1. PRINCIPLES OF PERIMETRY

2. HISTORY 1970- Octopus perimeter was first introduced 1982 Humphrey field analyser first displayed atAAO 1983 Michael Patella showed first clinical trial 1984 Became popularIllustrated 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 seaof 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 FIELDIllustrated 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 ofthe 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 ortarget 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 sensitivityIllustrated 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 correctionIllustrated Automated Static Perimetry , Detection of glaucoma field defects with Humphrey Filed Analyser , Dr G.R ReddyOcular-Pupil size - Media clarity - Refraction 8. Testing Variables-Technician -Background illumination -Stimulus size & Intensity -Stimulus exposure timeIllustrated 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 predeterminedconstant 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,amenableto statistical manipulation Threshold detection is more sensitive The standardised technology reduces the need for highly trained techniciansIllustrated Automated Static Perimetry , Detection of glaucoma field defects with Humphrey Filed Analyser , Dr G.R Reddy 11. DISADVANTAGES Large amounts of unfamiliar data are generatedmaking 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 ofvisual 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 thresholdpoints 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 kineticIllustrated Automated Static Perimetry , Detection of glaucoma field defects with Humphrey Filed Analyser , Dr G.R Reddy 15. ADVANTAGES Moving targets can define isopter contours andscotomas 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 aredifficult In Kinetic tests early or subtle changes can be overlooked Statistical analysis are difficultIllustrated 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 fieldwithin 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. Bjerrums area (arcuate area). That portion ofthe 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 depressionwithin 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 decibelunits 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 unitIllustrated 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 lightintensity-----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 usedby Octopus is 1000 apostilbs Apostilbs Humphrey db 10,000 0 1000 10 1 40 0.1 50Illustrated Automated Static Perimetry , Detection of glaucoma field defects with Humphrey Filed Analyser , Dr G.R ReddyOctopus db 0 30 40 26. db-asb scaleIllustrated 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 theintensity 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 suprathresholdIllustrated 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 outwhether 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 abnormalwhich 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 dbto 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 sensitivityIllustrated 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 itssensitivity 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 timesIllustrated Automated Static Perimetry , Detection of glaucoma field defects with Humphrey Filed Analyser , Dr G.R Reddy 31. Fall of retinal thresholdIllustrated Automated Static Perimetry , Detection of glaucoma field defects with Humphrey Filed Analyser , Dr G.R Reddy 32. References Illustrated Automated Static Perimetry, Detectionof glaucoma field defects with Humphrey Field Analyser , GR Reddy Becker Shaffer Diagnosis and therapy of the glaucomas 8 th editionIllustrated Automated Static Perimetry , Detection of glaucoma field defects with Humphrey Filed Analyser , Dr G.R Reddy 33. THANK YOUIllustrated Automated Static Perimetry , Detection of glaucoma field defects with Humphrey Filed Analyser , Dr G.R Reddy