Optics 2 - Final

What is radiometry?

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Select all that apply: Which of the following types of cones are respond to all wavelengths of light ? a) S b) M c) Lboth M & L cones are respond/sensitive at all wavelengthsHow many log units is sensitivity reduced from having 100% sensitivity to about 0% What is the range of visible light wavelengths?6 log units 380 - 760When you are in the dark, what is the peak sensitivity wavelength for the rods?510 nmThe change in the sensitivity from dark to light (510 to 555) or visa versa is calledthe Purkinji ShiftLuminous Flux?The flow of light per unit of time (F)Luminous Intensity?Simply Intensity (I) Lumens per solid Angle = Candellas by a point sourcesSteradian? Another word for? Unit of ?flux radiated per Solid Angle another word for candellas Luminous IntensityIlluminance aka Illuminance (E) Unit(s)?Flux falling on a surface Lumens/m^2 or Lux or / foot^2 = footcandle or / centimeter^2 = photLuminance?Lumens/Steradian/Area flux emitted per steradian per area from an extended light source or surface Unit: candela/m^2Amount of light coming from snellen chart, I would be measuring? a) Luminous Flux b) Luminous Intensity c) Luminance d) Illuminance e) IlluminatiLuminanceInverse Square Law describes how any type of energy is spread out. Hence, in photometry its called the Law of illuminace. What does 3 things does illuminance of an object depend on?1) the angle the surface is to the light 2) how far the light is from the object 3) how much is reflected from the surfaceE= Illuminance formula?E = I/d^2 I= intensity d= distanceAs distance doubles, the amount of light falling on the surface is divided by _______ if the surface is at a right angle to the point source of light4Why do we use the cosine law of illumination formula? what is it?if the surface is tilted at an angle from the point source E=(I/d^2)(cos)What is the color differences between specular and diffuse reflectionColor of Specular Ref = same as the source Color of Diffuse Ref = same as the surfaceLaw of Reflection?both angles =Which of the following type of reflection help deterimine the shape and features of an object? a) Diffuse b) Cruzart c) Specular d) Sinusoidalc) SpecularA chrome sphere has ______________ reflection but no ___________ reflectionhas specular but no diffuseThe amount of reflection is maximum when the surface and point source are ____ degrees90Diffuse reflection intensity is proportional to _______ angle reflectioncosLambertian Surface?an ideal "matte" or diffusely reflecting surface. The apparent brightness of a Lambertian surface to an observer is the same regardless of the observer's angle of view.Lamberts Law aka Cosine Law of Diffuse Reflection isI = (In) cos In = diffuse intensity along the normalReflectance Ratio isDiffusely reflected light / incident lightSpectral ReflectanceDiffusely reflected light / incident light *as a function of WAVELENGTH This is what gives objects its colorThe dress issue controversy. Why did this occurYou need to know the source of the illumination. People made assumptions of material and illumination need wider viewWhat is the unti of retinal illuminance?Target luminance x pupil area mmThe lenses of a camera should be aligned along a _____________ where their ___________ are joined and normal to all elements1) optic axis 2) centers of curvatureT/F the cornea/lens are aligned the same way the lenses of a camera are alignedFalse - there is no true optical axis for the eyeWhy is there no true optical axis of the eye?The cornea and lens are tiltedThe fovea is displaced _________ from the optical axis of the eyeTemporallyWhat is the entrance pupil?The center of the image of the pupil we see when we look into the eye of a pt formed by the corneaThe pupillary axis passes through what 3 main landmarks?1) Entrance pupil O 2) Nodal pt N 3) Center of rotation CWhat happens to rays that pass through the nodal pt of the eye?Do not refract - pass undeviated (hard to find)What landmark lies on the line of sight?The entrance pupil OWhat landmark(s) lies on the visual axis?The nodal pt & foveaWhat landmark lies on the fixation axis?The center of rotation CWhat are the 2 axises that can me measured in the clinic? What is the angle between these called?1) Pupillary Axis: normal to cornea 2) Line of sight: target to pupil ANGLE LAMBDAWhat # purkinje image do you see when doing topography or hirshberg testing?1Purkinje images are considered to be what kind of reflection?Specular ( no diffuse)What do we use to calculate how much percent of light is reflected when light travels from one medium to another?Fernel's Formula : (n2-n1)^2/(n2+n1)^2How much light does the tears from our eyes refect?2%A with motion specular reflection tells you the surface isConVEXAn against motion specular reflection tells you the surface isConCAVEThe 7 purkinje images are formed from ___________ & ____________Reflection and RefractionWhat is the distance from the front of the lens to the cornea?3.6 mmWhat is the lens thickness?3.6 mmWhat surface of the lens is steeper? Front or backBackWhen there is a change in refractive index is high, the ________ reflection you will getMoreHow many first order images are there? Who can see them?4 of them P1-P4 The doctor can see theseFirst order images are due to Reflection or Refraction?ReflectionWhere are Purkinjie images 1, 2, 3, 4 formed? What forms them?1: front cornea - pupil plane 2: back cornea - pupil plane 3: front lens - vitreous 4: back lens - pupil planeWhat purkinje images are considered lost light?1, 2, 3, 4 - first order imagesWhat first order images should move against and what should move with when moving a light?With: 1, 3 (front of cornea/lens) CONVEX surface Against: 4 (back of lens) CONCAVE surfaceWhat purkinjie images will you not see if someone is aphakic?3, 4What does purkinjie image 5 due to the contrast of the image seen? Why? What's the term for thisReduces contrast Image bounces off front of lens then front of cornea landing in the vitreous then dispersing its light all aroundHarmful light Pk images are #s ...5, 6How is purkinjie image 6 formed? What kind of image is formed?Reflected off back of lens then front of cornea Entoptic Image formed (eye itself creates this image)Purkinjie image 7 is the only Purkinjie image formed by ____________Refraction - this is the retinal image - useful lightPurkinjie images 1 & 4 are useful forEye movement monitors like in VFPurkinjie image 3 is useful forMeasuring accommodation in an optometerHow many refracting surfaces does Emsley reduced eye have? What is the power of this eye? AL?1 - radius of curvature: 5.5 mm power: 60 D Axial length: 22.22 mmDistortion is a type of __________ abberationSiedelWhat are the 2 types of aberrations that allow the eye to accommodate and for emmetrtopization?1) Blur/Defocus Abberation 2) Chromatic AbberationWhat's the difference between 1st order (lower) abberation and 2nd order (higher)?1st: anything that can be fixed by cyl/sph lens 2nd: anything that is not a 1st orderWhat do most types of abberation have in common?They reduce contrastWhat are the 3 sources of blur from a in focus image point?1) Scatter 2) Diffraction 3) AbberationsT/f The eye cares more about edges rather than point sourcesTrueT/f as defocus increases the point spread and edge spread function in min of arc also increasesTrueWhat's the difference between a square wave and a sine wave gratings? What's special about sine wave gratings?square wave: drastic dark to black Sin wave: gradual/sinusoidal change - maintain same spatial frequencies when blurredWhen the dark bars in a grating is 0, the contrast is _________ %100%Michelson Contrast formula =Lmax-Lmin / Lmax +LminWhat is a Modulation Transfer Function used for?To figure out the ability of the eye to transfer a spatial contrast from an object to a imageFor a regular lens, describe the modulation transfer function graphAs the spatial freq increases, the contrast of the image formed decreasesWhat formula do we use to calculate the image on the retina?Focal length x tan (angle lambda)THe formula w=deltaL x d is used for what?To calculate the diameter of the blur circle L is Diopters of Defocus D= mm of pupil size Answer will be in radiansThe size of a blurred image is how much bigger than the clear image due to defocus?You must add the size of the blue circle to the size of the clear image THe blurred image is larger than the clear image by the diameter of the blur circleWhat's special about a Gradiet index lens (GRIN)The n of the lens changes from the periphery to the centerWhy are blur circles round?They are reflections of the pupilIF the blur circles are identically if you are myopic or hyperopic, how does the eye know to acc only for hyperopes?There are many potential clues such as: -Myope: the image in front -Myope: image inverted -Shape of blur disk Some may or may not be usedWhat is 20/20 is cycles per degree?30 c/dIf there is no abberations in the eye (not usually the case) and the pupil is 6mm, whats the spatial freq it can resolve?>100 c/dWhat is the max spatial freq the following eyes can see: 1) Diffraction limited - 2mm 2) Abberation limited - 3 mm 3) Abberation limited - 6 mm1) 50 c/d 2) 30 c/d 3) 20 c/dA eye with 3 mm pupil with a normal abberations but is a: 1) 0.5 Hyperope or Myope 2) 1.0 Hyperope or Myope What is the max spacial freq they can see in c/d & in snellen format1) 0.5D - 15 c/d - 20/40 2) 1.0 D - 7 c/d - 20/80Why does defocus (ametropia) blur reduce contrast at high spatial freq but now low?The size of the blur circle compared to the grating detail sizeWhat 2 types of aberrations can cause spatial phase changes of the image?1) Spherical 2) Coma These can cause the image of the object to be out phase forming an asymmetric point spread functionWhn a spatial phase change occurs to an image, what part of the image is usually distorted? a) low spatial freq details b) high spatial freq detailshigh sf - fine detailsWhat feature of an image triggers myopia?low contrastT/F people with combos of defocus and aberrations can explain why people with aberrations dont become myopictrue because these form high contrast type images; high contrast images avoid formation of myopiaThe optical transfer function OTF is a combo of what 2 types of transfer functions?1) Modulation (contrast) 2) Phase (phase changes)why dont we see color fringes from chromatic abberations? 3 reasons1) small visual angle 2) low contrast 3) neural adaptationwhat are the 4 reasons we dont really have to correct for chromatic abberations?1) V lambda - how eyes are sensitive to low wavelength blue color frindges 2) Macula Lutea: absorbs blue light 3) Lens - yellow pigment: absorbs blue light 4) No S cones at foveaemmetropic pt - no acc - put +10 lens in front. What color wavelength is closest to the retinared - 700nmThe color findge outline of a hyperopic defocus is what colorredishMTF for myopic defocus - which color is transfered well?Red transfered very wellMTF for hyperopic defocus - which color is transfered well?blue transfered best b.c blue falls on retinaL cone contrast > M cone constrast > S cone contrast ? a) myopic defocus b) hyperopic defocusa) myopic defocusRaising an animal in red light - they get what kind of ametropia? what about in blue lightred: hyperopia blue: myopicFouriers TheoremAny complex waveform can be described as a sum of sine waves. These help figure out what the image will look like based of the object and MTFdefocus blur removes a) high spacial freq info b) low spacial freq infohighThe optical transfer function is a fourier transform of ________________ functionpoint spreadChromosteriopsis occurs because there is a _____________ shift between _______ & __________ images in opposite direction in each eyeSpatial phase - red/blueMajority of people see what blue or red in front due to chromosteriopsis? WhyRed - decentered pupils temporally 80% of pplMost eyes have LESS than _____#______ arc min of transverse chromatic aberration1 arc min (smaller than visual acuity threshold)If both eyes pupils are displaced temporally, we can produce what kind of kind of aberration? What is the result of this?TRANSVERSE CHROMATIC ABBERATION - binocular disparity betweeen red and blue targetsNasally decentered pupils people will say what color is in front? Blue or red?BlueWhy can you tell monocularly that the red checkered board is closer than the blue checkered board?The eye measures vergence of the colorsWhats the 2 types of glare?1) Discomfort glare: just discomfort - impairs vision 2) Disability glare- impairs visionThe following are true for what type of glare? 1) bright light causes discomfort 2) doesnt degrade retinal image 3) pupil size changes causes discomfort a) discomfort glare b) disability glarediscomfort glareWhat are 4 factors that determine the degree of discomfort glare?1) luminance of source 2) size of source 3) position of source to line of sight 4) background luminance of sourceThe following are true for what type of glare? 1) reduces contrast sensitivity 2) impare vision 3) contrast of retinal image reduced because of veiling luminance over the retinal image a) discomfort glare b) disability glareb) disability glareWhat is the main cause of stray light?scatter - small or large particle scater in the optical mediaThe __________-____________ effect reduces effect of stay lightStiles CrawfordWhat's another way of saying monochromatic aberrations?Wavefront abberationsNature's Aberration =Spherical wavefronts from objectsOptical vergence specifies ____________DistanceT/F Wavefront aberration gets larger towards the edges of the pupil rather than the centerTrueProcess of measuring wavefront aberration1) Shoot Laser spot into eye 2) light is scattered and is measured 3) a CCD charged coupled device maps the deviation of the light from a perfect grid pattern 4) the slopes of the rays are calculated 5) the wavefronts are then described as polynomial expansion equationsT/f its possible to get more higher order abberations post lasikTrueZernike Polynominals are defined in polar coordinates. What are these types of coordinates?Radial and Aguilar coordinatesspherical aberration is what order?4th order IN DA MIDDLEWhat are the 2 second order terms for aberration?1) astigmatism 2) DefocusComa falls under what order aberration?thirdodd orders 1,3,5,7 produce even or odd errors?they provide even errors same error infront or behind regardless [OPPOSITES]even orders 2,4,6 produce even or ordd errorsodd errors makes differnt images behind and infront retina [OPPOSITES]How much percent of retinal blur comes from higher order abberations? how about lower order (defocus/astig)/ innacurate accommodation?High Order Ab: 10% (small fraction) Low Order: 90%Up to how much microns of coma,trefoil,sph abberations can you expect for a large population before its a problem?0.2 micronsA person with supernormal vision can see what Snellen VA? what instrument can help get such vision?20/10 deformable mirror - adaptive optics____________ sph aberration contribues to night myopia a) + b) -positive most eyes have positive sph aberration when acc for far______________ sph aberration increases depth of focus a) + b) -negative sph aberratino becomes negative when acc for near periph of lens gets flatter, center gets steeperT/F abberations reduces spatial contrasts and spatial phasetrueWhen defocus and sph aberation have same sign what happens? what if opposite signs?same sign: bad! eye grows opposite: dont growWhat is an entoptic image?An image produced by the visual system and is projected into visual fieldWhat happens to the size of an entoptic image when you get closer and farther?Far away: large Close: smallWhy do we see floaters? Describe the movement of them.It tissue (retina,vitreous) that cast shadows on the retina. In reality they float up but look like they are sinking to the ptA sudden ↑ in floaters with flashes of light are a sign of ...Retinal detachmentWhy cant we see retinal blood vessels? When can we see them?They dont move - they are fixed - troxlers phenomenon . Retinoscopy, ophthalmoscope, slit lamp - light coming from the sideAngioscotomas?Areas of blindness in the shape of blood vessels - represented in the visual cortexT/f we can see a white and red blood cells passing through capillary loopsFalse - only white blood cells b.c they transmit lightT/f Every time the heart beats the white blood cells in retinal capillaries moveTrueHow can we use the blood free area of the fovea in the clinic?In diseases this area becomes bigger and bigger so we use this track the progress of the diseaseWhat color does the yellow macula lutea absorb?Blue - 430/490 nmWhat would you expect to see when steering at a bright blue light? How long does this lastA dark spot at fixation due to the macula lutea - short because the eye adapts - forms an after gray after imageWhat's the difference between Maxwells Tag aNd Haidinger Brush?Maxwells Tag - good for amblyopia/eccentric fixation - due to macula lutea Haidinger - due to polarization of macula lutea +RNFLHow are the pigment crystals in the macula arranged? What's the result of this?Radially - produces a dark band in a propeller/brush across the foveaT/f Haginders brush doesnt fadeFalse - it does due to troxlers fading. We can avoid this by rotating this in the Macula Intergrity Tester (MIT)What direction must light be in order for the RNFL and pigment need to be to ABSORB light?PerpendicularWhat can a person experience with conjunctivitis (mucus) glaucoma (edema in corneal epi) actinic conjunctivitis (snow blindness) etc..Pathological halosWhat are the 2 reasons we get a ciliary corona?1) Scatter of small particles in lens 2) Interference on retinaT/f we can get an entoptic image from the lens suturesTrue - 6 lined thingWhat is a phosphene?Visual sensation produced by stimul not light Pressure Electrical Field Magnetic Field X RaysWhat forms blue ares of the retina? (Phosphene)Small eye movements that trigger images of the Papillo macular bundles of the RNFL due to action potential currents triggering underneath photoreceptors [secondary stimulation] (engineers who work with LEDs)T/f A saccadic movement can produce a phospheneTrue - traction on the retina at the edges of the optic nerve (FLICK PHOSPHENE)Why can we get a scintillating Scotoma (relative scotoma)?Constriction/dilation of blood vessels in the visual cortex (with or without migraine headeache)What can a person with Charles Bonnet Syndrome say they see?People with poor vision that experience visual hallucinationsWhat are the 2 generaltypes of effects produced by the Stiles Crawford Effect?Type 1: Brightness Type 2: color When light enters through the center of the pupil it looks brighter and different color than if it entered through the edgeWhat 3 things does the stiles Crawford effect type 1 reduce?1) scattered light 2) size of pupil 3) aberrations and defocus blurWhat does the stiles crawford effect type 1 do to the depot of focus↑ it because makes pupil smallerWhat did Fincham conclude in regards to the stiles Crawford effect?it is the Stiles Crawford Effect (type 1) that allows the eye to measure the vergence of lightT/f cones are fiber optic in natureTrueWhat direction are the cones pointing too in the Stiles Crawford Effect? Why do they point this way?In the direction of the center of the pupil. They do not accept light coming off axis or large incident anglesWhat kind of filter does the Stiles Crawford Effect act as? What do these types of filters do to the dof?Anodizing - ↑ DOFIn reality are cones pointing in dead center of the pupil?No, its actually pointing 1mm Nasal from pupilIf you neutralize the Stiles Crawford Effect, what does it do to accommodationNothing, so the Stiles Crawford Effect is not providing info for focusingT/f depth of foveal pit had no effect on accommodationTrue - but we need to test pts with very flat foveal pitsRelectometry + Adaptive Optics can help find the orientation of what?ConesLight can form different patterns when falling into a cone due to what?InterferenceWhat 4 things determines what mode pattern light will take when it is in a cone?1) Diameter of cone 2) n 3) wavelength 4) angle of incidenceDo modal patterns change when light vergence changes?Eh not really, because in white light, the different wavelengths of light dont form such. These modal info gets lost after receptor levelWhat's different when light falls on cones in respect to their mode for a person who is myopic v hyperopicThe pattern of bleaching of cones is differentT/f Accommodation can be influenced by cognitive behaviorTrueWhy do we call the accommodative system adaptive?B.c it measures the blur and tries to change itWhat types of abberations does accommodation changeDefocus and spherical abberationT/f accommodation Maximizes contrast via positive feedbackFalse - negative feed backWhat happens if negative feedback is removed from the accommodative systemThe eye wont accommodateWhat instrument do we use to measure accommodation continuously?Infrared Optometer - Shack-Hartmann aberrometerWhat kind of oscillations do people show when they have accommodation problems?LARGE oscillations with sudden loss of focusesWhat happens when you use a reversed chromatic abberation lens and measure accommodation?The vergence of light will tell the eye to acc one way The chromatic abberation of light with tell the eye to acc the other eye It would be confusedWhat is the latency for accommodation (reaction time)?360 msWhat is the time constant for accomodation250 msDoes the accommodative system prefer slow or fast temp freq? How about High, Middle, Small Spatial Freq?Slow Temporal Feq Intermediate Spatial FreqT/F some people you CA to focus while others dontTrueIn hyperopic or myopic ppl - does the blood vessels interact with viewing snellen letters? Impact of this?Hyperopic - makes the letters higher contrast at intermediate spatial frequency with diff phase contrast. When the retina has higher contrast the eye doesnt grow into myopiaT/F Blur from feedback is too slow to provide sign of defocus for dynamic accommodationTrueT/F The retina detects vergence of lightTrueT/F Accommodation responds directly to light vergence itselfTrue

Optics 2 - Final

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