Question

1. What are the main components of an eye’s anatomy?

2. What are all the similarities between the function of an eye and a camera? What are the differences?

3. How does the f-number of the eye change in different lighting conditions?

4. How do the lenses of the eye work (cornea, eye lens)? Which one has more power and why?

5. What is accommodation?

6. How does the eye accommodate with ciliary muscles?

7. How is color perceived on the retina with rods and cones?

8. Where are rods and cones, and where is your blind spot?

9. How does the eye adapt when light levels are lowered? What causes the Purkinje shift?

10. What is farsightedness (myopia) and nearsightedness (hyperopia)?

11. What exactly is happening in myopia and hyperopia to cause the blurred images on the retina (image forms in front of retina vs image forms behind retina)

Answer 1

1.

The eyes are placed in cone-shaped cavities in the skull which are surrounded by muscles and multiple layers of fatty tissue that help to protect the eye and give it flexibility. Eyebrows, eyelashes, and eyelids also contribute to this effort.

The eye is having in general 10 components:.

Cornea The cornea is the outermost layer of the eye and is primarily responsible for focusing the light that comes into our eyes. There are 5 layers to the cornea. The outer layer acts as a kind of shield to the elements and can usually repair itself within a few days of suffering a minor injury. The deeper layers exist mainly to strengthen the eye.

Pupil The pupil is the black circle in the center of the eye, and its primary function is to monitor the amount of light that comes into the eye. When there is a lot of light, the pupil contracts to keep the light from overwhelming the eye. When there is very little light, the pupil expands so it can soak up as much as possible.

Iris The iris is the colored part of the eye. Although it might seem purely cosmetic, the iris actually functions to adjust the size of the pupil. It has muscles that contract or expand depending on the amount of light the pupil needs to process images.

Lens The lens exists behind the pupil and is responsible for allowing your eyes to focus on small details like words in a book. The lens is in a constant state of adjustment as it becomes thinner or thicker to accommodate the detailed input it receives.

Vitreous Humour The vitreous humour is a gel-like substance that helps to keep the eyeball in its proper, circular shape. This is the area in the eye where floaters develop as pieces of the vitreous humor clump together and cast shadows onto the retina.

Retina The retina is the area at the back of the eye that receives the refined, visual message from the front of the eye, and it transmits that visual message to the brain using electrical signals.

Sclera The sclera is the white part of the eye, and its main function is to provide strength, structure, and protection for the eye. The sclera contains blood vessels that can tell an eye doctor a lot about the state of your overall health.

2.

Eye is an organ of sight while a camera is equipment that is used to record images.

The first and the foremost difference between an eye and a camera is that an eye cannot record an image. The eyes use living cells to detect and interpret the light and convert these into electrical signals that are relayed to the brain and processed into an image. The camera on the other hand uses a diaphragm from where the image is recorded on film or like in modern cameras on tape or digitally.

camera sees in 2 dimensions while the eye sees in 3 dimensions. This means that when we see with our eyes we see height, width and depth. With a camera we only see height and width. There is no way to have the depth in the picture as a photograph is a flat medium. This is mainly achieved by the stereoscopic vision of the eye. A simple demonstration of this can be trying to bring the forefingers of both hands to meet from the sides. This is much simpler to do with both eyes open than with only one eye or almost impossible with a camera.

There are many similarities between the human eye and a camera, including:

• a diaphragm to control the amount of light that gets through to the lens. This is the shutter in a camera, and the pupil, at the center of the iris, in the human eye.
• a lens to focus the light and create an image. The image is real and inverted.
• a method of sensing the image. In a camera, film is used to record the image; in the eye, the image is focused on the retina, and a system of rods and cones is the front end of an image-processing system that converts the image to electrical impulses and sends the information along the optic nerve to the brain.
• 3. because of function of pupil
• 4,

  Light rays enter the eye through the cornea, the clear front “window” of the eye. The cornea’s refractive power bends the light rays in such a way that they pass freely through the pupil the opening in the center of the iris through which light enters the eye.

  The iris works like a shutter in a camera. It has the ability to enlarge and shrink, depending on how much light is entering the eye.

  After passing through the iris, the light rays pass thru the eye’s natural crystalline lens. This clear, flexible structure works like the lens in a camera, shortening and lengthening its width in order to focus light rays properly.

  Light rays pass through a dense, transparent gel-like substance, called the vitreous that fills the globe of the eyeball and helps the eye hold its spherical shape.

• 5,Accommodation (Acc) is the process by which the vertebrate eye changes optical power to maintain a clear image or focus on an object as its distance varies.

• 6.When the eye is relaxed and the interior lens is the least rounded, the lens has its maximum focal length for distant viewing . As the muscle tension around the ring of muscle is increased and the supporting fibers are thereby loosened, the interior lens rounds out to its minimum focal length..

• 7.

  The retina contains two types of photoreceptors, rods and cones. The rods are more numerous, some 120 million, and are more sensitive than the cones. However, they are not sensitive to color. The 6 to 7 million cones provide the eye's color sensitivity and they are much more concentrated in the central yellow spot known as the macula. In the center of that region is the " fovea centralis ", a 0.3 mm diameter rod-free area with very thin, densely packed cones.

  The experimental evidence suggests that among the cones there are three different types of color reception. Response curves for the three types of cones have been determined. Since the perception of color depends on the firing of these three types of nerve cells, it follows that visible color can be mapped in terms of three numbers

• 8.The natural blind spot (scotoma) is due to lack of receptors (rods or cones) where the optic nerve and blood vessels leave the eye. There can also be artificial blind spots when something blocks light from reaching the photoreceptors, or when there is local adaptation of the retina as just after seeing a bright light. Blindness is absence of seeing. It may be experienced as blackness, or very differently it may be nothing. The sudden blindness of switching off the light is blackness (and black is a colour); nothingness is lack of visual sensation, as for the world behind one’s head.

• 9.adaptation is the ability of the eye to adjust to various levels of darkness and light.

  The Purkinje effect (sometimes called the Purkinje shift, or dark adaptation and named after the Czech anatomist Jan Evangelista Purkyně) is the tendency for the peak luminance sensitivity of the human eye to shift toward the blue end of the color spectrum at low illumination levels.

  This effect introduces a difference in color contrast under different levels of illumination. For instance, in bright sunlight, geranium flowers appear bright red against the dull green of their leaves, or adjacent blue flowers, but in the same scene viewed at dusk, the contrast is reversed, with the red petals appearing a dark red or black, and the leaves and blue petals appearing relatively bright.

  The sensitivity to light in scotopic vision varies with wavelength, though the perception is essentially black-and-white. The Purkinje shift is the relation between the absorption maximum of rhodopsin, reaching a maximum at about 500 nm, and that of the opsins in the long-wavelength and medium-wavelength cones that dominate in photopic vision, about 555 nm.

• 10. Myopia or nearsightedness means you can see better up close than you can at far distances . Myopia occurs because the eye is larger than average. Since myopia is caused by the eye being longer than average, the light that is focused in the eye lands in front of the retina rather than on the retina.Hyperopia or farsightedness means that you can see better far away than you can close up. However, with higher amounts of hyperopia, you cannot see well either far away or close up! Hyperopia occurs because the eye is smaller than average. Since hyperopia is caused by the eye being smaller than average, the light that is focused in the eye lands behind the retina rather than on the retina

• 11.