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What is an increment threshold?

The minimum increase in luminance required to detect a light stimulus against a luminous background.

What is another name for increment threshold?

Differential Light Sensitivity (DLS) or liminal brightness increment.

What does ΔL represent?

The additional luminance (test light increment) required to detect a stimulus.

What does Lb represent?

Background luminance.

What is the difference between ΔL and Lb?

ΔL is the additional luminance of the test stimulus; Lb is the background luminance.

What is the formula for Weber's fraction?

Weber fraction = ΔL/Lb.

What is the purpose of increment threshold testing?

To measure brightness discrimination and visual sensitivity at different retinal locations.

What is the threshold stimulus?

The weakest test stimulus just visible at a particular location under specific testing conditions.

What is a suprathreshold stimulus?

A stimulus stronger (larger or brighter) than the threshold stimulus; it is visible.

What is an infrathreshold stimulus?

A stimulus weaker (smaller or dimmer) than the threshold stimulus; it is not seen.

What is the Hill of Vision?

A representation of visual sensitivity across the visual field, normally highest at the fovea and decreasing toward the periphery.

How does visual sensitivity change with retinal eccentricity?

Sensitivity normally decreases as eccentricity increases.

What is the relationship between visual threshold and sensitivity?

Lower threshold = higher sensitivity; higher threshold = lower sensitivity.

What is kinetic perimetry?

Visual field testing using a moving stimulus to determine the boundaries of visibility.

What is static perimetry?

Visual field testing using stationary stimuli of varying luminance to measure sensitivity at specific locations.

What is an isopter?

A line connecting points in the visual field with the same kinetic threshold for a particular stimulus.

What does an isopter represent?

The boundary between visibility and invisibility for a particular stimulus.

What is the difference between static and kinetic perimetry?

Static measures thresholds at fixed locations; kinetic measures visibility boundaries using moving stimuli.

What is the standard Goldmann stimulus size in clinical static perimetry?

Goldmann size III; size V is occasionally used.

What is the standard Humphrey visual field background luminance?

10 cd/m² (31.5 apostilbs).

What is the maximum test luminance in standard Humphrey white-on-white perimetry?

3,183 cd/m².

What is the typical duration of a visual field test stimulus?

100 or 200 ms.

What factors influence the visual field sensitivity profile?

Retinal eccentricity, stimulus size, background luminance, and age.

How does increasing stimulus size affect threshold?

It generally lowers threshold (improves detection) because of spatial summation.

How does aging affect visual field sensitivity?

Visual sensitivity generally decreases with age.

What information is included in a Humphrey visual field printout?

Demographics, reliability/fixation, threshold values, grayscale, global indices, local indices, and gaze tracking.

What are the major global indices in a Humphrey visual field?

Glaucoma Hemifield Test (GHT), mean deviation (MD), pattern standard deviation (PSD), and Visual Field Index (VFI).

What do dark areas on a grayscale visual field indicate?

Reduced visual sensitivity.

What is a TVI curve?

A threshold-versus-intensity curve showing how increment threshold (ΔL) changes with background luminance (Lb).

What are the four major regions of a TVI curve?

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

What happens to ΔL as background luminance increases?

ΔL generally increases; a stronger signal is required to detect the stimulus.

What is the linear or dark light region of the TVI curve?

Threshold remains approximately constant because internal retinal noise dominates.

What is the equation for the dark light region?

ΔLt = c; log ΔLt = log c.

What is internal retinal noise?

Spontaneous retinal activity that occurs even without external light stimulation.

What causes internal retinal noise?

Photopigment isomerization, spontaneous membrane channel opening, and spontaneous neurotransmitter release.

How does internal retinal noise affect visual thresholds?

It limits the ability to detect weak light because the stimulus must be distinguishable from internal noise.

Why does background luminance have little effect in the dark light region?

Background light is weaker than the inherent noise in the visual system.

What is the square root (de Vries-Rose) law?

Increment threshold increases in proportion to the square root of background luminance.

What is the equation for the de Vries-Rose law?

ΔL = k√Lb.

What is the slope of the de Vries-Rose region on a log ΔL vs. log Lb graph?

0.5.

What limits detection in the de Vries-Rose region?

Quantal fluctuations (photon noise) in background light.

Why is the de Vries-Rose law called the square root law?

Photon noise increases with the square root of the average number of photons.

If background luminance increases 4 times under the square root law, what happens to threshold?

Threshold increases 2 times (√4 = 2).

If background luminance increases 100 times under the square root law, what happens to threshold?

Threshold increases 10 times (√100 = 10).

Why does contrast detection improve in the square root region?

Background luminance increases faster than photon noise, so smaller proportional luminance differences become detectable.

What is Weber's law?

The increment threshold is proportional to background luminance, maintaining a constant Weber fraction.

What is the equation for Weber's law?

ΔL = kLb, or ΔL/Lb = k.

What is the slope of Weber's law on a log ΔL vs. log Lb graph?

1.

What is contrast constancy?

The Weber fraction remains approximately constant across a range of background luminances.

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

Threshold doubles.

What is the approximate Weber fraction for cones in the lecture?

0.5–1%.

What is the approximate Weber fraction for rods in the lecture?

10%.

Which pathway has better contrast sensitivity in the Weber region?

Cones, because their Weber fraction is smaller.

How do you convert Weber fraction to Weber contrast percentage?

(ΔL/Lb) × 100%.

If ΔL = 2 cd/m² and Lb = 100 cd/m², what is the Weber fraction?

2/100 = 0.02 = 2%.

If the Weber fraction is 1% and Lb = 100 cd/m², what is ΔL?

ΔL = 0.01 × 100 = 1 cd/m².

If the Weber fraction is 10% and Lb = 0.001 cd/m², what is ΔL?

ΔL = 0.10 × 0.001 = 0.0001 cd/m².

What is the saturation region of the TVI curve?

A region where threshold increases much more than predicted by Weber's law as background luminance increases.

Which photoreceptor pathway exhibits saturation at high luminance?

Rods.

Do cones normally show saturation like rods?

No; the lecture emphasizes that cones do not show comparable saturation under ordinary test conditions.

What happens to the rod pathway at saturation?

Rods cease to function effectively at sufficiently high adapting luminance.

What is the approximate slope of the rod Weber region in the lecture?

0.8 rather than 1.

What is the approximate rod saturation level described by Aguilar and Stiles?

5,000 scotopic trolands (approximately 300 scotopic cd/m²) under the specified conditions.

What may occur on a TVI curve when both rods and cones contribute?

A rod-cone break, reflecting a change in which pathway determines threshold.

What is visual adaptation?

Adjustment of visual sensitivity in response to changes in illumination.

Why is the photoreceptor response described as nonlinear?

Output does not increase proportionally with luminance across the full operating range.

What are the major sites of retinal adaptation?

Photoreceptors and post-receptoral retinal circuitry.

Which photoreceptors have more effective adaptation mechanisms?

Cones.

What are the two post-receptoral adaptation mechanisms described by Demb?

Rapid adaptation through fast inhibitory circuits and slow adaptation through sustained inhibitory pathways.

What mechanisms produce rapid post-receptoral adaptation?

Feedforward and feedback inhibition.

What is the function of slow post-receptoral adaptation?

Sustained inhibitory pathways modify ganglion cell responses over longer timescales.

What is equivalent background luminance?

The background luminance that produces the same increment threshold as a particular state of dark adaptation.

What is the Crawford transform?

The relationship connecting dark adaptation thresholds to equivalent background luminance on increment threshold curves.

What determines threshold during dark adaptation according to the equivalent background principle?

The equivalent background luminance.

How can ocular disease affect dark adaptation and visual field thresholds?

It can elevate thresholds, reduce sensitivity, and alter recovery after bleaching.

What is the photostress test?

A test measuring how long visual function takes to recover after exposure to bright light.

What is the normal photostress recovery time given in the lecture?

50 seconds or less.

What does prolonged photostress recovery suggest?

Abnormal visual recovery, potentially associated with retinal or macular disease.

Why is the photostress test clinically useful?

It helps assess visual recovery after bleaching and can reveal dysfunction associated with retinal disease.

What is saccadic suppression?

A temporary reduction in visual sensitivity around rapid eye movements (saccades).

When does saccadic suppression begin?

Approximately 50–100 ms before saccade onset.

How long does saccadic suppression typically last?

More than 100 ms.

Where is saccadic suppression controlled?

Centrally; it includes suppression of V1 neuronal responses before and during saccades.

Which visual pathway is selectively affected by saccadic suppression?

The magnocellular (achromatic) pathway.

Why does simulated retinal image displacement not fully reproduce saccadic suppression?

Saccadic suppression involves central neural mechanisms, not merely retinal image movement.

What is blink suppression?

A reduction in visual sensitivity associated with blinking.

When does blink suppression begin?

Before blink initiation.

Why is blink suppression considered neural?

Suppression occurs even when the eyelid does not obstruct the light stimulus.

Which visual pathway is affected by blink suppression?

The magnocellular (achromatic) pathway.

What is the function of saccadic and blink suppression in visual perception?

They reduce sensitivity to visual disturbances during eye movements and blinks.

What visual field abnormalities were found in the lecture's patient?

Both static and kinetic visual field loss, including multiple scotomata and inferior visual field loss.

How did the patient's visual field abnormalities explain her symptoms?

Inferior visual field loss made it difficult to detect toys on the floor, contributing to tripping.

Can a patient have 20/20 visual acuity but significant peripheral visual field loss?

Yes; central acuity may remain normal despite peripheral retinal dysfunction.

What does RNFL stand for?

Retinal nerve fiber layer.

What does an RNFL deviation map identify?

Areas of retinal nerve fiber layer loss on OCT, often highlighted in yellow or red.

How do RNFL OCT maps complement visual field testing?

OCT identifies structural nerve fiber loss, while visual fields identify functional sensitivity loss.

What is the relationship between decibels and stimulus luminance in Humphrey perimetry?

dB = 10 log10(Lmax/ΔL), where ΔL is the test increment relative to background.

How do you calculate the test increment from a Humphrey dB value?

ΔL = Lmax × 10^(-dB/10).

If maximum stimulus increment is 3,183 cd/m², what is the increment at 10 dB?

318.3 cd/m².