Human eye and its working - class-VIII

Sclera is the white membrane which lines the eyeball. It is the supporting wall of the eye and acts as a protective coating. It is seen in contrast with the iris.

When the ciliary muscle is relaxed, the choroid acts like a spring pulling on the lens via the zonule fibers causing the lens to become flat. When the ciliary muscle contracts, it stretches the choroid, releasing the tension on the lens and the lens becomes thicker. Cilliary muscles in the eye increase or decrease focal length of eye lens.

Human eye lens are convex in nature and form real and inverted images and when the object is kept before the focus point and the centre of the lens it form virtual and erect images. The image formed on retina are real and inverted and further the message sent by the optic nerve are chemical impulses to the brain, which turn them into erect images that we see with our eyes.

The space between the cornea and the lens is called the aqueous chamber and filled with thin watery transparent viscous fluid called aqueous humor which supplies nutrients to these structures as well as to the lens. Aqueous humour is produced by the ciliary processes in the posterior chamber and flows into the anterior chamber through the pupil.

The iris gives eyes their color, depending on how much melanin it contains, similar to the pigment found in skin. Also helping to determine color is the iris's front layer, or stroma, which contains melanocyte cells that produce melanin, and fibers that scatter the light reflected outward.
Hence, the statement is false.

It is known as persistent of vision which is the time for which an image persists in our retina.

Aqueous humor is low concentration protien liquid in eye lens.

The lens is a transparent structure behind the iris, the coloured part of the eye. The lens bends light rays so that they form a clear image at the back of the eye – on the retina. As the lens is elastic, it can change shape, getting fatter to focus close objects and thinner for distant objects.

The eyelens is adjustable focus double convex lens so that a real image is formed in retina.

Through a process called accommodation, this lens helps the eye automatically focus on near and approaching objects, like an autofocus camera lens. Light focused by the cornea and crystalline lens (and limited by the iris and pupil) then reaches the retina — the light-sensitive inner lining of the back of the eye.

cilliary muscles,contraction and relaxation changes the focal length of eye lens to focus the image of an object at varying distance.

Cone cells, or cones, are one of three types of photoreceptor cells in the retina of mammalian eyes(e.g. the human eye). They are responsible for color vision and function best in relatively bright light.

Human eyeball is spherical in shape. Its diameter is about 2.3 cm

The image formed on retina do not fade away instantaneously but its impression remains on the retina for about $\frac{1}{16}s$, even after removal of the object.

The space between cornea and eye lens is filled with a viscous liquid called aqueous humour and the space between eye lens and retina contains a transparent jelly called vitreous humour.

Nature has provided eyes with eyelids to protect them from any object entering the eyes. It also shut off the light when not required.

The photoreceptors in the octopus retina are located in the inner part of the eye while the cells that carry information to the brain,are in the outer portion of its eye.

Rods and cones are light sensitive cells. Rods respond to different degrees of brightness and darkness. Cones respond mainly to colour of the incident light.

Blind spot position varies in both eyes. Octopus do not have any blind spot.A point in our eyes where no image is formed,that point is known as blind spot.

Light enters the eye through a curved front surface known as cornea. It is transparent in nature.

Retina is the screen of eye. Photo-receptors like rodes and cones are present on retina. So it is sensitive to different colours.

The space between cornea and eye lens is filled with a viscous liquid known as  aqueous humour.

When light enters the eyes, most of the refraction occurs at the outer surface of cornea. It is the whitish part of eye.

Optic nerve carries information from retina to brain.

The light sensitive cells of the retina gets activated with the incidence of light and generates electric signals. The electric signals are sent to the brain by the optic nerve and the brain interprets the electric signals in such a way that we see an image which is erect and of the same size as the object.

In sunlight the size of pupil decreases but in dim light the pupil gets enlarged and thus lets more light into the eye.

The lens of the eye forms a real, inverted image of the object on the inner coat of the eye. The screen of eye is called the retina. It is a delicate membrane having enormous number of light sensitive cells or photo-receptors, i.e rod and cone cells. 

Aqueous humour is present between cornea and eye lens. It keeps the cornea moist and maintains the shape of eye ball.

Vitreous humour is a clear gelatinous gel like fluid that fills the space between the lens and the retina. It helps in maintaining the shape of the retina by holding it in its place.

Aqueous humour is a transparent, gelatinous fluid similar to plasma. It is present between the lens and the cornea. It helps in protection of the eye, provides nutrition to the eye, and allows exchange of gases & other substances between the eye & air. It also helps in maintaining the pressure in the eye. Vitreous humour is also a clear gelatinous gel like fluid that fills the space between the lens and the retina. It helps in maintaining the shape of the retina by holding the retina in its place. The eyeball is approximately spherical in shape with a diameter of about 2.3 cm. The crystalline eye lens provides the finer adjustment of focal length required to focus objects at different distances and forms an inverted real image of the object on the retina.

Vitreous humour is a clear gelatinous gel like fluid that fills the space between the lens and the retina. It helps in maintaining the shape of the retina by holding the retina in its place. The crystalline lens helps in finer adjustments of focal length required to focus objects at different distances and forms an inverted real image of the object on the retina. Aqueous humour is present between the lens and the cornea and helps in maintaining the pressure in the eye

Iris is a dark muscular diaphragm that controls the size of the pupil. It is located behind the cornea.

Aqueous humour is a transparent, gelatinous fluid similar to plasma. It is present between the lens and the cornea. It helps in protection of the eye, provides nutrition to the eye, and allows exchange of gases & other substances between the eye & air. It also helps in maintaining the pressure in the eye.

The eye lens is made up of a fibrous, jelly-like material. Its curvature can be modified to change its focal length to some extent by the ciliary muscles. When the muscles are relaxed, the curvature decreases making the lens thin and the focal length increases. Similarly when the ciliary muscles contract the curvature of the eye lens increases making them thicker, this decreases the focal length of the eye.

Images formed on retina of human eye are real and inverted by the convex nature of lens in eye. 

Persistence of Vision is used in cinematography or movie projectors. Persistence of vision works because the human eye and brain can only process 10 to 12 separate images per second, retaining an image for up to a sixteenth of a second. If a subsequent image replaces it in this period of time it will create the illusion of continuity. Animation works by using an optical illusion. By presenting a sequence of still images in quick enough succession, the viewer interprets them as a continuous moving image. This is the same principle that enables live action film making and projection to work. Film theorists often refer to this illusion of movement as the persistence of vision.

Retina is a part of human eye which act as a screen with photo receptor where image will be formed and signal will be sent to the brain.

The least distance of distinct vision for a normal eye is 25 cm.

Most of the refraction for the light rays entering the eye occurs at the outer surface of the cornea.

True

A. Iris is the muscular diaphragm in the human eye that controls the pupil.

In long sightedness eyes ball's size decrease or focal length of the lens increase due to which image will form behind in the retina.

The iris is the area of the eye that contains the pigment which gives the eye its colour.

In eye light passes through the eye's lens and falls on the retina. The mechanism is same as a convex lens converges parallel beams of light in its focus.

When the light is very bright, then iris makes the pupil contract so that less amount of light enters into the eye.

The ciliary muscle is found in the middle layer of eye.  It is responsible for viewing objects at various distances. It helps to change the shape of the lens within the eye and holds it in position.

Image on the retina remains for 1/20 sec.

Middle vascular coat that darkens the eye chamber and prevents refraction by absorbing the light rays is choroid.

Eye lens is a transparent double-convex lens. Its focal length is adjustable in a manner such that a real image is formed on the retina.

Eye lens contains a watery liquid called the aqueous humour. Its major functions are immunity, nutrition, maintaining spherical shape and maintaining the required refractive index.

Iris controls the amount of the light entering the eyes through the pupil by opening or closing. The iris is the ring of pigmented tissue surrounding the pupil that varies in color.

The eye consists of a screen called retina which generates the sensation of sight. When light rays are focussed on it, an image is formed on the retina. The retina consists of light sensing cells which send signals to the brain, whenever such images are formed.

Using Rayleigh's criterion, the angular resolution is theta = 1.22 * lambda / D. With lambda = 500 nm and D = 3 mm, theta = 1.22 * 500e-9 / 0.003 = 2.03e-4 radians. For a separation of 1 mm (0.001 m), the distance L = 0.001 / 2.03e-4, which is approximately 4.92 meters, rounding to 5 meters.

Reading words from a book involves light reflecting off the surface in many directions so that it can be seen from various angles. This scattering of light is known as diffused reflection.

Image formation, such as in a mirror or through a lens, relies on the regular, predictable reflection or refraction of light rays. This is characteristic of specular reflection.

Focal length of normal eye lens is equal to the distance between eye-lens and retina i.e, $x$  so that all rays converges on retina after passing through  eye-lens

The persistence of vision is the phenomenon where an image remains on the retina for a fraction of a second after the stimulus is removed, typically cited as 1/16th of a second.

Refraction of light in the human eye occurs primarily at the cornea, which provides most of the eye's refractive power, and is further adjusted by the crystalline lens.

Human eye cannot differentiate two images when the interval of separation between them is less than one-tenth of a second

Correct answer is (D)

Iris is the ring of pigmented tissue surrounding the pupil that varies in color from person to person, it contract and dilates to control the amount of light entering the eye through the pupil. The pupil is the opening in the center of the iris where light enters the eye. 

According to Persistence of Vision theory, the
human eye has the illusion of an after image still persisting. It is when our
eye has the ability to persist for 1/16 of a second after the image has removed.
It is used in animation to show fluent movement, normally after every two
frames one picture would be shown, so for every 24 frames 12 pictures will be
shown. This gives us the illusion of movement and the afterimage persists on
our retina. 

There are several advantages of our having two eyes instead of one.
(i) It gives a wider field view because human being has a horizontal field view of about 150∘150∘ with one eye and of about 180∘180∘with two eyes.
(ii) The ability to detect faint objects is enhanced with two detectors instead of one.
(iii) With one eye, the world looks flat, i.e., two dimensional-only. With two eyes, the view is three dimensional.
As our two eyes are separated by a few centimeters each eye observes a slightly different image. Our brain combines the two views into one and we get to know how close or far away the things observed are.

Correct answer ( B )

Circular aperture through which light enters the eye is known as pupil.It is the black circle in the center of the iris, when the light reaches the tissues at the back of the eye, it is absorbed making the pupil look black. The pupil controls the amount of light that enters the eye.

The ciliary muscle is located in the eye and surrounds the lens. It contracts or relaxes in order for an individual to see at multiple distances. When it contracts, it pulls forward, moving to a frontal portion to relax the fibers that hold the lens in place; this process also allows it to take on a more spherical shape to provide short range focus.

Eye lens refract the light and form image on retina of eye .

At the junction from where optic nerve enters eye, there are no cone or rod cells to sense the image , and hence no vision is possible at that spot.Hence, it is called blind spot.

Iris are the muscles that control the size of pupil to enable right amount of light to enter the eye.

Refraction of light in the eye occurs at both the cornea and the lens.

The lens system of the human eye acts as a convex lens, which forms a real and inverted image on the retina. The brain then interprets this image as upright.

Cornea is protective layer,it is transparent in nature. 

Size of the object perceived by an eye depends primarily on distance of object from eye or eye lens. As magnification is given by:

Answer is B.
Our eye lenses are convex lenses with variable focal lengths. The focal length of the eye lens is controlled by muscles according to the distance of the object from us that we are trying to see. The lens is flexible and when it is acted on by the ciliary muscle around it, the lens can be "flattened" to change the focus, or, when the muscle is relaxed, the lens can be assumed as having a more spherical shape. This is the principle of the eye to focus on objects nearer or farther away.

Laser surgery around retinal tear is often able to weld the retina to the underlying eyewall. This can prevented or limit retinal detachment.