Space 2 - Acuity, Binocularity

What is resolution acuity?

Resolution acuity is visual acuity that requires differentiating (resolving) multiple features of a target and is less cognitively demanding than recognition acuity.

What is recognition acuity?

Recognition acuity is visual acuity that requires recognition of a target or differentiation between multiple possible targets.

What are targets commonly called in recognition acuity testing?

Targets used in recognition acuity testing are called optotypes.

Why can recognition acuity testing be invalid?

Recognition acuity testing is invalid without sufficient knowledge of the different optotypes being presented.

What are the common Sloan (ETDRS) optotype letters?

The Sloan (ETDRS) optotype letters are C, D, H, K, N, O, R, S, V, and Z.

What is the Tumbling E optotype?

The Tumbling E is an optotype designed as a square-wave grating in which the orientation of the letter E is identified.

How wide is each bar of a Tumbling E optotype?

Each bar of a Tumbling E optotype is 1/5 of the total optotype width.

What does MAR stand for in visual acuity?

MAR stands for Minimum Angle of Resolution.

How does a full grating cycle relate to MAR?

A full grating cycle equals 2 × MAR.

For a 20/40 optotype, what is the MAR?

For a 20/40 optotype, the smallest resolved optotype subtends 10 arc-minutes at 20 feet, so the MAR is 2 arc-minutes.

How is spatial frequency calculated from a 20/40 optotype?

For a 20/40 optotype, MAR = 2 arc-minutes, a full grating cycle = 4 arc-minutes, and 15 cycles fit into 60 arc-minutes (1 degree), yielding 15 cycles/degree.

What spatial frequency corresponds to 20/40 visual acuity?

20/40 visual acuity corresponds to approximately 15 cycles per degree (cpd).

What visual acuity corresponds to 60 cycles per degree?

60 cycles per degree corresponds to approximately 20/10 visual acuity.

What task is performed with the Landolt C optotype?

The Landolt C test requires identifying whether the opening is up, down, left, or right.

What task is performed with the Broken Wheel acuity test?

The Broken Wheel test requires identifying which car has broken wheels.

What images are used in the Cardiff Acuity Test?

The Cardiff Acuity Test uses pictures such as a house, fish, dog, duck, train, boat, and car.

What is the Preferential Looking Test (PLT)?

The Preferential Looking Test assesses visual function by determining whether gaze is directed up or down, often using nystagmus responses.

What symbols are used in LEA Symbols testing?

LEA Symbols include an apple, circle, house, and square.

For what population are LEA Symbols commonly used?

LEA Symbols are commonly used for testing visual acuity in children.

What is minimum detectable acuity?

Minimum detectable acuity is the ability to detect a very small target, such as a thin wire on a high-contrast background.

What threshold principle does minimum detectable acuity employ?

Minimum detectable acuity employs an increment luminance threshold.

What visual angle can be detected in minimum detectable acuity?

Minimum detectable acuity can detect approximately 1 second of arc.

What Snellen equivalent corresponds to approximately 1 second of arc?

Approximately 1 second of arc corresponds to about 20/0.33 visual acuity.

What spatial frequency corresponds to approximately 1 second of arc resolution?

Approximately 1 second of arc resolution corresponds to about 1800 cycles per degree.

What are hyperacuities?

Hyperacuities are visual tasks that exceed ordinary resolution limits and generally rely on averaging across one dimension of space to obtain more information.

What is Vernier acuity?

Vernier acuity is a hyperacuity task involving detection of very small positional misalignments.

Which common clinical test uses hyperacuity?

The Amsler Grid uses hyperacuity principles.

What is azimuth in visual direction?

Azimuth is the horizontal angle of a visual target.

What is the horizontal meridian defined as in visual direction?

The horizontal meridian is defined as 0 degrees azimuth.

What is elevation in visual direction?

Elevation is the vertical angle of a visual target.

What is the vertical meridian defined as in visual direction?

The vertical meridian is defined as 0 degrees elevation.

What is eccentricity in visual direction?

Eccentricity is the distance, measured in degrees, from the center of gaze.

What does centripetal movement mean in visual direction?

Centripetal movement is movement toward the center of gaze.

What does centrifugal movement mean in visual direction?

Centrifugal movement is movement away from the center of gaze.

What are corresponding points in binocular visual direction?

Corresponding points are azimuth/elevation points (rays) for each eye that fall on the same specific retinal location in both eyes.

What is the horopter?

The horopter is the surface formed by mapping all corresponding points throughout the binocular visual field.

What is the origin of the term horopter?

Horopter comes from the Greek words horos meaning “boundary” and opter meaning “observer.”

What geometric structure approximates the horopter on the horizontal meridian?

The horopter is approximated by the Vieth-Müller circle on the horizontal meridian.

What defines the Vieth-Müller circle?

The Vieth-Müller circle traces a circle or sphere through the nodal point of each eye and the three-dimensional fixation point of both eyes.

How does the empirical horopter differ from the Vieth-Müller circle?

The empirical horopter tends to curve farther outward than the Vieth-Müller circle predicts.

What criterion defines points on the horopter?

Points on the horopter are corresponding points that yield a single, fused percept.

How is the coordinate system for the horopter established?

Fixation of both eyes on a point in space defines the 0,0 coordinate system.

How does the horopter behave during near vision?

For near vision at less than 1 meter, the horopter curves inward.

What is the abathic distance?

The abathic distance is approximately 1 meter, where the horopter is mostly flat.

How does the horopter behave during far vision?

For far vision greater than 1 meter, the horopter curves outward.

What does the Vieth-Müller model predict about the horopter surface?

The Vieth-Müller model predicts a flat horopter surface.

What is Panum’s fusional area?

Panum’s fusional area is the region in front of and behind the horopter where objects still appear fused in both eyes without diplopia.

What visual functions improve when using both eyes together?

Brightness perception, contrast sensitivity, visual acuity, and field of view improve when using both eyes together.

How does binocular viewing affect the field of view?

Binocular viewing increases the field of view from approximately 160 degrees to 200 degrees.

How much do brightness perception and contrast sensitivity improve binocularly?

Brightness perception and contrast sensitivity improve by approximately 40% with binocular viewing.

What mathematical relationship describes binocular improvement in brightness and contrast?

The improvement follows a quadratic summation ratio equal to the square root of 2 (√2).

How much does visual acuity improve with binocular summation?

Visual acuity improves by approximately 10% with binocular summation.

What logMAR improvement is associated with binocular summation?

Binocular summation produces approximately a 0.069 logMAR improvement.

How many Snellen letters are typically gained with binocular summation?

Binocular summation typically improves performance by about 3 Snellen letters.

What is an example of acuity improvement from binocular summation?

Acuity may improve from 20/20 to approximately 20/20+3, or about 20/17.

What is binocular suppression?

Binocular suppression occurs when each eye sees a significantly different scene and one image is suppressed.

What visual problem does binocular suppression help prevent?

Binocular suppression helps combat diplopia.

In which clinical conditions is binocular suppression significant?

Binocular suppression is clinically significant in strabismus, amblyopia, and anisometropia.

What is binocular rivalry?

Binocular rivalry is binocular suppression occurring in otherwise healthy vision.

What luminance-related factor can trigger binocular rivalry?

Large intraocular differences in luminance can trigger binocular rivalry.

What focal factor can trigger binocular rivalry?

Large intraocular differences in focal depth can trigger binocular rivalry.

What adaptation factor can trigger binocular rivalry?

Large intraocular differences in adaptation can trigger binocular rivalry.

How can monocular obstruction influence binocular rivalry?

Monocular obstruction can trigger binocular rivalry.

What happens when both eyes contain salient targets during binocular rivalry?

Perception may alternate between the two eyes during binocular rivalry.

How is binocular rivalry experimentally produced?

Binocular rivalry can be experimentally created using dichoptic presentation.

Can binocular rivalry be feature specific?

Yes, binocular rivalry can be specific to contour, color, or orientation features.

What is lustre in binocular vision?

Lustre is a percept experienced when a dichoptic stimulus is tri-stable and occurs during simultaneous perception or transitional states.

What is aniseikonia?

Aniseikonia is the perception of different image sizes from each eye.

What refractive condition commonly causes aniseikonia?

Anisometropia commonly causes aniseikonia.

How can strong spectacle prescriptions cause aniseikonia?

Strong prescriptions can magnify or shrink retinal image size, producing different image-size percepts between the eyes.

How can intraocular prescription differences contribute to aniseikonia?

A large prescription difference between the eyes can produce different perceived image sizes.

What retinal conditions can cause aniseikonia?

Retinal pucker, retinal swelling, and retinal scarring can cause aniseikonia.

How can aphakia cause aniseikonia?

Monocular aphakia following surgery can cause aniseikonia.

What is amblyopia?

Amblyopia, often called a “lazy eye,” is a condition in which one eye provides a weaker visual percept.

Which eye commonly becomes amblyopic?

The amblyopic eye is often the eye with reduced image quality caused by imbalanced refractive error, cataract, or another opacity.

How does binocular suppression contribute to amblyopia?

Binocular suppression leads to development of a preferred eye and reduced use of the other eye.

What is strabismus?

Strabismus is a condition in which the eyes are misaligned.

What is the leading cause of amblyopia?

Strabismus is the leading cause of amblyopia.

What happens if amblyopia is not corrected during the critical period?

The visual cortex prunes away inputs from the disfavored eye if amblyopia is not corrected during the critical period.

What is fixation disparity?

Fixation disparity is a mild form of amblyopia in which the image remains within Panum’s fusional area.

What are common causes of amblyopia mentioned in the lecture?

Common causes of amblyopia mentioned in the lecture are anisometropia, congenital cataract, and asymmetric ptosis.