Tiêu đề The Human Eye.pdf ✅

CLASS 10TH PHYSICS 05MARKS The Human Eye and the Colourful World ASTERISK CLASSES BY- BALVIR SIR www.asteriskclasses.com TUTION FROM 8TH - 12TH SANIK + JNV CLASSES ENGLISH WITH ROHIT SIR 1 THE HUMAN EYE The human eye is a remarkable organ with intricate components that work together to facilitate vision. It contains following parts: Cornea: The cornea is the clear, dome-shaped, outermost layer of the eye. • Function: It is the primary refractive surface, responsible for bending light as it enters the eye. The cornea's transparency and curvature are critical for focusing light onto the retina. It also serves as a protective barrier against dust, germs, and other foreign particles. The cornea is avascular (lacks blood vessels), relying on tear fluid and aqueous humour for oxygen and nutrients. Sclera: The sclera is the white, fibrous, and opaque outer layer of the eye. • Function: It provides structural support and protection to the internal components of the eye. The sclera's toughness helps maintain the eye's shape, preventing deformation due to internal pressure or external impact. It also serves as an attachment point for the extraocular muscles, which control eye movement. Iris: The iris is the coloured portion of the eye, lying between the cornea and the lens. • Function: The iris controls the size of the pupil, regulating the amount of light that enters the eye. It contains smooth muscles that contract or relax to adjust the pupil's size. The iris's pigmentation determines its colour, which varies among individuals. It also contributes to eye aesthetics, with unique patterns and textures. Pupil: The pupil is the black circular opening in the centre of the iris. • Function: It regulates the amount of light entering the eye. The size of the pupil changes in response to light intensity: it constricts (gets smaller) in bright light to reduce glare and dilates (gets larger) in low light to allow more light in. This adaptive mechanism is known as the pupillary light reflex. Lens: The lens is a transparent, flexible, biconvex structure located behind the iris. • Function: The lens focuses light onto the retina. It changes shape through a process called accommodation, which allows for clear vision at various distances. The lens becomes more rounded for near objects and flatter for distant objects. This flexibility decreases with age, leading to conditions like presbyopia (difficulty focusing on near objects). Ciliary Body: The ciliary body is a ring-shaped structure surrounding the lens, containing ciliary muscles and processes. • Function: The ciliary muscles control the shape of the lens for accommodation, adjusting focus. The ciliary body also produces aqueous humour which fills the space between the cornea and lens, maintaining intraocular pressure and providing nutrients to the cornea and lens. Aqueous Humour: A clear, watery fluid that fills the anterior chamber between the cornea and lens. • Function: It helps maintain intraocular pressure, nourishes the cornea and lens, and removes metabolic waste. It also provides a clear medium for light to pass through without distortion.

CLASS 10TH PHYSICS 05MARKS The Human Eye and the Colourful World ASTERISK CLASSES BY- BALVIR SIR www.asteriskclasses.com TUTION FROM 8TH - 12TH SANIK + JNV CLASSES ENGLISH WITH ROHIT SIR 3 How Accommodation Works • Lens Flexibility: The lens is naturally flexible, allowing it to change shape. This flexibility is controlled by the ciliary muscles in the ciliary body. • Focusing on Near Objects: When looking at something close, the ciliary muscles contract, allowing the lens to become more rounded. This increased curvature enhances the lens's refractive power, enabling clear focus on near objects. • Focusing on Distant Objects: For distant objects, the ciliary muscles relax, causing the lens to flatten, reducing its refractive power, which allows for clear distant vision. The Near Point and the Far Point • Near Point (Least Distance of Distinct Vision): This is the minimum distance at which objects can be seen clearly without strain. For a young adult with normal vision, this is about 25 cm. • Far Point: This is the farthest distance at which objects can be seen clearly. For a normal eye, this is effectively infinity. Measurement of Accommodation • Dioptres: The power of accommodation is typically measured in dioptres, indicating the degree of refractive change the lens can achieve. A higher dioptre value indicates greater accommodation capability. • Testing Accommodation: Eye care professionals test accommodation by assessing how well you can focus on objects at different distances. A common method involves reading text or looking at objects while adjusting the distance. Changes with Age 1. Presbyopia: As people age, the lens becomes less flexible, reducing its capacity to change shape. This age-related condition, known as presbyopia, typically becomes noticeable after age 40 and results in difficulty focusing on close objects. • Symptoms: Symptoms of presbyopia include the need to hold reading material at arm's length, eye strain, and blurred near vision. • Treatment: Presbyopia is often managed with reading glasses, bifocals, or multifocal contact lenses. 2. Cataract: A cataract is a condition in which the eye lens becomes milky or cloudy due to protein changes in the lens. This cloudiness impairs the lens's ability to focus light, leading to partial or complete vision loss. • Symptoms: Cataracts can cause blurry vision, glare, difficulty with night vision, and faded colours. • Treatment: Cataract surgery can restore vision. The procedure involves removing the cloudy lens and replacing it with an artificial intraocular lens (IOL). Importance of Accommodation Accommodation is crucial for everyday activities that require switching focus between near and distant objects, such as reading, driving, and working on computers. Without accommodation, it would be challenging to perform these tasks effectively. The Benefits of Having Two Eyes for Vision Having two eyes provides several advantages over having just one, contributing to a broader field of view, improved detection, and better depth perception. • Wider Field of View: Two eyes provide a horizontal field of view of about 180°, compared to 150° with one eye, allowing for better spatial awareness and safety.