5: Models of Ocular Optics Flashcards
the two main classes of schematic eyes are
- paraxial
- finite (wide angle)
2 criteria of paraxial schematic eyes
- spherical refracting surfaces
2. surfaces centered on a common optical axis
paraxial eyes are only accurate for paraxial ray tracing, which means:
that the rays must pass within the paraxial zone (to trace outside the paraxial zone with greater accuracy requires finite eyes)
list the 3 types of paraxial schematic eyes
- reduced eye
- simplified eye
- exact eye
a reduced eye has
only one refracting surface and its single refractive medium has a uniform refractive index
a simplified eye has
a single corneal surface and a crystalline lens with two surfaces and uniform refractive index
an exact eye has
at least two corneal surfaces and at least two crystalline lens surfaces
for Emsley’s reduced eye:
because the eye is emmetropic and contains but one refracting surface, its axial length corresponds to its ____
second principal focal length (f’)
for Emsley’s reduced eye:
what values are smaller than normal
the radius of curvature (r) and the axial length
for Emsley’s reduced eye:
the single refracting surface must contain power of
both corneal and crystalline lens
for Emsley’s reduced eye:
because the retina is artistic (drawn curved), this eye is not suitable for modeling what imaging properties?
not suitable for modeling peripheral imaging properties of the eye
the first principal focal point (F) of the eye is the point on axis at which:
an object must be placed to provide an image at optical infinity
the second principal focal point (F’) of the eye is the point on axis at which:
an image is formed from an object at optical infinity
in schematic eyes, why are the principle point conjugate?
they allow complicated schematic eye to be treated as if it were a thin lens
the aperture stop of the eye is the:
anatomical iris
the entrance pupil (E) is the:
image of the iris aperture when viewed from object space
the entrance pupil is _____(closer, farther) to the cornea than the aperture stop
closer
the entrance pupil is ______ (smaller, larger) than the aperture stop
larger
the exit pupil (E’) is the:
image of the iris aperture when viewed from image space
the exit pupil is _____(closer, farther) to the cornea than the aperture stop
farther
the exit pupil is ______ (smaller, larger) than the aperture stop
larger
a ray directed towards the center of the entrance pupil appears to emerge from the center of the exit pupil, this ray is called the
chief ray, or paraxial pupil ray
the center of rotation of the eye is approximately ____ mm behind the corneal vertex
15 mm behind the corneal vertex
the OSA line of sight (z-axis) is the path of the:
chief ray from the fixation point point to the center of the entrance pupil
the OSA x-axis and y-axis are located:
both are lying in a frontal plane through E
- the x-axis is horizontal
- the y-axis is vertical
the optical axis is defined as:
the line of ‘best fit’ through the centers of curvatures of all the surfaces
what is the significance of the line of sight?
is that it describes the center of the actual pencil of rays that enters the eye
the fovea is ____ to the optical axis on the retina
temporal
the visual axis is composed of ___ line segments
two
what are the two line segments of the visual axis?
- connects the fixation point to the first nodal point (N)
2. connects the second nodal point (N’) to the fovea
polychromatic rays incident on the eye are subject to the phenomenon of
dispersion
what can dispersion cause
rays entering the eye are usually refracted differently depending on their wavelength
what is the foveal achromatic axis?
where light rays of all wavelengths pass undisposed from fixation point to fovea
the pupillary axis is the line that is
normal to the anterior corneal surface (containing the center of curvature of the anterior corneal surface, Cc) that passes through the center of the entrance pupil (E)
the fixation axis is the line
connecting the fixation point to the presumed center of rotation of the eye
angle alpha is defined as the angle between the
optical axis and visual axis
angle lambda is defined as the angle between the
pupillary axis and line of sight
the significance of angle alpha is that
the fovea does not lie on the optical axis of the eye
the significance of angle lambda is that
the fixed relationship between pupillary axis and line of sight is useful in detection of strabismus
the clinical form of the Hirschberg test is useful as an:
objective, gross assessment of eye alignment, particularly in infants
in the Hirschberg test, the subject fixates a small source such as a penlight. light is reflected from the anterior corneal surface and is visible to the examiner as a small image, known as the
Purkinje-Sanson (PS) image
