Optic nerve axons: life and death before birth

Optic atrophy in prematurity: pathophysiology and clinical features

Optic atrophy is an important cause of visual impairment in children, and the aetiological profile has changed over time. Technological advancements led by neuroimaging of the visual pathway and imaging of the optic nerve with optical coherence tomography have accelerated the understanding of this condition. In the new millennium, an increasing prevalence of prematurity as a cause of optic atrophy in children has been highlighted. This new shift has been linked with increasing rates of premature births and improved neonatal survival of preterm infants. The available literature is limited to hospital and registry-based cohorts with modest sample sizes, methodological heterogeneity and selection bias limitations. Larger studies that are better designed are required to better understand the contribution of prematurity to the disease burden. In addition to considering other life-threatening aetiologies, screening for premature birth should be covered as part of a comprehensive history when evaluating a child with paediatric optic atrophy.

The impact of perinatal brain injury on retinal nerve fiber layer thickness and optic nerve head parameters of premature children

PURPOSE

This study aims to evaluate the impact of birth weight (BW), gestational age (GA), retinopathy of prematurity (ROP), and perinatal brain injury (PBI) on optic nerve head (ONH) parameters and nerve fiber layer thickness (RNFLT) in preterm children.

METHODS

ONH parameters and RNFLT were examined prospectively in 5-15-year-old preterm and full-term children with RTVue-100 OCT (Optovue, USA). The parameters of the two groups were compared and possible influences of BW, GA, ROP, and PBI analyzed in preterm children.

RESULTS

In total, 51 full-term and 55 preterm children were included. The mean age was 9.98 ± 3.4 years in full-term and 10.0 ± 2.5 years in preterm children. The mean GA in preterm children was 29.6 ± 3.8 weeks with a BW of 1523 ± 732 g. RNFLT was significantly lower in preterm than in full-term children in all but temporal quadrants. Cup area, volume, cup/disc area ratio, and horizontal cup/disc ratio (CDR) were significantly larger and rim area significantly thinner in preterm children. GA was positively correlated with superior, nasal, and overall RNFLT and negatively correlated with cup area, volume, and horizontal CDR. ROP stage correlated negatively with superior and nasal RNFLT. PBI was the only significant predicting factor for RNFL thinning in all but temporal quadrant in multiple regression analysis. Preterm children with PBI had a significantly larger optic cup (CDR 0.70 ± 0.33 vs. 0.37 ± 0.27) and thinner optic rim.

CONCLUSION

PBI correlated strongest with RNFL thinning, a thinner optic rim, and a larger optic cup in preterm children and should be evaluated in each patient to prevent incorrect diagnosis like glaucoma.

Signaling - transcription interactions in mouse retinal ganglion cells early axon pathfinding -a literature review

Sending an axon out of the eye and into the target brain nuclei is the defining feature of retinal ganglion cells (RGCs). The literature on RGC axon pathfinding is vast, but it focuses mostly on decision making events such as midline crossing at the optic chiasm or retinotopic mapping at the target nuclei. In comparison, the exit of RGC axons out of the eye is much less explored. The first checkpoint on the RGC axons' path is the optic cup - optic stalk junction (OC-OS). OC-OS development and the exit of the RGC pioneer axons out of the eye are coordinated spatially and temporally. By the time the optic nerve head domain is specified, the optic fissure margins are in contact and the fusion process is ongoing, the first RGCs are born in its proximity and send pioneer axons in the optic stalk. RGC differentiation continues in centrifugal waves. Later born RGC axons fasciculate with the more mature axons. Growth cones at the end of the axons respond to guidance cues to adopt a centripetal direction, maintain nerve fiber layer restriction and to leave the optic cup. Although there is extensive information on OC-OS development, we still have important unanswered questions regarding its contribution to the exit of the RGC axons out of the eye. We are still to distinguish the morphogens of the OC-OS from the axon guidance molecules which are expressed in the same place at the same time. The early RGC transcription programs responsible for axon emergence and pathfinding are also unknown. This review summarizes the molecular mechanisms for early RGC axon guidance by contextualizing mouse knock-out studies on OC-OS development with the recent transcriptomic studies on developing RGCs in an attempt to contribute to the understanding of human optic nerve developmental anomalies. The published data summarized here suggests that the developing optic nerve head provides a physical channel (the closing optic fissure) as well as molecular guidance cues for the pioneer RGC axons to exit the eye.

The rim area of the optic nerve head, assessed with Heidelberg retina tomography, is smaller in prematurely born children than in children born at term

PURPOSE

To examine the optic nerve head with Heidelberg tomography (HRT) in prematurely born school-age children and compare them to children born at term.

METHODS

Sixty-three 5-16-year-old children born with a gestational age (GA) of ≤32 weeks were included in the study and compared to 54 children of the same age, born at term. In the preterm group, 29 children had had retinopathy of prematurity (ROP) and nine children had neurological complications. The optic nerve head was assessed with HRT. Three measurements were performed, and the different topographic parameters were noted.

RESULTS

Rim area of the optic nerve was significantly smaller in prematurely born children than in children born at term. The mean difference was 0.146 mm² (p = 0.02). No difference between the groups was found regarding disc area or cup area. In the preterm group, both disc and rim areas were reduced with increasing GA. No correlations with birthweight, ROP or neurological complications were found.

CONCLUSION

Reduced rim area of the optic nerve head was found in preterm children of school age. Previous ROP or neurological complication did not influence the result, suggesting the preterm birth per se was the reason for the reduction. Establishing whether this finding was caused by disturbed maturation of the optic nerve or by injury of the axons, or a combination of the two, will require further research.

Retinal and optic nerve changes in microcephaly: An optical coherence tomography study

OBJECTIVE

To investigate the morphology of the retina and optic nerve (ON) in microcephaly.

METHODS

This was a prospective case-control study including 27 patients with microcephaly and 27 healthy controls. All participants underwent ophthalmologic examination and handheld optical coherence tomography (OCT) of the macula and ON head. The thickness of individual retinal layers was quantified at the foveal center and the parafovea (1,000 μm nasal and temporal to the fovea). For the ON head, disc diameter, cup diameter, cup-to-disc ratio, cup depth, horizontal rim diameter, rim area, peripapillary retinal thickness, and retinal nerve fiber layer thickness were measured.

RESULTS

Seventy-eight percent of patients had ophthalmologic abnormalities, mainly nystagmus (56%) and strabismus (52%). OCT abnormalities were found in 85% of patients. OCT revealed disruption of the ellipsoid zone, persistent inner retinal layers, and irregular foveal pits. Parafoveal retinal thickness was significantly reduced in patients with microcephaly compared to controls, nasally (307 ± 44 vs 342 ± 19 μm, p = 0.001) and temporally (279 ± 56 vs 325 ± 16 μm, p < 0.001). There was thinning of the ganglion cell layer and the inner segments of the photoreceptors in microcephaly. Total peripapillary retinal thickness was smaller in patients with microcephaly compared to controls for both temporal (275 vs 318 μm, p < 0.001) and nasal sides (239 vs 268 μm, p = 0.013).

CONCLUSIONS

Retinal and ON anomalies in microcephaly likely reflect retinal cell reduction and lamination alteration due to impaired neurogenic mitosis. OCT allows diagnosis and quantification of retinal and ON changes in microcephaly even if they are not detected on ophthalmoscopy.

Optic Nerve Aplasia: Case Report and Literature Review

Purpose:

To report three cases of optic nerve aplasia (ONA).

Case Report:

Herein three subjects with ONA are described, two subjects had unilateral involvement. In one of these cases, the fellow eye had an associated persistent hyperplastic primary vitreous (PHPV). The third patient had bilateral ONA with multiple intracranial anomalies. Previous reports are reviewed and reported findings are summarized. Orbital and brain magnetic resonance imaging (MRI) were normal in two of our cases and loss of corpus callosum in the third case. Narrow optic nerve was observed on the right side and normal appearance in other two patients.

Conclusion:

The diagnosis of optic nerve abnormalities in children requires a thorough ophthalmic examination and proper ancillary testing. Although MRI is valuable in the diagnosis of associated central nervous system anomalies, the optic nerve may appear in normal size and course on MRI images and thus one may not be able to diagnose ONA in eyes with opaque media.

Endocrine and pubertal disturbances in optic nerve hypoplasia, from infancy to adolescence

Background

Endocrinologic abnormalities are a common co-morbidity in patients with optic nerve hypoplasia (ONH), however the impact on puberty is unknown. The purpose of this study was to examine rates of endocrine dysfunction and pubertal disturbances in a pediatric population of ONH.

Methods

A retrospective chart review was conducted on a cohort of children with ONH between January 2005 and March 2013. Endocrine dysfunction was determined based on laboratory evidence of hormone deficiency or hormone replacement. Pubertal disturbances were characterized based on presence of micropenis, tanner staging, menarche and hormone replacement. Pituitary abnormalities were classified using MRI findings. Descriptive statistics were used, and comparisons between groups were performed using the chi-square test.

Results

During the study period, 101 patients underwent an endocrine evaluation (median age: 2.3 years [0.76 – 6.5]). Hypopituitarism was present in 73% of patients with growth hormone deficiency (56%) and hypothyroidism (54%) being the most common. Pubertal disturbances (n = 19) were common; micropenis in 31% (13/42) of males and 2% with precocious puberty. Half of adolescents (n = 4/8) were diagnosed with gonadotropin deficiency. Patients with MRI pituitary abnormalities were more likely to have endocrine dysfunction than those without (p = 0.004). The sensitivity and specificity of MRI pituitary abnormalities for hypopituitarism was 54% and 92%, respectively.

Conclusions

A significant proportion of children with ONH have endocrine dysfunction. The high frequency of pubertal disturbances in this study emphasizes the need for long-term monitoring of developing endocrinopathy. While pituitary gland abnormalities are a good predictor of endocrine dysfunction, a normal pituitary gland does not rule out endocrinopathy.

Bilateral visual field maps in a patient with only one hemisphere

In mammals smooth retinotopic maps of the visual field are formed along the visual processing pathway whereby the left visual field is represented in the right hemisphere and vice versa. The reorganization of retinotopic maps in the lateral geniculate nucleus (LGN) of the thalamus and early visual areas (V1-V3) is studied in a patient who was born with only one cerebral hemisphere. Before the seventh week of embryonic gestation, the development of the patient's right cerebral hemisphere terminated. Despite the complete loss of her right hemisphere (di- and telencephalon) at birth, the patient's remaining hemisphere has not only developed maps of the contralateral (right) visual hemifield but, surprisingly, also maps of the ipsilateral (left) visual hemifield. Retinal ganglion-cells changed their predetermined crossing pattern in the optic chiasm and grew to the ipsilateral LGN. In the visual cortex, islands of ipsilateral visual field representations were located along the representations of the vertical meridian. In V1, smooth and continuous maps from contra- and ipsilateral hemifield overlap each other, whereas in ventral V2 and V3 ipsilateral quarter field representations invaded small distinct cortical patches. This reveals a surprising flexibility of the self-organizing developmental mechanisms responsible for map formation.

Optic disc area and retinal area in amblyopia

PURPOSE

To compare retinal area to optic disc rim area ratios of hyperopic normal, strabismic eyes with equal acuity, amblyopic, and fellow eyes.

METHODS

Neuroretinal rim areas of 293 amblyopic and fellow eyes, and 77 non-amblyopic hyperopic right eyes, and 84 non-amblyopic strabismic right eyes were measured by magnification corrected retinal photography and planimetry. Retinal area estimates were based on axial lengths.

INCLUSION CRITERIA

All subjects had bilateral hyperopia. Patients with glaucoma or known optic nerve atrophy were excluded. The normal and strabismic groups had equal visual acuity in each eye better than 20/40. The amblyopic group had acuity worse than 20/40 in one eye uncorrectable with lenses and without gross anatomic defects.

RESULTS

The amblyopic group included 137 with strabismus and 89 with anisometropia exceeding 1.5 diopters. There were highly significant differences between the ratio of retinal area to optic disc rim area of the amblyopic and of normal eyes (unpaired t-test, p = 8.6 x 10(-6)), the amblyopic and strabismic right eyes (unpaired t-test, p = 4.22 x 10(-8)) as well between the fellow and amblyopic eyes (paired t-test, p = 2.13 x 10(-5)). The difference between the normal and strabismic eyes without amblyopia was not significant (p = 0.82). There was a 20 percent increase in the retinal receptor areas of hyperopic amblyopic eyes as compared to hyperopic eyes without amblyopia despite reduced retinal areas in the amblyopic eyes. Dysplastic and/or asymmetric optic discs were present in 163 of 293 (56 percent) amblyopic patients, 47 of 84 (56 percent) strabismic, and 10 of 77 (13 percent) normal patients.

CONCLUSIONS

The increase in the receptor area may be an explanation for diminished acuity and impaired visual function in amblyopic eyes.

Bilateral intraocular glandular choristomas in a Thoroughbred foal

Intraocular choristomas are rare anomalies in domestic animals and are often associated with multiple ocular malformations. A Thoroughbred foal presented for ocular abnormalities and was diagnosed with microphthalmia, corneal dermoids, severe anterior segment dysgenesis (including glandular choristomas), aphakia, retinal dysplasia, and optic nerve hypoplasia. Morphological, histochemical, and immunohistochemical comparisons were made between ocular choristomatous tissues from this foal and lacrimal gland, third eyelid gland, nasopharynx, trachea, and lacrimal sac/nasolacrimal duct from normal horses. Morphologically the choristomatous tissues (glands and epithelium lining the anterior segment) were most similar to the lacrimal sac. Histochemistry of glandular components found the glands associated with the lacrimal sac/nasolacrimal duct to be serous, as was the glandular intraocular choristomas. Our findings suggest that the origin of intraocular glandular choristomas in this case is from the lacrimal sac.

Developmental abnormalities of the optic nerve and chiasm

Developmental anomalies of the optic nerve are an important and growing cause of lifelong visual handicap and they are often associated with systemic abnormalities. This review focuses on the ocular and systemic aspects of developmental anomalies arising from defects of fetal fissure closure and retinal ganglion cell development, and covers some other optic-disc anomalies that have systemic significance.

Intraretinal projection of retinal ganglion cell axons as a model system for studying axon navigation

The initial step of retinal ganglion cell (RGC) axon pathfinding involves directed growth of RGC axons toward the center of the retina, the optic disc, a process termed "intraretinal guidance". Due to the accessibility of the system, and with various embryological, molecular and genetic approaches, significant progress has been made in recent years toward understanding the mechanisms involved in the precise guidance of the RGC axons. As axons are extending from RGCs located throughout the retina, a multitude of factors expressed along with the differentiation wave are important for the guidance of the RGC axons. To ensure that the RGC axons are oriented correctly, restricted to the optic fiber layer (OFL) of the retina, and exit the eye properly, different sets of positive and negative factors cooperate in the process. Fasciculation mediated by a number of cell adhesion molecules (CAMs) and modulation of axonal response to guidance factors provide additional mechanisms to ensure proper guidance of the RGC axons. The intraretinal axon guidance thus serves as an excellent model system for studying how different signals are regulated, modulated and integrated for guiding a large number of axons in three-dimensional space.