Are isolated ocular motor nerve palsies in the elderly truly 'low risk' for abnormal neuro-imaging outcomes?

BACKGROUND: Neurologically isolated ocular motor nerve palsies often present a management dilemma. Neuroimaging is more likely to be offered to patients <50 years without coexisting ischaemic risk factors as their risk of sinister underlying causes is thought to be higher. However, populations are rapidly ageing and advanced neuroimaging is now more widely available. We thus investigated the incidence of abnormal neuroimaging outcomes in the traditionally low-risk older patient group. METHODS: This is a retrospective cohort study of 353 patients presenting with isolated ocular motor nerve palsies to a tertiary neuro-ophthalmology service in Singapore over a four-year (2015 to 2019) period. Clinical data was obtained through manual review of case records. Common aetiologies, age-based differences in prevalence of causes and abnormal neuroimaging outcomes were statistically analysed. RESULTS: Abnormal neuroimaging outcomes were significantly greater in the younger cohort only when age segregation was performed at 60 years of age. In a multivariate analysis, acute onset rather than ischaemic risk factors were independently predictive of normal neuroimaging outcomes. After adjusting for prior cancer risk and clinical bias from presumed ischaemic palsies, abnormal neuroimaging outcomes were seen in 14.1% ≥ 50 yrs, 10.9% ≥ 60 yrs and 15.1% ≥ 70 yrs. CONCLUSIONS: In patients presenting with isolated ocular motor nerve palsies, acute onset may be a more reliable indicator of an ischaemic palsy rather than advanced age or presence of ischaemic risk factors. If onset is not acute, neuroimaging should be considered irrespective of age and coexisting ischaemic risk factors.

Coronavirus disease (COVID-19)-associated mucormycosis (CAM): The unholy triad of COVID-19, diabetes mellitus, and corticosteroid therapy.

The whole world has battled with multiple waves of coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 virus. However, the second wave of COVID-19 had caused a worldwide havoc in terms of disease transmissibility, severity, and mortality. India has been among the worst hit countries during the second wave, which substantially overburdened and overwhelmed the Indian health care system. While secondary infections and co-infections among COVID-19 patients were increasingly being reported, COVID-19-associated mucormycosis (CAM) emerged as a new challenge particularly from India and became a matter of immediate concern. The most common causes attributed to the rise of CAM were undiagnosed/uncontrolled diabetes mellitus, excessive use of corticosteroids, and prolonged hospital stay, all of which create a perfect environment for mucormycosis infection to set in.

Should Aquaporin-4 Antibody Test Be Performed in all Patients With Isolated Optic Neuritis?

BACKGROUND: Optic neuritis (ON) may be the initial manifestation of neuromyelitis optica spectrum disorder (NMOSD). Aquaporin-4 antibody (AQP4 Ab) is used to diagnose NMOSD. This has implications on prognosis and is important for optimal management. We aim to evaluate if clinical features can distinguish AQP4 Ab seropositive and seronegative ON patients. METHODS: We reviewed patients with first episode of isolated ON from Tan Tock Seng Hospital and Singapore National Eye Centre who tested for AQP4 Ab from 2008 to 2017. Demographic and clinical data were compared between seropositive and seronegative patients. RESULTS: Among 106 patients (120 eyes) with first episode of isolated ON, 23 (26 eyes; 22%) were AQP4 Ab positive and 83 (94 eyes; 78%) were AQP4 Ab negative. At presentation, AQP4 Ab positive patients had older mean onset age (47.9 ± 13.6 vs 36.8 ± 12.6 years, P < 0.001), worse nadir VA (OR 1.714; 95% CI, 1.36 to 2.16; P < 0.001), less optic disc swelling (OR 5.04; 95% CI, 1.682 to 15.073; p = 0.004), and higher proportions of concomitant anti-Ro antibody (17% vs 4%, p = 0.038) and anti-La antibody (17% vs 1%, p = 0.008). More AQP4 Ab positive patients received steroid-sparing immunosuppressants (74% vs 19%, p < 0.001) and plasma exchange (13% vs 0%, p = 0.009). AQP4 Ab positive patients had worse mean logMAR VA (visual acuity) at 12 months (0.70 ± 0.3 vs 0.29 ± 0.5, p = 0.051) and 36 months (0.37±0.4 vs 0.14 ± 0.2, p = 0.048) follow-up. CONCLUSION: Other than older onset age and retrobulbar optic neuritis, clinical features are non-discriminatory for NMOSD. We propose a low threshold for AQP4 Ab serology testing in inflammatory ON patients, particularly in high NMOSD prevalence populations, to minimize diagnostic and treatment delays.

Dental pulp stem cells retain mesenchymal phenotype despite differentiation toward retinal neuronal fate in vitro.

Dental pulp stem cells (DPSCs) are an easily accessible, heterogenous source of mesenchymal stem cells (MSCs) that are derived from the neural crest. Evidence suggests that they have neurotrophic qualities in their undifferentiated state and can also be differentiated into neuronal and retinal cell types. There is growing interest in using DPSCs in cell-based therapies to treat glaucoma and blinding retinal diseases. However, careful characterization of these cells is necessary as direct intravitreal and subretinal MSC transplantation is known to lead to deleterious glial reaction and fibrosis. In this study, we provide evidence for the mesenchymal-predominant nature of DPSCs and show that DPSCs maintain their mesenchymal phenotype despite upregulating mature retinal markers under retinal differentiation conditions. CD56, which was previously thought to be a specific marker of neural crest lineage, is robustly co-expressed with mesenchymal markers and may not be adequate for isolating a subpopulation of neural crest cells in DPSCs. Therefore, identification of more specific markers is required to elucidate the heterogeneity of the population and to successfully isolate a putative neural stem cell population before DPSCs can be used for retinal therapy.

Optic Neuritis in the Era of NMOSD and MOGAD: A Survey of Practice Patterns in Singapore.

PURPOSE: The Optic Neuritis Treatment Trial was a landmark study with implications worldwide. In the advent of antibody testing for neuromyelitis optica spectrum disease (NMOSD) and myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD), emerging concepts, such as routine antibody testing and management, remain controversial, resulting mostly from studies in White populations. We evaluate the practice patterns of optic neuritis investigation and management by neuro-ophthalmologists and neurologists in Singapore. DESIGN: 21-question online survey consisting of 4 clinical vignettes. METHODS: The survey was sent to all Singapore Medical Council- registered ophthalmologists and neurologists who regularly manage patients with optic neuritis. RESULTS: Forty-two recipients (17 formally trained neuro-ophthalmol-ogists [100% response rate] and 25 neurologists) responded. Participants opted for routine testing of anti-aquaporin-4 antibodies (88.1% in mild optic neuritis and 97.6% in severe optic neuritis). Anti-MOG antibodies were frequently obtained (76.2% in mild and 88.1% in severe optic neuritis). Plasmapheresis was rapidly initiated (85.7%) in cases of nonresponse to intravenous steroids, even before obtaining anti-aquaporin-4 or anti-MOG serology results. In both NMOSD and MOGAD, oral mycophenolate mofetil was the preferred option if chronic immunosuppression was necessary. Steroids were given for a longer duration and tapered more gradually than in idiopathic optic neuritis cases. CONCLUSIONS: Serological testing for NMOSD and MOGAD is considered as a routine procedure in cases of optic neuritis in Singapore, possibly due to local epidemiological features of these conditions. Chronic oral immunosuppression is preferred for the long term, but further research is necessary to establish the efficacy and cost-effectiveness of these practices.

Accuracy of a Deep Learning System for Classification of Papilledema Severity on Ocular Fundus Photographs.

OBJECTIVE: To evaluate the performance of a deep learning system (DLS) in classifying the severity of papilledema associated with increased intracranial pressure on standard retinal fundus photographs. METHODS: A DLS was trained to automatically classify papilledema severity in 965 patients (2,103 mydriatic fundus photographs), representing a multiethnic cohort of patients with confirmed elevated intracranial pressure. Training was performed on 1,052 photographs with mild/moderate papilledema (MP) and 1,051 photographs with severe papilledema (SP) classified by a panel of experts. The performance of the DLS and that of 3 independent neuro-ophthalmologists were tested in 111 patients (214 photographs, 92 with MP and 122 with SP) by calculating the area under the receiver operating characteristics curve (AUC), accuracy, sensitivity, and specificity. Kappa agreement scores between the DLS and each of the 3 graders and among the 3 graders were calculated. RESULTS: The DLS successfully discriminated between photographs of MP and SP, with an AUC of 0.93 (95% confidence interval [CI] 0.89-0.96) and an accuracy, sensitivity, and specificity of 87.9%, 91.8%, and 86.2%, respectively. This performance was comparable with that of the 3 neuro-ophthalmologists (84.1%, 91.8%, and 73.9%, p = 0.19, p = 1, p = 0.09, respectively). Misclassification by the DLS was mainly observed for moderate papilledema (Frisén grade 3). Agreement scores between the DLS and the neuro-ophthalmologists' evaluation was 0.62 (95% CI 0.57-0.68), whereas the intergrader agreement among the 3 neuro-ophthalmologists was 0.54 (95% CI 0.47-0.62). CONCLUSIONS: Our DLS accurately classified the severity of papilledema on an independent set of mydriatic fundus photographs, achieving a comparable performance with that of independent neuro-ophthalmologists. CLASSIFICATION OF EVIDENCE: This study provides Class II evidence that a DLS using mydriatic retinal fundus photographs accurately classified the severity of papilledema associated in patients with a diagnosis of increased intracranial pressure.

Artificial Intelligence to Detect Papilledema from Ocular Fundus Photographs.

BACKGROUND: Nonophthalmologist physicians do not confidently perform direct ophthalmoscopy. The use of artificial intelligence to detect papilledema and other optic-disk abnormalities from fundus photographs has not been well studied. METHODS: We trained, validated, and externally tested a deep-learning system to classify optic disks as being normal or having papilledema or other abnormalities from 15,846 retrospectively collected ocular fundus photographs that had been obtained with pharmacologic pupillary dilation and various digital cameras in persons from multiple ethnic populations. Of these photographs, 14,341 from 19 sites in 11 countries were used for training and validation, and 1505 photographs from 5 other sites were used for external testing. Performance at classifying the optic-disk appearance was evaluated by calculating the area under the receiver-operating-characteristic curve (AUC), sensitivity, and specificity, as compared with a reference standard of clinical diagnoses by neuro-ophthalmologists. RESULTS: The training and validation data sets from 6779 patients included 14,341 photographs: 9156 of normal disks, 2148 of disks with papilledema, and 3037 of disks with other abnormalities. The percentage classified as being normal ranged across sites from 9.8 to 100%; the percentage classified as having papilledema ranged across sites from zero to 59.5%. In the validation set, the system discriminated disks with papilledema from normal disks and disks with nonpapilledema abnormalities with an AUC of 0.99 (95% confidence interval [CI], 0.98 to 0.99) and normal from abnormal disks with an AUC of 0.99 (95% CI, 0.99 to 0.99). In the external-testing data set of 1505 photographs, the system had an AUC for the detection of papilledema of 0.96 (95% CI, 0.95 to 0.97), a sensitivity of 96.4% (95% CI, 93.9 to 98.3), and a specificity of 84.7% (95% CI, 82.3 to 87.1). CONCLUSIONS: A deep-learning system using fundus photographs with pharmacologically dilated pupils differentiated among optic disks with papilledema, normal disks, and disks with nonpapilledema abnormalities. (Funded by the Singapore National Medical Research Council and the SingHealth Duke-NUS Ophthalmology and Visual Sciences Academic Clinical Program.).

Rapid generation of purified human RPE from pluripotent stem cells using 2D cultures and lipoprotein uptake-based sorting.

BACKGROUND: Despite increasing demand, current protocols for human pluripotent stem cell (hPSC)-derived retinal pigment epithelium (RPE) remain time, labor, and cost intensive. Additionally, absence of robust methods for selective RPE purification and removal of non-RPE cell impurities prevents upscaling of clinical quality RPE production. We aimed to address these challenges by developing a simplified hPSC-derived RPE production and purification system that yields high-quality RPE monolayers within 90 days. METHODS: Human pluripotent stem cells were differentiated into RPE using an innovative time and cost-effective protocol relying entirely on 2D cultures and minimal use of cytokines. Once RPE identity was obtained, cells were transferred onto permeable membranes to acquire mature RPE morphology. RPE differentiation was verified by electron microscopy, polarized VEGF expression, establishment of high transepithelial electrical resistance and photoreceptor phagocytosis assay. After 4 weeks on permeable membranes, RPE cell cultures were incubated with Dil-AcLDL (DiI-conjugated acetylated low-density lipoproteins) and subjected to fluorescence-activated cell sorting (FACS) for purification and subculture. RESULTS: Using our 2D cytokine scarce protocol, hPSC-derived functional RPE cells can be obtained within 2 months. Nevertheless, at this stage, most samples contain a percentage of non-RPE/early RPE progenitor cells that make them unsuitable for clinical application. We demonstrate that functional RPE cells express high levels of lipoprotein receptors and that this correlates with their ability to uptake lipoproteins. Combining photoreceptor uptake assay with lipoprotein uptake assay further confirms that only functional RPE cells uptake AcLDL. Incubation of mixed RPE/non-RPE cell cultures with fluorophore conjugated AcLDL and subsequent FACS-based isolation of labeled cells allows selective purification of mature functional RPE. When subcultured, DiI-AcLDL-labeled cells rapidly form pure homogenous high-quality RPE monolayers. CONCLUSIONS: Pure functional RPE monolayers can be derived from hPSC within 90 days using simplified 2D cultures in conjunction with our RPE PLUS protocol (RPE Purification by Lipoprotein Uptake-based Sorting). The simplicity of this protocol makes it scalable, and the rapidity of production and purification allows for high-quality RPE to be produced in a short span of time making them ideally suited for downstream clinical and in vitro applications.

Artificial intelligence for detection of optic disc abnormalities.

PURPOSE OF REVIEW: The aim of this review is to highlight novel artificial intelligence-based methods for the detection of optic disc abnormalities, with particular focus on neurology and neuro-ophthalmology. RECENT FINDINGS: Methods for detection of optic disc abnormalities on retinal fundus images have evolved considerably over the last few years, from classical ophthalmoscopy to artificial intelligence-based identification methods being applied to retinal imaging with the aim of predicting sight and life-threatening complications of underlying brain or optic nerve conditions. SUMMARY: Artificial intelligence and in particular newly developed deep-learning systems are playing an increasingly important role for the detection and classification of acquired neuro-ophthalmic optic disc abnormalities on ocular fundus images. The implementation of automatic deep-learning methods for detection of abnormal optic discs, coupled with innovative hardware solutions for fundus imaging, could revolutionize the practice of neurologists and other non-ophthalmic healthcare providers.

Breast Filariasis Diagnosed by Real Time Sonographic Imaging: A Case Report.

A 30-year-old woman presented with a palpable subcutaneous nodule in the areolar region of the left breast. Sonomammographic examination revealed 2 cystic lesions showing typical "filarial dance" as vigorous twirling movement of multiple curvilinear echoes with mixed red blue color Doppler signals that was non-rhythmic, nonpulsatile, and the characteristic pulse Doppler trace due to irregular worm movement. Real time sonographic demonstration of these typical features is pathognomonic for filariasis, especially in endemic areas and treatment should be initiated without delay on the basis of ultrasound.

Multiple Isolated Enteric Duplication Cysts in an Infant - A Diagnostic Dilemma.

Completely isolated enteric duplication cysts are a rare variety of enteric duplication cysts having an independent blood supply with no communication with any part of the adjacent bowel segment. We report a case showing two completely isolated enteric duplication cysts originating in the greater omentum and transverse mesocolon in an infant. Multiple isolated enteric duplication cysts involving non-contiguous bowel segments have not been previously reported in the literature. In addition the transverse mesocolon duplication cyst was infected showing septations and loss of double wall sign resulting in difficulty in imaging diagnosis. Both the cysts were excised and confirmed on histopathology.

The Impact of Lens Vault on Visual Acuity and Refractive Error: Implications for Management of Primary Angle-closure Glaucoma.

PURPOSE: To investigate the relationship between lens vault (LV), visual acuity (VA), and refraction. METHODS: This was a cross-sectional study of 2047 subjects aged 50 years and older recruited from a community polyclinic. Anterior segment optical coherence tomography was performed, and customized software was used to measure LV. VA was measured using a logarithm of minimum angle of resolution chart (logMAR chart; Lighthouse Inc.), and was classified as normal (logMAR<0.3), mild impairment (0.30.6). Refraction was measured with an autorefractor machine and spherical equivalent was defined as sphere plus half cylinder. Angle closure was defined as posterior trabecular meshwork not visible for ≥2 quadrants on nonindentation gonioscopy. RESULTS: Complete data were available for 1372 subjects including 295 (21.5%) with angle closure. Angle-closure subjects were significantly older (P<0.001), with shorter axial length (P<0.001), shallower anterior chamber depth (P<0.001), and greater LV (P<0.001). There was no significant difference in VA (P=0.12) compared with those without angle closure. After adjusting for age, sex, axial length, anterior chamber depth, and spherical equivalent, there was no significant association between LV and VA (P=0.35) or between LV and spherical equivalent (P=0.06). CONCLUSIONS: The magnitude of LV was not associated with VA or spherical equivalent. Lens extraction may be a consideration in eyes with angle closure with large LV in the absence of visually significant cataract.

Dental stem cells: a future asset of ocular cell therapy.

Regenerative medicine using patient's own stem cells (SCs) to repair dysfunctional tissues is an attractive approach to complement surgical and pharmacological treatments for aging and degenerative disorders. Recently, dental SCs have drawn much attention owing to their accessibility, plasticity and applicability for regenerative use not only for dental, but also other body tissues. In ophthalmology, there has been increasing interest to differentiate dental pulp SC and periodontal ligament SC (PDLSC) towards ocular lineage. Both can commit to retinal fate expressing eye field transcription factors and generate rhodopsin-positive photoreceptor-like cells. This proposes a novel therapeutic alternative for retinal degeneration diseases. Moreover, as PDLSC shares similar cranial neural crest origin and proteoglycan secretion with corneal stromal keratoctyes and corneal endothelial cells, this offers the possibility of differentiating PDLSC to these corneal cell types. The advance could lead to a shift in the medical management of corneal opacities and endothelial disorders from highly invasive corneal transplantation using limited donor tissue to cell therapy utilizing autologous cells. This article provides an overview of dental SC research and the perspective of utilizing dental SCs for ocular regenerative medicine.

Acquisition of RGC phenotype in human Müller glia with stem cell characteristics is accompanied by upregulation of functional nicotinic acetylcholine receptors.

PURPOSE: Human Müller glia with stem cell characteristics (hMGSCs) can be induced to express genes and proteins of retinal ganglion cells (RGCs) upon in vitro inhibition of Notch-1 activity. However, it is not known whether expression of these markers is accompanied by acquisition of RGC function. This study investigated whether hMGSCs that express RGC markers also display neural functionality, as measured by their intracellular calcium concentration ([Ca(2+)]i) responsiveness following neurotransmitter stimulation in vitro. METHODS: Changes in mRNA expression of RGC markers and neurotransmitter receptors were assessed either by conventional or quantitative reverse transcription PCR (RT-PCR), while changes in protein levels were confirmed by immunocytochemistry. The [Ca(2+)]i levels were estimated by fluorescence microscopy. RESULTS: We showed that while undifferentiated hMGSCs displayed a profound elevation of [Ca(2+)]i after stimulation with N-methyl-D-aspartate (NMDA), this was lost following Notch-1 inhibition. Conversely, untreated hMGSCs did not respond to muscarinic receptor stimulation, whereas [Ca(2+)]i was increased in differentiated hMGSCs that expressed RGC precursor markers. Differentiated hMGSC-derived RGCs, but not undifferentiated hMGSCs, responded to stimulation by nicotine with a substantial rise in [Ca(2+)]i, which was inhibited by the α4ß2 and α6ß2 nicotinic receptor antagonist methyllycaconitine. Notch-1 attenuation not only caused a decrease in the gene expression of the Notch effector HES1 and increased expression of RGC markers, but also an increase in the gene and protein expression of α4 and α6 nicotinic receptor subunits. CONCLUSIONS: These observations suggest that in response to Notch-1 inhibition, hMGSCs differentiate into a population of RGCs that exhibit some of the functionality observed in differentiated RGCs.

Human Müller glia with stem cell characteristics differentiate into retinal ganglion cell (RGC) precursors in vitro and partially restore RGC function in vivo following transplantation.

Müller glia with stem cell characteristics have been identified in the adult human eye, and although there is no evidence that they regenerate retina in vivo, they can be induced to grow and differentiate into retinal neurons in vitro. We differentiated human Müller stem cells into retinal ganglion cell (RGC) precursors by stimulation with fibroblast growth factor 2 together with NOTCH inhibition using the γ-secretase inhibitor N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester (DAPT). Differentiation into RGC precursors was confirmed by gene and protein expression analysis, changes in cytosolic [Ca(2+)] in response to neurotransmitters, and green fluorescent protein (GFP) expression by cells transduced with a transcriptional BRN3b-GFP reporter vector. RGC precursors transplanted onto the inner retinal surface of Lister hooded rats depleted of RGCs by N-methyl-d-aspartate aligned onto the host RGC layer at the site of transplantation but did not extend long processes toward the optic nerve. Cells were observed extending processes into the RGC layer and expressing RGC markers in vivo. This migration was observed only when adjuvant anti-inflammatory and matrix degradation therapy was used for transplantation. RGC precursors induced a significant recovery of RGC function in the transplanted eyes as determined by improvement of the negative scotopic threshold response of the electroretinogram (indicative of RGC function). The results suggest that transplanted RGC precursors may be capable of establishing local interneuron synapses and possibly release neurotrophic factors that facilitate recovery of RGC function. These cells constitute a promising source of cells for cell-based therapies to treat retinal degenerative disease caused by RGC dysfunction.

Conventional and emerging treatments in the management of acute primary angle closure.

The management of acute primary angle closure is directed at lowering the intraocular pressure and relieving pupil block. Conventional treatment involves the use of medical treatment and laser peripheral iridotomy, respectively, as a means for achieving these aims. Newer therapeutic strategies have been described that are potentially useful adjuncts or alternatives to conventional treatment. Emerging strategies that lower intraocular pressure include anterior chamber paracentesis, as well as laser procedures such as iridoplasty and pupilloplasty. A possible alternative to relieving pupil block is lens extraction, and may be combined with adjunctive measures such as goniosynechiolysis and viscogoniosynechiolysis. Trabeculectomy has a limited role in the acute setting. This review paper reviews the current evidence regarding conventional and newer treatment modalities for acute primary angle closure.

Differences between the neurogenic and proliferative abilities of Müller glia with stem cell characteristics and the ciliary epithelium from the adult human eye.

Much controversy has arisen on the nature and sources of stem cells in the adult human retina. Whilst ciliary epithelium has been thought to constitute a source of neural stem cells, a population of Müller glia in the neural retina has also been shown to exhibit neurogenic characteristics. This study aimed to compare the neurogenic and proliferative abilities between these two major cell populations. It also examined whether differences exist between the pigmented and non-pigmented ciliary epithelium (CE) from the adult human eye. On this basis, Müller glia with stem cell characteristics and pigmented and non-pigmented CE were isolated from human neural retina and ciliary epithelium respectively. Expression of glial, epithelial and neural progenitor markers was examined in these cells following culture under adherent and non-adherent conditions and treatments to induce neural differentiation. Unlike pigmented CE which did not proliferate, non-pigmented CE cells exhibited limited proliferation in vitro, unless epidermal growth factor (EGF) was present in the culture medium to prolong their survival. In contrast, Müller glial stem cells (MSC) cultured as adherent monolayers reached confluence within a few weeks and continued to proliferative indefinitely in the absence of EGF. Both MSC and non-pigmented CE expressed markers of neural progenitors, including SOX2, PAX6, CHX10 and NOTCH. Nestin, a neural stem cell marker, was only expressed by MSC. Non-pigmented CE displayed epithelial morphology, limited photoreceptor gene expression and stained strongly for pigmented epithelial markers upon culture with neural differentiation factors. In contrast, MSC adopted neural morphology and expressed markers of retinal ganglion cells and photoreceptors when cultured under similar conditions. This study provides the first demonstration that pigmented CE possess different proliferative abilities from non-pigmented CE. It also showed that although non-pigmented CE express genes of retinal progenitors, they do not differentiate into neurons in vitro, as that seen with Müller glia that proliferate indefinitely in vitro and that acquire markers of retinal neurons in culture under neural differentiation protocols. From these observations it is possible to suggest that Müller glia that express markers of neural progenitors and become spontaneously immortalized in vitro constitute a potential source of retinal neurons for transplantation studies and fulfil the characteristics of true stem cells due to their proliferative and neurogenic ability.