Cataracts

Can we prevent, or at least delay the onset and slow the progression of, age-related cataracts in our animals?

a. Diabetic cataract in a 12-year-old Springer Spaniel. [Pupil partially dilated.]

b. Inherited cataract in a 6-year-old Labrador Retriever. This particular type is called a posterior polar subcapsular cataract. [Pupil widely dilated.]

c. Corticosteroid-induced cataract in a 7-year-old crossbred dog on oral prednisolone for 2 years. [Pupil widely dilated.]

d. Diabetic cataract in a 13-year-old domestic short-haired cat. [Pupil widely dilated.]

e. Mature cataract in a 22-year-old Thoroughbred horse. [Pupil, a horizontal rectangle in horses, not dilated.]

f. Post-traumatic cataract in a 4-year-old American scrub jay. [Pupil widely dilated.]

In this study, the age at which 50% of the group showed signs of cataract (C50) was about 2 years earlier in the NZ dogs:

* NZ — 7.5 years of age

* UK — 9.4 years of age

Statistically, this difference was highly significant (P = 0.005).

The age at which all dogs in the group had signs of cataract was also 2 years earlier in the NZ dogs:

* NZ — 11.5 years of age

* UK — 13.5 years of age

So, the greater UV light exposure in the dogs living in the southern hemisphere brought forward the age at which cataracts begin to develop by around 2 years.

limiting UV exposure

These studies suggest that we find ways to limit UV exposure in our animals, particularly when sunlight is strongest or brightest (middle of the day), and especially in environments where reflective UV exposure is greatest (e.g., sand, water, glass, metallic surfaces).

There are now various styles of sunglasses for dogs that have UV-blocking lenses similar to those worn by people. Here's an example:

Alternatively, you could keep the dog indoors or at least in the shade during the middle of the day.

“Doggles” (dog goggles) or similar are great for when you're taking your dog somewhere in the car. Not only do they limit both direct and reflected UV radiation, they provide the eyes with wind protection in dogs who love to hang their heads out the window.

Similar riffs on human sunglasses are now available for horses, although the typical mesh fly mask or fly veil does the job well enough in most locations.

If heat is an additional concern, then confining horses indoors during the day (under fans) and turning them out at night can work well for protection from both UV radiation and excessive heat.

. . .

Diet

Degradation of the crystalline proteins that give the lens its structure and its transparency is primarily caused by oxidation. Like rust, oxidative damage in the tissues of the body can take months or years to become obvious.

Oxidation is basically the chemical process by which electrons are lost to another atom or molecule. Its opposite is reduction (gaining electrons).

'LEO goes GER' is a mnemonic device some clever person came up with that helps me remember which is which: lose electrons, oxidation (LEO); gain electrons, reduction (GER).

Both are normal processes that occur in every living cell, every moment of every day. In fact, the two go hand-in hand in a kind of biochemical dance called the 'red-ox' reaction, cycle, dynamic, or balance. The 'yin and yang' of oxidation and reduction cycle endlessly for life — as an essential mechanism of life, and thus for a lifetime.

But while oxidation is essential for energy production and numerous other functions in a cell, an excess of oxidative products — reactive oxygen species (aka oxygen-derived free radicals), reactive nitrogen species, oxidized fats and proteins, advanced glycation endproducts, etc. — can result in cell and tissue damage if it is not counteracted.

A gradual accumulation of oxidative damage is at the root of many different types of age-related disorder and disease, including age-related or 'senile' cataracts.

Hence, a diet rich in antioxidants is expected to prevent, or at least delay the onset and slow the progression of, age-related cataracts.

antioxidants

In the canine studies Prof Williams briefly reviews, the antioxidant compounds most convincingly associated with preventing or slowing cataract progression included these:

* alpha lipoic acid

* astaxanthin ( pronounced “asta-zan-thin”)

* curcuminoids (the orange-yellow pigment in turmeric, whose botanical name is Curcuma longa, hence curcumin-oids)

BTW, alpha lipoic acid may be particularly useful in animals with diabetic cataracts, as it inhibits the enzyme (aldose reductase) that converts glucose to its alcohol, sorbitol, in the lens. Sorbitol draws water into the lens, creating or contributing to diabetic cataracts.

In this situation, a manufactured form of alpha lipoic acid (i.e., commercial supplement) is preferable to natural sources — which include kidney, heart, liver, spinach, broccoli, and yeast extract — as the amount in food is very low.

The evidence for vitamin C (ascorbic acid), vitamin E (alpha tocopherol), and the amino acid L-carnitine is less persuasive, but in theory these antioxidant nutrients should be useful, too.

Here is a more comprehensive (but still not exhaustive) list of possibly useful antioxidants that show up in “vision-support” supplements for dogs and cats, with some notes on natural sources of each:

* omega-3 fatty acids — for carnivores, use fish oil or marine algae; for herbivores, use marine algae or terrestrial plant sources (flax seed, hemp seed, etc.); for omnivores, take your pick

* vitamins C and E — use natural (food) sources or analogues when possible; fresh fruits and vegetables for vitamin C (a water-soluble vitamin); animal fats, oily fish, seeds, and nuts for vitamin E (a fat-soluble vitamin)

* trace minerals — especially copper, zinc, and selenium (which needs to partner with vitamin E for optimal antioxidant capacity); best whole-food sources are organically grown vegetables and seeds/nuts; trace minerals bound (chelated, complexed) with organic molecules such as amino acids are generally better absorbed than inorganic sources

* astaxanthin — natural sources include microalgae (freshwater or marine), krill, shrimp, and salmon (i.e., seafood with the characteristic pink or red color of this antioxidant pigment)

* curcuminoids — high-quality turmeric powder is a deep orange-yellow, indicating a higher percentage of curcuminoids (a type of polyphenol) than less intensely colored turmeric powder; some suppliers provide the % curcumin(oids) on the label

Polyphenols are a diverse group of naturally occurring molecules that have at least two (and often several) carbon rings with one or more little hydroxyl (-OH) 'arms' attached, which makes them very effective antioxidants. Many different plants contain polyphenols, as we shall see.

* carotenoids — natural pigments that contribute to the red/orange/yellow color of carrots, bell peppers (capsicums to us Aussies), and many other foods in the red—yellow portion of the “color wheel”; salmon and shrimp even contain carotenoids; two specific types of carotenoid (lutein and lycopene) are discussed separately below

* quercetin — a polyphenol found in many different fruits, vegetables, leaves, seeds, and grains

* resveratrol — a polyphenol found in the skins of grapes, various berries (blueberries, blackberries, raspberries, etc.), and even peanuts

* green tea — rich in polyphenols, green tea powder is a useful herbal supplement if you want the benefits without drinking a cup of tea

* grape seed extract — a source of procyanidins (a type of polyphenol) found in many other plants, including apples and berries

* lutein — a specific type of carotenoid that contributes a yellow pigment to many different vegetables, including leafy greens, broccoli, and carrots

* lycopene — another specific carotenoid that contributes a red pigment to tomatoes and other red fruits and vegetables

* coenzyme Q10 — a naturally occurring co-factor, highest in vegetable oils, meats, fish, and nuts

Notice a theme here?

All of the antioxidant compounds on that list are found in, or derived from, food. Made by living things. Even the trace minerals, which plants and animals get from the soil, are made more available to us by first being incorporated into the living cells of the plants and animals we eat.

Generally, studies of single antioxidants or commercial combinations (e.g., “vision-care” products) add the supplement to the typical kibble diet. Compared with this standard diet of industrially produced, highly processed, high-starch junk food, it's little wonder that adding even a single antioxidant compound can work wonders!

And even then, the devil's in the details. The following graph is taken from a Korean study of senior dogs (8+ years of age) that compared two different “vision-care” supplements with a control group of dogs who received no such supplements…

Park S, Kang S, Yoo S, et al. 'Effect of oral antioxidants on the progression of canine senile cataracts: a retrospective study.' Journal of Veterinary Science, 2022; 23(3): e43.

There were no significant differences in the rate of progression from incipient to immature cataracts among the three treatment groups.