Human Eye: Functioning MCQs Quiz | Class 10

Understanding the Human Eye: Structure and Function

The human eye is an incredibly complex and sensitive natural optical instrument that enables us to perceive the world around us. It works much like a camera, capturing light from objects and converting it into electrical signals that our brain interprets as images. Understanding its structure and how it functions, particularly the role of its lens and how images are formed, is crucial for comprehending one of our most vital senses.

Key Parts of the Human Eye and Their Functions

Our eyes are marvels of biological engineering, with each part playing a specific role in the process of vision:

• Cornea: This is the transparent, spherical front part of the eye. It acts as the primary refracting surface, bending light rays as they enter the eye. It also provides protection to the eye’s internal structures.
• Iris: The iris is the colored part of the eye, a muscular diaphragm located behind the cornea. Its primary function is to control the size of the pupil.
• Pupil: The pupil is the small, adjustable opening in the center of the iris. It regulates the amount of light entering the eye. In bright light, the iris contracts the pupil to reduce light entry, while in dim light, it expands to allow more light in.
• Ciliary Muscles: These muscles are attached to the eye lens. They play a vital role in modifying the curvature of the eye lens, thereby changing its focal length.
• Eye Lens: This is a transparent, flexible, biconvex lens situated behind the pupil. Its main function is to focus light rays onto the retina, forming a clear image. Unlike artificial lenses, the eye lens can change its focal length.
• Retina: The retina is the light-sensitive screen at the back of the eyeball. It contains millions of photoreceptor cells (rods and cones) that convert light energy into electrical impulses.
• Optic Nerve: This nerve transmits the electrical signals generated by the retina to the brain. The brain then processes these signals to form the perception of vision.
• Aqueous Humour: A watery fluid filling the space between the cornea and the eye lens. It nourishes the cornea and lens and maintains intraocular pressure.
• Vitreous Humour: A clear, jelly-like substance that fills the large space between the eye lens and the retina, helping to maintain the eye’s shape.

Functioning of the Eye Lens and Image Formation

The human eye lens is a natural convex lens. Its ability to adjust its focal length is known as accommodation. When we look at distant objects, the ciliary muscles relax, making the eye lens thinner and increasing its focal length. When we look at nearby objects, the ciliary muscles contract, making the eye lens thicker and decreasing its focal length, allowing the eye to focus sharply at different distances.

Light rays from an object first pass through the cornea, which performs most of the refraction. The refracted rays then pass through the pupil and are further refracted by the eye lens. Because the eye lens is convex, it converges these light rays to form a real, inverted, and diminished image on the retina. The photoreceptor cells in the retina detect this image and convert the light energy into electrical impulses. These impulses are then transmitted via the optic nerve to the brain. Remarkably, the brain interprets these inverted images as upright, allowing us to see the world correctly.

Major Parts and Their Roles: A Quick Summary

Quick Revision Points

• The human eye acts like a sophisticated camera, with the retina serving as the film or sensor.
• The eye lens is a convex lens, always forming a real, inverted, and diminished image on the retina.
• Accommodation is the unique ability of the eye lens to change its focal length with the help of ciliary muscles.
• The retina contains two types of photoreceptor cells: rods (for dim light and peripheral vision) and cones (for bright light and color vision).
• The brain plays a crucial role in interpreting the inverted retinal image as an upright visual perception.

Extra Practice Questions

1. What is the condition called when the eye lens loses its flexibility and transparency with age, leading to cloudy vision?
   1. Myopia
   2. Hypermetropia
   3. Cataract
   4. Astigmatism
2. Which cells in the retina are primarily responsible for our ability to perceive colors?
   1. Rods
   2. Cones
   3. Ganglion cells
   4. Amacrine cells
3. The space between the cornea and the eye lens is filled with a watery fluid known as:
   1. Vitreous humour
   2. Synovial fluid
   3. Aqueous humour
   4. Cerebrospinal fluid
4. When a normal eye views a very distant object, how do the ciliary muscles and the eye lens change?
   1. Ciliary muscles contract, lens becomes thicker
   2. Ciliary muscles relax, lens becomes thicker
   3. Ciliary muscles contract, lens becomes thinner
   4. Ciliary muscles relax, lens becomes thinner
5. Which part of the eye is often compared to the diaphragm of a camera because it regulates the amount of light entering?
   1. Retina
   2. Lens
   3. Iris
   4. Cornea