Chapter 4: Optic Nerve Disorders

CHAPTER OUTLINE

• ANATOMY OF THE OPTIC NERVE

  • Intraocular course

  • Intraorbital course

  • Intracanalicular course

  • Intracranial course

• CLINICAL EXPRESSION OF DISEASE

  • Pallor and cupping

  • Optic disc swelling (edema)

  • Accompanying signs

• ISCHEMIC OPTIC NEUROPATHIES

  • Nonarteritic anterior ischemic optic neuropathy

  • Arteritic anterior ischemic optic neuropathy

  • Diabetic papillopathy

  • Papillophlebitis

  • Radiation optic neuropathy

• OPTIC NEURITIS

• OPTIC PERINEURITIS

• PAPILLEDEMA

  • Mechanism of papilledema

  • Idiopathic intracranial hypertension (pseudotumor cerebri)

  • Other causes of papilledema

• COMPRESSIVE OPTIC NEUROPATHIES

  • Optic nerve sheath meningiomas

  • Other causes of optic nerve compression

• INTRINSIC NEOPLASMS

  • Optic nerve glioma

  • Lymphoproliferative disorders

  • Other intrinsic neoplasms

• INFLAMMATORY OPTIC NEUROPATHIES

• INFECTIOUS OPTIC NEUROPATHIES

  • Optic disc edema with a macular star

  • Cat-scratch neuroretinitis

  • Other infectious neuropathies

• TOXIC AND NUTRITIONAL OPTIC NEUROPATHIES

• HEREDITARY OPTIC NEUROPATHIES

  • Autosomal dominant (Kjer) optic atrophy

  • Leber hereditary optic neuropathy

• TRAUMATIC OPTIC NEUROPATHY

• GLAUCOMA

• OPTIC DISC DRUSEN

• ANOMALOUS OPTIC DISCS

  • Crowded optic discs

  • Elevated discs without drusen

  • Tilted optic discs

  • Myelinated retinal nerve fibers

  • Hypoplasia

  • Aplasia

  • Coloboma

• KEY POINTS

INTRODUCTION

In Chapter 3, the organization of axons in the sensory visual system provided the basis for understanding the patterns of visual field defects. In this chapter, the neuroanatomy of the anterior sensory visual system forms the foundation for understanding optic nerve disorders and their clinical expression.

ANATOMY OF THE OPTIC NERVE

The optic nerve originates at the confluence of retinal ganglion cell axons as they traverse the scleral canal to exit the globe, and ends anatomically as these axons merge with the axons of the fellow optic nerve at the chiasm. Anatomic divisions of the optic nerve include intraocular, intraorbital, intracanalicular, and intracranial portions (Figure 4–1).

INTRAOCULAR COURSE

The short intraocular course of the optic nerve is often referred to as the optic nerve head, and the portion that can be seen with the ophthalmoscope is called the optic disc. The optic disc is usually oval, measuring about 1.5 by 1.75 mm, with its long axis typically oriented vertically. In most subjects, the optic cup, devoid of axons, is seen centrally, surrounded by the pink, doughnut-shaped neuroretinal rim (Figure 4–2A). The rim consists of axons seen end-on, as they pass from the nerve fiber layer and make a right-angled turn into the scleral canal. Although the number of axons in normal subjects is relatively constant, the diameter of the scleral canal varies among individuals. When the scleral opening is small, the axons are crowded into a small space (Figure 4–2B). These small, cupless discs are often referred to as “discs at risk,” as they are frequently associated with optic disc infarction (anterior ischemic optic neuropathy [AION]). Individuals with large scleral openings may have large disks with large central cups, which may be mistaken ...