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Q1. What is the name of the transparent front part of the eye that protects it and allows light to enter?
The cornea is the transparent, dome-shaped front part of the eye. It protects the eye from dust, germs, and other harmful substances. It also helps to focus light as it enters the eye by refracting (bending) it. The cornea is avascular (has no blood vessels) and gets oxygen directly from the air, which keeps it clear for vision.
Q2. Which part of the eye controls the amount of light entering through the pupil?
The iris is the coloured part of the eye (blue, brown, green, etc.) that controls the amount of light entering the eye. It acts like a diaphragm in a camera. In bright light, the iris muscles contract the pupil (makes it smaller) to reduce the amount of light entering. In dim light, the iris muscles relax, making the pupil larger to allow more light in.
Q3. Where is the image formed in a human eye?
The image is formed on the retina, which is the light-sensitive layer at the back of the eye. The retina contains millions of photoreceptor cells (rods and cones) that detect light and convert it into electrical signals. These signals are then sent to the brain through the optic nerve. The image formed on the retina is real, inverted, and diminished.
Q4. What is the function of the eye lens?
The eye lens is a transparent, flexible, biconvex structure located just behind the iris. Its main function is to focus light rays onto the retina. The lens changes its shape (with the help of ciliary muscles) to focus light from objects at different distances. This ability to change shape is called accommodation.
Q5. The ability of the eye lens to change its focal length is called?
The power of accommodation is the ability of the eye lens to change its focal length to focus on objects at different distances. When we look at nearby objects, the ciliary muscles contract, making the lens thicker (increased curvature, shorter focal length). When we look at distant objects, the ciliary muscles relax, making the lens thinner (decreased curvature, longer focal length).
Q6. Which muscles are responsible for changing the shape of the eye lens?
The ciliary muscles are ring-shaped muscles attached to the eye lens by suspensory ligaments. When these muscles contract, they release tension on the lens, allowing it to become thicker and more curved (for near vision). When they relax, they pull on the suspensory ligaments, making the lens thinner and flatter (for distant vision). This changes the focal length of the lens.
Q7. For a normal adult eye, what is the approximate least distance of distinct vision?
The least distance of distinct vision (also called the near point) for a normal adult eye is about 25 cm. This is the closest distance at which the eye can see an object clearly without straining. At distances less than 25 cm, the eye cannot focus the image properly, and the object appears blurred. For children, the near point is smaller (about 15-20 cm), and for elderly people, it increases.
Q8. When we look at a distant object, what happens to the ciliary muscles and the lens?
When we look at a distant object, the ciliary muscles relax. This relaxation pulls on the suspensory ligaments, which stretch the lens and make it thinner and flatter. A thinner lens has less curvature, so it has a longer focal length. This allows the eye to focus the parallel rays from distant objects exactly on the retina.
Q9. A major advantage of having two eyes instead of one is better?
Having two eyes gives us binocular vision, which allows us to judge distance and depth accurately. Each eye sees the same object from a slightly different angle. The brain combines these two slightly different images to create a three-dimensional (3D) perception of the world. This depth perception helps us judge distances, catch objects, and navigate our surroundings safely.
Q10. Having two eyes also increases the?
Having two eyes increases the field of view. With one eye, we can see about 150° of our surroundings. With two eyes, the field of view increases to about 180° (slightly less, but significantly more than one eye). This wider field of view helps us detect objects and movements more effectively, which is important for safety and survival.
Q11. Which common eye defect is also known as nearsightedness?
Myopia is also called nearsightedness because a person with this defect can see nearby objects clearly but cannot see distant objects clearly. This happens because the image of distant objects is formed in front of the retina instead of on it. Myopia is usually caused by an elongated eyeball or excessive curvature of the cornea/lens.
Q12. What is the main cause of myopia?
Myopia occurs when the eyeball is too long (elongated) or when the cornea/lens has too much curvature. In both cases, light rays converge too quickly, and the image of distant objects is formed in front of the retina. This makes distant objects appear blurry. Myopia can be hereditary or develop due to excessive near work (like reading or screen time) during childhood.
Q13. What type of lens is used to correct myopia?
Myopia is corrected using concave lenses. A concave lens diverges (spreads out) light rays before they enter the eye. This reduces the converging power of the eye, moving the focus of distant objects back onto the retina. Concave lenses have negative power (e.g., -2.0 D). The stronger the myopia, the more negative the lens power required.
Q14. Which common eye defect is also known as farsightedness?
Hypermetropia is also called farsightedness because a person with this defect can see distant objects clearly but cannot see nearby objects clearly. This happens because the image of nearby objects is formed behind the retina instead of on it. Hypermetropia is usually caused by a shortened eyeball or a flattened lens/cornea with insufficient curvature.
Q15. What is the main cause of hypermetropia?
Hypermetropia occurs when the eyeball is too short (shortened) or when the eye lens is too flat (has insufficient curvature). In both cases, light rays are not converged enough, and the image of nearby objects is formed behind the retina. This makes nearby objects appear blurry. Hypermetropia is often present from birth and may also develop with age.
Q16. What type of lens is used to correct hypermetropia?
Hypermetropia is corrected using convex lenses. A convex lens converges (brings together) light rays before they enter the eye. This increases the converging power of the eye, moving the focus of nearby objects forward onto the retina. Convex lenses have positive power (e.g., +2.0 D). The stronger the hypermetropia, the more positive the lens power required.
Q17. The age-related defect where the eye gradually loses its power of accommodation is called?
Presbyopia is an age-related eye defect where the eye gradually loses its power of accommodation. As we age, the eye lens becomes harder and less flexible, and the ciliary muscles become weaker. This makes it difficult to focus on nearby objects. Presbyopia typically begins around the age of 40 and affects almost everyone as they get older. It is not a disease but a natural part of aging.
Q18. How is presbyopia commonly corrected?
Presbyopia is commonly corrected using bifocal lenses. A bifocal lens has two parts: the upper part is a concave or convex lens for distant vision (depending on the person’s other defects), and the lower part is a convex lens for near vision (reading). This allows the person to see both distant and nearby objects clearly. Progressive lenses (no visible line) are also used as a more modern alternative.
Q19. What is the name of the phenomenon where white light splits into its component colours?
Dispersion is the phenomenon where white light splits into its component colours (VIBGYOR) when it passes through a transparent medium like a prism. This happens because different colours (wavelengths) of light travel at different speeds in the medium, so they refract (bend) by different amounts. Violet light bends the most, and red light bends the least. Dispersion is responsible for the formation of rainbows.
Q20. Which optical element is typically used to demonstrate dispersion?
A glass prism is typically used to demonstrate the dispersion of light. When white light passes through a prism, it bends (refracts) and splits into its seven constituent colours (VIBGYOR). The prism has two non-parallel faces, which causes different colours to bend by different amounts and emerge separately. A rectangular glass slab does not cause dispersion because its faces are parallel.
Q21. When white light passes through a prism, which colour deviates the least?
Red light deviates (bends) the least when passing through a prism. This is because red light has the longest wavelength (about 700 nm) and travels fastest in glass, so it is refracted the least. Violet light, with the shortest wavelength (about 400 nm), travels slowest in glass and is refracted the most. This difference in deviation causes the dispersion of white light into its component colours.
Q22. When white light passes through a prism, which colour deviates the most?
Violet light deviates (bends) the most when passing through a prism. This is because violet light has the shortest wavelength (about 400 nm) and travels slowest in glass, so it is refracted the most. Red light, with the longest wavelength (about 700 nm), deviates the least. The sequence of deviation from most to least is: Violet > Indigo > Blue > Green > Yellow > Orange > Red.
Q23. The band of colours obtained after dispersion of white light is called a?
The band of colours obtained after the dispersion of white light is called a spectrum. The spectrum consists of seven colours: Violet, Indigo, Blue, Green, Yellow, Orange, and Red (VIBGYOR). This is also called the visible spectrum. A rainbow is a natural spectrum formed by the dispersion of sunlight through raindrops in the atmosphere.
Q24. What happens when the ciliary muscles contract?
When the ciliary muscles contract, the suspensory ligaments become loose, and the eye lens becomes thicker and more curved (more convex). This increases the converging power of the lens (shorter focal length), allowing the eye to focus on nearby objects. This is how accommodation works for near vision. When we look at distant objects, the ciliary muscles relax, making the lens thinner.
Q25. What is the role of the optic nerve?
The optic nerve is a bundle of nerve fibres that carries electrical signals from the photoreceptor cells in the retina to the brain. The retina converts light into electrical signals, and the optic nerve transmits these signals to the brain’s visual cortex. The brain then interprets these signals as the images we see. There are no photoreceptor cells where the optic nerve leaves the eye, creating a “blind spot.”
Q26. The small, central area of the retina with the sharpest vision is called the?
The fovea (also called the yellow spot) is a small, central area of the retina that has the highest concentration of cone cells (colour-sensitive photoreceptors). This is the area where vision is sharpest and most detailed. When we look directly at an object, the light is focused onto the fovea, allowing us to see fine details clearly. The fovea has no rod cells and is responsible for our central vision.
Q27. The point where the optic nerve leaves the eye is called the? It has no photoreceptor cells.
The blind spot is the point on the retina where the optic nerve leaves the eye. There are no photoreceptor cells (rods or cones) at this point, so it cannot detect light. Any image that falls on this spot is not perceived by the brain. However, we are usually not aware of our blind spots because the brain fills in the missing information using signals from the other eye or from surrounding areas of the retina.
Q28. What are the photoreceptor cells sensitive to dim light called?
Rods are photoreceptor cells in the retina that are highly sensitive to dim light. They are responsible for vision in low-light conditions (night vision). Rods are more numerous than cones and are spread throughout the retina, except at the fovea. However, rods cannot distinguish colours—they only detect shades of grey. This is why we cannot see colours clearly in dim light.
Q29. What are the photoreceptor cells responsible for colour vision called?
Cones are photoreceptor cells in the retina that are responsible for colour vision and sharp detailed vision. They function best in bright light and are concentrated in the fovea (central area of the retina). There are three types of cones, each sensitive to a different wavelength of light (red, green, and blue). The combination of signals from these three types allows us to see a wide range of colours.
Q30. The persistence of an image on the retina for about 1/16th of a second after removal of the object is called?
Persistence of vision is the phenomenon where an image continues to remain on the retina for about 1/16th of a second (0.0625 seconds) after the object is removed. This is why we do not notice the blank intervals between frames in a movie or animation. The brain retains each image for a fraction of a second, creating the illusion of continuous motion. This principle is used in cinematography and animation.
Q31. In a myopic eye, the image of a distant object is formed:
In a myopic eye, the image of a distant object is formed in front of the retina. This happens because the eyeball is too long or the lens/cornea is too curved, causing light rays to converge too quickly. As a result, the image is blurry by the time it reaches the retina. To correct this, a concave lens is used to diverge the light rays slightly, moving the focus back onto the retina.
Q32. The far point of a myopic eye is:
The far point of a myopic eye is closer than infinity. For a normal eye, the far point is at infinity, meaning it can see objects at any distance clearly. But for a myopic eye, the far point is at a finite distance—beyond this point, objects appear blurry. The more severe the myopia, the closer the far point. For example, a person with -5 D myopia can only see objects clearly up to about 20 cm.
Q33. In a hypermetropic eye, the image of a nearby object is formed:
In a hypermetropic eye, the image of a nearby object is formed behind the retina. This happens because the eyeball is too short or the lens is too flat, causing light rays to converge too slowly. As a result, the image is not formed in time to hit the retina, making nearby objects appear blurry. To correct this, a convex lens is used to converge light rays more, moving the focus forward onto the retina.
Q34. The near point of a hypermetropic eye is:
The near point of a hypermetropic eye is more than 25 cm away. For a normal eye, the near point is at 25 cm. In hypermetropia, the eye cannot focus on objects at the normal near point, so objects must be placed farther away to be seen clearly. The person has to hold reading material farther away to see it clearly. The more severe the hypermetropia, the farther away the near point.
Q35. The power of a lens is measured in units called:
The power of a lens is measured in dioptres (D). The power of a lens is defined as the reciprocal of its focal length in meters: P = 1/f. One dioptre is the power of a lens with a focal length of 1 meter. A convex lens has positive power, and a concave lens has negative power. For example, a lens with a focal length of +0.5 m has a power of +2.0 D.
Q36. A concave lens has a power that is:
A concave lens has negative power because its focal length is negative (by sign convention). The power of a lens is P = 1/f, and since f is negative for a concave lens, the power is also negative. Negative power indicates that the lens diverges (spreads out) light rays. Myopia is corrected using concave lenses, so prescriptions for myopia have negative values (e.g., -2.5 D).
Q37. A convex lens has a power that is:
A convex lens has positive power because its focal length is positive (by sign convention). The power of a lens is P = 1/f, and since f is positive for a convex lens, the power is also positive. Positive power indicates that the lens converges (brings together) light rays. Hypermetropia and presbyopia are corrected using convex lenses, so prescriptions for these have positive values (e.g., +2.0 D).
Q38. What is the white, tough outer layer of the eyeball called?
The sclera is the white, tough, fibrous outer layer of the eyeball. It provides structural support and protection to the eye. The sclera is what we commonly call the “white of the eye.” It is continuous with the cornea at the front of the eye. The sclera is made of collagen fibres and is very strong, helping to maintain the shape of the eyeball and protect it from injury.
Q39. The middle layer of the eye, which contains blood vessels, is called the:
The choroid is the middle layer of the eye, located between the sclera and the retina. It contains many blood vessels that supply oxygen and nutrients to the retina. The choroid is also darkly pigmented (contains melanin), which helps absorb scattered light inside the eye, preventing internal reflections that could blur vision. It also helps regulate the temperature of the eye.
Q40. The splitting of white light into colours occurs because different colours have different:
White light splits into its component colours (dispersion) because different colours (wavelengths) of light travel at different speeds in a medium like glass. Violet light travels slower in glass than red light, so it bends (refracts) more. This difference in speed causes the different colours to emerge at different angles, creating a spectrum. The intensity and source of light do not cause dispersion.
Q41. A person uses spectacles with concave lenses. What is the defect of vision?
If a person uses spectacles with concave lenses, they have myopia (nearsightedness). Concave lenses are used to correct myopia because they diverge light rays, moving the focus of distant objects onto the retina. Concave lenses have negative power (e.g., -3.0 D). People with myopia can see nearby objects clearly but have difficulty seeing distant objects.
Q42. A person uses spectacles with convex lenses. What could be the defect of vision?
If a person uses spectacles with convex lenses, they could have hypermetropia (farsightedness) or presbyopia (age-related loss of accommodation). Convex lenses converge light rays, helping the eye focus on nearby objects. For hypermetropia, the lenses are needed for all distances. For presbyopia, bifocal lenses are often used, with the lower part being convex for reading and the upper part for distance vision.
Q43. The ability of the eye to see objects both near and far is due to the:
The ability of the eye to see objects both near and far is due to the power of accommodation, which is the ability of the eye lens to change its focal length. The ciliary muscles contract or relax to change the shape and thickness of the lens. When the lens becomes thicker, its focal length decreases (for near vision). When it becomes thinner, its focal length increases (for distant vision).
Q44. The fluid present between the cornea and the lens is called:
The aqueous humour is a clear, watery fluid present in the anterior chamber of the eye, between the cornea and the lens. It provides nutrients to the cornea and lens (which have no blood vessels) and helps maintain the shape of the front part of the eye. The aqueous humour is continuously produced and drained to maintain proper intraocular pressure. The vitreous humour is a jelly-like fluid behind the lens.
Q45. The phenomenon of bending of light when it goes from one medium to another is called:
Refraction is the bending of light when it passes obliquely from one transparent medium to another. This happens because the speed of light changes in different media. Refraction is responsible for the bending of light by the cornea and lens in the eye, which focuses light onto the retina. It is also responsible for the apparent bending of a stick in water and the formation of images by lenses.
Q46. In the human eye, refraction of light mainly occurs at the:
In the human eye, refraction of light mainly occurs at the cornea and the eye lens. The cornea is responsible for about two-thirds (2/3) of the eye’s total refractive power because it has a curved surface and a refractive index higher than air. The eye lens provides the remaining one-third (1/3) and also allows fine focusing through accommodation. Together, they focus light onto the retina.
Q47. The far point of a normal eye is:
The far point of a normal eye is at infinity. This means a normal eye can see objects at any distance (from the near point of 25 cm to infinity) clearly without straining. The eye lens becomes thin and flat enough to focus parallel rays from distant objects exactly on the retina. For a myopic eye, the far point is closer than infinity, limiting how far the person can see clearly.
Q48. Which part of the eye is primarily responsible for the eye’s colour (e.g., blue, brown)?
The iris is the coloured part of the eye. It contains pigment cells that determine the eye’s colour. Blue eyes have less pigment, while brown eyes have more pigment. The iris also has muscles that control the size of the pupil, regulating the amount of light entering the eye. The colour of the iris is determined by genetics and can vary from blue, green, hazel, to brown.
Q49. What happens to the pupil in bright light?
In bright light, the pupil contracts (becomes smaller) to reduce the amount of light entering the eye. This is a protective mechanism that prevents too much light from damaging the retina. The iris muscles contract the pupil in response to bright light. This is why our pupils are smaller on a sunny day and larger in a dark room.
Q50. What happens to the pupil in dim light?
In dim light, the pupil expands (becomes larger) to allow more light to enter the eye. This helps improve vision in low-light conditions by allowing more photons to reach the retina. The iris muscles relax to make the pupil larger. The dilation and contraction of the pupil are automatic reflexes controlled by the autonomic nervous system, helping the eye adapt to different lighting conditions.