My cat has blood in his eye - what does it mean?

Cats’ eyes are adapted for hunting and surveying their surroundings. Their eyes, at optimal health, can detect subtle motions, and have much better low-light vision than we as humans do. Our pet cats are also very expressive with their eyes; many owners will have gazed into their cat’s eyes, and noticed the colour of their iris, the sheen of their cornea, and the varying size of pupil as they change from slits to wide saucers. So, it can be concerning to either see blood in your cat’s eye, or have your vet detect blood in their eye. But what does the presence of blood mean for your feline companion?

Anatomy of the Eye

The impact, and potential causes of blood in the eye, depend on the location and the cause. Eyes are often referred to as a globe, although the real shape varies between animal species. Eyes sit within a socket and are protected by the bony margins of the socket, as well as the eyelids and eyelashes. Lining the inside of the eyelids and socket is a soft tissue layer known as the conjunctiva. The lids and lashes are designed to minimise foreign material from getting into the eye, and the third eyelid, which sweeps across from the inner corner, helps spread tears across the eye surface. Tears protect the eye through lubrication, nourish the cornea with fluid, electrolytes and proteins, and contain infection-fighting proteins.

The globe of the eye is made up of various structures, which from front to back are: cornea, anterior chamber, iris and pupil, lens, posterior chamber, retina, and optic nerve. A series of muscles attach to the sclera, the white outer surface of the globe, to allow for movement. The front of the globe can be viewed just by looking at your pet. The structures behind the pupil require instruments, such as an ophthalmoscope, to examine.

Your vet will typically use an ophthalmoscope to assess all of the visible structures, as this instrument can highlight and magnify the different layers. The eye muscles, eye socket, and most of the sclera and conjunctiva are unable to be seen with an ophthalmoscope as these are hidden.

Function of the Eye Structures

The cornea is the clear outer surface of the fore-eye

It is made up of layers of cells and collagen. When healthy, it should appear completely clear and see-through, as well as have a shine to it due to the tear film. Its role is to focus light entering the eye, as well as protect the structures further back. Damage to this layer causes colour changes, or opaque areas which are less see-through or dull in appearance. This can alter the ability of the cornea to focus light, creating blurred vision or blind spots. Penetration of an object through this layer compromises the health and function of those structures behind it.

The anterior chamber of the eye sits in front of the iris and behind the cornea

It is filled with a liquid called aqueous humor. This liquid is produced in the posterior chamber and moves through the pupil into the anterior chamber where it drains. Normal aqueous humor movement and drainage provides a stable pressure within the eye (intraocular pressure, IOP). Healthy aqueous is see-through, allowing light to pass through. Disease or damage here can affect the IOP, risking painful glaucoma (optic nerve damage, usually from high IOP). Glaucoma can occur without an obvious visual change to the aqueous. If the aqueous becomes discoloured, or has a density change, then vision can be affected.

The iris is the coloured portion of the eye with a central slit, the pupil

The iris responds to light sensation by tightening or relaxing muscles which alter the size of the pupil. Cat’s pupils change from narrow slits to wide saucers very quickly, and you may notice this rapid change during playtime as your cat focuses on an object before pouncing. Irises are usually (but not exclusively), the same colour in both eyes, although they may change colour with age. Disease or damage to the iris impacts a cat’s ability to control the level of light entering the back of the eye which can lead to dazzling or UV damage to the retina.

Immediately behind the pupil is the lens

The lens is suspended by muscular fibres which pull or relax to change the thickness of the lens. This focuses the image onto the retina, accounting for distance of the object in sight. A healthy lens is see-through. Damage or disease here can impact the ability to focus, creating blurred vision. Opaque areas create blind spots.

The posterior chamber is mostly filled with vitreous humor

This gel-like substance that provides structure to the eye, maintaining the globe’s shape. Like the aqueous, it should be see-through to allow the passage of light. Disease or damage here, can lead to altered eye shape, glaucoma, or visual issues.

The retina constitutes the back surface of the inside of the eye

It contains layers of cells called photoreceptors, which detect the light. Associated with these receptor cells are nerve fibres which come together at the optic nerve to transmit the light stimulation to the brain for interpretation. Cats also have a reflective layer called the tapetum, and this is what gives the shine when a car’s headlights, or a torch, catch a cat’s eyes in the dark. Damage to these structures will cause complete or partial blindness.

Causes of Bleeding in the Eye

Blood in the anterior chamber is called hyphaema. As blood is heavier than the fluid of the aqueous humor, it will usually gravitate toward the bottom half of the chamber. This can make smaller quantities harder to spot, whereas larger quantities will be more obvious. Bleeding behind the lens generally won’t be visible to an owner. Your vet may detect bleeding here during a routine check-up, or during an eye assessment when other issues have been noted, or if vision is suspected to be impaired.

Trauma

One of the most common causes of bleeding within one or more parts of the eye, is trauma. Both indoor and outdoor cats can get up to mischief, but outdoor-going cats are especially at risk due to fighting, running through vegetation, hunting-related injuries, or being hit by a car. Sometimes, the cause of bleeding will be very obvious, such as when there are other wounds or injuries, or if an incident is witnessed. Other times, your cat may just come home with unexplained bleeding.

The cornea does not have its own blood supply. So, bleeding in this layer cannot occur. Watery or gelatinous blood that appears on the cornea will likely be external (mixed in with tears), or internal (within the aqueous). If the cornea is scratched or ulcerated, very fine, thread-like blood vessels grow across the cornea from the sclera. This is called neovascularisation, and it takes several days after injury to be seen. Larger areas of neovascularisation can be obvious at a glance, whereas smaller areas require the light or magnification of an ophthalmoscope to spot.

Traumatic hyphaema usually stems from the iris, or the lens attachments behind the iris. Both blunt-force trauma and penetrating objects can cause bleeding in this region. Bleeding in the back of the eye is less common, but blunt force trauma to the eye or eye socket can cause bleeding here. Bleeding in this region can migrate to the anterior chamber to contribute to hyphaema.

Unlike in our own eyes, very little of a cat’s sclera is visible. Although people occasionally see burst blood vessels in their own sclera, it is unlikely you would spot these in your cat’s eye without lifting the upper eyelid. As most cats won’t tolerate their owner doing this, bleeding in this region could easily be missed.

Disease

Inflammation of the iris and its connective tissues (uveitis) is the most common non-traumatic cause of hyphaema. Uveitis can itself result from trauma but is often associated with infectious diseases. Viral infections that cause uveitis include Feline Leukaemia Virus (FeLV), Feline Immunodeficiency Virus (FIV), and Feline Infectious Peritonitis (FIP) which is a complication of the Feline Coronavirus (FCoV). Parasites such as toxoplasmosis, and some fungal infections can also cause uveitis.

In older cats, high blood pressure (hypertension) can cause the fine blood vessels within the retina to burst. Hypertension can occur on its own or be associated with kidney disease, diabetes, or an overactive thyroid gland (hyperthyroidism). Your vet may spot small bleeds within the retina during examination. If this rupture is sudden or severe, it can cause the retina to peel off, rendering the cat suddenly blind. This same bleeding may seep into the humor within the eye chambers.

Other disease processes which can occasionally cause bleeding within the eye include anaemia (low red blood cell numbers), blood clotting disorders and tumours of the eye structures. Anaemia and blood clotting problems will usually have other more-obvious signs, such as low energy, pale gums, or bruising of the skin and gums. Hunting cats that might be exposed to rat baits are at risk of poison-induced bleeding problems. Tumours of the eye structures are uncommon but can be difficult to detect if they are behind the iris.

Management of Blood in the Eye

Wounds around the eye, as well as scratches on the cornea, can be very painful. If you see blood on, or within the eye, it is important to visit your vet clinic as soon as possible. If your pet’s eye or eyelids are painful, they risk rubbing it and making it worse. Also, infections within or around the eye tissues can delay healing or risk scarring, both of which compromise long-term vision. Your vet may put a dye (fluorescein) into your cat’s eye to help assess if the cornea has been compromised.

If severe hyphaema is present, it may be difficult to assess the back half of the eye if the blood is blocking the view through the pupil. Large volumes of hyphaema may also trigger glaucoma. Aside from using an ophthalmoscope to visually assess the eye, your vet may check for glaucoma using a device called a tonometer. This measures the pressure inside the eye (the intraocular pressure or IOP).

Some eye assessments could require a referral to a specialist or advanced practitioner eye vet (a veterinary ophthalmologist) or veterinary hospital. An ultrasound or CT scan may be necessary to visualise those parts of the eye that can’t usually be seen. This is especially the case if abscesses, foreign objects, or tumours are suspected behind the iris or the globe. A CT scan is also useful if the bony socket is suspected to have been broken.

Systemic diseases such as viruses and organ dysfunction will usually have other symptoms of ill-health in conjunction with eye bleeding. If your vet suspects a non-traumatic cause of bleeding, they will likely recommend tests to help diagnose the cause. This could include blood and urine tests to screen for kidney disease, diabetes and anaemia. Blood pressure may need to be measured, especially in senior cats. If your cat is a known hunter, a blood clotting panel may be warranted. Fighting cats may need to be screened for FeLV and FIV, both of which can be transmitted through bites.

Treatments

The immediate focus of treatment is to stop further bleeding, control pain, and protect vision. Once a cause and severity have been assessed, your vet will advise how this is best achieved for your cat’s specific circumstances. Some traumatic causes of bleeding will self-resolve once the initial bleeding has stopped. In many cases, some form of intervention will be needed, at least initially. Treatment can include topical eye medications, oral medications, and surgical intervention.

Topical medications are applied directly to the eye

They are typically liquids or gels and usually contain antibiotics, anti-inflammatories, lubricants or combinations of these. Eye drops are also available to manage glaucoma, provide local anaesthesia, or dilate the pupil if needed. Sometimes, for corneal injuries, your vet may recommend drawing blood from your cat to use either the whole blood or extracted serum as an eye drop. This is because the cornea doesn’t have a blood supply and can be slow to heal; the plasma drops help stop bacteria from digesting the delicate corneal tissues.

Oral medication for eye injuries will usually be pain killers

Many traumatic eye injuries are painful, as is glaucoma. Oral medication may also be needed to treat underlying diseases that have contributed to non-traumatic bleeds. Some of these may be temporary, such as treating rat bait toxicity or anaemia, or they can be lifelong if there is an organ dysfunction, hormonal imbalance, or high blood pressure. Your vet can advise how best to give this kind of medication to your cat if needed, or if there are alternatives to oral options.

Surgery may be necessary in some cases

This might be if there is corneal penetration, uncontrolled pain, or tumours. Corneal and iris tears may require stitching. Glaucoma can be a very painful condition, and if the symptoms cannot be improved, removal of the eye may be necessary as a form of pain control. Some eye tumours may be able to be cut out, or the eye may need to be sacrificed to remove the tumour. Whenever surgery within an eye is performed, there is the potential for some further bleeding into the eye immediately after.

Prognosis

In the majority of cases of bleeding, the problem will resolve or improve. Vision will return to normal as long as all structures regain their function and lose any opacity. Early intervention gives the best chance of success. Where a part of the eye loses its function, your vet can discuss the potential implications of this for your cat. This may be a small blind spot, or blurred vision, or it could be partial or total blindness.

It is important though to get regular eye check-ups to ensure any known problem is not getting worse. It is also important to follow-up with monitoring checks for those cats with systemic disease. These checks and repeat blood tests ensure that the prescribed medication is doing what it needs to. If you are ever struggling to medicate your cat, it is also essential to advise your veterinary team so that they can talk you through tips and tricks, or alternative options.

Conclusion

Bleeding in your cat’s eye can be a confronting and concerning thing to find and it is important to seek veterinary attention whenever this occurs. Trauma or underlying disease are the usual causes. It may take several tests to get to the bottom of the problem, or the cause may be immediately obvious. Your vet will aim to ensure that your cat’s pain is under control, as well as target additional health needs through further investigations and treatments. Many cases will improve with support and time, but your vet will advise if there could be residual vision impairment.

My cat has blood in his eye – what does it mean?