1. it's what patients need
2. financial success of practice
3. optics is dynamic field
4. optics diagnostic instruments

The scope of practice includes the diagnosis & treatment of what?

• refractive errors **
• binocular vision disorders
• ocular disease

• Laser (HOA, Aberrometer)
• Birefringence
• Optical Coherence Tomography

primary light source --> illumination of object --> eye --> retina --> lateral geniculate bodies --> primary visual cortex --> perceived image 

• reflects, bends, diffracts, & interference like a wave
• wave = defines how light travels through media 

• particles of light = photon
• packets of energy
• photon = defines how light interacts/effects matter 

c = 3x10⁸ m/s

slower in a more dense medium 

f = v/λ

frequency (cycles/sec or Hz) =  velocity / wavelength 

i.e. f = (3x10⁸m/s) / [wavelength (m)]

• ratio of speed of light in a vacuum to the speed of light in a material 
• no units 
• light travels slower in high index materials 

n = c/v_m

index of ref. = (speed of light) / (velocity in medium) 

v_m = (λf)_m

velocity in medium = (wavelength) x (frequency)

• 1/4 to 1/2 the speed of light in air (vacuum)
•  n (ophthalmic lenses) = 1.33 - 2.00
• impossible to have index of ref. less than 1

• wavelength dependent
• higher for short wavelengths (violets & blues)
• lower for long wavelengths (red)

588 nm (yellow)

when no subscript is used (n), the index of ref. for yellow helium light (n_d, λ = 588 nm) is used...used for white light

identified by a subscript; subscript refers to a spectral (or Fraunhofer) line

The traveling, reflecting, and refracting of light to form images is what study of optics?

(uses RAYS to define light)

• physical optics
• involves scatter, diffraction, reflection at interfaces, interference (constructive and destructive)

measurement of light

• brightness
• color 
• intensity

• absorption
• reflection
• scatter
• diffraction
• refraction ** (primary tool to correct vision)

• light energy is absorbed by material 
• absorption strength is a function of the incident wavelength of light 

• strong absorber is usually opaque unless very thin (gold)
• weak absorber is usually transparent unless very thick (water)

• surface or boundary phenomenon
• occurs when light is incident upon a medium having a different index of refraction than that of the medium through which the light was originally traveling

• wavelength dependent
• strong absorbers are strong reflectors (metals)
• weak absorbers are poor reflectors (water, glass)
• specular reflection from smooth surface
• diffuse reflection from a rough surface

• dispersion of light through an inhomogeneous material 
• translucent materials
• atmosphere
• wavelength & particle size dependent

• reduced amount of light in image on retina
• scattered light that falls on retina reduces contrast & obscures detail in the image of interest

• ability of light to propagate around corners
• more apparent for longer wavelengths
• due to relatively short wavelengths of visible light (400-700 nm) diffraction is often negligible EXCEPT if light passes through very small opening (small pupil)

• Refractus; to bend or break back (think pencil in water)
• due to speed of light in different media

• assumes light rays travel in a straight line
• allows for predictive nature of geometrical optics 

• neighboring rays travel independently 

aka law of refraction 

n₁sinθ₁ = n₂sinθ₂

(primary ind. of ref. x sinθ of incidence) =

(ind. of ref. of 2nd medium x sinθ angle of ref.)

• anything that gives off light & can be viewed 
• can be original source of light or seen by light reflecting off of it 

• a light source that is infinitely small or sufficiently far away that it acts infinitely small (like a star) 

• emits equally in all directions (3D)
• same speed in all directions
• light wave propagates energy
• light waves similar to 2D water waves; ripples known as wavefronts 

The shorter the radius of curvature, the ________ the curve. 

The longer the radius of curvature, the _________ the curve. 

The smaller the radius of curvature, the steeper the curve. 

The larger the radius of curvature, the flatter the curve. 

greater curvature = ______ divergence

less curvature = _______ divergence 

greater curvature = more divergence

less curvature = less divergence 

• drawn perpendicular to light wavefronts
• usually represented by arrows

Explain the following sentence:

Light "rays" don't really exist. 

• light is energy and light rays are imaginary (just a convenient way of showing convergence/divergence of wavefronts)
• allows us to predict things well
• allows us to trace light through lenses 

• 20 feet (or 6 meters)
• by the time light travels this distance from a point source, the waves are "flat enough" for clinical purposes & divergence is so small that its insignificant 

• light will always travel from left to right in our diagrams
• in reality, travels in all directions but only interested in light travelling in one particular direction (which will change depending on circumstance) 

• width b/n rays inc. as light moves away from the focus point
• used to illustrate wavefronts getting flatter (flatter = less divergence ---> divergent rays = wavefront becoming less divergent as it travels farther & farther) 

• width b/n rays dec. as the light moves toward the focus point
• illustrates wavefronts getting more curved/steeper

• composed of an infinite number of point sources 
• represented by arrow in problems
• has measurable area

• usually a physical object in space
• diverging pencil incident on an optical system 

• converging pencil leaving optical system
• location = point of convergence
• always created by optical system
• not natural in the physical world
• optically vs. physically real image 

• diverging pencil/wavefront leaving the optical system
• not able to be projected on a screen
• location = "origin" point of divergent rays
• many times are visible 

• converging pencil/wavefront incident on optical system
• location = point of convergence of rays
• optically real image can serve as a virtual object 

what the incident wavefront is doing

(real-diverging, virtual-converging)

what the exiting wavefront is doing

(real-converging, virtual-diverging) 

• lens causes shape of the wavefront to change
• change in vergence 

• pinhole doesn't focus light; doesn't cause change in shape of the wavefront
• pinhole can produce a relatively clear image

small hole allows paraxial rays through but not peripheral rays 

(smaller blur circles)

• assume rectilinear propagation
• each point produces blur circle on image screen
• size of blur directly proportional to aperature diameter
• resolution of image depends on blur circle size compared to overall image size 

M_L = h' / h = l' / l

image size related to object size by similar triangles

• improvement = blur caused by refractive error; provides guide for potential acuity
• no/minimal improvement = blur likely caused by disease

• non-uniform = less contrast (shadow not as noticeable)
• uniform = shadow more distinguishable 

What happens to the observations of floaters if the

floater moves forward in the eye over time?

• further from screen, shadow is larger with more penumbra than umbra (not as dark & distinct) 

• quantifies the curvature of the wavefront at a given point in space
• unit of measure is diopter (D)

optometry largely about manipulating vergence

• refractions
• contact lenses
• spectacles 

reciprocal of the distance from/to a point souce,

or 

reciprocal of the distance from/to a point focus

vergence is dependent upon what and assumes what?

• media dependent (index of ref. makes a difference; n for air = 1.00)
• assumes uniform media & spherical wavefronts

L = n / l

(vergence = ind. of ref. of light passing through / distance from point point of interest to point source/focus; aka radius of curvature of wavefront)

distances always in meters!

negative

• always measure object distances from the optical system/wavefront to the object
• if measuring in same direction as the light is travelling, distance is positive
• if measuring opposite direction as light is traveling, distance is negative 

• if the amount of vergence at point A is known, then the vergence at point B can be found
• 2 ways: calculated using L = n/l or using the "Downstream Vergence" formula