No, the defect of astigmatism is not specifically described in the NCERT book for class 10. However, the concept of defects of vision is discussed in general, including nearsightedness (myopia) and farsightedness (hyperopia).

**Defects of Vision in NCERT Class 10 Book:**
In the NCERT book for class 10, "Science: Physics," Chapter 11 - Light, the section "Human Eye and the Colorful World" explains the structure and working of the human eye, along with the common vision defects of myopia and hyperopia.

1. **Myopia (Nearsightedness):**
- In this condition, a person can see nearby objects clearly but has difficulty focusing on distant objects.
- The book explains that myopia occurs when the image is formed in front of the retina instead of directly on it, due to the elongation of the eyeball or excessive curvature of the lens.
- It also mentions that concave lenses are used to correct myopia by diverging the light rays before they enter the eye, allowing the image to focus directly on the retina.

2. **Hyperopia (Farsightedness):**
- Hyperopia is the opposite of myopia, where a person can see distant objects more clearly than nearby objects.
- The book states that hyperopia occurs when the image is formed behind the retina, due to the eyeball being too short or the lens being too flat.
- It explains that convex lenses are used to correct hyperopia by converging the light rays before they enter the eye, allowing the image to focus directly on the retina.

**Astigmatism:**
Astigmatism is a common vision condition that is not specifically mentioned in the NCERT book for class 10. However, it is worth noting that astigmatism is another defect of vision that affects how the eye focuses light. It occurs when the cornea or lens is irregularly shaped, leading to blurred or distorted vision at all distances.

Astigmatism can often occur in combination with myopia or hyperopia. The correction for astigmatism involves the use of cylindrical lenses that have different powers in different meridians to correct the irregular focus.

While astigmatism is not explicitly discussed in the NCERT book for class 10, it is important to understand that it is a common vision defect that may require correction through the use of specialized lenses prescribed by an eye care professional.