How we see 1: refraction and accommodation Flashcards
What is refraction?
the bending of light rays to form a sharp image on the retina
What is accommodation?
We can focus on far off or near objects by changing how much we bend light rays
What is a refractive error?
mismatch between how much we bend light rays
what are the 4 refractive media in the eyeball?
cornea, aqueous humor, lens and vitreous humor
What 2 parts of the eye do light rays bend at?
the cornea and the lens
How does the lens change when an object gets closer?
becomes thicker and more powerful
Is the cornea or lens more powerful bender of light?
cornea
Can the cornea or lens change its bending power?
lens
List the 3 components of accommodation
lens changes shape - thicker and more spherical
pupil constricts
eyes converge
Does the ciliary body contract via sympathetic or parasympathetic innervation?
parasympathetic
Describe what happens when the ciliary body contracts to the lens
contracts and bulges
suspensory ligaments become loose
lens becomes thicker and more rounder
Why does the pupil constrict during accommodation?
to only let a few light rays - of the object - in
What muscles and its innervation constricts the pupil?
constrictor pupillae
parasympathetic via the oculomotor (CN 3) nerve
What is the only part of accommodation you can actually see?
pupil constriction
What is the process of the eyes turning in to look at the object called?
convergence
What muscles and its innervation is responsible for convergence?
medial rectus by oculomotor nerve
Why is the medial rectus thicker than the lateral rectus muscle?
close work
Name the 4 refractive errors
myopia, hyperopia, presbyopia, astigmatism
What is myopia?
short sighted
What is hyperopia?
long sighted
What is presbyopia?
age related long sighted
What is astigmatism?
non spherical curvature of the cornea/lens
What is the term for someone with perfect vision?
emmetrope
What is the underlying problem in myopia?
eyeball a bit too long, lens a bit too powerful
In myopia where is the image focussed?
in front of the retina
Myopia symptoms
headache, cannot see far away objects, divergent squint in infants and loss in sports/people - more interested in books
Correction of myopia
biconcave lenses - decrease bending power
Hyperopia underlying problem
eyeball too short, lens not powerful enough and too flat
Hyperopia symptoms
eyestrain after reading
convergent squint
Why must a convergent squint be rectified right away to prevent?
lazy eye
Correction of hyperopia
biconvex lens
In astigmatism are close or far away objects hazy?
both - random
What 2 special corrections of astigmatism are used?
cylindrical glasses curved in one axis
toric contact lenses
What is the physiological cause of presbyopia?
lens becomes less mobile and less elastic to be able to change shape
Presbyopia - age, symptoms, correction
50’s, strain to read newspaper, biconvex reading glasses
