Lecture 6 - Axes And Angles Flashcards
Optical and Neural Axes of the human eye
Any two optical systems is required to be aligned coaxially to do efficient transmission.
The human eye has 4 major optical surfaces, 1 aperture, and the retina. All of these are all approximately coaxial.
The optical and neural components of the eye are rigidly attached and objects are placed on axis by rotating the eye.
There is a superior signal transmission when optical and. Neural axes are aligned with each other.
Optical and neural Axes of Eye
- Optical Axis
- Visual Axis
- Pupillary Axis
- Line of sight
- Achromatic Axis
- Fixation Axis
- Keratometric Axis
- Receptor axis
- Neural axis
- Optical Axis of the eye
Definition: the axis containing the centers of curvature of the eye’s optical surfaces.
Optical axis is a straight line along which a ray both enters and leaves the system
It is a line of rotational symmetry
Axes of the eye
Rotationally symmetric Optical systems need one axis - optical axis
Not rotationally symmetric systems need more axes (like in human eye)
Some axes dependent on idealized properties of the eye.
(Nodal points, center of rotation)
- Visual Axis
Definition: The Line connecting the ??? And the ??? ??? Passing through the nodal points.
Visual axis is also called as ??? As the rays passing through nodal points of the eye exhibit zero transverse chromatic aberration (TCA)
The place of intersection of visual Axis with the cornea is known as ???
Connecting the foveol and the fixation point
Also called fovea achromatic axis
Known as ophthalmometric pole
Ophthalmometric pole used in order to characterize cornea exactly.
- Pupillary Axis
Definition: The line normal to the cornea passing through the ???
This axis is used for aligning optical instruments to the eye.
The pupillary axis is used as an objective measure to judge the amount of eccentric fixation, the condition in which a retinal point other than the center of the fovea is used for fixation. ??? Is an adaptation to heterotropia (squint or turned eye)
Through the center of the pupil
Eccentric fixation
- Line of Sight (LoS)
Definition: Ray from fixation point that reaches the foveolar via center of the pupil
The position at which it intercepts the cornea is called ???
Corneal sighting center
- Achromatic Axis
Definition: the line connecting the ???? And the ????
This axis is also called ???
Nodal point and the center of the pupil
Foveal Achromatic Axis
- Fixation Axis
Definition: the line passing through the ??? And the ???
Fixation point and the center-of-rotation of the eye
- Keratometric Axis
Definition: The line passing through the ??? And the ???
The point at which the axis intercepts the cornea is sometimes called the ???
Fixation point and the center curvature of anterior cornea
Vertex normal
- Photoreceptors Axis
K
- Neural Axis
Gah
Angles between axes
1. Angle Alpha
The angle between the ??? and ???
Angle formed at the first nodal point by the optical and visual axis of the eye
The angle between the visual axis and the optical axis is considered to be ??? If the visual axis is on the nasal side of the optical axis in object space
The mean value of angle alpha is often taken to be about +5 degrees horizontally, but is usually in the +3 to +5, and is rarely negative.
The visual axis is also downwards relative to the optical axis by 2-3 degrees
Between the optical and visual axis
To be positive
Angles between axes
2. Angle lambda
The angle between the ??? And ???
Angle formed at the first nodal point by the optical and visual axis of the eye
For most patients, the pupillary axis is ??? To the line of sight in ??? Space.
This is taken as a ??? Angle
The angle lambda is important for diagnosis of
eccentric fixation (monocular testing) and
Heterotropia (binocular testing) [hirschberg test]
Between the pupillary axis and the line of sight (LoS)
Is temporal, in object space
Positive angle
Angles between axes
3. Angle Kappa
The angle between the ??? And ???
For practical purposes, angle ??? Is the same as angle ???
Between the pupillary axis and visual axis
Angle kappa is the same as angle lambda
Angles between axes
The angle between the ??? And the ???
Both of these angle pass through ???
The mean angle was determined to be +2.1 degrees
??? Sign indicates that visual axis is inclined nasally to the achromatic axis in ??? Space
Visual axis and the achromatic axis
Nodal points
Positive sign, object space
