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Level 178

Optics II


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Accomodation
The process by which the eye's lens changes shape to focus near or far objects on the retina
Electromagnetic Spectrum
a group of different types of waves (radio waves, microwaves, infrared waves, visible light, ultraviolet light, x-rays, gamma rays)
Triangular Prism
A prism whose bases are triangles
Primary Colour
Red, green, & blue; combine to make white
Secondary Colour
Coloured light that is produced when lights of two primary colours are mixed equally
Filter
Device that removes something from whatever passes through it
Rods and Cones
Specialised sensory receptors found in the eyes
Colour Blindness
Genetic inability to distinguish differences in hue
Photoreceptors
Cells inside the retina
ultrasound
sound waves at frequencies higher than 20 kHz
x-rays
electromagnetic waves used to make images of bones and teeth
Sonar
locates objects by using reflected ultrasonic pulses
laser
A device that produces a narrow beam of coherent light.
radar
a system that uses reflected waves to detect objects and measure their distance and speed
CAT scan
rotating x-rays produce a 3D image
MRI
uses magnetic fields and radio waves to produce images
reflected ray
rays that are reflected by an object
refracted ray
rays that are bent by a lens or other media
plane mirror
..., A flat mirror that produces an upright, virtual image the same size as the object
incident ray
rays of light coming from an object
inverted
For mirrors, when is M negative?
optics
branch of physics that studies the properties of light
near-sighted
occurs when the eyes' focal point falls in front of the retina
far-sighted
occurs when the eyes' focal point falls behind the retina
Diffraction
the bending and spreading of waves, usually around an obstacle
angle of incidence
angle between the incident ray and the normal
rarefaction
a part in a longitudinal wave where the particles are spread apart
Image Jump
the apparent displacement of an object as the eye crosses the top edge of the segment
Base down prism
What causes the image to jump upwards?
power of the add
What does the amount of image jump for any bifocal lens depend on?
through the top of the glasses
If we have a patient that is wearing bifocal spectacles and walking down the stairs, where should he/she be looking through the glasses?
When is there no image jump with bifocal glasses?
When the optical center of the segment is at the top of the segment
interrupted
If the patient has ADD in their spectacles, the gradual increase in prism amount is _______
Why is the image jump worse in glasses with a round top bifocal style?
the optical center of the bifocal is farther from the OC of the distance lens
True
T or F
NO IMAGE JUMP
What is the number one benefit of a progressive lens compared to a standard bifocal?
blind spot
Jump causes a _______ around the segment line
Scotoma
blind spot
False.
T or F
on a plus lens
When is a round top seg preferred to minimize image displacement?
on a minus lens
When is a FT segment preferred to minimize image displacement?
What is the difference between image displacement and image jump?
image displacement is the actual amount of prismatic power that occurs
prismatic imbalance
Whenever a patient looks through any part of his lenses besides the optical center, he experiences _______ if his Rx differs between OD and OS
90th meridian
What meridian are we comparing when observing vertical imbalance?
Anisometropia
difference in the distance refractive error between the two eyes
SV wearers are able to avoid prismatic effects by
moving or tilting their head so they are looking through the OC
When does a patient experience a vertical imbalance
if the difference between the Rx's is greater than or equal to 1.5D in the vertical meridian and each eye is correctable to 20/60 or better.
OD: +4.00x-1.00x180 add +2.00
+3.00 in vertical meridian
Slab-off technique
BU prism is ground on half of the lens in either the most minus or least plus lens
front surface slab-off
3 grinding techniques for slab-off prism
vertical
gravity only affects _______ components of acceleration
front, biccentric
_______ surface slab-off and _______ produce BU prism in the lower section of the lens
reverse, BD
_______ slab-off produces _______ prism in the lower portion of the lense
6D
What is the limit of how much induced prism that is canceled by slab-off
True
T/F. The vertical component of the projectile velocity is always accelerating toward the Earth at a rate of g.
Slab Grinding
method of adding prismatic effect in the reading area of a lens without producing prism in the distance vision area
on
slab _______ grinding is always performed on the more plus lens
1 to 3, 1.5 to 5
one can slab on _ to _ prism diopters and slab on __ to __ prism diopters
both cornea and lens are spherical refractive surfaces
All classic eye models are based on the following assumptions:
air to anterior cornea
6 refracting surfaces of the gullstrand schematic eye
nucleus core
two concentric lens surfaces of the gullstrand schematic eye
two discrete lens configurations
relaxed: looking at something at distance
Gullstrand #1
The gullstrand schematic eye is also know as
homogeneous
mixture that have uniform composition through out is called homogeneous.e.g air, gasoline and ice cream
no
is [1/(f₀+βy)](d²φ/dx² +d²φ/dy² the correct form of the quasigeostrophic vorticity, yes or no?
LeGrand schematic eye model
Which schematic eye model is known as the simplified gullstrand or gullstrand #2
air to aqueous
What are the 3 refracting surfaces of the simplified schematic eye model
lens
what are the 2 discrete indices of refraction of the simplified schematic eye model
the cornea is treated as an SSRS lens
In the simplifed schematic eye model, how is the cornea treated?
one refractive surface and one index of refraction
How many refractive surfaces and indices of refraction are there in the reduced schematic eye model.
Reduced Schematic model
Which schematic eye model is also known as the SSRS model or Emsley model?
simplified schematic eye
Which schematic eye model is also known as the gullstrand-emsley model
retro illumination
reflected light from the retinal surface
Retinal image schematic eye
a modern eye model
+60D
Reduced Eye model
60D, 22.22mm
An emmetropic eye as a power of _______ and an axial length of _______.