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Level 179

Optics III


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Refractive error
the difference between the power of vergence exiting the system and the power of the vergence required for emmetropia vergence coming in so light hits the retina
False
(T/F) Tycho Brahe was a Danish astronomer who confirmed Copernicus's theories by making many observations with his telescope.
SSRS, H plane
Correction at the _______ or _______ will be the opposite of their respective refractive error.
True,
The correction for a CL is the same as the correction at the SSRS or H plane. T or F
Glasses are at a distance from your eye
Why does a spectacle correction require a displacement between refractive surfaces?
Dnew=Dold/1-hDold
Effectivity Formula
Higher
The _______ the voltage, the more the electrons want to jump.
ciliary muscle, zonules
the lens of the eye is suspended within the band of the _______ by suspension ligaments known as _______
flexed, relaxed
During accommodation the ciliary muscles are _______ and the zonules are _______
False, it is passive
The accommodation response is generally ACTIVE. T or F
blur
What is the stimulus to accommodation
Accommodative Triad
accommodate to increase relative optical power
normal shape of lens = fully relaxed state
How did Tscherning think accommodation worked in the late 1800s?
tscherning
who invented the opthalmophakometer
Helmhotz thinking of accommodation:
normal shape of lens =accommodated state
How did Schacher think accommodation work?
contraction of ciliary muscles results in INCREASED tension at equatorial zonules with a concurrent DECREASE in tension at the more peripheral zonules
~15D in ahealthy child
How much can an individual accommodate?
Presbyopia
progressive loss of functional accommodation
Far Point
the farthest distance from the eye and object can be adequately resolved
optical infinity
Where is the far point for an emmetrope
Near Point
the closest distance from the eye that an object can adequately resolve
Distal point
a point where the distant object is resolved using correction
Proximal point
a point where a close object is resolved using correction
in the SAME location
Where is the far and near point of a myope without correction and accommodation?
in the SAME location -- optical infinity
Where is the far and near point of an emetrope without correction and accommodation?
virtual, does not functionally exist
Where is the far and near point of a hyperope without correction and without accommodation?
two different points
With accommodation, where is the near and far point of an uncorrected myope?
far point: optical infinity
Where is the far and near point of an emmetrope with accommodation?
they MAY be two different points
Where is the far and near point of a hyperope with accommodation?
false, they are NOT equal
The range of clarity and range of accommodation for a HYPEROPE are equal. T or F
functional emmetrope
Correction makes a myope and a hyperope a _______.
two discrete points
The distal and proximal point of a myope are _______ with correction and with accommodation.
distal: optical infinity
where is the distal and proximal point of a hyperope with correction and accommodation?
Far point RE of a myope
RE= power of lens - 60D
Far point RE of a hyperope
RE = power of lens - 60D
near point RE of a myope
RE = (power of lens+accommodative amplitude) - 60D
Range of clarity of hyperope
between optical infinity and focal point of RE+accommodative amplitude
range of accommodation of hyperope
between optical infinity and point of RE and accommodative amplitude plus from the far point the the retina
ACCOMMODATION
what is the ability to increase the relative power of the optical system or eye
stimulus
The accommodative reflex requires and inititiation or_______
Increase, divergent
Functionally, the eye can only _______ its power and compensate for _______ light
Vergence stimulus to accommodation
uncompensated vergence entering the eye
Stimulate to accommodation (S_acc)
S_acc = V_cornea + RE
accommodation
When is the only time that myopes have an advantage over emmetropes
hyperopes
Looking at things up close, _______ has to work the most
greater
Accommodative response for myope is _______ in CL compared to equivalent spectacle correction
less
Accommodative respone for hyperope is _______ in CL compared to equivalent spectacle correction
myopes
_______ can obtain a closer proximal point with spectacle correction compared to contact lens
hyperope
_______ can obtain a closer proximal point with CL correction compared to spectacle
glasses - image is larger
Retinal image for a hyerope with glasses and contacts
glasses - image is smaller
retinal image size for a myope with glasses and contacts
at the far point
Where do glasses focus light?
axial and refractive
What are the two types of refractive error?
axial length
What makes a person a very high myope?
1/1-hD
M_spectacle =
(M-1)*100
percent magnification =
M_sp = 1/(1-0.015*-4)
A patient wears -4D spectacles at 15mm. What is the difference in uncorrected vs corrected retinal image size when the pt puts on their glasses?
increases the minus power
For nearsighted people, what does pushing up the glasses do?
Reference Point
A _______ is a place or object used for comparison to determine if something is in motion.
vertex distance changes
Why is a CL Rx different than a GL Rx for a patient?
shape factor
What are the two terms that are important when we talk about spec mag with lenses
hD
power factor =
power of the spectacle
factors that affect spec mag
out
steepening the front surface of a lens moves the planes _______
thickness(t)
shape factor
power factor
vertex power
power factor x shape factor
The total magnification of a thick lens is equal to
m_power = 1/(1-vertex distance*lens power)
What percent magnification is produce by the shape factor of the following lens: +11.50D, 6mm thick, 13 mm vertex distance, index is 1.53, front surface power is +15D
m_shape = 1/(1-h*D1)
formula for shape factor
formula for power factor
m_power = 1/(1-vertex distance*lens power)
m_power = 1/(1-vertexdis*lens power)
What total spectacle magnification results from -5.00D, 2.2mm thick, 20mm vertex distance, index of 1.53, and front surface power of +4.25D
planes move forward and farther from the far point --> image gets bigger
If we steepen the front of the lens, in what direction do the principal planes shift?
back
As we flatten the front surface out, the plane shifts towards the _______ surface
How to decrease magnification of +lens
retinal image size can be reduced by shift H' towards F'
increase f'v
How to decrease minification of Minus Rx
increase D1
how to create a larger image in both minus and plus lenses
object size
y=u tan w
K readings - refractive
How can we tell if a patient has axial or refractive ametropia?
A-scan
measure the length of the eye
Wave
A disturbance in matter that carries energy from one place to another is called a _______.
crest
The section of a transverse wave above the equilibrium line.
trough
The section of a transverse wave below the equilibrium line.
rest position
in water, the level the water would be at if there were no waves
amplitude
distance of the highest amount of displacement from the origin; A
frequency (the symbol is f)
rate of repetition of a wave; measured in hertz (Hz), which is cycles per second
speed of a wave (the symbol is v)
determined by multiplying the wavelength with the frequency of a wave
electromagnetic radiation
energy that can travel through empty space in the form of waves
nanometre (nm)
one billionth of a metre
model
represents something in a more simple way to help us solve a problem
Property
a macroscopic characteristic of a system that is independent of path (or process)
wave model of light
model of light comparing light to water waves; in this model, similarities between light and the movement of waves on the surface of water are used to explain several properties of visible light
reflect
to bounce off an object, such as when a light wave strikes an object
additive colour theory
theory of light stating that white light is composed of different colours (wavelengths) of light
subtractive colour theory
theory of light stating that coloured matter selectively absorbs different colours, or wavelengths, of light; colours that are absorbed are "subtracted" from the reflective light seen by the eye