaluate the presence of amyloid in cortical cataract. Methods We obtained 39 lenses from 21 postmortem donors with AD and 15 lenses from age-matched controls. For 17 donors, AD was clinically diagnosed by general physicians and for 4 donors the AD diagno...
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Purpose To describe the rates of simple recurrence (SR) and clinically significant recurrence (CSR) of anterior dystrophies in donor corneas after penetrating or lamellar keratoplasty. Methods Retrospective case series of patients who underwent keratoplasty for anterior dystrophies from 1954 to 2008 with a minimum follow-up time of three years. Kap...
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Purpose Amyloid beta, the main protein component of Alzheimer (AD) plaques and tangles, is characterized by high levels of beta-sheets. Raman microspectroscopy allows quantitative analysis of this specific molecular conformation. We compared the beta-sheet levels in lens opacities and in plaques and tangles in the hippocampus of AD patients. Method...
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Purpose For the study of the biomechanical properties of lens and zonules in a stretching device, we wanted to investigate the effect of keeping the ciliary body intact or cutting it radially. Methods We studied the anterior eye segment of 3 pairs of presbyopic human donor eyes (ages 51-85). These segments, comprising of lens, zonules, ciliary body...
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Purpose Ex vivo measurement of the elastic properties of human lens zonules as a function of age in presbyopes. Methods We studied 16 presbyopic human donor eyes (ages 47 to 97). Anterior eye sections with crystalline lens, zonules, ciliary body and sclera were radially stretched. The stretching device consists of a chamber filled with balanced sal...
Article
Eye lenses from human donors with and without Alzheimer's disease (AD) were studied to evaluate the presence of amyloid in cortical cataract. We obtained 39 lenses from 21 postmortem donors with AD and 15 lenses from age-matched controls provided by the Banco de Ojos para Tratamientos de la Ceguera (Barcelona, Spain). For 17 donors, AD was clinical...
Article
Purpose To study the morphology of age-related cuneiform cortical cataracts. Methods We evaluated the gross morphology, location, and fiber cell architecture of equatorial cortical opacities in the aging human lens. Using dark-field stereomicroscopy, we photographed donor lenses in toto and as thick slices. In addition, we investigated the details...
Article
Purpose Analyze the outcomes of intracorneal ring segment (ICRS) implantation for the treatment of Keratoconus based on preoperative visual impairment. Design: Multicenter, retrospective, nonrandomized study. Methods 611 eyes of 361 keratoconic patients were evaluated. Subjects were classified according to their preoperative corrected distance visu...
Article
Purpose to describe the functional results and sight threatening post-operative complications of Type I Boston Keratoprosthesis. Methods retrospective descriptive study of Boston Keratoprosthesis patients from two European eye centers. Results A total of 66 eyes were included for analysis. Mean follow-up time was 28 months. Majority of patients had...
Article
Purpose: To investigate the elastic properties of human lens zonules as a function of age in presbyopes. Methods: We studied 16 presbyopic human donor eyes (ages 47-97). Anterior eye sections with crystalline lens, zonules, ciliary body, and sclera were stretched radially. The stretching device consisted of a chamber filled with balanced salt so...
Article
Background The aim of this study was to evaluate if iris color is associated with differences in visual functions such as intraocular straylight (IOSL), contrast sensitivity (CS), or best-corrected visual acuity (BCVA). Methods In this retrospective cohort study, which is a subgroup analysis of a large prospective trial about visual impairments...
Article
To evaluate by means of the Ocular Response Analyzer (ORA) the biomechanical changes that follow intracorneal ring segment (ICRS) implantation and to develop a predicting model for the postoperative visual outcome, considering these biomechanical changes and other clinical parameters. A total of 45 consecutive keratoconic eyes of 35 patients aged 1...
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To investigate the effect of iris pigment and pupil size in ultraviolet radiation (UVR)-induced cataract. Brown-Norway rats (pigmented) and Fischer-344 rats (non-pigmented) were unilaterally exposed in vivo to 5 kJ/m(2) UVR. Each strain was split into two groups, each receiving either mydriatic (tropicamide) or miotic (pilocarpine) eye-drops. One w...
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Purpose To review the current developments and new experimental applications of femtosecond lasers (FsL) in lens surgery, including cataract and the treatment of presbyopia. FsL lentotomy has been shown effective to soften the lens matter easing cataract extraction. Because the main cause for presbyopia is the stiffening of the lens nucleus with ag...
Article
Purpose We present a review of current developments to restore accommodation by means of electro optical materials embedded in glasses, contact lenses or intraocular lenses.Methods Considered electro optical effects include electro active polymers, electro refractive polymers and the electrowetting principle. Possible solutions about how to measure...
Article
To determine the value of electroretinography (ERG) and visual evoked potential (VEP) in predicting visual outcome in patients undergoing osteo-keratoprosthesis (OKP) or osteo-odonto-keratoprosthesis (OOKP) surgery. We performed a retrospective cohort study of 143 eyes in 101 patients who underwent OKP or OOKP surgery. The subjects underwent ERG, V...
Article
Full-text available
Cataract is a visible opacity in the lens substance, which, when located on the visual axis, leads to visual loss. Age-related cataract is a cause of blindness on a global scale involving genetic and environmental influences. With ageing, lens proteins undergo non-enzymatic, post-translational modification and the accumulation of fluorescent chromo...
Article
To report the long-term functional and anatomic outcomes of osteo-odonto-keratoprosthesis and tibial bone keratoprosthesis; to analyze the influence of clinical factors, such as surgical technique, primary diagnosis, age, and postoperative complications, on the final outcome. Retrospective cohort study. setting: Centro de Oftalmología Barraquer, be...
Article
Full-text available
To test the use of parameters obtained from the ocular response analyser (ORA) to distinguish between normal and keratoconic eyes, to determine the severity of keratoconus (KC), and to evaluate changes after treatment with cross-linking (CXL) and intrastromal corneal ring (ICR) implantation. In total, 42 parameters were derived from the ORA's appla...
Article
Purpose To study the correlation between posterior capsule opacification (PCO) and intraocular straylight and visual acuity.Methods We measured visual acuity (VA) (logMAR) and intraocular straylight (C-Quant straylight parameter log[s]) under photopic conditions before and 2 weeks after YAG capsulotomy in 41 patients (53 eyes) from the Centro de Of...
Article
Purpose To test the feasibility of calculating neural contrast sensitivity function (neural CSF) from conventionally measured total contrast sensitivity function (total CSF) and measured modulation transfer function (MTF). Neural CSF considers the retina and the brain, whereas total CSF considers the optical eye media, the retina and the brain toge...
Article
To analyze corneal astigmatic changes after implantation of intrastromal corneal ring segments (ICRS) in keratoconic eyes using the Alpins vectorial method. Vissum Corporation, Alicante, Spain. Keraring ICRS were implanted in eyes with a diagnosis of keratoconus. One of 3 surgeons performed the ICRS implantations using femtosecond technology and fo...
Article
Full-text available
To study the correlation between posterior capsule opacification (PCO) and intraocular straylight and visual acuity. Prospective noninterventional study. We measured visual acuity (VA), logarithm of minimal angle of resolution (logMAR) and intraocular straylight (C-Quant straylight parameter log[s]) under photopic conditions before and 2 weeks afte...
Article
To analyze the refractive, topographic, keratometric changes and the histopathologic findings after wedge resection to correct high astigmatism after penetrating keratoplasty for keratoconus. A retrospective study was done analyzing the following parameters preoperatively and at 1, 3, and 5 years postoperatively: uncorrected visual acuity, best-cor...
Article
Full-text available
Purpose: To test the performance of the C-quant straylight meter during the daily routine work in medical testing centres for driver license applicants and driver license holders in Spain. Methods: Altogether 914 subjects, of which 376 younger than 35 years, 428 between 35 and 60 years and 110 over 60 years were measured with the C-quant in three m...
Article
Full-text available
To evaluate the prevalence and association of different types and severities of cataract or pseudophakia with visual impairments in older European drivers. In this prospective European multicenter study, 2211 active drivers, 45 years of age and older, participated in an ophthalmologic examination, the measurement of visual functions, and were asked...
Article
Purpose. To evaluate the relationship of corneal biomechanical properties to refraction and corneal aberrometry in keratoconic eyes. Methods. A total of 81 consecutive keratoconic eyes of 81 patients ranging in age from 11 to 58 years were included in the study. Three groups were differentiated according to the severity of keratoconus: mild (37 eye...
Article
To test the feasibility of calculating neural contrast sensitivity function (neural CSF) from conventionally measured total contrast sensitivity function (total CSF) and measured modulation transfer function (MTF). Neural CSF considers the retina and the brain, whereas total CSF considers the optical eye media, the retina and the brain together. We...
Article
This study aimed to investigate the prevalence of impairment of visual function amongst European drivers. A total of 2422 drivers from five European countries underwent a battery of visual function tests, including tests for visual acuity (VA), visual field (VF), contrast sensitivity, straylight (glare sensitivity) and useful field of view (UFOV)....
Article
Purpose To analyse the refractive and biomechanical changes in the cornea after implantation of intrastromal ring segments.Methods The study included 43 eyes of 36 patients (mean age 38 years); 7 eyes had received Intacs® and 36 KeraRings®. Visual acuity, spherical equivalent, K readings, corneal hysteresis (CH) and corneal resistance factor (CRF)...
Article
Purpose To test the performance of the C-quant straylight meter during the daily routine work in medical testing centers for driver license applicants and driver license holders in Spain.Methods Altogether 914 subjects, of which 376 younger than 35 years, 428 between 35 and 60 years and 110 over 60 years were measured with the C-quant in three medi...
Article
To study the relationship between lens opacity and intraocular straylight, visual acuity and contrast sensitivity. We investigated 2422 drivers in five clinics in different European Union (EU) member states aged between 20 and 89 years as part of a European study into the prevalence of visual function disorders in drivers. We measured visual acuity...
Article
Purpose To compare the clinical experience with multifocal and focus shift IOLs in Austria, Germany and Spain.Methods We give a summary of published and unpublished data, reviews and meta-analyses. Main outcome measures are uncorrected distance and near visual acuity, and reading speed under different light conditions as well as subjective patient...
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Purpose To describe the indications, intraoperative complications, post-operative complications and anatomical and functional results of Type I Boston keratoprosthesis at our eye center in Barcelona.Methods Retrospective interventional case series on 24 eyes of 22 patients who underwent Boston keratoprosthesis implant from May 2006 to May 2008.Resu...