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IU School of Optometry Continuing Education The Diagnostic Dilemma of Optic Nerve Elevation Congenital Anomalies/Pseudopapilledema |
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Congenital Anomalies of the Optic Nerve Head:
Go to: Dx Dilemma of ON Elevation CE table of contents
Optic Nerve Head Drusen (ONHD) Optic nerve head drusen is the most common cause of pseudopapilledema, accounting for 75% of diagnostically challenging disc anomalies. ONHD affects 1% of the population, predominantly Caucasians of any age without sexual predilection. It is rarely seen in African Americans, whose scleral canal size is often larger. Disc elevation is a result of hyaline bodies within the optic nerve head's prelaminar portion. In early life, hyaline bodies remain deep in the nerve and always anterior to the lamina cribosa. In childhood, the hyaline bodies remain deep in the nerve, causing the disc to appear papilledema-like with no physiological cupping. ONHD appears in adults as spherical nodules on the disc surface that are highly reflective by the ophthalmoscope light and give the disc an appearance of having scalloped margins. The nodules typically become more visible at the disc surface in the second to third decades. Typically, patients with ONHD are asymptomatic. Clinical findings are usually discovered upon a routine eye examination, and most patients are not aware of the visual field defects due to the slowly progressive and insidious nature of optic nerve head drusen. Examination finds:
Conditions known to be associated with ONHD include retinitis pigmentosa (RP), angioid streaks with or without pseudoxanthoma elasticum (PXE), and anterior ischemic optic neuropathy (AION). The so-called "disc at risk" for ONHD and AION are small with little to no physiological cupping. Diagnostic Testing
OCT is an objective, noninvasive alternative to CT scans and FA. OCT enables evaluation of disc edema and RNFL thickness. It is another diagnostic tool used to determine the cause of disc elevation. In papilledema, the OCT shows an elevated nerve head along with excessive thickening of the RNFL. In ONHD, the OCT shows the elevation of the disc and the underlying nodular shadows caused by the drusen. The key differential is that there is significant thinning of the RNFL. In addition to visual field testing, the OCT provides an available option for long-term follow-up of the changes in RNFL thickness.
Complications of ONHD ONHD is frequently confused with papilledema. Although generally without visual significance, ONHD is occasionally associated with hemorrhages or areas of neovascularization which may occur adjacent to the disc. It is often associated with VF defects (arcuate, glaucomatous, constriction). Always take baseline photos and Humphrey's visual fields when patient has ONHD. Patients with ONHD can develop visual field defects and RNFL loss that resemble glaucoma. This raises the concern for the clinician that the patient in this case may develop glaucoma, thus making it difficult to interpret the cause of future nerve fiber and visual field loss. The OCT cannot distinguish nerve fiber layer loss that occurs from ONHD from that which occurs as a result of glaucoma. Documentation of visual field loss and RFNL reduction provides a baseline for progression. The lack of significant disc cupping of nerves with drusen contributes to the difficulty in managing patients who develop glaucoma.
[Return to top] Congenitally Full Disc (CFD) (also known as "crowded disc") Disc elevation is the result of a normal number or retinal axons passing through a small posterior scleral foramen (small ONH diameters) causing the axons to get crowded at the optic nerve head. It is asymptomatic: no headache, no transient visual obscurations (TVO). There is little to no physiological cupping, disc margins are indistinct, the neural rim tissue remains a healthy pink non-hyperemic color, although some may judge it to be slightly hyperemic. The vasculature is often tortuous with anomalous branching. The peripapillary vessels are not obscured, +SVP is present. There is a high association with hyperopic refractive errors. Visual acuities, color vision, and visual fields are not affected. A key sign of CFD is the presence of reverse loops--small, S-shaped bends in the retinal vessels that turn back toward the disc. B-scan is normal and would show NO calcifications on low gain (differential diagnosis ONHD). OCT would show a normal to thicker RNFL as well as a measurement of the overall disc diameter being smaller than average. Visual fields are normal (differential diagnosis ONHD). A careful history should be obtained to rule out neurological signs and symptoms that may indicate acquired optic nerve disease. In lieu of any associated findings, the patient is at little risk.
[Return to top] Optic nerve hypoplasia is a developmental optic nerve anomaly characterized by a subnormal number of axons (retinal nerve fiber layer and ganglion cells) in the optic nerve. It is one of the more common congenital anomalies causing visual impairment and is usually nonprogressive Optic nerve hypoplasia is typically bilateral (60%). Cases range from mild to severe, depending on the deficiency. In optic nerve hypoplasia, the nerve head is half the size of normal. It appears as a small, funny-looking disc that is somewhat pale and dirty. There may or may not be a double pigment ring sign (discolored zone represents the size of the normal optic nerve head)--a yellow halo. Retinal vessels of normal caliber (but seem to appear large relative to the size of the disc) exit and enter the disc centrally. The normally bright reflex from the nerve fiber layer is characteristically diminished. OCT would show diminished RNFL and small nerve diameter. Visual acuity ranges from normal to severe impairment with nystagmus. Visual field loss is common and variable, commonly arcuate. There is a variable degree of optic nerve dysfunction, depending upon the degree of hypoplasia. Strabismus (50% are esotropes) can result, especially if unilateral.
Optic nerve hypoplasia results from an insult (toxic, infectious, ischemic, idiopathic, hereditary) to the visual pathways before development is completed. 50% of cases are associated with fetal alcohol syndromes and maternal recreational drug use. It can also result from maternal CMV, syphilis, rubella, and diabetes. It is frequently associated with other developmental abnormalities and delays with multiple systemic and neurological abnormalities--especially if bilateral. Septo-Optic Dysplasia (SOD) is a hypoplasia or absence of septum pellucida. It is a birth defect characterized by a malformed optic disc and nerve, pituitary deficiencies, and often the absence of the septum pellucidum which separates the ventricles of the brain. Because of these abnormalities, visual impairment and inadequate growth hormones may occur. 13% of cases are associated with pituitary dysfunction, hypothalamic-pituitary dysfunction, and endocrine disorders. It can also be associated with mental retardation and/or cerebral palsy. The majority of optic nerve hypoplasia patients have no associated systemic abnormalities. Diagnostic Dilemma Appropriate management begins with proper diagnosis. It is important to recognize an associated developmental delay or endocrine abnormality for patient education and medical intervention as needed. This condition must be clearly distinguished from amblyopia when presented unilaterally or asymmetric bilaterally. Avoid unnecessary amblyopia or stabismus treatment. Although both amblyopia and ONH hypoplasia can present with reduced acuity, strabismus, and variable refractive error--the former remains a diagnosis of exclusion. Conventional amblyopia therapy is incapable of rendering improvement in cases of ONH hypoplasia. Treatment and Management There is no specific treatment for optic nerve hypoplasia. An additional systemic workup is indicated if there is any suspicion of systemic involvement and if presentation is bilateral.
[Return to top] Malinserted/Oblique Inserted Disc and Tilted Optic Disc Syndrome Disc elevation is due to the oblique insertion of the nerve to the globe. Primarily the nasal portion is elevated with the temporal portion depressed and often seen with a scleral crescent. It gives a papilledema appearance because the nasal margins are often blurred and elevated (heaped up). Be sure to look at family members.
Variations of tilts can occur and are very common. There is no optic nerve dysfunction and acuities are normal. Malinserted/oblique-inserted discs are often associated with various degrees of myopia. With obliquely inserted discs, the nerve fiber layer at the superior and inferior aspects of the disc will be without evidence of retinal edema; OCT is normal. In tilted optic disc syndrome, there is a constellation of tilted optic nerve along vertical axis with situs inversus, reduced acuity, and bitemperal visual field defect. (Situs inversus is when temporal branches of the central retinal artery and vein merge more nasally from the disc and course nasally before making a sharp turn temporally.) Eyes are usually mild to moderate myopic and astigmatic with oblique axis. Optic nerve function is typically intact. The disc is small with an oval appearance of tilting along the vertical axis, downward and nasally. Inferior nasal crescent (Fuchs' coloboma) and inferior nasal partial retinal-choroidal (pallor) staphyloma can be present, resulting in a superior temporal visual field defect or most commonly bitemporal hemianopia which does NOT respect the vertical midline (such as seen with a chiasmal lesion). The field defect can be made to improve by testing with the astigmatic correction.
[Return to top] Go to: Dx Dilemma of ON Elevation CE table of contents |
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