An 8-year-old Hispanic female presented for an ocular evaluation following referral from her pediatrician. Her pediatrician noted a difference between her right and left eyes while performing direct ophthalmoscopy on routine physical examination.
The patient was in excellent health and reported no problems with her vision. Her parents also confirmed that she had no difficulties with her vision.
On examination, her entering visual acuity measured 20/20 O.U. at distance and near. Extraocular motility testing was normal. Confrontation visual fields were full to careful finger counting O.U. Her pupils were equally round and reactive to light, with no afferent pupillary defect (APD). Her anterior segment examination was unremarkable.
1,2. Posterior pole images of our patients eyes (O.D. left, O.S. right). Note the asymmetry between the right and left optic nerves.
Dilated fundus exam of each eye demonstrated evident findings (figures 1-3). The macula and periphery appeared normal O.U.
3. A 2x magnified view of our patients left eye.
Take the Retina Quiz
1. What clinical finding would be most helpful in determining the severity of this condition?
a. Normal color vision testing.
b. The presence or absence of headaches.
c. The presence of a spontaneous venous pulse (SVP).
d. The absence of an APD.
2. What additional ancillary testing would be most useful to help confirm the diagnosis?
a. Threshold visual field testing.
b. Optical coherence tomography (OCT).
c. B-scan ultrasound.
d. No further testing is indicated.
3. What is the diagnosis?
a. Optic nerve hypoplasia.
b. Papillitis.
c. Optic neuritis.
d. Pseudo-disc edema.
4. What is the appropriate management?
a. Magnetic resonance imaging (MRI).
b. Referral for neurologic exam.
c. Threshold visual field testing.
d. Reassure and monitor.
For answers, see below.
Discussion
Our patient presented with a very dramatic and striking asymmetry between her right and left optic nerve. Normally, a healthy patients optic nerves will appear as mirror images of each other. In this case, our patients right eye demonstrated a moderate-sized cup that appears healthy, with good rim coloration and perfusion. However, her left optic nerve appears smaller in diameter than her right optic nerve, and there is no cup. Additionally, the left disc margins appear elevated, suggesting that the nerve may be swollen.
Does this finding represent true disc swelling? As clinicians, this is one of the most difficult and challenging decisions that we have to make. The typical scenario is that of a patient (often a child) who presents for a routine exam and incidentally is found to have blurred or elevated disc margins. The patient typically will have good corrected acuity without any optic nerve dysfunction or neurological problems. As a clinician, you have to decide if the patient has true optic nerve edema or if it is just pseudoedema.
More often than not, the nerves are simply anomalous, with no true disc edema. But, how do you distinguish between the two possible diagnoses?
One simple way to make this distinction is to determine if the patient has a spontaneous venous pulsation. An SVP is simply a physiologic pulsation of the retinal vein that is seen as the vein exits out of the lamina cribrosa and traverses the optic nerve. There is some debate as to why this occurs. Initial theories suggested that the pulsation occurred because of a rise in IOP secondary to increased pulse pressure.1 However, a more accepted theory is that the pulsations develop as a result of a variation in the pressure gradient between the intraocular space and the cerebrospinal fluid.1 In either case, as both the intracranial pressure and the intracranial pulse pressure rise to equal the intraocular pulse pressure, the spontaneous venous pulsations cease. Thus, the cessation of the spontaneous venous pulsation is indicative of increased intracranial pressure.1
If the patient does have an SVP, he or she has pseudo-disc edema. The SVP can be very subtle, and diagnosis requires an almost static view of the retinal veins as they exit out of the lamina cribosa. Often, patients will not be able to keep their eyes sufficiently steady, which makes it difficult to detect if SVP is present. The absence of an SVP does not necessarily indicate that the patient has disc edema, however. Indeed, 10% of normal patients will not have an SVP.2
In addition to looking for an SVP, there are other clinical features of the optic nerve that can help determine if true disc edema is present. In true disc edema, blurring of the disc margins occurs at the level of the retinal nerve fiber layer (RNFL)not at the retinal pigment epithelium (RPE), as occurs in pseudo-disc edema.2
Because blurring occurs at the level of the RNFL, the retinal vessels often will be obscured as they leave the optic nerve. In contrast, the retinal vessels are not obscured in pseudo-disc edema. Also, there may be a gray or black change around the nerve where the RPE terminates in pseudo-disc edema.
In true disc edema, you will often note hyperemia or a heightened reddish hue in the optic nerve due to congestion of the microvasculature. Also, the small vessels on the optic nerve may be dilated and telangiectatic. In more severe cases, nerve fiber hemorrhages may be present.
Optic nerve drusen or buried drusen is one of the most common causes of pseudopapilledema. Patients with optic nerve drusen often have scalloped or lumpy/ bumpy disc margins. Also, focal disc drusen may be seen along the edges of the nerve.
In younger patients, the drusen tend to be less calcific and may be buried deeper within the nerve, which makes them difficult to see on ophthalmoscopy. This, in turn, makes the diagnosis challenging. With disc drusen, there may be anomalous branching retinal vessels, loops, trifurcations and increased branching of the retinal vessels.
In this case, we performed an ultrasound B-scan and, indeed, optic nerve drusen were present O.D. This finding solidified our diagnosis of pseudo-disc edema. A visual field was performed, which came back normal.
1. Jacks AS, Miller NR. Spontaneous retinal venous pulsation: aetiology and significance. J Neurol Neurosurg Psychiatry 2003 Jan;74(1):7-9. Review.
2. Harder B, Jonas JB. Frequency of spontaneous pulsations of the central retinal vein. Br J Ophthalmol 2007 Mar;91(3): 401-2.
