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Editorials: Editorials

Prone to Blindness

Answers to Postoperative Visual Loss

Gayer, Steven MD, MBA

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doi: 10.1213/ANE.0b013e3181fe772d
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The cumulative impact of case reports, editorials, and collated data from the American Society of Anesthesiologists' postoperative visual loss (POVL) registry has heightened awareness of an association between prone-position surgery and the woeful phenomena of ischemic optic neuropathy and central retinal vascular occlusion.14 The American Society of Anesthesiologists has responded by establishing a task force and publishing a practice advisory, both of which have further increased awareness of this issue.5 The incidence of POVL, however, is exceedingly small and far outweighed by other eye pathologies encountered after non-ocular surgery.6 In this issue of Anesthesia & Analgesia, Gayat et al.7 present a case of bilateral acute angle-closure glaucoma in a patient who had undergone spinal surgery, a portion of which was conducted in the prone position. Their report serves as a reminder of other perioperative ocular risks and thus has great value to the journal's readership.

Corneal injuries, secondary to abrasion or exposure, are the most common ocular injuries following non-ophthalmic surgery.8 Loss of protective corneal reflexes and decreased production of tears during general anesthesia predispose patients to this injury.9 Less frequently, subconjunctival hemorrhage and chemical injury are causative. In the majority of such instances, a specific source for the abrasion or conjunctivitis cannot be determined.10

Rare anesthesia-related causes of postoperative visual issues may be encountered in phase I or II recovery areas, or days after surgery. For example, Valsalva retinopathy occurs as a consequence of capillary rupture after precipitous increases in globe venous and intraocular pressure (IOP). Although this may occur spontaneously in healthy individuals, it can arise after coughing and straining upon emergence from anesthesia or after postoperative retching and vomiting. Non-ocular surgery using nitrous oxide, in a patient after recent retinal detachment surgery that involved an injection of intravitreal gas, may increase IOP sufficiently to collapse the central retinal artery.11 This may result in severe, irreversible visual loss. As with ischemic optic neuropathy, central retinal vascular occlusion, pituitary apoplexy, and cortical blindness, pain is rarely a symptom.12

The case by Gayet et al. deals with an episode of angle-closure glaucoma. Glaucoma is a sight-threatening condition typically characterized by increased IOP and/or compromised perfusion of the optic nerve. Terminology can be confusing because glaucoma can be classified in several manners: acquired versus congenital, high IOP versus normal or low pressure, acute versus chronic, and open-angle versus narrow- or closed-angle. Chronic glaucoma, the most common form, manifests as a painless degradation of peripheral vision. Conversely, acute glaucoma, in which there is an abrupt increase in IOP, presents as a painful eye with potentially compromised visual acuity.

The pathophysiology of glaucoma is debated in the ophthalmology literature; it is thought to involve interruption of aqueous humor flow along its route from the ciliary body in the posterior chamber, through the anterior chamber onto the trabecular meshwork and Schlemm's canal, and ultimately exiting to the systemic venous circulation. Impedance of drainage at the trabecular meshwork produces open-angle glaucoma. Narrow-angle glaucoma, however, occurs when the space between the iris and cornea at the circumferential periphery of the anterior segment diminishes. Some individuals have naturally constricted angles. With age comes physical lens thickening that further restricts the area. Dilation of the pupil by sympatholytic or parasympathomimetic agents increases the girth of the iris, further narrowing the angle.13 Angle closure occurs when the peripheral iris moves into direct contact with the corneal surface, mechanically obstructing and physically blocking the natural outflow of aqueous fluid. In predisposed individuals, chronic narrow-angle glaucoma may acutely progress to full angle closure.

The clinical challenge for the anesthesiologist is to discern whether a painful eye after non-ocular surgery is attributable to corneal abrasion or acute angle-closure glaucoma.14 This is vital because the latter may be vision threatening and require urgent intervention. Both are typically detected during phase I recovery or within the first 3 hours after surgery. In this case report, the authors postulate that a delayed diagnosis may have resulted from masking of pain by analgesics.14

Corneal abrasion is often associated with unilateral pain, exacerbated by blinking and eye movement. Most patients complain of a foreign body sensation, blurred vision, tearing, and photophobia. On physical examination, the conjunctiva is hyperemic but pupil size and function are normal. Vision is frequently unaffected except with a central corneal abrasion. Discomfort is relieved by instillation of a few drops of topical local anesthetic. Importantly, the abrasion is often not readily detected by clinical examination unless a surface stain such as fluorescein, not usually part of the anesthesiologist's armamentarium, is used.

Acute angle-closure glaucoma is usually unilateral but may, as in this case, be bilateral. Pain can be intense and conjunctival hyperemia is common. In contrast to corneal abrasions, pupils are mid-to-fully dilated and the patient may complain of severely compromised vision. Also, pain is unaffected by topical local anesthetics, but may be alleviated by miosis-inducing drops. Urgent ophthalmologic consultation is critical for preservation of vision.15

Gayet et al. concluded that ephedrine was the primary factor triggering acute angle closure in a predisposed patient. Nefopam (a centrally acting non-opioid analgesic) may have been contributory as well. The fraction of parenterally administered drugs absorbed by the eye is exceedingly minimal, but case reports and clinical studies raise the awareness of the potential for mydriasis nonetheless.16,17 The effect of gravity in the prone position may also have encouraged forward shift of the lens/iris apparatus, precipitating the angle closure in this at-risk patient with baseline narrow angles.18 The important point for clinical emphasis in the article by Gayet et al. is that all ocular abnormalities associated with prone surgical positioning are not POVL, and an awareness of other conditions, especially when associated with pain and symptoms as described above, is requisite such that prompt and appropriate intervention is instituted.

REFERENCES

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AUTHOR CONTRIBUTIONS

Steven Gayer helped write the manuscript and approved the final manuscript.

© 2011 International Anesthesia Research Society