Vision Changes in Neuroendocrine Tumours

Neuroendocrine tumours (NETs) can cause a wide range of symptoms, often depending on their location and whether they produce excess hormones. 

While most people associate NETs with digestive issues, flushing, or hormonal imbalances, they can also affect vision in several ways. Vision changes in NET patients may result from hormonal fluctuations, metabolic imbalances, nerve involvement, or treatment-related side effects. 

Understanding the link between NETs and vision is essential for early detection and management.

This article explores how NETs impact vision, the mechanisms behind these changes, how they are diagnosed, and potential treatment options for preserving eye health.

Neuroendocrine Cancer Australia (NECA), is dedicated to assisting patients diagnosed with NETs and their loved ones. NECA offers a wealth of resources, educational programs, and advocacy efforts aimed at deepening the understanding of NETs, improving patient care, and encouraging research advancements. Patients can engage with NECA’s comprehensive support and information by calling the NET nurse line.

How NETs can affect vision

The symptoms of NETs aren’t usually limited to the neuroendocrine system. Vision changes in NET patients can arise from a variety of causes, including:

• Direct tumour effects: NETs affecting the brain, nerves, or eye structures.
• Hormonal imbalances: Excess hormone production leading to eye-related symptoms.
• Metabolic issues: Low or high blood sugar levels affecting vision.
• Treatment side effects: Medications, radiation, or surgery causing visual disturbances.

Because NETs can be slow-growing or asymptomatic for years, vision-related symptoms may go unnoticed or be misattributed to aging or unrelated conditions.

Direct vs. indirect causes of vision changes

It’s important to understand the distinction between direct and indirect causes of vision changes, particularly in the diagnosis and treatment phases.

• Direct causes: Tumour growth in or around the eyes, optic nerves, or brain regions involved in vision.
• Indirect causes: Hormonal or metabolic changes, medication effects, or radiation damage leading to vision disturbances.

Early identification of vision problems in NET patients is crucial, as they may signal tumour progression, treatment side effects, or secondary complications requiring intervention.

Hormonal and metabolic causes of vision issues

Functional NETs that produce excess hormones can affect multiple systems, including vision. Common hormone-related vision problems include:

• Blurred vision due to unstable blood glucose levels.
• Light sensitivity caused by excessive serotonin or histamine release.
• Dry eyes linked to hormonal imbalances and a side effect to some treatments, including chemotherapy.

Carcinoid syndrome and related ocular symptoms

Patients with carcinoid syndrome, caused by serotonin-secreting NETs, may experience flushing, watery eyes, light sensitivity, or even blurred vision. In some cases, prolonged exposure to high serotonin levels may contribute to retinal damage.

Impact of insulinomas on blood glucose levels and vision

Insulinomas, a rare type of pancreatic NET, produce excess insulin, leading to recurrent low blood glucose levels (hypoglycaemia). When blood glucose levels drop too low, patients may experience:

• Blurred or double vision.
• Temporary loss of vision field. 
• Dizziness or difficulty focusing.

Since these symptoms can resemble neurological conditions, insulinomas are sometimes misdiagnosed initially.

Von Hippel-Lindau Syndrome and vision loss

Von Hippel-Lindau (VHL) syndrome is a genetic condition linked to NETs and other tumours. VHL patients often develop retinal hemangioblastomas (benign tumours in the retina), which can cause vision loss or blindness if untreated. Regular ophthalmologic exams are essential for early detection.

Neurological effects of NETs on vision

While most NETs originate in the digestive tract or lungs, in rare cases, they can spread to the brain or optic nerve, causing:

• Visual field defects (partial blindness or blind spots).
• Optic nerve swelling (papilledema) leading to vision loss.
• Double vision from cranial nerve involvement.

These symptoms may indicate tumour progression or metastatic disease affecting the nervous system.

Treatment-related vision changes

Several vision changes are possible during the course of treatment for NETs. While these are rare, it’s important to note that every patient’s reaction to treatment will be different.

Side effects of somatostatin analogues (SSAs) on vision

Somatostatin analogues (SSAs) like octreotide and lanreotide are commonly used to manage hormone-producing NETs. Although generally well-tolerated, rare ocular side effects include:

• Dry eyes or irritation
• Mild visual disturbances (blurred vision or floaters)
• Changes in eye pressure

Patients using SSAs should have regular eye exams to monitor for any subtle changes.

Long-term effects of radiation on vision

For patients receiving radiation therapy near the head or neck, possible vision-related side effects include:

• Cataracts from prolonged radiation exposure.
• Optic neuropathy (damage to the optic nerve leading to vision loss).
• Retinal damage or inflammation.

Close monitoring and early intervention can help manage these risks effectively.

Diagnosing vision changes in NETpPatients

NET patients should immediately seek medical attention if they experience:

• Sudden vision loss.
• Persistent blurriness, floaters, or light sensitivity.
• Eye pain, swelling, or double vision.

Early diagnosis can prevent complications and help adjust treatment plans if necessary.

Common diagnostic tools for vision issues can include:

• Ophthalmic exams (to check for retinal damage, pressure changes).
• MRI or CT scans (if neurological involvement is suspected).
• Fluorescein angiography (to assess retinal blood flow in VHL patients).

Decisions around tests and courses of treatment should be made in conference with the patient, their family, and their primary care team.

Managing and treating vision changes

Fortunately, vision changes associated with NETs can be managed and treated. If a NET treatment is causing significant vision problems, oncologists may consider:

• Dose adjustments or switching therapies to minimise side effects.
• Supplementary medications to protect eye health.

Depending on the cause, treatments may include:

• Artificial tears or lubricants (for dry eyes due to SSAs).
• Blood sugar regulation (for insulinoma-induced vision changes).
• Surgical interventions (for VHL-related retinal tumours).

Lifestyle and supportive care for eye health

NET patients can help protect their vision by:

• Scheduling regular eye exams.
• Wearing UV-blocking sunglasses.
• Maintaining a healthy diet rich in omega-3s and antioxidants.

Future research and considerations

Researchers are exploring the molecular pathways linking NET-related hormones to vision problems, as well as potential treatments to prevent ocular damage.

With advances in targeted therapies and precision medicine, future NET treatments may reduce vision-related side effects while maintaining efficacy.

Final thoughts

Vision changes in NET patients can stem from hormonal imbalances, tumour location, metabolic disturbances, or treatment effects. 

While many cases are mild and manageable, some may indicate serious complications requiring immediate medical attention. 

Regular eye exams, early symptom recognition, and coordinated care between oncologists and ophthalmologists are crucial for maintaining long-term vision health in NET patients.

For additional support, patients can reach out to Neuroendocrine Cancer Australia for guidance and resources on managing NET-related vision concerns.