The cornea, pupil and lens serve which of the following primary functions? Image forming and transformation of images in to electrochemical signals Maintaining the shape of the eye Aiding audition Protection of the eye
Answers
Explanation:
Here I will briefly describe various parts of the eye:
Sclera
The sclera is the white of the eye. "Don't shoot until you see their scleras."
Exterior is smooth and whiteInterior is brown and groovedExtremely durableFlexibility adds strengthContinuous with sheath of optic nerveTendons 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 eyeIndex of refraction: n = 1.37Normally transparent and uniformly thickNearly avascularRichly supplied with nerve fibersSensitive to foreign bodies, cold air, chemical irritationNutrition from aqueous humor andTears maintain oxygen exchange and water contentTears prevent scattering and improve optical quality
Anterior & Posterior Chambers
The anterior chamber is between the cornea and the irisThe posterior chamber is between the iris and the lensContains the aqueous humorIndex of refraction: n = 1.33Specific 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 elementsAqueous humor generated from blood plasmaRenewal requires about an hourGlaucoma 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 pigmentedSphincter muscle to constrict or dilate the pupilPupil is the hole through which light passesPupil diameter ranges from about 3-7 mmArea 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 capsuleMade up of proteins and waterConsists of layers, like an onion, with firm nucleus, soft cortexGradient refractive index (1.38 - 1.40)Young person can change shape of the lens via ciliary musclesContraction of muscle causes lens to bulgeAt roughly age 50, the lens can no longer change shapeBecomes 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.