Perimetry

Perimetry and its application.

1. PERIMETRY Dr SHREEJI SHRESTHA

2. Presentation layout Introduction of visual field Perimetry - types Important terms bedside perimetry Formal perimetry Defects Short wavelength automated perimetry Frequency doubling technology

3. Introduction of visual field environment wherein a steadily fixating eye can detect visual stimulus. BASIS - presence of Photoreceptors with its visual pathways upto the periphery of retina away from point of fixation i.e fovea. IMPORTANCE – mapping extend - disorder or optic nerve and visual pathway

4. Extend

5. contour

6. Blind spot Corresponding to optic nerve head no photoreceptors 10-15 deg temporal to point of fixation Span – 5 deg horizontal -- 7 deg vertical 2 portion- absolute scotoma - relative scotoma

7. Definition of Perimetry Measurement of visual functions of the eye at topographically defined loci in the visual field 1 Measures differential light sensitivity, or the ability of a subject to distinguish a stimulus light from background illumination 2

8. Factors affecting sensitivity Pupil size - miosis Refractive error - myopia - posterior staphyloma - refraction scotoma. (glaucomatous field defect) Hypermetropia - alter threshold sensitivity Age - 20years Sensitivity dec - age (10yrs - 0.5-1 db) Clarity of ocular media Fatigue

9. types of perimetry According to the principal: Kinetic Static Clinically Automated static perimetry Manual kinetic and static perimetry using a Goldmann type bowl perimeter

10. Kinetic perimetry: outer visual field is determined by moving objects from the non-seeing area to the center. Uses a moving object of a fixed size and intensity. Advantages: Allows large areas to be traversed in a fairly short period. less expensive and durable. Perimetrist is constantly communicating with the patient so it is more comfortable. Disadvantage: Reproducibility and reliability is not constant in the manual kinetic perimetry.

11. Static perimetry: The outer boundary of the island of vision determined by measuring the retinal sensitivity at each point. The test location is fixed while the intensity of the test object of known size is varied. Octopus and Humphrey perimeters. Advantage: Reliability and reproducibility Disadvantage: Manual static perimetry is tedious.

12. Riddoch phenomenon Only moving object are seen and static object not seen Lesion in occipital lobe

13. Terms in perimetry Threshold: differential light sensitivity at which a stimulus of a given size and duration of presentation is seen 50% dimmest spot detected during testing. Suprathreshold: 95% of the projected times. stimulus - made suprathreshold - increasing size or duration. Infrathreshold : Low intensity stimulus - 5%

14. Isopter: a line on a visual field representation – connecting points with the same threshold. Depression: a decrease in retinal sensitivity s cotoma : an area of decreased retinal sensitivity within the visual field surrounded by an area of greater sensitivity. Decibel (dB): Its value depends on the maximum illumination of the perimeter. log units of attenuation of the maximum light intensity available in the perimeter being used. OdB is maximum stimulus intensity

15. variables Patient: attentiveness and fatigue Perimetrist: manual perimetry Fixation: fixation is off centered It is especially true in automated static tests. Background luminace: luminace of the surface on which stimulus is projected background luminance of 4-31.5 apostilbs. sensitivity is greatest at fixation Stimulus luminance greater size, duration, brighter- stimulus- visible

16. Size of stimulus: Standard stimulus - 0= 1/16mm2, 1= 1/14 mm2, 11 = 1mm2, 111 = 4mm2, 1v = 16mm2, v= 24mm2 Presentation time : longer time, the more visible a given stimulus(0.2) Speed of stimulus movement: if a kinetic target = quickly, by the time the patient responds, the target may have gone beyond its location The time period between visualization and response is termed the latency period or visual reaction time.

17. Bedside perimetry PR hand motion finger counting Hand identification Testing with neurological pin red desaturation

18. Amsler grid For Central 10 deg ( static ) Other eye occluded Near correction given Chart at held 28-30 cm – each small square subtends angle of 1 deg Patient fixates at central dot – tells whether all corners are seen simultaneously and about lines- parallel, distorted, missing Can be used for mapping blind spot – patient fixates at edge of grid Macular scarring- lines bow outward macular edema - lines appear closer

19. Perimetry

20. HFA

21. Zone 1-Parameters Test strategy Full threshold- each point stimulated 5 times, long duration SITA-standard- 90% point tested- remaining 10% not tested SITA fast- 80% point tested SITA relies on model of VF Region/pattern used ➢ 30-2 (test points = 76points) , 24-2(54) , 10-2(68points) Patient details ➢ date of birth, date of VF, pupil size, test time, VA, correction, eye tested

22. Zone 1- Reliability Fixation monitor Fixation target – central, small diamond Test duration Reliability indices Fixation losses <20 % False positives < 33% False negatives < 33 % Foveal threshold

23. Fixation loss Stimulus flashed in blind spot Limited value in patient with large defect surrounding blind spot sees stimulus Patient is not fixating at center and moving eye

24. Patient response to patient fail to respond audible click when he isn't seeing False positive/trigger happy False negative

25. Compare total & pattern deviation 3. Age Corrected plots Humphrey TM Z ero i n o n t h e p r ob a bili ty plo ts

26. Humphrey TM Compare total & pattern deviation actual local defect Media opacity

27. Zone 4: global indices single numbers to denote whole field MEAN DEVIATION : average loss of sensitivity from normal age matched population along with probability calculated from total deviation plot PATTERN STANDARD DEVIATION : range over which change of sensitivity at all the points has occurred, along with probability compensates for effect of generalized depression or elevation of field on mean deviation value local defects affect PSD > MD

28. Mean deviation Pattern standard deviation Visual field Normal Normal Normal Abnormal Normal Generalized depression normal Abnormal Localized defect in one location

29. 4.Glaucoma hemifield test

30. Outside normal limits All cluster pairs differ @ p < 1% OR 1 cluster pair differs @ p < 0.5% Borderline Hemifields differ @ p < 3% General reduction of sensitivity Overall field depressed @ p < 0.5% Abnormal high sensitivity Overall field elevated( best 15 % points) @ p < 0.5 % Within normal limits

31. Octopus HFA Bowl Spherical Aspherical stimulus size Goldman 111 v 1-v Duration 100ms 200ms Luminance for 0dB 4800asb 10,000asb test strategy 4-2-1 bracketing 4-2 bracketing Fixation loss Automatically discount Present

32. Ear l y Gl a u c o ma Defect 18 pts) below 5% and (10 pts) below 1%

33. Moderate Glaucoma Defect <50% (37 pts) <5% level and <25% (20pts) <1 % level Only 1 hemi field has point with sensitivity <15dB in the central 5 degree

34. Severe Glaucoma Defect On PD plot > 50% of pts < 5% level > 25% of pts < 1% level Both hemi-fields w/ pt(s) w/ sensitivity < 15 dB w/in th central 5

35. visual field defect Generalized depression (both peripheral and central contraction) e g cataract Peripheral Contraction – retinitis pigmentosa Temporal contraction - age Hemifield defect - hemianopia Altitudinal defect - glaucoma, OD drusen, AION

36. Progression in glaucoma Development of new defect Deepening or enlargement of preexisting defect Diffuse loss of sensitivity for follow up, 6 visual field examination in first 2 years for consistent baseline and RO aggressive disease then reduced to once/twice yearly

37. clover leaf artifact

38. Parietal lobe/pie in floor/BAUM loop Temporal lobe/ Meyer loop Sup Sup inf

39. Short wavelength automated perimetry Blue stimulus Yellow light- background - reduces sensitivity of RED and GREEN cones. Detect glaucomatous field defect early

40. Frequency doubling technology Based on frequency doubling illusion stimulus - series of black and white bands flickering at 25Hz Mediated by large ganglian cells (M ganglion cells) - magnocellular visual pathway M cells - sensitive to motion and contrast - glaucomatous damage Portable, inexpensive Also advocated for use in children Screening

41. Visual field easy app

42. Reference Jakobiec principle and practice of ophthalmology - 3rd edition - neuroophthalmology Shields textbook of glaucoma- assessment of visual field Ophthalmology investigation and examination technique-bruce James , Larry Benjamin AAO - glaucoma - section 10- pearls of glaucoma management- giaconi, law