172 CHAPTER 12 Diseases of the optic nerve
Optic pit
DEFINITION/OVERVIEW AND ETIOLOGY
An optic pit is a round oval depression in the optic disc (224). Optic pits are generally sporadic, although familial cases of AD inheritance have been reported.38 They are most likely due to a defect in development of the primitive epithelial papillae.
CLINICAL PRESENTATION
The pit may appear gray, white, or yellow. Optic pits may be located in any sector of the optic disc, although the temporal disc is commonly involved.30 Optic pits located temporally are often accompanied by adjacent peripapillary pigment epithelial changes. Cilioretinal arteries are common in eyes with optic pits. Although optic pits are typically unilateral, bilateral pits occur in 15% of cases.30 In unilateral cases, the involved disc is slightly larger than a normal disc. Histologically, the lamina cribrosa is defective in the area of the pit and some optic pits extend into the subarachnoid space.
DIAGNOSIS AND MANAGEMENT/TREATMENT
Visual acuity is typically normal unless there is subretinal fluid. Approximately 45% of eyes with congenital optic pits develop serous macular elevations.1 These elevations represent both retinoschisis and retinal detachment.39 Optic pitassociated macular retinoschisis/detachments often occur in the third and fourth decades of life. The risk of an eye developing retinoschises or detachment is greater with large pits and with temporally-located pits.40 These retinal elevations have been treated with laser photocoagulation, internal gas tamponade, and vitrectomy with variable success.41,42
Myelinated retinal nerve fibers
DEFINITION/OVERVIEW AND ETIOLOGY
During development, myelination starts at the lateral geniculate nucleus and stops at the lamina cribrosa. In some patients, retinal nerve fibers acquire a myelin sheath, and may arise from abnormal nests of oligodendrocytes within the retina and the optic nerve.
CLINICAL PRESENTATION AND MANAGEMENT/TREATMENT
Myelinated retinal nerve fibers (MRNFs) appear as a white area in the nerve fiber layer with frayed, feathered edges that follow the same orientation as a normal retinal nerve fiber layer (225). The myelinated nerve fibers may occur as an isolated patch or in several noncontiguous spots. MRNF are most commonly located along the optic disc margin (226). Retinal vessels are often obscured. Visual acuity ranges from normal to severe visual impairment. Some patients have associated unilateral high myopia as well as a hypoplastic macula.
If unilateral high myopia and amblyopia are present, appropriate optical correction and amblyopia therapy should be instituted.
Myelinated retinal nerve fibers 173
224
224 Optic nerve coloboma that contains a temporal optic nerve pit,left eye.Note the cilioretinal vessel emanating from the optic nerve pit.
225
225 Myelinated nerve fibers,right optic nerve. Myelinated nerve fibers obscure the disc and the disc margin,as well as some of the disc vessels. The feathery edges are illustrated.
226
226 Optic nerve with severe myelinated nerve fibers that obscure the disc and the disc vessels, right eye.
174 CHAPTER 12 Diseases of the optic nerve
Papilledema
DEFINITION/OVERVIEW AND ETIOLOGY
Papilledema is a sign of increased intracranial pressure (ICP). Because it is a sign and not a diagnosis in itself, the discovery of papilledema should lead to neuroimaging. The term papilledema should be reserved for disc edema that occurs from ICP. The ICP is transmitted to the optic nerve head through the subarachnoid space resulting in the disc appearance described below.
DIAGNOSIS
Clinical characteristics that suggest (but do not prove) papilledema include spared visual acuity, and intact color vision, as well as bilateral involvement. Papilledema initially impairs the peripheral visual field causing constriction, arcuate defects, and nasal steps. Peripheral visual field loss may eventually involve fixation resulting in loss of visual acuity. Some patients have loss of visual acuity from retinal edema or hemorrhage. Patients may have ‘a graying out’ or loss of vision that lasts several seconds, so-called transient visual obscurations.
MANAGEMENT/TREATMENT
CLINICAL PRESENTATION
Disc edema occurs from an insult at the optic nerve head that causes impaired intra-axonal transport. This causes swelling of the optic nerve axons at the disc. The disc appears elevated with obscuration of the retinal vessels at the disc margins and peripapillary retinal wrinkling (Paton’s lines) (227). The swollen disc may increase central retinal venous pressure, resulting in retinal venous dilation and tortuosity, disc hyperemia, intraretinal hemorrhages, and cotton-wool spots. Fluorescein angiography shows extracellular dye leakage at the disc.
227
Papilledema is a medical emergency. The differential diagnosis of papilledema includes an intracranial mass, meningitis, venous sinus thrombosis, and hydrocephalus. ICP may shift the brain stem resulting in a cranial nerve VI palsy and consequent diplopia. Associated systemic signs of elevated ICP include headache, nausea, and vomiting. Cranial MRI is indicated to detect any intracranial abnormality. If neuroimaging does not reveal an intracranial mass or hydrocephalus, a lumbar puncture is indicated to measure the ICP as well as to examine the cerebrospinal fluid content.
Pseudotumor cerebri is a syndrome defined by the presence of elevated ICP, normal cranial MRI and normal cerebrospinal fluid content. In contrast to adults, pseudotumor cerebri in children is not associated with obesity and occurs with equal frequency in males and females.43 Pseudotumor cerebri in children has been associated with drug use (tetracycline, doxycycline, and vitamin A), viral infections, growth hormone use, and thyroid medications. Treatment options, including acetazolamide, topiramate, optic nerve sheath fenestration, and shunting procedures are similar to those of adults.
227 Disc edema,right eye.Note the elevated disc,obscuration of disc vessels,Paton’s lines, venous dilation and tortuosity,and nerve fiber layer retinal hemorrhage.
Pseudopapilledema 175
Pseudopapilledema
DEFINITION/OVERVIEW AND ETIOLOGY
Pseudopapilledema is an elevated disc anomaly that may be confused with papilledema (228). Pseudopapilledema is often bilateral and familial. Etiologies include buried optic disc drusen and prominent glial tissue.
CLINICAL PRESENTATION AND DIAGNOSIS
Pseudopapilledema can be differentiated from papilledema by the absence of disc hyperemia, vessel obscurations, nerve fiber layer hemorrhages, and cotton-wool spots (229). There is often abnormal branching of the large fundus vessels.
Ultrasonography or CT may show buried disc drusen. Fluorescein angiography does not show the disc leakage that occurs with true papilledema.
228
228 Pseudopapilledema,right eye.Optic disc is elevated,however,there are no vessel obscuration,disc hyperemia,retinal hemorrhages,or cotton-wool spots.There is abnormal branching of the large retinal vessels.
229
229 Pseudopapilledema,right eye.The optic nerve is elevated.There are no disc hyperemia, obscuration of disc vessels,retinal hemorrhages, or cotton-wool spots.The large retinal vessels have an anomalous branching pattern.The nerve fiber layer has a shiny light reflex with no opacification.