Implantation of Intracorneal Ring Segments in Keratectasia: Effects on Corneal Biomechanics in 112 Eyes

PURPOSE

The aim of this study was to analyze changes in corneal biomechanical properties after implantation of intracorneal ring segments (ICRSs) in keratectasia.

METHODS

This retrospective single-center study included 112 patient eyes that underwent femtosecond laser-assisted ICRS implantation (Intacs SK; Addition Technology Inc, Des Plaines, IL) for keratectasia. Biomechanical analysis was performed using the Ocular Response Analyzer (ORA; Reichert Inc, Depew, NY), with determination of corneal resistance factor, corneal hysteresis, and Keratoconus Match Index, as well as by Corvis ST (OCULUS, Wetzlar, Germany), with determination of stiffness parameter A1, Ambrosio relational thickness to the horizontal profile (Arth), integrated radius, deformation amplitude ratio, and stress-strain index as well as Corvis Biomechanical Index and Tomographic Biomechanical Index. Data collection was performed preoperatively and 6 months postoperatively for ORA and Corvis ST and additionally after 1 and 2 years for ORA.

RESULTS

The corneal resistance factor decreased significantly postoperatively (5.8 ± 1.7 mm Hg) compared with preoperatively (6.75 ± 3.7 mm Hg; P = 0.021) and increased again during follow-up (6.2 ± 1.9 mm Hg; P = 0.024), without regaining preoperative values. Corneal hysteresis and Keratoconus Match Index did not change significantly. Stiffness parameter A1 ( P = 0.045) increased significantly after ICRS implantation and Arth decreased significantly from 181 ± 85 to 150 ± 92 ( P = 0.016). However, there was no significant postoperative change for others Corvis parameters.

CONCLUSIONS

Corneal biomechanical properties showed inconsistent changes after ICRS implantation. Classical corneal biomechanical parameters (using single central air-puff tonometers) do not seem to be suitable for follow-up after ICRS implantation.

Anterior chamber intraocular lens removal combined with triple DMEK: Quadruple DMEK for bullous keratopathy

PURPOSE

To present the outcomes of a patient with anterior chamber intraocular lens (ACIOL) related endothelial decompensation who underwent Descemet membrane endothelial keratoplasty (DMEK) and cataract surgery with intraocular lens (IOL) implantation in the capsular bag (so-called triple DMEK) combined with ACIOL removal (quadruple DMEK) in both eyes.

METHODS

Case report.

RESULTS

A 58-year-old female patient was referred due to decreased visual acuity within the last 18 months. She had a history of iris-claw ACIOL implantation 17 years before. The corrected distance visual acuity (CDVA) was 20/40 in both eyes. Due to low endothelial cell density and increased corneal thickness, ACIOL removal combined with triple DMEK (as quadruple DMEK) was performed for both eyes. Despite a graft detachment that was successfully managed with re-bubbling in the first eye, both eyes showed an increase in the CDVA (20/25 and 20/32, respectively) without any other significant complications in the follow-up of the patient. The corneas of both eyes were clear postoperatively.

CONCLUSION

This case report demonstrated that quadruple DMEK may provide feasible management for chronic endothelial cell decompensation secondary to iris-claw ACIOL implantation.

Descemet Membrane Endothelial Keratoplasty after failed penetrating keratoplasty- case series and review of the literature

BACKGROUND

This study aims to evaluate visual outcome, central corneal thickness, and re-bubbling rate in a cohort with undersized sequential Descemet Membrane Endothelial Keratoplasty (DMEK) due to endothelial graft decompensation following primary penetrating keratoplasty (PK).

METHODS

All patients who received a sequential DMEK (n = 16) or triple DMEK (n = 2) after failed primary PK between November 2020 and June 2022 were retrospectively evaluated. Analyzed parameters were corrected distance visual acuity (CDVA), central corneal thickness (CCT), re-bubbling rate and graft survival.

RESULTS

18 eyes of 18 patients were included. All patients underwent a DMEK with undersized graft after failed PK(s). Mean time between the last PK and DMEK was 102 ± 82 weeks. Mean follow-up time was 8.9 ± 4.6 months. CDVA increased significantly from 1.12 ± 0.60 logMAR preoperatively to 0.64 ± 0.49 logMAR 6 weeks postoperatively (p = 0.013). Mean CCT decreased significantly from 807 ± 224 μm before to 573 ± 151 μm 6 weeks after DMEK (p = 0.003). Re-bubbling was necessary in eight eyes (44.4%) after a median time of 7 days. The 12-month Kaplan Meier survival was 66.7%.

CONCLUSION

In case of endothelial graft decompensation without stromal scars after primary PK, a DMEK can be performed for selected patients who had satisfying CDVA before the endothelial decompensation. Prior to DMEK indication, an AS-OCT should routinely be performed to circularly search for posterior steps at the PK graft margin, as well as shortly after DMEK to exclude a detachment of the endothelial graft. All patients should be informed about a higher re-bubbling rate in comparison to primary DMEK.

Review for special issue: Corneal lamellar surgery: Present outcomes and future perspectives

Since the establishment of the first eye bank in the 1940s, their role has evolved to face new challenges. With the recent development of lamellar keratoplasties, eye banks play an even bigger role in the selection and preparation of donor tissues. The increasing number of keratoplasty techniques and the high demand for "ready-to-use" tissues are challenging eye banks to improve and develop new preparation techniques. Besides necessary examinations, new approaches of tissue analysis in eye banks allow a better/optimized selection of corneal tissues. These new challenges in tissue preservation, preparation, and selection are propelling eye banks into a new era of modern eye banking.

Leadership in ophthalmology training : Opportunities and risks of medical specialist education

Medical specialist training requires constant improvement and adaptation of the contents to the current situation. Nowadays, young physicians have the opportunity to select among the most renowned institutions and can choose the one most qualified for their training. Hospitals on the other hand still have the desire to recruit highly qualified physicians for their resident programs, which requires a good, well-rounded and reliable offer by the department under good leadership. Thus, among other issues a modern and multilingual homepage is already an important instrument for successfully addressing applicants and winning them over for the department. In addition to a well-planned and structured training plan (e.g., the "Homburg Curriculum") and a so-called "resident guide", many other additional offers are nowadays part of a successful training, such as structured internal and external specialist training courses, well thought out research concepts available to all interested parties, wet labs for practical exercises on pig's eyes and as the latest most innovative addition, a virtual reality simulator. Due to a structured curriculum with regular continuous education during the daily early morning meetings and an exchange program with another university eye hospital, not only the residents can benefit but ultimately also the department itself. In addition, future specialists are involved in the respective organization (so-called "service teams") from the very beginning. This conveys a great deal of knowledge and expertise but also organizational skills and thus improves the quality of training. In any case, standardized residency training with a view beyond the horizon, which is transparently organized and reliably carried out, improves the quality of training in order to become a certified ophthalmologist and increases the satisfaction of the residents. A department which is committed and can offer a wide range of services will benefit from motivated and satisfied employees in a good interpersonal climate, which in the end benefits not only the team but also the patients.

[Modern corneal diagnostics as the key for the correct classification of the disease and optimal treatment decisions]

Corneal diseases include a wide spectrum of different manifestations (inflammatory/noninflammatory) that need to be accurately classified for precise diagnosis and targeted treatment. In addition to the anamnesis and slit lamp biomicroscopy, further device-based examinations can be performed to narrow down the diagnosis. Nowadays, modern corneal imaging provides a variety of technologies, such as topography, tomography, in vivo confocal microscopy and analysis of biomechanics, which are able to reliably classify different pathologies. Knowledge of the available examination modalities helps to guide differential diagnostic considerations, facilitating the indication for stage-appropriate microsurgical intervention.

[Leadership in ophthalmology training : Opportunities and risks of medical specialist education]

Medical specialist training requires constant improvement and adaptation of the contents to the current situation. Nowadays, young physicians have the opportunity to select among the most renowned institutions and can choose the best qualified for their training. Hospitals on the other hand still have the desire to recruit highly qualified physicians for continuing education, which requires a good, well-rounded and reliable offer by the department under good leadership. Thus, among other issues a modern and multilingual homepage is already an important instrument for successfully addressing applicants and winning them over for the department. In addition to a well-planned and structured training plan (e.g., the Homburg curriculum) and a so-called resident guide, many other additional offers are nowadays part of a successful training, such as structured internal and external continuing education, well thought out research concepts available to all interested parties, wet labs for practical exercises on pig's eyes and as the latest most innovative addition, a virtual reality simulator. Due to a structured curriculum with regular continuous education during the daily early morning meetings and an exchange program with another university eye hospital, not only the residents can benefit but ultimately also the department itself. In addition, future specialists are involved in the respective organization (so-called service teams) from the very beginning. This conveys a great deal of knowledge and expertise but also organizational skills and thus improves the quality of training. In any case, standardized residency training with a view beyond the horizon, which is transparently organized and reliably carried out, improves the quality of training in order to become a certified ophthalmologist and increases the satisfaction of the residents. A department which is committed and can offer a wide range of services will benefit from motivated and satisfied employees in a good interpersonal climate, which in the end benefits not only the team but also the patients.

Baseline Characteristics of 1976 Patients With Ectatic Corneal Disorders at a Single Center From 2010 to 2021: A Cross-Sectional Study of the Homburg Keratoconus Center

OBJECTIVES

The study objective was to analyze the baseline characteristics of keratoconus (KC) patients at the Homburg Keratoconus Center from 2010 to 2021.

METHODS

This cross-sectional study included 3,674 eyes, with analysis of demographics, clinical findings, visual function, endothelial measurements, and topographic, tomographic, and corneal biomechanical data from the first visit.

RESULTS

Mean patient age was 36.3±13.8 years. The mean uncorrected distance visual acuity in log of minimal angle of resolution was 0.60 (20/80, Snellen equivalent), and the corrected mean was 0.3 (20/40). Of 1976 patients, 48.9% reported eye rubbing. Mean values (ranges) were 49.4±6.3 (36.3-78.0) D for steep keratometry, 462.4±66.0 (48.0-659.0) μm for thinnest corneal thickness, 9.7±8.7 (-0.5 to 88.8) for Belin/Ambrósio enhanced ectasia total deviation, 0.8±0.4 (0.0-1.0) for the Corvis biomechanical index, 0.9±0.2 (0.0-1.0) for the tomographic biomechanical index, 0.1±0.5 (-0.9 to 2.0) for the KC match index, 8.3±1.8 (2.2-17.7) mm Hg for corneal hysteresis, 7.1±2.2 (0.0-17.0) mm Hg for corneal resistance factor, and 2,562.9±326.3 (1,011-3,937) cells/mm2 for endothelial cell density. The average ABCDE KC stage was A2B3C1D1E2. Distance-corrected visual acuity correlated strongly with topometric, tomographic, and biomechanical data ( P <0.001).

CONCLUSIONS

This comprehensive description of baseline features of KC patients at a tertiary center provides a reference for further longitudinal and international multicentric studies.

P42-A105 Sterile donor tomography for improvement of refractive results after keratoplasty

PURPOSE

To evaluate the efficiency of using anterior segment optical coherence tomography (AS-OCT) as a non-invasive and sterile screening method in the eye bank to detect corneal grafts with curvature and/or thickness anomalies, thus improving the graft selection for corneal transplantation.

METHODS

1222 donor corneal tissues mounted in sterile organ culture flasks were imaged using an AS-OCT (CASIA 2 - Tomey, Nagoya, Japan) between January 2018 and September 2022. The corneal tissues were preserved at least 12 hours in organ culture medium 2 (containing 6% dextran T-500) before the measurement in order to allow deswelling prior to the examination. Depth scans were performed sterilely through the organ culture flask from the posterior surface of the corneal tissues within a 7 mm central zone to create 3D volume data. The volume data set was imported to MATLAB (MathWorks Inc., Natick, Massachusetts, USA) and, after preprocessing the data and defining the region of interest (ROI), the edge of the front and back surfaces of the corneal tissues was detected. Subsequently, the adaptation of a sphero-cylindrical surface model was carried out with raytracing. The radii of curvature for the front and back surfaces and the central corneal thickness were determined according to the method proposed by Mäurer, Eppig, Langenbucher et al at the Institute of Experimental Ophthalmology, Homburg/Saar, Germany.

RESULTS

The mean steep/flat front surface radius was 7.46 ± 0.29 (6.07 - 9.29)/7.69 ± 0.24 (6.70 - 9.50) mm, the corresponding values for the back surface being 6.48 ± 0.32 (5.30 - 8.00)/6.80 ± 0.31 (5.81 - 8.00) mm and the mean central thickness was 611.5 ± 85.6 (378.5 - 1457.2) μm. Anomalies (beyond ± 2 or ± 3 standard deviations SD) were found in 111 or 41 corneas (9.1% or 3.4%) for anterior surface curvature, 135 or 38 for corneas (11.0% or 3.1%) for the posterior surface, and 53 or 15 corneas (4.3% or 1.2%) for central corneal thickness.

CONCLUSION

The AS-OCT provides an objective, sterile and semi-automated screening method to identify corneal morphological and refractive alterations (e.g. keratoconus, status post keratorefractive surgery) to further optimize corneal donor selection in the eye bank. Corneal donors with curvature or thickness anomalies +/- 3 SD (eminence-based) do not have to be discarded but can be used for posterior lamellar keratoplasty, especially DMEK in Germany.

Ultrastructural Examination of the Corneal Interface after Predescemetic Deep Anterior Lamellar Keratoplasty (DALK) - A Case Report with Light and Transmission Electron Microscopy

PURPOSE

To examine corneal buttons with light and transmission electron microscopy (TEM) to visualize the interface area and highlight the ultrastructural corneal changes after deep anterior lamellar keratoplasty (DALK).

METHODS

Two patients underwent excimer laser-assisted penetrating repeat keratoplasty after predescemetic DALK. The corneal buttons were examined by light microscopy and TEM.

RESULTS

The light microscopic examination of the corneal buttons revealed fragments of a second Descemet's membrane in the central and midperipheral areas (Case 1). In both cases, visualization of the interface area was not possible by light microscopy. The donor and host stroma were tightly attached without dehiscence. TEM identified the interface area by irregularities in the collagen distribution between the donor and host stroma. The thickness of the remaining recipient corneal stroma measured approximately 30 µm (Case 1) and 100 µm (Case 2), respectively. In the host stroma, TEM revealed the absence or degeneration of keratocytes, accumulation of amorphous material between the collagen lamellae, and vacuolar inclusions dispersed in the stroma, forming a band-like zone anterior to Descemet's membrane.

CONCLUSION

The interface area after DALK has been mainly investigated by in vivo confocal microscopy. Light microscopy and TEM findings indicate remodeling processes after DALK that are associated with increased keratocyte degeneration and structural alterations of the extracellular matrix in the host stroma. The choice of surgical method may influence the postoperative morphological and functional outcome since these findings were primarily apparent in the remaining host stroma. Therefore, complete exposure of Descemet's membrane is an important prognostic factor for the postoperative visual outcome.

P08-A131 Comparison of sterile donor tomography in the eye bank and previous keratometric measurements during the donor's lifetime

PURPOSE

Sterile donor tomography in the eye bank can be used to minimise refractive surprises after corneal transplantation.The aim of this study was to compare sterile tomography of donor corneas in the eye bank with keratometric measurements of the same donors performed prior their death.

METHODS

Since 2018, 1246 donor sclerocorneal discs have been routinely measured using donor tomography, taken sterilely through their cell culture flask in medium II using the anterior segment optical coherence tomograph Casia 2 (Tomey Corp., Nagoya, Japan) and a custom-made Matlab software (The MathWorks Inc., Natick, Massachusetts, USA). Of all these donor corneas, 19 (1.5%) appeared to have been measured with Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany) in the donors before death. Both measurements, taken at a mean interval of 35 ± 26 months, were compared using a Wilcoxon signed-rank test.

RESULTS

The mean steepest/flattest front surface radius and anterior astigmatism of the corneas measured with Pentacam amounted 7.66±0.35/7.93±0.37 mm, and 0.27±0.43 mm. Corresponding values of sterile donor tomography were respectively 7.48±0.31 [p<0.01]/7.77±0.25 [p=0.01] mm, and 0.29±0.35 [p=0.78] mm.At the posterior corneal surface, the Pentacam measured a mean steepest/flattest surface radius and astigmatism of 6.27±0.33/6.72±0.48 mm and 0.45±0.47 mm, whereas values of sterile donor tomography amounted 6.55±0.30 [p<0.01]/6.94±0.33 [p=0.04] mm and 0.39±0.26 [p=0.63] mm, respectively.The central corneal thickness amounted 575±52 µm with Pentacam, and 597±80 µm [p=0.20] with sterile donor tomography.

CONCLUSION

The front and back surface astigmatism as well as the central corneal thickness remained statistically unchanged after corneal excision and preservation in organ culture in comparison to measurement of the donor prior death. The statistically non-similar anterior and posterior radius of curvature between both methods must be seen in light of the known differing corneal topography between swept-source anterior segment optical coherence tomography and Scheimpflug imaging. These results suggest a merely minimal deformation caused by the storage and attachment of donor corneas to their holder in the cell culture flask for sterile donor tomography, causing a steeper anterior surface curvature but leaving the astigmatism still congruent with previous in situ conditions.

Risk factors for keratoconus progression in children compared with young and middle-aged adults

Background: To investigate the risk factors for keratoconus progression in children (10-18 years old) compared to young adults (19-35 years old) and middle-aged adults (36-55 years old). Patients/Methods: 97 children, 445 young adults and 342 middle-aged adults underwent total ophthalmic examination including clinical refraction, slit lamp examination, corneal tomography, eye biometry and biomechanical properties measurements. Comparison among three age groups and between progressive and non-progressive eyes, were assessed. Logistic regression was applied to determine the potential prognostic factors for keratoconus progression in three age groups. Results: Univariate logistic regression analysis show that the most prominent factors associated with progression were corneal posterior vertical radius (RVP), eye rubbing (RUB), slit lamp corneal thinning (SLT), contact lens use (CL) and central corneal thickness (CCT) in all age groups. Additionally, the anterior chamber volume (ACV) and keratoconus match index (KMI) were associated with progression in age group 1. Location of thinnest corneal thickness at the vertical axis (TCTy), distance from apex to the thinnest point (BADISTAPEX), Scissor reflection in retinoscopy (SKIAREFLEX), and Vogt striae were associated with progression in age group 2, and TCTy, anterior and posterior asphericity (ASPA and ASPP, respectively), BADISTAPEX, SKIAREFLEX and Vogt Striae were associated with progression in age group 3. The multivariate model with the highest predictability indicated RVP, ACV and SLT as independent determinants of progression in age group 1 (AUC:90%, sensitivity: 88.9%, specificity: 90.9%), RVP, ACV, SLT and SKIAREFLEX in group 2 (AUC: 81.6%, sensitivity 88.5%, specificity: 70.3%) and RVP, SLT, Vogt Striae and CL in age group 3 (AUC: 80%, sensitivity 82.8%, specificity: 73%). Conclusion: Anterior chamber volume and keratoconus match index seem to play a major role in the progression of pediatric KC, compared to adults. This is probably due to different anatomical and biomechanical characteristics of a child’s eye globe. Abstrakt Hintergrund: Diese Studie untersucht die Risikofaktoren für das Fortschreiten des Keratokonus bei Kindern (10-18 Jahre) im Vergleich zu jungen Erwachsenen (19-35 Jahre) und Erwachsenen mittleren Alters (36-55 Jahre). Patienten und Methoden: 97 Kinder, 445 junge Erwachsene und 342 Erwachsene mittleren Alters unterzogen sich einer umfassenden augenärztlichen Untersuchung, die eine klinische Refraktion, eine Spaltlampenuntersuchung, eine Hornhauttomographie, eine Augenbiometrie und eine Messung der biomechanischen Eigenschaften umfasste. Es wurde ein Vergleich zwischen den drei Altersgruppen sowie zwischen progressiven und nicht-progressiven Augen vorgenommen. Mit Hilfe einer logistischen Regression wurden die potenziellen prognostischen Faktoren für das Fortschreiten des Keratokonus in den drei Altersgruppen verglichen. Ergebnisse: Eine univariate logistische Regressionsanalyse zeigt, dass die folgenden wichtigsten Faktoren mit dem Fortschreiten des Keratokonus in allen Altersgruppen assoziiert sind: vertikaler Krümmungsradius der hinteren Hornhaut (RVP), Augenreiben (RUB), Spaltlampen-Hornhautausdünnung (SLT), Tragen von Kontaktlinsen (CL) und zentrale Hornhaut dicke (CCT). Zusätzlich wurden das Vorderkammervolumen (ACV) und der Keratokonus-Match-Index (KMI) mit der Progression in der Altersgruppe 1 in Verbindung gebracht. Die Stelle der dünnsten Hornhautdicke an der vertikalen Achse (TCTy), der Abstand vom Apex zur dünnsten Stelle (BADISTAPEX), die helle Reflexion des nasalen Bereichs des Limbus (SKIAREFLEX) und die Vogt-Linien wurden mit der Progression in der Altersgruppe 2 assoziiert, und TCTy, vordere und hintere Asphärizität (ASPA bzw. ASPP), BADISTAPEX, SKIAREFLEX und Vogt-Linien wurden mit der Progression in der Altersgruppe 3 assoziiert. Das Multivarianzmodell mit der höchsten Vorhersagbarkeit zeigte RVP, ACV und SLT als unabhängige Determinanten der Progression in Altersgruppe 1 (AUC: 90%, Sensitivität: 88,9%, Spezifität: 90,9%), RVP, ACV, SLT und SKIAREFLEX in Gruppe 2 (AUC: 81,6%, Sensitivität 88,5%, Spezifität: 70,3%) und RVP, SLT, Vogt-Linien und CL in Altersgruppe 3 (AUC: 80%, Sensitivität 82,8%, Spezifität: 73%). Schlussfolgerungen: Das Volumen der Vorderkammer und der Keratokonus-Match-Index scheinen beim Fortschreiten des KC bei Kindern im Vergleich zu Erwachsenen eine größere Rolle zu spielen. Dies ist wahrscheinlich auf die unterschiedlichen anatomischen und biomechanischen Merkmale des kindlichen Augapfels zurückzuführen.

In situ donor keratometry in deceased patients as a novel screening technique for eye banking

PURPOSE

To investigate the potential role of keratometry on whole globes in situ of deceased patients by assessing its repeatability and comparing it with sterile donor tomography after excision and preservation in organ culture.

METHODS

A sequence of 5 measurements was taken from 40 eyes in situ of deceased patients < 24 h after death using the portable Retinomax K-plus 3 (Bon, Tokyo, Japan). Keratometry of whole globes in situ, from which sclerocorneal discs were taken for organ culture, was compared to those obtained after measuring these sclerocorneal disks through their cell culture flask in medium I after 5 ± 4 days using the anterior segment optical coherence tomograph Casia 2 (Tomey Corp., Nagoya, Japan), and to 964 different donor corneas in medium II.

RESULTS

Cronbach's alpha of the in situ keratometry was 0.891 and 0.942 for the steepest and flattest corneal power (P). The steepest (44.5D) and flattest (41.1D) P as well as the astigmatism (3.4D) of in situ corneas remained unchanged after preserving sclerocorneal discs in medium I (respectively 44.7D [p = 0.09]; 41.4D [p = 0.17]; 3.3D [p = 0.09]). The comparison of the in situ values with the 964 measured different donor corneas in medium II showed significantly (p < 0.001) higher P at the steep (45.4D) and flat (43.9D) meridian and smaller astigmatism (1.4D) for sterile donor tomography.

CONCLUSIONS

Measuring deceased patients' eyes in situ with the portable Retinomax K-plus 3 represents a feasible and reliably repeatable screening method in the eye bank. In comparison to donor tomography in medium I, it measures a similar power and astigmatism.

Corneal epithelial ingrowth after perforating corneal injury: a case report

BACKGROUND

Epithelial ingrowth is a rare complication after ocular perforation and can become manifest many years after the primary trauma.

CASE PRESENTATION

A 49-year-old patient presented with a positive Seidel test of unclear origin at her left eye, as well as a sharply defined anterior-stromal corneal scar at both eyes. Prior operations included a bilateral laser-assisted blepharoplasty 3 months earlier. The patient indicated to have been on holiday to France 5 months earlier, during an ongoing oak processionary moth caterpillars infestation. The examination using confocal microscopy confirmed a corneal perforation at the left eye and revealed corneal epithelial ingrowth capped with scarred stroma in both eyes. We performed a penetrating keratoplasty at the left eye. The scarred and perforated host cornea was divided into 4 pieces for further investigation: microbiology (negative), virology (negative), histology and transmission electron microscopy (TEM). Histology revealed differently structured epithelium, centrally inverted into the stroma through defects in Bowman's layer. TEM revealed full thickness corneal perforation with an epithelial plug extending to the lower third of the cornea, but without evidence of epithelial cell migration into the anterior chamber. Our differential diagnosis of the unclear positive Seidel test with epithelial ingrowth was as follows: (1) corneal perforation by hairs of the oak processionary moth caterpillar, although no hairs could be found histologically; (2) corneal perforation during laser-assisted blepharoplasty, which may be supported by the presence of pigmented cells on the posterior surface of Descemet´s membrane, pointing to a possible iris injury.

CONCLUSION

Consequently, we highlighted that contact lenses can be useful, safe and inexpensive protective devices in upper eyelid procedures to protect the cornea against mechanical iatrogenic trauma.

Reliability and efficiency of corneal thickness measurements using sterile donor tomography in the eye bank

To evaluate the reliability and efficiency of sterile pachymetric measurements of donor corneas based on tomographic data using two different methods: a "manual" and a "(semi-)automated" method. Twenty-five (25) donor corneas (50%) stored in MI and 25 (50%) in MII were imaged 5 times consecutively using an anterior segment OCT (AS-OCT). The central corneal thickness (CCT) was measured both with the manual measurement tool of the AS-OCT (= CCTm) and with a MATLAB self-programmed software allowing (semi-)automated analysis (= CCTa). We analyzed the reliability of CCTm and CCTa using Cronbach´s alpha (α) and Wilcoxon signed-Rank Test. Concerning CCTm, 68 measurements (54.4%) in MI and 46 (36.8%) in MII presented distortions in the imaged 3D-volumes and were discarded. Concerning CCTa, 5 (4%) in MI and 1 (0.8%) in MII were not analyzable. The mean (± SD) CCTm was 1129 ± 6.8 in MI and 820 ± 5.1 µm in MII. The mean CCTa was 1149 ± 2.7 and 811 ± 2.4 µm, respectively. Both methods showed a high reliability with a Cronbach´s α for CCTm of 1.0 (MI/MII) and for CCTa of 0.99 (MI) and 1.0 (MII). Nevertheless, the mean SD of the 5 measurements was significantly higher for CCTm compared to CCTa in MI (p = 0.03), but not in MII (p = 0.92). Sterile donor tomography proves to be highly reliable for assessment of CCT with both methods. However, due to frequent distortions regarding the manual method, the (semi-)automated method is more efficient and should be preferred.

16 Reliability and efficiency of corneal thickness measurements using sterile donor tomography in the eye bank

PURPOSE

To evaluate the reliability and efficiency of sterile corneal thickness measurements of donor corneas stored in a plastic culture flask filled with organ culture medium I (MI) or II (MII) based on tomographic data using two different software: the built-in software of the anterior segment OCT (AS-OCT) and a MATLAB self-programmed software.

METHODS

Twenty-five (25) donor corneas (50%) stored in MI and 25 (50%) in MII were imaged 5 times consecutively using an AS-OCT. The central corneal thickness (CCT) was measured both with the manual measurement tool of the AS-OCT (=CCTm) and with a MATLAB self-programmed software allowing (semi-)automated analysis (=CCTa). We analyzed the reliability of CCTm and CCTa using Cronbach´s alpha (α) and Wilcoxon signed-rank test.

RESULTS

Concerning CCTm, 68 measurements (54.4%) in MI and 46 (36.8%) in MII presented distortions in the imaged 3D-volumes and were discarded. Concerning CCTa, 5 (4%) in MI and 1 (0.8%) in MII were not analyzable. The mean (± SD) CCTm was 1129 ± 6.8 in MI and 820 ± 5.1 µm in MII. The mean CCTa was 1149 ± 2.7 and 811 ± 2.4 µm, respectively. Both methods showed a high reliability with a Cronbach´s α for CCTm of 1.0 (MI/MII) and for CCTa of 0.99 (MI) and 1.0 (MII). Nevertheless, the mean SD of the 5 measurements was significantly higher for CCTm compared to CCTa in MI (p = 0.03), but not in MII (p = 0.92).

CONCLUSIONS

Sterile donor tomography proves to be highly reliable for assessment of CCT with both methods. However, due to frequent distortions regarding the manual method, the (semi-)automated method seems to be more efficient and should be preferred.

Outcomes of Severe Fungal Keratitis Using in vivo Confocal Microscopy and Early Therapeutic Penetrating Keratoplasty

Purpose

The purpose of this study was to assess the impact of early diagnosis using in vivo confocal microscopy and early therapeutic penetrating keratoplasty (TPK) on the outcomes of severe cases of fungal keratitis.

Methods

This retrospective single-center study included 38 patients (40 eyes) with fungal keratitis who presented between December 2013 and February 2020. Preoperative, intraoperative, and postoperative parameters were recorded to assess the role of early correct diagnosis and early surgical therapy on visual acuity outcome and enucleation rate during follow-up.

Results

The mean patient age was 51 years (71% females). The initial external diagnosis was correct in 20 cases (50%). The mean time from symptom onset until admission to our department was 46.8 ± 68.0 (median 28.5) days. The mean time to correct diagnosis after admission to our department was 1 day with in vivo confocal microscopy (IVCM). IVCM was performed in 38 cases, of which 36 (sensitivity: 94.7%) were positive for fungal infection. Twenty-seven out of 40 (67.5%) eyes received a TPK 4.2 ± 3.9 days after admission, with a mean graft size of 8.9 ± 1.9 mm. Three eyes (7.5%) were enucleated. The corrected distance visual acuity of the entire study population increased from 2.0 ± 1.2 LogMAR to 0.96 ± 1.17 LogMAR.

Conclusion

In vivo confocal microscopy is a powerful tool for the early detection of fungal organisms in infectious keratitis. An early TPK with a large graft helps to eradicate the infection timely and results in a favorable visual acuity outcome and lower enucleation rate, especially when treating filamentous fungi.

YB-1 Structure/Function Relationship in the Packaging of mRNPs and Consequences for Translation Regulation and Stress Granule Assembly in Cells

From their synthesis in the nucleus to their degradation in the cytoplasm, all mRNAs have the same objective, which is to translate the DNA-stored genetic information into functional proteins at the proper time and location. To this end, many proteins are generally associated with mRNAs as soon as transcription takes place in the nucleus to organize spatiotemporal regulation of the gene expression in cells. Here we reviewed how YB-1 (YBX1 gene), one of the major mRNA-binding proteins in the cytoplasm, packaged mRNAs into either compact or extended linear nucleoprotein mRNPs. Interestingly the structural plasticity of mRNPs coordinated by YB-1 could provide means for the contextual regulation of mRNA translation. Posttranslational modification of YB-1, notably in the long unstructured YB-1 C-terminal domain (CTD), and/or the protein partners of YB-1 may play a key role in activation/inactivation of mRNPs in the cells notably in response to cellular stress.

Morphological characterization and clinical effects of stromal alterations after intracorneal ring segment implantation in keratoconus

PURPOSE

To analyze the histological and (ultra)structural stromal tissue changes after femtosecond (Fs) laser-assisted intracorneal ring segment (ICRS) implantation and their refractive and topographic effects in patients with keratoconus.

METHODS

This monocentric retrospective case series included 15 consecutive patients with clinical peri-segmental lamellar channel deposits after treatment with Fs-ICRS implantation for keratoconus. The stromal changes were investigated using in vivo confocal microscopy. Two patients underwent a penetrating keratoplasty after the Fs-ICRS implantation; the explanted corneas were processed for histopathology and transmission electron microscopy (TEM). Refractive and topographic effects were investigated comparing the uncorrected (UDVA) and corrected (CDVA) distance visual acuity, spherical equivalent (SE), flat (K1), steep (K2), and steepest (Kmax) keratometry before and after detection of lamellar channel deposits.

RESULTS

In vivo confocal microscopy revealed diffuse linear and focal granular hyperreflective structures. Histologically, there was mild proliferation of fibroblasts and fibrosis. TEM demonstrated focal accumulations of degenerated keratocytes with cytoplasmic lipid inclusions. There were no significant changes for UDVA (Δ = 0.0 ± 0.2 logMAR; p = 0.67), CDVA (Δ = 0.0 ± 0.1 logMAR; p = 0.32), SE (Δ 0.1 ± 0.9 D; p = 0.22), K1 (Δ = 0.3 ± 1.0 D; p = 0.28), K2 (Δ = 0.1 ± 0.9 D; p = 0.51), and Kmax (Δ = 0.3 ± 1.5 D; p = 0.17).

CONCLUSIONS

Two types of structural stromal changes were identified: (1) diffuse peri-segmental fibrosis and (2) lamellar channel deposits. These structural changes showed no evidence of a relevant refractive or topographic effect.

[Stage-appropriate treatment of keratoconus]

Keratoconus (KC) is a progressive cone-shaped corneal protrusion that causes paracentral thinning at the apex of the cone and typically occurs asymmetrically on both sides. After a careful anamnesis and classification of the degree of severity a targeted treatment appropriate to the stage of the disease is available. If the visual acuity is no longer sufficient, rigid gas-permeable contact lenses (CL) are fitted by a specialist. Riboflavin UVA cross-linking (CXL) is recommended in cases of progression and visual acuity that is still useful for the patient. Intracorneal ring segments (ICRS) are indicated for CL intolerance in cases of reduced visual acuity and a clear central cornea. If the stage is more advanced, deep anterior lamellar keratoplasty (DALK) or penetrating keratoplasty (PKP) is recommended. A PKP is contraindicated in acute KC but deep stromal sutures for readaptation of the Descemet tear with gas filling of the anterior chamber can considerably shorten the course. Almost no other eye disease is nowadays as easily accessible for an early instrument-based diagnosis and stage-appropriate treatment as KC.

[Coinfections in contact lens-associated mycotic keratitis with Pseudomonas or Acanthamoeba]

Kontaktlinsenassoziierte Keratitiden werden immer häufiger. Die mykotische Keratitis ist ein relativ seltenes, aber sehr ernst zu nehmendes Krankheitsbild. Meist wird im Frühstadium eine falsche Diagnose gestellt und dadurch die adäquate Therapie verzögert. Bei der therapierefraktären kontaktlinsenassoziierten mykotischen Keratitis können nicht selten auch Koinfektionen oder Superinfektionen bestehen. Wir stellen 2 Patienten mit initial unklarer Keratitis vor, bei denen eine Mischinfektion der mykotischen Keratitis mit Pseudomonas aeruginosa bzw. Akanthamöben nachgewiesen werden konnte. In beiden Fällen war die zeitnahe perforierende Excimerlaser-Keratoplastik mit Einzelknüpfnähten und adäquater Lokaltherapie über 8 Wochen therapeutisch erfolgreich.

OCT Application for Sterile Corneal Graft Screening in the Eye Bank

BACKGROUND AND OBJECTIVE

Sterile donor tomography enables the detection of corneal tissues with refractive anomalies. The aim of this study was to determine the curvature and thickness of donor corneas to support proper selection in the eye bank.

METHODS

704 donor corneas (Klaus Faber Center, LIONS Eye Bank Saar-Lor-Lux, Trier/Westpfalz, in Homburg/Saar) were measured using the anterior segment optical coherence tomograph (AS-OCT) CASIA 2 (Tomey Corp., Nagoya, Japan). The corneoscleral discs were measured in their cell culture flask, which was positioned in a holder on the chin rest of the AS-OCT, after conversion to medium II (with 6% dextran T-500). The measured raw data were analysed and processed in MATLAB (MathWorks Inc., Natick, Massachusetts, USA), after which the refractive power of the steep and flat meridian at the anterior and posterior surface and the central corneal thickness (CCT) of the donor corneas were determined. Results values are expressed as mean x̅ ± standard deviation SD.

RESULTS

The mean refractive power of the steep/flat meridian at the anterior surface was 45.4 ± 1.8 D/44.0 ± 1.3 D, the corresponding values for the posterior surface were - 6.2 ± 0.3 D/- 5.9 ± 0.2 D, and the mean CCT was 616.3 ± 85.1 µm. Of the 704 (100%) measured donor tissues, 590 (83.8%)/670 (95.2%) donor corneas showed no anomaly beyond respectively x̅ ± 2 SD/x̅ ± 3 SD among the 5 examined parameters. 72 (10.3%)/23 (3.3%) donor corneas had only 1 anomaly, 26 (3.7%)/10 (1.4%) had 2 anomalies, 10 (1.4%)/1 (0.1%), 3 anomalies, 5 (0.7%)/0 (0.0%), 4 anomalies, and 1 (0.1%)/0 (0.0%), 5 anomalies.

CONCLUSIONS

AS-OCT provides an objective and sterile screening method to identify corneal tissues with curvature anomalies in order to further optimise donor selection in the eye bank. To avoid postoperative refractive surprises, donor corneas with a total refractive power that deviates > ± 3 SD from the mean should not be used for penetrating or anterior lamellar keratoplasty, but may be suitable for posterior lamellar keratoplasty (DMEK or DSAEK). In the future, sterile donor tomography could enable: (1) the harmonisation of donor and recipient tomography, which may minimise residual astigmatism for a particular donor-recipient pair; and (2) the improvement of IOL power calculation in a classical triple procedure by means of regression analysis between pre- and postoperative total refractive power of corneal grafts.

[Excimer laser-assisted DALK: a case report from the Homburg Keratoconus Center (HKC)]

Indikationen

Ziel der Excimerlaser-gestützten DALK (Excimer-DALK) ist, wie bei der mechanischen DALK, die Behandlung von Keratektasien (Keratokonus und pellucide marginale Degeneration), stromalen Narben oder stromalen Hornhautdystrophien. Voraussetzung für die Operation ist die Abwesenheit von (prä)descemetalen Narben sowie ein gesundes Endothel.

Operationstechnik

Nach der Excimerlaser-gestützten Trepanation auf 80 % der kornealen Dicke an der Trepanationsstelle, einer intrastromalen Lufteingabe (sog. „Big-Bubble“) sowie einer lamellären Hornhautpräparation erfolgt eine lamelläre anteriore Transplantation des endothelfreien Spendergewebes. Diese Technik kombiniert die Vorteile einer DALK und einer Excimerlaser-Trepanation. Wir beschreiben die Schritte einer Excimer-DALK aus unserem Homburger Keratokonus Center (HKC).

Schlussfolgerungen

Die Excimer-DALK stellt bei Patienten mit gutem Endothel eine gute Behandlungsmöglichkeit dar. Bei einer intraoperativen Perforation bleibt die Möglichkeit einer sog. Konversion zur Excimer-PKP mit allen Vorteilen der Excimerlaser-Trepanation.

Video online

Die Online-Version dieses Beitrags (10.1007/s00347-021-01342-3) enthält ein Video.

Vergleich der sterilen Spendertomographie in der Hornhautbank mit der Tomographie des Transplantates nach perforierender Keratoplastik

Hintergrund

Seit 2018 verwenden wir die sterile Spendertomographie in der Hornhautbank routinemäßig, um refraktive Überraschungen nach Keratoplastik zu vermeiden. Ziel dieser Studie war es, Spendertomographieparameter mit Tomographieparametern des Transplantates nach perforierender Keratoplastik (PKP) zu vergleichen.

Methoden

Diese Studie umfasste 193 Spendergewebe der Hornhautbank, die für eine PKP verwendet wurden (Transplantatdurchmesser 8,2 ± 0,7 mm). Messungen wurden mit dem optischen Kohärenztomographen des vorderen Augenabschnittes (VAA-OCT) Casia 2 (Tomey Corp., Nagoya, Japan) präoperativ sowie postoperativ nach 5 ± 4 Monaten bei liegenden Fäden und nach 22 ± 4 Monaten ohne Fäden durchgeführt. Post- und präoperative Werte wurden mithilfe des Wilcoxon-Rangsummentests verglichen.

Ergebnisse

Postoperativ, bei liegenden (bzw. ohne) Fäden, war die Brechkraft (P) der Hornhautvorderfläche (v) im steilen Meridian (S) (PvS) unverändert (−0,2 dpt; p = 0,78) (um 2,7 dpt größer [p < 0,01]) und im flachen Meridian (F) (PvF) um 4,5 dpt (2,8 dpt) niedriger (p < 0,01) im Vergleich zu den Spendertomographiewerten. Der Astigmatismus (v) war um 4,3 dpt (5,4 dpt) größer (p < 0,01). An der Rückfläche (r) war PrS um 0,9 dpt (0,9 dpt) und PrF um 0,3 dpt (p < 0,01) (0,1 dpt [p = 0,42]) kleiner, während der Astigmatismus (r) um 0,7 dpt (0,9 dpt) größer war (p < 0,01). Die zentrale Hornhautdicke war um 55,7 μm (p < 0,01) (27,5 µm [p = 0,01]) kleiner. Die Gesamtbrechkraft ohne Fäden änderte sich nicht signifikant im Vergleich zur Hornhautbankmessung.

Schlussfolgerung

Zentrale Hornhautdicke, Brechkraft (P) und Astigmatismus veränderten sich postoperativ im Vergleich zu den Spendertomographiewerten, mit Ausnahme von P im steilen Meridian der Vorderfläche bei liegenden Fäden sowie von P im flachen Meridian der Rückfläche nach Entfernung aller Fäden. Die Gesamtbrechkraft ohne Fäden ändert sich allerdings nicht signifikant. Diese Informationen könnten für eine Verbesserung der Kunstlinsenberechnung bei klassischer „Triple-Procedure“ von Bedeutung sein.

Keratoconus staging by decades: a baseline ABCD classification of 1000 patients in the Homburg Keratoconus Center

Background

This retrospective cross-sectional study aims to analyse the keratoconus (KC) stage distribution at different ages within the Homburg Keratoconus Center (HKC).

Methods

1917 corneae (1000 patients) were allocated to decades of age, classified according to Belin’s ABCD KC grading system and the stage distribution was analysed.

Results

73 per cent (n=728) of the patients were males, 27% (n=272) were females. The highest KC prevalence occurred between 21 and 30 years (n=585 corneae, 294 patients). Regarding anterior (A) and posterior (B) curvature, the frequency of A was significantly higher than B in all age groups for stage 0, 1 and 2 (A0>B0; A1>B1; A2>B2; p<0.03, Wilcoxon matched-pairs test). There was no significant difference between the number of A3 and B3, but significantly more corneae were classified as B4 than A4 in all age groups (p<0.02). The most frequent A|B combinations were A4|B4 (n=451), A0|B0 (n=311), A2|B4 (n=242), A2|B2 (n=189) and A1|B2 (n=154). Concerning thinnest pachymetry (C), most corneae in all age groups were classified as C0>C1>C2>C3>C4 (p<0.04, Wilcoxon matched-pairs test). For the best distance visual acuity (D), a significantly higher number of corneae were classified as D1 compared to D0 (p<0.008; D1>D0>D2>D3>D4).

Conclusion

The stage distributions in all age groups were similar. Early KC rather becomes manifest in the posterior than the anterior corneal curvature whereas advanced stages of posterior corneal curvature coincide with early and advanced stages of anterior corneal curvature. Thus, this study emphasises the necessity of posterior corneal surface assessment in KC as enabled by the ABCD grading system.

ITSN1 regulates SAM68 solubility through SH3 domain interactions with SAM68 proline-rich motifs

SAM68 is an mRNA-binding protein involved in mRNA processing in the nucleus that forms membraneless compartments called SAM68 Nuclear Bodies (SNBs). We found that intersectin 1 (ITSN1), a multidomain scaffold protein harboring five soluble SH3 domains, interacts with SAM68 proline-rich motifs (PRMs) surrounded by self-adhesive low complexity domains. While SAM68 is poorly soluble in vitro, the interaction of ITSN1 SH3 domains and mRNA with SAM68 enhances its solubility. In HeLa cells, the interaction between the first ITSN1 SH3 domain (SH3A) and P0, the N-terminal PRM of SAM68, induces the dissociation of SNBs. In addition, we reveal the ability of another SH3 domain (SH3D) of ITSN1 to bind to mRNAs. ITSN1 and mRNA may thus act in concert to promote SAM68 solubilization, consistent with the absence of mRNA in SNBs in cells. Together, these results support the notion of a specific chaperoning of PRM-rich SAM68 within nuclear ribonucleoprotein complexes by ITSN1 that may regulate the processing of a fraction of nuclear mRNAs, notably SAM68-controlled splicing events related to higher neuronal functions or cancer progression. This observation may also serve as a putative model of the interaction between other PRM-rich RBPs and signaling proteins harboring SH3 domains.

NH₃ biofiltration of piggery air

An aboveground pilot-scale biofilter filled with wood chips was tested to treat ammonia emissions from a piggery located in Brittany (France). Two long-term tests ("summer" and "autumn" experiments) were carried out to improve biofilter applications for agriculture. The influence of climatic conditions on biofilter performance was taken into account. During summer 2012, the biofilter was operated for 74 days at different empty bed residence times (EBRTs) from 6 to 15 s. Inlet NH3 concentrations were relatively constant (around 15 mg m(-3)). Significant NH3 reductions were achieved at EBRT = 12 s (removal efficiencies, RE, ranged between 90 and 100% for loading rates, LR, of around 4 g m(-3) h(-1)). At a lower EBRT (6 s), RE dropped to roughly 30-50%. This was due to the dramatic increase in the loading rate (LR up to 12 g m(-3) h(-1)) but the results showed that the change in atmospheric conditions (temperature and relative humidity) also had a significant influence on biofilter performance. It was evidenced that the use of a humidifier upstream of the biofilter must be taken into account for large-scale biofilter design, but only for specific conditions (the spraying of the biofilter having to be carried out exceptionally). During autumn 2012, the biofilter was operated for 116 days at EBRT = 12 s. RE were around 80% for LR of around 3 g m(-3) h(-1). In such autumnal atmospheric conditions, a demister system should be installed upstream of the biofilter in order to avoid water accumulation in the bed material. Although biofiltration was suitable for NH3 treatment of piggery air, the need to control accurately the medium moisture content implies that biofilters would not be easily managed by a pig farmer.

Structural basis for the association of MAP6 protein with microtubules and its regulation by calmodulin

Microtubules are highly dynamic αβ-tubulin polymers. In vitro and in living cells, microtubules are most often cold- and nocodazole-sensitive. When present, the MAP6/STOP family of proteins protects microtubules from cold- and nocodazole-induced depolymerization but the molecular and structure determinants by which these proteins stabilize microtubules remain under debate. We show here that a short protein fragment from MAP6-N, which encompasses its Mn1 and Mn2 modules (MAP6(90-177)), recapitulates the function of the full-length MAP6-N protein toward microtubules, i.e. its ability to stabilize microtubules in vitro and in cultured cells in ice-cold conditions or in the presence of nocodazole. We further show for the first time, using biochemical assays and NMR spectroscopy, that these effects result from the binding of MAP6(90-177) to microtubules with a 1:1 MAP6(90-177):tubulin heterodimer stoichiometry. NMR data demonstrate that the binding of MAP6(90-177) to microtubules involve its two Mn modules but that a single one is also able to interact with microtubules in a closely similar manner. This suggests that the Mn modules represent each a full microtubule binding domain and that MAP6 proteins may stabilize microtubules by bridging tubulin heterodimers from adjacent protofilaments or within a protofilament. Finally, we demonstrate that Ca(2+)-calmodulin competes with microtubules for MAP6(90-177) binding and that the binding mode of MAP6(90-177) to microtubules and Ca(2+)-calmodulin involves a common stretch of amino acid residues on the MAP6(90-177) side. This result accounts for the regulation of microtubule stability in cold condition by Ca(2+)-calmodulin.

Effect of the multifunctional proteins RPA, YB-1, and XPC repair factor on AP site cleavage by DNA glycosylase NEIL1

DNA glycosylases are key enzymes in the first step of base excision DNA repair, recognizing DNA damage and catalyzing the release of damaged nucleobases. Bifunctional DNA glycosylases also possess associated apurinic/apyrimidinic (AP) lyase activity that nick the damaged DNA strand at an abasic (or AP) site, formed either spontaneously or at the first step of repair. NEIL1 is a bifunctional DNA glycosylase capable of processing lesions, including AP sites, not only in double-stranded but also in single-stranded DNA. Here, we show that proteins participating in DNA damage response, YB-1 and RPA, affect AP site cleavage by NEIL1. Stimulation of the AP lyase activity of NEIL1 was observed when an AP site was located in a 60 nt-long double-stranded DNA. Both RPA and YB-1 inhibited AP site cleavage by NEIL1 when the AP site was located in single-stranded DNA. Taking into account a direct interaction of YB-1 with the AP site, located in single-stranded DNA, and the high affinity of both YB-1 and RPA for single-stranded DNA, this behavior is presumably a consequence of a competition with NEIL1 for the DNA substrate. Xeroderma pigmentosum complementation group C protein (XPC), a key protein of another DNA repair pathway, was shown to interact directly with AP sites but had no effect on AP site cleavage by NEIL1.

Macromolecular crowding regulates assembly of mRNA stress granules after osmotic stress: new role for compatible osmolytes

The massive uptake of compatible osmolytes such as betaine, taurine, and myo-inositol is a protective response shared by all eukaryotes exposed to hypertonic stress. Their accumulation results mostly from the expression of specific transporters triggered by the transcriptional factor NFAT5/TonEBP. This allows the recovery of the cell volume without increasing intracellular ionic strength. In this study we consider the assembly and dissociation of mRNA stress granules (SGs) in hypertonic-stressed cells and the role of compatible osmolytes. In agreement with in vitro results obtained on isolated mRNAs, both macromolecular crowding and a high ionic strength favor the assembly of SGs in normal rat kidney epithelial cells. However, after hours of constant hypertonicity, the slow accumulation in the cytoplasm of compatible osmolytes via specific transporters both reduces macromolecular crowding and ionic strength, thus leading to the progressive dissociation of SGs. In line with this, when cells are exposed to hypertonicity to accumulate a large amount of compatible osmolytes, the formation of SGs is severely impaired, and cells increase their chances of survival to another hypertonic episode. Altogether, these results indicate that the impact of compatible osmolytes on the mRNA-associated machineries and especially that associated with SGs may play an important role in cell resistance and adaption to hyperosmolarity in many tissues like kidney and liver.

Rapid assembly and collective behavior of microtubule bundles in the presence of polyamines

Microtubules (MTs) are cylindrical cytoskeleton polymers composed of α-β tubulin heterodimers whose dynamic properties are essential to fulfill their numerous cellular functions. In response to spatial confinement, dynamic MTs, even in the absence of protein partners, were shown to self-organize into higher order structures (spindle or striped structures) which lead to interesting dynamical properties (MT oscillations). In this study, we considered the assembly and sensitivity of dynamic MTs when in bundles. To perform this study, spermine, a natural tetravalent polyamine present at high concentrations in all eukaryote cells, was used to trigger MT bundling while preserving MT dynamics. Interestingly, we first show that, near physiological ionic strengths, spermine promotes the bundling of MTs whereas it does not lead to aggregation of free tubulin, which would have been detrimental to MT polymerization. Experimental and theoretical results also indicate that, to obtain a high rate of bundle assembly, bundling should take place at the beginning of assembly when rapid rotational movements of short and newly nucleated MTs are still possible. On the other hand, the bundling process is significantly slowed down for long MTs. Finally, we found that short MT bundles exhibit a higher sensitivity to cold exposure than do isolated MTs. To account for this phenomenon, we suggest that a collective behavior takes place within MT bundles because an MT entering into a phase of shortening could increase the probability of the other MTs in the same bundle to enter into shortening phase due to their close proximity. We then elaborate on some putative applications of our findings to in vivo conditions including neurons.

Gap junctions favor normal rat kidney epithelial cell adaptation to chronic hypertonicity

Upon hypertonic stress most often resulting from high salinity, cells need to balance their osmotic pressure by accumulating neutral osmolytes called compatible osmolytes like betaine, myo-inositol, and taurine. However, the massive uptake of compatible osmolytes is a slow process compared with other defense mechanisms related to oxidative or heat stress. This is especially critical for cycling cells as they have to double their volume while keeping a hospitable intracellular environment for the molecular machineries. Here we propose that clustered cells can accelerate the supply of compatible osmolytes to cycling cells via the transit, mediated by gap junctions, of compatible osmolytes from arrested to cycling cells. Both experimental results in epithelial normal rat kidney cells and theoretical estimations show that gap junctions indeed play a key role in cell adaptation to chronic hypertonicity. These results can provide basis for a better understanding of the functions of gap junctions in osmoregulation not only for the kidney but also for many other epithelia. In addition to this, we suggest that cancer cells that do not communicate via gap junctions poorly cope with hypertonic environments thus explaining the rare occurrence of cancer coming from the kidney medulla.

Tacticity and surface chemistry effects on the glass transition temperature of thin supported PMMA films

The glass transition temperature (Tg) of thin supported films of stereoregular poly(methyl methacrylate) on silicon has been investigated by ellipsometry in temperature. The Tg of the spin coated layers of isotactic PMMA increases for thickness lower than 100 nm whereas a depression of the Tg is observed for the syndiotactic PMMA. This opposite trend in the Tg variation in thin layer between the two isomers evidenced a fascinating effect of the chain organization at an interacting interface. Hydrofluric acid surface etching of the silicon wafer was shown to decrease the threshold thickness at which the change in Tg occurs for both PMMA isomers. The influence of the interfacial interactions along with the tacticity dependent characteristics of the polymer will be discussed.

Specific DNA-protein interactions on mica investigated by atomic force microscopy

DNA processing by site-specific proteins on surface remains a challenging issue for nanobioscience applications and, in particular, for high-resolution imaging by atomic force microscopy (AFM). To obtain high-resolution conditions, mica, an atomically flat and negatively charged surface, is generally used. However, even though many specific DNA/protein interactions have already been observed by AFM, little is known about DNA accessibility to specific enzymes on mica. Here we measured the accessibility of adsorbed DNA to restriction endonucleases (EcoRI and EcoRV) using AFM. By increasing the concentration of divalent or multivalent salts, DNA adsorption on mica switches from weak to strong binding. Interestingly, while the accessibility of strongly bound DNA was inhibited, loosely adsorbed DNA was efficiently cleaved on mica. This result opens new perspective to study DNA/protein interaction by AFM or to modify specifically DNA on surface.