the defect (Fig. 5.10). Colobomas can be unilateral or bilateral and asymmetric (Fig. 5.11). Microophthalmos may be associated with the colobomas. Unilateral optic disc colobomas can present with strabismus, decreased vision, or amblyopia.

5.4.6  Treatment

Generally, no treatment is necessary for this condition. There is a possibility of retinal detachment occurring later in life. Yearly examinations are indicated because of this. Amblyopia should be treated aggressively unless significant macular destruction is present. The presence of an afferent pupillary defect may indicate poor response to treatment. Bilateral defects warrant investigation with MRI scans to rule out associated central nervous system problems. Examination of family members is necessary to rule out a genetic predisposition.

5.5  Optic Nerve Tumor

Tumors involving the optic nerve head may be primary, contiguous from the adjacent ocular structures or metastatic from distant sites. Certain ocular conditions may present with elevated optic nerve head that resembles tumor. Optic nerve lesions can be classified as shown in Table 5.5 [82, 83].

Table 5.5  Types of optic nerve lesions

Tumors originating from in the optic nerve or its sheaths

 Optic glioma

 Meningioma

 Astrocytoma

Intraocular origion extending onto the optic nerve

 Melanocytic tumors

 Melanocytoma

 Malignant melanoma of the choroid

 Pigment epithelial proliferation and neoplasia

 Astrocyctoma

 Retinoblastoma

Metastatic tumors to the optic nerve   Leukemia

Non-inflammatory, nontumorous disc elevation

5.5.1  Glioma

5.5.1.1  Introduction

Gliomas can be divided into two groups based on its location: glioma of the anterior visual pathway (optic nerve glioma) and chiasmal glioma. Glioma of the anterior visual pathway usually presents with symptoms during the first two decades of life. It often has a benign clinical course in children contrary to the highly aggressive nature of the tumor in adults. There is no consistent gender bias in combined series. Children with chiasmal gliomas invading hypothalamus often first develop symptoms related to growth failure rather than visual problems. Many children with optic nerve glioma are asymptomatic, and the tumor is identified during CT or MR imaging performed for screening of neurofibromatosis or unrelated reasons.

5.5.2  Overview with Clinical Significance

5.5.2.1  Optic Nerve Glioma

Optic nerve gliomas are usually unilateral with bilateral involvement seen mainly in patients with neurofibromatosis (NF-1).

Proptosis is often the presenting sign that brings patients to medical attention. Impairment of visual acuity is highly variable and poorly correlated with the size of the tumor [84, 85]. Visual field defects include central scotomas, arcuate and altitudinal defects, and generalized peripheral contraction. If the tumor extends into the chiasm, junctional scotomas and bitemporal hemianopias may be found.

The optic disc appears either normal or pale (Fig. 5.12a). Optic disc edema may rarely be seen with more aggressive growth. Central retinal vein occlusion infrequently occurs as a result of intraneural con­ striction. Optociliary shunt vessels, which are seen commonly with optic nerve meningiomas, occur rarely with gliomas.

Roughly 25% of patients have ophthalmoplegia [86]. Causes for abnormal eye movement include compression of the extraocular muscles or ocular motor nerves by the tumor expanding into the orbital apex and monocular visual sensory deprivation.