Hypoxia and the Physical Organism

As crucial as the condition of the sky is the physical condition of the observer. The observer may have the perfect combination of sky conditions and observing technique yet is unable to see the faintest details of objects or see at all if he is betrayed by his own physical condition. Two key contributors to the physical health and efficiency of the eyes are adequate supplies of vitamin A and the ability to respi-rate and metabolize oxygen. In any modern industrial society, vitamin A deficiencies are almost unheard of. Taking massive quantities of it will not give anyone super-human vision and can in fact be harmful. Still, a healthy diet is a must for good ocular health.

A greater factor that affects many people is the body's ability to take in (respi-rate), distribute and metabolize oxygen. The inability of the body to deliver oxygen

2 In an unfortunate "mistake", the state Senate "lost" the bill and failed to physically deliver it to Governor Jean Smart for her signature. Since it went missing for more than ten days and the Legislature was no longer in session, the promising legislation was accidentally "pocket vetoed" under the provisions of the Massachusetts constitution. That's politics!

to the tissues is called "hypoxia." Hypoxia can result from many potential factors. The eyes are the most oxygen hungry organs in the body and their efficiency rapidly deteriorates when an adequate supply of oxygen is not available. To make matters worse, the first part of the eye to be affected by hypoxia is the rod cells of the retina, the detectors of low-level light. Several potential factors can be involved in determining how efficiently the body can distribute and metabolize oxygen. The first such variable is the amount of oxygen available in the atmosphere. Hypoxia caused by a lack of oxygen is called "hypoxic hypoxia." At sea level, the partial pressure of oxygen in the atmosphere is approximately 220 millibars. This amount of oxygen is plenty for the body to use but in order to get the oxygen into the bloodstream; it must be forced through the walls of the aveoli. This is done by ambient air pressure, which at sea level is approximately 1,013 millibars (29.92 inches Hg). As you climb higher in the atmosphere, the ratio of oxygen to other gasses remains the same.3 But the pressure of the air falls off dramatically with increasing altitude. This is of interest to us because many astronomers seek to flee the effects of light pollution and weather by climbing the mountains. Today, many of the world's premier observatories are on extremely high mountaintops ranging 14,000 feet or higher above sea level. At this altitude, the partial pressure of oxygen in the atmosphere is only 130 millibars. This is only about 60% of what was available at sea level. From this, you might initially assume that you are getting only 60% of your sea level efficiency from your lungs. This assumption falls flat when you stop to consider that the total air pressure at 14,000 feet is only 600 millibars. That means not only is there less oxygen to breathe but the efficiency of the body in delivering that oxygen to the blood is greatly impaired. The eyes will be among the first of the body's users of oxygen to feel the effects as the rods begin to fail due to oxygen deprivation. The key to preventing this if you climb the mountains to see the stars is to breathe supplemental oxygen. But what if you're not going to Mauna Kea to observe? At what altitude should one consider this step? A lot lower than you might think. The Federal Aviation Administration's guidelines for pilots seems to be a good reference since the eyes are affected so early and night vision in particular is affected. Pilots are not required to begin using oxygen until they are higher than 12,500 feet after thirty continuous minutes but because of the detrimental effects of hypoxia on night vision the FAA strongly recommends that oxygen be used at night any time operating above 5,000 feet. If it works for pilots, it will work for you.

Even while observing at sea level, hypoxia symptoms can become an impediment to good night vision due to several potential factors. Anything that comes between an oxygen molecule and the cells of the body can cause hypoxia. Hypoxia can affect you even though plenty of oxygen is available. If you are in poor cardiovascular health, your night vision will suffer from effects very similar to those induced by high altitude. If the heart does not circulate blood adequately, the oxygen cannot reach the tissues with the speed the body demands resulting in what is called stagnant hypoxia. Though the cause is different the result is very much

3 The atmosphere is about 78% nitrogen, 21% oxygen with the last 1% divided up between carbon dioxide, water vapor and other noble gasses. Water vapor can, during extremely humid conditions, make up more than 4% of the atmosphere.

the same. The heart does not pump the blood at an adequate rate to keep the tissues of the body oxygenated and night vision begins to suffer. A hypoxic reaction can also be induced by poor hematological health. Anemic hypoxia is caused by the inability of the red blood cells to absorb and transport oxygen even though oxygen itself may be plentiful. Sickle cell anemia, a condition that primarily occurs in African-American males, is a leading cause of this. The rest of us should be aware that many other forms of anemia exist that are not so racially discriminatory. Anemia can also be induced by poor diet. You can also induce hypoxic symptoms yourself by taking certain substances into your own body. Alcohol and many drugs can reduce the ability of the red blood cells to carry oxygen, a form of hypoxia called histotoxic hypoxia.

The health of the eye itself is critical as well. Many individuals suffer from some form of ocular pathology. The most common include myopia (near-sightedness), presbyopia (far-sightedness) and astigmatism. Myopia often occurs at a fairly young age (I began wearing glasses at age 9). It is caused by a misshaped cornea, which causes light from distant objects to come to focus prior to reaching the retina. The result is badly distorted images of distant objects. The problem is easily corrected by using corrective lenses such as glasses or contact lenses which induce a focusing error in the light path that is exactly the opposite of that created by the flawed cornea. The result is a properly focused image. Presbyopia commonly affects older individuals. As the eyes age, the cornea begins to become rigid and less flexible. This causes the eye to have difficulty focusing on objects that are relatively close. The cure is the same as for myopia: corrective lenses that eliminate the fault by introducing an equal and opposite error. Astigmatism is a somewhat more difficult and complex problem for ophthalmologists to deal with. Astigmatism is a flaw in the cornea that causes images to appear distorted, even though they are well focused. A properly focused star appears as a perfect pinpoint of light while the same star might appear to have a "diffraction spike" radiating from it when viewed through an astigmatic eye. Correcting the flaw using contact lenses is particularly difficult and most users with severe astigmatisms must use eyeglasses to correct them. This is particularly painful at the eyepiece of the telescope and even more so during astrophotography. The telescope and camera see and focus at "20/20"4. In order to properly focus them, you must also see 20/20. Glasses make seeing through a camera or telescope particularly awkward. Most astronomers who need eye correction prefer to use contact lenses.

Many people are taking action today to repair eyesight damaged by age or genetics. Surgical fixes for eye problems have been with us for many years. The first such procedure for correcting bad eyesight was called "radial keratotomy." This surgical procedure involved slicing the cornea, pizza style with a scalpel and refiguring it into the proper shape. Radial keratotomy did work but often resulted in heavy scarring and if the results were not perfect, it could not be reversed, changed or performed again. Another technique that enjoyed some popularity in the early 1990s was "orthokeratology." Orthokeratology involved the use of special hard

4 The first number tells how close the viewer must be to an object to focus on it. The second number refers to the distance that a person with normal vision can focus on the object. The larger the second number is, the more near-sighted you are.

contact lenses that functioned in a way not unlike a dental retainer. These lenses over time reshape the cornea, gradually forcing it toward the proper shape. The user would regularly change to a new set of lenses that would continue to refine the correction until it is completed. The corrective process takes about six months. Once 20/20 vision was restored, the patient would continue to periodically wear contact lenses to maintain the shape of his corneas. The advantages of this procedure were obvious in that no surgery was necessary and no scarring ever took place. If it did not work, the effects were completely reversible. The disadvantages were that if the user stopped using his retainer lenses, the eyes would eventually return to their original flawed state.

The technique most favored today is called "laser keratotomy." In laser kerato-tomy a scalpel is used only to make an initial slot in the cornea. The slot allows the lens to relax while a precision laser figures the lens to the correct shape. Like in other forms of keratotomy, the effects are irreversible so if you are unhappy with the outcome, too bad. Unlike traditional surgery, there is no scarring and recovery time is quick. Usually the patient is out of the office within an hour and seeing normally within two or three days without optical aid. Some surgeons are now performing newer forms of the surgery without using any blades at all. There is one important drawback to laser keratotomy. Current Food and Drug Administration rules limit the scope of the surgery to the inner 6-millimeter radius from the pupil center. The problem is if you are one of those people who have a very wide opening pupil after dark adaptation. If the pupil can open wider than the surgically repaired area of the cornea, the result can be severely distorted night vision. One common effect is "haloing" of bright lights. Your vision is normal in the center but as light travels across the non-repaired outer cornea into the eye, the fringes of lights become distorted and create halos around the light source. As an amateur astronomer and a pilot, my night vision is crucial to both my livelihood and my hobby. Because of this, I have decided for myself to forgo any surgery or other vision correction until the medical procedure evolves further. Contact lenses do an adequate job for my near-sightedness, and evolving technology has finally created a contact lens that corrects my particular astigmatism.

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