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What is an increment threshold?

Minimum additional luminance needed to detect a test stimulus against a background.

What is Differential Light Sensitivity (DLS)?

Ability to detect differences in luminance; measured using increment thresholds.

What does ΔL represent?

Additional luminance of the test stimulus compared with the background.

What does Lb represent?

Background luminance.

What does ΔLt represent?

Threshold increment: the minimum additional luminance needed for detection.

How are increment threshold and visual sensitivity related?

Low threshold = high sensitivity; high threshold = low sensitivity.

What is a threshold stimulus?

Weakest test stimulus that is just visible under specific testing conditions.

What is a suprathreshold stimulus?

Stimulus stronger than threshold and visible to the observer.

What is an infrathreshold stimulus?

Stimulus weaker than threshold and not detected.

What is static perimetry?

Uses stationary test lights of varying luminance to measure sensitivity at specific visual field locations.

What is kinetic perimetry?

Uses moving test stimuli to determine the boundaries of visual field sensitivity.

What is an isopter?

Line connecting points of equal kinetic threshold; boundary between visible and invisible regions for a given stimulus.

What is the Hill of Vision?

3D representation of visual sensitivity across the visual field.

Where is sensitivity normally highest on the Hill of Vision?

Fovea; sensitivity generally decreases with eccentricity.

Why is there a blind spot in the Hill of Vision?

Optic disc contains no photoreceptors.

What is a scotoma?

Area of reduced or absent visual sensitivity within the visual field.

What happens to visual field sensitivity with increasing age?

Sensitivity generally decreases.

How does increasing test stimulus size affect sensitivity?

Larger stimuli generally increase measured sensitivity due partly to spatial summation.

What is Ricco's law?

Within a critical area, threshold depends on the total light energy summed across the stimulus area.

What is the standard Goldmann stimulus size in clinical perimetry?

Goldmann III; Goldmann V is occasionally used.

What background luminance is commonly used in Humphrey white-on-white perimetry?

10 cd/m² (31.5 apostilbs).

What is the maximum test luminance in the lecture's Humphrey perimeter?

3,183 cd/m².

What does a higher Humphrey sensitivity value in dB indicate?

Higher sensitivity; a dimmer test light can be detected.

What is a TVI curve?

Threshold Versus Intensity curve; shows how increment threshold changes with background luminance.

What are the four main TVI regions?

Dark light (linear), square root (de Vries-Rose), Weber's law, and saturation.

What characterizes the dark light region?

Internal retinal noise limits detection; threshold remains approximately constant.

What is the equation for the dark light region?

ΔLt = c, where c is a constant.

What is the log-log TVI slope in the dark light region?

0.

What are possible sources of internal retinal noise?

Spontaneous photopigment isomerization, membrane channel opening, and neurotransmitter release.

What characterizes the square root (de Vries-Rose) region?

Detection is limited by random photon fluctuations in the background.

What is the square root law equation?

ΔLt ∝ √Lb.

What is the log-log TVI slope for the square root law?

0.5.

What happens to threshold if background luminance increases 4 times under the square root law?

Threshold increases 2 times.

What happens to threshold if background luminance increases 9 times under the square root law?

Threshold increases 3 times.

What statistical distribution describes photon-count fluctuations?

Poisson distribution; variance equals the mean and standard deviation equals its square root.

Why does Weber contrast threshold decrease in the square root region?

Background luminance increases faster than photon noise, allowing detection of smaller percentage differences.

What characterizes Weber's law?

Increment threshold increases proportionally with background luminance; Weber contrast stays constant.

What is the equation for Weber's law?

ΔLt = kw × Lb.

What is Weber's fraction?

ΔL/Lb; ratio of additional luminance to background luminance.

What does kw represent?

Weber's constant, the fixed contrast threshold in the Weber region.

What is the log-log TVI slope for Weber's law?

1 for ideal Weber behavior.

What happens to threshold if background luminance doubles under Weber's law?

Threshold doubles; Weber contrast stays constant.

What is contrast constancy?

Maintaining approximately the same contrast threshold despite changes in background luminance.

What is the approximate rod Weber contrast in the lecture?

10% (0.10).

What is the approximate cone Weber contrast in the lecture?

0.5–1% (0.005–0.01).

How do you calculate additional luminance using Weber's constant?

ΔL = kw × Lb.

If Lb = 100 cd/m² and kw = 0.01, what is ΔL?

1 cd/m².

How is the required contrast different in square root and Weber regions?

Square root: required contrast decreases as background increases; Weber: required contrast remains constant.

What characterizes the saturation region?

Rod thresholds rise steeply beyond Weber's law predictions; rods eventually cease functioning effectively.

Do rods or cones exhibit saturation at high luminances in the lecture?

Rods saturate; cones continue adapting under the conditions discussed.

What is the approximate slope of the rod Weber-like region?

0.8, rather than an ideal slope of 1.

What is the rod-cone break in a TVI curve?

Transition between rod-dominated and cone-dominated detection under certain stimulus conditions.

What is visual adaptation?

Adjustment of visual sensitivity to changes in ambient light levels.

What happens during light adaptation?

Visual sensitivity decreases as the eye adjusts to brighter conditions.

What happens during dark adaptation?

Visual sensitivity increases as the eye adjusts to darkness.

Why are photoreceptor responses nonlinear?

Response changes are not proportional to light increases across all intensities, helping prevent saturation.

Which photoreceptors have more effective adaptation mechanisms?

Cones.

What are the two levels of retinal adaptation described in the lecture?

Photoreceptor adaptation and post-receptoral adaptation.

What are the two post-receptoral adaptation mechanisms?

Rapid inhibition through feedforward/feedback circuits and slow adaptation through sustained inhibitory pathways.

What is equivalent background luminance?

Hypothetical background luminance producing the same threshold as a particular state of dark adaptation.

What is another name for the equivalent background principle?

Crawford transform.

What happens to equivalent background luminance during dark adaptation?

It decreases as visual sensitivity improves and threshold decreases.

What is the purpose of the clinical photostress test?

Measure how long vision takes to recover after bright light exposure.

What normal photostress recovery time was used in the lecture's cited study?

50 seconds or less.

How can ocular disease affect photostress recovery?

Some retinal diseases prolong recovery after photopigment bleaching.

What is saccadic suppression?

Temporary reduction in visual sensitivity before and during rapid eye movements.

When does saccadic suppression begin?

Approximately 50–100 ms before saccade onset.

What is blink suppression?

Neural reduction in visual sensitivity associated with blinking; begins before the blink.

Which visual pathway is particularly affected by blink and saccadic suppression?

Achromatic magnocellular pathway.

How can a patient have 20/20 acuity but still trip over objects?

Central acuity may be normal despite peripheral or inferior visual field loss.