Vision Flashcards
Light rays bend to form a sharp image on the retina, this is known as
refraction
We can focus on near or distant objects by changing how much we bend the light rays, this is known as
accommodation
Sometimes there is a mismatch between how much we bend the light rays which leads to
refractive errors
An image is seen through
phototransduction
What is accommodation?
The ability to focus on objects which are far away or close by changing how much we bend the light rays
What three things comprise accommodation when focusing on something close and happen simultaneously?
Lens changes shape becoming thicker and more spherical
Pupils constrict
Eyes converge
Ciliary body contraction causes the ciliary body to
bulge - decreasing the space between the body and the lens
What effect does ciliary body contraction have on the suspensory ligaments and therefore the lens?
Suspensory ligaments become relaxed, the lens is no longer under stretch so becomes thicker
Is a thicker lens more or less powerful?
More
To sharpen the focus on an object, the pupil
constricts - to allow only a few rays from the object to pass through
What is the pupillary constrictor?
A concentric muscle around the border of the pupil which gets parasympathetic innervation
Eyes converge when
focusing on a close up object
What muscles of the eye are used to converge the eyes?
Medial recti muscles of both eyes
Why are the medial recti muscles thicker than the lateral recti muscles in humans?
Humans spend a lot of time focussing on close up objects e.g. when reading so the medial recti muscles are used more frequently
What is myopia?
Short sightedness
What is hyperopia?
Long sightedness
What is astigmatism?
Non-spherical curvature of the cornea or lens
What is presbyopia?
Long sightedness due to old age
What is emmetropia?
perfect vision
Myopia causes
close objects to look clear but distant objects to appear hazy
What is the most common cause of myopia?
Eyeball too long for the strength of lens and cornea
In myopia, when the cornea and lens bend the rays of light, the image is not formed on the retina but
in front of the retina
What are the common symptoms of myopia?
Headaches
Complaints from children of being unable to see board in classroom
Divergent squint in infants and pre-verbal children
Toddlers with loss of interest in sports and people
How is myopia corrected?
Biconcave lenses or laser eye surgery - decreases bending power
Hyperopia causes close objects to appear
hazy, while further away objects are clear
What are the symptoms of hyperopia?
Eye strain after reading/working
Convergent squint in children/toddlers
How is hyperopia treated?
Biconvex lenses or laser eye surgery
What does astigmatism cause?
Close and distant objects to appear hazy, due to the surface of the eye having different curvatures in different medians
How is astigmatism corrected?
Using cylindrical glasses which are curved in only one axis, laser eye surgery or toric lenses
What happens to the lens in presbyopia?
With increasing age the lens becomes less mobile and less elastic, ciliary muscle still contracts but the lens is more rigid so less able to change its shape
How is presbyopia corrected?
Biconvex glasses/lenses for reading
What is phototransduction?
The conversion of light energy into an electrochemical response by the photoreceptors (rods and cones)
Visible light is an
electromagnetic wave
The phototransduced rods and cones activate
the optic nerve neurons which generate an action potential which is transmitted to the brain
What is rhodopsin?
A visual pigment found in the rods of the retina - extremely sensitive to light so enables vision in low lighting
What will any condition affecting vitamin A absorption affect?
Vision, cause night blindness as well as abnormal conjunctiva and corneal epithelium
What two types of light-sensitive cells are contained in the retina?
Rods and cones
Rods work in
low light conditions to help with vision at night
Cones work in
daylight and are responsible for colour discrimination
Colour blindness is usually caused by
faulty cones or a defect in the pathway from the cone to the brain
In increased illumination, the parasympathetic system causes the pupils to
constrict
In low illumination, the sympathetic system causes the pupils to
dilate
What muscles are responsible for the change in pupil diameter?
Constrictor pupillae and dilator pupillae
All fibres from the eye pass through the
optic nerve to the optic chiasm
The optic chiasm sits on top of the
pituitary gland
At the optic chiasm the medial nasal fibres
cross to the opposite side
The optic tract contains fibres from
the temporal half of the ipsilateral eye and the nasal fibres from the contralateral eye
Fibres from the optic tract synapse at the
Lateral Geniculate Body
From the lateral geniculate body, the optic radiation passes
behind the internal capsule to reach the primary visual cortex
What lobe is the primary visual cortex found in?
Occipital
The right visual cortex sees
the left half of the visual field
The intrinsic muscles of the eye control
pupil diameter and help alter the lens curvature in order to see close objects
The extrinsic muscles of the eye control
eye movement
Name the 6 extra ocular muscles
Medial rectus Lateral rectus Inferior rectus Superior rectus Inferior oblique Superior oblique
The recti muscles of the eye arise from
the apex of the orbit from an annular fibrous ring
The superior oblique arises from
the roof of the orbit, posteriorly
The inferior oblique arises from the
floor of the orbit, anteriorly
What muscle runs superiorly to and elevates the upper eyelid?
Levator palpebrae superioris
When the eye is abducted, the superior rectus causes
elevation
When the eye is adducted, the superior rectus causes
intorsion
When the eye is abducted, the inferior rectus causes
depression
When the eye is adducted, the inferior rectus causes
extorsion
When the eye is adducted, the superior oblique causes
depression
When the eye is adducted, the inferior oblique causes
elevation
The medial rectus causes
adduction
The lateral rectus causes
abduction
