HUMAN EYE

• The human eye enables us to see objects around us and uses light
• The human eye has a lens in its structure
• The lens in the human eye forms an image on the retina, a light-sensitive screen
• Light enters the eye through the cornea, a thin membrane on the front surface of the eyeball
• The eyeball is approximately spherical in shape with a diameter of about 2.3 cm
• Most refraction for light rays entering the eye occurs at the outer surface of the cornea
• The crystalline lens provides finer adjustment of focal length to focus objects at different distances on the retina
• The iris, a dark muscular diaphragm behind the cornea, controls the size of the pupil to regulate the amount of light entering the eye
• The eye lens forms an inverted real image of the object on the retina, which has light-sensitive cells that generate electrical signals upon illumination
• The electrical signals are sent to the brain via the optic nerves for interpretation and processing, allowing us to perceive objects
• The power of accommodation of the eye allows the eye lens to adjust its focal length
• When looking at distant objects, the lens becomes thin to increase its focal length
• When looking at nearby objects, the lens becomes thicker to decrease its focal length
• The minimum distance for distinct vision is called the least distance of distinct vision or the near point of the eye, which is about 25 cm for a young adult with normal vision
• The far point of the eye is infinity for a normal eye, allowing clear vision between 25 cm and infinity
• Presbyopia is a condition where the power of accommodation decreases with age, making it difficult to see nearby objects clearly without corrective eyeglasses
• Common refractive defects of vision are myopia (near-sightedness), hypermetropia (far-sightedness), and presbyopia
• Myopia causes difficulty in seeing distant objects clearly and can be corrected with a concave lens
• Hypermetropia causes difficulty in seeing nearby objects clearly and can be corrected with a convex lens
• Presbyopia is age-related and results in difficulty seeing nearby objects clearly, often requiring bifocal lenses for correction
• Refractive defects can also be corrected with contact lenses or through surgical interventions
• The angle at which the emergent ray bends in a glass prism is called the angle of deviation
• The sequence of colours seen when white light is dispersed by a prism is Violet, Indigo, Blue, Green, Yellow, Orange, and Red
• The splitting of white light into its component colours is called dispersion
• Different colours of light bend through different angles with respect to the incident ray as they pass through a prism
• Red light bends the least while violet light bends the most when passing through a prism
• The scattering of light by colloidal particles gives rise to the Tyndall effect, making the path of the beam visible
• The blue colour of the sky is due to the scattering of shorter wavelengths by fine particles in the atmosphere
• The reddish appearance of the Sun at sunrise or sunset is due to the scattering of blue light by particles in the atmosphere, allowing longer wavelengths to reach our eyes