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Chapter 2

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Matthias Niemeier

Chapter Two First Steps in Vision A Little Light Physics Light is a form of electromagnetic radiation (energy produced by vibrations of electrically charged material) oOnly make up tiny portion of this spectrum ( gamma rays w shortest wavelength to radioTV waves with longest wavelength Visible light is from 400 700 nm (10 ^ -9 m) in wavelength = 400 violet & 650 red 2 ways to conceptualize : As wave when it moves around the world & As photos when its being absorbed Once star- light enters the atmosphere some photos will be absorbed & some will be scattered BUT most will hit the surface of an object Light STRIKE a LIGHT-COLOURED surface most of light will be REFLECTED to re-direct something that strikes a surface especially light, sound, or heat usually back toward its point of origin oSTRIKE a DARK-SURFACE is ABSORBED Light neither reflected or absorbed is TRANSMITTED to convey something form one place or thing to another Light is REFRACTED to alter the course of a wave of energy that passes into something from another medium (light in air that strike a water) oDo this in the eye-exam determine how much light must be BENT by eye-glasses for it to properly focused on retina Eyes that See Light Single-celled organism such as Amboea detect light & change direction accordingly to it BUT eyeball of humans (& other) can form image to recognize objects Light FIRST encounters CORNEA a transparent window into the world oReason why its transparent because fibres w no blood vessels or blood which could absorb light oSince its transparent most of light photos are transmitted (not reflected or absorbed) oHave rich supply of transparent sensory nerve ending which force eye to close & produce tears of when its scratched (preserving its transparency) These external layers regenerate quickly so even it scratched heals win 24 H AQUEOUS HUMOR fluid derived from blood that fills the space immediately behind the cornea & supply oxygen, nutrients and removes waste from cornea & crystalline lens CRYSTALLINE LENS also transparent since it has no blood supply & its shape can be controlled by CILIARY MUSCLE Light must pass through the PUPIL to get to the LENS PUPIL is a hole in a muscular structure called the IRIS (which gives the eye its distinct colour) - it controls the amount of light that reaches the RETINA via PUPILLARY LIGHT REFLEX oWhen light level increase decrease the IRIS contracts expand automatically to allow moreless light into eye ENTER A light room from dark room eyes contricts & have photonic sneeze reflex After passing via LENS light enters the VITEROUS CHMABER (space bw lens & retina) where it will refracted for the fourth & final time by the VITREOUS HUMOR oCHAMBER there is floaters which are bio debris flat around this why you think you see debris in sunny day when you look up oHUMOR is comprises 80% of the internal volume of eye its the longest journey Light is brought into FOCUS at the RETINA where the seeing actually beings this where light is detect aspects of light that are related to objects in the world Shining Starlight onto the Retina Refraction is necessary to focus light rays CORNEA is highly CURVED & has higher REFRACTIVE INDEX than air - it forms the most POWERFUL REFRACTIVE surface in the eye oAQUEOUS & VITREOUS CHAMBER also help refract light oRefractive power of these 3 structure is FIXED thus, they CANNOT be used to bring CLOSE OBJECTS into FOCUS This job performed by LENS can ALTER the REFRACTIVE POWER by changing its shape - a process called ACCOMMODATION Accommodation ( change in focus) accomplished via CONTRACTION of the CILIARY MUSCLE - the LENS is attached to this muscle via the tiny fibres (ZONULES OF ZINN)
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