Physical and clinical refraction . Ametropia Topic 13
Optics of the eye
Light is the visible portion of electromagnetic radiation spectrum and from 400nm to 700nm with seven colours VIBGYOR (violet, indigo,blue,green,and yellow, orange,red)
The media of the eye is permeable to 600nm to 390nm
The cornea absorbs light rays shorter than 295 nm so rays between 600-295 only reach the lens
The lens absorbs rays shorter than 350 nm thus rays between 600-350 n reach retina, in people with lens phakic eye) in aphakic no lens absorption thus 600-295 reach the retina
This is just referring to absorption of the light rays
But for proper vision , we need to adjust the rays properly in order to view normally which is known as optics.
Reflection = change of path of light rays without change in medium
Have different laws to refraction,
Incident ray (incoming ) and reflected ray (outgoing) and the normal (which is a line drawn at right angle to the surface) all lie on the same plane and
An angle of incidence =angle of reflection
Refraction of light
Change of path of light when going from one medium to another
= change of the velocity of light in going from one medium to another
Laws= incident ray and refracted rayà on opposite side
Ratio of sine of angle of incidence and cosine of angle of refraction is constant for the part of the media in contact aka refractive index
Total internal reflection = when a ray of light travels from an optically dense medium to an optically rare
!!in optic when light ray hits A-B interface , the direction of refraction is determined by difference in density
If medium A is less dense than B then refracted ray will be close to the medium thus angle of refraction is less than angle of incidence but as it leaves medium B to A (e.g.
from light to glass) it travels from more dense to less dense thus gets refracted more thus angle of refraction is greater than angle of incidence . optical density is mentioned So at eye you got light to cornea, cornea is more dense than light thus angle of refraction is greater so light rays converge and at cornea lens interval further convergence occurs as lens is more optically dense than cornea thus angle of refraction is greater than angle of incidence