Complete hemianopia is a type of vision loss where a person cannot see the entire half of their visual world. This condition is caused by damage to the brain’s visual processing centers or the pathways carrying visual information, not by a problem with the eyes themselves. The term “hemianopia” literally means “half-blindness,” resulting in a complete loss of visual perception on either the left or the right side of a person’s visual field.
Defining Complete Hemianopia
The visual field represents the entire area a person can see when their eyes are fixed. For a person with complete hemianopia, the total loss of vision affects half of this field, extending from the center point all the way to the periphery. This means half of the surrounding environment effectively disappears from view.
The most common form is homonymous hemianopia, where the vision loss occurs on the same side in both eyes. For example, losing the entire right side of vision in both eyes creates a large blind area, forcing the person to constantly turn their head to perceive that half of space.
The “complete” aspect differentiates this condition from partial hemianopia, where some vision remains, or from quadrantanopia, which involves only one-quarter of the visual field. Complete hemianopia involves a total absence of visual information, resulting in a sharply defined boundary between the seeing and blind sides.
Causes and Visual Pathway Damage
Complete hemianopia is a consequence of damage to the retrochiasmal visual pathway, which handles visual signals after the optic nerves cross at the optic chiasm. The most frequent cause of this damage in adults is a stroke, accounting for up to 89% of cases, involving either an ischemic blockage or a hemorrhagic bleed. Brain tumors, traumatic brain injuries (TBI), and neurosurgical procedures are common causes that disrupt the visual fibers.
Visual information travels from the eyes along the optic tracts, through the lateral geniculate nucleus, and into the optic radiations before reaching the visual cortex in the occipital lobe. Damage to any of these structures after the optic chiasm results in vision loss on the side opposite the brain injury. For instance, an injury to the right side of the brain leads to a loss of the left visual field in both eyes.
A complete hemianopia can result from a large lesion anywhere along this pathway. Lesions in the optic tract or the optic radiations frequently result in this total loss of the corresponding half-field. The occipital lobe, which houses the visual cortex, is a common site of injury.
Diagnosis and Functional Limitations
The standard method for diagnosing complete hemianopia is formal perimetry, also known as a visual field test, which precisely maps the extent and shape of the vision loss. This assessment uses specialized instruments, such as the Humphrey automated visual field analyzer, to present lights while the patient maintains a fixed gaze. The results confirm a defect that respects the vertical midline.
This loss creates significant functional limitations, especially concerning navigation and reading. Patients often bump into objects, trip, or startle easily because they are unaware of obstacles or people approaching from the blind side. This reduced spatial awareness can be compounded by visual neglect, where the brain fails to acknowledge the entire side of space.
Reading ability is particularly affected, with the specific side of the loss dictating the challenge. Individuals with a right hemianopia struggle because they lose sight of the next word in a sentence, making it difficult to continue reading smoothly. Those with a left hemianopia often have trouble locating the beginning of the next line of text, leading to constant re-reading or skipping of lines. The inability to safely drive is another major restriction, as the loss of peripheral vision compromises the ability to detect hazards.
Management and Compensatory Techniques
Management for permanent complete hemianopia focuses on teaching the patient to compensate for the lost visual field through visual rehabilitation therapy. The goal of this rehabilitation is not to restore vision but to help the person use their remaining sight more efficiently. Compensatory scanning training is a primary treatment that teaches the patient to make systematic, wide eye and head movements into the blind field.
This training improves the accuracy and speed of eye movements, called saccades, allowing the person to consciously explore the blind side of their environment. By actively scanning, the patient can bring objects from the blind field into their seeing field, improving navigation and hazard detection. Occupational therapy helps patients adapt their environment and daily routines to maximize safety and independence.
Optical aids, such as prism lenses, may be used to shift the visual image from the blind field into the seeing field. These specialized glasses are designed to expand the functional visual area and are often applied to the lens on the side of the vision loss. While prisms can help with mobility, they require an adjustment period and rely on the patient’s brain to interpret the shifted image.