Facts about eyes

  1. How many times do our eyes blink?
  2. When was the first pair of spectacles invented?
  3. Are bats blind?
  4. How powerful are eagle's eyes?
  5. How do we see?
  6. How big is our cornea?
  7. Can UV rays damage our eyes?
  8. What are the basic types of contact lenses?
  9. Is only the lens required to focus an image?
  10. Does diabetes affect eyesight?
  11. What does colour blind mean?
  12. What causes 'red eye' in photos?
  13. What is the difference between an Ophthalmologist, an Optometrist, and an Optician?
  14. Why do we cry when we are cutting onions?

Question 1

How many times do our eyes blink?

The average person blinks about 12 times a minute or about 10,080 blinks in a day.

Question 2

When was the first pair of spectacles invented?

The first documented reference on the use of lenses for optical purposes was made by England's Roger Bacon in 1268. However, evidence has shown that the Chinese were using magnifying glasses as early as the 10th century. Eyeglasses first appeared in Italy in around 1280. In about 1760, Benjamin Franklin invented the first pair of bifocal glasses. But nobody really knows when the first pair of spectacles was invented.

Question 3

Are bats blind?

It has been said that bats are blind. How then do they see where they are going? Although their sense of sight is well developed, bats use sound waves in the process of echolocation to navigate their way. They emit high pitched sound waves and listen for the echoes created when the sound waves bounce off of an object.

Question 4

How powerful are eagle's eyes?

Eagles can see a lot farther than humans. They can see a rabbit about 1 mile away, which is more than 3.5 times of an average human eye.

Question 5

How do we see?

Until around 1000 AD, it was belied that light was emitted by the eyes and that the light somehow formed a picture. People thought that if a hand was put in front of their eyes, there would be no image because the light would be unable to come out. However, around 1020 AD, the Arab scientist Alhazen correctly suggested that the eyes actually take in light rather than emit it. During the following centuries, doctors and scientists studied the eye’s anatomy in detail. They learned that the eye’s lens projects an image onto a living screen called the retina. The eye forms an image much the same way as a camera does. Light travels through the lens and is focused on the retina, which is full of light-sensitive nerve endings. When light strikes these nerves, they transmit signals through the optic nerve to the brain. The retinal image is upside down, but the brain analyzes the signal and turns it right-side up.

Question 6

How big is our cornea?

The cornea, which is the clear covering on the very front of the eye, is about the size and thickness of a dime.

Question 7

Can UV rays damage our eyes?

Yes, excessive exposure without sufficient protection may cause some serious damages to the eyes. These damages include eye surface burns, cataracts, pterygium, and macular degeneration. A good pair of sunglasses can filter out up to 99–100% of the UV light.

Question 8

What are the basic types of contact lenses?

There are two basic types of contact lenses: soft and rigid gas permeable (RGP) lenses.

RGP lenses require a long adaptation period but are relatively inexpensive and allow excellent oxygen flow to the eyes. These lenses are especially useful for children, people with keratoconus, and people with corneal irregularities.

Soft contact lenses are available in many different modalities. In general, these lenses require a short adaptation time but do not offer the same quality of vision available with RGPs. Daily-wear soft contact lenses are designed to be disposed of once a year; they are available both with and without tints. Disposable soft contact lenses are designed to be disposed of daily, bi-weekly, monthly, or even quarterly depending on the lens; these lenses are also available with and without tints. Extended wear lenses are designed for overnight wear; newer soft lens extended wear designs are approved for a month of continuous wear, after which these lenses are to be disposed of.

Question 9

Is only the lens required to focus an image?

The lens only accounts for about 20% of the eye’s focusing power; the other 80% is accomplished by the cornea.

Question 10

Does diabetes affect eyesight?

Diabetes may put you at a greater risk of developing blindness. Uncontrolled diabetes can damage the small blood vessels in the eyes, which can lead to insufficient oxygen and nutrients being delivered to the retina. In the early stages of damage, you may not notice any changes in your vision. These changes in the eye are known as diabetic retinopathy.

Question 11

What does colour blind mean?

Does it mean that you can see only black and white? Well, not really. People who are color blind are usually only colour deficient, which means that they cannot see as many colors as people who have normal vision. People with colour vision deficiencies also mix up colors like red, green, and purple, but all colour deficient people do not mix up the same colors. There are some people who are actually color blind, and only see the world in shades of grey; this condition is very rare.

Question 12

What causes ‘red eye’ in photos?

The red eye effect occurs when pictures are taken using a flash, and occurs especially when the flash is located near the lens of the camera. This phenomenon is caused by light from the flash illuminating the blood vessels of the retina at the back of the eyes.

There are many photo-editing software programs available that have a special function that removes red eyes from a photograph.

Question 13

What is the difference between an Ophthalmologist, an Optometrist, and an Optician?

Opticians are technicians who dispense, adjust, and fit corrective eyewear from a doctor’s prescription. These technicians receive 2 years of training from colleges or technical schools.

Optometrists (O.D.) are primary health care providers whose responsibilities include examining, assessing, and treating diseases and disorders relating to the human visual system. Optometrists prescribe eyeglasses, contact lenses, and in some parts of Canada, medications. Optometrists typically have 3 to 4 years of undergraduate education followed by a 4 year program leading to the Doctor of Optometry degree (O.D.).

Ophthalmologists (M.D. or D.O.) are medical doctors that specialize in diseases of the human visual system. Ophthalmologists are secondary or tertiary health care providers. These doctors prescribe medications and perform eye surgeries.

Question 14

Why do we cry when we are cutting onions?

When an onion is cut, the onion’s cells are sliced open. The gaseous substances released by the cells are made of sulphur compounds. When this gas makes contact with the tears, it is changed into sulphuric acid, which irritates the eyes. The eyes produce more tears in an attempt to both dilute and wash away the irritant.

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