Fig. 3.1
Schematic for mechanisms of visual loss from orbital cellulitis in relation to an illustration of the visual pathways. (1) Angle closure glaucoma. External photograph showing conjunctival injection and corneal edema from acute angle closure glaucoma. (2) Serous retinal detachment. Optical coherence tomography showing elevation of the retina with hypointensity consistent with subretinal fluid. (3) Retinal vein occlusion. Fundus photograph of the left eye showing multiple retinal hemorrhages and optic disc edema from a central retinal vein occlusion. (4) Retinal artery occlusion. Fundus photograph of the left eye showing cotton wool spots with retinal whitening from an inferior branch retinal artery occlusion. (5) Venous sinus thrombosis. Coronal image from magnetic resonance venography showing an occluded right transverse sinus (white arrow) compared to the normally filled left side. (6) Compressive optic neuropathy/orbital apex syndrome. Magnetic resonance imaging with contrast, axial T1-weighted image, showing an inflammatory mass involving the left orbital apex and compressing the left optic nerve. (7) Ischemic optic neuropathy. Fundus photograph of the left eye showing hyperemic optic disc edema from anterior ischemic optic neuropathy. (8) Inflammatory optic neuropathy. Magnetic resonance imaging with contrast, coronal T1-weighted image, showing enhancement of the left intraorbital optic nerve from inflammation. (9) Papilledema. Fundus photographs showing optic disc edema with hemorrhages and cotton wool spots in each eye. (10) Compressive optic neuropathy. Computed tomography, axial view, showing hyperdensity in the right ethmoid paranasal sinus from a mucocele, resulting in compression of the right globe and optic nerve. (11) Stroke. Magnetic resonance imaging, axial diffusion-weighted sequence, showing hyperintensity within the occipital lobes on each side consistent with acute stroke. (12) Infiltration. Magnetic resonance imaging with contrast, axial T1-weighted image, showing enhancement in a ring pattern from an intracranial abscess
Table 3.1
Summary of most commonly cited mechanisms of visual loss based on anatomic site of involvement in patients with orbital cellulitis
Most commonly noted disease processes | |||||
|---|---|---|---|---|---|
Anatomic location of visual impairment | Compression | Inflammation | Infiltration | Vasculitis/thrombosis | |
Anterior segment | Proptosis causing exposure keratopathy | Ciliary body rotation causing angle closure glaucoma | – | – | |
Retina | CRAO, CRVO combined retinal artery and vein occlusion | CRAO, CRVO, exudative retinal detachment, endophthalmitis | CRAO, CRVO | CRAO, CRVO | |
Choroid | – | Choroidal effusion and angle closure glaucoma | – | Choroidal infarction | |
Optic nerve | Ischemic optic neuropathy, direct compression from abscess or mucocele formation, stretch optic neuropathy | Ischemic optic neuropathy, optic neuritis | Ischemic optic neuropathy, direct infiltration of optic nerve (particularly with fungal involvement) | Cavernous sinus thrombosis-related papilledema, ischemic optic neuropathy | |
Optic chiasm/tract | Compression from abscess formation | – | Fungal invasion | – | |
Cerebral cortex | – | – | Fungal invasion | Stroke from cerebral venous sinus thrombosis | |
Anterior Segment
Involvement of the anterior segment is typically readily apparent. Proptosis from the underlying orbitopathy may cause exposure keratopathy and, in more severe cases, corneal ulceration [1]. Anterior extension from posterior involvement in endophthalmitis rarely may involve the ciliary body and anterior segment. Orbital cellulitis is also a rare cause of choroidal effusion [2], which may cause anterior rotation of the ciliary body and subsequent forward lens displacement, resulting in acute angle closure glaucoma. This has been reported in a case series of three patients with idiopathic orbital inflammation (orbital pseudotumor) [3], and a similar presentation may be possible in patients with orbital cellulitis.
Retinopathy and Choroidopathy
Retinovascular occlusion has been noted in isolation or combined with optic neuropathy in relation to orbital infection. Retinal artery occlusion appears to be the most common form of retinovascular occlusion related to orbital cellulitis. Occlusion commonly results from compression of the central retinal artery due to increased orbital pressure. Four reported cases of central retinal artery occlusion (CRAO) in the setting of orbital cellulitis noted rapidly increasing intraocular pressure (IOP) prior to the onset of CRAO and in the absence of any sign of coagulopathy [4–6]. However, this does not mean that all cases of CRAO in orbital cellulitis are due to compression of the central retinal artery. Retinal artery occlusion may also occur from thrombosis. At least two cases have been reported in pregnant women with CRAO in the setting of orbital cellulitis with normal or mildly elevated IOP. The CRAO in these patients was more suggestive of a thrombotic etiology, especially considering the hypercoagulable state in pregnancy [7, 8]. Direct infiltration or inflammation (vasculitis) of the central retinal artery could also lead to CRAO, although pathologic confirmation is lacking for this mechanism. Retinal vein occlusion may likewise occur secondary to compressive, thrombotic, infiltrative, or inflammatory processes [9]. Central retinal vein occlusion (CRVO) attributed to cavernous sinus thrombosis has also been described [10] and may be possible in the setting of orbital cellulitis.
In addition to retinovascular occlusion, exudative retinal detachment secondary to orbital cellulitis may also result in visual loss. Three cases have been reported of retinal detachment in the setting of orbital cellulitis, all of which had recovery of vision following successful treatment of the orbital infection [11–13]. The mechanism by which exudative retinal detachment occurs in orbital cellulitis is not known. One possibility is that orbital cellulitis results in septicemia, which is known to cause exudative retinal detachment [14]. Whatever the cause of the retinal detachment, this is likely a rare cause of vision loss in orbital cellulitis. Orbital inflammation involving the sclera may result in exudative detachment of the choroid, and scleral abscess formation, in the setting of orbital cellulitis following ocular trauma, with vision loss has also been reported [15].
Much like the exudative retinal detachments in orbital cellulitis, a case report of choroidal detachment and associated vision loss also showed resolution of visual symptoms following successful treatment of the infection [11]. Another reported cause of visual loss due to choroidal involvement includes choroidal infarction, which has been described in combination with retinal infarction [16].
Endophthalmitis can be a devastating complication of orbital infection and is covered thoroughly in Chap. 15.
Optic Neuropathy
Papilledema Related to Cerebral Venous Sinus Thrombosis and Meningitis
Perhaps one of the most dreaded complications of orbital cellulitis is cavernous sinus thrombosis (CST) . The inferior and superior ophthalmic veins drain directly into the cavernous sinus, and infiltration of these routes by infectious organisms or propagation of clot from inflammation may lead to CST. In addition, the valveless pterygoid plexus of veins, angular veins, and nasofrontal veins connect directly to the ophthalmic veins. Infection can then spread to the cavernous sinus from the paranasal sinuses and nasofrontal region, which are often the sources of infection leading to orbital cellulitis. Vision loss may result from subsequent central retinal vein occlusion (see section on retinopathy), papilledema, optic neuritis, or ischemia to a variety of structures due to compression of the carotid artery. It can also lead to stroke or meningitis (discussed below). In part because of the extensive interconnections between the two cavernous sinuses, thrombosis on one side may affect the contralateral eye, a hallmark of CST [17]. Involvement of the intracranial cerebral venous sinus system may also result in elevated intracranial pressure.
A hallmark of papilledema in most patients is the relative parallel between the level of visual dysfunction and the optic disc appearance, and visual acuity loss is generally a sign of severe or prolonged papilledema. The mechanism of visual loss from papilledema is thought to be due to mechanical effects of elevated intracranial pressure followed by ischemia of the optic nerve head due to compression of its blood supply secondary to axoplasmic flow stasis [18]. Blood flow to the optic nerve head is highly sensitive to changes in pressure. Elevated intracranial pressure is transmitted through the optic nerve sheath and disrupts the normal gradient between the intraocular pressure and intracranial pressure. An increase in the retrolaminar pressure may cause stasis of axoplasmic flow as the nerve fibers course through the lamina cribrosa. The stasis results in a further increase in pressure and possibly intra-axonal edema. The increase in pressure may eventually occlude branches of the short posterior arteries supplying the nerve fibers resulting in ischemia [18].
Similarly, involvement of the meninges from posterior spread of an orbital infection may impair cerebrospinal fluid resorption resulting in elevated intracranial pressure and papilledema. Intracranial complications related to orbital cellulitis are discussed more thoroughly in Chap. 14.
Ischemic Optic Neuropathy
The optic nerve may be categorized into anterior and posterior segments based on the differences in their blood supplies. The anterior portion of the optic nerve, including the optic disc, is supplied by the short posterior ciliary arteries arising from the ophthalmic artery. The posterior portion of the optic nerve receives its blood supply from the pial plexus, which arises from the ophthalmic and internal carotid arteries [19]. Inflammation, infiltration, or compression of the posterior ciliary arteries or pial plexus in the setting of orbital cellulitis may cause an anterior or posterior ischemic optic neuropathy, respectively. Though such occlusion would be difficult to show in vivo, imaging studies may show findings suggestive of ischemia. In one reported case of a patient with invasive fungal orbital cellulitis, diffusion-weighted sequences of magnetic resonance imaging (MRI) with contrast showed hyperintensity of the optic nerve of the affected eye, suggestive of ischemia [20]. Follow-up MRI, several weeks later after the infection resolved, showed improvement in the optic nerve hyperintensity consistent with resolution of the ischemia. Although such imaging may demonstrate optic nerve ischemia, it cannot differentiate between inflammation, infiltration, or compression as the underlying cause. In another case of orbital cellulitis and visual loss from 1945 [21], postmortem biopsy revealed severe thromboangiitis of the optic nerve vasculature and significant optic nerve necrosis [22, 23]. These pathologic findings provide some of the best evidence for an inflammatory etiology of ischemic optic neuropathy in orbital cellulitis, though they are not likely to be confirmed because improvements in therapy generally have limited mortality.
Inflammatory Optic Neuropathy
Optic neuritis, or inflammation of the optic nerve, is typically associated with multiple sclerosis, neuromyelitis optica, and other related autoimmune disorders, where it is a sterile inflammatory process. In addition to these autoimmune disorders, several systemic infections are known to cause optic neuropathy. Such parainfectious optic neuropathies may develop secondary to infection with Bartonella henselae, Mycobacterium tuberculosis, Brucella species, Borrelia burgdorferi, Treponema pallidum, Cryptococcus neoformans, and human immunodeficiency virus (HIV) [24]. Although these infectious causes occur more commonly in the absence of orbital involvement, optic neuropathy following orbital cellulitis with Streptococcus pyogenes has been described [25]. In this report, MRI showed optic nerve enhancement consistent with optic neuritis without evidence of central retinal artery occlusion, central retinal vein occlusion, cavernous sinus thrombosis, or compressive optic neuropathy. In the setting of orbital cellulitis, the physiologic inflammation present to combat infection may spread to the optic nerve due to its close proximity and cause an inflammatory optic neuropathy [26–28]. Involvement of the more posterior (ethmoid and sphenoid) paranasal sinuses by infectious organisms has been thought to predispose to an inflammatory optic neuropathy although this has been somewhat controversial [22, 27, 29–31]. One case series of children with CST found that five out of ten patients had concomitant orbital cellulitis [32]. Of these five patients, however, three suffered from visual loss from optic neuritis implied by contrast enhancement of the optic nerve on MRI, without evidence of papilledema or vascular occlusion. This suggests that despite the presence of CST, the underlying cause of vision loss was actually inflammation of the optic nerve.
Infiltration
Direct infiltration of the optic nerve may also cause visual loss. Invasive infectious disease is most common with fungal infection such as that due to aspergillosis and mucormycosis. Infection may spread intracranially from the optic nerve and may also result in an abscess at any point along its path (see sections on optic tract and cerebral involvement), and this has been histopathologically confirmed. A patient with rhinocerebral mucormycosis showed gross ulceration and pathologic confirmation of direct invasion of the optic nerve [33]. The patient was immunosuppressed following liver transplantation and chemotherapy. Immunosuppression from HIV or uncontrolled diabetes is a common feature of patients with these types of infections [34].
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