Does a cat's diet really have an impact on its eye health? Ask the expert!

Q: “I have noticed off-the-shelf cat food touting ingredients that promote eye health. Does a cat’s diet really have an impact on its eye health? If so, what are the key nutrients that they require for optimal eye health, how do they impact the cat’s vision, and what are good sources of these nutrients?”
By Pets Team
Published on Monday, 23 March 2020

A:  Cats need several different kinds of nutrients to survive: amino acids from protein, fatty acids and carbohydrates, vitamins, minerals and water. Like most carnivorous animals, cats can obtain most of their protein from meat, fish and other animal products. Some animal-based protein is easier to digest than plant-based protein and is better suited to the cat’s digestive system.  Dietary protein contains 10 specific amino acids that neither cats nor dogs can make on their own. Known as essential amino acids, they provide the building blocks for many important biologically-active compounds and proteins. In addition, they provide the carbon chains needed to make glucose for energy. High-quality proteins have a good balance of all of the essential amino acids.

Taurine Top Up
Taurine (an amino acid) is especially important for cats. Taurine is an essential amino acid (a building block of proteins) that must be supplied in their diet because cats cannot manufacture it themselves. Found abundantly in many fish, birds, small rodents, and most red/white meats, taurine is either absent or present only in trace amounts in plants. Strict vegetarian diets are not appropriate for cats unless supplemented with nutrients essential for cats that are not found in plants. 

Taurine deficiency in cats causes several metabolic and clinical problems, including a potential risk of total blindness (a condition called FCRD — feline central retinal degeneration). It also causes dilated cardiomyopathy in cats, a disease of heart muscle conducing to heart failure. The two conditions can occur alone or together in any individual cat. Taurine retinopathy, also called FCRD, is deterioration and “death” of the retina that is caused by a deficiency of taurine in the diet of cats.  

Within 10 weeks of eating a diet low in taurine, the cone photoreceptors of the retina begin to deteriorate. The cones are responsible for bright-light and colour vision. Within 20 weeks, many of the cones are “dead”. If taurine remains deficient, eventually the rod photoreceptors (responsible for dim-light vision) are also affected. Taurine affects both eyes in a symmetrical fashion, and the end result is complete blindness. Taurine deficiency in cats causes can also cause deafness, cardiomyopathy inadequate immune response, poor neonatal growth, reproductive failure and congenital defects.  

Since the discovery in 1987 that taurine deficiency can cause dilated cardiomyopathy, commercial cat foods have been manufactured with a higher content of taurine. For reasons yet to be fully understood, wet cat food requires twice the level of taurine supplementation of dry food, to allow the cat to absorb adequate levels of the nutrient. Taurine retinopathy may occur in cats that eat predominantly dog food or leftovers alone, because taurine is not supplemented in canine diets. Dogs can make taurine themselves from other dietary components. Taurine retinopathy is also sometimes found in cats that have been strays and in those exposed to poor-quality food. Cats that consistently eat a well-balanced commercial food rarely develop the disease.

Good fats
Fats (and oils) are composed of fatty acids, sometimes referred to as “vitamin F.” Linoleic (LA) and arachidonic acids have long been considered to be EFAs essential fatty acids for cats. More recently, docosahexaenoic acid (DHA) has been added due to its important contribution to feline vision, reproductive health and the immune system. Eicosapentaenoic acid (EPA) may also be of benefit. EFAs must be obtained from food sources. Unlike some animals, felines don’t efficiently convert plant sources of EFAs to the needed derivatives. For example, cats must eat meat to obtain arachidonic acid. Also, they don’t convert LA to gammalinolenic acid GLA (as some animals do), and studies show that GLA can benefit the health of feline skin and coat.  

Cats cannot synthesise some vitamins from precursors (pre-vitamin structures) in the diet. Cats are a bit different from other animals in that their ability to convert betacarotene to vitamin A is extremely limited. Because of this, cats must get all of the vitamin A and niacin they need directly from the food they eat. 

Deficiencies in vitamin A can adversely affect the health of the eyes, and adult cats deprived of niacin in their diet will lose weight and may even die because of it. The diets fed to many cats — especially canned food containing fat-laden fish products — make them more susceptible to deficiencies of certain vitamins, such as vitamin E. Vitamin E, an antioxidant, provides protection against oxidative damage. Some vitamins are not only essential in small doses, but are also toxic in excess amounts. Too much vitamin A — a natural consequence of feeding large amounts of liver to growing kittens — can cause hypervitaminosis A, a condition characterised by a variety of skeletal lesions.  

Basically my recommendations are that you make sure your feed your cat an adequate diet for his age, preferably from a reputable brand, as these are surely nicely- balanced, fully-supplemented diets. This way, you avoid spending more money and using extras supplements to complete cats diets.  

These Premium foods are grain-free and will always list a source of animal protein origin as the first ingredient. Never purchase a cat food that is made with corn, wheat or soy ingredients, or one that uses artificial additives like colours, flavours and artificial preservatives. Don’t try to compound or do an homemade diet to your cat without supervision of a veterinarian with nutritional know-how. Don’t forget: cats are carnivores (not herbivores or omnivores as we are), so protein should be the main focus of their diet and this needs to come from a premium animal source. 

Rui Rodrigues Oliveira, Veterinary Ophthalmologist, Amber Vet
A veterinary ophthalmologist with international work engagements, Dr Rui Oliveira spends time working extensively in ophthalmology in the United Kingdom, Spain, Portugal, China, Hong Kong, Dubai and Singapore. He attained the Certificate in Veterinary Ophthalmology awarded by the Royal College of Veterinary Surgeons London (RCVS) in 2012.  

Dr Oliveira enjoys treating eye cases in a wide variety of animals, and regularly performs surgery for cataract, glaucoma and conditions of the eyelids, cornea and retina.