17. Refraction. Emetropia, ametropia. Flashcards
what is refraction ?
change in light wave propagation , because it enters into a different transmission medium
between the boundary of both media ,
waves velocity altered
wavelength increases or decreases
but frequency stays the same
what is emmetropia ?
nomra refractive state
parallel rays of light rom distant object brough to focus on retina
eyes at rest
not accommodating -
can see sharply in the distance without accomidation
what is ammetropia?
abnormal refractive state
parallel light rays are not brough to focus on the retina in an eye at rest
a change in refraction required to get a sharp vision
what is myopia
short sightedness
light entering the eye are focussed infract of the retina-
causing distant objects to be blurry
severe myopia increases the risk of ?
retinal detachment
cataract - clouding of the lens
glaucoma - increased
what is the cause of myopia ?
genetic and
environmental factors
work with near focussing
great time spend inside
family history
what is the underlying mechanism for myopia ?
curvature of the cornea increased
increase of anterior posterior diameter of the eye ball - axial myopia
or lens is too strong - refractive index too high
how can we correct myopia ?
minus concave lens
what is hyperopia ?
light is focussed behind the retina , long sightedness
what is the underlying mechanism to hypermetropia
decrease in the anterior posterior eye ball
decrease curvature of the cornea
lens with lens refractive index
what is the risk factors to hyperopia ?
family history
diabetes
medication on eye
tumor around the eye
what are the rare complication with hyperopia ?
strabismus - eye do not properly align with one another when looking at an object
amblyopia - lazy eye -part of the brain receiving images from the affected eye is not stimulated properly and does not develop to its full visual potential
astygmatism causes what ?
different point of focuss
