Automated perimetry

Automated perimetry

1. AUTOMATED PERIMETRY dr samarth mishra

2. VISUAL FIELD The 3 dimensional area of a subjects surrounding that can be seen at any one time around an object of fixation. Traquair defined visual field as “ island or hill of vision surrounded by the sea of darkness” The shape of hill of vision correlates to density of photoreceptors and their receptive field sizes.

3. PERIMETRY Perimetry is the systematic measurement of visual field function. It is the measurement of Hill of Vision in terms of establishing the patient’s differential light sensitivity across the visual field.

4. TYPES OF PERIMETRY KINETIC PERIMETRY STATIC PERIMETRY Confrontation Tangent screen Goldmann Humphrey Octopus

5. Humphrey automated perimetry THE MACHINE HAS 2 PARTS- - perimetric unit- bowl type screen - control unit- computer Use static stimuli Viewing distance of 33 cms . Background luminance- 31.5 asb Stimulus size-( Goldmann stimulus size 1-V ) Stimulus duration-0.2 sec

6. Stimulus Size and Intensity Stimulus- size- diameter-mm area- mm2 0 0.28 1/16 I 0.56 ¼ II 1.13 1 III 2.26 4 IV 4.51 16 V 9.03 64 Most commonly Goldmann size III is used In SWAP Goldmann size V is the standard stimulus

7. Fixation Monitoring Heijl-Krakau method of fixation monitoring - It provides index of quality of patient fixation during examination by periodically exposing stimuli in blind spot Eye Monitoring by perimetrist Infra red Gaze Monitors

8. Threshold Strategies SUPRATHRESHOLD TESTING THRESHOLD TESTING Full threshold FASTPAC SITA standard SITAFAST

9. SUPRATHRESHOLD TESTING Field is mapped with a stimulus that is 4 to 6 dB above the threshold Very rapid evaluation Screening purpose

10. THRESHOLD TESTING In this technique light sensitivity ( threshold) is determined at each testing location in the field. Provides more accurate hill of vision Capable of detecting early and shallow focal loss

11. TEST POINT PATTERNS AVAILABLE IN THRESHOLD TESTING Central 30-2 – 76 points are tested. Each point 6 deg apart Central 24-2 – 56 points are tested. Each point 6 deg apart Central 10-2 – 68 points are tested . Each point 2 deg apart Macular threshold test – square grid of 16 points each 2 deg apart Nasal step - 14 points peripheral field testing 60-4 - 60 points .

12. Macular programme Useful to determine macular split Used when only central 5 deg of field remains If a defect impinges on fixation , but other points are preserved macular pogramme is used in addition to other programmes .

13. Determination of threshold Bracketing or staircase procedure ( the 4-2 algorithm)

14. FASTPAC LESS TIME CONSUMING IT CHANGES THE STIMULUS INTENSITY IN 3 dB steps either increasing it or decreasing it depending on patients initial response High intratest variability i.e. Short-term Fluctuation

15. SITA( Swedish Interactive Threshold Algorithm) More efficient estimation of threshold 2 strategies- SITA Standard SITA FAST short test time without compromising on the sensitivity SITA creates prior probability models for normal and glaucomatous populations The pace of the test is dependant on patient’s response It uses informative index derived from visual field model for each point that determines when to stop.

16. TESTING METHOD Ambient light- dim Distance- 30cm Full refractive correction Pt chin on chin holder One eye occluded Pt hands on button ,explained about the test Presents 4 points one in each quadrant and thresholds them 9d from horizontal and vertical meridians – 25dB Size- III4e Pupil- 3-4mm

17. ANALYSIS OF VISUAL FIELD DATA(single field printout) Zone 1 : Reproduciblity Zone 2: Reliability indices and foveal threshold Zone 3: Gray scale Zone 4:Total deviation plot Zone 5: Pattern deviation plot Zone 6: Global Indices Zone 7: Glaucoma hemifield test Zone 8: Raw data

18. False positive error- number of times pt responds when no stimulus shown,Trigger happy,<33%, white scotomas False negative error -brighter stimulus presented which was previosly sensitive,if pt not respond- inattentive/fatigue,<33%,clover leaf pattern Fixation losses- <20%

19. GRAY SCALE A rough indicator of the extent of field damage, but can be misleading. Each point on the gray scale is represented by a symbol of varying darkness which corresponds to the threshold level at that point. These are not indicative of disease.

20. Total deviation plot (Zone-4) is created by subtracting the actual raw data from the expected value for age matched controls, at each point. The Pattern deviation plot (Zone-5) based on further calculations, is derived from the total deviation data and the overall depression of the visual field. It highlights focal changes which are concealed within diffuse changes

21. GLOBAL INDICES Mean deviation (MD ): It is the weighted score of all the points on the total deviation plot. It takes into account both the severity of loss and amount of field affected Pattern standard deviation (PSD ): It measures the extent to which the damaged points vary from the expected hill of vision (localized loss) Short term fluctuation (SF ): Though listed under global indices it is a good indicator of intra test reliability. It measures the variation at each point on repeated thresholding in the same test.

22. Corrected pattern standard deviation (CPSD ): It is calculated with the help of SF to adjust the PSD.

23. Glaucoma Hemifield test (Zone-8 ) is a sophisticated analysis of 5 geometric point clusters in the superior and the inferior arcuate regions whose probability maps are compared with one another. It is very sensitive and specific at detecting asymmetry between these regions as well as symmetric deviations from normal data.

24. Possible test outcomes Outside Normal Limits Borderline General reduction of sensitivity Abnormally high sensitivity Within normal limits

25. Glaucoma Hemifield Test

26. Anderson Criteria 3 or more congrous ‘non edge points’ in typical arcuate area on 30-2 programme depressed @ p< 5% with at least one point @ p<1% PSD/CPSD@ P<5% GHT-outside normal limits Must be demonstrated on 2 field tests

27. INDICATIONS OF PERIMETRY Detection of glaucoma, progression Chorioretinal lesions Optic disc and optic nerve lesions Neuro -ophthalmological diseases

28. Enlargement of blind spot

29. Arcuate scotoma

30. Advanced glaucomatous field defect

31. ALTITUDINAL FIELD DEFECT

32. HOMONYMOUS HEMIANOPIA

33. SERIAL FIELD ANALYSIS Establishing a base line Overview printout Change Analysis Printout Glaucoma Change Probability Analysis Glaucoma Progression Analysis

34. Overview printouts

35. CHANGE ANALYSIS PRINTOUT

36. Glaucoma change probability

37. Glaucoma Progression Analysis

38. AETEFACTS OBSTRUCTION .Rim Artefact . Ptosis .Media Opacities . Angioscotoma MIOSIS REFRACTIVE ARTEFACTS

39. OCTOPUS PERIMETRY Projection system perimeters which can perform full threshold programme Stimulus is Goldmann target size III

40. Reproducibility (Zone-1) Reliability factors (Zone-2) Gray scale (Zone-3) Comparison (Zone-4) Corrected comparison (Zone-5) Numeric data/raw data(Zone-6) Visual field indices (Zone-7): Bebie.’s curve (Zone-8)

41. ADVANCED TECHNIQUES FOR VISUAL FIELD EXAMINATION SWAP[Short Wave Automated Perimetry ] FDP[Frequency Doubling Perimetry ] HPRP[High Pass Resolution Perimetry ] Flicker Perimetry Multifocal Electroretinography ACCUMAP[Multifocal Visual Evoked Potential] Motion Perimetry

42. SWAP Helps to diagnose damage due to glaucoma at an early stage Yellow background is used to highlight isolated blue cone response HFA and Octopus perimeters have incorporated the SWAP SWAP uses Goldmann target V stimulus to enhance spatial summation It is influenced by nuclear sclerosis as lens acts a blue filter

43. FDP FDP is based on detecting damage to M ‘ y’cells which are a subset of Magnocellular cells Test stimulus- series of white and black bands flickering at 25 Hz Uses target of 10 deg square FDP full threshold strategy has 2 programmes 1)C-20- 17 points are tested 2)N-30-19 points are tested

44. HPRP HPRP is ring perimetry Series of ring of different sizes and having a light centre and dark annular surround are presented These targets are spatially high pass filtered vanishing targets for determination of resolution of central 30 deg HPRP tests the parvocellular system selectively Based on resolution method rather than differential light sensitivity

45. HPRP

46. FLICKER PERIMETRY It detects light and dark stimulus alternations(flicker) at various locations in the field It targets magnocellular pathway( responsible for flicker perception) Not influenced by media opacities and refractive error Two types- 1)Critical Fusion Frequency 2) Temporal Modulation Perimetry