Human vision and eye

Compound light microscope

A compound light microscope uses two convex lenses with relatively short focal lengths to magnify small objects.

Focus problems

A lot of people have trouble focussing clearly at some time in their lives. It usually happens in the teenage years. It happens as the shape of the eye changes. The change can affect their ability to focus and many need to get glasses that can help them to focus. AS adults age, their flexibility of their lens often decreases which is why it becomes harder to focus on nearby objects.

Refracting telescopes

A telescope has an objective lens and an eyepiece lens. The objective lens in a telescope has a longer focal point than in a microscope.

Forming an image

All the light that enters the eye from the base of an object comes together again in one place at the top of the retina. In the same way, all the light that enters the eye from the top of an object comes together again in one place at the bottom of the retina. Thus, the image is inverted. Our brain interprets the image as upright.

Convex lens

Behind the pupil is a flexible convex lens. The light rays pass through the lens and focus on a screen behind the eye called the retina.

Cone cells

Cone cells are rounder than rod cells. They allow us to detect colour. We have three kinds of cone cells, each possessing a slightly different kind of pigment. Since that we can see all the colour of the rainbow with only red, green and blue, if our brain receives an equal amount of all the three colours then we see the object as white.

Cornea

Covering the pupil and iris is a transparent tissue called the cornea. The cornea is made up of cells that are transparent enough to let light pass through, yet tough enough to hold the eye together.

too close

If the screen is too close,then the light rays do not fully converge by the time they hit the screen. The image will be blurry.

too far

If the screen is too far then the converged light rays will begin to diverge before they strike the screen. The image will be blurry.

Blindness

It can be any vision problem that keeps people from doing important life activities. It happens rarely that a blind person cannot detect any light or whatsoever.

Astigmatism

It is a condition in where your cornea has a distorted shape. A normal cornea is shaped like a soccer ball. A asg eye has an irregularly-shaped cornea. This causes an image to focus on more than one spot on the retina, causing in blurred vision. Eyeglasses, contact lenses and laser surgery can be used to correct this problem. The laser surgery will reshape the cornea.

Far-sighted

It is a condition in which people can see objects that are far away clearly, but cannot focus on nearby objects no matter how hard they try. Light rays from a far object are nearly parallel and require less refraction to converge them than light from a nearby object. The light rays are diverging as they enter the eye. A convex lens is needed for the light rays to come into focus exactly on the retina.

Normal vision.

Light rays are nearly parallel when they enter the eye. The convex lens causes the rays to converge at the retina, producing a sharp image. Light rays from a nearby object are diverging as they enter the eye That is why the muscles in the eye cause the lens to change shape causing the lens to thicken. This gives the lens a greater ability to converge the light rays to form a clear image.

focussing

Light rays begin to get focussed as soon as they pass into the cornea.

Near-sighted

People who can see near objects clearly but not far objects are called near-sighted. It happens as the lens converges the light to form an image in front of the retina. By the time the light rays have actually hit the retina, they have begun to spread out again, causing the person to see a fuzzy image. A concave lens is used to diverge the parallel rays slightly so that the image forms further back on the retina.

Rod cells

Rod cells are longer cylindrical cells. They can absorb almost any colour of light, but they absorb green light really well. Signals from rod cells do not detect colour. They just detect shades of light and dark. This is called out black-and-white vision system and an also detect shapes in low-light conditions.

Sclera

Surrounding the cornea is an opaque tissue called the sclera. We se the sclera as the white region surrounding the iris.

Blind spot

The blind spot is where the optic nerve enters the retina in which there are no light-sensing cells. Each eye sees what the other misses as the blind spots are not in the same spots.

Black and white vision

The cells that absorb the light begin their job once the light rays are focussed on the retina. The cells specialize in two different areas. Some specialize in detecting low levels of light. The other cells detect bright light.

Retina

The retina is a screen where the image is formed. Special light-sensitive cells in the retina detect the image. Other cells in the retina convert the light rays into electrical signals that are sent to the brain through a thick nerve called the optic nerve.

How to bring an object into focus.

The screen that is receiving the image must be the correct distance away from the lens in order for the light rays passing through the lens to form a clear image.

Binoculars

They are two refracting telescopes mounted side by side. They have prisms in them that serve as plane mirrors. The prisms reflect the light back and forth in the short tube.

Extending human vision

We had very limited knowledge about our planet and the universe until we developed tools that have the ability to peer into the tiny world of tiny world of micro-organisms and out into the vast reaches of the outer space. The tools are based on light, mirrors and lenses.

introduction

human eye can focus on objects both near and far. They can also adapt to blazing light and the dimmest of moonlight. We have one vision system to see in colour and another to see in only shades of gray

iris

is the coloured circle of muscle surrounding the pupil. It is the surface of what we are referring to when we talk about someone's eye colour.in dim light he iris expands to get more light In bright light the iris grows smaller to get lesser light.

lens focussing

lens fine-tunes our focus by automatically changing its shape. When certain muscles in the eye contract, there is less tension on the lens, allowing it to become thicker. Thicker lens focusses better on near objects. When you look at distant objects, these muscles relax causing the tension on your lens to increase. The lens become thinner when this happens.

How light enters your eye.(pupil)

light enters your eye through your pupil. Pupil is an opening that appears dark as light passes through it without reflecting back.

cornea focussing

the cornea refracts incoming light rays so that they converge toward the retina. It also does most of the focussing done by our eyes. (lens does remaining focus)

Focussing system

the focussing system involves the cornea, lens and spaces in the eye filled with watery fluid. The fluid between the lens and cornea supports both the cornea and the lens, and provides nutrients to the cornea, which does not have any blood vessels.

Human brain

the human brain can combine and balance the different colour signals that it receives. This is why the white page of a book can appear white to us under varying amounts of sunlight.