Ophthalmologic Complications Related to Cervical Spine Surgery
Geoffrey Kaung
Usha R. Pinninti
Robert A. Hart
Ophthalmologic complications are rare but potentially devastating complications of cervical spine surgery. The reported incidence of these complications varies from 0.028% to 1.0%. Most of what is known on this subject is through retrospective reviews and case reports on spine surgery regardless of anatomic location; much less is known regarding visual complications resulting specifically from cervical spine surgery. There are four major causes of visual impairment in patients undergoing spine surgery: corneal injury, ischemic optic neuropathy (ION), central retinal artery occlusion (CRAO), and cortical blindness. Prone positioning as well as direct pressure on the eye has been shown to compromise vascular supply to the eye. Other associated risk factors include perioperative anemia, hypotension, lengthy operating times, high blood loss, diabetes, and peripheral vascular disease. Visual loss is often permanent, so prevention by maintaining adequate blood pressure to the brain and eye, and avoiding pressure on the eye, is critical.
ANATOMY
VISUAL TRACT
The visual sensory system begins with the cornea and lens focusing light onto the retina in the dorsal segment of the eye (Fig. 119.1). The retina, consisting of seven layers of cells and fibers, lines the interior surface of the eye and converts light into a neural signal. The temporal visual field is perceived by the nasal hemiretina while the nasal visual field falls on the temporal hemiretina. The retinal nerve fiber layer collects into the optic nerve and transmits this visual signal to the occipital cortex (Fig. 119.2).
The optic nerve exits the globe through the lamina cribrosa, travels in the optic canal, and acquires a dural sheath at this location. This allows free circulation of cerebrospinal fluid (CSF) around the optic nerve. The optic canal begins at the apex of the bony orbit, transmits the optic nerve and ophthalmic artery, and lies within the sphenoid bone. The intracranial segments of each optic nerve coalesce into the optic chiasm. Within the chiasm, there is a decussation of the nasal retinal fibers (temporal visual field) from each nerve, which join the uncrossed temporal retinal fibers (nasal visual field) of the other eye and continue on as the optic tracts.
The optic tracts terminate at their respective lateral geniculate bodies. The lateral geniculates, located in the dorsal thalami, group the incoming fibers into layers based on spatial and color perception versus motion detection. After synapsing here, the axons travel dorsally in the brain as optic radiations and terminate in the primary visual cortex in the occipital lobe. The primary visual area (V1, striate cortex, Brodmann area 17) sits along the horizontal calcarine fissure, which divides the medial surface of the occipital lobe.
VASCULAR SUPPLY
The main blood supply to the occipital lobes is through the middle and posterior cerebral arteries. The intrac-ranial optic nerves and the chiasm are supplied by small branches of the proximal anterior cerebral artery and anterior communicating artery.
Upon emerging from the cavernous sinus, the internal carotid artery gives off the ophthalmic artery (Fig. 119.3), which then enters the orbit through the optic canal. The ophthalmic artery then gives off the central retinal artery approximately 10 mm dorsal to the globe. Thus, most of the blood supply to the optic nerve comes from the ophthalmic artery via pial branches of the surrounding arachnoid. The central retinal artery and vein travel within the ventral 10 mm of the optic nerve and enter the eye.
The central retinal artery is responsible for supplying the ventral two-thirds of the retina. The terminal ophthalmic artery gives additional branches that form the posterior ciliary arteries, supplying the dorsal third of the retina, choroid, and optic disk. In approximately 30% of individuals, the posterior ciliary arteries also supply a portion of the inner retina as the cilioretinal arteries. These individuals can retain their macular and central vision despite a CRAO.
INCIDENCE
The true incidence of ophthalmologic complications in spine surgery is difficult to estimate but ranges from 0.028% to 1.0% in published reports (Table 119.1).
Patients undergoing deformity surgery and posterior lumbar fusions appear to be at greater risk; by contrast, ventral lumbar fusions and cervical fusions have a lower reported incidence of ophthalmologic complications (8). Despite the low incidence, the frequency of these complications has been increasing. This may reflect an increasing number of adult spinal deformity surgeries performed, as well as an increase in the number of longer procedures overall.
Patients undergoing deformity surgery and posterior lumbar fusions appear to be at greater risk; by contrast, ventral lumbar fusions and cervical fusions have a lower reported incidence of ophthalmologic complications (8). Despite the low incidence, the frequency of these complications has been increasing. This may reflect an increasing number of adult spinal deformity surgeries performed, as well as an increase in the number of longer procedures overall.
 Figure 119.1. Local anatomy of the globe. Ref. (1). (Martini FH. Fundamentals of anatomy and physiology, 3rd ed. Upper Saddle River: Prentice Hall, 1995:564.) |
 Figure 119.2. Anatomy of the visual pathway. Ref. (2). (Zide BM, Luce C, Jelks GW. Surgical anatomy of the orbit. New York: Raven Press, 1995.) |
 Figure 119.3. Vascular supply to the eye. Ref. (2). From Lobato EB, Gravenstein N, Kirby RR, Complications in Anesthesiology 4th ed. Philadelphia: Lippincott Williams& Wilkins, 2007 with permission. |
Most published reports have been retrospective in nature, originating from review of cases from referral centers or previously published data, or from surveys of spine surgeons. Many of these studies lack data on sample size and hence do not allow an estimate of the incidence of ophthalmologic complications. To date, no studies have focused solely on complications resulting from cervical spine surgery.
Chang and Miller (3) reviewed 20 years of data from the Johns Hopkins Hospital and found four cases of posterior ischemic optic neuropathy (PION) following spine surgery in 14,102 patients, with a resulting incidence of 0.028%. Three of the four cases were performed in the prone position, with the remaining case being performed in the lateral decubitus position. All four deficits were unilateral.
Stevens et al. (10) reviewed a series of 3,450 spinal procedures performed at three separate institutions and found seven patients with new-onset loss of visual acuity (0.20%). There were four cases of ION, two cases of
cortical blindness, and one case of central retinal vein occlusion (CRVO). The only cervical level case involved a 57-year-old patient with ankylosing spondylitis and a chinon-chest deformity who underwent a dorsal osteotomy at C7. His etiology was cortical blindness that improved with emergent hyperbaric oxygen therapy.
cortical blindness, and one case of central retinal vein occlusion (CRVO). The only cervical level case involved a 57-year-old patient with ankylosing spondylitis and a chinon-chest deformity who underwent a dorsal osteotomy at C7. His etiology was cortical blindness that improved with emergent hyperbaric oxygen therapy.
TABLE 119.1 Incidence of Ophthalmologic Comp lications in Spine Surgery 1 | |||||||||||||||||||||||||||||||||||||||||||||
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