Optics: Axes And Angles Flashcards
Any two optical systems is required to be aligned ___________ to do efficient transmission
Coaxially
The human eye have ___ major optical surfaces, ___ aperture, and the retina
4, 1
The optical and neural components of the eye are ___________ attached and objects are placed on-axis by _________________
Rigidly, rotating the eye
There is a superior signal transmission when…
Optical and neural axes are aligned with each other
Optical and neural axes of the 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
Axis containing the centers of curvature of the eyes optical surfaces
Optical axis is a _______ line along which…
Straight, a ray both enters and exits the system
Rotationally symmetric optical systems need one axis. Which axis?
Optical axis
Non-rotationally symmetric systems need more _____
Axes
Visual axis:
The line connecting the fovea and the fixation point passing through the nodal points
Place of intersection of visual axis with the cornea is called ___________________
Ophthalmometric pole
Ophthalmometric pole is used to…
Characterize the cornea exactly
The curvature of the cornea __________ as it moves away from apex.
Flattens
The ophthallmometric pole is NOT influenced by:
-pupil fluctuations or accommodation
The visual axis is convenient reference point for ________________
Visual functions
Visual axis does NOT depend on:
Pupil position
Visual axis acts are the reference point for:
-alignment of corrective lenses
-determinations of treatment location for laser procedures
-positioning of IOL during cataract surgery
-alignment of visual axes between both eyes
Pupillary axis:
Line normal to the cornea passing through the center of the pupil
Pupillary axis is used for….
Aligning optical instruments to the eye
The pupillary axis is used as an objective measure to judge the amount of _____________ fixation
Eccentric fixation
Eccentric fixation
Retinal point other than the center of the fovea is used for fixation (adaptation to heterotropia)
Hadingers brush apparatus is used to:
Detect, diagnose, and train amblyopia due to eccentric fixation
Acuity is reduced in eccentric fixation because…
The person fixates with a part of the peripheral retina instead of macula
Line of sight:
Ray from fixation point that reaches the foveolar via center of the pupil
Position where line of sight intercepts the cornea is called:
Corneal sighting center
Line if sight is critical during:
-VF testing
-refractive surgery planning
-macular disease evals
Achromatic axis:
Line connecting the nodal point and the center of the pupil
Achromatic axis is also called the…
Fovea achromatic axis
The ray passing through the achromatic axies does NOT..
Suffer from any transverse chromatic aberration
Achromatic axis is similar to optical axis, but dependent on ______________
Pupil position
Fixation axis:
Line passing through the fixation point and the center-of-rotation of the eye
The fixation axis is the reference for measuring __________________
Eye movements
Fixation axis is an ________________ and depends on the direction of ____________
Approximation, rotation
Fixation axis is important for:
-eye elignment
-strabismus
-refractive surgery
Keratometric axis:
Line passing through the fixation point and the center of curvature of anterior cornea
Keratometric axis is used for…
Alignment in topography measurements
Point at which the Keratometric axis intercepts the cornea is called:
Vertex normal
Photoreceptor axis :
????
Neural axis:
????
Angles between axes:
-angle alpha
-angle lambda
-angle kappa
-angle psi
-angle gamma
Angle alpha:
-Angle between the optical and visual axis
-formed art first nodal point
Angle alpha is positive when:
The visual axis is on the nasal side of the optical axis in object space
Angle alpha primary application:
-Guiding the placement of the IOL during cataract surgery
**large angle alpha causes issues with lens contraction and visual quality
Angle lambda:
Angle between the pupillary axis and the line of sight
Angle lambda is the 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 . Making a ________ angle
Temporal, object, positive
Angle lambda application:
Ensure accurate contraction during ant seg surgeries like corneal transplants or laser refractive procedures
Large angle lambda can lead to…
Misalignment of the surgical site or implanted device
A normal angle lambda indicates the corneal light reflex is ______________ to the pupillary center reflecting _______________ if the visual axis
Slightly nasal, proper alignment
Angle kappa:
Angle between the pupillary axis and visual axis (angle kappa is same as angle lambda)
Large Angle kappa clinical implications:
-hyperopic pts have large K values
-increased risk of patients complaints of post-operative glare and halo
Angle psi:
Angle between the visual axis and achromatic axis (both planes pass through nodal points)
Positive sign angle psi indicates:
Visual axis is inclined along the nasal side
Mean value for angle psi:
+2.1 degrees
Angle gamma:
Angle between the optical axis and fixation axis
Angle gamma is within _____ of angle alpha for object distances greater than 50cm
1%
Application of angle gamma:
-Identify situations where the macula is not centered on the visual axis
When significant angle gamma is present, it can impact the…
Optical placement of IOL during cataract surgery to ensure proper visual correction
