Human Eye
* The human eye is an optical device that serves as our organ of sight. It transforms light waves reflected from objects we see into images.
The major parts of the human eye and their functions are:
* Sclera: Protects and contains internal parts
* Cornea: Refracts incident light
* Aqueous humour: Prevents collapse of the eye due to atmospheric pressure changes.
* Iris: Adjusts the size of pupil
* Crystalline lens: Focuses the light reflected by objects on the retina
* Ciliary muscles: Alter focal length of the crystalline lens
* Retina: Receives optical image and converts it to optical impulse
* Vitreous humour: Maintains the shape of the eye
* Optic nerve: Carries optical impulses to the brain
* Accommodation is the ability of the eye to change the focus from distant to near objects by altering the curvature of the lens.
* Cataracts result in a cloudy translucent eye lens. The cloudiness affects the ability of eye to accommodate.
* Far point is the maximum distance from the eye at which the eye can obtain focus of an object without straining.
* Least Distance of Distinct Vision is the minimum distance required between the object and the eye, for the eye to be able to view the object comfortably.
With two eyes, we can:
* Have 180° field of view
* Determine the exact location of an object
* Obtain better depth perception
Defects of vision: Distorted or limited vision
| Defect | Symptom | Reason | Remedy |
| Myopia | Inability to see distant objects clearly |
Higher converging power of the eye lens; results in image focusing short of retina |
Placing a high diverging power concave lens before the eye |
| Hypermetropia | Inability to see nearby objects clearly |
Lower converging power of the eye lens; results in image focusing behind retina |
Placing a high diverging power convex lens before the eye |
| Presbyopia | Inability of the eye to provide sufficient accommodation for seeing objects clearly |
Decreased elasticity of ciliary muscles, reduces its ability to alter focal length of big eye lens |
Using a bifocal lens |
* The converging or diverging capacity of a lens is ascertained by its power. It is measured in dioptres (D).
Dispersion and Scattering of Light
* A prism is a piece of glass or any other transparent material, having two triangular and three rectangular faces. A light ray refracts twice as it propagates through a prism.
* Refracting surfaces are the rectangular faces of a triangular prism.
* The refracting edge is the line along which the two refracting surfaces meet.
* The angle of a prism is the angle between the two refracting faces. It is denoted by capital letter A.
* The base of the prism is one of the rectangular faces of the prism that does not take part in refraction.
* The incident ray is the ray of light that is incident on a refracting surface.
* The refracted ray is the ray that deviates at the point of incidence and travels inside the prism between two refracting surfaces.
* The emergent ray is the light ray emerging from the prism after refraction.
* Angle of incidence is the angle formed between the refracted ray and the normal at the point of incidence.
* Angle of refraction is the angle between the normal and the refracted ray at the point of incidence.
* Angle of deviation is the angle between the incident ray and the emergent ray. It is represented by Greek letter or d or D.
* Dispersion is the splitting of light into its constituents, revealing different colours depending on the wavelengths.
* Atmospheric refraction is the apparent random wavering or flickering of objects seen due to inconsistency in the physical conditions of the refracting medium such as air.
* Scattering is the deviation of light rays from its straight path.
* Tyndall effect is the scattering of a light beam by colloidal particles, illuminating the path of the beam.
* The Tyndall beam is the illuminated path of a light beam in a colloidal solution.