Double vision (diplopia) is the perception of two images from a single object. Although alarming, it is a recognized, though uncommon, neurological complication following major cardiac procedures like coronary artery bypass grafting (CABG) or valve replacement surgery. The visual system is highly sensitive to the physiological stress imposed by the operation. This article explores the underlying mechanisms linking heart surgery to this visual disturbance.
Systemic Causes Related to Blood Flow
Post-surgical visual issues often relate to the body’s response to the extraordinary demands of the operation. Most major heart procedures require the use of a cardiopulmonary bypass (CPB) machine to temporarily take over the function of the heart and lungs. This extracorporeal circulation can lead to periods of reduced blood flow (hypoperfusion) throughout the body, including the delicate blood vessels supplying the eyes and brain.
The transient reduction in blood flow, coupled with significant fluctuations in arterial blood pressure during or immediately after surgery, can cause localized ischemia. Ischemia is a lack of oxygen reaching specific tissues due to insufficient blood supply. The small blood vessels that nourish the optic nerve are particularly susceptible to this low-flow state.
This hypoperfusion can result in Ischemic Optic Neuropathy (ION), a condition where the optic nerve is damaged due to insufficient blood supply. Furthermore, the CPB circuit can release microscopic particles, such as air bubbles or fragmented plaques, into the bloodstream. These microemboli can travel to the brain and eyes, lodging in small arteries and causing blockages in the visual pathways.
Specific Nerve and Brain Injuries
Beyond systemic perfusion issues, double vision can signal a localized injury to the nerves or brain regions controlling eye movement. Single vision coordination is managed by three pairs of muscles in each eye, directed by three cranial nerves: the Oculomotor (CN III), Trochlear (CN IV), and Abducens (CN VI) nerves. These nerves are highly vulnerable to localized damage from ischemia or pressure changes post-operatively.
Damage to any of these motor nerves results in a Cranial Nerve Palsy, which weakens or paralyzes the corresponding eye muscle. This causes the eyes to become misaligned, leading to binocular diplopia. A specific and rare cause is pituitary apoplexy, involving sudden hemorrhage or infarction of the pituitary gland. This swelling can compress the adjacent Oculomotor nerve (CN III), immediately causing double vision and often a drooping eyelid (ptosis).
In severe cases, visual symptoms may manifest as a post-operative stroke, which occurs in a small percentage of patients. A stroke in the brainstem can disrupt the centers coordinating eye movement. Conversely, a stroke in the occipital lobe can affect the visual processing center, potentially leading to cortical blindness. Though rare, these injuries represent a direct structural cause of persistent visual deficits.
Temporary Contributing Factors
Not all causes of post-surgical diplopia relate to a permanent neurological event; many are transient and resolve quickly. The residual effects of general anesthesia and sedatives used for pain management can temporarily slow neurological function, including the precise coordination of eye muscles. These medications can cause transient blurring or unsteadiness that mimics diplopia until the drugs are fully metabolized.
Prolonged positioning during the procedure can also contribute to temporary issues. External pressure on the eye from an unsuitable headrest or surgical mask can momentarily raise intraocular pressure. This leads to a short-term disturbance in blood flow to the retina or optic nerve. Additionally, the use of intravenous fluids during surgery can cause temporary fluid retention and swelling around the eyes (peri-orbital edema), which interferes with normal eye movement until the body clears the excess fluid.
Medical Response and Prognosis
Any new onset of double vision after heart surgery warrants immediate investigation to distinguish between a transient issue and a serious neurological injury. The diagnostic process typically involves a detailed neurological examination and imaging studies, such as a computed tomography (CT) scan or magnetic resonance imaging (MRI) of the brain. These scans quickly rule out a post-operative stroke or hemorrhage requiring urgent intervention.
If symptoms are persistent, an ophthalmology consultation is necessary to assess eye alignment and nerve function. Management often begins with conservative measures, such as eye patching to block the double image or the use of specialized glasses containing prisms. These prisms help fuse the two separate images into one, improving comfort and function.
The prognosis for post-surgical diplopia is generally favorable, especially when the cause is attributed to systemic or temporary factors. Most transient visual disturbances and many mild cranial nerve palsies resolve spontaneously as the patient recovers from the operation’s stress. Complete resolution can occur within a few weeks to several months. However, a small number of patients with damage from a stroke or severe Ischemic Optic Neuropathy may experience permanent visual deficits.