The Major Ciliary Isoforms of RPGR Build Different Interaction Complexes with INPP5E and RPGRIP1L.

X-linked retinitis pigmentosa (XLRP) is frequently caused by mutations in the retinitis pigmentosa GTPase regulator (RPGR) gene. A complex splicing process acts on the RPGR gene resulting in three major isoforms: RPGRex1-19, RPGRORF15 and RPGRskip14/15. We characterized the widely expressed, alternatively spliced transcript RPGRskip14/15 lacking exons 14 and 15. Using the CRISPR/eSpCas9 system, we generated HEK293T cell lines exclusively expressing the RPGRskip14/15 transcript from the endogenous RPGR gene. RPGRex1-19 and RPGRORF15 were knocked out. Immunocytochemistry demonstrated that the RPGRskip14/15 protein localizes along primary cilia, resembling the expression pattern of RPGRex1-19. The number of cilia-carrying cells was not affected by the absence of the RPGRex1-19 and RPGRORF15 isoforms. Co-immunoprecipitation assays demonstrated that both RPGRex1-19 and RPGRskip14/15 interact with PDE6D, further supporting that RPGRskip14/15 is associated with the protein networks along the primary cilium. Interestingly, interaction complexes with INPP5E or RPGRIP1L were only detectable with isoform RPGRex1-19, but not with RPGRskip14/15, demonstrating distinct functional properties of the major RPGR isoforms in spite of their similar subcellular localization. Our findings lead to the conclusion that protein binding sites within RPGR are mediated through alternative splicing. A tissue-specific expression ratio between RPGRskip14/15 and RPGRex1-19 seems required to regulate the ciliary concentration of RPGR interaction partners.

Trifocal diffractive intraocular lens implantation in patients after previous corneal refractive laser surgery for myopia.

BACKGROUND: With the difficulties in IOL power calculation and the potential side effects occurring postoperatively, multifocal IOL implantation after previous corneal refractive surgery are rarely reported especially for the trifocal IOL. Herein we report the clinical observation of trifocal IOL implantation in patients with previous myopia excimer laser correction. In this study, a multi-formula average method was performed for the IOLs power calculation to improve the accuracy. Visual and refractive outcomes were analyzed, and the subjective quality of patients' life was evaluated by questionnaires survey. METHODS: This retrospective case series included patients with previous myopia excimer laser correction who underwent femtosecond laser assisted phacoemulsification and trifocal IOL (AT LISA tri 839 MP) implantation. Follow-up was done at 1-day, 1-month and 3-month to assess the visual outcomes. Outcome measures were uncorrected distance, intermediate and near visual acuity (UDVA, UIVA, UNVA), manifest refraction, defocus curve, and subjective quality of vision. RESULTS: Twenty-one Eyes from sixteen patients (14 eyes with previous laser in situ keratomileusis and 7 eyes with previous photorefractive keratectomy) were included. Mean postoperative spherical equivalent (SE) at 3-month was - 0.56 D ± 0.49 SD, wherein, 10 eyes (47.6%) were within ±0.50 D of the desired emmetropia and 19 eyes (90.5%) were within ±1.0 D. Mean monocular UDVA, UIVA and UNVA (logMAR) at last visit were 0.02 ± 0.07, 0.10 ± 0.10, and 0.15 ± 0.11 respectively. Three patients (19%) reported halos and glare in postoperative 3 months, two of them needed to use spectacles to improve the intermediate visual acuity. Fifteen patients (94%) reported a satisfaction score of ≥3.5 out of 4.0, without any difficulty in daily activity. Thirteen patients (81%) did not need spectacles at all distances, while the other 3 patients (19%) used spectacles for near-distance related visual activity. Mean composite score of the VF-14 questionnaire was 95.00 ± 7.29 out of 100. CONCLUSIONS: Trifocal IOL implantation after myopia excimer laser correction could restore good distance, intermediate visual acuity and acceptable near visual acuity, and provide accurate refractive outcomes as well as high spectacles independence rate.

Using Transcriptomic Analysis to Assess Double-Strand Break Repair Activity: Towards Precise in vivo Genome Editing.

Mutations in more than 200 retina-specific genes have been associated with inherited retinal diseases. Genome editing represents a promising emerging field in the treatment of monogenic disorders, as it aims to correct disease-causing mutations within the genome. Genome editing relies on highly specific endonucleases and the capacity of the cells to repair double-strand breaks (DSBs). As DSB pathways are cell-cycle dependent, their activity in postmitotic retinal neurons, with a focus on photoreceptors, needs to be assessed in order to develop therapeutic in vivo genome editing. Three DSB-repair pathways are found in mammalian cells: Non-homologous end joining (NHEJ); microhomology-mediated end joining (MMEJ); and homology-directed repair (HDR). While NHEJ can be used to knock out mutant alleles in dominant disorders, HDR and MMEJ are better suited for precise genome editing, or for replacing entire mutation hotspots in genomic regions. Here, we analyzed transcriptomic in vivo and in vitro data and revealed that HDR is indeed downregulated in postmitotic neurons, whereas MMEJ and NHEJ are active. Using single-cell RNA sequencing analysis, we characterized the dynamics of DSB repair pathways in the transition from dividing cells to postmitotic retinal cells. Time-course bulk RNA-seq data confirmed DSB repair gene expression in both in vivo and in vitro samples. Transcriptomic DSB repair pathway profiles are very similar in adult human, macaque, and mouse retinas, but not in ground squirrel retinas. Moreover, human-induced pluripotent stem-cell-derived neurons and retinal organoids can serve as well suited in vitro testbeds for developing genomic engineering approaches in photoreceptors. Our study provides additional support for designing precise in vivo genome-editing approaches via MMEJ, which is active in mature photoreceptors.

[Fluorescence Angiography-assisted Management of Recurrences in Aggressive Posterior Retinopathy of Prematurity (APROP) after Intravitreal Monotherapy with 0.312 mg Bevacizumab]. / Fluoreszenzangiografieassistiertes Management von Rezidiven bei aggressiver posteriorer Frühgeborenenretinopathie (APROP) nach intravitrealer Monotherapie mit 0,312 mg Bevacizumab.

BACKGROUND: In cases of aggressive posterior retinopathy of prematurity (APROP), recurrences can occur after intravitreal injection of bevacizumab (IVB), in spite of successful treatment of the acute stage. Therefore, long-term examinations in extremely premature patients are needed. We defined recurrences as a relapse of plus disease and leakage (with or without proliferation) at the vascularisation border, but also anterior and posterior to it. METHODS: RetCam wide-field colour images and fluorescein angiography were performed before the first IVB (0.312 mg bevacizumab in 0.025 ml per eye), before each further therapy, i.e. additional intravitreal injection, laser- or cryocoagulation or pars-plana vitrectomy, and at the end of the therapy. We analysed the images of 18 eyes with APROP of 9 extreme premature patients treated between 08/2007 and 12/2017 (GA 21 - 27 weeks, BW 430 - 890 g). RESULTS: Long-term therapeutic success was achieved in only 4 eyes/2 children (22%) with one single injection. In 2 eyes/2 children (11%), a second and third injection was given within 2 weeks because of an insufficient therapeutic effect. Up to 3 injections together with laser coagulation were needed in 12 eyes/6 children (67%), in order to achieve complete resolution of ROP activity. In 6 eyes/2 children (33%), resolution of leakage at the original vascularisation border was achieved only with further laser coagulation. In one single eye, retinal detachment occurred after unsuccessful retinal surgery. Before IVB, fluorescein angiography disclosed leakage due to proliferation in most of the patients (12 eyes/6 children). In recurrences after IVB, a posterior shift of the leakage site was found (14 eyes/4 children), whereas after laser photocoagulation proliferative changes were also detected anterior to the vascularisation border (5 eyes/3 children). Treatment was indicated based on angiographic findings in 14 eyes/4 children where wide-field colour images did not show plus disease or proliferation. CONCLUSIONS: Intravitreal injection of 0.312 mg bevacizumab has been shown to be an effective therapy for the acute stage of APROP. Long-term success required consequent monitoring and treatment of APROP recurrences. Fluorescein angiography was particularly useful to detect recurrences that were not evident in wide-field colour images.

Structure-Function Correlation in Hemianopic Vision Loss in Children Aged 3-6 Years Using OCT and SVOP, and Comparison with Adult Eyes.

PURPOSE: To correlate visual field assessment with saccadic vector optokinetic perimetry (SVOP) in children with ganglion cell loss due to anterior pathway pathologies resulting in hemianopic visual field defects measured with optical coherence tomography (OCT). METHODS: 5 young (aged 3-6 years) and 5 adult patients with hemianopia, 10 healthy preschoolers (mean age 4.4 years), and 10 healthy adults (mean age 25.3 years) were tested with SVOP and OCT (focusing on the ganglion cell layer, GCL+). In adults, visual field testing was also performed with static and fundus-controlled perimetry. RESULTS: OCT allowed precise structure analysis and showed a vertical border with GCL+ loss on the hemianopic side in children and adults compared to controls. SVOP showed visual field defects on the hemianopic side in peripheral regions and inadequate results at the parafoveal positions in both groups. In contrast, static and fundus-controlled perimetry showed a clear border in foveal and parafoveal regions. CONCLUSIONS: All children underwent SVOP with minimal restrictions, allowing functional evaluation of peripheral visual field positions. Parafoveal positions showed multiple false-positive results. The function-structure relationship is measurable even in young children by using the GCL+ analysis. This combination of novel child-friendly techniques allows collecting objectively measured values and simplifies diagnosis and follow-up in treatment.

Choroidal Thickness with Swept-Source Optical Coherence Tomography versus Foveal Morphology in Young Children with a History of Prematurity.

AIM: Comparison of choroidal thickness (CT) and foveal morphology as seen with swept-source optical coherence tomography (SS-OCT) in children with a history of treated or spontaneously regressed retinopathy of prematurity (tROP or srROP) to assess the impact on best-corrected visual acuity (BCVA). METHODS: CT was measured by SS-OCT (DRI-OCT Triton; Topcon, USA) single scans of a 6-mm diameter around the fovea in 17 children with tROP or srROP (4-7 years of age) and compared to 25 controls (age-matched children and adults). The disproportion of the outer nuclear layer and inner retinal layers at the fovea (i.e., the ONL+/IRL ratio) as a measure of macular developmental arrest (MDA) was manually analyzed. BCVA was tested with ETDRS letter charts and correlated with the morphology. RESULTS: CT was significantly thinner in children with tROP and srROP compared to term-born healthy children (nKids) at all measurement marks (p < 0.001), and mostly affected in the subfoveal area. tROP showed the lowest CT. CT allowed no direct conclusion about ONL+/IRL, but correlated positively with BCVA. CONCLUSIONS: Reduced CT in children with a history of ROP is linked to ROP severity. These findings overlap with the degree of MDA. CT appears to be involved in ROP, but MDA showed a higher impact on the BCVA of the examined cohort.

RETINAL VASCULAR DEVELOPMENT WITH 0.312 MG INTRAVITREAL BEVACIZUMAB TO TREAT SEVERE POSTERIOR RETINOPATHY OF PREMATURITY: A Longitudinal Fluorescein Angiographic Study.

PURPOSE: To report the outcome of intravitreal 0.312 mg bevacizumab (IVB) monotherapy in acute retinopathy of prematurity (ROP) and to describe the vascular development over time. METHODS: Seventeen prematurely born infants were treated with IVB (0.312 mg in 0.025 mL per eye) because of acute ROP in posterior Zone II or Zone I, including aggressive posterior ROP. Infants were examined by fluorescein angiography (FA) using RetCam II or III (Clarity Medical Systems Inc) before IVB (n = 21 eyes), within 6 weeks (n = 23 eyes), 8 to 13 weeks (n = 22 eyes), and up to 45 months (n = 10 eyes). RESULTS: Acute ROP regressed in 19 out of 27 analyzed eyes (70%), including 100% and 80% of posterior Zone II and Zone I eyes, respectively, but only 25% of aggressive posterior ROP eyes. Early recurrences (11%, all aggressive posterior ROP) and late reactivations (18%) were observed within 1 week and at 9 to 12 weeks, respectively. All eyes showed leakage at the junction of the vascularized zone and capillary malformation on FA before treatment. Vessel branching abnormalities and circumferential vessel formation were typical FA features after treatment. Vascular outgrowth after one IVB became complete in 87.5% of eyes for which FA was available up to at least 9 weeks after IVB. CONCLUSION: A single dose of 0.312 mg bevacizumab was efficient to induce regression of ROP in posterior Zone II and most of Zone I cases, but not in aggressive posterior ROP. FA describes vascular abnormalities, the importance of which warrants further investigation.

Spatially Resolved Spectral Sensitivities as a Potential Read-out Parameter in Clinical Gene Therapeutic Trials.

PURPOSE: Spatially resolved functional assessment of rods and cones under photopic and scotopic conditions is desirable to evaluate the treatment outcome of gene therapeutic applications in inherited retinal disorders, such as early- onset severe retinal dystrophy (EOSRD) or achromatopsia. METHODS: A sample of 3 healthy subjects, 6 patients with RPE65 deficiency (aged 11-45 years), and 3 patients with cone dysfunction disorders underwent spectral sensitivity testing (SST) under conditions of dark and light adaptation using a Humphrey Field Analyzer modified perimeter. RESULTS: SST in healthy subjects revealed sensitivity curves corresponding well with the CIE (International Commission on Illumination) standard fundamentals. Absence of cone function was observed in patients with cone dysfunction disorders. In patients with RPE65 mutations, SST under conditions of both dark and light adaptation revealed similar curves at typical cone sensitivities. S cone-related thresholds were diminished in young patients (11-14 years) and absent in adults (19 years and over). CONCLUSION: In the present study, residual vision was cone mediated both under photopic and scotopic conditions in young patients with EOSRD associated with RPE65 mutations, but S cone function was severely reduced early on. In rod monochromats, vision was rod mediated both under conditions of dark and light adaptation. These observations are important for ongoing and future clinical trials employing gene therapeutic strategies in both rod-cone dystrophies and achromatopsia.

Detection of the Vascular Endothelial Growth Factor with a Novel Bioluminescence Resonance Energy Transfer Pair Using a Two-Component System.

In this paper we describe a two-component BRET (bioluminescence resonance energy transfer)-based method to detect vascular endothelial growth factor (VEGF) molecules in unknown samples as the basis for subsequent in vivo use. A luminescent VEGF binding molecule, which binds in the receptor binding motif of VEGF, is used as the energy donor, transferred to a fluorophore-coupled VEGF binding molecule (acceptor), which binds to the neuropilin binding motif of VEGF, thus enabling energy transfer from the donor to the acceptor molecule. This leads to the emission of light at a longer wavelength and thus the generation of an increased BRET signal only when VEGF is bound to both the donor and acceptor molecules. We further describe a novel BRET pair that uses the Renilla reniformis mutant luciferase RLuc8 and the chemically engineered fluorophore PerCP-Cy5.5®, which exhibits superior peak separation of approximately 300 nm. The implantation of capsules consisting of the two BRET components in solution, permeable for VEGF for its in vivo detection, would provide a new and improved method for monitoring VEGF-induced pathologies and thus an adjustment of therapy to patient needs.

[The Impact of Macular Development on Full-field and Multifocal ERG in Extremely Preterm-born Children with and without Acute Retinopathy of Prematurity]. / Einfluss der Makulareifung auf Ganzfeld- und multifokales ERG bei ehemaligen Extremfrühgeborenen mit und ohne akute Frühgeborenenretinopathie.

Introduction Retinal development is a complex process that can continue into early childhood and beyond. Prematurity can affect the maturation of the central retina, characterised by a flatter foveal pit and overlying inner retinal layers (IRL), leading to a disturbed ratio of outer retinal layers to IRL ("macular developmental arrest": MDA) and functional impairment (Bowl et al. 2016 18). The purpose of this study was to correlate functional results by electrophysiology with the morphological appearance of the fovea in children with spontaneously regressed and without ROP and term-born age-matched controls. Methods We investigated n = 60 preterm-born children with spontaneously regressed (srROP, n = 15) and without ROP (noROP, n = 50) as part of an extensive prospective cohort study and compared them to n = 10 term-born age-matched controls (Term). Full-field electroretinogram (ffERG) and multifocal ERG (mfERG) based on ISCEV-standards were performed in every child for functional evaluation. Foveal morphology was evaluated with optical coherence tomography (SD-OCT, Spectralis, Heidelberg Engineering, Germany). Results Analysis of the scotopic ffERG showed significantly modified b-wave amplitudes in srROP and noROP, especially when MDA was found on SD-OCT. The mfERG exhibited a modified P1-component of the central hexagon and the second concentric ring in children with MDA. No other parameters were significantly changed. Conclusions Electrophysiological changes can be found in extremely preterm-born children, especially with OCT-confirmed foveal maturation impairment (MDA), namely in children with spontaneously regressed ROP as well as in children without ROP. The reduced b-wave in the scotopic ffERG and the reduced P1-component in the mfERG indicate involvement of bipolar cells in extremely prematurely born children with MDA. In particular, the correlation of MDA with ffERG could be a sign of more global retinal maturation disturbance accompanying MDA, and this is seen even without acute ROP.

Fundus-controlled two-color dark adaptometry with the Microperimeter MP1.

PURPOSE: The aim of this study was to provide fundus-controlled two-color adaptometry with an existing device. A quick and easy approach extends the application possibilities of a commercial fundus-controlled perimeter. METHODS: An external filter holder was placed in front the objective lens of the MP1 (Nidek, Italy) and fitted with filters to modify background, stimulus intensity, and color. Prior to dark adaptometry, the subject's visual sensitivity profile was measured for red and blue stimuli to determine whether rods or cones or both mediated the absolute threshold. After light adaptation, 20 healthy subjects were investigated with a pattern covering six spots at the posterior pole of the retina up to 45 min of dark adaptation. Thresholds were determined using a 200 ms red Goldmann IV and a blue Goldmann II stimulus. RESULTS: The pre-test sensitivity showed a typical distribution of values along the meridian, with high peripheral light increment sensitivity (LIS) and low central LIS for rods and the reverse for cones. After bleach, threshold recovery had a classic biphasic shape. The absolute threshold was reached after approximately 10 min for the red and 15 min for the blue stimulus. CONCLUSIONS: Two-color fundus-controlled adaptometry with a commercial MP1 without internal changes to the device provides a quick and easy examination of rod and cone function during dark adaptation at defined retinal loci of the posterior pole. This innovative method will be helpful to measure rod vs. cone function at known loci of the posterior pole in early stages of retinal degenerations.

Shared decision-making, control preferences and psychological well-being in patients with RPE65 deficiency awaiting experimental gene therapy.

PURPOSE: Retinal gene therapy trials are currently ongoing in a small number of inherited retinal disorders and this number is expected to rise significantly. The aim of this study was to analyze the psychological aspects of patients with RPE65 deficiency awaiting potential enrollment in gene therapy trials. METHODS: Five patients with genetically proven RPE65 deficiency took part in this study. They were asked to complete the German versions of (i) the Patient Health Questionnaire (PHQ-D), (ii) the National Eye Institute Visual Function Questionnaire (NEI-VFQ), (iii) the Shared Decision Making Questionnaire (PEF-FB-9), and (iv) the Autonomy Preference Index (API-Dm), and in addition they took part in qualitative interviews. RESULTS: The evaluations of the questionnaires and the interviews showed that the patients have quite high information needs and wish to take part in medical decisions. The perspective to participate in gene therapy trials does not seem to cause pronounced worries. Only the insecurity about if and when enrollment in a trial takes place may be burdensome. DISCUSSION: This study generated important data about the psychological situation of patients awaiting potential enrollment in clinical trials, which can be used to improve patient care in the increasing number of future gene therapy trials around the world.

Long-Term Porcine Retina Explants as an Alternative to In Vivo Experimentation.

Purpose: The porcine retina represents an optimal model system to study treatment approaches for inherited retinal dystrophies owing to close anatomical similarities to the human retina, including a cone enriched visual streak. The aim of this work was to establish a protocol to keep explants in culture for up to 28 days with good morphological preservation. Methods: Two to four retina explants per eye were obtained from the central part of the retina and transferred onto a membrane insert with the photoreceptors facing down. Different medium compositions using Neurobasal-A medium containing 100 or 450 mg/dL glucose and combinations of fetal calf serum, B-27 with or without insulin and N-2 were tested. We developed a tissue quality score with robust markers for different retinal cell types (protein kinase C alpha, peanut agglutinin and 4',6-diamidino-2-phenylindol). Results: Retinae were kept until 28 days with only little degradation. The best results were attained using Neurobasal-A medium containing 100 mg/dL glucose supplemented with B-27 containing insulin and N-2. For an easy preparation process, it is necessary to minimize transport time and keep the eyes on ice until dissected. Heat-mediated decontamination by the butcher has to be avoided. Conclusions: Using a standardized protocol, porcine retina explants represent an easy to handle intermediate model between in vitro and in vivo experimentation. This model system is robustly reproducible and contributes to the implementation of the 3R principle to minimize animal experimentation. Translational Relevance: This model can be used to test future therapeutic approaches for inherited retinal dystrophies.

Clinical significance of signal shadowing during intraoperative optical coherence tomography-assisted vitreoretinal surgery.

This study aimed to analyze the clinical significance of signal shadowing during intraoperative optical coherence tomography (iOCT)-assisted vitreoretinal surgery caused by vitreoretinal instruments, tissue dyes, and vitreous substitutes, and to objectively quantify its impact on iOCT imaging. This is a retrospective observational study of postoperative image analysis from one hundred seventeen (117) patients who underwent iOCT-assisted vitrectomy. The image data were divided into three groups: vitreoretinal instruments, tissue dyes, and vitreous substitutes. The data was then processed using graphic software to measure the grade of picture quality distortion and compared to paired image controls without clinically perceptive interference, then analyzed statistically. The intraocular portion of all studied vitreoretinal instruments caused a high average gray level interference compared to controls ranging from 32 to 68% reduction, obscuring the area of interest significantly. The tips of the instruments produced low-grade shadowing, allowing the underlying tissue to be distinguished. The analyzed dyes demonstrated a wide interference range: ICG (- 75.12%), and triamcinolone (- 26.13%) showed dose-dependent high shadowing, while VITREODYNE™ (49.3%) and brilliant blue G (14.06%) exhibited no perceived distortions whilst increasing average gray levels. All analyzed vitreous substitutes (air, SF6, C3F8, PFCL, and silicone oil) showed an insignificant shadowing effect on iOCT. Certain dyes and vitreous substitutes produce a negligible shadowing effect compared to controls and other dyes, providing an advantage during real-time iOCT imaging. All analyzed vitreoretinal instruments showed a significant interference that should prompt the development of new imaging techniques or the implementation of materials with low-grade interference to overcome a clinically relevant shadowing effect on iOCT, maximizing the technology's visual accuracy and surgical diagnostic aid proficiency.

Rapid and Reliable Quantification of Prime Editing Targeting Within the Porcine ABCA4 Gene Using a BRET-Based Sensor.

Stargardt disease (STGD) leads to blindness in children and young adults. So far, no curative therapy is available and gene augmentation therapies have not yet advanced to the clinics, in part, due to the limited packaging capacity of adeno-associated viruses used to transfer genes into photoreceptor cells. Prime editing offers a new perspective to treat mutations on the genomic level. A nicking variant of Cas9 fused to a reverse transcriptase complex with an elongated guideRNA force intracellular mismatch repair to correct the targeted mutation even in postmitotic cells such as photoreceptors in the eye. Using a custom-made bioluminescence resonance energy transfer (BRET)-based editing sensor in HEK293 cells, we tested 27 different prime editing guide RNAs (pegRNAs) and additional 4 nicking guide RNAs (ngRNAs) with regard to their efficiency to induce sequences changes in exon 43 of the porcine ATP binding cassette subfamily A member 4 (ABCA4) gene that eliminate a mutagenic adenine frameshift insertion, which has been associated with STGD in humans. We identified nine working pegRNAs, and in combination with ngRNAs, we achieved a correction rate of up to ≈92% measured with the BRET-based reporter system. Our data prove the high efficiency of prime editors to correct mutations and highlight the importance of optimal ngRNA design, thus offering a promising editing tool to correct ABCA4 mutations in the disease context.

Retinal Pigment Epithelium Cell Development: Extrapolating Basic Biology to Stem Cell Research.

The retinal pigment epithelium (RPE) forms an important cellular monolayer, which contributes to the normal physiology of the eye. Damage to the RPE leads to the development of degenerative diseases, such as age-related macular degeneration (AMD). Apart from acting as a physical barrier between the retina and choroidal blood vessels, the RPE is crucial in maintaining photoreceptor (PR) and visual functions. Current clinical intervention to treat early stages of AMD includes stem cell-derived RPE transplantation, which is still in its early stages of evolution. Therefore, it becomes essential to derive RPEs which are functional and exhibit features as observed in native human RPE cells. The conventional strategy is to use the knowledge obtained from developmental studies using various animal models and stem cell-based exploratory studies to understand RPE biogenies and developmental trajectory. This article emphasises such studies and aims to present a comprehensive understanding of the basic biology, including the genetics and molecular pathways of RPE development. It encompasses basic developmental biology and stem cell-based developmental studies to uncover RPE differentiation. Knowledge of the in utero developmental cues provides an inclusive methodology required for deriving RPEs using stem cells.

Progress in Stem Cells-Based Replacement Therapy for Retinal Pigment Epithelium: In Vitro Differentiation to In Vivo Delivery.

Retinal pigment epithelium (RPE) is a critical cell monolayer forming the blood-retina-barrier (BRB) and a permeable bridge between the choriocapillaris and the retina. RPE is also crucial in maintaining photoreceptor function and for completing the visual cycle. Loss of the RPE is associated with the development of degenerative diseases like age-related macular degeneration (AMD). To treat diseases like AMD, pluripotent stem cell-derived RPE (pRPE) has been recently explored extensively as a regenerative module. pRPE like other ectodermal tissues requires specific lineage differentiation and long-term in vitro culturing for maturation. Therefore, understanding the differentiation process of RPE could be useful for stem cell-based RPE derivation. Developing pRPE-based transplants and delivering them into the subretinal space is another aspect that has garnered interest in the last decade. In this review, we discuss the basic strategies currently employed for stem cell-based RPE derivation, their delivery, and recent clinical studies related to pRPE transplantation in patients. We have also discussed a few limitations with in vitro RPE culture and potential solutions to overcome such problems which can be helpful in developing functional RPE tissue.

A simple twist technique for lens-sparing one-handed peripheral vitrectomy in phakic patients: a learning approach for junior surgeons.

The evolution of vitrectomy has led to improved suturless techniques and minimally invasive surgery. Nevertheless, the procedure requires great bimanual dexterity and poses risk for lens touch, especially in the hands of less experienced junior surgeons. We hereby present a twist technique which allows for one-handed (right or left) peripheral vitrectomy without the need for one or several hand-switches with the vitreous cutter and avoids lens touch. The technique can be used as a learning approach for junior vitreoretinal surgeons.

Characterization of Double-Strand Break Repair Protein Ku80 Location Within the Murine Retina.

Purpose: To characterize the spatial distribution of the DNA-double strand break-repair protein Ku80 in the murine retina. Even though robust data exist on the complexity of DNA repair mechanisms in dividing cells in vitro, almost nothing is known about it in post-mitotic neurons or photoreceptors (PRs). This knowledge is an important prerequisite for in vivo therapeutic approaches by genome editing in retina and PRs. Recently, it was shown that mouse rod PRs are incapable of repairing double-strand breaks induced by radiation. Material and Methods: Retinae from wild-type, rd10, and RPGR-KI mouse lines were obtained and stained with antibodies against Ku80, and cellular markers CtBP2, beta-Dystropglycan, Lamin B, and peanut agglutinin. Organotypic explant cultures were generated and maintained for up to 10 days. Laser microdissection was performed to obtain photoreceptor nuclei, and Ku80 expression was compared to whole retina by real-time PCR (RT-PCR). Results: Strong Ku80 immunoreactivity was observed in rod but not cone photoreceptor terminals localized in the outer plexiform layer of the retina in all three mouse lines. During retinal explant culture, we observed that Ku80-positive globules translocate into the heterochromatin region of nuclei in the outer nuclear layer (ONL). By quantitative PCR, we showed upregulation of relative Ku80 expression in the ONL during wild-type retinal explant culture. Discussion: The unexpected localization of Ku80 to murine rod terminals indicates another tissue-specific modification to the canonical DNA repair mechanisms and warrants further investigation.

Subretinal Implantation of Human Primary RPE Cells Cultured on Nanofibrous Membranes in Minipigs.

PURPOSE: The development of primary human retinal pigmented epithelium (hRPE) for clinical transplantation purposes on biodegradable scaffolds is indispensable. We hereby report the results of the subretinal implantation of hRPE cells on nanofibrous membranes in minipigs. METHODS: The hRPEs were collected from human cadaver donor eyes and cultivated on ultrathin nanofibrous carriers prepared via the electrospinning of poly(L-lactide-co-DL-lactide) (PDLLA). "Libechov" minipigs (12-36 months old) were used in the study, supported by preoperative tacrolimus immunosuppressive therapy. The subretinal implantation of the hRPE-nanofibrous carrier was conducted using general anesthesia via a custom-made injector during standard three-port 23-gauge vitrectomy, followed by silicone oil endotamponade. The observational period lasted 1, 2, 6 and 8 weeks, and included in vivo optical coherence tomography (OCT) of the retina, as well as post mortem immunohistochemistry using the following antibodies: HNAA and STEM121 (human cell markers); Bestrophin and CRALBP (hRPE cell markers); peanut agglutining (PNA) (cone photoreceptor marker); PKCα (rod bipolar marker); Vimentin, GFAP (macroglial markers); and Iba1 (microglial marker). RESULTS: The hRPEs assumed cobblestone morphology, persistent pigmentation and measurable trans-epithelial electrical resistance on the nanofibrous PDLLA carrier. The surgical delivery of the implants in the subretinal space of the immunosuppressed minipigs was successfully achieved and monitored by fundus imaging and OCT. The implanted hRPEs were positive for HNAA and STEM121 and were located between the minipig's neuroretina and RPE layers at week 2 post-implantation, which was gradually attenuated until week 8. The neuroretina over the implants showed rosette or hypertrophic reaction at week 6. The implanted cells expressed the typical RPE marker bestrophin throughout the whole observation period, and a gradual diminishing of the CRALBP expression in the area of implantation at week 8 post-implantation was observed. The transplanted hRPEs appeared not to form a confluent layer and were less capable of keeping the inner and outer retinal segments intact. The cone photoreceptors adjacent to the implant scaffold were unchanged initially, but underwent a gradual change in structure after hRPE implantation; the retina above and below the implant appeared relatively healthy. The glial reaction of the transplanted and host retina showed Vimentin and GFAP positivity from week 1 onward. Microglial activation appeared in the retinal area of the transplant early after the surgery, which seemed to move into the transplant area over time. CONCLUSIONS: The differentiated hRPEs can serve as an alternative cell source for RPE replacement in animal studies. These cells can be cultivated on nanofibrous PDLLA and implanted subretinally into minipigs using standard 23-gauge vitrectomy and implantation injector. The hRPE-laden scaffolds demonstrated relatively good incorporation into the host retina over an eight-week observation period, with some indication of a gliotic scar formation, and a likely neuroinflammatory response in the transplanted area despite the use of immunosuppression.