The cornea makes up the anterior most portion of the sclera. The sclera is a fibrous outer layer that provides both protection and rigidity to maintain the shape of the eye. The cornea is a transparent structure that permits light to pass into the internal ocular structures before forming a retinal image.
The cornea is densely innervated by the ophthalmic division (V1) of the trigeminal nerve (CN V) via the long and short ciliary nerves. Research suggests that the cornea’s dense sensory innveration is 300-600 times that of the skin, making injury to the cornea excruciatingly painful (Table 95-1).
TABLE 95-1Corneal Pathology and Systemic Disease |Favorite Table|Download (.pdf) TABLE 95-1 Corneal Pathology and Systemic Disease
|Metabolic Disease ||Connective Tissue Disease |
|Carbohydrate metabolism disorders ||Ankylosing spondylosis |
|Chronic renal failure ||Scleroderma |
|Cystinosis ||Sjögren syndrome |
|Gout ||Wegener granulomatosis |
|Graves’ disease ||Inflammatory Disease |
|Wilson disease ||Behçet syndrome |
|Skin Disorders ||Reiter syndrome |
|Erythema multiforme ||Rheumatoid arthritis |
|Pemphigus ||Sarcoidosis |
Corneal abrasion is the most common ocular complication of general anesthesia. Symptoms include foreign body sensation, pain, tearing, and photophobia. The pain is exacerbated by blinking and ocular movement. Iatrogenic mechanisms of injury include damage caused by anesthetic masks, surgical drapes, intravenous line tubing, stethoscopes, hospital identification cards, and watch bands. Ocular injury may also occur due to loss of pain sensation or decreased tear production. Chemical injury from antiseptic solutions has also been implicated in corneal abrasion due to de-epithelialization (Table 95-2).
TABLE 95-2Corneal Abrasions Due to Antiseptic Solutions |Favorite Table|Download (.pdf) TABLE 95-2 Corneal Abrasions Due to Antiseptic Solutions
|Povidone-iodine containing alcohols |
The incidence of abrasion varies between 0.03% and 0.17%, depending on the method of reporting. Prolonged surgery, lateral or prone positioning during surgery and operations on the head and neck are the main risk factors. They are most commonly caused by exposure keratopathy, chemical injury, and direct trauma.
General anesthesia reduces the tonic contraction of the orbicularis oculi muscle, which causes lagophthalmos (the inability to close eyelids completely) in a majority of patients. If the eyes are not fully closed, exposure keratopathy may occur in 27%-44% of patients. Anesthesia also inhibits the protective mechanism afforded by Bell’s phenomenon (in which the eyeball turns upward during sleep, hence protecting the cornea). This combination of effects may lead to corneal epithelial drying and loss of protection.
Common practice for injury prevention involves taping the eyelids closed after induction and during mask ventilation and laryngoscopy. Some providers apply protective goggles and/or instill lubricant to the conjuctiva. Several disadvantages of ointments include possible allergy, inflammation, and blurry vision postoperatively. ...