Geometric optics Flashcards
Define nodal point
The point on the axis through which light passes undeviated. For a single spherical refracting interface, the nodal point is the center of curvature.
Lateral magnification
Image height/object height
Image location/object location
Object vergence/image vergence
How does internal reflection occur
If the incident angle (angle entering) is larger than critical angle.
Only occurs when going from dense –> rare
Ex: water –> air (similar to aqueous -> air)
Snell’s Law
(n1)(sintheta1)=(n2)(sintheta2)
Stops: 2 elements that limit an optical systems field of view
Aperture stop- Physical entity that limits the amount of light passing into an optical system when viewing an object. (Pupil is the anatomical aperture stop of the eye)
Field stop- Limits the size of the object that can be imaged by the system.
*both limit FOV.
The anatomical aperture stop of the eye
Pupil
Images of the aperture stop formed by lenses in front or behind the stop constitute
Pupils
Entrance pupil and exit pupil
Entrance pupil
Image of the aperture stop formed by all the lenses in front of it. If there are no lenses in front, the entrance pupil itself is the aperture stop.
Determines the size of the cone of light that enters the system.
How to find:
- Go to the axial object point
- Look towards the front of the system
- The EP is the element or image of an element that subtends the smallest angle.
Exit pupil
Image of the aperture stop formed by all of the lenses behind it. If there are no lenses behind it, the exit pupil itself is the aperture stop. The exit pupil determines the size of the cone of light that exits the system.
Images of the field stop formed by the lenses in front of or behind the stop constitute
Ports
Entrance port
Image of the field stop formed by the lenses in front of it
Exit port
Image of the field stop formed by lenses behind it
Depth of focus vs depth of field
Depth of focus- Interval surrounding the RETINA If light is focused in this area, the object will be in focus.
Depth f field- Interval surrounding the FIXATION PLANE in which an object can reside and still be in focus with NO CHANGE IN ACCOM. If the object is located in this region, there will be no perceivable blur.
How do these affect depth of field
- Focal length
- Aperature size
Decrease focal length –> increased depth of field
Increase aperture size –> decreased depth of field and decreased depth of focus (opposite of pin hole effect??)
How does PH improve vision
It increases the depth of focus- the interval surrounding the retina in which an eye sees an object as in focus.
Field of view
Extent of the object plane that is imaged.
A minus lens increases FOV, plus lens decreases
Field of fixation
angle made from the optical axis by the entrance port as measured at the center of rotation of the eye- usually 14mm from the cornea.
COLC
- What is it
- Measured in what units
- located where
Point of best focus for a lens
Measured in diopters
Located between the 2 line images that are formed in the principal meridians.
Interval of Sturm
- What is it
- Measured in what
Distance between two foci of the principal meridians. It is linear! Distance between the locations of the horizontal and vertical line formation.
How does the equivalent power of a thick lens change if you increase the index of refraction?
Fe increases
How does the equivalent power of a thick lens change if the thickness of the lens is increased?
Fe will decrease
Another name for pantoscopic tilt
-and what is it
Retroscopic tilt
Rotation about the 180 meridian
Faceform tilt refers to rotation about the __ meridian.
90
Rotating a lens with minus cyl with the following axes will result in:
- Pantoscopic tilt of a minus lens
- Pantoscopic tilt of a plus lens
- Faceform tilt of a minus lens
- Faceform tilt of a plus lens
- Minus cyl x 180
- Minus cyl x 090 / plus at 180
- Minus cyl x 090
- Minus cyl x 180 / plus at 090
What is the critical angle
Angle of incidence where the light ray that enters the surface has an angle of refraction of 90
Ex: The critical angle is 30 degrees, what is the corresponding angle of refraction? 90
Collimating lens
Lens that creates parallel light from a given target or light source.
The object for a collimating lens is located at the primary focal point.
How to connect apical angle of the prism, index, and deviation angle
Ex: A 10 degree prism deviates light by 5 degrees. What is its index of refraction?
Deviation angle of the prism = (nprism - 1)(apical angle of prism)
During keratometry, the cornea acts as a _____
The corneal reflex is ___ and ___
Acts as a minus mirror (convex)
The corneal reflex is upright and virtual- purkinje image #1
The virtual image becomes the object for the objective lens, which creates an image that is real and magnified. The keratometer measures the size of the real image and then converts it to radius of curvature.
What direction (axis or power) is where the cyl power is maximum?
Power
Axis direction is where cyl is zero
Which has the longest wavelength/shortest frequency?
Which has the shortest wavelength/longest frequency
Radio
Gamma
Order of wavelengths from shortest to longest
Gamma x Ray UV Visible IR Microwave Radar TV Radio
Scanning laser polarimetry
Utilizes polarized light to measure the thickness of the RNFL.
Polarized sunglasses
-What direction is the transmission axis? What direction is the absorption axis?
Vertical is transmission axis
Horizontal is absorption axis— blocks horizontal glare
Nd:YAG can be used for what 3 procedures
SLT
PCO
LPI
Near infrared is used when (IR-A)
OCT
Excimer lasers are used for
Refractive surgeries- PRK and LAIK
Argon lasers are used for
PRP, ALT, LPI
