2,4 This fact makes SVP an essential component in the evaluation of patients with suspected papilledema secondary to increased intracranial pressure-the documentation of an SVP will often rule out papilledema. This is because there is no longer a pressure gradient to produce the venous pulsation. However, when there is a rise in intracranial CSF pressure such that it equates to the intraocular pulse pressure, the SVP ceases to occur. Typically, the intraocular pressure is greater than the intracranial CSF pressure. 2-4īecause portions of the ON and central retinal vein are exposed to the subarachnoid space before traversing the lamina cribrosa, the pressure difference between the subarachnoid space and intraocular space gives rise to the SVP-in essence, the SVP is a physical manifestation of this pressure difference.
2 These pulsations are synchronized with the patient’s cardiac cycle, with the venous caliber steadily narrowing during systole and expanding with diastole. The phenomenon is defined as rhythmic pulsations occurring in the retinal vein(s) as they cross the optic disc. Optic nerve swelling secondary to increased intracranial pressure with loss of SVP. Finally, it is important to remember that the central retinal vein and artery enter the intraorbital segment of the ON and continue towards the retina.īecause of these anatomic orientations, the ON and central retinal vein are exposed to, and influenced by, changes in intracranial cerebrospinal fluid (CSF) pressure. Furthermore, the subarachnoid space of the brain is contiguous with the subarachnoid space around the ON. With the exception of the intraocular segment, the entirety of the ON is surrounded by the same meningeal layers as the brain-pia, arachnoid and dura. Finally, the intracranial segment (10mm) extends from the optic canal to the optic chiasm. Next is the intracanalicular segment (4mm to 9mm), which travels within the bony optic canal. The ON continues on as the intraorbital segment, which measures 20mm to 30mm and extends from the posterior globe to the orbital apex. The first is the intraocular segment, which measures only 1mm in length and is evident on routine funduscopic examinations at the level of the lamina cribrosa. The ON runs from the retina towards the optic chiasm and is classified into four segments. To understand the clinical and physiologic importance of the SVP, it is important to recall the course of the optic nerve (ON). In such cases, the most helpful element of the examination is the presence or absence of a spontaneous venous pulse (SVP). The presence or absence of distinct disc margins is noted as it is an essential clue in determining the etiology of disc swelling and/or suspected papilledema.įrequently, the optometrist is faced with very subtle findings and is forced to decide whether these represent normal variations or something that warrants an emergent workup and referral. The structure and integrity of the neuroretinal rim must be assessed, as well as the presence of adequate optic nerve perfusion. The evaluation of the optic nerve is an essential part of any ocular health examination.