The eye is constantly producing energy and using oxygen. In addition, its light-sensitive cells contain fats that can be easily damaged by unstable molecules called free radicals. This means the retina needs strong antioxidant protection to help limit any damage.
Of course, nutrition can't prevent every eye condition. Genetics, ageing, injury and underlying disease all play a role. But there are certain nutrients involved in maintaining the structure and normal function of the eye, and we can ensure we are offering them in our dog’s diet or in supplement form.
Here are some we like to think about.
Vitamin C
Vitamin C is an antioxidant and is involved in collagen synthesis. Collagen provides structural support throughout the body, including within the tissues surrounding the eye.
Vitamin C is also found within ocular fluids, where it forms part of the eye's antioxidant defence system.
Unlike humans, dogs can produce vitamin C themselves in their liver, but in times of high need, or when the liver has been under a lot of burden, but we can also find it in foods such as leafy greens, parsley, peppers and berries.
What about supplementation?
If we want to provide additional vitamin C, we can also supplement liposomal vitamin C. Liposomal vitamin C is encapsulated within tiny lipid structures, which may improve absorption compared with some standard oral forms. Rather than relying on one large dose, we prefer to provide smaller amounts throughout the day.
Vitamin E
The light-sensitive cells in the retina contain lots of DHA, an omega-3 fatty acid that helps them work properly. However, DHA is also particularly vulnerable to damage.
Vitamin E helps protect these fats from damage. When one fat molecule becomes damaged, it can trigger damage to others around it. Vitamin E helps stop this chain reaction from spreading, protecting the cells in the eye.
Food sources of vitamin E include eggs, seeds and certain plant oils.
What about supplementation?
Vitamin E can also be supplemented, particularly when we're increasing omega-3 intake.
If choosing a supplement, look for natural vitamin E, usually listed as d-alpha-tocopherol, rather than the synthetic form, dl-alpha-tocopherol. Mixed tocopherols can also be a useful option as they provide a broader range of vitamin E compounds.
Vitamin E supplementation should be considered alongside the dog's overall diet and particularly their intake of polyunsaturated fats.
Zinc
Zinc is involved in many processes throughout the body and is found in high concentrations within the eye, particularly the retina.
It also helps the body use vitamin A, which is needed to make the pigments that allow the eye to respond to light. This makes zinc particularly important for normal vision, including seeing in low-light conditions.
Food sources of zinc for dogs include beef, lamb and seafood.
What about supplementation?
Zinc can be supplemented, but this is another nutrient where we need to look at the whole diet first.
The amount of zinc a dog absorbs isn't simply determined by how much zinc is in their food. Other nutrients can influence its absorption, and diets containing high levels of calcium, iron or certain plant compounds such as phytates may reduce zinc availability.
If the diet is low in zinc, a well-absorbed form such as zinc citrate or a chelated zinc can be considered.
Again, more isn't always better. We'd use it where the diet suggests additional zinc is actually needed.
Lutein and Zeaxanthin
Lutein and zeaxanthin are carotenoids, the naturally occurring pigments responsible for some of the yellow, orange and green colours we see in plants.
They've received a lot of attention in human eye research because they accumulate within retinal tissue, where they can absorb certain wavelengths of light and contribute to antioxidant defence.
We need to be careful translating human research directly to dogs, particularly research looking at age-related macular degeneration as dogs don't have the same retinal anatomy as humans. However, carotenoids are still interesting from a canine nutrition perspective, and lutein has been studied in dogs in relation to antioxidant and immune function.
Food sources of lutein and zeaxanthin include spinach, kale, carrots, kiwi, orange/yellow peppers, corn, broccoli and peas.
But most interestingly, studies show the lutein in egg yolks is absorbed better by the body compared to other food sources or supplements.
Omega-3 Fatty Acids
DHA is an omega-3 fatty acid found in high amounts in the brain and retina. It forms an important part of the light-sensitive cells in the eye and helps them work properly. DHA is particularly important during early development, when the brain and eyes are growing rapidly. Dogs can make some DHA from the plant-based omega-3 ALA, but they aren't very efficient at doing this. Providing EPA and DHA directly from marine foods is therefore a better option.
Oily fish such as sardines, mackerel, herring and salmon are good sources.
What about krill oil?
If we're looking at supplementation, we like krill oil.
Krill provides EPA and DHA alongside astaxanthin, a naturally occurring antioxidant that gives krill its red-orange colour.
When choosing a marine oil, check how much EPA and DHA it actually provides rather than simply looking at the total amount of oil. Quality is important too. Look for good sourcing and testing for contaminants and oxidation, and always store the oil correctly.
Can Nutrition Support Healthy Tears?
Tears aren't simply water. They also contain mucus, which helps tears spread across the eye, and fats that help stop them evaporating too quickly.
So, can nutrition help support healthy tears?
It sure can.
Vitamin A
Vitamin A helps keep the surface of the eye healthy. It also supports the cells that produce mucus, helping tears spread across and stay on the eye.
Omega-3 Fatty Acids
EPA and DHA may also help support a healthy tear film.
Small glands along the eyelids produce the oily part of tears, which helps stop them evaporating too quickly. Omega-3 fatty acids may help support these glands as well as a healthy inflammatory response.
There is some research looking at omega-3 supplementation alongside conventional treatment for dry eye in dogs, although the evidence is still limited.
Zinc
Zinc works closely with vitamin A and helps maintain the healthy tissues around the surface of the eye. This doesn't mean that adding extra zinc will make your dog produce more tears but we do want to make sure the diet provides enough zinc to support normal eye health.
The eyes are highly active organs and need a good supply of nutrients to maintain their structure and normal function.
Vitamin C, vitamin E, zinc, lutein, zeaxanthin and omega-3 fatty acids all support eye health in different ways. Some help protect the delicate tissues of the eye from damage, while others support the retina, cell membranes and normal visual function. These nutrients also work together, which is why we always want to consider the whole diet.
Nutrition can support healthy tears too. Vitamin A helps maintain the surface of the eye and normal mucus production, while EPA and DHA support the oily layer of the tear film, helping to prevent tears from evaporating too quickly. Zinc also supports vitamin A metabolism and healthy eye tissue.
Fresh foods such as oily fish, eggs, liver, meat, seafood and a variety of fruits and vegetables may provide these nutrients. Where additional support is needed, supplements may be considered under the guidance of a practitioner.
Lisa Hannaby-Aird
A Registered Associate Nutritionist and author of Nutrition for Dogs, Lisa combines expertise in nutrition, psychology, biochemistry, and neuroscience to help dog owners understand the science behind canine health, behaviour, and nutrition.