Optic Nerve / Optic Pathway Glioma (OPG)
An optic nerve glioma – also known as an optic pathway glioma (OPG) – is a slow-growing brain tumour that forms around the nerves that carry information from the eye to the brain. As the tumour grows it affects the nerves, causing problems with vision.
This is usually a young person’s brain tumour – three quarters of optic nerve glioma cases are diagnosed in children and teenagers rather than in adults. This is a serious tumour but in most cases optic nerve gliomas can be successfully treated. Only rarely does this tumour result in blindness.
How common is an optic nerve pathway glioma?
This is a rare type of tumour; optic nerve gliomas account for around 5% of all childhood brain tumours. It occurs fairly evenly amongst boys and girls, and is typically diagnosed at around five years of age.
What grade is an optic nerve glioma?
An optic nerve glioma is usually classified as a benign WHO (World Health Organisation) grade 1 pilocytic astrocytoma, which is a low-grade (slow growing) glioma brain tumour. They rarely progress to a higher grade.
Very occasionally, an optic nerve glioma can be classified as a pilomyxoid astrocytoma. These typically behave more aggressively than pilocytic astrocytoma, and can return despite treatment to remove it.
Rare examples of the primary occurrence of anaplastic astrocytomas and glioblastomas in the optic pathway in adults have been reported.
What are the symptoms of an optic nerve or optic pathway glioma?
Symptoms can include the following:
- Worsening vision
- Reading becoming more difficult
- Flickering eyes
- Double vision
- Blind spots
- Head tilt
- Eye protruding forward
If there is increased pressure in the head due to the size of the tumour, symptoms may also include:
- Nausea and vomiting
- Lethargy and irritability
In young children, these symptoms may be picked up as increased clumsiness, moodiness and sitting closer to watch television for example.
There may be a number of reasons why someone displays one or more of the symptoms listed above and may not indicate having a brain tumour. Always discuss symptoms with a GP / optometrist or ophthalmologist to best identify underlying causes and suitable treatment.
How is an optic nerve / optic pathway glioma diagnosed?
CT and MRI scans - An MRI scan will provide detailed information in order to establish whether or not an optic pathway glioma is present. CT scans are useful in some cases, but give less detailed information than an MRI scan.
Ophthalmic assessment – Full assessments of a patient’s vision will be needed from point of diagnosis, as well during and after treatment for the tumour.
Endocrine assessment – If there is evidence of the tumour pressing on the hypothalamus or pituitary gland, a full test of the patient’s hormones will be needed, usually involving some routine blood tests.
What causes an optic nerve / optic pathway glioma?
It is not known what causes a brain tumour generally, but research has identified that around 50% of optic nerve gliomas diagnosed in children and teenagers are associated with a genetic condition called Neurofibromatosis 1 (NF1). A blood test can establish if a patient has NF1. This can be inherited from a parent but in about 50% of cases the child will be the first affected in the family.
Previous radiotherapy to the head (for example, for another type of brain tumour) is also recognised as a possible cause of optic nerve glioma.
Treatment of optic nerve / optic pathway gliomas
Surgery – Not always used for optic pathway gliomas, due to the risk of damage in sensitive areas. If a patient is experiencing problems with vision in one eye, clinicians may recommend surgery to protect vision on the better side.
Chemotherapy – This is offered with the aim of shrinking the tumour and stabilising / improving the patient’s vision. Nearly all drugs and combinations of chemotherapy drugs show similar response rates of 50% - 70% so specific application will be related to the patient’s age.
Radiotherapy – This is usually offered to patients after chemotherapy if needed, although not those who test positive for NF1, where the risk of secondary tumours after radiotherapy is considered too high.
How can we find a cure for optic nerve gliomas?
Research we are funding across all of our Centres of Excellence will help lead towards finding a cure for optic nerve glioma brain tumours.
Pioneering research at our Brain Tumour Research Centre of Excellence at Queen Mary University of London is focused on using GBM stem cells to help develop unique, patient-specific treatments.
Our team at the University of Plymouth Low-Grade Brain Tumour Centre of Excellence are researching a range of mutations in brain tumour cells that initiate tumour progression and drive growth, transforming slow-growing low-grade gliomas into high-grade gliomas.
Their discoveries are designed to enable new treatments to be developed and tested in order to halt and hopefully reverse this process. The team are also testing combination therapies for low-grade brain tumours, designed to enhance the effectiveness of existing treatments.
The team of research and clinical experts at our Centre of Excellence at Imperial College, London, are part of a global collaboration looking at how the ketogenic diet can influence glioma metabolism and help in the effective treatment and management of living with this brain tumour.
Scientists at our Centre of Excellence in the University of Portsmouth are looking at mitochondria in glioma, exploring ways to ‘shut down’ these ‘batteries’ that supply energy to the brain tumours.
We also fund BRAIN UK at Southampton University, the country’s only national tissue bank registry providing crucial access to brain tumour samples for researchers from all clinical neuroscience centres in the UK, effectively covering about 90% of the UK population, and an essential component in the fight to find a cure for glioma brain tumours.
Page last updated in February 2019. Next review - January 2020.