The document discusses principles of perimetry, which is the measurement of visual functions across the visual field. It describes the history of automated perimeters beginning in 1970. Static perimetry uses computerized testing to determine contrast sensitivity thresholds at preset locations, while kinetic perimetry manually maps sensitivity points along meridians. Both methods are used to identify decreases in retinal sensitivity indicative of conditions like glaucoma. Automated static perimetry provides quantifiable and reproducible data but is time-consuming, while kinetic perimetry rapidly defines field contours but requires more operator skill.

1. PRINCIPLES OF PERIMETRY

2. HISTORY
 1970- Octopus perimeter was first introduced
 1982 – Humphrey field analyser first displayed at
AAO
 1983 – Michael Patella showed first clinical trial
 1984 – Became popular
Illustrated Automated Static Perimetry
, Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

3. VISUAL FIELD
 Visual field is defined as ―A hill of island in a sea
of darkness”.It is the part of environment that is
visible to the steadily fixing eye.
 Deviation of the hill from normal is visual field
defect.
Illustrated Automated Static Perimetry
, Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

4. EXTENSION OF VISUAL FIELD
Illustrated Automated Static Perimetry
, Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

5. PERIMETRY
 Perimetry is the measurement of visual functions of
the eye at topographically defined loci in the
visual field.
 Usually each eye is tested seperately,however when
both eyes are tested together it is binocular field of
vision .
Illustrated Automated Static Perimetry
, Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

6. CONTRAST SENSITIVITY
 It is the ability to detect a stimulus or spot of light or
target against a darker or brighter background but
different points in the area perceived have
different contrast sensitivity corresponding to the
areas on retina relative to fovea with fovea having
highest sensitivity
Illustrated Automated Static Perimetry ,
Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

7. VARIABLES IN FIELD OF
VISION
Patient variables
Variables
-Age
-Fixation
-Reliability
correction
Illustrated Automated Static Perimetry
, Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy
Ocular
-Pupil size
- Media clarity
- Refraction

8.  Testing Variables
-Technician
-Background illumination
-Stimulus size & Intensity
-Stimulus exposure time
Illustrated Automated Static Perimetry ,
Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

9. STATIC PERIMETRY
 Computerised
 Stimulus size is maintained constant
 Brightness varied at various predetermined
constant locations in order to find out the
threshold at these locations
 In other words contrast sensitivity is tested thro
out the extent of area perceived
 Final outcome is the threshold value
determination at predetermined
locations{numerical value}
 This type is concerned with altitude or vertical Z
axis of island of vision
Illustrated Automated Static Perimetry
, Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

10. ADVANTAGES
 The data are quantifiable,reproducable,amenable
to statistical manipulation
 Threshold detection is more sensitive
 The standardised technology reduces the need for
highly trained technicians
Illustrated Automated Static Perimetry ,
Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

11. DISADVANTAGES
 Large amounts of unfamiliar data are generated
making interpretation difficult
 Computerised threshold testing is tedious and time
consuming making significant demands on both
patients and on office routines
 The equipment is expensive.
Illustrated Automated Static Perimetry ,
Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

12. When island hill of vision is explored along Z
axis:plane perpendicular to the surface of
sea,varying points of sensitivity is identified.These
areIllustrated Automated Static Perimetry as meridional cuts
thresholds displayed
, Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

13. KINETIC PERIMETRY
 Manual
 Stimulus is moved from a nonseeing area of
visual field to a seeing area along a set meridian
and other meridians which are usually 15
degrees apart
 The speed,size,colour and brightness of target
are the different variables
 The resultant field of vision is by connecting many
of threshold points by a line,charted in the form of
isopters for each target variable
Illustrated Automated Static Perimetry
, Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

14.  Isopter is a border that connects the threshold
points of a given stimulus
 Mapping the extent of scotoma is more precise with
kinetic ,whereas the depth is more precise with
static
 Humphrey is both static and kinetic
Illustrated Automated Static Perimetry
, Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

15. ADVANTAGES
 Moving targets can define isopter contours and
scotomas rapidly
 Isopter patterns from kinetic testing constitute a
familiar visual field for many practitioners
 Goldmann type of machines are relatively
inexpensive and durable
 Patients are comfortable with human contact of
examination
Illustrated Automated Static Perimetry ,
Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

16. DISADVANTAGES
 Technical skill,training and retraining personnel are
difficult
 In Kinetic tests early or subtle changes can be
overlooked
 Statistical analysis are difficult
Illustrated Automated Static Perimetry ,
Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

17. Island hill of vision is kinetically explored along X-Y
axis[a plane parallel to the surface of sea].Location
of points with same threshold are identified
Illustrated Automated Static Perimetry
, Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

18. Fixation.
 That part of the visual field corresponding to the
fovea centralis.
 Central field. That portion of the visual field
within 30?of fixation.
 Peripheral field. That portion of the visual field
from 30?to the far periphery.
 Threshold. At a given retinal point, the intensity
of a stimulus that is perceived 50% of the times it is
presented.
Illustrated Automated Static Perimetry
, Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

19.  Bjerrum’s area (arcuate area). That portion of
the central field extending from the blind spot
and arcing above or below fixation in a
broadening path to end at the horizontal raphe
nasal to fixation. Bjerrum?s area usually is
considered to be within the central 25?of the
visual field.
Illustrated Automated Static Perimetry
, Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

20.  Scotoma. A localized defect or depression
within the visual field.
 Absolute defect. A field defect that persists
when the maximum stimulus of the testing
apparatus is used. The normal blind spot is an
absolute scotoma.
 Relative defect. A field defect that is present
to weaker stimuli but disappears when tested
with brighter stimuli. A defect that is not absolute.
Illustrated Automated Static Perimetry ,
Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

21. BASIC PHYSICS
 LIGHT INTENSITY
 Usually expressed in apostilbs[asb units]or decibel
units
 Let us consider Humphrey,
 It projects maximum intensity of light of 10,000 asb
units-Assigned as 0 decibel[which means there is no
attenuation of light]
 0 db = 10,000 asb units =brightest light projected by
the perimeter
Illustrated Automated Static Perimetry ,
Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

22. Conversion of asb units to db
units
 Attenuation of light is expressed in lograthamic





units more commonly in tenths of lograthamic unit
1 db =1/10 log unit of attenuation of maximum
available stimulus[10,000 asb units for current
Humphrey perimeter]
10 db=1 log unit[less intense than maximum
stimulus of 10,000 asb units =1000 asb units]
20 db= 2 log units less=100 asb units
30 db=3 log units less=10 asb units
40 db=4 log units less=1 asb unit
Illustrated Automated Static Perimetry ,
Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

23.  So in Humphrey,40 db=1 asb unit[least projected




stimulus intensity]
0 db=10,000 asb units[maximum intensity of light
projected]
Apostilbs- absolute units of light intensity
100 asb intensity in one instrument is same as 100
asb on another instrument
Decibel-relative unit depends on maximum intensity
projected by each perimeter
Illustrated Automated Static Perimetry ,
Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

24.  HIGH db VALUE-----more attenuation of light
intensity-----which results in projecting low
intensity of light stimulus------if retinal points
respond to less intensity of light stimulus-----HIGH
RETINAL SENSITIVITY
 LOW db VALUE-----less attenuation of light
intensity stimulus which results in projecting high
intensity of light stimulus-----if retinal points
respond to high intensity of light stimulus-----LOW RETINAL SENSITIVITY
Illustrated Automated Static Perimetry
, Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

25.  Similarly in Octopus,maximum intensity of light used
by Octopus is 1000 apostilbs
 Apostilbs
Humphrey db
10,000
0
1000
10
1
40
0.1
50
Illustrated Automated Static Perimetry ,
Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy
Octopus db
0
30
40

26. db-asb scale
Illustrated Automated Static Perimetry ,
Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

27. THRESHOLD
 Threshold of a particular point on the retina is the
intensity of light with the probability of detection
being 50%
 Therefore if the threshold intensity is shown at a
particular point 100 times,the person will respond 50
times and he will miss it 50 times.Any intensity of
light which is brighter than threshold intensity is
suprathreshold
Illustrated Automated Static Perimetry ,
Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

28. RETINAL SENSITIVITY
 The entire visual field testing is to find out
whether there is any decrease in retinal sensitivity
or not.The following points to be noted when
there is decrease in retinal sensitivity
1.Degree of decrease in retinal threshold[in terms
of db value]
2.Location of decrease of retinal threshold—
whether its in arcuate region or how far it is from
the fixation point
3.Is the degree of fall of retinal sensitivity
statistically abnormal—which is represented by P
Illustrated Automated Static Perimetry ,
value in Humphrey
Detection of glaucoma field defects withfield print outs
Humphrey Filed Analyser , Dr G.R Reddy

29.  Fall of retinal sensitivity by 5 db[that is from 40 db
to 35 db]35 db point of retina requires 3.2 asb
units of light intensity to get the response.That
means that particular point requires 3 times the
original stimulus to get the threshold response.
 3 db decreases in measured threshold value
always means that the eye lost approximately half
of the retinal sensitivity
Illustrated Automated Static Perimetry
, Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

30.  If retinal sensitivity falls by 10 db-----retina loses its
sensitivity by 10 times
 If retinal sensitivity falls by 20 db-----retina loses its
sensitivity by 100 times
 If retinal sensitivity falls by 30 db-----retina loses its
sensitivity by 1000 times
 If retinal sensitivity falls by 40 db-----retina loses its
sensitivity by 10000 times
Illustrated Automated Static Perimetry ,
Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

31. Fall of retinal threshold
Illustrated Automated Static Perimetry ,
Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

32. References
 Illustrated Automated Static Perimetry, Detection
of glaucoma field defects with Humphrey Field
Analyser , GR Reddy
 Becker – Shaffer Diagnosis and therapy of the
glaucomas
8 th edition
Illustrated Automated Static Perimetry ,
Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy

33. THANK YOU
Illustrated Automated Static Perimetry ,
Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr G.R Reddy