Understanding the Human Eye and Common Vision Conditions

Aqueous Humor

The aqueous humor is the first medium that light travels through, limited by the cornea. Behind it is the lens, which is a convex lens. Finally, the vitreous humor is the fluid that fills the eyeball.

Eyeball Structure

The eyeball has three layers:

1. Sclera: The outer membrane, very hard, protects the eye. It is white and opaque to the passage of light, except for the cornea.
2. Choroid: Dark in appearance. It contains the iris, which controls the passage of light by opening or closing the pupil.
3. Retina: The innermost layer, formed by light-sensitive nerve cells called rods and cones.

Accommodation of the Eye

Distance vision is possible through the lens. If an object is at infinity, the lens is at rest. To focus on closer objects, the ciliary muscles compress the lens, increasing its radius of curvature and reducing the focal length. This allows images to be formed at the same distance on the retina. This involuntary process is called accommodation.

Presbyopia

Presbyopia (eyestrain) occurs due to issues with accommodation. The ciliary muscles may become fatigued, or the lens may lose elasticity. It does not affect distance vision. Correction: Converging lenses, often in the form of bifocals.

Myopia

Myopia is a loss of accommodation because the lens has excess convergence. Light rays from a point come together between the lens and the retina. The clear image is formed there and not on the retina, resulting in a blurry image. Correction: Diverging lenses to focus the light further back.

Hyperopia

Hyperopia is a loss of accommodation due to the opposite effect of myopia. It is a defect of convergence. Light rays from a point come together behind the retina, resulting in a blurred image. The lens has less sharpness than normal. Correction: Converging lenses that bring the focus forward to the lens.

Astigmatism

Astigmatism is caused by an irregularity in the curvature of the cornea. It results in an inability to see two perpendicular straight lines clearly. Correction: Cylindrical lenses that focus light at the same point.

Work-Energy Theorem

The work done by all forces acting on a particle is invested in changing the kinetic energy of the particle.

Conservation of Energy

Only non-conservative forces are capable of modifying the mechanical energy of a system. Energy is neither created nor destroyed, only transformed.

Kepler's Laws of Planetary Motion

First Law

The trajectory of the planets around the sun is elliptical, and the sun is at one focus.

Second Law

The velocity of a planet in its orbit is not constant. The speed is such that the radius vector (the segment between the sun and a planet) sweeps out equal areas in equal times.

Third Law

If we compare the orbits of several planets, the cube of the mean radius of each orbit is proportional to the square of the orbital period.

Universal Gravitation

All bodies in the universe attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.