Q. A patient presents with one eye bulging out. Thorough examination of patient history shows development of an intrinsic tumor of the optic nerve: a glioma. The physician refers to the patient’s condition as proptosis. He begins to lightly tap both of the patient’s eyes with a pen-like tool called a Tonopen. What is a Tonopen used for and what will be the patient’s treatment options?

A. Proptosis is the anterior displacement of the eye from the orbit. Since the orbit is closed off posteriorly, medially, and laterally, any enlargement of structures located within the orbit will cause the anterior displacement of the eye. Such displacement will increase the intraocular pressure behind and inside the eye. As the intraocular pressure increases, risks for other eye diseases such as glaucoma also increase — thus, even if the glioma is benign, it is important to take action before the condition worsens and leads to other diseases. Tonopens measure intraocular pressure, which is the pressure inside the eye. During the process, tetracane will be applied to numb the eye. The patient is then asked to look forward while the device is lightly tapped against the eye. Generally, a pressure between 10-21 is considered normal. In the patient that I saw, the pressure of the right eye (bulging) was 46, while the pressure of the left eye (normal) was 20. After confirming that the pressure of the bulging eye was indeed higher, an ophthalmology consult was called into the ED for further assessment. It is recommended that most patients with unilateral optic nerve gliomas are followed at regular intervals clinically and undergo neuroimaging without further intervention. Only if there is cosmetically unacceptable proptosis, progressive deterioration of visual function, definite tumour enlargement as evidenced by MR imaging, should surgical excision of the lesion be considered. Resources: