Of all the conditions and diseases that affect the anterior segment, there are some that are more well known than others. Corneal ulcers and cataracts spring to mind, as do conjunctivitis and refractive errors, maybe even aphakic bullous keratopathy. One of the less well known conditions, especially in the lay community, is optic nerve glioma (ONG).
This is perhaps not surprising as ONG is a relatively rare condition and frontline ophthalmologists are unlikely to encounter it on a daily basis. While of course, the rarity of any disease or condition should be considered to be positive — especially from the patient’s perspective — it means that this otherwise medically fascinating condition is under researched. Over the last two years, a number of papers have been published to remedy this situation.
ONGs are benign tumors and are classified as pilocytic astrocytomas. They make up half of all primary optic nerve tumors (an already rare condition), and between 1.5 and 4% of all orbital tumors. While this does make them relatively rare overall, optic nerve gliomas are still more common than other primary tumours, like malignant optic nerve glioma, optic nerve sheath meningioma and ganglioglioma.1
Will Someone Please Think of the Children?
The symptoms of ONG are similar to other optical nerve tumors and include nausea and vomiting, problems with balancing, visual disturbances and severe headaches. Patients may also feel fatigued, have poor memory recall, and may experience a loss of appetite. As ONGs tend to grow slowly, the symptoms may take a considerable amount of time to become apparent.
What makes ONG particularly interesting as a condition, is that it primarily affects people under 20-years-old — in fact, one could say that its primary defining feature is that it disproportionately affects the young. According to one particularly comprehensive study that examined 80 years of reporting on and treating optic nerve glioma, it is only found in young individuals. However, the same paper makes the point that”‘traditional histopathologic techniques have not been reliably predictive of clinical course.”2
Most patients are also affected by neurofibromatosis type 1 (NF-1). This form of lesion is characterized by having a somewhat indolent course; at least 50% of patients have no evidence of visual loss when diagnosed with ONG. The gold standard for diagnosis and follow-up are thorough neuro-ophthalmic examinations with specific attention to visual acuity. This can be followed with chemotherapy or surgery if the tumor worsens.3
More to the City of Brotherly Love than Rocky
Many studies dedicated to ONG reference the fact that there is scarcity of data and research on the disease. This has spurred a number of researchers at various institutions to consider new methods of diagnosis for optic nerve glioma, as well as its management and treatment. This was the aim of a group of researchers at the Perelman School of Medicine at the University of Pennsylvania, who published Current Treatment of Optic Nerve Gliomas.
Establishing that the standard treatment course is chemotherapy, they also investigated new molecular targeted therapies, radiation therapy, and surgical resection and debulking. The researchers concluded that newer molecular-target therapies such as MEK inhibitors and bevacizumab show promise in refractory cases, and may become more widely used. They also stated that when children manifest a decline in visual acuity, visual field or significant radiologic progression, chemotherapy with vincristine and carboplatin should be used as a first option.4
The paper also warns against using radiotherapy and radical surgical resections as they are associated with high morbidity, and therefore should be reserved as a last resort. Their conclusion on debulking surgery using a lateral orbitotomy approach (which came with some fantastic images), can be used for those patients with a large orbital component resulting in pain and disfigurement. This procedure was reported to have excellent cosmetic results and came with a minimal risk of progression of the residual tumor.
Clearly there are some exciting developments in optical nerve glioma and as more research papers are published in the coming years, we are likely to witness further developments in treatment. More research would be welcome, especially into areas of treatment other than standard chemotherapy.
References
1. Huang M, Patel J, Patel BC. Optic Nerve Glioma. Treasure Island (FL): StatPearls Publishing; 2020
2. Cameron JD, Rodriguez FJ, Rushing E, et al. An 80-year Experience with Optic Nerve Glioma Cases at the Armed Forces Institute of Pathology: Evolution from Museum to Molecular Evaluation Suggests Possible Interventions in the Cellular Senescence and Microglial Pathways (an American Ophthalmological Society Thesis). Trans Am Ophthalmol Soc. 2014;112:11–25.
3. Rasool N, Odel JG, Kazim M. Optic Pathway Glioma of Childhood. Curr Opin Ophthalmol. 2017;28(3):289-295.
4. Farazdaghi MK, Katowitz WR, Avery RA. Current Treatment of Optic Nerve Gliomas. Curr Opin Ophthalmol. 2019;30(5):356-363.
