For Healthier Eyes

N-Acetylcarnosine May Help with Cataracts
NAC eye drops show benefits in both preventing and treating this age-related condition
By Will Block

Normal vision, and vision with a moderately severe cataract.
ere’s the answer to what could be a $1000 Jeopardy question in the category The Human Body: “It is the body’s only organ that never regenerates its cells.” Contestant quickly hits button, pauses, thinks hard, finally asks, “What is the lens of the eye, Alex?” And Alex says, “That’s correct!”

Did you know that? It’s odd, isn’t it? All the other organs of the body undergo gradual regeneration through the normal processes of cell death and the creation of new cells to replace them. But the lenses you’re born with are the same lenses—the very same lenses—you’ll die with. Unless, of course, you have them surgically removed and replaced with artificial ones. That’s what millions of people do every year when their vision has become so impaired by cataracts that they can no longer see well enough to read or drive a car or do work that requires sharp vision.

Cataracts Are the Leading Cause of Blindness

Unfortunately, countless other people can’t afford cataract surgery, or it’s not even available to them in the first place because there just aren’t enough surgeons around to do it. Worldwide, cataracts are the leading cause of blindness, affecting about 17 million people. Injuries to the eye account for some cases, but the majority are caused by that old bugbear, aging. About 20% of all people over 60 have at least the beginning of a cataract in one or both eyes, and that figure rises to 80% for people over 75. Clearly, getting older is bad for our eyes.

Is it simply because we have used our eyes for so long? In a sense, yes, because a common cause of cataracts is believed to be the cumulative ultraviolet radiation damage from all the time we spent outdoors without sunglasses. Other causes include heredity, poor nutrition, smoking, high blood pressure, kidney disease, diabetes, and the long-term use of corticosteroids (the last two are major risk factors for cataracts).

Oxidative Damage Clouds Our Lenses

In the most common of the three kinds of cataract, called a nuclear cataract, the cumulative damage done to the lens’s molecular architecture causes a cloudy haze to develop inside the lens.* This haze is the physical manifestation of a random clumping together of the previously beautifully ordered arrangement of lens proteins called crystallins. The chemical reactions that produce this clumping are believed to be caused in large part by oxidative free radicals, which damage vital biomolecules, including lipids as well as proteins. The resulting deterioration of cellular function is one of the hallmarks of aging. The antidote to free radicals is, of course, antioxidants, such as glutathione, lipoic acid, and vitamins C and E.

*Less common, except in diabetics, is a cortical cataract, which begins in the cortex (periphery) of the lens and extends inward. Least common is a posterior subcapsular cataract, which occurs on the back side of the lens.

As the cataract develops in size and density (it’s typically completely painless, by the way), it not only reduces the amount of light that passes through the lens (which looks and acts like a magnifying glass), it also scatters the light that does get through. Thus, instead of all the light rays being focused precisely to a point on the retina, forming a sharp, clear image of what we are seeing, many of the rays are spread out across the retina, forming a fuzzy image. Colors may be dulled or distorted, and there may be an annoying halo of light around bright objects, causing a glare effect.

Even Cataract Surgery Carries Some Risk

As the lens becomes ever more opaque, vision becomes so impaired that surgery is eventually required to prevent total blindness. In the hands of an expert ophthalmic surgeon, the operation is quick and easy, the recovery is fast, and the results are spectacular: clear vision once again. Cataract surgery is the most commonly performed operation in the United States today (over 1.5 million annually). It consists of making a tiny incision in the eye, removing all or part of the diseased natural lens, and replacing it with one made of a plastic or silicone material. Complications are rare, but they can include pain, infection, swelling, bleeding, and even retinal detachment and blindness.

Many Nutrients Can Benefit Our Eyes

As with any disease, surgery should be the last resort. Prevention is the Holy Grail. Good nutrition is a key element of effective prevention for most age-related diseases, and it’s a key element of effective therapy if the disease has taken hold. Good nutrition, of course, encompasses not just eating good, healthy food, but also the judicious use of dietary supplements to make up for deficiencies in even a good diet, and for the changing needs of our bodies as they grow older and become less able to synthesize some of the essential nutrient molecules that were abundant in our youthful selves.

The list of supplemental nutrients that can benefit our eyes in one way or another—including the prevention of diseases such as cataracts, glaucoma, and macular degeneration—is surprisingly long. It includes the tripeptide glutathione (the most abundant and important antioxidant in the human body, and critical for protecting the lens from free radical damage); vitamins A and C (both very important); vitamin E and some of the B vitamins; various bioflavonoids (especially quercetin and hesperidin) and carotenoids (especially lutein and zeaxanthin); the amino acids taurine, N-acetylcysteine, and acetyl L-carnitine; the hormone melatonin; the alkaloid vinpocetine; the herbs bilberry, ginkgo, and garlic; the minerals zinc and selenium; and, last but certainly not least, the saturated fatty acid lipoic acid (“the antioxidant’s antioxidant”), which plays a central role in maintaining the body’s antioxidant network.

Eye of Newt (not Gingrich)
When Shakespeare had the witch in Macbeth call for “eye of newt and toe of frog, wool of bat and tongue of dog,” he was onto something that even he, genius though he was, probably didn’t realize. It turns out that the only creatures in the animal kingdom that can regenerate the cells in the lenses of their eyes are . . . newts (plus a few other obscure amphibians and some fishes). Why newts, of all things? And why can’t we do what they can do? No one knows, but researchers are investigating this question in the hope of finding genetic engineering methods for preventing or treating diseases of the lens, such as cataracts.

Their prospects might seem dim but for one extremely important fact: it is possible to induce the lens cells of humans—even aged humans—to regenerate in laboratory experiments. This means that Mother Nature has provided us with the biochemical mechanism for lens regeneration, but She has unaccountably prevented it from occurring naturally—except in those darned newts. Needless to say, newt genes are the subject of intense scientific interest for that reason. It serves to illustrate, yet again, how vital it is to protect and preserve all species of animals and plants—even those that appear to be “unimportant” or “useless.” Who knows what invaluable gifts to mankind they may harbor in their genes?

In any event, perhaps scientists should have a closer look at toe of frog, wool of bat, and tongue of dog, just in case Shakespeare was an even greater visionary genius than we thought.

N-Acetylcarnosine Is Also a Beneficial Eye Nutrient

With the notable exception of glutathione, which does not survive the digestive tract and must be synthesized by the body, the nutrients listed above can be taken as dietary supplements. The molecules in question pass through the digestive tract, enter the bloodstream, and find their way to the eyes, as well as to all other organs of the body. A more direct route to the eyes, of course, is through eye drops, and they are the preferred delivery vehicle for yet another molecule that has been found to be beneficial for eye health, particularly with regard to cataracts.

That molecule is N-acetylcarnosine, or NAC for short.* It occurs naturally throughout the human body, but its parent compound, carnosine, is much more abundant; both compounds are found primarily in the heart and skeletal muscles (the word carnosine is derived from the Latin word for flesh) and in the brain. Carnosine was discovered in 1900 in Russia, and it is in Russia where most of the recent research on the N-acetylcarnosine derivative has been carried out, demonstrating that NAC is effective not only in preventing cataracts but also in treating them: it has been shown to improve vision by partially reversing the development of the cataract, thus increasing its transmissivity to light.

*N-acetylcarnosine should not be confused with N-acetylcysteine (also called NAC), nor should it be confused with acetyl L-carnitine (ALC); both of these compounds are also known to provide some protection against cataracts.

N-Acetylcarnosine Delivers Carnosine to the Lens

Carnosine is a dipeptide, meaning that it consists of two amino acids (in this case, alanine and histidine) connected to each other by a chemical bond called the peptide bond. Dipeptides are very common in our bodies, as are tripeptides (such as glutathione) and polypeptides (which contain more than three amino acids). Polypeptide chains consisting of more than several dozen amino acids are called proteins, which typically contain hundreds or even thousands of amino acids.

The eyes treated with NAC were
substantially improved in terms of
transmissivity of the lenses, visual
acuity, and glare sensitivity.

But getting back to NAC, what does the “N-acetyl” mean? It means that one hydrogen atom in carnosine has been replaced by an acetyl group (CH3CO–), and this substitution has occurred at a nitrogen atom. An important difference between carnosine and N-acetylcarnosine is that carnosine is relatively insoluble in lipids (fats and fatty compounds), whereas N-acetylcarnosine is relatively soluble in lipids (as well as in water). This means that N-acetylcarnosine is better able than carnosine to pass through the lipid membranes of the corneal and lens cells, thereby gaining access to the cells’ interior, which is primarily aqueous. There the N-acetylcarnosine is gradually broken down to carnosine, which then exerts its beneficial effects.†

†A further advantage of N-acetylcarnosine is that it is immune to the enzyme carnosinase, which is present in extracellular fluid. This enzyme degrades carnosine before it can reach the cell interior, making carnosine unsuitable for use in eye drops.

N-Acetylcarnosine Reduces Cataracts

A normal eye, and the same eye as it would appear with a moderately severe cataract.
Based on research performed mainly by Russian scientists, it is believed that carnosine is effective both in preventing and treating cataracts, largely because of its antioxidant properties and its ability to inhibit a chemical process called glycation, which leads to deleterious substances called AGEs (advanced glycation end products). These are chemical complexes that result from common but undesirable reactions between blood sugars, such as glucose, and proteins in many parts of our bodies, including the lenses of our eyes. The sugar-protein complexes become chemically cross-linked and degrade cellular functions. The aptly named AGEs are thought to be an important factor in the aging process.

In a recent study, the Russian scientists‡ conducted two randomized, double-blind, placebo-controlled trials, of 6 months and 24 months duration, with eye drops consisting of a 1% aqueous solution of NAC administered as two drops twice daily.1 They treated a total of 49 elderly patients (average age 65) with cataracts ranging in severity from minimal to advanced (but not to the point of requiring surgery); the total number of eyes affected was 76. Using a variety of sophisticated optical techniques, they monitored the condition of the cataracts and the patients’ visual acuity and glare sensitivity.

‡It should be noted that the principal researcher and four of his colleagues in this study were employed by Innovative Vision Products, a leading producer of N-acetylcarnosine.

The eyes treated with NAC were substantially improved in 6 months: the measured transmissivity of the lenses increased in 42% of the eyes, by 12–50%; in 90% of the eyes, visual acuity improved, by 7–100%; and in 89% of the eyes, glare sensitivity improved, by 27–100%. These improvements were sustainable for the duration of the 24-month trial. In no eyes was any worsening of the condition seen. By contrast, the condition of the untreated eyes in the control group did worsen: in 89% of them, visual acuity dropped by 17–80% after 24 months. The authors stated (twice) that in “most of the patients” treated with NAC, tolerance of the eye drops was good. Elsewhere in the same paper, they said it was excellent, with no adverse effects in any patients.

Do You See the Point?

Even if you were to let the rest of your body go to seed, chances are you would spare no effort to protect your precious eyesight. It’s easy to see why, so to speak. Close your eyes for a moment, right now, and pretend that you could never, ever open them again.

If you’re reading these words, you must have opened your eyes—but it was a frightening thought, wasn’t it? Fortunately, cataracts are easy to treat and cure, but the point is, preventing them is a much better approach and carries zero risk of postoperative problems. So do whatever you can, including the use of nutritional supplements, to keep your eyes clear and healthy for the rest of your life. Start by saying, “I declare (declare comes from the Latin for ‘to make clear’) that I will be good to my eyes.”


Babizhayev MA, Deyev AI, Yermakova VN, Semiletov YA, Davydova NG, Kurysheva NI, Zhokotskii AV, Goldman IM. N-Acetylcarnosine, a natural histidine-containing dipeptide, as a potent ophthalmic drug in treatment of human cataracts. Peptides 2001;22:979-94.