Diagram of the Eye – Lions Eye Institute

The eye – one of the most complex organisms in the human body.

It is made up of many different parts working in unison together. In order for the eye to work at its best, all parts must work well collectively.

To understand the eye and its functions, it’s important to understand how the eye works, see below diagrams for both the external eye and the internal eye.

The External Eye

• Instructions

  Click the parts of the eye to see a description for each. Hover the diagram to zoom.

• Eyelid

  An eyelid is a thin fold of skin that covers and protects the eye.

• Pupil

  The pupil is the opening in the centre of the iris that regulates the amount of light entering the eye. The size of the pupil determines the amount of light that enters.

• Iris

  The iris is the coloured part of the eye which surrounds the pupil. It controls light levels inside the eye, similar to the aperture on a camera. The iris contains tiny muscles that widen and narrow the pupil size. The colour, texture, and pattern of an iris are as unique as a fingerprint.

• Sclera

  The sclera is the white covering that protects the eye, commonly known as ‘the white of the eye’. Part of the sclera can be seen at the front of the eye. It is tough tissue which serves as the eye’s protective outer coat.

The Internal Eye

• Instructions

  Click the parts of the eye to see a description for each. Hover the diagram to zoom.

• Iris

  The iris is the coloured part of the eye which surrounds the pupil. It controls light levels inside the eye, similar to the aperture on a camera. The iris contains tiny muscles that widen and narrow the pupil size. The colour, texture, and pattern of an iris are as unique as a fingerprint.

• Lens

  The lens of the eye is located behind the pupil, its purpose is to focus light onto the retina. The natural lens is clear like glass.

• Pupil

  The pupil is the opening in the centre of the iris that regulates the amount of light entering the eye. The size of the pupil determines the amount of light that enters.

• Cornea

  The cornea is the clear window of the eye and helps focus the light onto the retina. Injury, disease, or hereditary conditions can cause clouding, distortion, or scarring of the cornea, which may all interfere with vision.

• Ciliary Body

  The ciliary body lies just behind the iris and releases a transparent liquid called the aqueous humor within the eye. It also contains the ciliary muscle, which changes the shape of the lens when the eye focuses, this movement is called ‘accommodation’.

• Sclera

  The sclera is the white covering that protects the eye, commonly known as ‘the white of the eye’. Part of the sclera can be seen at the front of the eye. It is tough tissue which serves as the eye’s protective outer coat.

• Vitreous Gel

  Lying between the lens and the retina, the vitreous is a clear jelly-like substance which occupies about two-thirds of the eye. Composed of over 99% water, it also contains collagen fibres and proteins.

• Choroid

  The choroid lies between the retina and sclera. It is composed of layers of blood vessels that supply nutrients to inner parts of the eye.

• Fovea

  The fovea is located in the centre of the macula region of the retina. This tiny area is responsible for sharp central vision essential for reading, driving, and any activity where visual detail is important.

• Macula

  The macula is the centre of the retina. It is a very small area but has a high concentration of light sensitive cells (photoreceptors) that allow us to read and see in fine detail. The detailed vision is known as our central vision. The remaining larger area of the retina is responsible for our peripheral, or side, vision.

• Retina

  The retina is a thin layer of tissue that lines the inside of the back of the eye and is like the film in the back of a camera. When light hits the retina, a picture travels through the optic nerve to the brain.

• Optic Nerve

  The optic nerve is a thick bundle of nerve fibers that connect the back of the eye (retina) to the brain. It transfers all the visual information to the brain which then interprets them as images.

• Iris
• Lens
• Pupil
• Cornea
• Ciliary Body
• Sclera
• Vitreous Gel
• Choroid
• Fovea
• Macula
• Retina
• Optic Nerve

Sensory Structures | BioNinja

Skill:

•  Labelling a diagram of the structure of the human eye

    
The human eye is the sensory organ responsible for vision (sight perception)

• It consists of two fluid-filled cavities separated by a lens (anterior = aqueous humour, posterior = vitreous humour)
• The lens is attached to ciliary muscles, which can contract or relax to change the focus of the lens
• The amount of light that enters the eye via the pupil is controlled by the constriction and dilation of the iris
• The exposed portion of the eye is coated by a transparent layer called the cornea, which is lubricated by conjunctiva
• The internal surface of the eye is composed of three layers – the sclera (outer), choroid (middle) and retina (inner)
• The region of the retina responsible for sharpest vision (i. e. focal point) is the fovea centralis (or fovea for short)
• Nerve signals from the retina are sent via an optic nerve to the brain (no retina in this region creates a visual blind spot)

Diagram of the Human Eye

⇒  Click on the diagram to show / hide labels

Skill:

•  Annotation of a diagram of the retina to show the cell types and the direction in which light moves

    
The retina is the light-sensitive layer of tissue that forms the innermost coat of the internal surface of the eye

• Two types of photoreceptors (rods and cones) convert light stimuli into electrical nerve impulses
• These nerve impulses are transmitted via bipolar cells to ganglion cells, whose fibres from the optic nerve tract
• The photoreceptors line the rear of the retina (adjacent to the choroid), meaning light passes through the other cell layers

Diagram of the Human Retina

Skill:

•  Labelling a diagram of the structure of the human ear

   
The human ear is the sensory organ responsible for hearing (sound perception)

• The external part of the ear is called the pinna, whereas the internal part of the ear is divided into three sections
• The outer ear contains the auditory canal, which channel sound waves to the tympanic membrane (or eardrum)
• The middle ear contains three small bones called the ossicles, which transfer vibrations to the oval window
• The inner ear consists of the cochlea and semicircular canals, as well as a round window which dissipates vibrations
• The cochlear converts sound stimuli into electrical nerve impulses, which are transmitted via the auditory nerve to the brain

Diagram of the Human Ear

⇒  Click on the diagram to show / hide labels

Parts of the Eye

Parts of the Eye

Parts
of the Eye

Here I will briefly describe
various parts of the eye:

Sclera

The sclera
is the white of the eye. “Don’t shoot until you see their scleras.”

• Exterior is smooth
  and white
• Interior is brown and
  grooved
• Extremely durable
• Flexibility adds strength
• Continuous with sheath
  of optic nerve
• Tendons attached to
  it

The
Cornea

The cornea
is the clear bulging surface in front of the eye. It is the main refractive
surface of the eye.

• Primary refractive
  surface of the eye
• Index of refraction:
  n = 1.37
• Normally transparent
  and uniformly thick
• Nearly avascular
• Richly supplied with
  nerve fibers
• Sensitive to foreign
  bodies, cold air, chemical irritation
• Nutrition from aqueous
  humor and
• Tears maintain oxygen
  exchange and water content
• Tears prevent scattering
  and improve optical quality

Anterior
& Posterior Chambers

• The anterior chamber
  is between the cornea and the iris
• The posterior chamber
  is between the iris and the lens
• Contains the aqueous
  humor
• Index of refraction:
  n = 1. 33
• Specific viscosity
  of the aqueous just over 1.0 (like water, hence the name)
• Pressure of 15-18 mm
  of mercury maintains shape of eye and spacing of the elements
• Aqueous humor generated
  from blood plasma
• Renewal requires about
  an hour
• Glaucoma is a result
  of the increased fluid pressure in the eye due to the reduction or blockage
  of aqueous from the anterior to posterior chambers.

Iris/Pupil

• Iris is heavily pigmented
• Sphincter muscle to
  constrict or dilate the pupil
• Pupil is the hole through
  which light passes
• Pupil diameter ranges
  from about 3-7 mm
• Area of 7-38 square
  mm (factor of 5)
• Eye color (brown, green,
  blue, etc.) dependent on amount and distribution of the pigment melanin

Lens

• Transparent body enclosed
  in an elastic capsule
• Made up of proteins
  and water
• Consists of layers,
  like an onion, with firm nucleus, soft cortex
• Gradient refractive
  index (1. 38 – 1.40)
• Young person can change
  shape of the lens via ciliary muscles
• Contraction of muscle
  causes lens to bulge
• At roughly age 50,
  the lens can no longer change shape
• Becomes more yellow
  with age: Cataracts

The graph
on the right shows the optical density (-log transmittance) of the lens as a
function of wavelength. The curves show the change in density with age. More
short wavelength light is blocked at increases ages.

Vitreous
Humor

• Fills the space between
  lens and retina
• Transparent gelatinous
  body
• Specific viscosity
  of 1.8 – 2.0 (jelly-like consistency)
• Index of refraction,
  n=1.33
• Nutrition from retinal
  vessels, ciliary body, aqueous
• Floaters, shadows of
  sloughed off material/debris in the vitreous
• Also maintains eye
  shape

Retina

This next
picture shows a schematic of the cells in the retina:

Speaking
of the optic nerve…

The location
where the optic nerve is bundled and leaves the retina is known as the optic
disk. There are no photoreceptors at the location of the optic disk and
hence there is a blind spot. The scientific term for a blind spot is a scotoma.
So the blind spot due to the optic disk is a natural permanent scotoma in normal
vision. Here is a demonstration of the natural permanent scotoma:

You should
see the “smiley” in the top figure disappear when it falls in your
blind spot. When the gap in the bottom figure falls on the blind spot, the visual
system “fills in” the line. So why don’t we notice the blind spot
in normal vision? For one, we have two eyes and the blind spots are in non-corresponding
locations (they are nasally located (towards the nose) on the retina so the
blind spots are temporal (towards the temple) in the visual field). In addition,
the filling in process makes the blind spot less noticeable especially in a
peripheral area of sight that has less visual acuity (the ability to see detail).

The
Fovea

The fovea
is the location on the retina of central gaze. When you look directly, or fixate,
at a stimulus you the retinal locus of this central fixation is the fovea. There
are only cones in the human fovea (no rods). They are thinner, elongated, any
very tightly packed. Because of this, the fovea is the location of highest visual
acuity and best color vision.

In the diagram
below you can see that the retinal layers are pulled aside (the axons of the
receptors are elongated) leaving a clearer path for the light to reach the receptors.
There is actually a little indentation or pit at the location of the fovea due
to this and it is a clear landmark in the retina during an ophthalmic examination.
The elongated outer segments of the cones (where the photopigment is and where
the transduction occurs) increase the sensitivity by increasing the amount of
photopigment. There is no vasculature in the central fovea.

The
Macula

Covering
the fovea is a pigment called the macula. it is thought that the macula serves
as a protective filter over the foviea that absorbs blue and ultraviolet radiation.
This pigment varies from observer to oberver and is a source of individual variation
in color vision. Usually we do not notice the filtering of the macula but under
special conditions we can notice its presence causing what is known as Maxwell’s
spot.

Here is a
plot of the density of the macula as a function of wavelength:

The
Ophthalmoscope

OK, the ophthalmoscope
is not a part of the eye…

If you want
to see into someone’s eye you have a problem. Your head will block the light
entering the eye. Attributed to Helmholtz, the ophthalmoscope solves this problem
by shining a small beam of light in to the eye. The reflected light is then
available for viewing.

Draw a neat well labelled diagram of a human eye.

Human eye, in humans, specialized sense organ capable of receiving visual images, which are then carried to the brain. cross section of the human eye. A horizontal cross section of the human eye, showing the major parts of the eye, including the protective covering of the cornea over the front of the eye.Made of many working parts, the human eye functions much like a digital camera. … Its job is to convert images into electronic signals and send them to the optic nerve. The optic nerve then transmits these signals to the visual cortex of the brain which creates our sense of sight.

the parts of the eye that make up vision

• Cornea: This is the front layer of your eye. …
• Pupil: The pupil is the black dot in the center of your eye that acts as a gateway for light. …
• Iris: This part is typically referred to as your eye color. …
• Lens: The lens is behind the iris and pupil.

• Parts of the Eye. Here I will briefly describe various parts of the eye:
• Sclera. The sclera is the white of the eye. …
• The Cornea. The cornea is the clear bulging surface in front of the eye. …
• Anterior & Posterior Chambers. The anterior chamber is between the cornea and the iris. …
• Iris/Pupil. …
• Lens. …
• Vitreous Humor. …
• Retina.

When you’re born, your eyes are about 16.5 millimeters in diameter. That’s a bit bigger than a pea. During your first 2 years of life, they get bigger. Then during puberty, they go through another growth spurt.

When light hits the retina (a light-sensitive layer of tissue at the back of the eye), special cells called photoreceptors turn the light into electrical signals. These electrical signals travel from the retina through the optic nerve to the brain. Then the brain turns the signals into the images you see.

Read All

All about the structure of the human eye

13 February 2020

Author: Kate Green

Anatomy of the eye

The human eye is an incredible organ. Made up of many intricate parts working together, the end result is something that almost everyone relies on heavily every single day – our vision. Even though we value our vision the most of all our senses (accounting for 80% of all impressions), a lot of people know surprisingly little about how our eyes work. We can break the eye down into parts that we see externally when looking in the mirror, and parts which aren’t visible because they’re inside the eye, or further towards the back.

Visible parts of the eye

Eyelid: Your eyelid covers your eye to protect it from dust, grit, and perspiration that could cause damage. It opens and closes both voluntarily and involuntarily, and facilitates blinking to help keep the eye hydrated and well-lubricated.

Pupil: The pupil is the part of the eye which we see through, and changes size depending on light levels. If you are in a particularly bright environment, the pupil contracts to let less light in, while if you’re in a darker setting, it will expand to let more light in. This helps us to see well in different light levels, making sure that the correct amount of light reaches the retina at the back of the eye.

Sclera: The sclera is the white part of your eye, providing a protective outer layer. It covers the optic nerve and its can also be a good indication of your eye health. For example, a red sclera might suggest that your eyes and tired or dry, while a yellow-tinted sclera could indicate liver problems.

Iris: The iris is the coloured part of your eye and is what actually controls the size of the pupil. This means that it regulates how much light gets into the eye. This iris is made from connective tissue and muscle surrounding the pupil, and its structure, pattern and colour are just as unique as your fingerprint!

Internal parts of the eye

Cornea: The cornea is the clear surface at the front of your eye, allowing light to enter the eye. It directly covers your iris and pupil, providing a layer of protection. The cornea is what we operate on for laser eye surgery procedures, as it is imperfections in the curve of your cornea that create an eye prescription, requiring you to need glasses. The smoother the surface of your cornea is, the better your vision will be.

Lens: The lens is located behind your iris and is the part of the eye which provides focus. The lens can change shape to alter the focal distance of the eye, focusing light rays that pass through it to hit the retina at the right angle. As you get older, a build-up of protein in the eye can mean that the lens becomes cloudy. This is called a cataract. Thankfully, your lens is easily removable and can be replaced with an artificial clear lens to provide good vision again.

Aqueous humour: The aqueous humour is a watery fluid that your eyes constantly produce in order to maintain good eye pressure and nourish your cornea. This keeps your eyes healthy and, in turn, contributes to good vision. It is drained from the eye at the same rate that it is produced (when this rate isn’t constant, it leads to glaucoma) and its presence is vital for good vision.

Ciliary muscle: The ciliary muscle is the part of the eye that actually changes the shape of the lens, allowing it to focus on different distances. It also holds the lens in the correct position in the eye’s middle layer and regulates the flow of the aqueous humour within the eye.

Medial rectus muscle: There are six extraocular movement muscles in your eye (medial rectus, lateral rectus, superior oblique, superior rectus, inferior rectus, and the inferior oblique) and the medical rectus is the largest of them. It moves the pupil closer to the midline of your body (towards your nose) and makes sure that the eye is aligned correctly. If there are problems with the medial rectus, it can lead to strabismus.

Lateral rectus muscle: This is the muscle which is responsible for lateral – or sideways – movement of the eye, particularly movements away from the midline. Again, if there are issues with the lateral rectus muscle, you may experience esotropia. This is a form of strabismus where the eye turns inwards because the muscle is either too weak, or isn’t working properly to move it away from the midline.

Retina: The retina is a layer of tissue at the back of the eye. The primary purpose of the retina is to receive light from the lens and send signals to the brain to process it into a visual image. The retina contains two types of photoreceptor cells: rods and cones. Rods are responsible for picking up on motion, dark and light, while cones detect colour vision. Problems with the retina can lead to loss of vision, so preserving your retinal health is crucial.

Choroid: This is a major blood vessel which sits between the retina and the sclera at the back of the eye. It nourishes the outer layers of the retina and keeps the eye at the right temperature. It also provides the right amount of oxygen and blood flow to the retina, helping the eye to function well.

Macula: The macula is the central part of your retina and is around 5mm in diameter. A healthy macula means we will have clear vision and be able to see fine details. When the macula becomes diseased, such as with macular degeneration, your central vision is affected. This obviously has a huge impact on your day to day life, and can keep worsening until all vision is lost.

Optic nerve: The optic nerve is the part of your eye which transmits visual signals from the retina to the brain, to be processed into images. It contains over a million nerve fibres and is actually considered to be part of the central nervous system. One of the most common ways the optic nerve can be damaged is by glaucoma. Eye pressure builds up, compressing the optic nerve, meaning visual signals can’t be transmitted effectively anymore.

Vitreous humour: The vitreous humour is a liquid in your eye with the consistency of gel, and sits behind your lens but in front of your retina. If any substances enter the vitreous humour, they are referred to as floaters. They can be small flecks of blood or clusters of cells and, while they can be annoying to see in your line of vision, they are typically harmless. With age, your vitreous thins and can separate from the retina, causing “posterior vitreous detachment”. This causes even more floaters but isn’t sight-threatening.

If you have any questions about your eye health, please don’t hesitate to get in touch with us on 0800 093 110 or by emailing [email protected]. We’ll be able to assess your visual needs at a consultation and recommend a treatment for you, based on your eye health and prescription.

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Labeled Eye Diagram | Science Trends

Photo: (https://commons.wikimedia.org/w/index.php?curid=1597930) By Rhcastilhos. And Jmarchn. – Schematic_diagram_of_the_human_eye_with_English_annotations.svg, CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)

The human eye is composed of many different parts that work together to interpret the world around us. What you want to interpret as a major part of the human eye is somewhat up to the individual, but in general there are seven parts of the human eye: the cornea, the pupil, the iris, the lens, the vitreous humor, the retina, and the sclera.

Let’s take a closer look at each of these components individually.

The Cornea

The cornea is the outermost portion of the eyeball. The responsibility of the cornea is to focus the light that enters our eyes. The cornea is transparent, and it covers the pupil, iris, and anterior chamber. The cornea itself is composed of five different layers, and the function of the outermost layer is to protect the eye from dirt and foreign objects, augmented by tears which keep the eye moist and clean out dirt.

The cornea is one of the most sensitive regions of tissue in the entire body, owing to the fact that it has many, densely connected nerve fibers running through it. The receptors in the cornea could have concentrations somewhere between 300 to 600 times greater than the density of the pain receptors in a patch of skin.

The cornea of the eye is composed of five different layers: the corneal epithelium, Bowman’s layer, the corneal stroma, Descemet’s membrane, and the corneal endothelium. Each of these layers has a function and they work together to transform the light entering the eye as well as protect and support the eye in general.

Photo: (https://pixabay.com/photos/eye-iris-look-focus-green-1132531/) Skitterphoto via Pixabay, Pixabay License (https://pixabay.com/service/license/)

The Iris

The iris is a structure found in the eyes of most mammals, and along with the pupil it controls how much light enters the eye. The iris is comprised of two different layers: the stroma, and the pigmented epithelial cells. The upper layer, the stroma, is linked to muscles that contract and dilate the pupil. The iris is divided into six different layers: the anterior layer, the stroma of iris, the iris sphincter muscle, the iris dilator muscles, the anterior pigment epithelium, and the posterior pigment epithelium. The two muscles found in the eye are what control the dilating and contraction of the pupil.

The rear portion of the iris is filled in with pigmented epithelial cells. The function of the pigment is to prevent light from penetrating the retina, ensuring that the only region where light enters the eye at is the pupil. The pigment of the eye is typically brown, gray, green, hazel, or blue in coloration. Although there are some rare conditions that can make the iris colors like a pinkish-white.

The Pupil

The pupil isn’t really a structure in the traditional sense, although it is still a major component of the eye. There pupil is an opening within the iris that allows light to enter the eye, channeling the light toward the retina of the eye, where it will be collected and converted into electrical signals. The pupil of the eye is usually almost perfectly round and black, and the dark black appearance of the pupil results from the fact that the pupil isn’t reflecting any light back, rather it is absorbing the light. The pupil and the iris work together to control the amount of light that enters the eye. If you want to think about it in terms of a camera lens, the eye’s aperture is the pupil and the iris controls the aperture.

The size of the pupil is affected by small muscles found in the iris. One muscle is responsible for dilating the pupil, while the other muscle is responsible for constricting the pupil. The pupil dilates in conditions of low light to improve vision, while in bright conditions the pupil will constrict, imposing a limit on how much light can enter the eye. The size of a person’s pupil can change with age, with children having larger pupils than adults. A typical adult has a pupil size of roughly 2 to 4 mm undilated and 4 to 8 mm when dilated in the dark.

The Lens

The lens of the eye, much like a camera lens, is what changes the eye’s focal distance, bringing things in and out of focus. The lens of the eye takes the light that has passed through the pupil and bends them in ways that allow the retina to collect clear images of objects. These objects can be located at many different distances, but the lens is able to focus on them all. The lens focuses light with the assistance of the cornea.

The lens is in a biconvex, ellipsoid shape. Biconvex means that the lens is rounded on both halves, or sides, and the fact that its an ellipsoid means that it is a stretched curve, like the shape of an olive. The lens changes shape as it shifts its focus, but in general, the lens is about 4 mm in width front to back and 10 mm across in adults.

The lens is made out of three different parts: the lens fibers, the lens epithelium and the lens capsule. The lens capsule is the outermost layer, and it is a smooth transparent layer that fits over the lens epithelium and fibers. The lens epithelium is found under the capsule and it has the responsibility of stabilizing the lens and creating lens fibers. The lens fibers are the innermost layer of the lens and they are thin, long, transparent fibers that compose most of the lens’ volume.

Photo: (https://commons.wikimedia.org/w/index.php?curid=29025014) By BruceBlaus. When using this image in external sources it can be cited as:Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014”. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. – Own work, CC BY 3.0, (https://creativecommons.org/licenses/by/3.0)

The Vitreous Humor

The vitreous humor is comprised of a clear substance that fills in the area between the back of the eye and the retina. The eye has to process visual data, and because of this the gel-like vitreous humor must be clear enough that light can filter through it. The vitreous humor is an immobile fluid, and it isn’t replenished or regenerated in any way, it is also not served by blood vessels. Substances which enter the humor will stay floating in the gel of the humor, and this causes “floaters” which can interfere with a person’s vision. The vitreous humor tends to thin as people age.

The Retina

The retina is responsible for converting light into electrical signals that will be carried to the brain for processing. The retina uses photoreceptor cells to process the light that comes through the vitreous. The light-sensitive cells pick up both light-intensity and color and transmit these to the brain. The layers of the retina are comprised of neurons joined together by synapses. Two different types of cells capture the vast majority of the light that hits the retina: cones and rods. Cones are cells responsible for interpreting color, and they function only in well-lit environments. In contrast, rods interpret black and white vision, and they function in conditions of dim light.

There are two distinct layers of the retina. These layers are responsible for four different stages of processing: photoreception, the transmission of the received info to bipolar cells, the transmission of the information to the ganglion cells, and transmission of the signal along the optic nerve.

The retina routes the signals it receives through the optic nerve, and when the brain receives these signals it interprets them. Damage to the retina can cause irreversible blindness, as the brain cannot receive visual stimuli.

The Sclera

The sclera us also referred to as the white of the eye, and it is comprised primarily of collagen and elastic fibers. The sclera is an opaque substance that functions to support and protect the rest of the eye, helping maintain the globe shape of the eye and resist both external and internal forces. It is made out of four layers: the episclera, the stroma, the lamina fusca, and the endothelium.

While some animals have a pupil large enough to obscure most of the sclera, humans have pupils that are relatively small in comparison and where the sclera is prominently shown. Because of the fact that this makes determining where an individual is looking simpler, it is possible that the size of the pupil and the sclera evolved as a method of nonverbal communication.

The Occipital Lobe

Photo: (https://commons.wikimedia.org/w/index.php?curid=19131987) By Anatomist90 – Own work, CC BY-SA 3.0, (https://creativecommons.org/licenses/by-sa/3.0)

While not part of the eye, the occipital lobe plays an incredibly important role in our vision. The occipital lobe is found at the back of the brain, and it is the visual processing center of the human brain. The occipital lobe it takes the electrical signals originating from the retina and carried via the optic nerve, and converts these signals into our visual perception of the world. If the occipital love sustains damage, partial or complete blindness can end up happening. The occipital lobe is divided into several different regions, including the primary visual cortex, which is itself subdivided into the dorsal stream, the ventral stream, and the dorsal medial area.

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Structure And Function Of The Eye – Vision

The human eye is an organ that reacts with light and allows light perception, color vision, and depth perception.

The photoreceptive cells of the eye, where transduction of light to nervous impulses occurs, are located in the retina (shown in Figure 1) on the inner surface of the back of the eye. But light does not impinge on the retina unaltered. It passes through other layers that process it so that it can be interpreted by the retina (Figure 1b). The cornea, the front transparent layer of the eye, and the crystalline lens, a transparent convex structure behind the cornea, both refract (bend) light to focus the image on the retina. The iris, which is conspicuous as the colored part of the eye, is a circular muscular ring lying between the lens and cornea that regulates the amount of light entering the eye. In conditions of high ambient light, the iris contracts, reducing the size of the pupil at its center. In conditions of low light, the iris relaxes and the pupil enlarges.

The main function of the lens is to focus light on the retina and fovea centralis. The lens is dynamic, focusing and re-focusing light as the eye rests on near and far objects in the visual field. The lens is operated by muscles that stretch it flat or allow it to thicken, changing the focal length of light coming through it to focus it sharply on the retina. With age comes the loss of the flexibility of the lens, and a form of farsightedness called presbyopia results. Presbyopia occurs because the image focuses behind the retina. Presbyopia is a deficit similar to a different type of farsightedness called hyperopia caused by an eyeball that is too short. For both defects, images in the distance are clear but images nearby are blurry. Myopia (nearsightedness) occurs when an eyeball is elongated and the image focus falls in front of the retina. In this case, images in the distance are blurry but images nearby are clear.

There are two types of photoreceptors in the retina: rods and cones, named for their general appearance as illustrated in Figure 2. Rods are strongly photosensitive and are located in the outer edges of the retina. They detect dim light and are used primarily for peripheral and nighttime vision. Cones are weakly photosensitive and are located near the center of the retina. They respond to bright light, and their primary role is in daytime, color vision.

The fovea is the region in the center back of the eye that is responsible for acute vision. The fovea has a high density of cones. When you bring your gaze to an object to examine it intently in bright light, the eyes orient so that the object’s image falls on the fovea. However, when looking at a star in the night sky or other object in dim light, the object can be better viewed by the peripheral vision because it is the rods at the edges of the retina, rather than the cones at the center, that operate better in low light. In humans, cones far outnumber rods in the fovea.

Practice Questions

Khan Academy 

MCAT Official Prep (AAMC)

Physics Online Flashcards Question 5

Sample Test C/P Section Question 43

Practice Exam 1 C/P Section Passage 6 Question 30

Sample Test B/B Section Passage 7 Question 36

Sample Test B/B Section Passage 7 Question 39

Section Bank P/S Section Question 65

Sample Test P/S Section Passage 9 Question 49

Sample Test P/S Section Question 59

Practice Exam 1 P/S Section Question 11

Practice Exam 2 P/S Section Passage 1 Question 1

Practice Exam 3 P/S Section Question 10

Practice Exam 4 C/P Section Passage 3 Question 12

Key Points

• The cornea and the lens bend light to focus the image on the retina; the iris and pupil regulate the amount of light entering the eye.

• The aqueous humour maintains the convex shape of the cornea; the vitreous humour supports the lens and maintains the shape of the entire eye.

• Presbyopia occurs because the image focuses behind the retina; it is similar to hyperopia (farsightedness), which is caused by an eyeball that is too short.

• Myopia (nearsightedness) occurs when an eyeball is elongated; images in the distance appear blurry, but images nearby are clear.

• Rods are used for peripheral and nighttime vision; cones are used for daytime and color vision.

• The fovea is responsible for acute vision because it has a high density of cones.

Key Terms

Cornea: The transparent layer forming the front of the eye.

Lens: a transparent biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retinaA

Iris: the opaque contractile diaphragm perforated by the pupil and forming the colored portion of the eyeT

Presbyopia: Farsightedness caused by loss of elasticity of the lens of the eye, occurring typically in middle and old age.

Hyperopia: A condition in which visual images come to a focus behind the retina of the eye and vision is better for distant than for near objects.

Myopia: A vision condition in which people can see close objects clearly, but objects farther away appear blurred.

Retina: the thin layer of cells at the back of the eyeball where light is converted into neural signals sent to the brain.

Rod: A rod-shaped cell located in the outer retina of the eye that is extremely sensitive to light.

Cone: A cell located near the center of the retina that is weakly photosensitive and is responsible for color vision in relatively bright light.

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90,000 Why are you better off using pie charts (or not)?

– In a sense, showing a person a pie chart, you can offend his intellectual abilities

K.G. Carsten, “Diagrams and Graphs” (1923)

The first negative attacks towards pie (pie) charts began more than 100 years ago. In 1914, visualization engineer and proponent Willard Brinton published a work entitled Graphical Methods, widely regarded as the first book on properly visualizing data for a wide audience. He was the Edward Taft of his day: a propagandist for the visual exchange of information and a pamphleteer of bad forms.

Much of Brinton’s book warns readers against using pie charts.In the very first chapter, describing the “building blocks,” the author explains:

“The pie chart is probably used much more often than any other form to show the proportions of elements. However, a wedge circle is far from the optimal shape, as it is not nearly as expressive as a bar chart. The disadvantage of the sector representation is the impossibility of placing the parts in such a way that they can be easily compared or summed up. “

Since Brinton wrote these words, many statisticians and visualization experts have opposed pie charts and pushed for a variety of alternatives. Although critics initially appealed to logic in their judgments, over the past 40 years they have found experimental evidence that indicates the inferiority of such diagrams in terms of the accuracy of information transfer.

However, pie charts remain in high demand.Large publishers and media corporations such as The Walt Street Journal and Target Corporation still use them to display their data. In addition, some web resources also use this rather controversial graphical technique.

To understand the problem, let’s go back to its origins and consider the arguments of the proponents and critics of pie charts.

History of origin

The father of modern data visualization is William Playfair.He was born in Scotland in 1759 and led a very fascinating lifestyle. Playfair took part in the capture of the Bastille, contributed to the development of the telegraph and, of course, published the first pie chart. He is also the creator of bar and line charts.

The pie chart is one of the many innovations of the Scottish “rogue” William Playfair

At the turn of the 18th century, the use of illustrations in serious intellectual literature was considered too childish.But, as a free-thinking person, this did not stop Playfair.

In 1801, he published Statistical Breviary, a book on the demographic and economic data of European countries. In this work, which contained the first pie chart, Playfair argued the value of using graphic elements: “Creating a visual image for our eyes while maintaining all proportions and sizes is the most optimal and readable way to express a certain idea.”

The pie chart published on the pages of the Statistical Breviary is shown below. It depicts the shares of the land plots of the Turkish Empire located in Asia, Africa and Europe at that time. This drawing is considered to be the first pie chart, where the idea of ​​the whole was presented in the form of a circle, and color was used to distinguish sectors.

The distribution of the area of ​​the Turkish Empire is the first known pie chart

But how did Playfair come up with such an idea?

Some experts believe that the pie chart owes its origin to circles, which were used to represent concepts in philosophy and mathematics.Playfair’s brother, John, was a respected mathematician and scientist. It is likely that William saw a split circle depicting the constituent parts of a category in one of his works. Mathematicians and philosophers have been using this type of illustration since the 14th century.

An example of using a circle to represent constituent parts in the 14th century

Sector vs Area diagram

The pie chart, however, like other innovations of Playfair, did not become widespread immediately.At the time, William was considered a “crook” and a dishonest businessman, so his ideas were generally ignored.

This continued until the 1850s, when the pie chart found another important supporter – the French engineer Charles Joseph-Minard, who confirmed the effectiveness of this method. Minard was the “pioneer” of statistical charting and, according to many, the creator of the most ingenious data visualization techniques.

A cartographer first and foremost, Minard supplemented his maps with pie charts.In the example below, he depicted in the form of such diagrams the amount of meat supplied to Parisian stores from various regions of France. The size of the circle represents the total amount of meat, and each circle is proportionally divided by the proportions of lamb, veal and beef:

Map created by data visualization pioneer Charles Joseph-Minard in 1858 using pie charts

The invention of the pie chart is sometimes mistakenly credited to the legendary British nurse and public figure Florence Nightingale.In 1858, she distributed the causes of death of British soldiers in the Crimean War by month. Florence used this chart to persuade the UK government to improve sanitation and nutrition in military camps.

Despite the fact that her drawing looks very powerful and convincing, it is actually not a pie chart. This is the so-called polar-area chart, in which the circle is divided into equal parts, but their length depends on the value of the variable:

Florence Nightingale area chart, which is often confused with the pie chart

Criticism in pie chart address

The first hundred years of the pie chart’s history were peaceful times, but the storm was already looming.Brinton’s words, which we quoted at the beginning of the post, are the earliest examples of criticism towards this innovation, but by 1920 there was even more literature in the world strongly condemning this method.

In 1923, the American economist Karl G. Karsten agreed with Brinton’s warning about pie charts. Karsten’s statements in his book Charts and Graphs are remarkably similar to what we hear today:

“The pie chart has many flaws.First, the human eye cannot normally compare the length of the arc of a circle, since the sectors are directed in different directions. Secondly, human vision is not adapted to comparing angles in principle …

Finally, it is impossible to effectively estimate the size of the areas, especially if they are represented as uneven sectors in a circle. There is no way to compare the components of a circular shape as quickly and accurately as parts of a straight line or column. “

However, while such attacks have been on the rise, statistician Walter Crosby Eells noted that many of the criticisms are based “purely on personal preference.”Eells and others decided to test this assumption.

Early research in this area was aimed at figuring out whether the proportions of which divided figure – a circle or a column – people determine more accurately. In a 1927 experiment by Frederick Croxton and Roy Stryker, scientists asked more than 800 subjects to guess the proportions of each component of various segmented shapes:

In this case, the proportions are almost identical.

The researchers calculated the average error of the respondents’ assumptions, but in this experiment and many other experiments, scientists have not been able to find any serious arguments to discredit the pie charts. Proponents of this type of visualization still use the results of research conducted in 1927 to argue their point of view.

However, as scientist Michael Macdonald-Ross pointed out in his extensive review of Circle and Column Confrontation, these initial experiments do not really represent the reality.Despite the fact that the segmented bar was considered the main alternative to the circle at the time, today experts almost always suggest using bar charts or scatter charts.

The main and perhaps most powerful blow to pie charts came in the 1980s, thanks to the efforts of statistician William Cleveland. Cleveland is the author of the groundbreaking book The Elements of Data Graphics, which is widely believed to be the science behind data visualization.His work not only describes the basic “perceptual problems” that are solved when viewing a diagram (for example, judgments about length or area), but also asserts which of them people do best.

In an experiment in 1984, Cleveland and his friend, researcher Robet McGill tested a pie chart. Instead of comparing it to a segmented column, they compared the splitted circle to its true competitor, the histogram :.

In Cleveland’s experiment, the task of perceiving the histogram was to determine the position on the scale, and when viewing pie charts, the angle of the segment. The researchers found that the hypotheses about the heights of the histogram bars were 1.96 times more accurate than the judgments about the angle. Cleveland noted, “Pie charts do not effectively communicate value differences.”

Since then, statistician Naomi Robbins has done research to understand why we are so bad at determining angles.In her book Creating More Effective Graphs, she writes that people tend to underestimate sharp corners and overestimate blunt ones. Robbins also argues that the outward-facing segments of the circle appear larger than those at the top or bottom.

The study reassured ardent opponents of pie charts, including today’s leading data visualization experts, Edward Tuft and Spethen Few.Taft writes: “A spreadsheet is almost always better than a stupid pie chart, and Few adds,“ You can save the pies for dessert ”(pie is English).

In addition, pie charts are constantly mocked by popular media such as the Washington Post and the New York Times:

Pie chart showing the effectiveness of a pie chart

However, this tool also has its defenders.

Pie Chart Defense

According to many users, the main benefit of a pie chart is that all the segments appear to be part of something whole.For example, looking at the graph of the population of a country by age group, the viewer understands that the data presented applies to all people living in that country. This assumption will not be as obvious in the case of histograms.

Some scholars also dispute the empirical literature that sharply criticizes pie charts. Perhaps no person has spent more time searching for arguments in favor of these diagrams than psychologist Ian Spence.In his book No Humble Pie: The Origins and Usage of a Statistical Chart, he actively defends this deprecated visual element.

Spence argues that research into the perception of pie charts is poorly developed. He considers Cleveland’s work to be erroneous, because it asks subjects to compare the sizes of individual segments of a circle, rather than assess the size of the segment in relation to the whole figure. In his opinion, pie charts are more often used for the second purpose.Referring to another 1987 study, Spence states that pie charts and segmented bars are exactly the same in this regard. He writes:

“In my opinion, pie charts were most often criticized by people who wanted to do more than they really could. A pie chart is a simple informational graph and its main purpose is to show the relationship between a segment and a whole shape. “

A 2013 study on human interpretation of pie charts and bars gave pie advocates even more arguments.An experiment conducted by Tufts University used near infrared spectroscopy to measure the psychic energy required when viewing various graphs. The authors found that pie charts are just as accurate and that the average person does not find it more tedious to study them than looking at bar charts.

However, in criticizing this study, Stephen Few argues that the claims made by psychologists are wrong and irresponsible.The experiment tested people’s ability to make hypotheses about separate charts (pie and bar), not the same one. According to Few, in fact, looking at these graphs, the respondents should not have acted that way, so this work does not really matter.

Others believe that a pie chart can be useful when it is rarely used and for aesthetic purposes. Nathan Yau of Flowing Datapoints says that even if the assumptions about the angles in the pie chart are not as accurate as in other cases, it is not very important, because in practice, such assumptions should almost never be made (in particular, when only two or three values ​​are shown in the drawing).Under certain circumstances, it is even better to choose a pie chart, purely for design reasons:

This chart is not very informative in terms of data presentation, but it is beautiful and original (Sky is the sky, Sunny side of pyramid is the sunny side of the pyramid, Shady side of pyramid – the shadow side of the pyramid)

Instead of conclusion

Even after centuries of debate about their usefulness, pie charts have not gone anywhere.Much energy has gone into defending (as well as criticizing) this visual data presentation tool, and scientists have never been able to explain the figure’s attractiveness. Perhaps it has to do with the fact that this is the first type of diagram that people come across in school, or we just love circles. Or maybe we should blame Microsoft for adding pie charts to Excel.

One way or another, as the role of information and digital data in modern life increases, their competent visualization requires more and more attention.Many are already advocating for statistics to become a mandatory discipline for high school students. Who knows, perhaps thanks to the increased use of bar charts and other graphing techniques, pie charts will finally lose their relevance. Or not.

High conversions for you!

Based on materials from: priceonomics.com image source Sandra Eterovic

11/27/2015

Serial Chart — ArcGIS Dashboards | Documentation

A series chart displays one or more series of data points along the horizontal (x) axis and vertical (y) axis.Serial charts can display more than one series of data. The following chart presents two series of data, one showing the number of crimes per day and the other showing a three-day rolling average of the number of crimes. Each series in a serial chart has a type that determines how the data points are rendered.

The following example describes the components of a series chart where the series showing the number of crimes by day is of the bar type and the series showing the three-day moving average of the crimes is of the linear type.

1. Scroll bar – used to control the number of displayed data categories.
2. Text On Hover — Displays additional information about the data point when you hover over it.
3. Gridlines – Improve the readability of the chart. You can control the display of horizontal and vertical grid lines.
4. Guides – Provide context for the data displayed in a chart by presenting goals or thresholds.Guides can be lines that represent a single value, or shaded areas that represent a range of values. Serial charts can have multiple guides.
5. Legend – conveys the meaning of the colors used in the chart. How the data in the chart is configured determines the position of the chart legend.
6. Label – Describes categories and meaning. Labels are generated automatically; but you can overwrite them while customizing the appearance of the chart. For example, when dates are displayed on the category axis, you can customize their display by using date formatting.You can also control the labels on the value axes using unit prefixes or number formatting.
7. Axis Title — Summarizes the types of categories or values ​​shown along the axis. Each axis can have its own title.
8. Axis – One axis in the sequential chart displays the category of each data point, while the other axis displays its numeric value. The category axis can display discrete or continuous values ​​such as dates. In the previous chart, categories are displayed along the horizontal axis and values ​​along the vertical axis.However, you can change this setting. You can display vertical bars horizontally by reorienting the axes so that the horizontal axis displays values ​​and the vertical axis displays categories.

Series Types

Serial charts can be either bar charts, line charts, or smoothed line charts. There is a suitable batch type for different types of data. You can select the type of series from the Series tab.

Column charts

In a bar chart, data points in a series are represented by a rectangle whose height is determined by the numerical values ​​of the points.Columns can be horizontal or vertical, depending on the orientation of the chart. Column charts are best for data with discrete categories, but you can also use them to display data with continuous categories.

Line and anti-aliased line charts

Data with continuous categories such as dates is best for line and anti-aliased line charts.

Line charts and anti-aliased line charts with Date Handling enabled that have missing or blank data points can be configured to connect data points or preserve line breaks.You can turn line and anti-aliased line charts into area charts by increasing their fill opacity on the Series tab.

Multi-Series Charts

There are two ways to create multi-series charts. The method used depends on how the chart is categorized from its data. If the chart categories are based on group values, you can create a multi-series chart by choosing Break by Field. If the chart categories are object-based, you can manually include multiple series in the chart by clicking Add Series.See Data Series for details on how to define the basis for defining chart categories.

When each series in a multi-series chart is of a different type, such as the first chart in this section, it is treated as a combination chart. When all series are of the same type, they can be grouped, stacked or 100% stacked. When you create multi-series charts, a grouped chart is created by default. You can choose to use accumulation in the Series tab.

Prompt:

The axis value of a chart with one or more series can be plotted on a log scale, but not for stacked or 100% stacked series.

Grouped charts

Grouped charts are used to display information about various subgroups of the main categories. A separate column or line represents each of the subgroups, which are displayed in different colors to distinguish them. When setting up a grouped chart, limit the information so that it is easy to understand.

Stacked charts

Stacked charts allow you to stack series without overlapping. A stacked chart is similar to a grouped chart in that it can be used to display information about subgroups from different categories. In a stacked chart, data points representing subgroups are stacked on top of each other (or side-by-side when the chart is displayed horizontally). Different colors are used to indicate the quantitative components of various subgroups.The total is the total size of the category.

100% Stacked Charts

A variation of a Stacked Chart is a 100% Stacked chart. It shows the relative values ​​in each category. The grand total of each column is always 100%, and the length of each subgroup is its distribution relative to the total as a percentage.

Actions

In an interactive panel, a serial chart can be both the source and target of an action. When used as a source, the chart can be configured for single or multiple selection.This determines the number of data points that can be selected at a time. When the diagram is the source of action, it can, for example, move and scale the map, or filter another element of the dashboard. When the chart is the target of an action, such as changing the extent of the map, you can filter the chart so that the displayed data matches the new extent of the map.

Feedback on this section?

90,000 Pie Chart Pie –

Pie Chart is a built-in chart type in Excel.Pie charts are designed to express a part-to-whole relationship where all parts together make up 100%.

Pie charts are best for displaying data with a small number of categories (2-5). A pie chart allows you to add additional categories to a pie chart without making a pie chart that is too difficult to read. When customizing a pie chart, Excel provides an option that moves the n smallest pieces of the pie chart to another smaller pie circle where n can be adjusted according to the data.

Pie charts should be avoided when there are many categories or when the total of the categories is not 100%. The human eye cannot compare the relative sizes of slices in a pie chart, and this problem is compounded by the pie of diversity.

Pluses

• An easy way to handle more categories in a pie chart
• Read “at a glance” in restricted categories
• Excel can automatically calculate and display percentages as data labels

Cons

• Difficult to compare relative slice sizes
• Get cluttered and dense as you add categories
• Limited to data from part to whole
• Shows poorly changes over time

Tips

• Restriction categories
• Avoid all 3D options

Examples of diagrams

Survey Results Favorite Ice Cream Taste Pie charts are one of the simplest types of charts in Excel and are good for showing part-to-whole relationships with data in a small number of categories.