give short note on all the parts of the eyes
l will give 15 marks
Answers
Answer:
Light, Lens, Action
After light enters the pupil, it hits the lens. The lens sits behind the iris and is clear and colorless. The lens' job is to focus light rays on the back of the eyeball — a part called the retina (say: RET-i-nuh). The lens works much like the lens of a movie projector at the movies.
Answer:
Scleraimage from http://www.ctlens.co.uk/problems.htm
The sclera is the white of the eye. "Don't shoot until you see their scleras."
Exterior is smooth and white
Interior is brown and grooved
Extremely durable
Flexibility adds strength
Continuous with sheath of optic nerve
Tendons attached to it
The Cornea
The cornea is the clear bulging surface in front of the eye. It is the main refractive surface of the eye.
Primary refractive surface of the eye
Index of refraction: n = 1.37
Normally transparent and uniformly thick
Nearly avascular
Richly supplied with nerve fibers
Sensitive to foreign bodies, cold air, chemical irritation
Nutrition from aqueous humor and
Tears maintain oxygen exchange and water content
Tears prevent scattering and improve optical quality
Anterior & Posterior Chambers
The anterior chamber is between the cornea and the iris
The posterior chamber is between the iris and the lens
Contains the aqueous humor
Index of refraction: n = 1.33
Specific viscosity of the aqueous just over 1.0 (like water, hence the name)
Pressure of 15-18 mm of mercury maintains shape of eye and spacing of the elements
Aqueous humor generated from blood plasma
Renewal requires about an hour
Glaucoma is a result of the increased fluid pressure in the eye due to the reduction or blockage of aqueous from the anterior to posterior chambers.
Iris/Pupil
Iris is heavily pigmented
Sphincter muscle to constrict or dilate the pupil
Pupil is the hole through which light passes
Pupil diameter ranges from about 3-7 mm
Area of 7-38 square mm (factor of 5)
Eye color (brown, green, blue, etc.) dependent on amount and distribution of the pigment melanin
Lens
Transparent body enclosed in an elastic capsule
Made up of proteins and water
Consists of layers, like an onion, with firm nucleus, soft cortex
Gradient refractive index (1.38 - 1.40)
Young person can change shape of the lens via ciliary muscles
Contraction of muscle causes lens to bulge
At roughly age 50, the lens can no longer change shape
Becomes more yellow with age: Cataracts
The graph on the right shows the optical density (-log transmittance) of the lens as a function of wavelength. The curves show the change in density with age. More short wavelength light is blocked at increases ages.
Vitreous Humor
Fills the space between lens and retina
Transparent gelatinous body
Specific viscosity of 1.8 - 2.0 (jelly-like consistency)
Index of refraction, n=1.33
Nutrition from retinal vessels, ciliary body, aqueous
Floaters, shadows of sloughed off material/debris in the vitreous
Also maintains eye shape
Explanation: