Optics 3 Exam 2 Content lecture 40-43

as pupil size increases what happens to aberrations

aberrations increase

an increase in aberrations has what affect on VA's

results in poor visual acuity

as pupil size decreases what happens to diffraction

diffraction increases

an increase in diffraction has what affect on MAR and VA

increases MAR and results in poor visual acuity

on optical axis terms

stop, aperture, and aperture stop

off optical axis terms

field of view and field stop

stop

whatever structure prevents rays from entering

aperture

area in the stop that allows light to pass through

aperture stop

light limiter of the system

field of view

the area of the object that does have rays pass through the system

field stop

the stop that causes the limitation of the field of view

entrance pupil

the image of the aperture stop formed by all the lenses/refracting surfaces in front of it. ("How does cornea refract my pupil")

exit pupil

the image of the aperture stop formed by all the

lenses/refracting surfaces behind it. ("How does the lens refract my pupil")

signs of objective and ocular lens for galilean telescope

objective is positive and and ocular is negative

signs of objective and ocular lens for keplerian telescope

objective is positive and and ocular is positive

objective lens of the telescope serves as the

aperture stop and entrance pupil

for galilean exit pupil will form what type of image/exit pupil

virtual and inside telescope

for keplerian exit pupil will form what type of image/exit pupil

real and outside telescope

purkinje images

the images created when the surfaces of the cornea and lens behave as MIRRORS

purkinje image I

reflection off the front surface of the cornea

purkinje image II

reflection off the back surface of the cornea

purkinje image III

reflection off the front surface of the lens

purkinje image IV

reflection off the posterior surface of the lens

purkinje images 1, 2, and 3 have what in common

they are all made by convex surfaces (positive radius)

purkinje image 4 is made by

a concave surface (negative radius)

reflection off a convex mirror will form what type of image

upright and virtual located behind mirror

reflection off a concave mirror will form what type of image

inverted and real located in front of mirror

F equation for mirrors

F= -2n/r

which purkinje image is used in clinical settings

image I

depth of focus

linear range of image positions slightly in front of and slightly behind the retina that still result in a clear perception of the object

blur circle

the distance between the image positions (the range of clarity)

the farther the image positions are apart the ___________ the blur circle

larger the blur circle

the closer the image positions are apart the ___________ the blur circle

smaller the blur circle

depth of field

linear range of object positions slightly in front of and slightly behind the retina that still result in a clear perception of the object

linear positions of depth of focus and depth of field are both expressed in terms of

diopters

true amplitude of accommodation

accommodation only

apparent amplitude of accommmodation

accommodation and depth of focus/field

true accommodation equation

apparent accommodation - total depth of focus

what is the relationship between depth of field/focus and pupil size

inversely proportional

as you get older what happens to your depth of field

it increases because your pupil size gets smaller

when doing depth of focus calculations what index do we use and why

1.33 because images are in the eye

when doing depth of field calculations what index do we use and why

1 because the objects we see are in air

aberration

an element of an optical system that degrades the quality of the image

paraxial assumption

the further you are from the axis the more the rays will bend

paraxial rays

are close to the axis so they bend less

marginal rays

are further from the axis so they bend More

how does paraxial vs marginal impact aberrations

marginal rays will have more profound aberrations

spherical (defocus) aberration blur circle

spherical

coma aberration blur circle

off centered circles

oblique astigmatism aberration blur circle

oval shaped

curvature field aberration

blur at periphery

pincushion distortion is what lens

plus lens

barrel distortion is what lens

minus lens

what causes spherical (defocus) aberration

the difference in refracting power between the light rays focused by the periphery system and light rays focused by the center of the system

what naturally helps reduce spherical (defocus) and coma aberrations

our iris

coma aberration

an off-axis phenomenon meaning the rays do not enter parallel to the optic axis

as pupil size increases spherical and coma aberrations will ______________ and visual acuities will be _____________

spherical and coma aberrations will increase and visual acuities will become worse

what is the difference between diffraction and aberration relationship to pupil size and VA

smaller pupil size causes an increase in diffraction which worsens VA while smaller pupil size causes a decrease in aberrations which improves VA

distortion is caused by

differences in MAGNIFICATION of marginal vs paraxial rays

a plus lens will cause more (mag or mini)

magnification

a minus lens will cause more (mag or mini)

minification

oblique astigmatism is caused by

rays hitting at an angle oblique to the visual axis causing 2 points of focus

what is a method used to reduce oblique astigmatism aberrations

pantoscopic tilt

how do we minimize curvature of field aberrations

selecting the proper base curve for spectacles

chromatic aberrations only occur with

polychromatic light

shorter wavelengths have a _________ index of refraction and bend __________

shorter wavelengths have a higher index of refraction and bend more

longer wavelengths have a ___________ index of refraction and bend ___________

longer wavelengths have a lower index of refraction and bend less

will myopes see red or green as more clear

red

will hyperopes see red or green as more clear

green

red-green balance preferred end points

red and green are equally clear or red is more clear

is a patient is fogged you would anticipate that which side appears more clear

red

is a patient is over minused you would anticipate that which side appears more clear

green

A patient with an eye power of +61.50 DS is wearing spectacles of prescription +1.50 DS. Which side of the duochrome chart will be clearer?

Red

seidel aberrations are all

monochromatic

wavefront sensing or wavefront aberrometry

measures aberrations by comparing the way rays exit a given eye compared to how they exit to a theoretical "perfect" eye

in a perfect eye the array of point foci on the sensor are _____________ while in an imperfect eye they are _____________

in a perfect eye the array of point foci on the sensor are evenly separated while in an imperfect eye they are disorganized

higher order aberration means ___________ degradation of the image

worse

spherical and coma are _________ order aberrations

low

adaptive optics

design a customized system to correct all aberrations

limitations of adaptive optics

thickness of cornea, healing of the cornea, ability to correct for aberrations with mirrors