The Human Eye

The Human Eye

The human eye is the organ which gives us the sense of sight, allowing us to observe and learn more about the surrounding world than we do with any of the other four senses.  We use our eyes in almost every activity we perform, whether reading, working, watching television, writing a letter, driving a car, and in countless other ways.  Most people probably would agree that sight is the sense they value more than all the rest.

The eye allows us to see and interpret the shapes, colors, and dimensions of objects in the world by processing the light they reflect or emit.  The eye is able to detect bright light or dim light, but it cannot sense objects when light is absent.

Process of vision:

Light waves from an object (such as a tree) enter the eye first through the cornea, which is the clear dome at the front of the eye.  It is like a window that allows light to enter the eye.  The light then progresses through the pupil, the circular opening in the center of the colored iris.

Fluctuations in the intensity of incoming light change the size of the eye’s pupil.  As the light entering the eye becomes brighter, the pupil will constrict (get smaller), due to the pupillary light response.  As the entering light becomes dimmer, the pupil will dilate (get larger).

Initially, the light waves are bent or converged first by the cornea, and then further by the crystalline lens (located immediately behind the iris and the pupil), to a nodal point (N) located immediately behind the back surface of the lens.  At that point, the image becomes reversed (turned backwards) and inverted (turned upside-down).

The light continues through the vitreous humor, the clear gel that makes up about 80% of the eye’s volume, and then, ideally, back to a clear focus on the retina, behind the vitreous.  The small central area of the retina is the macula, which provides the best vision of any location in the retina.  If the eye is considered to be a type of camera (albeit, an extremely complex one), the retina is equivalent to the film inside of the camera, registering the tiny photons of light interacting with it.

Within the layers of the retina, light impulses are changed into electrical signals.  Then they are sent through the optic nerve, along the visual pathway, to the occipital cortex at the posterior (back) of the brain.  Here, the electrical signals are interpreted or “seen” by the brain as a visual image.

Actually, then, we do not “see” with our eyes but, rather, with our brains.  Our eyes merely are the beginning of the visual process.  Watch an 11½-minute film, created in 1941, about the anatomy and physiology of the eye: How the Eye Functions.

Myopia, hyperopia, astigmatism:

If the incoming light from a far away object focuses before it gets to the back of the eye, that eye’s refractive error is called “myopia” (nearsightedness).  If incoming light from something far away has not focused by the time it reaches the back of the eye, that eye’s refractive error is “hyperopia” (farsightedness).
In the case of “astigmatism,” one or more surfaces of the cornea or lens (the eye structures which focus incoming light) are not spherical (shaped like the side of a basketball) but, instead, are cylindrical or toric (shaped a bit like the side of a football).  As a result, there is no distinct point of focus inside the eye but, rather, a smeared or spread-out focus.  Astigmatism is the most common refractive error.

Presbyopia (“after 40” vision):

After age 40, and most noticeably after age 45, the human eye is affected by presbyopia.  This natural condition results in greater difficulty maintaining a clear focus at a near distance with an eye which sees clearly far away.

Presbyopia is caused by a lessening of flexibility of the crystalline lens, as well as to a weakening of the ciliary muscles which control lens focusing.  Both are attributable to the aging process.

An eye can see clearly at a far distance naturally, or it can be made to see clearly artificially, such as with the aid of eyeglasses or contact lenses, or else following a photorefractive procedure such as LASIK (laser-assisted in situ keratomileusis).  Nevertheless, presbyopia eventually will affect the near focusing of every human eye.

Eye growth:

The average newborn’s eyeball is about 18 millimeters in diameter, from front to back (axial length).  In an infant, the eye grows slightly to a length of approximately 19½ millimeters.

The eye continues to grow, gradually, to a length of about 24-25 millimeters, or about 1 inch, in adulthood.  A ping-pong ball is about 1½ inch in diameter, which makes the average adult eyeball about 2/3 the size of a ping-pong ball.

The eyeball is set in a protective cone-shaped cavity in the skull called the “orbit” or “socket.”  This bony orbit also enlarges as the eye grows.

Extraocular muscles:

The orbit is surrounded by layers of soft, fatty tissue.  These layers protect the eye and enable it to turn easily.

Traversing the fatty tissue are three pairs of extraocular muscles, which regulate the motion of each eye: the medial & lateral rectus muscles, the superior & inferior rectus muscles, and the superior & inferior oblique muscles.

Eye structures:

Several structures compose the human eye.  Among the most important anatomical components are the conjunctiva, cornea, crystalline lens, extraocular muscles, iris, macula, optic nerve, retina, and vitreous humor.

Nutrition and Eye Health:

Nutrition is an important aspect of your ability to achieve and maintain proper eye health. Current research is being done to help show that carotenoids play a pivotal role in the health of the human eye. Lutein and zeaxanthin are two major carotenoids, found in the macula of the eye, that are being specifically researched to identify their role in the pathogenesis eye disorders such as age-related macular degeneration and cataracts. Macular degeneration is especially prevalent in the U.S. as it affects roughly 1.75 million Americans each year. It has been discovered that having lower levels of lutein and zeaxanthin within the macula of the eye may be associated with an increase in the risk of age-related macular degeneration. Lutein and zeaxanthin are molecules that act as antioxidants that protect the retina and macula of the eye from oxidative damage from high-energy light waves.As the high-energy light waves enter the eye they excite electrons that can cause harm to the cells in the eye, but before they can cause oxidative damage that may lead to macular degeneration or cataracts lutein and zeaxanthin bind to the electron free radicle and are reduced rendering the electron safe. There are many ways to ensure a diet rich in lutein and zeaxanthin, the best of which is to eat dark green vegetables including kale, spinach, broccoli and turnip greens.

Effects of aging

There are many diseases, disorders, and age-related changes that may affect the eyes and surrounding structures.

As the eye ages, certain changes occur that can be attributed solely to the aging process. Most of these anatomic and physiologic processes follow a gradual decline. With aging, the quality of vision worsens due to reasons independent of diseases of the aging eye. While there are many changes of significance in the non-diseased eye, the most functionally important changes seem to be a reduction in pupil size and the loss of accommodation or focusing capability (presbyopia). The area of the pupil governs the amount of light that can reach the retina. The extent to which the pupil dilates decreases with age, leading to a substantial decrease in light received at the retina. In comparison to younger people, it is as though older persons are constantly wearing medium-density sunglasses. Therefore, for any detailed visually guided tasks on which performance varies with illumination, older persons require extra lighting. Certain ocular diseases can come from sexually transmitted diseases such as herpes and genital warts. If contact between the eye and area of infection occurs, the STD can be transmitted to the eye.

With aging, a prominent white ring develops in the periphery of the cornea called arcus senilis. Aging causes laxity, downward shift of eyelid tissues and atrophy of the orbital fat. These changes contribute to the etiology of several eyelid disorders such as ectropion, entropion, dermatochalasis, and ptosis. The vitreous gel undergoes liquefaction (posterior vitreous detachment or PVD) and its opacities — visible as floaters — gradually increase in number.

Various eye care professionals, including ophthalmologists, optometrists, and opticians, are involved in the treatment and management of ocular and vision disorders. A Snellen chart is one type of eye chart used to measure visual acuity. At the conclusion of a complete eye examination, the eye doctor might provide the patient with an eyeglass prescription for corrective lenses. Some disorders of the eyes for which corrective lenses are prescribed include myopia (near-sightedness) which affects about one-third[citation needed] of the human population, hyperopia (far-sightedness) which affects about one quarter of the population, astigmatism, and presbyopia (the loss of focusing range during aging).

What happens when water is poured into boiling liquid?

What happens when water is poured into boiling liquid?

The whole place blows up and get into fire. This is because water and oil don’t mix and water is more dense than oil. When one pours water into a flaming pan of oil, it wants to sink to the bottom. When it does, it comes in contact with the very hot pan and the oil which is above the boiling point of water. So water instantly vaporizes into steam. 

The instantaneous phase change, from a liquid to a gaseous state, is accompanied by a tremendous expansion. Because the water (now steam) is below the oil, it expands rapidly upward, explosively expelling the flaming oil. It atomizes the oil, in the process, oxygenating it and effectively creating a volcanic blow torch. 

So don't do that in your houses. Every year hundreds of people get admitted in hospital because of this explosion. Check out other stuffs from this blog to Explore Your Knowledge.
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Why is the Sun so hot?

Why Is The Sun Hot?

The Sun is the hottest place in the Solar System. The surface of the Sun is a mere 5,800 

Kelvin, but down at the core of the Sun, the temperatures reach 15 million Kelvin.

The Sun is just a big plasma ball of hydrogen, held together by the mutual gravity of all its mass. This enormous mass pulls inward, trying to compress the Sun down. It’s the same reason why the Earth and the rest of the planets are spheres. 

As the pull of gravity compresses the gas inside the Sun together, it increases the temperature and pressure in the core which results in small, sudden bursts of heat and energy, called nano-flares, responsible for hot temperature of the sun's tenuous atmosphere.

The process where protons are merged together into atoms of helium is called nuclear fusion. It can only happen in hot temperatures, and under incredible pressures. 

But the process of fusion gives off more energy than it uses. So once it gets going, each fusion reaction gives off gamma radiation. It’s the radiation pressure of this light created in the core of the Sun that actually stops it from compressing any more.
Gravity is trying to squeeze it together into a little ball, but this creates the right conditions for fusion and increases its temperature to a greater extent.

Flu Myths

10 Flu Myths

If you've ever had the flu, you know how sick you can be. Chances are good that some of the advice friends and family gave you about avoiding or dealing with the flu was wrong. There seems to be no shortage of misinformation and bad advice when it comes to dealing with the flu.

Here are 10 common myths about the flu:-

1.You can catch the flu from the vaccine.

The vaccine is made from an inactivated virus that can't transmit infection. So people who get sick after receiving a flu vaccination were going to get sick anyway. It takes a week or two to get protection from the vaccine. But people assume that because they got sick after getting the vaccine, the shot caused their illness.

2.Healthy people don't need to be vaccinated.

It's true that the flu vaccination is routinely recommended for people who have a chronic illness. But anyone — even healthy folks — can benefit from being vaccinated. Current guidelines suggest that children ages 6 months to 19 years old, pregnant women, and anyone over age 49 be vaccinated each year. In addition, the flu shot is recommended for healthy people who might spread the virus to others who are particularly susceptible. For this reason, health care workers are routinely advised to get the flu vaccination to protect their patients.

3.Getting the flu vaccination is all you need to do to protect yourself from the flu.

There are a number of steps you can take to protect yourself during flu season besides vaccination. Avoid contact with people who have the flu, wash your hands frequently, and consider taking anti-viral medications if you were exposed to the flu before being vaccinated.

4.The flu is just a bad cold.

Influenza may cause bad cold symptoms. But in the United States alone, 36,000 people die and more than 200,000 are hospitalized each year because of the flu.

5.You can't spread the flu if you're feeling well.

Actually, 20% to 30% of people carrying the influenza virus have no symptoms.

6.You don't need to get a flu shot every year.

The influenza virus changes (mutates) each year. So getting vaccinated each year is important to make sure you have immunity to the strains most likely to cause an outbreak.

7.You can catch the flu from going out in cold weather without a coat, with wet hair or by sitting near a drafty window.

The only way to catch the flu is by being exposed to the influenza virus. Flu season coincides with the cold weather. So people often associate the flu with a cold, drafty environment. But, they are not related.

8.Feed a cold, starve a fever. 

If you have the flu (or a cold) and a fever, you need more fluids. There's little reason to increase or decrease how much you eat. Though you may have no appetite, "starving" yourself will accomplish little. And poor nutrition will not help you get better.

9.Chicken soup will speed your recovery from the flu.

Hot liquids can soothe a sore throat and provide much needed fluids. But chicken soup has no other specific qualities that can help fight the flu.

10.If you have a high fever with the flu that lasts more than a day or two, antibiotics may be necessary.

Antibiotics work well against bacteria, but they aren't effective for a viral infection like the flu. Then again, some people develop a bacterial infection as a complication of the flu, so it may be a good idea to get checked out if your symptoms drag on or worsen.

                      The flu is a good example of how medical myths can get in the way of good medical care. When it's flu season, take the necessary steps to stay healthy. That includes separating fact from myth.

The Sun

The Sun

The Sun or Sol, is the star at the centre of our solar system and is responsible for the Earth’s climate and weather. The Sun is an almost perfect sphere with a difference of just 10km in diameter between the poles and the equator. The average radius of the Sun is 695,508 km (109.2 x that of the Earth) of which 20–25% is the core.

Star Profile

Age: 4.6 Billion Years
Type: Yellow Dwarf (G2V)
Diameter: 1,392,684 km
Circumference at Equator: 4,370,005.6 km
Mass: 1,989,100,000,000,000,000,000 billion kg (333,060 x Earth)
Surface Temperature: 5500 °C

Size Of The Sun

Facts About The Sun

One million Earths could fit inside the Sun:
If a hollow Sun was filled up with spherical Earths then around 960,000 would fit inside. On the other hand if these Earths were squished inside with no wasted space then around 1,300,000 would fit inside. The Suns surface area is 11,990 times that of the Earth’s.

Eventually, the Sun will consume the Earth:
When all the Hydrogen has been burned, the Sun will continue for about 130 million more years, burning Helium, during which time it will expand to the point that it will engulf Mercury and Venus and the Earth. At this stage it will have become a red giant

The Sun will one day be about the size of Earth:
After its red giant phase, the Sun will collapse, retaining its enormous mass, but containing the approximate volume of our planet. When this happens, it will be called a white dwarf.

The Sun contains 99.86% of the mass in the Solar System:
The mass of the Sun is approximately 330,000 times greater than that of Earth. It is almost three quarters Hydrogen, whilst most of the remaining mass is Helium.

The Sun is an almost perfect sphere:
There is only a 10 kilometre difference in its polar diameter compared to its equatorial diameter. Considering the vast expanse of the Sun, this means it is the closest thing to a perfect sphere that has been observed in nature.

Light from the Sun takes eight minutes to reach Earth:
With a mean average distance of 150 million kilometres from Earth and with light travelling at 300,000 kilometres per second, dividing one by the other gives us an approximate time of 500 seconds, or eight minutes and 20 seconds. Although this energy reaches Earth in a few minutes, it will already have taken millions of years to travel from the Sun’s core to its surface.

The Sun travels at 220 kilometres per second:
The Sun is 24,000-26,000 light years from the galactic centre and it takes the Sun 225-250 million years to complete an orbit of the centre of the Milky Way.

The distance from the Sun to Earth changes throughout the year:
Because the Earth travels on an elliptical orbit around the Sun, the distance between the two bodies varies from 147 to 152 million kilometres. The distance between the Earth and the Sun is called an Astronomical Unit (AU).

The Sun is middle-aged:
At around 4.5 billion years old, the Sun has already burned off about half of its store of Hydrogen. It has enough left to continue to burn Hydrogen for approximately another 5 billion years. The Sun is currently a type of star known as a Yellow Dwarf

The Sun has a very strong magnetic field:
Solar flares occur when magnetic energy is released by the Sun during magnetic storms, which we see as sunspots. In sunspots, the magnetic lines are twisted and they spin, much like a tornado would on Earth.

The temperature inside the Sun can reach 15 million degrees Celsius:
At the Sun’s core, energy is generated by nuclear fusion, as Hydrogen converts to Helium. Because hot objects generally expand, the Sun would explode like a giant bomb if it weren’t for its enormous gravitational force.

The Sun generates solar wind:
This is a stream of charged particles, which travels through the Solar System at approximately 450 kilometres per second. Solar wind occurs where the magnetic field of the Sun extends into space instead of following its surface.

Satellites

Name  Distance from Sun  Type
Mercury  57,909,227 km (0.39 AU)          Planet
Venus  108,209,475 km (0.73 AU)         Planet

Earth  149,598,262 km (1 AU)          Planet

Mars  227,943,824 km (1.38 AU)         Planet

Ceres  413,700,000 km (2.77 AU)         Dwarf Planet
Jupiter  778,340,821 km (5.20 AU)         Planet

Saturn  1,426,666,422 km (9.58 AU)         Planet

Uranus  2,870,658,186 km (19.22 AU)         Planet

Neptune  4,498,396,441 km (30.10 AU)         Planet

Pluto  5,874,000,000 km (39.26 AU)         Dwarf Planet

Haumea  6,452,000,000 km (43.13 AU)         Dwarf Planet

Makemake 6,850,000,000 km (45.79 AU)         Dwarf Planet

Eris  10,120,000,000 km (68.01 AU)         Dwarf Planet

About Cold

What is a cold?

A cold is a contagious viral disease that infects the soft lining (mucous membrane) of the nose.

There are more than 100 different viruses that can result in a cold. The characteristic symptom is a runny nose.

Usually, it's a mild condition, with recovery taking place within about a week. But sometimes the same symptoms can be more serious – like influenza.

It's most common during the cold winter months and affects children and adults of all ages. Most people will catch a cold two to four times a year.

How do we catch a cold?

A person's contagious from the day before the illness breaks out, until one to three days after they feel better. The infection is spread by airborne droplets, when the sufferer coughs or sneezes.

It can also be spread by hand, if someone has the virus on their hands and then puts them close to their eyes or nose. This is possibly the most common way of catching a cold.

What are the symptoms of a cold?

A sore throat.

There may be pain on swallowing.

Sneezing.

The nose begins to run, with a water-like secretion that gradually becomes thicker and more yellow.

As the mucous membrane of the nose swells, it may be hard to breathe through the nose.

An aching feeling in the ears.

Headache.

Coughing.

A feeling of being unwell.

A high temperature. Children are more likely to run a temperature than adults.

What can you do to avoid catching a cold?

If possible, stay away from people with colds.

Avoid crowded places, where the risk of infection is greater.

Do not touch your nose or eyes after being in physical contact with somebody that has a cold.

Wash your hands thoroughly, especially after blowing your nose.

Keep rooms well aired.

How does the doctor make a diagnosis?

Consultations with a doctor are unnecessary, unless the cold is severe.

Outlook

Usually a common cold causes no serious trouble, and symptoms will clear up in one to two weeks.

Possible complications include inflammation of the eyes, sinusitis, inflammation of the middle ear, tonsillitis, and pneumonia.

The reason for these complications may be that a bacterium infects the irritated mucous membrane.

How do you treat a cold ?

1.There's no effective way of treating an ordinary cold to make it go away quicker. If the sufferer has no other diseases than the common cold, and it goes away in one to two weeks, there's no reason to see a doctor. Since a cold is caused by a virus, antibiotics are not appropriate.

2.Make sure you drink plenty of non-alcoholic fluids, ideally water – this is especially important for children. Many symptoms can also be soothed by warm drinks.

3.Sleep with the head on a high pillow.

4.There's no need to reduce daily activities. But you should expect to become tired more easily. Children with a cold should be allowed to get plenty of rest.

5.Avoid smoking. It irritates the mucous membrane of the nose further.

6.A blocked nose and chesty cough can be eased by using steam inhalations, which help to loosen mucus. Sit with your head over a bowl of hot water, place a towel over your head, close your eyes and breathe deeply to inhale the steam. This isn't recommended for children because of the risk of scalding.

7.Symptoms such as cough, sore throat, nasal congestion and headache can be relieved by a variety of over-the-counter medicines. Nasal decongestants may ease breathing. You can get advice from a pharmacist about which are most suitable for you and your symptoms.

8.Coughs and colds in children will usually go away on their own in a few days. Over-the-counter cough and cold remedies are no longer recommended for children under six years of age because there's no evidence that they work – and they can potentially cause side-effects, such as allergic reactions, effects on sleep or hallucinations. If your child seems uncomfortable or has a fever, you can give them paracetamol or ibuprofen to relieve pain and lower their temperature. If they have a cough, you can give them a simple soothing cough syrup containing glycerol, honey or lemon. For children over six years of age, other medicines are available from pharmacies – ask your pharmacist for advice. Any medicine should be administered carefully using the spoon or measuring device supplied to ensure the maximum dose is not exceeded.

9.For young babies who are having difficulty feeding due to a stuffy nose, saline nasal drops, available from pharmacies, can be helpful to thin and clear nasal secretions. Vapour rubs and inhalant decongestants, which can be applied to a child’s clothing, can also be used to provide relief from a stuffy nose. You should never apply these directly underneath or inside the child's nose.

10.You should avoid using more than one cough and cold medicine at the same time, particularly when treating children's symptoms. Different medicines may contain the same active ingredient(s), and using more than one may lead to you exceeding the maximum recommended dose(s). Ask your pharmacist for more advice.

11.Throw away paper tissues after use to prevent the spread of infection.