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Midterm

PSYC 2390 Study Guide - Midterm Guide: Bifocals, Opsin, Phacoemulsification


Department
Psychology
Course Code
PSYC 2390
Professor
Lana Trick
Study Guide
Midterm

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Sensation and Perception Lecture Notes
Introduction to Vision
B. Pupil/ Iris
2. Disorders/problems
a. Reduction of pupil size with age depth field
It develops layers with age, but it does not have a lot of room to
grow. This causes the cells to be squished together.
b. Albinism (Iris): has melanin that gives colour to the iris, It has to do
with your skin colour as well. If you have a lot your eyes are brown.
Albinism is a disorder that either does not make melanin or it is not
functional. Their iris does not have much melanin, this causes a lot of
light to reach the back of the eye. They have problems with lighting
conditions, with acuity some are legally blind (cannot drive).
o Rabbit pink eyes, you are seeing a reflection of the blood
vessels.
C. Lens
Description/Function:
A flexible structure that coordinates with the cornea to focus light.

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Accommodation: There are ciliary muscles on the ends of the
muscles, changes the size of the lens depending on the amount of
light that is being let in.
o For near focusing situations: To bend the light the lens
becomes round meaning the ciliary muscles relax, refract the
light. The light ray will then create one point in your eye.
o For far focusing situations: The lens flattens out and ciliary
muscles constrict, the light does not bend a lot.
The yellow tin protects your eye from ultraviolet light.
Disorders/problems of the Lens
a. Disorders of Accommodation/and cures
i. Myopia(nearsightedness)
Axial myopia: is due to an elongated eye, close light
rays from distance in front of the back of the eye. The
focal point occurs before the back of the eye, far things
to be out of focus. Near thing
Refraction myopia: lens and cornea together are too
powerful, bend the light too much.
It can come into focus at the back of your eye,
the concave lenses in glasses widen the rays of
light out.
Laser Eye Surgery shape the cornea by shaving
some of it off, to make the lens and the cornea
less powerful.
ii. Hyperopia(farsightedness)
The focal point would land behind the back of the eye,
the ciliary muscles try to relax the lens as much as
possible (bulky and round), but this is not enough. This
causes eye strain ( ciliary muscles tried)- as you get
older they attain a headache.
Axial Hyperopia: has a flattened out eyeball, it is
shortened. However when an object is near, the
focal point is behind the eye because the eye ball
is shorter.
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Refracted Hyperopia: Cornea and the lens are not
powerful enough, therefore object don’t come into
focus because the light does not bend enough.
Convex lens glasses it bulges outwards, You
are trying to compensate for the flattened
out lens. It narrows the light rays, so that
they can come to a focus at the back of the
eye. It takes the wide range of angles, and
narrows down the rays of light.
Excimer Laser Surgery: they will carve the
cornea to create a bulging combinations.
iii. Presbyopia
Middle age (old)
Trouble focusing near things, they become farsighted
with age.
The lens stretches, the lens tissue becomes packed,
When you become older it does not bend the light very
well. The eye can no longer cope with nearby things
anymore- ciliary muscles get weaker.
Nearsighted and Presbyopia: use bifocals, you
have two lenses in one, the bottom half has a
convex lens for the developed presbyopia
(farsightedness), and the top half is a nearsighted
lens concave lens.
b. The aging lens and colour perception: as you age you see colour
differently due to the yellowing of the lens, blue green end of the
colour spectrum’s perceptions is altered.
c. Cataracts: lens becomes milky can cause you to do blind,
whitening of the lens blocks light and makes it difficult to focus light.
o Congenital: born with it
o Aging (most prevalent)
o Damage to the eye
Phacoemulsification: slit made in the cornea vibratory
put inside (high frequency vibrations) to make the lends
vibrate apart, vaccum out lends and pit in an artificial
lens.
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