Cancer and Your Vision

How Cancer Affects the Different Areas of the Eye

While many people associate the word 'melanoma' or 'carcinoma' strictly with the skin, the delicate machinery of the human eye is equally susceptible to malignant growths. Ocular oncology – the specialized branch of medicine dedicated to eye tumours – is a highly nuanced field. Because the eye is comprised of distinct layers, tissues, and fluid chambers, cancer affects different areas of the eye in fundamentally unique ways.\

Primary eye cancer (cancer that starts in the eye) is quite rare, with around 880 cases diagnosed in the UK each year. However, secondary eye cancer – where malignancies spread, or metastasise, from other organs like the breasts or lungs – is more common.

To understand how cancer behaves in this part of the body, it is easiest to break the eye down into three distinct structural zones: the inside of the eyeball, the surface of the eye, and the surrounding structures.

1. Intraocular Cancers: Inside the Eyeball

Intraocular cancers develop deep within the globe of the eye itself. Because these tumours grow out of sight, they are often first spotted during routine visits to an optician (optometrist) rather than by the patient.

The Uveal Tract (The Middle Layer)

The uvea is the vascular, pigmented middle layer of the eye. It is divided into three parts, all of which contain melanin-producing cells (melanocytes) that can mutate into uveal melanoma, the most common primary eye cancer in adults.

• The Iris: This is the coloured part of the eye. Melanomas here usually present as a growing dark spot. Fortunately, iris melanomas are often caught early because they are visible in the mirror, and they tend to grow slowly.
  

• The Ciliary Body: Located just behind the iris, this ring of muscle alters the shape of your lens and produces the fluid inside your eye. Tumours here can grow quite large before causing symptoms, often pushing against the lens to cause blurred vision.
  

• The Choroid: Lining the back of the eye between the retina and the white of the eye (sclera), the choroid is the most common site for uveal melanomas. A choroidal melanoma can cause shadows, flashes of light, floaters, or a painless loss of peripheral vision as it grows and lifts the retina.
  

The Retina (The Back of the Eye)

The retina is the light-sensitive "film" at the back of the eye that translates images to the brain.

• Retinoblastoma: This is the most common primary intraocular cancer in children, usually affecting infants and children under the age of five. It occurs when nerve cells in the retina mutate. A signature warning sign is leukocoria: a white reflection or "glow" in the pupil when a flash photograph is taken, rather than the standard "red-eye" effect.
  

• Primary Intraocular Lymphoma (PIOL): A very rare cancer involving the white blood cells (lymphocytes). It typically affects the retina and the vitreous humour (the jelly-like fluid filling the eye). It is unique because it is heavily linked with lymphoma of the central nervous system and often affects both eyes.
  

2. Conjunctival Cancers: The Ocular Surface

The surface of the eye is protected by a thin, clear membrane called the conjunctiva, which covers the white portion of the eye (bulbar conjunctiva) and lines the inside of the eyelids (palpebral conjunctiva). Cancers here are highly exposed to environmental factors, particularly ultraviolet (UV) radiation from sunlight or sunbeds.

• Squamous Cell Carcinoma (SCC) of the Conjunctiva: This is the most frequent malignancy on the eye's surface. It often appears as a painless, fleshy, white, or pinkish growth, sometimes accompanied by chronic redness or a persistent feeling that something is stuck in the eye. While it can aggressively invade surrounding local tissues, it has a low risk of spreading to distant organs.
  

• Conjunctival Melanoma: Distinct from intraocular melanoma, this arises from the surface tissue. It often develops from pre-existing flat, brown patches on the eye (known as primary acquired melanosis). Unlike SCC, conjunctival melanoma carries a much higher risk of spreading to the local lymph nodes and other parts of the body.
  

3. Adnexal and Orbital Cancers: Surrounding Structures

Cancer can also strike the complex structural scaffolding that supports, moves, and protects the eyeball. These are broadly categorized as adnexal (eyelid and tear duct) or orbital (eye socket) tumours.

The Eyelids

Eyelid tumours are essentially skin cancers, heavily linked to sun exposure.

• Basal Cell Carcinoma (BCC): Accounting for upwards of 90% of eyelid malignancies, BCCs most frequently appear on the lower eyelid. They often look like a firm, pearly nodule with a small crater or ulcer in the middle. They grow slowly and rarely spread elsewhere, but if left untreated, they can cause extensive damage to the local eye structure.
  

• Sebaceous Gland Carcinoma: A rare but aggressive cancer originating in the oil-secreting glands of the eyelids (Meibomian glands). It is notoriously difficult to diagnose because it masquerades perfectly as a harmless chalazion (a stye-like lump) or chronic blepharitis (inflamed eyelids), leading to dangerous treatment delays.
  

The Orbit (The Eye Socket)

The orbit is the bony cavity containing the eyeball, muscles, fat, nerves, and blood vessels.

• Orbital Lymphoma: The most common primary malignancy of the adult orbit. As the tumour expands within the tight confines of the socket, it causes a characteristic forward bulging of the eye (proptosis or exophthalmos), alongside swelling and double vision.
  

• Rhabdomyosarcoma: A rapid-growing, malignant tumour of the soft tissues or muscles that move the eye. While exceptionally rare, it is the most common primary orbital malignancy in children and requires urgent intervention.
  

Summarising the Impact by Location

The clinical presentation, prognosis, and treatment path depend entirely on the specific geography of the tumour:

Area of the Eye	Common Malignancies	Key Potential Symptoms	Primary Treatment Approaches
Inside the Globe (Intraocular)	Uveal Melanoma, Retinoblastoma, Lymphoma	Flashes, floaters, shadows, white pupil reflex (children), painless vision loss	Radiotherapy (plaques or external beam), proton beam therapy, transpupillary thermotherapy, enucleation (removal of the eye)
Eye Surface (Conjunctival)	Squamous Cell Carcinoma, Conjunctival Melanoma	Fleshy growth, chronic red eye, localized irritation	Surgical excision with cryotherapy (freezing the edges), topical chemotherapy drops
Surrounding Tissues (Adnexal/Orbital)	Basal Cell Carcinoma, Sebaceous Carcinoma, Orbital Lymphoma	Eyelid lumps that bleed or ulcerate, bulging eye, double vision, dropping eyelid	Surgical removal (Mohs micrographic surgery for eyelids), external radiotherapy, systemic chemotherapy

When to Seek Medical Advice

Because many forms of eye cancer develop without causing any pain, regular eye examinations with an optician are vital; they possess the specialized equipment (like ophthalmoscopes and slit lamps) to view the interior structures clearly.

You should always book an appointment with a GP or optician if you notice any persistent changes, including:

• Shadows, flashes of light, or sudden "wiggly lines" in your field of vision.

• A dark patch on your iris or the white of your eye that appears to be growing.

• Blurred or double vision, or a partial loss of sight in one eye.

• A physical bulge in one of your eyes.

• A lump or ulcer on your eyelid that doesn't heal within a few weeks.