by Leo Anghart
The cornea is about half a millimeter thick at the center of the pupil and consists of several layers. The outer layer is the tear film, which nourishes the cornea as well as being a part of the refractive elements of the eye. You have probably noticed that blinking your eyes improves your ability to see. The physical surface of the cornea is called the epithelium, which consists of a protective layer of relatively hard surface cells. Its function is to protect the eye from damage. Extended wearing of contact lenses, especially hard lenses, eventually wears down the corneal epithelium and contact lenses can no longer be worn.
Just a few cells below the surface we have Bowman’s layer. This is a layer of collagen-like cells that help the cornea to keep its shape. This layer never heals if there has been a surgical intervention. Bowman’s layer is like the stiffeners in your shirt collar. The largest part of the cornea is the stroma. This layer is where laser surgery is performed. Part of the stroma layer is blasted away in order to thin the cornea so that the refractive power will change. Since there are no blood vessels in the cornea it takes as much as six months to heal. Also there is an unavoidable weakening of the cornea due to the surgery.
Optical dimensions of the eye
This section is for those of you who are interested in the scientific aspects of the eye’s optical dimensions. I am amazed that the eye is so small and that there are such huge differences in dioptric power between the cornea and the lens.
The lens
While the cornea provides most of the optical power of the eye, the lens is an important part of the optical system. The lens is about 10 mm in diameter and consists of crystalline cells that are completely transparent so light can shine through.
The lens is suspended in space by tiny fibers called zonules. Because of its high water content the lens is very flexible and the pull of the zonules alters the shape of the lens. When the ciliary ring muscle is relaxed, the zonules are tightened and the lens becomes flatter – thus having less focusing power. On the other hand, when the ciliary muscle is contracted the zonules are relaxed and the lens bulges out and thus increases its focal power. When the ciliary muscle is relaxed the eye is said to have “accommodated.”
In vision tests, the drug atropine is sometimes used to paralyze the ciliary muscle. The rationale is that when ciliary muscle activity is eliminated you will then get the “true” visual status. Some optometrists believe that this is the only valid test. Applying the same logic, you might wonder why your spine is not paralyzed when its height is measured to eliminate the possibility that you will stretch up and become taller!
The crystalline cells of the lens remain the same throughout life. Each year a new layer grows like an onion. Between age 20 and 80 the lens will have doubled in thickness. The lens has no blood vessels and is therefore nourished only by the aqueous humor that is continuously secreted from the ciliary body. Vitamin C is the most important supplement for the lens. The lens has the highest concentration of vitamin C in the entire body. Oxidation damage by free radicals causes the crystalline cells in the lens to become opaque. This condition is known as cataracts. Since the lens is only a small part of the optical system of the eye, you can still see even if your lens has been removed – approximately 10 percent loss of visual acuity (or two lines on the eye-chart). Thus you could still be driving legally even without lenses in your eyes. The legal limit for driving is 20/40 visual acuity.
The retina
The retina is a paper-thin layer at the back of the eye which contains light sensitive cells. If the retina is damaged there will be permanent loss of vision. The most serious retina problems are macular degeneration and diabetic retinopathy, both of which are a form of deterioration of the integrity of the retina. Another problem is retinal detachment, which occurs in people with a high degree of myopia.
Light sensitivity
The trade-off between visual resolution and visual sensitivity is largely due to the way rod and cone cells are connected to the post-receptoral elements of the retina.
Rod cells are connected in such a way that they sum up information over space producing great sensitivity but poor resolution. Mother Nature achieves this by connecting many more rod cells in parallel to a single nerve fiber (ganglion cell). The scotopic vision manifests great spatial summation. On the other hand cone cell connections maximize visual resolution and the expanse of sensitivity.
A ganglion cell requires ten quantal absorptions before it signals an event. Also the light must be present within a certain time frame, or it is lost.
Photosensitive cells
There are two kinds of photosensitive cells in the eyes: one is the rod cell, which operates under dim light conditions, referred to as scotopic vision; the other light sensitive cell is the cone cell, which gives you sharp vision and color perception.
Rod cells are the most numerous – about 120 million. They are highly sensitive to low light and motion. Rod cells do not detect color and their visual acuity is about 20/200. For sharp focus and color perception it is the cone cells that are used. These are concentrated in the central fovea located directly behind the iris and the other optical parts of the eye. Cone cell perception is referred to as photopic vision.
There are three types of cone cells, each sensitive to a specific range of light frequencies: the photo-pigments erothyrolabe are sensitive to long-wave red light, chlorolabe is sensitive to mid-range green light and cyanolabe is sensitive to short-wave blue light. The three primary colors red, green and blue enable you to see all the colors in the spectrum. Blending these three basic colors can produce every color imaginable. There are about six million cone cells in each eye with the highest density situated in the central fovea. However, cone cells are present all the way to the periphery of the retina and only about 4 percent of all cone cells are located in the fovea. Interestingly enough, there are no blue sensitive cone cells in the fovea; their peak density lies just outside the central fovea. This accounts for the inability to see very small blue objects when they are centrally fixated.
The rod cells contain the photosensitive pigment rohodosin or visual purple. Named after its appearance, the rod cell consists of about 1,000 tiny disks, with each disk holding about 10,000 molecules of rohodosin. Each molecule is capable of capturing one photon of light. The huge number of rohodosin molecules therefore have tremendous capacity for capturing light. When light falls on a rod cell, the rohodosin becomes bleached. Only one quanta of light is required to bleach a molecule of rohodosin. In fact the scotopic spectral sensitivity of the eye corresponds to the properties of rohodosin.
The macula
The retina has a central area, directly behind the cornea and lens, called the macula. At the center of the macula is the fovea. In this part of the eye vision and color perception are perfectly clear. In the fovea, the photoreceptors have the densest concentration of light sensitive cone cells, approximately 150,000 per square millimeter. These cells are also connected to a very large area of the visual cortex, enabling you to see clearly.
The macula is covered with a yellow pigment consisting of the carotenoids lutein and zeaxanthin. Traditionally it was believed that yellow pigments aided in visual resolution by filtering out the shorter blue light wavelength. Nowadays this filtration effect is considered to be a protection against blue light damage and indirectly a way of squelching free radical oxidation. Incidentally, the distribution of zeaxanthin seems to parallel that of cone cell photoreceptors.
The best dietary sources of carotenoids are dark-green leafy vegetables and yellow and red fruits. Carrots are the best source of beta-carotene and tomatoes supply lycopene. Zeaxanthin is the dominant carotenoid in vegetables such as orange peppers and sweetcorn, while most other vegetables such as cabbage, spinach and watercress are rich in lutein and beta-carotene.
Lutein, taken as a sublingual spray, is one of the most effective ways to stop the progress of macular degeneration, a disease where the integrity of the macula progressively deteriorates.
> 5. Healthy Eyes
Not only are your eyes a mirror of your soul, they are also a reflection of your overall physical health, emotional wellbeing and level of vital energy. Physical exercise is one important factor contributing to your general health. Everyone expects a person to have vibrant wellness if they exercise and are active. Working out and sports are the main activities for keeping fit.
There is a lot to be said for the old adage: “You are what you eat.” Nutrition is not really a part of Vision Training, but the information is just too important not to include. I do not believe that I can just take a pill and get clear eyesight. Healthy nutrition is clearly an important aspect of good vision, so it makes sense to create a condition where all the necessary nutrients are available.
What’s needed for optimum eye health?
There are two nutrients that are vital for your eyes. The first is vitamin C. The lens, aqueous humor and vitreous humor have about seven times the level of vitamin C than any other part of the body. Vitamin C is an important antioxidant that fights oxidative damage caused by free radicals, spurred on by a photo-reactive process. These start a chain reaction where the end result is the formation of cataracts. Cataracts will cause blindness if not treated. This treatment usually means removing the lens surgically.
The second vital nutrient needed by the eye is vitamin A, which is required for the process of converting light into nerve energy. Vitamin A deficiency is directly related to night blindness. Two other beta-carotene nutrients are important for the proper functioning of the macula – the part of the eye where you have absolute clear vision. Lutein and zeaxanthin supply the yellow coating over the macular region of the eye, which protects the light sensitive cells from damaging blue light.
With the condition macular degeneration – the deterioration of the maculae – the light sensitive cells are damaged and permanent loss of vision is the result. More and more studies link nutrition and poor digestion to the increase in macular degeneration. It used to be a problem afflicting only older people. Unfortunately, younger people are now developing this condition. Currently the most effective way to prevent and deal with macular degeneration is nutritional and most important of all, the sublingual application of lutein.
What can I do to maintain optimum eye health?
I don’t believe in mega doses of supplements. My concern is maintaining the body’s natural ability to synthesize the nutrients it needs from the food we eat.
Today more people are buying and eating organically grown foods. The beautiful tomatoes you see in the supermarket were most likely plucked green from the plant and artificially ripened during transport to the store. Additionally, the plant was almost certainly enhanced to produce thicker skin and bigger fruits to satisfy your visual expectation of a pleasing tomato – and all this most probably at the expense of nutritional values.
If you have ever eaten tomatoes taken directly from the plant when fully ripened you will know that there is a huge difference. A few years ago I traveled by roads in Mexico that were lined with orange groves. We stopped and bought a sack of tree-ripened fruit. The juice made from these oranges was heavenly and full of vitamin C – grown the natural way. Fruits are generally best in the countries where they grow naturally and can be obtained from local farms.
On the other hand I can’t imagine myself eating spinach every day, as one study suggests. I love spinach, but not daily. So the solution is to supplement. I take the word “supplements” quite literally. I take vitamins and minerals as supplements, not as a substitute for food.
Good nutrition is a very confusing topic with trends and opinions shifting every few months. Some purists advocate the advantages of a diet consisting entirely of raw foods. They maintain that heating vegetables to 60° Celsius destroys most of the nutrients. I like salads, but living exclusively on raw food would be a challenge for most people. The middle ground may be the best way to go. So make it a point to include plenty of dark-green and orange vegetables in your salad. Your intake of vegetables is higher if you drink them as juice.
The following is a list of the nutritional elements you need for good eye health. Try to get these vitamins and minerals in your normal diet and supplement as necessary. However, remember that Mother Nature does it best.
Vitamin A
This is vital for natural vision. It is consumed by exposure to heat and glare, flickering fluorescent lights, computer monitors and TV screens. The nicotine in cigarettes and alcohol also burn vitamin A.
Beta-carotene is stored in the liver and converted into vitamin A on demand. It is safer to take beta-carotene since there is no limit to how much you can consume. For vitamin A the limit is no more than 10,000 international units (IU) of vitamin A per day over a long period of time. The recommended supplement dosage is 5,000 to 25,000 IU in a carotene complex.
The best source of beta-carotene is carrots, especially in fresh carrot juice. It is also found in yellow and green fruits and vegetables.
There are two other carotene compounds that are important for the eyes. One is lutein and the other is zeaxanthin. Lutein is the yellow pigment layer that covers the macula. It is thought to protect against the damage of blue light. Zeaxanthin is found mostly in the area of the central fovea where vision is crystal clear.
Lutein comes from vegetables such as cabbage, spinach and watercress. The recommended dosage is 6–20 mg. Zeaxanthin is found in orange peppers, yellow corn and egg yolks. The recommended dosage is 90 mg taken with lutein.
Vitamin B complex
These supplements are best taken together since they must be balanced for the body to be able to absorb them. B complex vitamins are burned up by stress.
Vitamin B1 (thiamine)
Vitamin B1 keeps the eye muscles working. It is usually included in breakfast cereals and is found in whole grains, egg yolks, soya milk and milk. The recommended supplement dosage is 10–50 mg.
Vitamin B2 (riboflavin)
Vitamin B2 aids with the ability to be comfortable in bright light and appears to play a role in the circulation of nutrients to the lens. Lack of B2 causes constant eye fatigue, burning eyes and the inability to see during twilight hours. Cataract patients lack vitamin B2. It is found in almonds, brewer’s yeast, milk and soybeans. The recommended supplement dosage is 15–50 mg.
Vitamin B6 (pyridoxine HCL)
Vitamin B6 is important for emotional balance. It is found in bananas, brewer’s yeast, brown rice, carrots, chicken, eggs, fish and whole grain cereals. The recommended supplement dosage is 50–100 mg. Avoid dosages higher than 300 mg per day.
Vitamin B12 (cyanocobalamin)
Below average levels of vitamin B12 are apparent in individuals who suffer from cataracts and glaucoma. This vitamin is found in clams, fish, eggs, dairy products and sea vegetables. The recommended supplement dosage is 200–400 mg. Sources of vitamin B are dark-green vegetables, brewer’s yeast, eggs, nuts and seeds.
Vitamin C (ascorbic acid)
This is vital for the health of your lenses which contain seven times more vitamin C than any other part of the body. Vitamin C is an important antioxidant – needed to fight oxidation damage by free radicals. Note that smoking diminishes vitamin C levels and is a significant risk factor in developing cataracts. To be fully effective vitamin C supplements must contain bioflavonoids. Bioflavonoids are found in blackcurrants, grapes and cranberries. The recommended supplement dosage is 200–500 mg per day. Natural sources of vitamin C are citrus fruits, such as lemon, lime and orange. It can also be found in melon and tomatoes.
Vitamin D
Vitamin D controls calcium levels and is found in cod liver oil, oily fish and egg yolks. It is usually added to milk.
Vitamin E (α-tocopherol acetate)
This enables the bloodstream to carry necessary oxygen and nutrients to all parts of the body, including the eyes. Vitamin E also appears to be important for maintaining the elasticity of the eye muscles and lens. It is found in wheat germ, almonds and other
nuts as well as cold-pressed oils. Avoid the synthetic vitamin E – α-tocopherol. Normally, you will get most of the vitamins you need from the food you eat and from multivitamin supplements.
Calcium
Several studies have found that higher levels of calcium have a positive effect on myopia, detached retina and glaucoma. It appears that calcium dehydrates the fluid within the eyes, thus making the eyeball shorter. Sugar, found in carbonated drinks, appears to be one of the factors that cause myopia. However, when calcium is present, the eyeball reverts back to its normal shape.
Calcium is found in milk, leafy greens and sardines. Calcium should be taken together with magnesium (vital for enzyme activity and energy).
6. Visual Acuity
While the reading 20/20 is commonly held to represent normal vision, most people with good eyesight actually measure better than 20/20. This evaluation represents the upper limit of good vision. Research conducted by Elliot and co-workers (1995) shows a slight decline in visual acuity, from approximately 20/14 at age 25, to just a fraction better than 20/20 at age 75. This is surprising news to most people, since the common belief is that vision starts declining in childhood.