The Human Eye

To solve the problem, we need to identify the muscular diaphragm in the eye that lies between the aqueous humour and the lens.

1. Understanding the Eye's Anatomy:
The eye has several key structures that help in vision. The area between the aqueous humour (a fluid-filled chamber) and the lens contains a muscular diaphragm that controls the size of the pupil and thus regulates the amount of light entering the eye.

2. Role of the Iris:
The iris is the muscular diaphragm that controls the size of the pupil. It is located between the aqueous humour and the lens. The iris adjusts the pupil size to control the amount of light entering the eye, which helps in proper focusing and vision.

3. Verifying Other Options:
- The pupil is the opening in the center of the iris, but it is not the diaphragm itself.
- The retina is the light-sensitive layer at the back of the eye, not involved in controlling light entry.
- The cornea is the transparent front layer of the eye, but it does not serve as a diaphragm for light control.

Final Answer:
The muscular diaphragm between the aqueous humour and the lens is called the .

To solve the problem, we need to determine the angle of vision of a healthy adult human.

1. Understanding the Angle of Vision:
The angle of vision is the maximum angle through which a healthy human can clearly see objects without difficulty. This is typically determined by the visual range of the eyes.

2. General Knowledge:
For a healthy adult human, the normal angle of vision is approximately . This means a person can comfortably view an object within a angle from their central line of sight.

Final Answer:
The angle of vision of a healthy adult human is .

To solve the problem, we need to identify which parts of the human eye are responsible for controlling the intensity of light entering the eye.

1. Function of the Iris:
The iris is the colored part of the eye that controls the diameter and size of the pupil. It acts like a diaphragm that adjusts the amount of light entering the eye based on lighting conditions.

2. Role of the Pupil:
The pupil is the opening in the center of the iris through which light enters the eye. The iris changes the size of the pupil to regulate the intensity of light entering the eye.

3. Combined Action:
Together, the iris and the pupil control the light intensity. The iris contracts or dilates the pupil based on whether the surroundings are bright or dim, thus adjusting the light that reaches the retina.

Final Answer:
The parts of the eye that control the intensity of light are .

To solve the problem, we need to recall the standard value for the least distance of distinct vision in a normal human eye.

1. Definition:
The least distance of distinct vision is the minimum distance at which the human eye can see objects clearly without any strain. This is the closest point to the eye at which an object can be brought into sharp focus.

2. Standard Value:
For a normal human eye, the least distance of distinct vision is:

Final Answer:
The least distance of distinct vision is

To solve the problem, we need to identify which among the given eye defects is primarily related to aging.

1. Understanding Presbyopia:

Presbyopia is an age-related eye condition in which the eye’s lens loses its flexibility, making it difficult to focus on close objects. It typically occurs after the age of 40 and is due to the weakening of the ciliary muscles and loss of elasticity of the eye lens.

2. Differentiating from Other Defects:

- Myopia (short-sightedness) and Hypermetropia (long-sightedness) are refractive defects but not specifically age-related.

- Colour blindness is a genetic disorder and is present from birth in most cases.

- Presbyopia, on the other hand, develops with age.

Final Answer:
The age-related eye defect is .

To solve the problem, we need to identify which part of the eye carries the sensation of vision from the retina to the brain.

1. Understanding the Role of the Retina:
The retina contains photoreceptor cells (rods and cones) that detect light and convert it into electrical signals.

2. Pathway to the Brain:
These electrical signals need to be transmitted to the brain so they can be interpreted as visual images. This transmission is done by the optic nerve.

3. Functions of Other Options:
- The cornea is responsible for focusing light into the eye.
- The ciliary muscle controls the shape of the lens for focusing.
- None is incorrect as the optic nerve is the right answer.

Final Answer:
The sensation of vision in the retina is carried to the brain by the optic nerve.