Unit 1 Flashcards
Vergence
The simultaneous movement of the pupils of the eyes during focusing
Optics
Light reaches the eye and we see
Christian Huygens
Proposed wave theory of light: lights comes in waves and spreads out in all directions.
Isaac Newton
-Corpuscular theory of light: light is emitted by tiny particles called corpuscles
-geometric nature of reflection could be explained if light were made from particles
-7 visible colours
James Clerk Maxwell
-Father of modern physics
-electromagnetic theory of light
-light waves have electrical and magnetic properties
Max Planck
Light waves travel as packages of energy called photons
-quantum theory
Albert Einstein
-light waves travel at a constant speed
-theory of relativity
Leon Foucault
Accurately determined speed of light
Wavelength, frequency, speed
Frequency=speed/wavelength
F=v/λ
Frequency is inversely related to wavelength
Electromagnetic spectrum wavelengths: shortest-longest
Gamma rays, x-rays, UV, visible spectrum, Infrared, Microwaves, radio waves
Electromagnetic spectrum wavelengths: longest to shortest
Radio waves, microwaves, infrared, visible, UV, x-rays, gamma rays
Foot candle
Light from a single candle falling on a surface 1 foot away (1lumen/sq. ft.)
Lumen (luminous flux)
-Quantity of light emitted per second
-16 lumens per watt
Lux
1 lux is produced when 1 lumen is incident on one square meter area. 1 Lux is always 1 lumen/sq. m.
-1 lux = 10.764 lumens
Geometric optics
-Branch of optics dealing with light rays
-study of effect of mirrors and lenses on light rays
Real image
Point source on left, image on left
Virtual image
Point source on left, image on right
Concave mirrors
-Real, inverted, minified
-converging mirror
Convex mirror
-virtual, erect, minified
-diverging mirror
Refraction of light
Light moves from less dense material to more dense material and the shape bends. (Like a straw in a glass of water)
Index of refraction
N=speed of light in (medium 1)/ speed of light in (medium 2)
N=n1/n2
Snell’s law
(n1)sin(θ1)=(n2)sin(θ2)
Where n=refractive index of medium
And θ=angle of incidence(1) and refraction(2)
(The numbers here are not numbers but distinctions and should be in subscript)
Light bends toward ______ of prism
Base
1 prism diopter will displace an image 1 __ at a distance of 1__
-express in equation form
-1cm at a distance of 1m
-P=C/D
Where P=prism power (PD)
C=displacement (in cm)
D=object distance from prism (in m)
Convex and concave: positive or negative powers
Convex: + power
Concave: - power
Converging lens
-plus power
-Focal point is behind convex lens
Diverging lens
-minus power
-Focal point is in front of concave lens
Vergence power
-measured in diopters (D)
-Reciprocal of the distance between a point of reference and the point of focus
-P=1/f
Where P=vergence power
f=distance (in m) from point of focus
Distance of the OBJECT from the lens
U= 1/u
Where U= vergence of the object rays (D)
u=distance from lens (m)
Distance of the IMAGE from the lens
V=1/v
Where V=vergence of the image (D)
v=distance (m)
Image AND object vergence equation
V=U+P
Image and object vergence: location of positive and negative figures
Positive: image is behind lens
Negative: image is in front of lens
P=C/D
P=prism power (PD)
C=displacement (cm)
D=object distance from prism (m)
P=1/f
P=vergence power (D)
f=distance from point of focus (m)
U=1/u
U=vergence of the OBJECT rays (D)
u=distance (m)
V=U+P
V=vergence of image
U=vergence of object rays
P=power of lens
U=
V=
u=
v=
U=vergence of OBJECT rays
V=vergence of IMAGE RAYS
u=distance of the OBJECT from the lens
v=distance of the IMAGE from the lens
Magnification
Image size/object size
OR
Image distance/object distance
Plano
No sphere power
Perscription transposition how to
Sph/cyl/ax
A B C
1)A+B
2)change sign of B
3) rotate axis
Spherical equivalent
-A way to convert astigmatism prescription into just sphere for contact lenses
-if cylinder is less than 1
How to determine spherical equivalent
-add half of the cylinder power to the sphere power
-remove cylinder and axis
Refractive interfaces within the eye
Anterior cornea, posterior cornea, anterior lens, posterior lens
Refractive power of the eye
-corneal power
-lens power
-total refractive power: 60D
-corneal power: 43D
-lens power: +15D to +20D
The reduced or simplified eye (Gullstrand’s schematic)
-assumes all power occurs at the corneal interface
-is 58.60D
-is 22.6mm in length
-anterior focal point is 17mm in front of cornea
-nodal point is 5.6mm behind cornea
Optical pathway
-retina
-optic nerve
-optic chiasm
-Lateral genticulate body (LGB)
-optic radiations
-visual cortex
Emmetropia
The focal point for parallel rays coming into the eye is ON the retina (needs no correction)
Ametropia
-refractive error is present
-myopia (short but forms a point) (eyeball is longer)
-hyperopia (long but forms a point)(eyeball is shorter)
-astigmatism (doesn’t form a particular point)
Conoid of Sturm
Spherocylincrical lens produces two perpendicular focal lines
-circle of least confusion is the area closest to a sphere. Occurs midway between the lines. Best overall focus
Aniseikonia
Unequal image size between eyes. If not corrected can cause lazy eyes. The better eye will get used and the worse eye will stop being used.
Anisometropia
Unequal refractive powers between eyes.
Antimetropia
Eyes are positive and negative
Accommodation
Eye changes it’s power to focus on near objects. Ciliary muscle contracts to cause increased power of eye’s lens.
Amplitude of accommodation
Measured in Diopters. Gradually decreases with age. Lens becomes less flexible.
Donder’s table
Age: 10 20. 30. 40. 50. 60. 70.
Acom: 14 10. 7 4.5 2.5 1 0.25
Accommodative conditions
Presbyopia- loss of accommodation with aging
Latent hyperopia- amount of hyperopia that can be overcome with accommodation.
