ULTRASTRUCTURAL STUDY ON THE INVASION OF RETINAL INNER LIMITING MEMBRANE BY THE MALIGNANT TUMOR CELLS

To observe the process of invasion, retina of rat was used as a model to substitute the inner limiting membrane of retina for the basement membrane. Retina invaded by esophageal carcinoma cells and B16 melanoma cells upon the inner limiting membrane was studied by scanning and transmission electron microscopy. The results showed that the inner limiting membrane was destroyed by both kinds of tumor cells. The process of destruction was followed by a series of transformations in the inner limiting membrane, i.e. folding, swelling, thickening, and granular change. The inner limiting membrane was dissolved focally as a result of transformation, and then tumor cells invaded the retina through these dissolved regions. It seems that, as a barrier, the inner limiting membrane plays a similar role as the basement membrane.

The future of retinal gene therapy: evolving from subretinal to intravitreal vector delivery

Inherited retinal degenerations are a leading and untreatbale cause of blindness, and as such they are targets for gene therapy. Numerous gene therapy treatments have progressed from laboratory research to clinical trails, and a pioneering gene therapy received the first ever FDA approval for treating patients. However, currently retinal gene therapy mostly involves subretinal injection of the therapeutic agent, which treats a limited area, entails retinal detachment and other potential complications, and requires general anesthesia with consequent risks, costs and prolonged recovery. Therefore there is great impetus to develop safer, less invasive and cheapter methods of gene delivery. A promising method is intravitreal injection, that does not cause retinal detachment, can lead to pan-retinal transduction and can be performed under local anesthesia in outpatient clinics. Intravitreally-injected vectors face several obstacles. First, the vector is diluted by the vitreous and has to overcome a long diffusion distance to the target cells. Second, the vector is exposed to the host's immune response, risking neutralization by pre-existing antibodies and triggering a stronger immune response to the injection. Third, the vector has to cross the inner limiting membrane which is both a physical and a biological barrier as it contains binding sites that could cause the vector's sequestration. Finally, in the target cell the vector is prone to proteasome degradation before delivering the transgene to the nucleus. Strategies to overcome these obstacles include modifications of the viral capsid, through rational design or directed evolution, which allow resistance to the immune system, enhancement of penetration through the inner limiting membrane or reduced degradation by intracellular proteasomes. Furthermore, physical and chemical manipulations of the inner limiting membrane and vitreous aim to improve vector penetration. Finally, compact non-viral vectors that can overcome the immunological, physical and anatomical and barriers have been developed. This paper reviews ongoing efforts to develop novel, safe and efficacious methods for intravitreal delivery of therapeutic genes for inherited retinal degenerations. To date, the most promising results are achieved in rodents with robust, pan-retinal transduction following intravitreal delivery. Trials in larger animal models demonstrate transduction mostly of inner retinal layers. Despite ongoing efforts, currently no intravitreally-injected vector has demonstrated outer retinal transduction efficacy comparable to that of subretinal delivery. Further work is warranted to test promising new viral and non-viral vectors on large animal models of inherited retinal degenerations. Positive results will pave the way to development of the next generation of treatments for inherited retinal degeneration.

New technique for removal of perfluorocarbon liquid related sticky silicone oil and literature review

AIM:To investigate the safety and efficacy of sticky silicone oil(SSO)removal using a 22-gauge vein detained needle and inner limiting membrane(ILM)wrap-and-peel technique.METHODS:This retrospective consecutive case series reviewed the records of patients with a history of retinal detachment who had received silicone oil and perfluorocarbon liquid(PFCL)as intraocular tamponades.Patients were included in the analysis if they exhibited SSO remnants during silicone oil removal.The aspiration of most of the SSO remnants was performed by a 22-gauge vein detained needle.The small amounts of droplets adhered to the macula and epi-macular membrane were subsequently removed by the ILM warp-and-peel technique.The anatomical and functional outcomes,and postoperative complications were recorded.In vitro experiments were performed to simulate the formation of SSO remnants in four groups.RESULTS:Of 711 patients who underwent silicone oil removal during the study period,9 patients exhibited SSO remnants and underwent follow-up for at least 3mo.Seven eyes(78%)underwent the ILM wrap-and-peel technique to completely remove small droplets of SSO that were glued to the macula and epi-macular membrane.No obvious complications occurred.Postoperative optical coherence tomography revealed normal retinal structure in all patients.In vitro analyses showed that balanced salt solution and prolonged vibration(for 1wk)had the strongest effects on silicone oil and PFCL compound opacities.CONCLUSION:SSO remnants could be removed in an intact manner and without complications,using a vein detained needle-assisted and ILM wrap-and-peel technique.The findings suggest that PFCL and infusion fluid should be completely removed before silicone oil injection to prevent SSO formation.

Comparison of cross sectional optical coherence tomography images of elevated optic nerve heads across acquisition devices and scan protocols

Background:Optic nerve head measurements extracted from optical coherence tomography(OCT)show promise for monitoring clinical conditions with elevated optic nerve heads.The aim of this study is to compare reliability within and between raters and between image acquisition devices of optic nerve measurements derived from OCT scans in eyes with varying degrees of optic nerve elevation.Methods:Wide angle line scans and narrow angle radial scans through optic nerve heads were obtained using three spectral domain(SD)OCT devices on 5 subjects(6 swollen optic nerves,4 normal optic nerves).Three raters independently semi-manually segmented the internal limiting membrane(ILM)and Bruch’s membrane(BM)on each scan using customized software.One rater segmented each scan twice.Segmentations were qualitatively and quantitatively compared.Inter-rater,intra-rater and inter-device reliability was assessed for the optic nerve cross sectional area calculated from the ILM and BM segmentations using intraclass correlation coefficients and graphical comparison.Results:Line scans from all devices were qualitatively similar.Radial scans for which frame rate could not be adjusted were of lower quality.Intra-rater reliability for segmentation and optic nerve cross sectional area was better than inter-rater reliability,which was better than inter-device reliability,though all ICC exceeded 0.95.Reliability was not impacted by the degree of optic nerve elevation.Conclusions:SD-OCT devices acquired similar quality scans of the optic nerve head,with choice of scan protocol affecting the quality.For image derived markers,variability between devices was greater than that attributable to inter and intra-rater differences.