What two structures in the eye are responsible for focusing the image on the retina?

To understand how certain problems can affect your child's vision, it’s important to know how normal vision happens. For children with normal vision, the following things happen in this order:

Nội dung chính Show

You are here
Anatomy of the eye
How vision works
What makes up an eye
Our website - share your feedback
Which two parts of the eye are involved in focussing?
Which two structures can focus the image?
What are the 2 sensory cells on the retina?
What focuses the image on the retina?

Light enters the eye through the cornea. This is the clear, dome-shaped surface that covers the front of the eye.

From the cornea, the light passes through the pupil. The iris, or the colored part of your eye, controls the amount of light passing through.

From there, it then hits the lens. This is the clear structure inside the eye that focuses light rays onto the retina.

Next, light passes through the vitreous humor. This is the clear, jelly-like substance that fills the center of the eye. It helps to keep the eye round in shape.

Finally, the light reaches the retina. This is the light-sensitive nerve layer that lines the back of the eye. Here the image is inverted.

The optic nerve is then responsible for carrying the signals to the visual cortex of the brain. The visual cortex turns the signals into images (for example, our vision).

Find out about different parts of the eye.

Basically, the role of the eye is to convert light into electrical signals called nerve impulses that the brain converts into images of our surroundings. Light rays pass through the pupil in the cornea.

Aqueous humour – maintains the pressure in your eye and nourishes the cornea and the lens by supplying amino acids and glucose, as well as vitamin C.

Choroid – a thin layer of blood vessels that nourish the retina and absorb scattered light.

Ciliary muscles – a circular muscle that relaxes or tightens to enable the lens to change shape for focusing.

Cornea – a clear covering on the front of your eye that focuses light entering the eye.

Fovea – a tiny pit in the macula that provides the sharp central vision that you need for activities, such as reading and driving.

Iris – the coloured part of your eye that regulates the amount of light entering.

Lens – the clear part of the eye behind the iris that helps to focus light, or an image, onto the retina.

Macula – the sensitive area in the centre of the retina responsible for what you see ahead of you (central vision).

Optic nerve – a bundle of more than one million nerve fibres that carries visual messages from the retina to the brain.

Pupil – this is the opening in the centre of the iris that lets in light. It is regulated by the iris.

Retina – the light-sensitive tissue lining at the back of your eye that converts light into electrical impulses that are sent along the optical nerve to the brain.

Sclera – also known as the white of your eye, this is the outer layer of the human eye.

Vitreous humour – a clear gel that fills the inside of the eye and helps it to retain its shape.

Tears

Tears have three main components; a watery component, an oily component and mucus. These create a film which covers the white of the eye and the cornea. A problem with any of the three layers may cause dry eye.

Anatomy of the eye

Our eyes might be small, but they provide us with what many people consider to be the most important of our senses – vision.

How vision works

Vision occurs when light enters the eye through the pupil. With help from other important structures in the eye, like the iris and cornea, the appropriate amount of light is directed towards the lens.

Just like a lens in a camera sends a message to produce a film, the lens in the eye 'refracts' (bends) incoming light onto the retina. The retina is made up by millions of specialised cells known as rods and cones, which work together to transform the image into electrical energy, which is sent to the optic disk on the retina and transferred via electrical impulses along the optic nerve to be processed by the brain.

Anatomy of the eye

What makes up an eye

Iris: regulates the amount of light that enters your eye. It forms the coloured, visible part of your eye in front of the lens. Light enters through a central opening called the pupil.
Pupil: the circular opening in the centre of the iris through which light passes into the lens of the eye. The iris controls widening and narrowing (dilation and constriction) of the pupil.
Cornea: the transparent circular part of the front of the eyeball. It refracts the light entering the eye onto the lens, which then focuses it onto the retina. The cornea contains no blood vessels and is extremely sensitive to pain.
Lens: a transparent structure situated behind your pupil. It is enclosed in a thin transparent capsule and helps to refract incoming light and focus it onto the retina. A cataract is when the lens becomes cloudy, and a cataract operation involves the replacement of the cloudy lens with an artificial plastic lens.
Choroid: the middle layer of the eye between the retina and the sclera. It also contains a pigment that absorbs excess light so preventing blurring of vision.
Ciliary body: the part of the eye that connects the choroid to the iris.
Retina: a light sensitive layer that lines the interior of the eye. It is composed of light sensitive cells known as rods and cones. The human eye contains about 125 million rods, which are necessary for seeing in dim light. Cones, on the other hand, function best in bright light. There are between 6 and 7 million cones in the eye and they are essential for receiving a sharp accurate image and for distinguishing colours. The retina works much in the same way as film in a camera.
Macula: a yellow spot on the retina at the back of the eye which surrounds the fovea.
Fovea: forms a small indentation at the centre of the macula and is the area with the greatest concentration of cone cells. When the eye is directed at an object, the part of the image that is focused on the fovea is the image most accurately registered by the brain.
Optic disc: the visible (when the eye is examined) portion of the optic nerve, also found on the retina. The optic disc identifies the start of the optic nerve where messages from cone and rod cells leave the eye via nerve fibres to the optic centre of the brain. This area is also known as the 'blind spot’.
Optic nerve: leaves the eye at the optic disc and transfers all the visual information to the brain.
Sclera: the white part of the eye, a tough covering with which the cornea forms the external protective coat of the eye.
Rod cells are one of the two types of light-sensitive cells in the retina of the eye. There are about 125 million rods, which are necessary for seeing in dim light.
Cone cells are the second type of light sensitive cells in the retina of the eye. The human retina contains between six and seven million cones; they function best in bright light and are essential for acute vision (receiving a sharp accurate image). It is thought that there are three types of cones, each sensitive to the wavelength of a different primary colour – red, green or blue. Other colours are seen as combinations of these primary colours.

We are in the process of redeveloping our website to make it more accessible and relevant for its users. Please share your views with us via a short (five-minute) survey.

Your responses in this survey are completely anonymous. We do not collect any personal or identifiable information within this survey. The responses you provide will be used for the purpose of research in the development of our new website. All the information collected is securely stored and will be removed after our research is concluded. Please complete the survey using the link below.

Moorfields Eye Hospital website user survey

Last updated: 18th August 2022

Which two parts of the eye are involved in focussing?

The cornea and the crystalline lens are both important for the eye to focus light.

Which two structures can focus the image?

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.

What are the 2 sensory cells on the retina?

There are two types of light-sensitive elements in the retina: rods and cones.

What focuses the image on the retina?

The lens is a clear disc-like structure that helps to focus light on the retina. It can do this because it is adjustable, and uses a muscle called the ciliary muscle to change shape and help us focus on objects at different distances.