Vision Practical Flashcards
The visible range for humans is from about
380 nm to 750nm
insects
see deeper into the ultra violet range than mammals and some snakes have organs that allow them to detect inferred light (body heat) given off by their prey/
which neurones in the eye are primarily responsible for color differentiation
cones
what are rods responsible for
contrast (light and dark) resolution
where are the cones predominantly found
in the fovea, the region of highest visual acuity.
are rods found in the fovea
no
what is the optic disc
refers to the region where the nerves and retinal blood vessels enter and exit. this area is devoid of receptors.
what is the optic disc often referred as
the blind spot
how would you describe the cornea
an avascular transparent epithelial layer
what does the cornea play a significant role in
focusing light on the retina, contributing some 65 to 75% of the total focusing power of the eye .
what is the size of the pupil controlled by
by the iris, which consists of muscle fibres that constrict or dilate the pupil.
can light pass through the iris
no, because at the back of the iris is a layer of epithelial cells that are highly pigmented with melanin.
effects of the parasympathetic nervous system on eye muscles
Parasympathetic nervous system causes ciliary muscle to constrict therefore lens become fatter, accommodating short vision
Also causes contraction of circular muscle which results in pupil constriction
effects of the sympathetic nervous system on eye muscles
Sympathetic nervous system causes ciliary muscle to relax, therefore lens is stretched
contraction of radial muscle, controlled by sympathetic nervous system (B3 receptor), dilates the pupil
how would you describe the lens
another avascular structure, whose curvature is controlled by the ciliary muscles and is adjusted so that the light from objects at different distances can be properly focused on the retina - a process known as ‘accommodation’
how would you describe the vitreous humour
an avascular transparent gel that fills the space between the lens and the retina and provides some support for the retina
describe the retina
light sensitive tissue that lines the inner surface of the eye
glial cell function in the retina
As well as the nerve cells, the retina also contains glial cells (Müller cells) that may, among their other functions, assist in funneling light to the rods and cones.
what must light pass through before the reaching the photoreceptors
ganglion cells and bipolar cells
are there more cone cells or rod cells in the eye ?
rod cells ! 90 million compared to 4 million cone cells are concentrated in a small pit in the macular region called the fovea , the region of highest visual acuity
which cells are responsible for our night vision
rod cells
vision in daylight lighting
is due to the work of cone cells
which cells allow us to perceive color
cone cells
the optic disc is located towards the temporal side of the retina. true or false
false, nasal side
which provides higher visual acuity, rod cells or cone cells
cone cells
which detects lower light levels, rod cells or cone cells
rod cells
rod cells are most sensitive to which wavelengths
wavelengths in the blue region (around 498nm) and are completely insensitive to wavelengths in the red region (above 640 nm )
what is the role of the pigmented epithelium at the back of the eye
At the back for the retina, the retinal pigment epithelium controls the fluid and nutrient environment of the retina by electively transporting ions and nutrients between the blood and the retina.
how many types of opsins are in our eyes
3
types of cones in eye
Our eyes have 3 sets of cones with peak sensitivities at light wavelengths of 564 nm (red), 534 nm (green) and 420 nm (blue). Cones in our eye contain one of three opsins that give the photopigments different spectral sensitivities.
how many types of photopigments are there in rod cells
only one called rhodopsin
Congenital color vision deficiencies
Congenital color vision deficiencies overwhelmingly affect the red cones or the green cones.
describe deficiencies in red cones
The term protan is used for a defect in the red cones. People who have some altered sensitivity in the red cone function are referred to as having a protanomaly. Complete red cone deficiency is called protanopia.
describe deficiencies in green cones
The term deutan is used for a defect in the green cones. People who have some altered sensitivity in the green cone function are referred to as having a deutanomaly. Complete green cone deficiency is called deutanopia.
describe deficiencies in blue cones
The term tritan is used for a defect in the blue cones. Altered sensitivity in blue cone function is not seen. Complete blue cone deficiency is called tritanopia.
what is used to measure visual acuity
The Snellen Test Chart is usually employed in routine tests of visual acuity.
in myopia, ..
In myopia, the focal point of the image is before the light reaches the retina
how do you correct for myopia
To correct for myopia, it is necessary to bend the light rays outwards before they reach the cornea. For this, a concave lens is used.
in hyperopia,
in hyperopia, the focal point of the image is not reached by the time that the light reaches the retina
how do you correct for hyperopia
To correct for hyperopia, it is necessary to bend the light rays inwards before they reach the cornea. For this, a convex lens is used
myopia
(short-sightedness)
hyperopia
long-sightedness
presbyopia
inability to focus on near objects with aging
astigmatism
blurred vision due to differences in the curvatures of the cornea or lens
how is the image focused on the retina
With normal vision, the image is focused by the combined contributions of the cornea (about 3/4) and the lens (about 1/4) on the retina.
people with normal vision can resolve..
he can resolve points separated by one minute of arc, i.e. that he has normal vision
what is accommodative power
Accommodative power (AP) is the measure of the range over which a subject can change the focal length of their lens and it is quantified in dioptres.
what is refraction
is the change of speed and direction of a wave (e.g. light) due to a change
in refractive index (n) of the medium it is passing through.
focal length (FL) of a lens is determined…
focal length (FL) of a lens is determined
by its refractive index and the curvature of
the lens surface.
what is focusing
Focusing is the process of changing FL so
that the focal point of the lens lands on the
retina by changing the curvature of the lens
what is presbyopia?
Presbyopia is a condition associated with aging of the eye that results in progressively worsening ability to focus clearly on close objects
