Optom. Rawaa A. El Dous Lecture Overview Perimetry Definition Visual Field Definition Perimetric Techniques Important Issues in Humphrey Visual.

Optom. Rawaa A. El Dous

Lecture Overview

Perimetry Definition

Visual Field Definition

Perimetric Techniques

Important Issues in Humphrey Visual Field Analyzer

Systemic Interpretation Of Visual Field Printout


What’s Perimetry

Is a procedure for measurement of an individual’s visual field; what they are able to see peripherally as well as Centrally. It aims to:

Detection of field defects (screening programs)

Quantitation of the size, shape, and depth of all defects


Now…

What's Visual Field?


≈ ≈60º60º

100-110100-110 ºº

70-7570-75 ºº

≈≈ 6060 ºº

Central field

Peripheral field


Techniques of perimetry

Kinetic

Static


Techniques of Perimetry

Kinetic - a moving stimulus of fixed intensity and size is moved at a constant rate from non– seeing to seeing regions, identifying points of initial perception.

These points map out an isopter, a defined locus of identical retinal sensitivity.


Goldman stimulus sizes

0(0.0625 mm² ), I (0.25 mm²), II( 1 mm² ), III (4 mm² ), IV (16 mm²), and V (64 mm² ).


isopter

Fixation point


Techniques of Perimetry Cont…

Static - a stationary stimulus at a fixed location is gradually increased in intensity or size until the stimulus is initially perceived.

This initial perception determines the retinal threshold sensitivity at that point and the presence and depth of a scotoma may thereby be determined.

Static testing at various points along a meridian defines a profile, or vertical cross-section of the hill of vision


Stimulus intensity


100-110100-110 ºº≈≈ 6060 ºº

≈ ≈60º60º

70-7570-75 ºº

Point of fixation

blind spot (Absolute scotoma)

Horizontal section

Vertical section


What does it measure?

How?

Automated static perimetry


Threshold determination


Retinal threshold determination


I. Threshold testing strategies

1. Full threshold strategy2. Faster threshold strategies

Fast threshold strategy Full from prior data strategy Swedish interactive threshold algorithm (SITA) FAST PAC

II. Screening (suprathreshold) strategies

Strategies


Full threshold strategy

4/2 dB


Fast threshold strategy


Full from prior data strategy


FAST PAC


Swedish interactive threshold algorithm (SITA)

it’s a new strategy that dramatically reduces test time.

It is available as either SITA standard or SITA fast.

The SITA standard test was intended to gather the same information as a full threshold field in much less time.

The SITA strategy is designed to use data in a more intelligent fashion so that less information has to be gathered from the patient.


The SITA test calculates expected thresholds and is thus able to begin testing close to the actual threshold.

This strategy uses the patient's age, normal and abnormal databases, and the patient's responses to calculate the expected results for each point. These calculations are constantly updated as more information is gathered.

The SITA strategy employs frequency of seeing curves to shorten the time required to threshold each point. The SITA also customizes the interval between test stimuli to the patient's response time.

Swedish interactive threshold algorithm (SITA)


Screening (suprathreshold) strategies (SITA)

• Although screening strategies are faster than full threshold strategies, they are generally inadequate for following patients with glaucoma.

• The simplest strategy, called the "threshold related screening" strategy, tests the point a second time and shows only whether a point is normal or not.

• A second, more complex, strategy, called the "three-zone screening" strategy, tells whether the defect is relative or absolute by projecting the brightest possible light into the abnormal area.

• The most complex screening strategy, called a "quantify defects screening" strategy, calculates a threshold on each abnormal point


Screening (suprathreshold) strategies


Automated Perimeters


Humphrey visual field analyzer


Issues in perimeter design

Stimulus size and intensity

Background illumination

Stimulus duration

Stimulus location and fixation monitoring


STATPAC

STATPAC is a computerized analysis package that is included in the operating system of all Humphrey perimeters.

STATPAC greatly simplifies visual field interpretation by differentiating between normal and abnormal visual fields, and by identifying significant change in a series of visual fields.

STATPAC determines if a patient's visual field results fall within the range normal for his or her age.


A STATPAC analysis may also involve comparing test results with the patient's own baseline from earlier tests in order to determine if the observed change is larger than that typically seen when stable patients return for follow-up testing.

Standard threshold test results may be printed out in any of four formats:

Single Field Analysis Overview Glaucoma Change Probability And Change Analysis

STATPAC


Single visual Field printout



Systemic interpretation of visual field printout

1. What type of visual field test was performed?

2. What are the patient demographics and clinical characteristics?

3. How reliable is the visual field?

4. Is the visual field abnormal?

5. What is the pattern of abnormality?

6. Is the field worsening?

7. Is the abnormality or worsening due to disease or artifact?


What type of visual field test was performed?



1. What type of visual field test was performed?2. What are the patient demographics and

clinical characteristics?3. How reliable is the visual field?4. Is the visual field abnormal?5. What is the pattern of abnormality?6. Is the field worsening?7. Is the abnormality or worsening due to disease

or artifact?


What are the patient demographics and clinical characteristics?





or artifact?


3. How reliable is the visual field?







or artifact?






or artifact?



Glaucoma Hemifield Test

Glaucoma HemifieldTest





or artifact?


6. Is the field

worsening?


Systemic Interpretation Of Visual Field Printout



or artifact?


Are the abnormality or worsening due to disease or artifact?

Lens rim artifact



After1month

After1month

Learning Learning effecteffect


Optometrist:Rawaa A. El Dous

Optom. Rawaa A. El Dous Lecture Overview Perimetry Definition Visual Field Definition Perimetric Techniques Important Issues in Humphrey Visual.

Documents

dous slide

dous stimulus intensity

dous fast pac slide

db slide

threshold field

dous whats perimetry

prior data strategy

sita strategy