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Selektive wellenfrontgeführte Ablation der Hornhaut zur Korrektur refraktiver Fehler nach Implantation einer trifokalen Intraokularlinse
Get PDFBrillouin Spectroscopy of Normal and Keratoconus Corneas.
No full textPURPOSE
To investigate the age dependence of Brillouin spectroscopy of the cornea and to compare normal and keratoconus corneas.
DESIGN
Retrospective case-control study.
METHODS
Study Population: Healthy patients and patients suffering from keratoconus seen at the Institut für Refraktive und Ophthalmo-Chirurgie (IROC) between December 2016 and March 2017. Brillouin frequency shifts of patients of 2 different groups were examined with Brillouin spectroscopy perpendicular to the corneal surface. Group 1 consisted of 47 healthy eyes, whereas Group 2 included 36 eyes with keratoconus of unclear progression. Besides Brillouin examinations, corneal tomographies were acquired so that correlations and comparisons between geometric parameters and Brillouin frequency shifts could be evaluated.
MAIN OUTCOME MEASURES
Corneal Brillouin frequency shifts averaged over full corneal thickness.
RESULTS
A significant correlation between age and central Brillouin frequency shift was identified (P = .011) with an increase in Brillouin frequency shift of 4 MHz per decade in normal corneas. Keratoconus corneas have a significantly reduced Brillouin frequency shift at the thinnest point compared to normal corneas (5.7072 ± 0.0214 vs 5.7236 ± 0.0146 GHz, P < .001). The Brillouin frequency shift at the point of maximum posterior elevation showed best correlation with geometry-derived keratoconus indices. The receiver operating characteristic curve analysis of Brillouin frequency shift showed substantially worse sensitivity and specificity compared to K and thinnest pachymetry for keratoconus detection.
CONCLUSION
Noninvasive Brillouin spectroscopy adds clinical information about the biomechanical state of the cornea perpendicular to the surface. An age-dependent stiffening of the cornea has been found and keratoconus corneas are statistically significantly different from normal corneas, but for precise differentiating of keratoconus stages (including normal corneas) the method is currently neither specific nor sensitive enough. Further development including standardized mapping and establishment of new indices may increase the potential of Brillouin spectroscopy substantially
Continued Long-term Flattening After Corneal Cross-linking for Keratoconus.
No full textPURPOSE
To report 3 cases with continued long-term flattening after corneal cross-linking (CXL) for keratoconus and to determine its prevalence.
METHODS
Case series.
RESULTS
Three eyes of three patients presented with an ongoing corneal flattening over 10 years after CXL in the absence of corneal opacities. Of the initial 433 eyes treated with CXL between 2005 to 2007, only 45 eyes completed the 10-year follow-up period, indicating a prevalence of 6.7%.
CONCLUSIONS
Besides continuous flattening due to scars and intense early flattening, a third entity of continuous flattening can be observed after CXL. Continuous long-term flattening after CXL seems to affect more patients than initially anticipated and should be considered as a late-onset complication of CXL. [J Refract Surg. 2018;34(8):567-570.]
The influence of hydration on different mechanical moduli of the cornea.
Get PDFPURPOSE
To determine the interrelation of different elastic moduli of the cornea and to investigate their dependency on corneal hydration.
METHODS
Rabbit eyes were divided into four groups. Corneas were excised and mounted into a Barron artificial anterior chamber. Various corneal hydration steady states were achieved with different dextran T-500 concentrations in the anterior chamber, as well as on the corneal anterior surface. The treatment-solutions of each group contained either 5, 10, 15, or 20% w/w dextran. Ultrasound pachymetry was used to measure central corneal thickness. Brillouin microscopy of the central cornea determined the longitudinal bulk modulus by means of Brillouin frequency shift. Subsequently, a 5-mm-wide central strip was taken for extensiometry to measure the tangential elastic modulus.
RESULTS
The longitudinal bulk modulus was 1.2-times higher in corneas dehydrated with 20% dextran compared to those hydrated with 5% dextran. In contrast, the tangential elastic modulus increased by 4.4 times. The obtained longitudinal bulk moduli were two orders of magnitude bigger than the tangential elastic moduli. Regression analysis of longitudinal bulk modulus and tangential elastic modulus revealed a quadratic relation. The bulk modulus seemed to be independent of tension, whereas the elastic modulus was tension-dependent. Greater corneal hydration led to significantly thicker pachymetry.
CONCLUSION
Corneal biomechanics are highly dependent on the level of corneal hydration. Surprisingly, tangential elastic moduli were more sensitive to hydration changes than longitudinal bulk moduli. A quadratic relation was found between both moduli
Dissatisfaction After Trifocal IOL Implantation and Its Improvement by Selective Wavefront-Guided LASIK.
No full textPURPOSE
To evaluate a substantially improved wavefront acquisition technique (Peramis; SCHWIND eye-tech-solutions, Kleinostheim, Germany) for selective wavefront-guided aberration correction to improve satisfaction after implantation of trifocal intraocular lenses (IOLs).
METHODS
Of 213 eyes from 108 consecutive patients receiving cataract surgery with multifocal IOL implantation (FineVision; PhysIOL, Liége, Belgium), 56 eyes (26%) of 42 dissatisfied patients were treated with selective wavefront-guided laser in situ keratomileusis (LASIK) (Amaris 1050; SCHWIND eye-tech-solutions) free of cost with a follow-up of 12 months. Selective wavefront-guided ablation corrected for all aberrations except spherical aberrations to preserve the apodization and therefore to enhance the multifocal effect. The degree of satisfaction after trifocal IOL implantation, its increase after selective wavefront-guided LASIK, and the refractive error (spherical equivalent, refractive astigmatism) before and after selective wavefront-guided LASIK were evaluated.
RESULTS
Refractive astigmatism of greater than 0.50 diopters (D) was the most frequent residual refractive error (63%), followed by myopia (45%), hyperopia (20%), and increased ocular higher order aberrations (13%). After selective wavefront-guided LASIK, the refractive target (±0.50 D) was achieved in 98% and refractive astigmatism was 0.50 D or less in 93% of the eyes operated on. The overall satisfaction score in dissatisfied patients increased from 2.1 ± 0.8 preoperatively to 3.6 ± 0.8 (out of 4). Eighty-eight percent of initially dissatisfied patients would choose this procedure again.
CONCLUSIONS
Selective wavefront-guided LASIK reduced refractive errors and significantly increased spectacle independence and satisfaction, which may lead to a better acceptance of trifocal IOLs. [J Refract Surg. 2019;35(6):346-352.]
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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