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Q1. The horizontal field of view with two eyes is about
With two eyes, the horizontal field of view is about 180°. With one eye, it is about 150°. The extra 30° provided by having two eyes helps us see a wider area and improves depth perception. This wider field of view is important for detecting movement and potential dangers in our surroundings.
Q2. Loss of power of accommodation leads to
Loss of power of accommodation (the ability to change focal length) leads to blurred vision, especially for nearby objects. This happens because the eye cannot adjust its lens shape properly to focus light on the retina. This condition is called presbyopia and typically occurs with ageing.
Q3. Human eyes are positioned
Human eyes are positioned on the front of the head. This gives us binocular vision (both eyes seeing the same scene from slightly different angles), which allows us to judge depth and distance accurately (stereopsis). Predators typically have eyes on the front of the head, while prey animals often have eyes on the sides for a wider field of view.
Q4. A hypermetropic person can see clearly
A hypermetropic (far-sighted) person can see distant objects clearly but cannot see nearby objects clearly. In hypermetropia, the image of nearby objects is formed behind the retina. This is corrected using convex lenses, which converge light more, moving the focus onto the retina.
Q5. Myopia is also called
Myopia is also called near-sightedness because a person with myopia can see nearby objects clearly but cannot see distant objects clearly. In myopia, the image of distant objects is formed in front of the retina. It is corrected using concave lenses, which diverge light to move the focus onto the retina.
Q6. With one eye closed, the world appears
With one eye closed, the world appears flat and two-dimensional because we lose binocular depth perception. Depth perception (the ability to judge distance) depends on the brain combining slightly different images from both eyes. With one eye, we rely on other cues like size, motion, and shadows, but the 3D effect is lost.
Q7. A person suffering from both myopia and hypermetropia needs
A person suffering from both myopia and hypermetropia needs bifocal lenses. A bifocal lens has two parts: the upper part corrects distance vision (myopia) and the lower part corrects near vision (hypermetropia). This allows the person to see both distant and nearby objects clearly without changing glasses.
Q8. Myopia may be caused by
Myopia may be caused by excessive curvature of the eye lens (or cornea) or by elongation of the eyeball. Both conditions cause light to converge too quickly, forming the image of distant objects in front of the retina. Short eyeball causes hypermetropia, not myopia.
Q9. Refractive defects occur due to
Refractive defects (myopia, hypermetropia, and presbyopia) occur due to improper refraction of light in the eye. In a normal eye, light is refracted correctly to focus on the retina. In refractive defects, the light focuses either in front of or behind the retina, causing blurred vision. These defects are corrected using lenses.
Q10. The concave part of bifocal lens helps in
In a bifocal lens, the concave part (upper part) helps in distant vision. A concave lens diverges light, which is needed to correct myopia (near-sightedness) for seeing distant objects. The convex part (lower part) helps in near vision (reading) by converging light.
Q11. Prey animals usually have their eyes positioned
Prey animals (like rabbits, deer, and horses) usually have their eyes positioned on opposite sides of the head. This gives them a very wide field of view (almost 360°), which helps them detect predators approaching from any direction. The wide field of view is more important for survival than depth perception.
Q12. Convex lenses are also called
Convex lenses are also called converging lenses because they converge (bring together) parallel rays of light to a point (the focus). Convex lenses are thicker in the middle and thinner at the edges. They have positive power and are used to correct hypermetropia (far-sightedness).
Q13. Hypermetropia is also known as
Hypermetropia is also known as far-sightedness because a person with hypermetropia can see distant objects clearly but cannot see nearby objects clearly. In hypermetropia, the image of nearby objects is formed behind the retina. It is corrected using convex lenses.
Q14. Having two eyes helps in detecting
Having two eyes does not help in detecting colours—that is the function of cone cells in the retina. Having two eyes helps with depth perception and wider field of view, but colour vision is possible even with one eye. Heat is detected by skin receptors, and sounds by ears.
Q15. In presbyopia, the power of accommodation
In presbyopia, the power of accommodation gradually decreases with age. This happens because the eye lens becomes harder and less flexible, and the ciliary muscles weaken. The person loses the ability to focus on nearby objects, requiring reading glasses. Presbyopia typically begins around age 40.
Q16. Another cause of myopia is
Another cause of myopia (besides excessive curvature of the lens/cornea) is elongation (lengthening) of the eyeball. When the eyeball is too long, the distance between the lens and retina increases, causing the image of distant objects to form in front of the retina. This results in blurred distance vision.
Q17. The number of common refractive defects discussed is
The three common refractive defects discussed in Class 10th are myopia (near-sightedness), hypermetropia (far-sightedness), and presbyopia (age-related loss of accommodation). Each of these defects is caused by improper refraction of light in the eye and is corrected using appropriate lenses.
Q18. The lower part of bifocal lens is
The lower part of a bifocal lens is convex. This part is used for near vision (reading). A convex lens converges light, helping to focus nearby objects on the retina. The upper part is concave (for distant vision). Together, they allow a person to see both near and far objects clearly.
Q19. In a myopic eye, 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 to converge too quickly. As a result, distant objects appear blurry. Concave lenses are used to diverge light, moving the focus back onto the retina.
Q20. Humans have two eyes mainly to get
Humans have two eyes mainly to get a wider field of view (about 180°) and stereoscopic vision (depth perception). Having two eyes also helps with judging distance and detecting movement. Colour vision and night vision are functions of the retina, not the number of eyes.
Q21. Presbyopia generally occurs due to
Presbyopia generally occurs due to ageing. As a person ages (usually after age 40), the eye lens becomes harder and less flexible, and the ciliary muscles weaken. This reduces the eye’s ability to focus on nearby objects. Presbyopia is a natural part of ageing and affects almost everyone to some degree.
Q22. Presbyopia also occurs due to
Presbyopia occurs due to diminished flexibility of the eye lens. As the lens becomes harder and less flexible with age, it cannot change shape easily for accommodation. This makes it difficult to focus on nearby objects. The ciliary muscles also weaken, further reducing accommodation.
Q23. The part mainly used for transplantation in eye donation is
In eye donation, the part mainly used for transplantation is the cornea. The cornea is the transparent front part of the eye. Corneal transplantation (keratoplasty) can restore vision in people whose cornea has become damaged or cloudy due to injury, infection, or disease. The cornea has no blood vessels, making it easier to transplant without rejection.
Q24. Hypermetropia occurs due to
Hypermetropia occurs due to shortening of the eyeball or flattening of the eye lens/cornea. When the eyeball is too short, light rays are not converged enough, and the image of nearby objects is formed behind the retina. This causes blurred near vision. Convex lenses are used to correct hypermetropia by converging light more.
Q25. Which of the following is NOT a refractive defect?
Cataract is NOT a refractive defect—it is a condition where the eye lens becomes cloudy (opaque). Refractive defects (myopia, hypermetropia, and presbyopia) are caused by improper refraction of light due to the shape of the eye or lens. Cataract is caused by clouding of the lens and is treated with surgery, not lenses.
Q26. Another cause of hypermetropia is
Another cause of hypermetropia is a lens with a long focal length (i.e., a flatter lens). A lens with a long focal length cannot converge light enough, causing the image of nearby objects to form behind the retina. This results in blurred near vision. Short focal length (more curved lens) causes myopia.
Q27. Each eye sees a
Each eye sees a slightly different image of the same object because the eyes are about 6-7 cm apart. This difference in perspective (binocular disparity) is used by the brain to create depth perception (3D vision). The brain combines these two slightly different images into a single, three-dimensional image.
Q28. In hypermetropia, image of a nearby object is formed
In hypermetropia, 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 to converge too slowly. As a result, nearby objects appear blurry. Convex lenses are used to converge light more, moving the focus onto the retina.
Q29. Eyes can be donated
Eyes can be donated by people of any age or sex, provided the cornea is healthy. There is no age limit for eye donation. People can donate their eyes after death, regardless of age, gender, or blood type. Even people who wear glasses can donate their eyes.
Q30. The horizontal field of view with one eye is about
The horizontal field of view with one eye is about 150°. With two eyes, it is about 180°. The extra 30° from having two eyes provides a wider field of view and helps with depth perception. The field of view can vary slightly from person to person.
Q31. In hypermetropia, the near point is
In hypermetropia, the near point is farther than 25 cm (the normal near point). A person with hypermetropia cannot see objects clearly at 25 cm (the normal reading distance). They must hold objects farther away to see them clearly. This is because the image of nearby objects is formed behind the retina.
Q32. The brain combines images from both eyes to judge
The brain combines images from both eyes to judge distance (depth perception). The two eyes see the same object from slightly different angles. The brain uses this difference (binocular disparity) to calculate how far away the object is. This is called stereopsis or stereoscopic vision.
Q33. Surgical intervention can correct
Surgical intervention can correct refractive defects. Procedures like LASIK (Laser-Assisted In Situ Keratomileusis) use lasers to reshape the cornea, correcting myopia, hypermetropia, and astigmatism. Refractive surgery reduces or eliminates the need for glasses or contact lenses. However, it is not suitable for everyone.
Q34. Presbyopia is caused by weakening of
Presbyopia is caused by weakening of the ciliary muscles and hardening of the eye lens. The ciliary muscles become weaker with age and cannot change the shape of the lens effectively. This reduces the power of accommodation, making it difficult to focus on nearby objects.
Q35. A concave lens helps by
A concave lens helps by diverging light rays, which moves the focus of distant objects from in front of the retina to the retina. This corrects myopia. The concave lens has negative power and spreads out light before it enters the eye, reducing excessive convergence.
Q36. Myopia is corrected using
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 from in front of the retina to the retina. Concave lenses have negative power.
Q37. People who have undergone cataract surgery
People who have undergone cataract surgery can still donate their eyes. The artificial lens implanted during cataract surgery does not prevent eye donation. The cornea, which is used for transplantation, remains healthy and suitable for donation. Many donated eyes come from people who had cataract surgery.
Q38. One pair of donated eyes can give vision to
One pair of donated eyes (two corneas) can give vision to two people. Each cornea from one eye is transplanted to one recipient. Corneal transplantation is a common and successful procedure that can restore vision in people with corneal blindness.
Q39. In myopia, the far point is
In myopia, the far point is nearer than infinity. For a normal eye, the far point is at infinity. In myopia, the far point is at a finite distance—beyond this point, objects appear blurry. The more severe the myopia, the closer the far point. Concave lenses move the far point back to infinity.
Q40. Eye donation does NOT cause
Eye donation does NOT cause pain to the donor because the eyes are removed after death, when the person cannot feel pain. Eye donation is a selfless act that can give vision to two people. It does not delay the funeral or cause disfigurement—the body is treated with respect and dignity.
Q41. Stereopsis gives us the sense of
Stereopsis gives us the sense of depth. It is the ability to perceive the world in three dimensions (3D) and judge the distance of objects. Stereopsis depends on the brain combining slightly different images from the two eyes. Without stereopsis, the world would appear flat (two-dimensional).
Q42. Hypermetropia is corrected using
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 from behind the retina onto the retina. Convex lenses have positive power.
Q43. The upper part of bifocal lens is
The upper part of a bifocal lens is concave (for distant vision). This part corrects myopia (near-sightedness) by diverging light for seeing distant objects. The lower part is convex (for near vision, like reading). Bifocal lenses help people who have both myopia and hypermetropia.
Q44. The positioning of human eyes helps in
The positioning of human eyes on the front of the head helps in stereopsis (depth perception). The overlapping fields of view from both eyes allow the brain to combine slightly different images, creating a three-dimensional perception of the world. This helps us judge distances accurately.
Q45. A myopic person can see clearly
A myopic person can see nearby objects clearly but cannot see distant objects clearly. In myopia, the image of distant objects is formed in front of the retina. This makes distant objects appear blurry. Concave lenses are used to correct myopia.
Q46. The convex part of bifocal lens helps in
The convex part of a bifocal lens helps in near vision (reading). A convex lens converges light, helping to focus nearby objects on the retina. This is needed for people with hypermetropia or presbyopia. The concave part of the bifocal lens helps in distant vision.
Q47. Refractive defects can also be corrected using
Refractive defects can also be corrected using contact lenses. Contact lenses work similarly to spectacle lenses but are worn directly on the eye. They are available for correcting myopia, hypermetropia, astigmatism, and presbyopia. They provide a wider field of view and are more convenient for some people.
Q48. Eyes should be removed within
Eyes should be removed within 4–6 hours after death for successful corneal transplantation. After this time, the cornea begins to deteriorate and may not be suitable for transplantation. Quick removal ensures that the cornea remains healthy and can be used to restore vision in a recipient.
Q49. Eye removal takes about
Eye removal (enucleation) for eye donation takes about 10–15 minutes. It is a simple surgical procedure performed by trained professionals. The procedure is done with care and respect, and it does not delay the funeral or cause any disfigurement. The body can still be viewed in an open casket.
Q50. With both eyes open, we see the world in
With both eyes open, we see the world in three dimensions (3D). This is because the brain combines slightly different images from each eye to create depth perception. This allows us to judge the distance, size, and shape of objects. With one eye, the world appears flat (two-dimensional).