The sense of sight may seem very simple but it’s really the most complicated of all the senses. Sight is a complex process that involves various parts of the eye. To understand the workings of the human eye, it’s essential to learn how these parts work to make it possible for humans to see. Let’s begin by looking at the parts of the human eye.
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The Parts of the Human Eye
The eye’s outermost layer, the cornea shields the front of the eye. It is clear and shaped like a dome. The cornea is nourished by tears, and the aqueous humor in the chamber directly behind it. Other than protecting the eye, the cornea also refracts light, making it possible for humans to see. The next part is the iris. It regulates how much light enters the eye. This function can be observed when the pupils dilate in dim light and contract in bright light. The iris is the colored part of the eye. Next, the lens bends the light rays of a particular image. The shape and thickness of the lens is controlled by the ciliary muscle. As the thickness of the lens is related to its power, the ciliary muscle is essential in regulating the eye’s focus.
Located between the retina and the lens, the vitreous humor is a clear gel that helps maintain the round shape of the eye. The retina, an inner lining of the eye, is light sensitive. In the retina, the light of a physical image is transformed into electrical impulses. It has the capacity to change according to the amount of light received. The retina has a yellow spot, a minute area called the macula where the finest details and sharpest images can be seen. The macula is the most used and highly sensitive part of the eye. Finally, there’s the optical nerve which is attached to the retina. The point where the optical nerve and retina meet is called the blind spot as no images can be seen in that place. The optical nerves transmit the images from the retina to the brain, completing the process of sight.
* Parts of the Eye: An overview of the parts with diagrams and images.
* Gross Anatomy of the Eye: Discusses the different parts of the eye.
* Diagram of the Eye: Interactive diagram of the parts of the eye.
* Test: Try this test to see if you can name the parts correctly.
How Do the Eyes Work?
All these parts are involved in refraction: a process that helps people see an image. It happens four times from when the light ray reaches your eye, transmitting it to the brain. When you view an object, the light rays from the object get reflected to your cornea. The cornea, lens, and vitreous humor then bend and refract these light rays, helping to focus on the image. The lens ensures that light rays are clear on the retina. An upside down image is formed on the retina and the light rays are converted to electrical impulses. The cornea then transmits the upside down image to the brain, and while transmitting, flips the image to the original position.
- The Visual System: Interactive activity to learn how eyes work.
- How Your Eyes Work: Describes how the different parts of the eye work to provide vision.
- Sense of Sight: Explains how the eye processes the sense of sight.
- How Does Your Eye Work?: Shows how the eye works with interactive diagram.
Eye Genetics and Eye Color
Eyes can be brown, blue, green, gray or shades of the same. Eye color is determined by genetics. It’s primarily the amount and type of melanin pigment in the iris, the part that can be seen by others. Each person has two sets of genes from the parents. Eye color is determined by a combination of these genes. Pigments on the front and back surface of the iris reflects light in a shade of brown while little or no pigment on the front surface reflects light in a gray or blue shade. The size, shape, and spacing of the stromal cells found in the iris also determine the intensity of blue or green shade in the eyes. Eye color can change as a person grows up.
- Genetics of Human Eye Color: An article about how eye color is related to genetics.
- Eye Color Calculator: Special tool to calculate the color of your children’s eyes.
- Eye Color: Myths about genetics and eye color.
- The Genetics of Eye Color: Overview of the factors that determine eye color.
Eye Exams
Regular eye examinations help detect any eye problems or changes in vision. A series of tests are done by a trained doctor. A routine checkup consists of the Snellan chart which is an exercise involving the reading of letters from a chart on the wall. An examination of the eye through an ophthalmoscope allows the doctor to see inside the eye and observe the retina, blood vessels, and the optic nerve. Eye drops may be given prior to the test. Other tests may be administered as per your requirement.
- Standard Ophthalmic Exam: Provides information on this eye test to check overall health of the eyes.
- Eye Fitness: Take this simple test to see if you need an eye exam right away.
- Eye Tests: A list of tests like the Amsler Grid, AMD Test, Visual Field Grid, and more.
- The Snellan Chart: Provides information on the most well-known eye exam.
Games and Activities about Sight
There are a lot of games and activities involving sight and these games and activities can be used to improve visual perception, tracking, and focusing. Partial pictures, picture puzzles, memory games, and objects in different shapes all help to improve visual perception. Three dimensional picture viewing helps to use both eyes by cross eyed viewing.
- The Blind Spot: An experiment that demonstrates the blind spot.
- Eyesight Challenge: Eqt this food to save your eyesight.
- Optical Illusions: Some activities that help to explain the idea of optical illusion.