Visual Field Basics - Ocular Neurology Summer 2026

The Island of Vision (Pic)

The Island of Vision (Pic)

on the fovea

Is an individual more sensitive to stimuli in the periphery or on the fovea?

-the outline of the limits or extent of the visual field within which a certain size and intensity of test stimulus can be seen

-the set of threshold points for a test object of given size and intensity

What is an isopter?

From Island to Isopter (Pic)

From Island to Isopter (Pic)

-stimulus size

-stimulus luminance

-background luminance

-stimulus position

-stimulus focus

-presentation time

-speed of movement

-stimulus color

What aspects of the stimulus do we have control over as we conduct visual field testing?

The Goldmann Perimeter (Pic)

The Goldmann Perimeter (Pic)

V4e

Largest Size & Brightest Stimulus on Perimetry

III

What stimulus size is used for modern threshold tests & HFA threshold testing (social security & legal blindness testing)?

V

What is the largest stimulus size on perimetry?

4e

What is the brightest combination of filters on perimetry?

0.5

Each course filter is a _____ log unit change on perimetry (1,2,3,4 setting)

0.1

Each fine filter is a _____ log unit change on perimetry (a,b,c,d,e setting)

31.5 asb

What is the background luminance of a perimeter in apostilbs?

1000 asb

What is the max stimulus luminance of a perimeter in apostilbs?

300mm

What is the testing distance for a perimeter?

luminance

Apostilbs are a measure of _______

3.142 aspotilbs

1 cd/m^2 = how many apostilbs?

Each unit on the scale represents an equal interval (Going from 1 to 2 is the same as going from 10 to 11)

Describe a linear (interval) scale

rule or tape measure

What is an example of a linear (interval) scale?

different

Log scales are (the same/different) as/from linear scales

an equal ratio

On a log scale, each unit represents what?

true

True or False:

Log scales play an important role in describing the stimuli we use in VF testing

-Each Goldmann Spot Size is a 4x change in area

-Each course filter is a 0.5 log unit change

-Each fine filter is a 0.1 log unit change

Examples of Log Scale with Perimetry

Perimetry Linear Scale -- Goldmann Filter v Luminance (Pic)

Perimetry Linear Scale -- Goldmann Filter v Luminance (Pic)

Perimetry Log Scale -- Goldmann Filter v Luminance (Pic)

Perimetry Log Scale -- Goldmann Filter v Luminance (Pic)

decibel

All modern automated perimeters use a _____ scale to indicate threshold luminance

attenuation

The decibel is a unit of _______

1/10

1 dB = _______ log unit

10

1 log unit is a factor of _____

0.1

Example of dB Values to Remember

1dB = _____ log units

4/5 = 0.8x

Example of dB Values to Remember

1dB = 0.1 log units = ______ratio

0.3

Example of dB Values to Remember

3dB = ____ log units

1/2 = 0.5x

Example of dB Values to Remember

3dB = 0.3 log units = ______ratio

1

Example of dB Values to Remember

10dB = ____ log units

1/10 = 0.1x

Example of dB Values to Remember

10 dB = 1 log units = _____ ratio

that luminance for which the decibel value is zero (the most unattenuated luminance or most intense that the machine can produce)

What is a reference luminance in automated perimetry?

relative luminance

All luminances are expressed relative to the _______

3

A luminance 1/2 the reference luminance will be a ____ dB stimulus

1,000 asb

Reference Luminance in a Goldmann Perimeter

10,000 asb

Reference Luminance in a Humphrey Perimeter

4,000 asb

Reference Luminance in a Octopus Perimeter

-dB = (logRef - logStim) x 10

-dB = (log (10,000) - log(10)) x 10

-dB = (4-1) x 10 = 30dB

-30dB

Conversion Between Decibels, Log Units and Luminance

Find the dB value for 10 asb on the Humphrey Field Analyzer (10,000 asb reference luminance)

-dB = (logRef - logStim) x 10

-21 = (log(10,000) - log(Stim)) x 10

-21 = (4 - log(Stim)) x 10

-21/10 -4 = -log(Stim)

-1.9 = log(Stim)

-80asb = stimulus intensity

Conversion Between Decibels, Log Units and Luminance

Find the stimulus intensity in asb for a 21 dB stimulus on the Humphrey Field Analyzer (10,000 asb reference luminance)