Astigmatism is quite a difficult concept to explain to patients and students. Searching over the internet is unlikely to lead to a satisfactory simple definition. In relatively simple terms, what it means is that the optical system focuses lines oriented in one direction at a different point to those in all other directions. In optics, these directions are called meridians. If the optical system is circular the meridians are analogous to the lines of longitude of the earth where the optical centre is the North Pole and the lines extend around the globe to the other pole.

In astigmatism, some of these lines are more tightly curved than others. The lines with the highest and lowest curvature are called the principal meridians and in regular astigmatism, these are always at 90 degrees to one another. An example of a shape which would have this effect when made as a lens is a barrel. Imagine that the optical centre is at one point on the widest point of the barrel. Lines drawn out at each clock hour would each have a different curve – the most curved would be the meridian which goes around the barrel and the least curved would be the meridian heading towards the top and bottom of the barrel. In its extreme form the barrel becomes a cylinder and the up and down meridian has no curve at all – this shape, as a lens, is termed a cylindrical lens.

You can immediately see from this analogy that the meridians can only take values from 0 to 180 degrees : 190 degrees is the same as 10 degrees.

In ophthalmology, when we consider astigmatism, we do so in one of two ways. An optical element can be described either as the sum of 2 cylinders such as 10D x 90 degrees + 20D x 0 degrees or as a sphere (normal lens) plus cylinder – in this case 10D + 10D x 0 degrees (called the sphero-cylindrical form). These forms are easy to interconvert and both completely describe the element provided that it displays regular astigmatism. Transposing the spherocylindrical form is a trivial task- in this case it is 20D – 10D x 90 degrees. Just remember that the amount of cylinder always stays the same.

The spherical equivalent of a sphero-cylindrical lens is equal to the sphere plus half the cylinder. This is the best approximation to the lens by a spherical lens only As a basic check of your arithmetic remember that when you transpose the cylinder, the spherical equivalent always stays the same. Also, if you add thin lenses in contact with one another, the spherical equivalents always add algebraically.

Addition and subtraction of thin lenses in contact with one another is easy if the principal meridians of the astigmatism are aligned. In that case, the spheres and cylinders just add together. For example, take two lenses

* 0 + 1 x 90 degrees
* 3 +2 x 0 degrees

transposing the second one we get

* 5 -2 x 90 degrees

adding together now is

* 5 -1x 90 degrees

checking the spherical equivalents we have 0.5 + 4 from the combination and the result is also 4.5D

It gets much more tricky when you have to add lenses together that are not aligned You might guess that you can use vector addition from high school physics but try this :

* 0 + 1 x 90 degrees and
* 0 + 1 x 0 degrees

Vector addition would yield 1.4 by 45 degrees but the correct answer is 1D sphere.

To understand what is going on here, have a look at the top half of this diagram I have illustrated the addition of a 2D x 0 degrees (blue) and 2D x 45 degrees (red). Along the x axis is the meridians and the y axis shows the power for each meridian. The green line is the net power. Obviously if those sine waves were 0 degrees and 90 degrees they would be completely out of phase and add to a straight line (the sphere) of 2D. ; The matrix mathematics to solve directly is hinted at below.

Any lens can be considered to be a matrix like this and if multiple lenses are in contact, the matrix elements just add up. You then need to pull the three parameters out the matrix and solve for S, C and theta. This is basic first year university mathematics.

Luckily for you, i have created an on-line calculator to add or subtract lenses. Feel free to leave comments on the blog if you find it helpful. And if there are any engineers who can expand the scope of this article to include elements not in contact with one another, please drop me a line.

Marc Sarossy is an Ophthalmologist and Affiliate member of the IEEE. He has interests in the mathematical analysis of biological signals – especially those related to the eye. He consults from his clinic in Broadmeadows Melbourne.

Intruder alert! Intruder alert! Unknown attacker has breached the perimeter.

Histamines, the foot soldiers of your body’s immune system, rush to the front lines, desperate to keep you safe. They gather in your throat, tightening its muscles in order to block entry. They gather in your eyes, trying to wash the intruder away in a flood of tears. And they gather in your sinuses, prepared to forcibly expel the attacker with a tremendous sneeze.

Your body doesn’t understand that this is a false alarm. Harmless substances such as pet dander, dust, and pollen are viewed as a threat because you have an immune system disorder. Your body is being maddeningly overprotective.

It’s kind of like “little dog syndrome.” Little dogs can sometimes feel so weak and vulnerable that they begin to perceive everything as a threat to their wellbeing, and they become aggressive. This is what’s happening with your immune system. This overprotective dynamic is created because your immune system is weak and therefore feels vulnerable.

The best option is to avoid those things that cause you to have an allergic reaction. But sometimes that’s not possible. How do you avoid the airborne allergens that cause hay fever or cedar fever? You can take steps to minimize your contact, but unless you want to live in a bubble, it’s not practical to think that you can avoid them altogether.

You need to strengthen your immune system to, in essence, build its confidence. Once it’s confident, your “little dog” immune system will be better equipped to take those allergens in stride. The allergens will become more of an annoyance than a full-blown threat. The histamine foot soldiers will always be at the ready – there’s no cure for allergies – but you can take them out of red alert status.

My top five tips for natural ways of strengthening your immune system:

1. Get plenty of vitamin C. Our bodies can’t produce vitamin C on their own, and yet, we rely on this hardworking vitamin to stimulate the production of the white blood cells that are so vital in our fight against disease. That means we have to get our vitamin C from dietary sources such as citrus fruits, melons, tomatoes, and leafy green vegetables.
2. Exercise regularly, doing something you enjoy. You don’t have to go out and run a marathon, if the mere idea of it makes you cringe. You don’t have to lift weights or swim across Lake Austin pulling a party barge in your wake. Do something fun, and do it often. In addition to the immunological benefits of exercise, you’ll get the immune booster shot that laughter provides.
3. Sleep 7-9 hours per night. In today’s rush-rush world, a full night of sleep is a rare and precious commodity for many people. Allergy sufferers in particular should prioritize sleep for its rejuvenating properties. Think you’re on edge if you haven’t gotten enough sleep? Imagine how that histamine foot soldier on the front line feels. Trigger happy, ready to jump at the slightest shadow.
4. Drink lots of water. Water is by far the most valuable tool in the natural health toolbox. In addition to keeping your body lubricated, water literally flushes impurities out of your system. That means there’s less work for your immune system to do, and a relaxed immune system is a healthy immune system.
5. Visit your chiropractor. That’s right, I said chiropractor. Your immune system is inextricably linked with the health of your central nervous system. When your spine is out of alignment – even by a miniscule amount – stress is put on your nerves, which can cause a host of problems, including making your immune system more prone to dangerous overreaction. Your chiropractor will make a series of gentle adjustments to bring your body back into proper alignment.

With these natural health methods of boosting your immune system, you may find you no longer have to rely on drugs to get you through the day. No more chemicals in your body, no more drowsiness. And no more feeling as though your body is at war with itself.

Dr. Eric Murphy is a Doctor of Chiropractic who operates Murphy Family Chiropractic, Round Rock, Texas, serving the Austin area. With nine years of post-secondary education and numerous certifications in healthcare and nutrition, Dr. Murphy helps patients past acute pain and then guides them into a life of wellness.

Article Source: http://EzineArticles.com/?expert=Dr._Eric_Murphy

Cracking knuckles is not taken seriously by many of us as we have bent out fingers quite often to hear a cracking sound from the knuckles. Medical evidence gathered by researchers who have inserted sound probes in human knuckles have raised a serious concern about this practice. The doctors have gained new insight by studying the ultra sound patterns that are emanated form the knuckle joints when we crack them.

Initially it was thought that the popping sound that we hear while cracking knuckles was due to the escape of harmless gases at the knuckle joints. But these medical researchers have found definite and conclusive evidence of that the cracking sound that we hear is not just from gases that escape from in between the joints but also from the ligaments that are stretched along with the escaping gases. These ligaments are not very flexible and tend to loosen with repeated pulling while we crack our knuckles. Repairing these ligaments is difficult and is resorted to only in cases where the patient cannot grip anything properly.

The habit of cracking knuckles starts with some of us as a demonstrative method of eliminating stress from our knuckle joints after performing strenuous tasks like typing out a long report or finishing a lengthy written examination. How can we avoid this habit? This is more of a behavioral pattern and requires the help of a therapist or support group to eliminate the problem of knuckle cracking.

Identifying the reasons why you go in for cracking knuckles is the first step that you have to take for solving the problem. Once you do this, you can find alternate methods to keep away from this practice. For example, if you are in the habit of cracking knuckles after finishing an exhausting bit of work, you can switch on your preferred music station on the radio to prevent an urge to crack your knuckles.

You could also paste or hang banners in your office or home reminding you of the danger of cracking knuckles. This will serve as an ever-present reminder and help in getting rid of this habit. Maintaining a contact group with others who are trying to avoid the habit of cracking knuckles is a good way of finding innovative solutions to stopping this practice. You could also get the vital emotional support and encouragement that you need to get rid of this habit that can cause serious health concerns if left unchecked.

Attention deficit disorder (ADHD) treatment: ADHD most commonly involves impulsive behavior, the inability to stay focused, and possibly hyperactivity. ADHD can sometimes include mental and behavioral disorders that can keep one from learning or performing well. About 5-10 percent of children in the US are affected, and treatment is 10 times more frequently seen in boys. ADHD treatment can begin between the ages of 4 and 7 years of age and can sometimes go into ones adulthood.

The American Psychiatric Association lists 14 signs of which at least 8 must be present to be officially diagnosed as Attention Deficit Disorder or receive ADHD treatment. The 14 signs of ADHD are:

*Often fidgets with hands or feet (restlessness)

*Has difficulty remaining seated when required to do so

*Easily distracted by extraneous stimuli

*Has difficulty in following instructions

*Has difficulty awaiting turn in games and group activities

*Has difficulty playing quietly

*Often talks excessively

*Often shifts from one uncompleted task to another

*Has difficulty sustaining attention in tasks

*Often interrupts or intrudes on others

*Often loses things necessary for tasks

*Often engages in physically dangerous activities with considering consequences

*Often does not seem to be listening to what is being said

*Often blurts out answers before questions are completed

Conventional ADHD treatment: ADHD treatment usually consists of stimulants such as amphetamines, most commonly in the form of Ritalin. Common side effects of Ritalin according to the Merck Manual may include sleep disturbances, depression or sadness, decreased learning, reduction of growth, behavioral changes, headache, stomachache, suppressed appetite, and elevated blood pressure, not to mention ADHD drugs such as amphetamines can be highly additive drugs.

Natural ADHD Treatment: Pycnogenol an extract from the bark of the French maritime pine, consisting of phenolic acids, catechin, taxifolin and procyanidins, treatment for ADHD with pycnogenol has shown significant reduction of hyperactivity and improvement of concentration in children with ADHD.

Results Show: According to a 4 week randomized, placebo-control double-blind study, sixty-one children with ADHD were supplemented with 1 mg /kg/day of Pycnogenol. After one month of treatment with Pycnogenol, results were superior to that of placebo. In the placebo group no positive effects were found. One month after treatment and termination of Pycnogenol administration a relapse of symptoms was noted. Our results point to an option of ADHD treatment with Pycnogenol as a natural supplement to relieve ADHD symptoms of children. European Child and Adolescent Psychiatry. 2006;15:329-335.

Best Source for Pycnogenol: A natural supplement Isotonix OPC-3 (Oligomeric Proanthocyanidins) is an isotonic-capable food supplement that is made from a combination of bilberry, grape seed, red wine, pine bark extracts and citrus extract bioflavonoids, all found to be potent antioxidants. Isotonix OPC-3 contains the only isotonic form of Pycnogenol in the world.