Mechanism Of Vision
Approximately 80% of our sensory responses from the environment is believed to be perceived through the eyes. This processing of visual perception is estimated to take up one-quarter of a person’s brain. The process of visual perception is an incredibly complex process, and is composed of three main sections:
Optics of the Eye
Detection of Photons and the First Image Processing in the Retina
The processing of the visual cortex of the brain and the transmission of signals
Table of Contents
Structure of the Eye
The eye, although small, is the most complex organ of the human body. It is situated in a bony socket in the skull, with only a small part visible externally. Its wall consists of three layers: the inner layer, the outer layer, and the middle layer.
Innermost Layer:
The retina is located directly behind the eyeball and is the light sensitive part of the eye. It contains many photoreceptors, which are divided into two types: rods and cones. Rods are responsible for black and white vision and allow us to see in the dark. Cones, meanwhile, are responsible for colour vision. The middle choroid provides nourishment to the retina when available.
Middle Layer:
The choroid is composed of black pigmented cells that are abundantly supplied with blood capillaries. This layer makes up the ciliary body and iris.
Outermost Layer:
The sclera, also known as the white, tough layer of tissue that holds the shape of the eyeball, is composed of several connected parts and is primarily responsible for protecting the eye.
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Different Parts of the Eye
The Eye: An Overview
The eye is composed of several structures, which are outlined in the following table:
| Structure | Function |
|---|---|
| Cornea | Transparent outer covering of the eye |
| Iris | Colored part of the eye that regulates the amount of light entering the eye |
| Pupil | Opening in the center of the iris that allows light to pass through |
| Lens | Focuses light onto the retina |
| Retina | Contains cells that sense light and convert it into electrical signals |
| Optic nerve | Carries electrical signals from the retina to the brain |
| Eye Structure | Description |
| Cornea | It is a dome-shaped structure that protects the eye from potential harm. |
| Lens | It is a transparent layer that captures ambient light and focuses it onto the retina after passing through the pupils. |
| Sclera | It forms the outermost part of the eye and is white in appearance. It is responsible for maintaining the shape of the eyeball. |
| Retina | Located at the back of the eye, the retina’s main role is to receive light from the focus and convert it into electrical impulses that are sent to the brain. |
| Pupil | It is seen at the eye’s center. It is like a black dot with a small hole that allows light to pass through. |
| Choroid | Forms the interface between the sclera and the retina, responsible for providing nutrients to other parts of the eye. |
| Macula | A small area near the center of the retina that helps the eye focus on an object. |
| Conjunctiva | The conjunctiva gland is a part of the eye that produces mucus to keep the eye moist. If this gland malfunctions or fails, it can cause severe itching or pain. Additionally, it helps to protect the cornea. |
| Iris | The iris is the part of the eye that determines the color of the eye and surrounds the pupil. It can shrink and widen the pupil based on the intensity of the light entering the eye, widening the pupil when the light is low and vice versa. |
| Optic Nerves | Bundle of nerves carrying impulses to the brain from the retina. |
| Anterior Chamber | Posterior Chamber |
|---|---|
| The front part in the interior of the eye section | The back part in the interior of the eye section |
Physiology of Vision
The visual process involves a series of steps during visual perception. The image of an object is focused on the retina, which then leads to the production of the visual perception of that object.
The physiological events which take place are as follows:
The refraction of light entering the eye
The lens accommodates to focus on the retina of the eye.
Image Convergence
The Photochemical Activity of the Retina and Its Conversion into Neural Impulses
To process in the brain and then perceive
The cornea is the clear front layer of the eye. It is dome-shaped and bends light to help the eye focus. All the parts of the eye work together to enable us to see, beginning with the cornea which allows light to enter the eye.
The pupil opening allows some of the light to pass through the eye. The iris, the coloured part of the eye, controls the amount of light that enters the pupil.
Light passes through the lens, where it is focused by the cornea on the retina. Special cells on the retina, called photoreceptors, convert the light into electrical signals. These signals are then sent to the brain via the optic nerve, which interprets the signals as images we can see.
Frequently Asked Questions
What are the Components of the Visual Pathway?
The visual pathway consists of:
- Optic Nerves
- Retina
- Optic Tracts
- Optic Chiasm
- Optic Radiations
- Visual Cortex
- Lateral Geniculate Bodies
How Does the Physiology of Sight Work?
Light rays from an object are refracted and brought to a focus on the retina, where the image is inverted. Rods and cones of the retina convert the energy in the visual spectrum into electrical impulses, which are then sent to the cerebral cortex through the optic nerve. The cerebral cortex then produces the sensation of vision.
What are the Functions of Rods and Cones?
Rods and cones are the two types of photoreceptor cells in the retina of the eye. Rods are responsible for vision in low light and detecting motion, while cones are responsible for color vision and detailed vision in bright light.
Rods are responsible for dim light vision or night vision or scotopic vision as they are very sensitive to light and have a low threshold. On the other hand, cones have a high threshold for light stimulus and are sensitive only to bright light. Thus, cone cells are the receptors of bright light vision or daylight vision or photopic vision.
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