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Physics of the Eye

Physics of the Eye

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The eye is what allows us to see the world around us. It does this by turning light into electrical signals that our brains can understand. Animals like us have eyes that are placed in the front of our heads. This gives us the ability to see things in 3D. So, how does this all work?

The eye is round and has a jelly-like substance inside called vitreous humor. This is what helps us see things clearly. The front part of the eye, called the cornea, focuses light onto the pupil. The pupil is the black of your eye that can get bigger or depending on much light there. The colored part of your eye, called the iris, controls the size of your pupil. It also gives your eyes their color. Depending on how light reflects off the surface, your eyes can be brown, black, green, blue, or hazel.

Behind the pupil is the lens. This is what projects the light to the back of the eye onto the retina. The retina is where the magic happens. It turns the light into an electrical signal that can be sent to the brain. The optic nerve is what carries this signal to the brain.

It's incredible to think about the Physics of the Eye and how it all comes together to give us our sense of sight. By understanding this, we can appreciate just how complex and amazing our vision really is.

Structure of the eye

There are many types of eyes, subdivided into two categories, compound and non-compound. These have further subcategories:

Detail of the compound eye of a fly

Physics of the eye: The eye as a lens

A lens is an optical device that is used to focus or disperse light rays. It works by bending light rays that pass through it through refraction. The lens is made of a transparent material, such as glass or plastic, and it is typically curved in shape. shape of the lens, it can be classified as either a convex lens or a concave lens. A convex lens is thicker in the middle and thinner at the edges, while a concave lens is thinner in the middle and thicker at the edges.

Convex lenses are used to focus light, while concave lenses are used to disperse light. When light passes through a convex lens, the light rays are bent inward and focused on a single point. This is known as converging light. On the other hand, when light passes through a concave lens, the light rays are bent outward and spread out. This is known as diverging light.

The lens of the eye works in a similar way. It is made up of two curved surfaces, the cornea and the lens, which work together to focus light on the retina. The cornea is a, transparent surface that helps to refract light and focus it on the lens. The lens is a flexible, transparent structure that can change shape to focus light on the retina. When the eye looks at a distant object, the lens flattens, allowing the light to be focused on the retina. When the eye looks at a nearby object, the lens thickens, allowing the light to be focused on the retina.

Physics of the eye: Light and color processing

When we see an object, it's not just about how bright it is, but also its color. To detect these qualities, the retina has two types of photosensitive cells: rod cells and cone cells.

Cone cells are located in the center of the retina and are less sensitive to light than rod cells. There are three types of cone cells that can each detect a different range of the light spectrum. L-cones detect lower wavelengths, so they are associated with blue colors. M-cones detect middle wavelengths, so they are associated with green colors. Finally, S-cones detect small wavelengths, so they are associated with red colors.

Rod cells, on the other hand, are located on the outer edges of the retina. There are twenty times more rods than cones, and they are much more sensitive to light than cones. This is why they are responsible for night vision and peripheral vision. However, they don't detect color. This is why we can't distinguish colors at night.

Understanding how our eyes detect light and color is crucial to appreciating the complexity of our vision.

Spectrum of trichromatic vision, the peaks correspond to the maximum values o sensitivity o the cone cell in the human eye
Spectrum of trichromatic vision, the peaks correspond to the maximum values o sensitivity o the cone cell in the human eye

Physics of the eye: Defects of vision

The eye is a sphere to catch the light from a wide angle, but a spherical lens will alter an image (Figure 5). The inhomogeneous liquid corrects this inside the eye because it has a refractive index higher than the air. This avoids image alterations.

A drop of water alter light after passing through it
A drop of water alter light after passing through it

Sometimes floaters form in this liquid, little clumps of viscous material inside the eye. They often appear within the range of vision but are harmless.

Alterations of the structure can cause defects in vision. For example, myopia occurs when the focus of the eye's lens is in front of the retina instead of on it. These distant objects to be blurry causes. When the focus of the lens is behind the retina, we talk of hypermetropia.

How can we correct defects of vision?

Many things can go wrong with vision. Corrections range from using glasses to surgical operations depending on which part of the eye is compromised or not working properly.

Physics of the eye: Glasses and lenses

When there is an issue with the focus within the eye, such as myopia (ightedness), hyperopia (farsightedness), or astigmatism, it can be corrected with the use of appropriate lenses. These lenses work by modifying the angle of incidence of the light entering the eye to correct the focus.

For example, a person with myopia has an elongated eyeball, which causes light to focus in front of the retina instead of directly on it. To correct this, lenses with a concave shape are used to diverge the light entering the eye, so it can focus correctly on the retina. These lenses effectively change the angle of incidence of the light to focus further away and compensate for the shortened focus of the eye.

Similarly, a person with hyperopia has a shorter eyeball, which causes light to focus behind the retina. To correct this, lenses with a convex shape are used to converge the light entering the eye, so it can focus correctly on the retina.

In the case of astigmatism, the cornea is abnormally shaped, causing light to focus on multiple points on the retina. Corrective lenses are designed to adjust the angle of incidence of the light to compensate for the irregularities in the shape of the cornea, allowing the light to focus on a single point on the retina.

Corrective lenses are a powerful tool in correcting vision and allowing people to see clearly. They work by manipulating the angle of incidence of the light to adjust the focus and compensate for any abnormalities in the shape of the eye.

Correction of hypermetropia. The lens alters the incoming light in a way that the eye's lens focuses on the retina
Correction of hypermetropia. The lens alters the incoming light in a way that the eye's lens focuses on the retina

Key Takeaways:

  • Eyes allow us to perceive images by focusing light onto the retina.
  • The retina contains two types of cells, cones and rods, which are responsible for color vision and night vision, respectively.
  • Cones detect colors but are less sensitive to light, while rods are more sensitive to light but cannot distinguish colors.
  • The eye is spherical, allowing for a wide range of sight, and has an inhomogeneous liquid inside that corrects for refraction.
  • Lenses can be used to correct focus-related sight problems by modifying the angle of light entering the eye to achieve correct incidence on the retina.

Physics of the Eye

What gives my eyes their color?

The stroma of the iris is the part that gives color to the eye. It varies from light brown to black and, in the case of blue, green or hazel eyes, is due to the scattering of light on the stroma.

How many kinds of eyes exist?

There are two main categories of eyes: compound and non-compound, and each of them has several subcategories.

What are those transparent things passing in my visual range?

These are known as floaters. Little clumps of vitreous material can form in the liquid present in the eye, casting shadows on the retina.

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