Axes and angles Flashcards
any two optical system is required to be aligned _________ to do efficient transmission
aligned coaxially
the pupil is decentered________ and the fovea is decentered_____________
Pupil: nasally
Fovea: temporally
what is the optical axis of the eye?
- the axis containing the centers of curvature of the eye’s optical surfaces
- line of rotational symmetry
can purkinji images reflected from four surfaces of decentered eye be aligned?
nope
rotationally symmetric optical systems need one axis, which is what?
optical axis
what is the visual axis?
- the line connecting the foveola and the fixation point passing through the nodal points
- no chromatic aberrations
the place of intersection of visual axis with the cornea is called…
ophthalmometric pole
is the visual axis dependent on pupil position?
-nope
what is the pupillary axis?
the line normal to the cornea passing through the center of the pupil
-we do not care if it hits the fovea
what axis is good to measure the amount of eccentris fixation?
the pupillary axis
eccentric fixation is an adaptation to what?
heterotropia
what is the line of sight?
ray from fixation point that reaches the foveolar via center of the pupil
what is the point called where the line of sight intercepts the cornea?
corneal sighting center
the line of sight is a useful reference when examining what?
corneas that are undergoing refractive surgery
what is the achromatic axis?
- the line connecting the nodal point and the center of the pupil
- no chromatic aberrations
- DEPENDENT ON PUPIL POSITION
what is the fixation axis?
the line passing through the fixation point and the center of rotation of the eye
-depends on direction of rotation
what is the fixation axis a good reference for?
measuring eye movements
what is the keratometric axis?
the line passing through the fixation point and the center of curvature of anterior cornea
the keratometric axis is used for alignment in what?
corneal topography measurements
the point at which the keratometric axis intercepts the cornea is called what>
vertex normal
what is the photoreceptor axis?
-light arriving a the retinal plane along the photoreceptor axis will be totally internally reflected and have a higher probability of being absorbed by the photopigment
what is the neural axis?
increasing eccentricity declines image quality because there are less cones
what is angle alpha?
- angle between the optical and visual axis
- angle formed at first nodal point by the optical axis and visual axis
if the angle between the visual axis and the optical axis is considered to be positive when?
when the visual axis is on the NASAL side of the optical axis in OBJECT space
what is angle lambda?
angle between the pupillary axis and the line of sight
what is considered positive angle lambda?
-the pupillary axis is TEMPORAL to the line of sight in OBJECT space
angle lambda is important for diagnosing what?
- eccentric fixation
- heterotropia
what is angle kappa?
angle between the pupillary axis and visual axis
angle kappa is the same as what?
angle lambda
what is angle psi?
the angle between the visual axis and the achromatic axis
-both go through nodal points
what is positive angle psi?
-the visual axis is inclined NASALLY to the achromatic axis in OBJECT space
what is angle gamma?
the angle between the optical axis and the fixation axis
angle gamma is within 1% of angle alpha for object distances_______________
greater than 50cm
