Gesine B. Jaissle

New views on RPE65 deficiency: the rod system is the source of vision in a mouse model of Leber congenital amaurosis.

Leber congenital amaurosis (LCA) is the most serious form of the autosomal recessive childhood-onset retinal dystrophies. Mutations in the gene encoding RPE65, a protein vital for regeneration of the visual pigment rhodopsin in the retinal pigment epithelium, account for 10–15% of LCA cases. Whereas previous studies of RPE65 deficiency in both animal models and patients attributed remaining visual function to cones, we show here that light-evoked retinal responses in fact originate from rods. For this purpose, we selectively impaired either rod or cone function in Rpe65−/− mice by generating double– mutant mice with models of pure cone function (rhodopsin-deficient mice; Rho−/−) and pure rod function (cyclic nucleotide–gated channel α3–deficient mice; Cnga3−/−). The electroretinograms (ERGs) of Rpe65−/− and Rpe65−/−Cnga3−/− mice were almost identical, whereas there was no assessable response in Rpe65−/−Rho−/− mice. Thus, we conclude that the rod system is the source of vision in RPE65 deficiency. Furthermore, we found that lack of RPE65 enables rods to mimic cone function by responding under normally cone-isolating lighting conditions. We propose as a mechanism decreased rod sensitivity due to a reduction in rhodopsin content to less than 1%. In general, the dissection of pathophysiological processes in animal models through the introduction of additional, selective mutations is a promising concept in functional genetics.

Inactivation of the murine X-linked juvenile retinoschisis gene, Rs1h, suggests a role of retinoschisin in retinal cell layer organization and synaptic structure

Deleterious mutations in RS1 encoding retinoschisin are associated with X-linked juvenile retinoschisis (RS), a common form of macular degeneration in males. The disorder is characterized by a negative electroretinogram pattern and by a splitting of the inner retina. To gain further insight into the function of the retinoschisin protein and its role in the cellular pathology of RS, we have generated knockout mice deficient in Rs1h, the murine ortholog of the human RS1 gene. We show that pathologic changes in hemizygous Rs1h−/Y male mice are evenly distributed across the retina, apparently contrasting with the macula-dominated features in human. Similar functional anomalies in human and Rs1h−/Y mice, however, suggest that both conditions are a disease of the entire retina affecting the organization of the retinal cell layers as well as structural properties of the retinal synapse.

Z-suture: a new knotless technique for transscleral suture fixation of intraocular implants

The presented Z-suture is a simple, rapid and safe knotless technique that facilitates transscleral suture fixation of various intraocular implants in the ciliary sulcus, such as sutured intraocular lenses, artificial iris prostheses and iris diaphragms. As the knotless approach reliably avoids suture erosion, external fixation can be performed without any protecting scleral flaps or lamellar grooves. The needle is simply passed through the sulcus and the emerging polypropylene suture is secured in the sclera using a zigzag-shaped intrascleral suture (Z-suture). Each pass starts directly adjacent to the exiting site. Five passes are sufficient to reliably fix the suture so that it resists even maximum tractive forces. Once this procedure is done, the suture can be cut without any knot. By avoiding suture knots, and hence the need for intrascleral flaps, this knotless approach may help to reduce suture-related complications such as scleral atrophy, suture erosion and infections.

Rapid degradation of dominant-negative Rab27 proteins in vivo precludes their use in transgenic mouse models

BackgroundTransgenic mice have proven to be a powerful system to study normal and pathological gene functions. Here we describe an attempt to generate a transgenic mouse model for choroideremia (CHM), a slow-onset X-linked retinal degeneration caused by mutations in the Rab Escort Protein-1 (REP1) gene. REP1 is part of the Rab geranylgeranylation machinery, a modification that is essential for Rab function in membrane traffic. The loss of REP1 in CHM patients may trigger retinal degeneration through its effects on Rab proteins. We have previously reported that Rab27a is the Rab most affected in CHM lymphoblasts and hypothesised that the selective dysfunction of Rab27a (and possibly a few other Rab GTPases) plays an essential role in the retinal degenerative process.ResultsTo investigate this hypothesis, we generated several lines of dominant-negative, constitutively-active and wild-type Rab27a (and Rab27b) transgenic mice whose expression was driven either by the pigment cell-specific tyrosinase promoter or the ubiquitous β-actin promoter. High levels of mRNA and protein were observed in transgenic lines expressing wild-type or constitutively active Rab27a and Rab27b. However, only modest levels of transgenic protein were expressed. Pulse-chase experiments suggest that the dominant-negative proteins, but not the constitutively-active or wild type proteins, are rapidly degraded. Consistently, no significant phenotype was observed in our transgenic lines. Coat-colour was normal, indicating normal Rab27a activity. Retinal function as determined by fundoscopy, angiography, electroretinography and histology was also normal.ConclusionsWe suggest that the instability of the dominant-negative mutant Rab27 proteins in vivo precludes the use of this approach to generate mouse models of disease caused by Rab27 GTPases.

The distribution, release kinetics, and biocompatibility of triamcinolone injected and dispersed in silicone oil.

PURPOSE Triamcinolone acetonide (TA) has been proposed as an adjuvant to pars plana vitrectomy with silicone oil for the surgical treatment of proliferative vitreoretinopathy and proliferative diabetic retinopathy. However, to date no data about the distribution and pharmacokinetics of lipophilic TA injected into silicone oil have been reported. METHODS An artificial vitreous space chamber was filled with silicone oil. TA was either injected or dispersed into silicone oil. TA release using a continuous flow model was measured spectrophotometrically. To determine the antiproliferative or cytotoxic effect of the released TA, monolayer cultures of retinal pigment epithelial cells (ARPE19) and retinal ganglion cells (RGC5) were used. Bromodeoxyuridine incorporation, MTT assay, and scanning electron microscopy were performed. RESULTS Injected TA sank slowly through the silicone oil and started to sediment below the silicone oil bubble shortly after injection. After the simulated intravitreal injection, no TA could be retrieved from the silicone oil bubble. In contrast, when a suspension of silicone oil and TA was prepared before injection, stable noncytotoxic amounts of TA (25 microg/mL) could be retrieved for up to 90 days. After mere injection (without previous suspension in silicone oil), the sedimented TA crystals showed a pronounced cytotoxic effect. CONCLUSIONS Intravitreally injected TA does not mix with silicone oil. TA crystals that sediment at the lower border of a silicone oil bubble may be harmful to retinal cells. A suspension of TA in silicone oil may exhibit safer extended release over several days.

A case of cutaneous melanoma metastatic to the vitreous cavity: possible pathomechanism and review of the literature

BackgroundIsolated vitreous metastases are extremely rare and the pathogenesis of metastasis is still unclear. Here we present the detailed description of the disease progression in a 68-year-old patient with vitreous seeding of a metastatic cutaneous melanoma beginning at a very early stage.MethodsInterventional case report and review of the literature.ResultsThe initial retrohyaloidal metastatic lesion was identified adjacent to a small epiretinal hemorrhage. As the disease progressed golden brown spherules appeared in the posterior vitreous emanating from the area of the lesion. Further progression led to a dense metastatic infiltration of the entire vitreous cavity and a decline of the visual acuity to 20/1200. Diagnostic and therapeutic pars plana vitrectomy was performed to confirm the diagnosis and preserve the eye and useful vision.ConclusionsFor the first time the formation of vitreous metastases derived from cutaneous melanoma was carefully studied beginning at a very early stage. This made it possible to analyze the rare mechanism of vitreous metastasis, which has not been conclusively known till now. The features of metastatic cutaneous melanoma to the vitreous are discussed in context of a review of the literature that resulted from the study of 17 patients with 22 affected eyes.

Grid laser photocoagulation for macular oedema due to branch retinal vein occlusion in the age of bevacizumab? Results of a prospective study with crossover design

Background and aim To investigate the long term effectiveness of grid laser photocoagulation (GLP) versus intravitreal bevacizumab (BEV) in macular oedema (MO) secondary to branch retinal vein occlusion (BRVO), and to evaluate the treatment courses after treatments were switched. Methods In this prospective interventional consecutive case series, previously untreated eyes with perfused MO were enclosed over a period of 16 months for BEV and for 29 months for GLP. The follow-up period was 1 year. Patients with persistent MO after 12 months of BEV were offered GLP and vice versa, and were followed-up for another 12 months. Results Both BEV (23 eyes) and GLP (21 eyes) caused a significant (p<0.05) reduction in central retinal thickness (CRT) at 12 months although this was delayed with GLP. However, BEV revealed a significantly better best corrected visual acuity (BCVA) compared with GLP (0.2 vs 0.5 logMAR; p<0.04). Switching therapy for non-responders revealed a reduced CRT at another 12 months, although this was not significant. Conclusions Functionally and anatomically, BEV appears to be more effective than GLP for the therapy of MO due to BRVO. BCVA is significantly better after 1 year and the anatomical response of the MO is faster. Furthermore, non-responders with persistent MO despite BEV or GLP treatment might benefit from switching therapy.

Suppression of Melanoma-Associated Neoangiogenesis by Bevacizumab

BACKGROUND Bevacizumab, a potent antibody against the vascular endothelial growth factor (VEGF), has been shown to be effective for treatment of colorectal cancer. Recently, high effectiveness of bevacizumab in combination with paclitaxel has been reported in a single metastatic melanoma case. To our knowledge, we demonstrate for the first time the antiangiogenetic effect of bevacizumab in a patient with a vitreous melanoma metastasis. OBSERVATIONS A 68-year-old man with a vitreous melanoma metastasis of the left eye was treated with a revitrectomy combined with intravitreal bevacizumab application because of iris neovascularization and progressive epiretinal tumor plaques. Four days after the treatment, the melanoma-associated neovascularization completely disappeared, but it recurred after 6 weeks. Although repetitive administration of local bevacizumab produced the same antiangiogenetic effect, progression of the epiretinal tumor plaques could not be stopped with the local bevacizumab treatment. CONCLUSIONS Intraocular administration of the anti-VEGF drug bevacizumab causes immediate and complete regression of melanoma-associated angiogenesis. The rationale for the therapeutic strategy in our patient was an elevated level of VEGF in the vitreous cavity. Because we could not demonstrate a direct antiproliferative effect of bevacizumab on melanoma metastasis, bevacizumab seems most promising if evaluated in combination with antiproliferative agents.

Epiretinal Deposit of Triamcinolone Acetonide at the Posterior Pole After Intravitreal Injection

The anatomic response to intravitreal bevacizumab injection in three patients with aggressive, posterior retinopathy of prematurity is described. In all cases, the worse eye was treated with a single intravitreal injection of 0.75 mg of bevacizumab as monotherapy or complementary to laser therapy. In 24 hours, all injected eyes showed regression of the tunica vasculosa lentis and iris vessel engorgement and disappearance of iris rigidity. In addition, plus disease and retinal proliferation began to regress. None of the eyes required additional treatment. Follow-up of up to 10 months

Erratum to: Bone spicule pigment formation in retinitis pigmentosa: insights from a mouse model

U. WolfrumInstitute for Zoology, University Mainz,Mainz, GermanyP. HumphriesOcular Genetics Unit, Trinity College,Smurfit Institute,Dublin, IrelandPresent Address:A. GieslDepartment of Biology and Animal Physiology,University of Erlangen-Nuernberg,Erlangen, GermanyGraefes Arch Clin Exp Ophthalmol (2010) 248:1365DOI 10.1007/s00417-010-1357-2