Optic Nerve Hypoplasia
Optic Nerve Hypoplasia (ONH) is a non-progressive, medical condition that arises from the underdevelopment of the eye’s optic nerve(s) before birth. The likely course of Optic Nerve Hypoplasia is variable, as many people are able to live relatively unaffected lives, but others can experience severe vision impairment with the inability to receive light in one eye (unilateral) or both (bilateral).
Visual perception arises from signals transmitted from optic nerves to the brain. Given that underdeveloped optic nerves reduce the ability to transmit signals, visual function is diminished for people experiencing ONH.
Although there is no cure for ONH, early detection is important and certain strategies and low vision devices such as eSight can help enhance vision to those affected.
Optic Nerve Hypoplasia (ONH) is a non-progressive, congenital condition in which the optic nerve is underdeveloped in one eye (unilateral) or both (bilateral). It is characterized by short optic nerves and loss of the ganglion cell layer (GCL) and retinal nerve fiber layer (RNFL).
Optic Nerve Hypoplasia is a condition that isn’t progressive, meaning it does not get worse over time. It is mainly characterized by having short optic nerves that under developed before birth.
Since you see things as your eyes receive impulses from the optic nerves, your vision function is diminished when optic nerves are underdeveloped, as in the case of ONH. Since Optic Nerve Hypoplasia is present from birth, it is one of the most prevalent causes of vision impairment and blindness in children, accounting for 15%-25% of severe visual loss in children.
Optic Nerve Hypoplasia accounts for 15%-25% of severe visual loss in children.
Optic Nerve Hypoplasia can occur alone or in combination with other ocular abnormalities, such as nystagmus which is defined as involuntary, abnormal eye movements. When you have ONH, you may only receive a sliver of light in one or both eyes, and your level of disability can range from minor to severe.
ONH is rarely isolated and frequently occurs in conjunction with other functional and anatomic abnormalities of the central nervous system. It can be a part of the septo-optic dysplasia (de Morsier’s syndrome) syndrome, including a midline brain malformation and hypopituitarism.
Prevalence of Optic Nerve Hypoplasia
The prevalence of ONH appears to be increasing with time.
- Researchers believe that ONH affects females and males at the same rate.
- The prevalence of this disease is approximately 1 in 10,000 children, according to the National Organization of Rare Diseases.
- ONH accounts for approximately 25% of vision loss in infants, according to a report from the Oman Journal of Ophthalmology.
- ONH was the third most common cause of any vision impairment (after cortical visual impairment and retinopathy of prematurity).
Signs and Symptoms
Vision Symptoms of Optic Nerve Hypoplasia
Visual impairment is the main symptom of Optic Nerve Hypoplasia. While Optic Nerve Hypoplasia is manifested at the time of birth, symptoms might not be evident until the infant reaches adolescence. Vision problems in one or both eyes is common. Nystagmus (involuntary eye movements) appears typically between the ages of one and three months, followed by eye misalignment or crossed eyes. Most children may see some improvement in their vision in the first few years of life.
ONH vision symptoms may include:
- Lack of visual detail and general blurring of vision
- Unaware of people or objects in the periphery
- Visual acuity ranging from having no perception of light to being near normal
- Lack of depth perception, leading to the inability to locate objects in space correctly
- Avoiding light by limiting outdoor activities (mild Photophobia)
Behavioral Symptoms of Optic Nerve Hypoplasia
Children may display some behavioral symptoms of ONH including:
- Experiencing delays in acquiring skills to coordinate their muscular and mental activity
- Squinting, lowering their head, or refusing to participate in outdoor activities to avoid light if they have photophobia
- Having very limited food preferences, and could exhibit excessive lip-smacking while eating
Laboratory or radiographic tests cannot currently detect ONH. It can only be diagnosed through a comprehensive direct eye examination by an ophthalmologist.
For those suspected of having ONH, techniques such as Magnetic Resonance Imaging (MRI) or Optical Coherence Tomography (OCT) are used to examine the corpus callosum and optic nerves. Because various abnormalities can resemble the MRI findings of ONH, ONH may be suspected but not diagnosed based on MRI results. In addition, blood testing can identify abnormal cortisol and growth hormone deficiency levels which are confirmatory in the diagnosis of ONH.
Ophthalmoscopic confirmation of a small optic disc is required for the diagnosis of ONH. Direct ophthalmoscopy, using a handheld device to examine the eye, is the best method for diagnosing ONH in young children. A number of funduscopic findings help to confirm the diagnosis of ONH. The most important is a comparison of the disc’s area to the size of the central retinal arteries overlying it. ONH can be established by taking measurements of the optic disc from fundus pictures and comparing the diameter or area of the disc to various retinal landmarks. The horizontal disc diameter (DD) to the distance between the macular and the temporal margin of the disc is one technique (DM). With normal vision, the DD/DM ratio of optic nerves is considered to be larger than 0.35. The majority of individuals with DD/DM ratios less than 0.35 are considered to have ONH, while some people with DD/DM ratios of 0.30 to 0.35 have normal vision. Therefore, those with a smaller nerve head are more likely to have ONH.
Another feature of ONH is the presence of convoluted retinal arterioles, venules, or both. However, vessels that are unusually straight and have little branching may also be present. Children with primary growth hormone deficiency have non-branching vascular patterns. There may or may not be a hypopigmented halo surrounding the nerves, the so-called “double-ring sign” that implies a smaller optic nerve than a scleral canal. Measuring the width of the optic nerve head can be challenging, which makes mild dysfunction difficult to diagnose.
Small Optic Disc
One sign of having Optic Nerve Hypoplasia is an optic disc that is smaller than average. The optic disk is the part of the eye responsible for the “blind spot” where there are no light-detecting cells, because it is where retina nerve fibers meet to create the optic nerve, connecting from the back of the eye to the brain. An eye doctor can determine the size of a patient’s optic disc by investigating with an ophthalmoscope.
Corpus Callosum and Septum Pellucidum
In children with Optic Nerve Hypoplasia, abnormalities of the corpus callosum, such as hypoplasia and partial or total agenesis of the corpus callosum, are common neuro-radiographic findings. The most common type is Corpus Callosum Hypoplasia.
A report from the Children’s Hospital of Los Angeles indicates that patients with ONH sometimes lack a corpus callosum (or have an abnormal one), which connects the left and right sides of the brain. Or, patients may have a malformed septum pellucidum, which is a membrane that connects lateral ventricles in the brain.
Neither of these defects will affect the function of the brain, but they do sometimes occur with ONH.
The frequency of Corpus Callosum Hypoplasia in the general population is estimated to be 1.8-2.1 per 10,000, and it affects 2.3% of developmentally disabled people. Nearly half of individuals with Corpus Callosum Hypoplasia have other central nervous system abnormalities, such as non-midline defects (cortical heterotopias, schizencephaly, white matter hypoplasia, polymicrogyria) that are also related with ONH. On the other hand, ONH occurs in less than 10% of children with Corpus Callosum Hypoplasia.
Magnetic Resonance Imaging (MRI)
Magnetic Resonance Imaging (MRI) is common for people suspected of having ONH. In patients with unilateral disorders, an MRI of the orbit may reveal a variation in the optic nerve diameter.
The fundamental cause of Optic Nerve Hypoplasia is not yet understood, according to the National Organization of Rare Diseases, which noted that, “in most cases, the disorder appears to occur randomly for unknown reasons.” However, researchers do know that ONH is a congenital condition.
Potential Risk Factors
Although the cause of ONH is unknown, there are studies that have shown some risk factors affecting a low number of cases.
Maternal and Prenatal Risk Factors
According to a study published in PubMed, young maternal age, first parity, maternal smoking, preterm birth, and variables related to preterm birth were all risk factors for ONH. Optic Nerve Hypoplasia appears to be linked to a variety of other anomalies, including those of the central nervous system, as well as symptoms of prenatal development disruption.
Smoking, alcohol, recreational drugs, anti-depressants, anti-convulsants, anti-emetics, anti-fungal medicines, infertility therapy, and quinine have all been linked to prenatal exposure.
Genetic Risk Factors
Due to a clinical overlap with previously recognized central nervous system disorders, a causal relationship to ONH has been assigned to several genes and transcription factors. The identification of some gene mutations, some leading to lack of development of the forebrain, pituitary gland abnormalities, and ocular structures defects, can play an important role in diagnosis and medical care for those affected with ONH.Read more about Genetic causes of optic nerve hypoplasia.
There are no treatment options for ONH as optic nerves cannot be repaired once damaged. Early detection and support from an eye specialist may minimize the impact of vision loss and help to improve development in children. Although medical and surgical treatments do not exist, there are strategies and low vision devices that can change everyday life.
Strategies for Children with ONH
Children with ONH should have their vision checked at least once a year, and any refractive problems should be addressed once the visual acuity reaches a functional level.
- Encourage fine and gross motor activities to help them develop and learn aspects of depth perception, such as ball throwing, pouring, and stacking
- Minimize effects of light sensitivity through adjusting lighting levels and reducing surface glare
- Consider all underlying behavioral conditions when developing an education plan
- Consult professionals to help create a positive feeding experience for those with limited food preferences
Most children with ONH require physical, occupational, and/or speech treatment. The need for early intervention to treat the developmental deficiencies associated with ONH is crucial.
To overcome an aversion to certain textures of food, therapists should focus on early development of oral motor skills. Youngsters who are demonstrating autistic symptoms should be assessed by a neuropsychologist who specializes in autism evaluations as well as evaluations of visually impaired children.
If such abilities are lacking, the neuropsychologist should consult a visually impaired teacher to alter the evaluation method.
Incorporating discussion into song can help with delayed verbal communication.
Low doses of melatonin in the evening or soporific dosages at night can be used to treat children with disrupted sleep cycles. This could make retraining the circadian clock easier.
Low Vision Apps
Your smartphone can be a handy resource by installing low vision apps, and the operating system may already come with options for disabled individuals.
- LookTel Money Reader instantly recognizes currency and speaks the denomination, enabling people experiencing visual impairments or blindness to quickly and easily identify and count bills.
- TapTapSee is designed to help the blind and visually impaired identify objects they encounter in their daily lives. Simply double-tap the screen and take a photo of anything, at any angle. You’ll hear the app speak the identification back to you.
- Bright Focus Foundation offers a brief overview of apps for people with low vision.
- American Foundation for the Blind suggests various accessible apps specifically for Android devices.