1b// Visual System Flashcards
when are tears produced by the lacrimal gland?
basal, reflex and emotional responses
Label.
Label.
What are the layers of the eye and describe them?
Sclera - hard and opaque aka white of eye
Choroid - pigmented and vascular
Retina - neurosensory tissue
What is the role of the sclera and what does it have a lot of?
tough, opaque tissue that serves as the eye’s protective outer coat
high water content
What is the vascular coat of the eyeball called and where does it lie?
Choroid and lies between the sclera and retina.
Waht are the parts of the uvea?
Composed of three parts – iris, ciliary body and choroid.
Intimately connected and a disease of one part also affects the other portions though not necessarily to the same degree.
What is the role of thhe retina?
Very thin layer of tissue that lines the inner part of the eye.
Responsible for capturing the light rays that enter the eye. Much like the film’s role in photography.
These light impulses are then sent to the brain for processing, via the optic nerve.
What is the role of the optic nerve?
transmits electrical impulses from the retina to the brain
connects to the back of the eye near the macula
visible portion is called the optic disc
What is the macula and what is it’s role? And what is the centre of the macula?
Located roughly in the centre of the retina, temporal to the optic nerve
A small and highly sensitive part of the retina responsible for detailed central vision
The fovea is the very centre of the macula. The macula allows us to appreciate detail and perform tasks that require central vision such reading.
What is the “blind spot”?
Where the optic nerve meets the retina there are no light sensitive cells. It is a blind spot
What is the corresponding anatomic landmark for the physiological blind spot?
Optic Disc
what is the cornea?
transparent, dome shaped window covering front of eye
low water content
provides 2/3 of focusing power
what is the choroid?
lies between retina and sclera
layers of blood vessels
what is the iris?
muscular to dilate and constrict the pupil size
controls light levels inside the eye
what is the role of the fovea?
appreciates detail and focuses central vision
What are the types of vision? (2)
central and peripheral
What does the fovea have high concentration of?
Fovea has the highest concentration of cone photoreceptors
what is central vision?
detail day/colour vision
reading, facial recognition
by fovea of macula
what is the fovea? what does it have a high concetration of?
most sensitive part of retina - centre of macula
highest concentration of cones, low concentration of rods
what is peripheral vision?
shape, movement, navigation and night vision
how is central vision tested?
visual acuity assessment
loss of foveal vision= poor visual acuity
how is peripheral vision tested?
visual field assessment
what happens with loss of central vision?
poor visual acuity e.g reading
what happens with loss of peripheral vision?
inability to navigate environment, patient may need white stick even with perfect visual acuity
what is the overall structure of the retina?
outer - photoreceptors (1st order neuron)
middle - bipolar cells (2nd order)
inner - retinal ganglion cells (3rd order)
what is the function of retinal photoreceptors?
detection of light
what is the function of bipolar cells of the retina?
local signalling processing to improve contrast sensitivity and regulate sensitivity
transmits from photoreceptors to retinal ganglion cells
what is the function of retinal ganglion cells of the retina?
transmission of signal from eye to brain
what are the classes of photoreceptors?
rods and cones
what are rods? and what do they contain?
long outer segment
contains photo-sensitive pigment
slow response to light and responsible for NIGHT vision (scotopic vision)
100x more sensntive to light than cones
which is more abundant, rods or cones?
rods 120mil to 6 mil cones
compare cone cells to rod cells.
cones are…
shorter outer segment
less sensitive to light as rods but faster response
day, fine vision and colour (photopic vision)
which cones detect blue wavelengths?
s cones
which cones detect green light?
m cones
which cones detect red light?
L cones
What idea is refraction based on?
Refraction is based on the idea that light is passing through one medium into another.
As light goes from one medium to another, the velocity CHANGES
what is the index of refraction (n) and how is it calculated?
ratio of the speed of light before and after hitting a boundary
speed of light in vaccum (air)/speed of light in new medium
what happens when light meets a boundary?
some is reflected, some refracts through the boundary into the new medium
what are the two types of lenses and how do they differ?
convex - takes light rays at brings them to a point
concave - takes light rays and spreads them outwards
what is emmetropia?
basically normal, clear vision
adequate correlation between axial length and refractive power
parallel light rays fall on the retina - no accomodation
What is a refractive error of vision called? and what is it?
Ametropia
mismatch between axial length and refractive power
parallel rays dont fall on retina
what are the types of ametropia?
myopia (near sightedness)
hyperopia (far sighted)
presbyopia
what is myopia?
near-sightedness (far objects are blurry, close objects in focus)
Parallel rays converge at a focal point anterior to the retina
what are the causes of myopia?
excessive long globe (axial myopia) more common
excessive refractive power (refractive myopia)
What is the etiology of myopia?
not clear, genetic factor
what are the symptoms of myopia?
blurred distance vision
squint in an attempt to improve uncorrected visual acuity
headaches
how is myopia treated?
negative/diverging (concave) lenses
contact lenses
removal of lens
what is hyperopia? in terms of rays?
far sightedness (close objects blurry, distance fine) Parallel rays converge at a focal point posterior to the retina
what are the causes of hyperopia?
excessive short globe (axial hyperopia)
insufficient refractive power (refractive hyperopia)