Perimetry 1

An intro of Perimetry ,... hope to be useful

1. PRINCIPLES OF PERIMETRY

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

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 Ocular Variables -Age -Pupil size -Fixation - Media clarity -Reliability - Refraction correction Illustrated Automated Static Perimetry , Detection of glaucoma field defects with Humphrey Filed Analyser , Dr G.R Reddy

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

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 are thresholds displayed as meridional cuts Illustrated Automated Static Perimetry , 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 Octopus db 10,000 0 - 1000 10 0 1 40 30 0.1 50 40 Illustrated Automated Static Perimetry , Detection of glaucoma field defects with Humphrey Filed Analyser , Dr G.R Reddy

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 value in Humphrey field print outs Illustrated Automated Static Perimetry , Detection of glaucoma field defects with 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