General anesthesia, a temporary state of unconsciousness induced for medical procedures, requires careful management of the patient’s entire system, including vision. Although the eye is rarely the focus of non-ophthalmic surgery, the anesthetic process and surgical environment can unexpectedly affect eyesight. Vision changes range from common, temporary irritations to extremely rare but severe, permanent vision loss. Understanding these mechanisms helps explain the precautions taken during any procedure.
Common Temporary Ocular Side Effects
The most frequent complication involving the eyes after general anesthesia is a corneal abrasion—a scratch on the clear outer layer of the eye. This injury occurs because the eye’s protective reflexes are suppressed during anesthesia. Approximately 60% of patients do not fully close their eyes naturally while anesthetized, a condition called lagophthalmos, which exposes the cornea.
This exposure is compounded by a significant decrease in tear production, leading to corneal drying. The dry cornea can be injured by minor mechanical trauma from surgical drapes, face masks, or when the eyelid tears the epithelium upon awakening. Although abrasions occur in a small percentage of cases, they are typically painful, causing a foreign body sensation, light sensitivity, and temporary blurring.
Other temporary effects include mild conjunctivitis (redness or irritation) or a temporary droopy eyelid (ptosis) due to nerve pressure. Temporary ocular side effects like abrasions heal completely within a few days without long-term effects on vision. Specialized ointments or eye drops used during recovery may also cause temporary irritation or blurring.
Anesthesia’s Impact on Ocular Blood Flow
A rare complication involves the blood supply to the optic nerve, leading to Postoperative Visual Loss (POVL). The most frequent cause of POVL is Ischemic Optic Neuropathy (ION), which results from insufficient blood flow and oxygen delivery to the optic nerve. The optic nerve connects the eye to the brain, and its blood supply is sensitive to changes in circulation.
General anesthesia often causes a drop in systemic blood pressure, which the anesthesia team manages carefully. However, a prolonged or severe decrease in blood pressure, known as relative hypotension, can reduce perfusion pressure to the optic nerve head. This reduced flow can cause an infarction, or tissue death, in the nerve. Vision loss from ION is typically painless and can be unilateral or bilateral, presenting as decreased visual acuity or visual field defects.
Types of Ischemic Optic Neuropathy
The specific type of ION depends on the damage location: anterior ION affects the front part of the nerve, while posterior ION affects the deeper, retrobulbar portion. This ischemic event is often linked to periods of significant blood loss requiring large volumes of intravenous fluids. Maintaining adequate blood pressure and oxygenation is essential in preventing this type of damage.
Surgical and Patient Risk Factors
The risk of Ischemic Optic Neuropathy is concentrated in certain operations and patient groups. Procedures involving significant blood loss, prolonged surgery times, and specific patient positioning carry the highest risk. Spinal fusion surgery, particularly when performed in the prone (face-down) position, is frequently associated with POVL.
Prolonged cardiac surgery, especially those involving cardiopulmonary bypass, and radical neck dissections also present elevated risk. The duration of anesthesia is a factor, with operating times of nearly seven hours noted in some ION cases. Improper head positioning in the prone position can cause pressure on the eyeball, leading to Central Retinal Artery Occlusion, which blocks the main artery supplying the retina.
Patient health factors also increase susceptibility to ION. Pre-existing conditions that compromise the vascular system, such as severe anemia, high blood pressure, and diabetes, increase the risk. Patients who are obese or have pre-existing glaucoma may also be vulnerable. These conditions make the small blood vessels supplying the optic nerve less resilient to temporary circulatory changes induced by anesthesia.
Protective Measures in the Operating Room
Surgical teams employ specific protocols to prevent ocular damage. To prevent corneal abrasions and dryness, the most common strategy involves applying lubricating gel or ointment to the eyes. The eyelids are then secured shut using hypoallergenic tape immediately after anesthesia induction. Taping the eyes prevents lagophthalmos, ensuring the cornea remains moist and protected from mechanical contact.
For patients requiring the prone position, specialized headrests, cushions, or goggles are used to ensure no direct pressure is placed on the eyes. Preventing external pressure on the globe is a direct measure against Central Retinal Artery Occlusion and helps avoid increased intraocular pressure.
The anesthesia team continuously monitors the patient’s systemic stability to mitigate the risk of Ischemic Optic Neuropathy (ION). This monitoring includes maintaining blood pressure within a carefully controlled range to ensure adequate perfusion of the optic nerve. They also manage the patient’s fluid balance and monitor oxygen saturation levels throughout the procedure. These systemic measures, combined with physical eye protection, safeguard the patient’s eyesight during unconsciousness.