Brain tumors can sometimes affect vision and the eyes. Depending on the location and size of the tumor, it may compress or damage parts of the brain and cranial nerves that are critical for vision and eye movement. Some of the most common visual symptoms associated with brain tumors include blurry vision, double vision (diplopia), visual field deficits, and vision loss.
The brain is responsible for processing visual information and controlling eye movement and coordination. The eyes themselves do not contain brain tissue, but they are connected to the brain via the optic nerve and cranial nerves that control eye muscles. Because of these connections, brain tumors can sometimes impact vision and ocular health. Not all brain tumors affect the eyes, but some do depending on their location in the brain. Some of the key ways that brain tumors may affect vision and the eyes include:
- Compressing the optic nerves or visual pathway
- Damaging parts of the brain involved in visual processing
- Compressing cranial nerves that control eye muscles and movement
- Increasing intracranial pressure, which can affect the optic nerve
- Causing secondary effects like hormone deficiencies that impact vision
The specific visual symptoms experienced can help identify the location of the tumor and which pathways or nerves are being impacted. Some brain tumor-related visual disturbances are treatable with medications or surgery, while others may be permanent.
How Do Brain Tumors Impact Vision?
Brain tumors can impair vision in several ways, depending on where they are located in the brain and what structures they compress.
Some key ways brain tumors may affect eyesight include:
Compression of the Optic Nerve or Optic Chiasm
The optic nerve carries visual information from the retina to the brain’s visual cortex where it is processed into the images we see. The optic chiasm is the X-shaped structure where the optic nerves from each eye cross. Tumors near the base of the brain, such as pituitary tumors, craniopharyngiomas, and meningiomas, may compress the optic chiasm or optic nerve pathways. This can cause vision loss, starting with peripheral vision loss that can advance to complete blindness if untreated.
Damage to the Occipital Lobe or Visual Cortex
The occipital lobe located at the back of the brain contains the visual cortex which processes visual stimuli. Tumors in this area, such as occipital lobe metastases, can cause visual hallucinations, visual field deficits, or even blindness in severe cases.
Compression of Cranial Nerves III, IV, or VI
Cranial nerves control eye muscles and movement. The oculomotor nerve (CN III) controls most eye muscles, the trochlear nerve (CN IV) controls the superior oblique muscle, and the abducens nerve (CN VI) controls the lateral rectus muscle. Brainstem tumors like pontine gliomas can compress these nerves and cause double vision, blurred vision, drooping eyelids (ptosis), and abnormal eye movements.
Increased Intracranial Pressure
Brain tumors can obstruct cerebrospinal fluid flow and cause a dangerous buildup of intracranial pressure (ICP). High ICP can damage the optic nerve head, causing vision loss and symptoms like blurry vision or eye pain with movement. Papilledema, or optic disc swelling, is a key sign of increased ICP.
Hormone Deficiencies
Pituitary tumors near the hypothalamus/pituitary region can impact hormone levels. Since thyroid hormone and cortisol influence optic nerve health and eye muscles, deficiencies in these hormones may contribute to vision changes like blurred or double vision.
What Visual Symptoms Can Brain Tumors Cause?
Some of the most common visual symptoms linked to brain tumors include:
Blurred Vision
Both eyes typically experience blurred vision. It may be intermittent at first and worsen over time as the tumor grows.
Double Vision (Diplopia)
Seeing two overlapping images instead of a single image. This results from impairment of cranial nerves controlling eye muscle coordination. The double vision may be constant or intermittent.
Visual Field Deficits
A loss of peripheral vision or blank spots in the visual field. These “blind spots” result from damage to the optic nerves or visual cortex.
Decreased Visual Acuity
A worsening sharpness of vision. Visual acuity is tested using a Snellen eye chart. Brain tumors can gradually reduce acuity.
Vision Loss
Complete loss of sight in one or both eyes. This severe symptom typically occurs with optic nerve damage. Vision loss may be rapid or gradual.
Photophobia
Increased light sensitivity, causing discomfort/pain when exposed to light. This results from optic nerve inflammation.
Eye or Eyelid Drooping (Ptosis)
A drooping upper eyelid due to nerve compression or muscle impairment. Ptosis makes it difficult to open the eyelids fully.
Papilledema
Swelling of the optic nerve head due to increased intracranial pressure. Papilledema produces eye pain, blurry vision, and visual field deficits.
Nystagmus
Involuntary, rapid eye movements that oscillate back and forth or up and down. Nystagmus is caused by dysfunction of the brain’s vestibular system or cerebellum.
Ocular Misalignment
The eyes do not track or focus properly on images due to cranial nerve deficits, causing diplopia.
Pupillary Abnormalities
Unequal pupil sizes (anisocoria) or sluggish/absent pupil light reflexes signal cranial nerve compression.
Visual Hallucinations
Seeing shapes, flashes of light, or vivid scenes that aren’t real, from tumor-related damage to the visual cortex.
Which Brain Tumors Commonly Cause Visual Symptoms?
The location of a brain tumor significantly influences whether vision problems develop. Some of the most common types of brain tumors that impair vision include:
Pituitary Adenomas
Benign tumors of the pituitary gland near the optic chiasm often cause bitemporal hemianopsia visual field deficits as they grow. They may also compress cranial nerves. Other pituitary dysfunction symptoms are common.
Craniopharyngiomas
These benign suprasellar tumors near the optic chiasm compress the visual pathways, causing severe visual loss in over half of cases. They predominantly occur in children.
Optic Nerve Gliomas
These rare, slow-growing tumors arise from the optic nerve itself. Vision loss is common, but occurs gradually over time. They are most prevalent in young children with neurofibromatosis type 1.
Meningiomas
Benign tumors developing from the meninges (membranes covering the brain) may compress the optic nerve or invade the orbit. Vision loss, proptosis, and optic disc swelling can result.
Glioblastomas
Highly aggressive malignant brain tumors that most often arise in the temporal and parietal lobes. They can expand rapidly to affect vision.
Medulloblastomas
Common pediatric malignant brain tumors that originate in the cerebellum. They may obstruct cerebrospinal fluid and cause increased intracranial pressure.
Brain Metastases
Secondary brain tumors spread from cancers like lung, breast, skin (melanoma), kidney, colon and others. If occurring in the occipital lobe, severe visual deficits may rapidly develop.
How Are Brain Tumor-Related Vision Problems Diagnosed?
A neuro-ophthalmological exam is key for diagnosing vision issues linked to a suspected brain tumor. Diagnostic approaches may include:
- Visual acuity testing – Using a Snellen chart to check sharpness of vision in each eye
- Refraction exam – To test prescription correction
- Pupillary reflex tests
- Ocular motility exam – Checking eye muscle function
- Slit lamp exam – Inspecting the front of the eye
- Dilated eye exam – Examining the back of the eye including the retina and optic nerve head
- Visual field testing – Mapping out any blind spots or vision loss areas
- Neuroimaging – CT, MRI, fMRI scans to view the tumor and affected brain regions
The pattern of visual deficits can help locate a tumor and determine whether it is affecting the optic pathways, cranial nerves, or visual cortex. Prompt diagnosis is essential for optimal treatment outcomes.
Can Vision Loss from Brain Tumors Be Treated or Corrected?
In some cases, vision changes related to brain tumors may be reversed or improved with appropriate treatment:
- Medications like corticosteroids help reduce inflammation and edema that can impair optic nerves and surrounding structures.
- Surgery to remove a tumor compressing the visual pathways may significantly recover visual function if performed early before permanent optic nerve damage occurs.
- Radiation targeting tumors can stop further visual loss in cases of inoperable tumors like optic nerve gliomas.
- Chemotherapy may similarly slow visual deterioration with some tumor types when combined with radiation.
- Treating hormone deficiencies from pituitary and hypothalamic tumors can alleviate some visual disturbances.
- Prism lenses can aid with double vision by keeping the eyes aligned and fused.
However, complete vision restoration is not always possible if a tumor has extensively damaged the visual pathways or cortex. In these severe cases, vision aids, occupational therapy, or vision rehabilitation may help maximize remaining vision.
Can a Brain Tumor Itself Be Seen in the Eyes?
A brain tumor located in the brain cannot be directly observed in the eyes. However, sometimes secondary effects of brain tumors can be visible in the eyes upon clinical examination by an ophthalmologist or optometrist. Signs of a possible brain tumor that may be detectable in the eyes include:
- Papilledema – Optic disc swelling due to increased intracranial pressure from a tumor.
- Optic nerve atrophy – Pallor and cupping of the optic nerve head signaling compressed blood supply.
- Retinal hemorrhages – Leaking blood vessels in the retina related to high pressure.
- Abnormal dilated pupil exam – Showing nerve compression through pupil asymmetry, poor response, or abnormal retinal findings.
Though not a view of the actual tumor, these eye exam findings provide important clues signaling that a brain tumor may be present and necessitating neuroimaging to locate it. The ophthalmologist works closely with the neurologist and oncologist in diagnosing the cause based on the full picture of eye and neurological symptoms.
Conclusion
While the eyes themselves do not contain brain matter, they have direct connections to the brain through the optic nerves and cranial nerves controlling eye muscles. Due to these pathways, brain tumors in certain locations can significantly impact vision and ocular health. Compression of visual pathways or cranial nerves is the primary mechanism, but increased intracranial pressure and hormonal changes also play a role.
Symptoms like blurred vision, double vision, partial vision loss, and eye movement problems should prompt an urgent medical evaluation. While some vision damage may be permanent if a tumor is not treated quickly, other visual symptoms can improve with medications, surgery, and other therapies targeting the tumor itself. Ophthalmologists and neuro-ophthalmologists can diagnose vision-related brain tumors based on a detailed eye exam combined with neuroimaging. If vision loss is caught early, the outlook for maintaining functional vision is much better. Increased awareness of the diverse vision and eye disturbances brain tumors can cause leads to faster diagnosis and treatment to preserve sight.