Optic nerve hypoplasia: a review

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.

Genetic causes of optic nerve hypoplasia

Optic nerve hypoplasia (ONH) is the most common congenital optic nerve anomaly and a leading cause of blindness in the USA. Although most cases of ONH occur as isolated cases within their respective families, the advancement in molecular diagnostic technology has made us realise that a substantial fraction of cases has identifiable genetic causes, typically de novo mutations. An increasing number of genes has been reported, mutations of which can cause ONH. Many of the genes involved serve as transcription factors, participating in an intricate multistep process critical to eye development and neurogenesis in the neural retina. This review will discuss the respective genes and mutations, human phenotypes, and animal models that have been created to gain a deeper understanding of the disorders. The identification of the underlying gene and mutation provides an important step in diagnosis, medical care and counselling for the affected individuals and their families. We envision that future research will lead to further disease gene identification, but will also teach us about gene-gene and gene-environment interactions relevant to optic nerve development. How much of the functional impairment of the various forms of ONH is a reflection of altered morphogenesis versus neuronal homeostasis will determine the prospect of therapeutic intervention, with the ultimate goal of improving the quality of life of the individuals affected with ONH.

Comparison of human expert and computer-automated systems using magnitude-squared coherence (MSC) and bootstrap distribution statistics for the interpretation of pattern electroretinograms (PERGs) in infants with optic nerve hypoplasia (ONH)

PURPOSE

Pattern electroretinograms (PERGs) have inherently low signal-to-noise ratios and can be difficult to detect when degraded by pathology or noise. We compare an objective system for automated PERG analysis with expert human interpretation in children with optic nerve hypoplasia (ONH) with PERGs ranging from clear to undetectable.

METHODS

PERGs were recorded uniocularly with chloral hydrate sedation in children with ONH (aged 3.5-35 months). Stimuli were reversing checks of four sizes focused using an optical system incorporating the cycloplegic refraction. Forty PERG records were analysed; 20 selected at random and 20 from eyes with good vision (fellow eyes or eyes with mild ONH) from over 300 records. Two experts identified P50 and N95 of the PERGs after manually deleting trials with movement artefact, slow-wave EEG (4-8 Hz) or other noise from raw data for 150 check reversals. The automated system first identified present/not-present responses using a magnitude-squared coherence criterion and then, for responses confirmed as present, estimated the P50 and N95 cardinal positions as the turning points in local third-order polynomials fitted in the -3 dB bandwidth [0.25 … 45] Hz. Confidence limits were estimated from bootstrap re-sampling with replacement. The automated system uses an interactive Internet-available webpage tool (see http://clinengnhs.liv.ac.uk/esp_perg_1.htm).

RESULTS

The automated system detected 28 PERG signals above the noise level (p ≤ 0.05 for H0). Good subjective quality ratings were indicative of significant PERGs; however, poor subjective quality did not necessarily predict non-significant signals. P50 and N95 implicit times showed good agreement between the two experts and between experts and the automated system. For the N95 amplitude measured to P50, the experts differed by an average of 13% consistent with differing interpretations of peaks within noise, while the automated amplitude measure was highly correlated with the expert measures but was proportionally larger. Trial-by-trial review of these data required approximately 6.5 h for each human expert, while automated data processing required <4 min, excluding overheads relating to data transfer.

CONCLUSIONS

An automated computer system for PERG analysis, using a panel of signal processing and statistical techniques, provides objective present/not-present detection and cursor positioning with explicit confidence intervals. The system achieves, within an efficient and robust statistical framework, estimates of P50 and N95 amplitudes and implicit times similar to those of clinical experts.

Optic nerve hypoplasia in children and adolescents; prevalence, ocular characteristics and behavioural problems

PURPOSE

To report prevalence, ocular characteristics and coexisting behavioural problems in children and adolescents with optic nerve hypoplasia (ONH), which is a common cause of visual impairment in children in western countries, often associated with neurological or endocrinological problems and where autism has been reported in severe cases with blindness.

METHODS

This is a population-based cross-sectional study of patients <20 years of age who had been diagnosed with ONH and lived in the county of Stockholm in December 2009. Ophthalmological assessments including fundus photographs with optic disc analyses were made. A questionnaire was used to screen for behaviour and development.

RESULTS

The prevalence of ONH in all living children <18 years of age in Stockholm was 17.3/100 000 with a prevalence of visual impairment (<0.3) of 3.9/100 000. In total, 66 patients, median age 9.3 years (0.6-19.4), 36 with bilateral and 30 with unilateral ONH, were included in the current study; 53 were re-examined clinically, group A, and 13 agreed to retrospective analyses of existing medical records, group B. Analyses of the optic discs were made in fundus photographs from 53 patients comparing a semi-automated (Retinal Size Tool) and a manual method (Zeki). There was a strong curvilinear correlation (r(S)  = -0.91 p < 0.0001 for both eyes). Behavioural problems were more common (p < 0.05) in bilateral ONH.

CONCLUSION

Optic nerve hypoplasia is a common ocular malformation with a prevalence of 17.3/100 000 children and adolescents <18 years of age in Stockholm. Unilateral ONH seems as common as bilateral.

Acceleration of puberty during growth hormone therapy in a child with septo-optic dysplasia

Septo-optic dysplasia (SOD) is a heterogeneous disorder of the central nervous system characterized by various endocrinological and neurological findings. It is a complex disease caused by a combination of genetic and environmental factors. Herein, we report the case of a 5.5-year-old girl who presented with short stature and strabismus. Ophthalmological examination revealed bilateral optic nerve hypoplasia. Ectopic posterior pituitary and bilateral optic hypoplasia were detected on brain magnetic resonance imaging. The presence of bilateral optic nerve hypoplasia and hypopituitarism led to the diagnosis of SOD. An abated growth hormone (GH) response was found in the GH stimulation test and GH replacement therapy was initiated. At the end of the first year of clinical follow-up, secondary hypothyroidism was detected and L-thyroxine was added to the treatment. At the age of 8.25 years, thelarche was noted and 6 months later, the patient presented with menarche. At this time, the bone age was 12 years and the basal luteinizing hormone level was 7 mIU/mL. These findings indicated acceleration in the process of pubertal development. We report this case (i) to emphasize the need to investigate hypopituitarism in cases with bilateral optic nerve hypoplasia and (ii) to draw attention to the fact that during the follow-up of SOD cases receiving GH therapy, inappropriate acceleration of growth velocity and rapid improvement in bone age may be predictive of central precocious puberty development.

Sequencing analysis of the ATOH7 gene in individuals with optic nerve hypoplasia

BACKGROUND

The Atonal Homolog 7 (ATOH7) gene has been implicated in association studies with optic nerve head diameter size. Hence, we screened optic nerve hypoplasia (ONH) patient DNA samples from Australia, France, and the United States for sequence variants in theATOH7 gene using Sanger sequencing.

METHODS

Sanger sequencing of theATOH7 gene was performed on 34 affected individual DNA samples. Sequencing was also carried out in three unaffected family members to confirm segregation of identified single nucleotide variations.

RESULTS

Seven sequence variations were identified in ATOH7. No disease-causing sequence changes in the ATOH7 gene was discovered in the ONH patient samples.

CONCLUSIONS

Mutations within the ATOH7 gene are not implicated in the pathogenesis of optic nerve hypoplasia in our patient cohort.

Abnormal course of the oculomotor nerve on the clivus combined with a petroclival meningioma: case report

The course of the oculomotor nerve on the clivus was abnormal in a patient with petroclival meningioma. He complained of gait disturbance. A gadolinium-enhanced magnetic resonance image demonstrated a 4.4-cm enhancing mass in the petroclival region. The tumor was removed via an anterior transpetrosal-transtentorial approach. Normally, the oculomotor nerve originates from the brainstem and enters the oculomotor trigone. In this patient, the oculomotor nerve entered the dura mater at the upper clivus, behind the posterior clinoid process, and coursed parallel to the basilar artery. This entrance is lower than the normal entry point of the oculomotor nerve. The abnormal entrance of the oculomotor nerve may reflect an atypical developmental relationship among the cranial nerves, meninges, and bones during embryogenesis.

Retinal function in infants with optic nerve hypoplasia: electroretinograms to large patterns and photopic flash

AIMS

Optic nerve hypoplasia (ONH), which is defined as a congenital deficiency of retinal ganglion cells, may also involve more distal layers of the retina. We investigated electrophysiological function of the retina in ONH using electroretinograms (ERGs).

METHODS

ERGs were recorded from 48 subjects (3.5-35 months) with unilateral or bilateral ONH. Pattern reversal (4 degrees checks) was presented under chloral hydrate sedation, using an optical system to correct a cycloplegic refraction. A photopic flash stimulus was also used. Fundus photographs were used to measure the disk diameter/disk macula ratio (DD/DM), and to document other clinical signs. Eyes were classified as moderate (0.15-0.3) or severe (<0.15) ONH, and those with DD/DM greater than 0.3 were used as reference eyes.

RESULTS

Pattern ERG recording was completed in 89 eyes and was detectable in 80% of eyes with ONH (61/76 tested) and in all 13 reference eyes. Photopic flash ERGs were of good quality in all eyes. The severity of ONH correlates with the amplitude of the photopic flash b-waves and with the amplitude of the N95 component of the pattern ERG (P<0.01). However, the ERGs to large patterns were well preserved (>3.5 microV) in 10 of 35 eyes with severe ONH. Tortuous retinal vessels in eyes with either moderate or severe ONH were associated with smaller amplitude photopic b-waves and markedly diminished or undetectable pattern ERGs.

CONCLUSIONS

This study supports the hypothesis that retinal dysfunction distal to the ganglion cells is common in ONH, but is not predictable on the basis of ONH severity alone. Additionally, tortuous retinal vessels in ONH may be a sign associated with retinal dysfunction.

The classification of cortical dysplasias through molecular genetics

Recent genetic insight into the mechanisms of human brain malformation have allowed one to consider a classification of these disorders by the genetic disruption. In this article an attempt is made to classify human cortical dysplasias by the known genetic disruptions or insults that lead to them. The discussion of malformation is within the context of the embryologic processes that have thought to have gone awry. Human disorders of segmentation, cell proliferation, telencephalic cleavage, differentiation, and neuronal migration are discussed. As this is a rapidly changing area, the reader is encouraged to check online databases for updates on the genetic insights that have been gained since the publication of this article.

Brain development and the genetics of brain development

The progress made in the understanding of the genetics of human brain malformations has lead to insight into the formation of brain and into mechanisms of disease affecting brain. It bears upon neurologists and geneticists to recognize the patterns of diseases of brain formation, to properly diagnose such disorders, to assess the recurrence risk of these malformations, and to guide families with appropriate expectations for outcomes. This article may serve as a guide to neurologists in their approach to these disorders. Because this area is one of rapid progress, the clinician is advised to seek more current information that may be available through on-line databases and other sources.

Optic nerve hypoplasia in association with brain anomalies and an abnormal electroretinogram

Abnormal electroretinograms (decreased amplitude and prolonged implicit time > 2 standard deviations) in several patients with optic nerve hypoplasia (ONH) and developmental brain anomalies led us to study the electroretinogram (ERG) in 34 consecutive cases of ONH presenting to our practice. Ages of the subjects were between 7 months and 13 years (mean, 4 years). ERGs were recorded from each eye by means of a contact lens electrode and ganzfeld stimuli. Rod-dominated dark-adapted responses were recorded as well as cone-dominated light-adapted responses. When clinically indicated, brain imaging by either computed tomography (CT) or magnetic resonance imaging (MRI) was performed. The ERG was abnormal in 12 (35%) of the children, including five (42%) with unilateral ONH. Imaging studies of the brain in 12 children with ONH and an abnormal ERG disclosed brain malformations in nine (75%) of them compared to five (23%) in the group with ONH and a normal ERG. An abnormal ERG associated with ONH and brain malformations may represent retinal or transsynaptic degeneration beyond the ganglion cell layer and implies a shared causative mechanism.

The septum pellucidum and spatial ability of children with optic nerve hypoplasia

Animal studies suggest that spatial skills are dependent on an intact septum pellucidum. This theory was tested by comparing patients who were visually impaired due to bilateral optic nerve hypoplasia: 13 with a septum pellucidum were compared with six children without a septum pellucidum. There was no difference in spatial ability. The finding of an absent septum pellucidum may only indicate the timing of a congenital brain insult, and it cannot be used to predict specific clinical, neuroendocrinological, cognitive or spatial abnormalities.

Increased lenticular aldose reductase activity and high incidence of congenital cataract in the offspring of diabetic rats

In previous experimental studies we have found a 47% incidence of congenital cataracts among the fetuses of manifestly diabetic (MD) rats, and 4% of the offspring of normal (N) rats. The aim of the present study was to clarify the role of the sorbitol shunt in the pathogenesis of this congenital defect. Light microscopical evaluation of the fetal lenses revealed excessive formation of vacuoles in offspring of MD rats compared to N offspring. On gestational day 16 we found that aldose reductase (AR) activity was doubled in the lenses of fetuses of MD rats as compared to that of N fetuses. This difference as well as the net activity of AR declined in both groups during subsequent development. The sorbitol concentration was elevated more than ten-fold in the MD fetal lenses compared to N fetal lenses at all time points. The sorbitol concentration in both the MD and the N group decreased from day 16 to day 20 and increased again slightly on day 22. We conclude that the diabetic uterine milieu induces elevated AR activity and sorbitol formation in the fetal lens. This over-activity of the sorbitol shunt may produce metabolic and osmotic imbalances in the fetal lens, resulting in excessive vacuole formation and subsequent development of congenital cataract.

Optic nerve hypoplasia, encephalopathy, and neurodevelopmental handicap

Abnormalities of the central nervous system are frequently described in optic nerve hypoplasia. In a longitudinal study of 46 consecutive children (32 term, 14 preterm) with bilateral optic nerve hypoplasia 32 (69.5%) had associated neurodevelopmental handicap. Of these, 90% had structural central nervous system abnormalities on computed tomographic brain scans. Neurodevelopmental handicap occurred in 62.5% of the term and 86% of the preterm infants respectively. Term infants had a greater incidence of ventral developmental midline defects and proportionately fewer maternal and/or neonatal complications throughout pregnancy, while encephaloclastic lesions were commoner among the premature infants. An association of optic nerve hypoplasia with the twin transfusion syndrome and prenatal vascular encephalopathies is described.

Pallor of the optic disc in children

This report discusses the subject of pallor of the optic disc from the viewpoint of a paediatric neurologist. The paper is divided into two sections, one on optic atrophy in childhood and the second on optic nerve hypoplasia. Optic atrophy in children is a topic which is very poorly covered in standard textbooks either of neurology or ophthalmology. This review attempts to develop a working approach to the management of children who present with optic nerve atrophy as their primary neurological finding.

Optic nerve hypoplasia

Optic nerve hypoplasia is an easily overlooked, nonprogressive developmental anomaly which results in a wide range of visual deficits. It is frequently associated with clinically significant central nervous system and endocrine abnormalities. Maternal substance abuse is increasingly recognized in many cases. A supranormal regression of optic nerve axons in utero, rather than a primary failure of differentiation, is proposed as the pathogenesis.