Developmental abnormalities of the optic nerve and chiasm

Characteristic deviations of the optic disc and macula in optic nerve hypoplasia based on OCT

PURPOSE

The purpose of this study was to evaluate the optic disc and macula in a large cohort of patients with different severity of optic nerve hypoplasia (ONH) using high-resolution spectral domain optical coherence tomography (SD-OCT).

METHODS

In total, 36 patients (52 ONH eyes and 17 fellow eyes in unilateral cases) and 45 healthy right eyes from 45 controls were evaluated. All patients underwent an examination to confirm the diagnosis. SD-OCT images of the disc and macula were obtained and analysed both quantitatively and qualitatively.

RESULTS

OCT in ONH eyes demonstrated a shorter disc diameter (1061 ± 375 μm vs. 1751 ± 221 μm, p < 0.001), shallower mean cup depth (427 ± 171 μm vs. 551 ± 152 μm, p = 0.01), thinner ganglion cell complex (GCC) perifoveally (47.3 ± 13.0 μm, 60.8 ± 6.0 μm, p < 0.001) and reduced foveal depth (61 ± 36 μm, 119 ± 19 μm, p < 0.001) compared to control eyes. Qualitative analysis showed that 1/3rd of ONH eyes lacked signs of an optic cup, and 2/3rd had reduced or no sign of a foveal pit. Fellow eyes had shorter disc diameter (1446 ± 404 μm vs. 1751 ± 221 μm, p = 0.004) and reduced foveal depth (93 ± 27 μm vs. 119 ± 19 μm, p < 0.001) but similar GCC thickness (60.8 ± 7.1 μm vs. 60.8 ± 6.0 μm, p = 0.738) compared to controls. Disc diameter showed the best correlation with visual acuity in ONH eyes (ρ = 0.517, p < 0.001).

CONCLUSION

ONH eyes have reduced GCC thickness and reduced or no foveal pit. Fellow eyes in presumed unilateral cases have a smaller disc diameter and reduced foveal depth compared to controls, suggesting the possibility of subclinical/mild disease. However, GCC thickness was normal. The correlation between structure and visual function is not always straightforward.

Neuroimaging Features in Children with Optic Nerve Hypoplasia and Septo-Optic-Pituitary Dysplasia

BACKGROUND

Optic nerve hypoplasia (ONH) and septo-optic-pituitary dysplasia (SOD) are common causes of congenital visual impairment. Our primary aim was to investigate the prevalence of abnormal neuroimaging features in patients with these disorders in Manitoba, Canada, and compare them with published reports.

METHODS

A retrospective neuroimaging review was performed in patients resident in Manitoba with ONH/SOD.

RESULTS

There were 128 patients (M = 70) with ONH/SOD who had neuroimaging. Their mean age (SD) at the end of the study was 13.2 (7.5) years. Males were significantly more likely to have bilateral ONH and a small optic chiasm size, while females were more likely to have a left ONH and a small left optic chiasm size on neuroimaging (p = 0.049). ONH and small optic chiasm size were seen in most patients on neuroimaging. Absent septum pellucidum was noted in 40%, small pituitary gland size in 28%, neuronal migration disorders (NMD) in 20% (>1 type and bilateral in 13 cases), corpus callosum abnormalities were present in 9%, while olfactory bulbs-tracts and olfactory sulci were absent in 8.6% of cases. Unilateral ONH was not significantly associated with other structural brain abnormalities, while NMD were significantly associated with other midline brain abnormalities including a symmetrically small optic chiasm size.

CONCLUSION

The prevalence of structural neuroimaging abnormalities in our cohort with ONH/SOD was generally in the same range reported in other studies with corpus callosum abnormalities being relatively less common in our study. Bilateral NMD were relatively common among patients with NMD. The association between sex and ONH laterality requires further study.

Prevalence of common and rare ophthalmic findings in adults attending a medical survey institute

PURPOSE

To examine the ophthalmic data from a large database of people attending a general medical survey institute, and to investigate ophthalmic findings of the eye and its adnexa, including differences in age and sex.

METHODS

Retrospective analysis including medical data of all consecutive individuals whose ophthalmic data and the prevalences of ocular pathologies were extracted from a very large database of subjects examined at a single general medical survey institute.

RESULTS

Data were derived from 184,589 visits of 3676 patients (mean age 52 years, 68% males). The prevalence of the following eye pathologies were extracted. Eyelids: blepharitis (n = 4885, 13.3%), dermatochalasis (n = 4666, 12.7%), ptosis (n = 677, 1.8%), ectropion (n = 73, 0.2%), and xanthelasma (n = 160, 0.4%). Anterior segment: pinguecula (n = 3368, 9.2%), pterygium (n = 852, 2.3%), and cataract or pseudophakia (n = 9381, 27.1%). Cataract type (percentage of all phakic patients): nuclear sclerosis (n = 8908, 24.2%), posterior subcapsular (n = 846, 2.3%), and capsular anterior (n = 781, 2.1%). Pseudophakia was recorded for 697 patients (4.6%), and posterior subcapsular opacification for 229 (0.6%) patients. Optic nerve head (ONH): peripapillary atrophy (n = 4947, 13.5%), tilted disc (n = 3344, 9.1%), temporal slope (n = 410, 1.1%), ONH notch (n = 61, 0.2%), myelinated nerve fiber layer (n = 94, 0.3%), ONH drusen (n = 37, 0.1%), optic pit (n = 3, 0.0%), and ON coloboma (n = 4, 0.0%). Most pathologies were more common in males except for ONH, and most pathologies demonstrated a higher prevalence with increasing age.

CONCLUSIONS

Normal ophthalmic data and the prevalences of ocular pathologies were extracted from a very large database of subjects seen at a single medical survey institute.

Pathophysiological Heterogeneity of the BBSOA Neurodevelopmental Syndrome

The formation and maturation of the human brain is regulated by highly coordinated developmental events, such as neural cell proliferation, migration and differentiation. Any impairment of these interconnected multi-factorial processes can affect brain structure and function and lead to distinctive neurodevelopmental disorders. Here, we review the pathophysiology of the Bosch–Boonstra–Schaaf Optic Atrophy Syndrome (BBSOAS; OMIM 615722; ORPHA 401777), a recently described monogenic neurodevelopmental syndrome caused by the haploinsufficiency of NR2F1 gene, a key transcriptional regulator of brain development. Although intellectual disability, developmental delay and visual impairment are arguably the most common symptoms affecting BBSOAS patients, multiple additional features are often reported, including epilepsy, autistic traits and hypotonia. The presence of specific symptoms and their variable level of severity might depend on still poorly characterized genotype–phenotype correlations. We begin with an overview of the several mutations of NR2F1 identified to date, then further focuses on the main pathological features of BBSOAS patients, providing evidence—whenever possible—for the existing genotype–phenotype correlations. On the clinical side, we lay out an up-to-date list of clinical examinations and therapeutic interventions recommended for children with BBSOAS. On the experimental side, we describe state-of-the-art in vivo and in vitro studies aiming at deciphering the role of mouse Nr2f1, in physiological conditions and in pathological contexts, underlying the BBSOAS features. Furthermore, by modeling distinct NR2F1 genetic alterations in terms of dimer formation and nuclear receptor binding efficiencies, we attempt to estimate the total amounts of functional NR2F1 acting in developing brain cells in normal and pathological conditions. Finally, using the NR2F1 gene and BBSOAS as a paradigm of monogenic rare neurodevelopmental disorder, we aim to set the path for future explorations of causative links between impaired brain development and the appearance of symptoms in human neurological syndromes.

Pathogenic NR2F1 variants cause a developmental ocular phenotype recapitulated in a mutant mouse model

Pathogenic NR2F1 variants cause a rare autosomal dominant neurodevelopmental disorder referred to as the Bosch-Boonstra-Schaaf Optic Atrophy Syndrome. Although visual loss is a prominent feature seen in affected individuals, the molecular and cellular mechanisms contributing to visual impairment are still poorly characterized. We conducted a deep phenotyping study on a cohort of 22 individuals carrying pathogenic NR2F1 variants to document the neurodevelopmental and ophthalmological manifestations, in particular the structural and functional changes within the retina and the optic nerve, which have not been detailed previously. The visual impairment became apparent in early childhood with small and/or tilted hypoplastic optic nerves observed in 10 cases. High-resolution optical coherence tomography imaging confirmed significant loss of retinal ganglion cells with thinning of the ganglion cell layer, consistent with electrophysiological evidence of retinal ganglion cells dysfunction. Interestingly, for those individuals with available longitudinal ophthalmological data, there was no significant deterioration in visual function during the period of follow-up. Diffusion tensor imaging tractography studies showed defective connections and disorganization of the extracortical visual pathways. To further investigate how pathogenic NR2F1 variants impact on retinal and optic nerve development, we took advantage of an Nr2f1 mutant mouse disease model. Abnormal retinogenesis in early stages of development was observed in Nr2f1 mutant mice with decreased retinal ganglion cell density and disruption of retinal ganglion cell axonal guidance from the neural retina into the optic stalk, accounting for the development of optic nerve hypoplasia. The mutant mice showed significantly reduced visual acuity based on electrophysiological parameters with marked conduction delay and decreased amplitude of the recordings in the superficial layers of the visual cortex. The clinical observations in our study cohort, supported by the mouse data, suggest an early neurodevelopmental origin for the retinal and optic nerve head defects caused by NR2F1 pathogenic variants, resulting in congenital vision loss that seems to be non-progressive. We propose NR2F1 as a major gene that orchestrates early retinal and optic nerve head development, playing a key role in the maturation of the visual system.

RINT1 Loss Impairs Retinogenesis Through TRP53-Mediated Apoptosis

Genomic instability in the central nervous system (CNS) is associated with defective neurodevelopment and neurodegeneration. Congenital human syndromes that affect the CNS development originate from mutations in genes of the DNA damage response (DDR) pathways. RINT1 (Rad50-interacting protein 1) is a partner of RAD50, that participates in the cellular responses to DNA double-strand breaks (DSB). Recently, we showed that Rint1 regulates cell survival in the developing brain and its loss led to premature lethality associated with genomic stability. To bypass the lethality of Rint1 inactivation in the embryonic brain and better understand the roles of RINT1 in CNS development, we conditionally inactivated Rint1 in retinal progenitor cells (RPCs) during embryogenesis. Rint1 loss led to accumulation of endogenous DNA damage, but RINT1 was not necessary for the cell cycle checkpoint activation in these neural progenitor cells. As a consequence, proliferating progenitors and postmitotic neurons underwent apoptosis causing defective neurogenesis of retinal ganglion cells, malformation of the optic nerve and blindness. Notably, inactivation of Trp53 prevented apoptosis of the RPCs and rescued the generation of retinal neurons and vision loss. Together, these results revealed an essential role for TRP53-mediated apoptosis in the malformations of the visual system caused by RINT1 loss and suggests that defective responses to DNA damage drive retinal malformations.

Thin-section 3D Steady-State MRI in Optic Nerve Coloboma

Optic nerve colobomas are congenital defects in the posterior globe of eye with typical funduscopic appearances. We report a two-year-old child suspected of morning glory disc anomaly who underwent thin-section 3D steady-state magnetic resonance imaging which showed characteristic findings of a tiny defect and discontinuity in the optic nerve head.

Abnormalities of the Optic Nerve in Down Syndrome and Associations With Visual Acuity

Background: Various ocular anomalies are present in the vast majority of individuals with Down syndrome; however, we know little about optic nerve abnormalities. The aim of this cross-sectional comparative study was to describe optic disc morphology in patients with Down syndrome and to determine if the differences found are potentially related to visual acuity.

Subjects/methods: Assessable fundus images were obtained in 50 children with Down syndrome and 52 children without Down syndrome. Morphological analysis of the optic nerve was performed, including the disc-to-macula distance (DM) to disc diameter (DD) ratio (DM/DD), the cup-to-disc ratio and optic disc ovality. Data relating to ophthalmological status were retrospectively analyzed to evaluate the possible causes of reduced visual acuity.

Results: DM/DD was significantly larger (p = 0.0036) and the cup-to-disc ratio was significantly smaller (p = 0.018) in children with Down syndrome, compared to controls. The optic discs were also more frequently torted (p = 0.034), tilted (p = 0.0049) and oval (p = 0.026). Furthermore, crescents (p = 0.0002), peripapillary atrophy (p = 0.0009), and pigment anomalies (p < 0.0001) were also more prevalent in children with Down syndrome than in those without. Visual acuity was significantly lower in children with Down syndrome compared to controls with similar refraction problems and strabismus prevalence (p < 0.0001). The mean DM/DD and the presence of a crescent was not directly related to visual acuity (r = 0.39, p = 0.31), (r = 0.35, p = 0.12) respectively. Visual acuity was diminished in 80% of children with Down syndrome and the smallest discs and in 84% of those with tilted discs. However, other causes may contribute to the diminished visual acuity in these cases.

Conclusion: The optic nerve head in children with Down syndrome is affected by various anatomical and developmental abnormalities. Unrelated to refraction (spherical equivalent), the optic discs appear smaller and more frequently mal-inserted in Down syndrome. Optic disc hypoplasia, as well as severe tilting, may reduce vision but they do not represent major contributors to the decrease of vision in such children. As these children often have multiple ocular and neurosensory problems, it remains challenging to relate visual acuity problems with a specific abnormality. Smaller discs may lead to optic disc drusen formation in children with Down syndrome.

Prevalence of the optic disc anomalies in the adult South Indian population

Purpose

To determine the prevalence of congenitally abnormal disc (all anomalies) in an adult population in southern India.

Methods

Subjects aged ≥40 years (n=6013) underwent a complete ophthalmic examination. Optic disc anomalies were diagnosed according to the definitions given in the article.

Results

Optic disc anomalies were found in 81 eyes of 66 (1.1%, 95% CIs 0.00834 to 0.01361) patients. The prevalence of each anomaly in the descending order was peripapillary myelinated nerve fibre (0.28%), epipapillary glial tissue on the optic disc (0.28%), peripapillary vascular loops (0.16%), tilted disc (0.09%), optic disc coloboma (0.08%), optic nerve hypoplasia (0.04%), optic disc pit (0.04%), optic disc pigmentation (0.03%), optic nerve head drusen (0.03%), Bergmeister’s papilla (0.03%), optic disc pit and coloboma (0.01%).

Conclusions

The prevalence of optic disc anomalies is 1.1% in the adult South Indian population.

Optic Nerve Measurement on MRI in the Pediatric Population: Normative Values and Correlations

BACKGROUND AND PURPOSE

Few articles in the literature have looked at the diameter of the optic nerve on MR imaging, especially in children, in whom observations are subjective and no normative data exist. The aim of this study was to establish a data base for optic nerve diameter measurements on MR imaging in the pediatric population.

MATERIALS AND METHODS

This was a retrospective study on the MR imaging of pediatric subjects (younger than 18 years of age) at the Department of Diagnostic Radiology at the American University of Beirut Medical Center, Beirut, Lebanon. The optic nerve measurements were obtained by 3 raters on axial and coronal sections at 3 mm (retrobulbar) and 7 mm (intraorbital) posterior to the lamina cribrosa.

RESULTS

Of 211 scans of patients (422 optic nerves), 377 optic nerves were measured and included. Ninety-four patients were female (45%) and the median age at MR imaging was 8.6 years (interquartile range, 3.9-13.3 years). Optic nerves were divided into 5 age groups: 0-6 months (n = 18), 6 months-2 years (n = 44), 2-6 years (n = 86), 6-12 years (n = 120), and 12-18 years (n = 109). An increase in optic nerve diameter was observed with age, especially in the first 2 years of life. Measurements did not differ with eye laterality or sex.

CONCLUSIONS

We report normative values of optic nerve diameter measured on MR imaging in children from birth to 18 years of age. A rapid increase in optic nerve diameter was demonstrated during the first 2 years of life, followed by a slower increase. This was independent of sex or eye laterality.

MRI measurements of the normal pediatric optic nerve pathway

The purpose of this work is to establish a reference scale of optic nerve pathway measurements in pediatric patients according to age using MRI. Optic nerve pathway measurements were retrospectively analyzed using an orbits equivalent sequence on brain MRI scans of 137 pediatric patients (72 male, 65 female, average age = 7.7 years, standard deviation  = 5.3). The examinations were performed on a 1.5-T or 3-T Siemens MR system using routine imaging protocols. Measurements include diameters of the orbital optic nerves (OON), prechiasmatic optic nerves (PON), optic tracts (OT), and optic chiasm (OC). Measurements were performed manually by 2 neuroradiologists, using post-processing software. Patients were stratified into five age groups for measurement analyses: (I) 0-1.49 years, (II) 1.5-2.99 years, (III) 3-5.99 years, (IV) 6-11.99 years, and (V) 12-18 years. The observed value range of OON mean diameter was 2.7 mm (Interquartile range (IQR) = 2.4-2.9), PON was 3.2 mm (IQR  =  3.05-3.5), OT 2.6 mm (IQR = 2-2.9). A strong positive correlation was established between age and mean diameter of OON (r = 0.73, p < .001), PON (r = 0.59, p < .001), and OT (r = 0.72, p < .001). A significant difference in mean OON diameters was found between age groups I-II (d = 0.3, p = .01), II-III (d = 0.5, p < .001), III-IV (d = 0.5, p < .001) followed by a plateau between IV-V (d = 0.l0, p = .19). OON/OT ratio maintained a steady mean value 1 (IQR = 0.93-1.1) regardless of age (p = .7). The diameter of optic pathways was found to increase as a function of age with consistent positive correlation between nerve and tract for all ages.

Congenital optic nerve anomalies

OBJECTIVE

To update the current knowledge about congenital optic disc anomalies.

METHODS

A comprehensive literature search was performed in the major biomedical databases.

RESULTS

Patients with these anomalies usually have poor vision in infancy. Refractive errors are common, and serous retinal detachment may develop in some of these anomalies. It is critically important to clinically differentiate between these congenital optic disc anomalies, as central nervous system malformations are common in some, whereas others may be associated with systemic anomalies.

CONCLUSIONS

Congenital optic disc anomalies are a heterogeneous group of pathologies with characteristic fundus appearance and systemic associations. We should always try to make a correct diagnosis, in order to ask for specific tests, as well as to provide an adequate follow-up.

VEP analysis methods in children with optic nerve hypoplasia: relationship to visual acuity and optic disc diameter

PURPOSE

Assessing vision in young children with optic nerve hypoplasia (ONH) is challenging due to multi-directional infantile nystagmus, the range of optic nerve loss, and cognitive delay. This study examined visual evoked potential (VEP) responses and averaging techniques in children with ONH. The assumption is that EEG epochs with inconsistent temporal phase would be associated with nystagmus, signal reduction due to axon loss, and visual inattention.

METHODS

A retrospective chart review was performed on 44 children (average age 2.2 years; SD 1.9). Optic disc diameter was estimated by ophthalmoscopy. Visual function was measured under binocular viewing and then compared to the eye with the larger optic disc to exclude secondary amblyopia. Visual acuity was measured by Teller cards or by recognition optotypes, and both measures were converted into log minimum angle of resolution (logMAR). VEPs were recorded to onset/offset of horizontal gratings and to reversing checkerboards. Signal-to-noise ratios (SNRs) were estimated from phase consistency across epochs in the Fourier domain. VEPs were also averaged after (1) correction of epochs for phase shifts across a limited bandwidth, or (2) selection of only epochs showing phase consistency.

RESULTS

Optic disc diameter, logMAR, VEP amplitudes, and VEP SNR were all significantly inter-correlated. Optic disc diameter correlated best with VEP SNR (Spearman rho = 0.82; p < 0.001). Age-corrected logMAR correlated with optic disc diameter and VEP SNR (Spearman rho = -0.695 and 0.70, respectively; p < 0.001). VEP latency poorly correlated with optic disc diameter or logMAR. Correction of phase shifts or selection of epochs based on phase consistency significantly increased VEP amplitude and SNR for children with optic disc diameters <1000 microns. Correction of phase inconsistency did not improve the correlation of VEP parameters with optic disc diameter or with logMAR.

CONCLUSIONS

In ONH, the size of the optic nerve is correlated with VEP SNR and logMAR. The results imply a direct relationship between the reduction in optic nerve axons and generalized reduction in visual function. Our calculation of VEP SNR provides objective assessment of optic nerve function that is independent of subjective scoring of VEP peaks.

A Rare Case of Symptomatic Double Optic Disc Pit without Maculopathy

Optic disc pits are an uncommon congenital abnormality. Patients remain asymptomatic unless they develop maculopathy. We present a rare case of a double optic disc pit of which only three others have been reported worldwide. A 51-year-old gentleman presented with blurred vision. Fundoscopy revealed a right double optic disc pit. Though he was symptomatic there was no evidence of maculopathy. OCT of macula and disc was otherwise unremarkable. Visual field demonstrated a paracentral defect. Although optic disc pits are rare they are still an important clinical entity. Prompt identification and treatment of complications are required to prevent a poor visual prognosis.

Retinal ischaemia and delayed fibrovascular proliferation associated with an optic nerve coloboma

CASE REPORT

A patient with a left optic nerve coloboma with late development (at 15 years of age) of vitreoretinal fibrovascular proliferation and tractional retinal detachment (TRD). Sectorial retinal photocoagulation was performed with regression of the proliferative tissue and exudation.

DISCUSSION

Congenital optic nerve anomalies may be associated with significant retinal avascularity, ischaemia and late fibrovascular proliferation. Laser is effective for regression of the neovascular tissue and preventing TRD progression.

Retinal complications associated with congenital optic disc anomalies determined by swept source optical coherence tomography

Optical coherence tomography has evolved over the past 2 decades to be an important ancillary method to evaluate diseases of the anterior and posterior segments of the eye. The more recent development of swept-source optical coherence tomography (SS-OCT) with a wavelength-tunable laser centered at 1050 nm and deeper imaging depth of 2.6 mm has enabled clinicians to evaluate congenital optic disc anomalies including optic disc pits, optic disc colobomas, and morning glory syndrome in more detail. The SS-OCT findings of the posterior precortical vitreous pocket, Cloquet's canal, lamina cribrosa that is torn from the peripapillary sclera, and the retrobulbar subarachnoid space immediately posterior to the highly reflective tissue lining the bottom of the excavation are presented. In addition, abnormal communications between the vitreous cavity and the subretinal and subarachnoid spaces in eyes with congenital optic disc anomalies are also reviewed. The retinal complications associated with congenital optic disc anomalies are treated by vitreous surgery, silicone oil tamponade, and peripapillary laser photocoagulation or scleral buckling. However, the surgical outcomes are limited and not entirely satisfactory. Analyses by SS-OCT of congenital optic disc anomalies should make the treatment correspond better with the pathological findings.

Congenital optic tract hypoplasia

We report a case of isolated unilateral optic tract hypoplasia, described only twice previously. Bilateral optic disk hypoplasia was seen ophthalmoscopically and visual field studies showed an incongruous right homonymous hemianopia. Magnetic resonance imaging showed bilateral hypoplasia of both optic nerves and the left optic tract. Spectral domain optical coherence tomography mapping correlated well with the visual field studies.

High-Resolution Imaging of the Optic Nerve and Retina in Optic Nerve Hypoplasia

PURPOSE

To investigate the optic nerve and macular morphology in patients with optic nerve hypoplasia (ONH) using spectral-domain optical coherence tomography (SD OCT).

DESIGN

Prospective, cross-sectional, observational study.

SUBJECTS

A total of 16 participants with ONH (10 female and 6 male; mean age, 17.2 years; 6 bilateral involvement) and 32 gender-, age-, ethnicity-, and refraction-matched healthy controls.

METHODS

High-resolution SD OCT (Copernicus [Optopol Technology S.A., Zawiercie, Poland], 3 μm resolution) and handheld SD OCT (Bioptigen Inc [Research Triangle Park, NC], 2.6 μm resolution) devices were used to acquire horizontal scans through the center of the optic disc and macula.

MAIN OUTCOME MEASURES

Horizontal optic disc/cup and rim diameters, cup depth, peripapillary retinal nerve fiber layer (RNFL), and thickness of individual retinal layers in participants with ONH and in controls.

RESULTS

Patients with ONH had significantly smaller discs (P < 0.03 and P < 0.001 compared with unaffected eye and healthy controls, respectively), horizontal cup diameter (P < 0.02 for both), and cup depth (P < 0.02 and P < 0.01, respectively). In the macula, significantly thinner RNFL (nasally), ganglion cell layer (GCL) (nasally and temporally), inner plexiform layer (IPL) (nasally), outer nuclear layer (ONL) (nasally), and inner segment (centrally and temporally) were found in patients with ONH compared with the control group (P < 0.05 for all comparisons). Continuation of significantly thicker GCL, IPL, and outer plexiform layer in the central retinal area (i.e., foveal hypoplasia) was found in more than 80% of patients with ONH. Clinically unaffected fellow eyes of patients with ONH showed mild features of underdevelopment. Visual acuity and presence of septo-optic dysplasia were associated with changes in GCL and IPL. Sensitivity and specificity for the detection of ONH based on disc and retinal optical coherence tomography (OCT) parameters were >80%.

CONCLUSIONS

Our study provides evidence of retinal changes in ONH. In addition to thinning of retina layers mainly involving the RNFL and GCL, signs reminiscent of foveal hypoplasia were observed in patients with ONH. Optic nerve and foveal parameters measured using OCT showed high sensitivity and specificity for detecting ONH, demonstrating their useful for clinical diagnosis.

In vitro organogenesis in three dimensions: self-organising stem cells

Organ formation during embryogenesis is a complex process that involves various local cell-cell interactions at the molecular and mechanical levels. Despite this complexity, organogenesis can be modelled in vitro. In this article, we focus on two recent examples in which embryonic stem cells can self-organise into three-dimensional structures - the optic cup and the pituitary epithelium; and one case of self-organising adult stem cells - the gut epithelium. We summarise how these approaches have revealed intrinsic programs that drive locally autonomous modes of organogenesis and homeostasis. We also attempt to interpret the results of previous in vivo studies of retinal development in light of the self-organising nature of the retina.

[Incidental finding of bilateral altitudinal visual field defects]

A 28-year-old woman presented with surprisingly asymptomatic bilateral inferior altitudinal visual field defects. Fundoscopy disclosed superior hypoplastic optic discs which was diagnosed as bilateral superior segmental optic hypoplasia. The patient suffered from maternal diabetes and sacral agenesis syndrome, which is also frequently associated with maternal diabetes.

Aberrant forebrain signaling during early development underlies the generation of holoprosencephaly and coloboma

In this review, we highlight recent literature concerning the signaling mechanisms underlying the development of two neural birth defects, holoprosencephaly and coloboma. Holoprosencephaly, the most common forebrain defect, occurs when the cerebral hemispheres fail to separate and is typically associated with mispatterning of embryonic midline tissue. Coloboma results when the choroid fissure in the eye fails to close. It is clear that Sonic hedgehog (Shh) signaling regulates both forebrain and eye development, with defects in Shh, or components of the Shh signaling cascade leading to the generation of both birth defects. In addition, other intercellular signaling pathways are known factors in the incidence of holoprosencephaly and coloboma. This review will outline recent advances in our understanding of forebrain and eye embryonic pattern formation, with a focus on zebrafish studies of Shh and retinoic acid pathways. Given the clear overlap in the mechanisms that generate both diseases, we propose that holoprosencephaly and coloboma can represent mild and severe aspects of single phenotypic spectrum resulting from aberrant forebrain development. This article is part of a Special Issue entitled Zebrafish Models of Neurological Diseases.

Eye development

The vertebrate eye comprises tissues from different embryonic origins: the lens and the cornea are derived from the surface ectoderm, but the retina and the epithelial layers of the iris and ciliary body are from the anterior neural plate. The timely action of transcription factors and inductive signals ensure the correct development of the different eye components. Establishing the genetic basis of eye defects in zebrafishes, mouse, and human has been an important tool for the detailed analysis of this complex process. A single eye field forms centrally within the anterior neural plate during gastrulation; it is characterized on the molecular level by the expression of "eye-field transcription factors." The single eye field is separated into two, forming the optic vesicle and later (under influence of the lens placode) the optic cup. The lens develops from the lens placode (surface ectoderm) under influence of the underlying optic vesicle. Pax6 acts in this phase as master control gene, and genes encoding cytoskeletal proteins, structural proteins, or membrane proteins become activated. The cornea forms from the surface ectoderm, and cells from the periocular mesenchyme migrate into the cornea giving rise for the future cornea stroma. Similarly, the iris and ciliary body form from the optic cup. The outer layer of the optic cup becomes the retinal pigmented epithelium, and the main part of the inner layer of the optic cup forms later the neural retina with six different types of cells including the photoreceptors. The retinal ganglion cells grow toward the optic stalk forming the optic nerve. This review describes the major molecular players and cellular processes during eye development as they are known from frogs, zebrafish, chick, and mice-showing also differences among species and missing links for future research. The relevance to human disorders is one of the major aspects covered throughout the review.

Childhood visual impairment: normal and abnormal visual function in the context of developmental disability

Abnormal or failed development of vision in children may give rise to varying degrees of visual impairment and disability. Disease and organ-specific mechanisms by which visual impairments arise are presented. The presentation of these mechanisms, along with an explanation of established pathologic processes and correlative up-to-date clinical and social research in the field of pediatrics, ophthalmology, and rehabilitation medicine are discussed. The goal of this article is to enhance the practitioner's recognition and care for children with developmental disability associated with visual impairment.