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PRINCIPLES OF PERIMETRY
HISTORY
 1970- Octopus perimeter was first introduced
 1982 – Humphrey field analyser first displayed at

AAO
 1983 – M...
VISUAL FIELD
 Visual field is defined as ―A hill of island in a sea

of darkness”.It is the part of environment that is
v...
EXTENSION OF VISUAL FIELD

Illustrated Automated Static Perimetry
, Detection of glaucoma field defects with
Humphrey File...
PERIMETRY

 Perimetry is the measurement of visual functions of

the eye at topographically defined loci in the
visual fi...
CONTRAST SENSITIVITY

 It is the ability to detect a stimulus or spot of light or

target against a darker or brighter ba...
VARIABLES IN FIELD OF
VISION
Patient variables
Variables
-Age
-Fixation
-Reliability
correction

Illustrated Automated Sta...
 Testing Variables

-Technician
-Background illumination
-Stimulus size & Intensity
-Stimulus exposure time

Illustrated ...
STATIC PERIMETRY
 Computerised
 Stimulus size is maintained constant

 Brightness varied at various predetermined

cons...
ADVANTAGES
 The data are quantifiable,reproducable,amenable

to statistical manipulation
 Threshold detection is more se...
DISADVANTAGES
 Large amounts of unfamiliar data are generated

making interpretation difficult
 Computerised threshold t...
When island hill of vision is explored along Z
axis:plane perpendicular to the surface of
sea,varying points of sensitivit...
KINETIC PERIMETRY
 Manual
 Stimulus is moved from a nonseeing area of

visual field to a seeing area along a set meridia...
 Isopter is a border that connects the threshold

points of a given stimulus
 Mapping the extent of scotoma is more prec...
ADVANTAGES
 Moving targets can define isopter contours and

scotomas rapidly
 Isopter patterns from kinetic testing cons...
DISADVANTAGES
 Technical skill,training and retraining personnel are

difficult
 In Kinetic tests early or subtle change...
Island hill of vision is kinetically explored along X-Y
axis[a plane parallel to the surface of sea].Location
of points wi...
Fixation.
 That part of the visual field corresponding to the
fovea centralis.
 Central field. That portion of the visua...
 Bjerrum’s area (arcuate area). That portion of

the central field extending from the blind spot
and arcing above or belo...
 Scotoma. A localized defect or depression

within the visual field.
 Absolute defect. A field defect that persists
when...
BASIC PHYSICS
 LIGHT INTENSITY
 Usually expressed in apostilbs[asb units]or decibel

units
 Let us consider Humphrey,
...
Conversion of asb units to db
units
 Attenuation of light is expressed in lograthamic








units more commonly in...
 So in Humphrey,40 db=1 asb unit[least projected






stimulus intensity]
0 db=10,000 asb units[maximum intensity of...
 HIGH db VALUE-----more attenuation of light

intensity-----which results in projecting low
intensity of light stimulus--...
 Similarly in Octopus,maximum intensity of light used

by Octopus is 1000 apostilbs
 Apostilbs
Humphrey db
10,000
0
1000...
db-asb scale

Illustrated Automated Static Perimetry ,
Detection of glaucoma field defects with
Humphrey Filed Analyser , ...
THRESHOLD
 Threshold of a particular point on the retina is the

intensity of light with the probability of detection
bei...
RETINAL SENSITIVITY
 The entire visual field testing is to find out

whether there is any decrease in retinal sensitivity...
 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 i...
 If retinal sensitivity falls by 10 db-----retina loses its

sensitivity by 10 times
 If retinal sensitivity falls by 20...
Fall of retinal threshold

Illustrated Automated Static Perimetry ,
Detection of glaucoma field defects with
Humphrey File...
References
 Illustrated Automated Static Perimetry, Detection

of glaucoma field defects with Humphrey Field
Analyser , G...
THANK YOU

Illustrated Automated Static Perimetry ,
Detection of glaucoma field defects with
Humphrey Filed Analyser , Dr ...
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Perimetry 1

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Perimetry 1

  1. 1. PRINCIPLES OF PERIMETRY
  2. 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. 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. 4. EXTENSION OF VISUAL FIELD Illustrated Automated Static Perimetry , Detection of glaucoma field defects with Humphrey Filed Analyser , Dr G.R Reddy
  5. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 26. db-asb scale Illustrated Automated Static Perimetry , Detection of glaucoma field defects with Humphrey Filed Analyser , Dr G.R Reddy
  27. 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. 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. 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. 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. 31. Fall of retinal threshold Illustrated Automated Static Perimetry , Detection of glaucoma field defects with Humphrey Filed Analyser , Dr G.R Reddy
  32. 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. 33. THANK YOU Illustrated Automated Static Perimetry , Detection of glaucoma field defects with Humphrey Filed Analyser , Dr G.R Reddy

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