Any two optical systems are required to be aligned _______ to do efficient transmission
Coaxially
The human eye has 4 major optical surfaces, 1 aperture, and the retina, all of these are approximately ________
Equal
What are the axes of the eye
- Optical axis
- Pupillary axis
- Pupillary axis
- Line of sight
- Achromatic axis
- Fixation axis
- Keratometric axis
- Receptor axis
- Neural axis
The axis containing the centers of curvature of the eyes optical surfaces
Optical axis
The straight line along whihc a ray both enters and leaves the system
Optical axis
This axis a line of rotational symmetry
Optical axis
What are the decentered lights reflected off the surface of the eye
Purkinji images
-from 4 surfaces of decentered eye, and cant be aligned
Roatationally symmetric optical systems need one axis, which is
Optical axis
Not rationally symmetrical systems need _______
More axes
Like humans do
Some axes are dependent on
Idealized properties of the eye (nodal points, center of rotation)
This axis is used for all visual functions
Visual axis
The lone connecting the foveola and the fixation point passing through the nodal points
Visual axis (fovea achromatic axis)
Visual axis is called as ____________ as the rays passing through nodal points of the eye exhibit zero transverse chromatic aberration (TCA)
Foveal achromatic axis
The place of intersection of visual axis with the cornea is known as ____________, whihc is used in order to characterize cornea exactly
Ophthalmometric pole
The curvature of the cornea ________ as it moves away from the apex
Flattens
_______________ exactly locates the postion on the cornea
Ophthalmic pole
What is the ophthalmometric pole not influenced by?
Pupil fluctuations or accommodation
This axis is convenient reference point for visual functions
Visual axis
What does the visual axis not depend on
Pupil position
The line normal to the cornea passing through the center of the pupil
Pupillary axis
Which axis is important for treating eccentric fixation
Pupillary axis
This axis is used for aligning optical instruments to the eye
Pupillary axis
If the eye was a centered system and the pupil was also centered, the pupillary axis would lie along what axis
Optical
Adaptation to heterotropia
Eccentric fixation
Ray from fixation point that reaches the foveolar via center of the pupil
Line of sight
The path of foveal chief ray from fixation point
Line of sight
The paraxial optics, line of sight is called
Paraxial pupil ray
The postion at which the line of sight intersects the cornea is called the
Corneal sighting center
Where is the corneal sighting center in relation to the ophthalmometric pole
Superior
As useful reference when examining corneas that are undergoing refractive surgery
Line of sight axis
The line connecting the nodal point and the center of the pupil
Achromatic axis (foveal achromatic axis)
The ray passing through the achromatic axis does not suffer from what
Any transverse chromatic aberration (TCA)
Achromatic axis is similar to optical axis, but dependent on what
Pupil position
The line passing through the fixation point and the center of rotation of the eye
Fixation axis
This axis is the reference for measuring eye movements
Fixation axis
This axis is just an approximation, depends on direction of rotation
Fixation axis
The line passing through the fixation point and the center of curvature of anterior cornea
Keratometric axis
This axis is used for alignment of corneal topography measurements
Keratometric axis
The point at which the keratometric axis intercepts the cornea is sometimes called the what
Vertex normal
__________ is the center videokeratographs showing corneal contour
Vertex normal
Light from pupil has to be _______ to cone receptors
Coaxially
Due to the fiber optics characteristics of the retinal photoreceptors, light arriving at the retinal plane along the photoreceptors axis will be ___________ and have a higher probability of being absorbed by the photopigment
Totally internally reflected
Why are humans more sensitive to light passing through the section of the pupil that is coaxial with the receptor axis
Due to the fiber optics characteristics of the retinal photoreceptors, light arriving at the retinal plane along the photoreceptors axis will be totally internally reflected and have a higher probability of being absorbed by the photopigment.
The pupil appears to apodized
Light brighter centrally than peripherally. Cones like signaled from center of pupil, not peripherally
Apodization
The sampling density, and hence the spatial band-width of the neural image peaks at the _______ and declines monotonically with increasing eccentricity
Foveola
Angle between the optical and visual axis
Angle alpha
Angle formed at the first nodal point by the optical and visual axis of the eye
Alpha angle
The angle between the visual axis and the optical axis (angle alpha) is considered to be ______ if the visual axis is on the _______ side of the optical axis in _________
- positive
- nasal side
- object space
The mean value of angle alpha is often taken to be about _________
+3-+5 degrees horizontally
The visual axis is downwards relative to the optical axis by _____
2-3 degrees
Angle between the pupillary axis and line of sight (LOS)
Angle lambda
Angle formed at the first nodal point by the optical and visual axis of the eye
Angle lambda
For most patients, the pupillary axis is _______ to the line of sight in ________. This is called a ______ angle
Temporal
Object space
Positive
Angle lambda between the two eyes
Should be similar
The angle lambda is important for diagnosis of
- eccentric fixation (monocular testing)
- heterotropia (binocular testing) (Hirschberg)
Angle between the pupillary axis and visual axis
Angle Kappa (k)
For practical purposes, angle kappa is the same as _____
Angle lambda
Angle between the visual axis and achromatic axis
Angle psi
Both the visual axis and and achromatic axis both pass through the ____
Nodal points
The mean psi angle was determined to be _____
+2.1 degrees
Positive sign of angle psi indicates that visual axis is incline ______ to the achromatic axis in _____ space
- nasally
- object
Angle between the optical axis and he fixation
Angle gamma
The angle gamma is within _____ of angle alpha for objects distances greater than 50cm
1%
The images formed by reflection off the optical surfaces of the eye are referred to as
Purkinje images
What is the brightest purkinje image
PI off the anterior cornea
What Purkinje image is real and innerverted?
PIV from the posterior lens
What are the major refracting surfaces what produce a purkinje image
- anterior corneal surface
- posterior corneal surface
- anterior lens surface
- posterior lens surface
What are some things that purkinje images are important for
- keratometry
- corneal topography
- alignment of optical instruments
What are the steps for calculating the location of the Purkinje image I?
- Calculate the reflective power of the cornea
- Location of the reflected image
- Distance from the corneal surface
Determine the location of the PI by treating the anterior corneal surface as a _______
Mirror
Consider the light source to be at infinity and anterior cornea is 7.80mm, calculate PI
P=F=-2/r
F=-2/(.0078)
F=-256.41D
L’=L+F
L’=0-256.41D (light at infinity =0)
L’=-256.41
L’=-1/l
L’=-1/-256.41=.0038=3.90mm
Alternate method for finding PI if light is at infinity
F=r/2
F=(7.8mm)/2
F=3.90mm
A light is located 10.00cm anterior to the cornea of the eye. Assuming that the anterior surface of the cornea has a radius of 7.80mm, locate the first purkinje image
P=F=-2/r
-2/.00780=-256.41
L’=L+F
L’=-1/.1 + -256.41
L= -266.41
L’=-1/l
I’=-1/-266.41
I’=3.75mm
Purkinje image located 3.75mm to the right of the cornea
Combining the refracting surface and mirror as a single system
Equivalent mirror
Steps for finding the location of PIII image
- Calculate the reflective power of the cornea
- Treating the anterior lens as the object, find its image after refraction by the cornea
- Next, treat the anterior lens’ center of curvature as an object and find its image after refraction by the cornea