enlarged optic disc. They result from incomplete or abnormal closure of the embryonic optic fissure. Minimal peripapillary pigmentation is present. Occurrence is split equally between unilateral and bilateral cases. Visual function may be decreased mildly or severely depending on involvement of the papillomacular bundle. Optic disc colobomas are seen in conjunction with other systemic anomalies such as Aicardi or Goldenhar syndrome and have been linked to a mutation of PAX6.1 Ultrasonography B-scan clearly delineates the inferior location of these excavations and also may demonstrate the small diameter of the associated optic nerve (Fig. 6).
Morning Glory Disc Anomaly
Morning glory disc is a rare congenital anomaly characterized by a funnel-shaped excavation of the optic nerve surrounded by a wide annulus of choriopapillary depigmentation. It is associated with intracranial abnormalities including agenesis of the corpus callosum and basal encephalocele and an increased frequency of retinal detachment. Ultrasonography B-scan is useful to confirm the centralized location of the depression in morning glory disc as compared with the asymmetric inferiorly located depression found in coloboma.24,25
Tilted Optic Disc
High myopia often is associated with tilted optic discs that appear to have an elevated nasal rim. Cup-to-disc ratio cannot be evaluated adequately because of the oblique view of the nerve head on ophthalmoscopy. This may raise suspicion of the presence of optic disc edema. In an asymptomatic patient without dyschromatopsia or an afferent papillary defect, ultrasonographic studies should be obtained. Ultrasonography and optical
Fig. 6. Optic disc coloboma. Longitudinal B-scan in an eye with coloboma. Note vitreous hemorrhage, a shallow retinal detachment (arrow) and coloboma at the inferior portion of the optic nerve head (arrowhead).
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coherence tomography (OCT) of the disc reveal a normal nerve fiber layer thickness (Fig. 7). In conjunction with a negative 30 test, these patients can be followed clinically without the need for further imaging or lumbar puncture.
Pseudodoubling of the Optic Disc
Pseudodoubling of the optic disc is a rare clinical occurrence associated with chorioretinal coloboma. In this entity, there is the appearance of two optic nerves because of the presence of focal anomalous vascular anastomoses between the choroidal and retinal circulations adjacent to the coloboma (Fig. 8). B-scan ultrasound can image the coloboma and rule out other retrobulbar optic nerve pathology. Vascular channels can be delineated further using color Doppler imaging.26
RETROBULBAR OPTIC NERVE LESIONS
Asymmetric optic nerve sheath diameters should raise suspicion of retrobulbar lesions of the optic nerve. Glioma, meningioma, circumpapillary choroidal melanoma,27 and demyelinating optic neuritis28 have been examined ultrasonographically. Sudan and colleagues29 presented a case of optic nerve cysticercosis in which a cystic lesion was present just posterior to the globe on ultrasonography B-scan. Following treatment, involution of the cyst could be observed ultrasonographically.
GAZE-EVOKED AMAUROSIS
Gaze-evoked amaurosis is a transient blurring of vision associated with movement of the eye. It usually is caused by an underlying posterior orbital mass that compresses the optic nerve and its blood supply in extremes of gaze. Gaze-evoked amaurosis also may be caused by vitreopapillary traction at the optic nerve.30 Ultrasonography demonstrated elevation of the nerve head associated with partial posterior vitreous detachment in which persistent vitreopapillary attachments were present. The authors postulated that traction upon eye movement was transmitted to the nerve fibers in the papilla, causing phosphenes followed by gaze-evoked amaurosis.
ORBITALTRAUMA
Avulsion of the optic nerve appears on B-scan as a hypolucent area in the region of the optic nerve head that may be associated with a defect in the posterior sclera. This can aid in planning potential intervention in instances of orbital trauma associated with poor visualization of the fundus caused by hemorrhage.31
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Fig. 7. Tilted optic disc. Fundus photograph shows apparent elevation of the nasal rim (arrow) of the optic disc right eye (A) and left eye (B). Axial B-scan images show mild optic disc elevation without buried drusen or optic disc edema of the right eye (C) and left eye (D).
GIANT CELL ARTERITIS
Although ultrasound of the optic nerve is not directly useful in the diagnosis of visual loss because of anterior ischemic optic neuropathy,
ultrasonography is useful to evaluate inflammation within the superficial temporal artery, associated with this disease.32 Correlation of histologic findings with ultrasonography of the superficial
Fig. 8. Pseudodoubling of the optic disc. Fundus photograph of left eye showing the appearance of two optic discs (A). The secondary vascular supply (arrow) comes from anastomoses between choroidal and retinal circulations adjacent to the coloboma. Longitudinal B-scan shows mild-to-moderate elevation of the anomalous optic disc (arrow) and optic nerve head pit (arrowhead) (B).
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Fig. 9. Hypoechoic vessel wall changes in acute arteritis (halo sign) of an 80-year old man with biopsy-proven, acute temporal arteritis. Main stem of the common superficial artery. Typical halo effect in the axial plane (A, long arrows). The same vessel segment with halo in the longitudinal plane (B, long arrows). Note the less hypoechoic reflexes in the edematous vessel wall (short arrows). (From Reinhard M, Schmidt D, Hetzel A. Color-coded sonography in suspected temporal arteritis—experiences after 83 cases. Rheumatol Int 2004;24:343; with kind permission of Springer Science and Business Media.)
temporal artery, in 36 patients presenting with signs |
8. Kimberly HH, Shah S, Marill K, et al. Correlation of |
and symptoms suggestive of giant cell arteritis, |
optic nerve sheath diameter with direct measure- |
revealed a dark halo around the lumen of the tem- |
ment of intracranial pressure. Acad Emerg Med |
poral arteries bilaterally corresponding with posi- |
2008;15(2):201–4. |
tive biopsy results (Fig. 9). Equivocal or negative |
9. Goel R, Goyal N, Dharap S, et al. Utility of optic |
ultrasound results, however, were found in patients |
nerve ultrasonography in head injury. Injury 2008; |
with both positive and negative biopsies and were |
39(5):519–24. |
not associated with ocular disease. Further study |
10. Karakitsos D, Soldatos T, Gouliamos A, et al. Trans- |
in larger number of patients is needed to establish |
orbital sonographic monitoring of optic nerve diam- |
definitive guidelines about the need for biopsy. |
eter in patients with severe brain injury. Transplant |
|
Proc 2006;38(10):3700–6. |
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