Axes And Angles Flashcards by Sarah Heath

Any two optical systems are required to be aligned _______ to do efficient transmission

Coaxially

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The human eye has 4 major optical surfaces, 1 aperture, and the retina, all of these are approximately ________

Equal

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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

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The axis containing the centers of curvature of the eyes optical surfaces

Optical axis

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The straight line along whihc a ray both enters and leaves the system

Optical axis

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This axis a line of rotational symmetry

Optical axis

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What are the decentered lights reflected off the surface of the eye

Purkinji images

-from 4 surfaces of decentered eye, and cant be aligned

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Roatationally symmetric optical systems need one axis, which is

Optical axis

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Not rationally symmetrical systems need _______

More axes

Like humans do

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Some axes are dependent on

Idealized properties of the eye (nodal points, center of rotation)

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This axis is used for all visual functions

Visual axis

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The lone connecting the foveola and the fixation point passing through the nodal points

Visual axis (fovea achromatic axis)

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Visual axis is called as ____________ as the rays passing through nodal points of the eye exhibit zero transverse chromatic aberration (TCA)

Foveal achromatic axis

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The place of intersection of visual axis with the cornea is known as ____________, whihc is used in order to characterize cornea exactly

Ophthalmometric pole

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The curvature of the cornea ________ as it moves away from the apex

Flattens

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_______________ exactly locates the postion on the cornea

Ophthalmic pole

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What is the ophthalmometric pole not influenced by?

Pupil fluctuations or accommodation

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This axis is convenient reference point for visual functions

Visual axis

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What does the visual axis not depend on

Pupil position

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The line normal to the cornea passing through the center of the pupil

Pupillary axis

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Which axis is important for treating eccentric fixation

Pupillary axis

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This axis is used for aligning optical instruments to the eye

Pupillary axis

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If the eye was a centered system and the pupil was also centered, the pupillary axis would lie along what axis

Optical

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Adaptation to heterotropia

Eccentric fixation

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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

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?

1. Calculate the reflective power of the cornea 2. Location of the reflected image 3. 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

1. Calculate the reflective power of the cornea 2. Treating the anterior lens as the object, find its image after refraction by the cornea 3. Next, treat the anterior lens' center of curvature as an object and find its image after refraction by the cornea