automated perimetry/ Humphrey's visual field.pptx

Automated perimetry/ visual fields

1. INTERPRETATION OF AUTOMATED PERIMETRY

2. Automated Perimetry Automated threshold static perimetry quantifies the sensitivity of a patient’s central vision using efficient and standardized testing algorithms. Perimetry is essential in glaucoma management and also frequently useful in diagnosis and management of some neurological and retinal diseases.

3. Visual field is a 3-D structure akin to a Hill-of-Vision Normal field is horizontally oval with a shallow inferonasal depression 50 ˚ superiorly 60 ˚ nasally 70 ˚ inferiorly , and 90 ˚ temporally

4. Terminol o gies Isopter Line on a visual field representation connecting points with same visible threshold.

5. Scotoma It is an area of reduced(‘relative’) or total(‘absolute’)loss of vision that is surrounded by a field of normal or a relatively well-preserved vision. Blind spot Physiological scotoma corresponding to optic nerve head b/w 10-20 ˚ .It is located temporally and slightly inferiorly.

6. LUMINANCE Intensity/brightness of a light stimulus measured in apostilb or decibel (logarithmic unit) The humphrey perimeter presents white light stimuli that can be varied in brightness with maximum brightness of 0dB (10000asb) and minimum brightness of 51dB(0.08asb). In standardized testing,the dimmest stimulus that can be seen by a young well trained observer is little less than 40dB.

7. Visible threshold Luminance of a given stimulus at which it is perceived 50 % of the time when presented statically.

8. PERIMETRY VS CAMPIMETRY Perimetry – measurement of visual field by projecting targets onto a curved surface Campimetry – measurement of visual field by projecting targets onto a flat surface

9. Types of Perimetry Kinetic Static

10. Why Automation? Removes subjectivity of perimetrist Improves uniformity and reproducibility Computer provides facility of random presentation of targets, estimation of patient reliability and statistical evaluation of data Faster ,more accurate and informative

11. Zone 1- patients data and test data Test Data Fixation monitor: Blind spot Fixation Target: Central Colour of the stimulus: White Back ground illumination: 31.5asb Stimulus size: Goldmann Size III Threshold test pattern: Testing strategy: Patient Data Name of the patient: Date of birth and age: Pupil Diameter: Visual Acuity: Refractive error correction for N.V.

12. DOB OF THE PATIENT- Since the interpretation of raw data by STATPAC is age dependent, it is very important to enter the age of the patient accurately. Otherwise the patients raw data will be compared to mean normal threshold value of a wrong age group and thus derived decibel deviations from the normal will form the numerical plot . SIZE OF THE STIMULUS – The Humphrey Perimeter is capable of testing with five standard Goldman stimulus sizes. Size III stimulus is used almost exclusively. Size V stimulus is sometimes employed in advanced field loss. Sizes I,II and IV are almost never used in static visual field testing.

13. EFFECT OF SIZE OF PUPIL- . Normal size 3-4 mm. . Constricted pupil is thought to give rise to diffuse visual field defects and edge scotomas . Pupil size less than 2mm is more likely to exert a significant effect on the overall level of the visual field.

14. Constricted field d/t miosis Pupil Diameter: 1.0mm

15. Repeat Perimetry with Pupil Diameter: 2.5 mm

16. REFRACTIVE ERROR- Refractive blur reduces visual sensitivity to perimetric stimuli. One dioptre of refractive blur in undilated patient will produce a little more than 1dB of depression of field of vision when testing with Goldmann Size III stimulus. Hence near vision must be properly corrected , otherwise the visual field will show a generalized depression .

17. Strategies Suprathreshold – Suprathreshold perimetry involves testing with stimuli of luminance above the expected normal threshold levels for an age-matched population to assess whether these are detected; in other words, testing to check that a subject can see stimuli that would be seen by a normal person of the same age. It enables testing to be carried out rapidly to indicate whether function is grossly normal or not. However, it is not highly quantitative, and so is usually reserved for screening.

18. Threshold perimetry It is used for detailed assessment of the hill of vision by plotting the threshold luminance value in various locations in the visual field and comparing the results with age-matched ‘normal’ values. Here the threshold is crossed in one direction with large increments, then crossed again to ‘fine- tune’ the result with smaller increments. Threshold testing is quantitatively detailed and is therefore used for monitoring glaucomatous fields.

19. SITA (Swedish Interactive Threshold Algorithm): A newer, faster thresholding algorithm Shows more abnormal points in PDP than the full-threshold programme. Provides shorter testing time with good accuracy & reproducibility by less number of stimuli. Types : SITA standard – Average testing time 50% of FTT SITA fast - 30% less time than SITA std but less accurate.

20. TESTING PATTERNS Most important defects in glaucoma occur within the central 30° radius of field, so this is the area most commonly tested. The 30-2 test pattern measures visual sensitivity at 76 locations within 30° of fixation. The 24-2 test pattern consists of 54 most central test locations of the 30-2 pattern .

21. The number after the dash (–2 or sometimes –1) describes the pattern of the points tested. The –2 strategy involves a grid of test points spaced 6° apart, offset from the vertical and horizontal meridia whereas the -1 includes points along the vertical and horizontal meridia.

22. Other examples include- 10–2 which is used to assess an area of central radius 10° – as defects here may threaten central vision as in macular diseases and FF (‘full field’) – 120 (120°) is used to assess neurological defects

23. ZONE 2- FOVEAL THRESHOLD AND RELIABILITY INDICES Foveal threshold –it is useful to measure the foveal threshold at the very beginning of the test . If the patient is not properly focused on the bowl ,foveal sensitivity will be reduced along with the remainder of the field. Visual Acuity-BCVA should be 6/36 or better for the visual field to be tested.

24. Reliability indices- Fixation losses- The fixation loss rate measures patients gaze stability.During the test 5% of the stimulus will be presented on the blind spot. The patients response to this stimulus presentation will tell that the patient is not gazing straight or is looking from side to side during test. fixation losses more than 20% are considered to be of fixation unreliable.

25. False positive response- These are detected when stimulus is accompanied by a sound.If the sound alone is presented and the patient still responds,a false positive is recorded. - FP >15% is strongly associated with compromised test. -With a high FP score,grey scale appears abnormally pale.

26. Fal s e n e g a ti v e response- These are detected by presenting a stimulus much (9dB)brighter than threshold at a location where the threshold has already been determined. If the patient fails to respond a false negative is recorded - In general >30% of FN is considered abnormal

27. ZONE-3 RAW DATA The r a w d a ta is t h e ex a ct r e ti n al s e n s i ti v ity in dB units of the selected points calculated by field analyser. In raw data 0 dB = absolute scotoma. 40 dB is the highest retinal sensitivity. In same patient the raw data calculated by different strategies is not exactly similar .

28. ZONE-4 GREY SCALE

29. ZONE-5 TOTAL DEVIATION NUMERICAL PLOT The measured retinal sensitivity is now compared with the mean normal sensitivity of those points of same age groups of the patient and calculates the difference between them at each point and plots them as TDNP.

30. If there is no field loss – TDNP must have deviation value 0 to -2 L o c a li z ed f i e l d l o s s - h i gh d e v i at i on v a l u e s at those particular areas. Uniform generalized field loss-all the deviation values will be almost symmetrical and the difference between max and min deviation values will be minimal. In irregular generalized field defects – the deviation values in TDNP will show dissimilar deviation values and the difference between max and min values will be very high .

31. Conversion of numerical data to probability data P<5% indicates the retinal sensitivity of that point is seen in < 5% of normal population. P<2%, P<1%,P<0.5% Probability statements are based on the distribution seen in the normal population . Darker the symbol,the greater the probability of abnormality as indicated by P value. Higher the P value lesser the chances of field being abnormal

32. ZON E - 6 TOTAL DEVIATION PROBABILITY PLOT STATPAC calculates the P value of each dB deviation in the TDNP. A symbol is given to each P value as shown in the fig. Each deviation in TDNP is converted to a symbolic form according to its P value and plotted as TDPP. By seeing TDPP we cannot tell the depth of defect at that point .

33. ZONE-7 PATTERN DEVIATION NUMERICAL PLOT PDNP is derived from the t o tal de v i ation val u es any adjusted for gener a lized decrea s e in sensitivity in the overall field which might be caused by other factors such as lens opacities or miosis. It demonstrates therefore loca l i z ed defe c ts su c h as occ u r in glaucoma.

34. ZONE 8 PATTERN DEVIATION PROBABILITY PLOT PDPP is the symbolic representation of P value of each numerical threshold deviation values of PDNP or the symbolic representation of p value of each measured retinal sensitivity corrected for generalized loss. In uniform generalized depression we do not see any scotoma in PDPP. In irregular generalized depression, the mild and moderate field defects are eliminated and the deep defects are highlighted in the PDPP.

35. ZONE-9 GLOBAL INDICES The basic global field indices are- Mean deviation(MD) Short term fluctuation (SF) Pattern standard deviation(PSD) Corrected pattern standard deviation(CPSD)

36. MEAN DEVIATION MD gives an indication of the overall sensitivity of the field. The positive value indicates better overall retinal sensitivity than normal observer. Negative value indicates that the patient’s overall sensitivity is worse than the average normal individual.

37. PATTERN STANDARD DEVIATION It is a measure of focal loss or variability within the field taking into account any generalized depression in the hill of vision. An increased PSD is therefore a more specific indicator of glaucomatous damage than MD.

38. F L UCT U ATION It is an index of intra test variation. At 10 preselected points the retinal sensitivity will be calculated twice. The result of 1 st series of the threshold values at these points are compared with the 2 nd series of threshold values at these points and the difference between them is calculated . It is not available for SITA strategy. A high SF means either decreased reliability or an early finding indicative of glaucoma .

39. CORRECTED PATTERN STANDARD DEVIATION(CPSD) It is the PSD corrected for short term fluctuations. It indicate the variability between adjacent points that may be due to disease rather than due to intra-test variability .

40. ZONE-10 GLAUCOMA HEMIFIELD TEST GHT evaluates 5 zones in the upper field and compares these zones to their mirror image zones in the lower field . The zones are constructed in the approx patterns of retinal nerve fibres.

41. Depending upon the values between upper and lower clusters of points the following five messages may be displayed ; Outside normal limit –It is displayed whenever at least one zone pair differs by an amount found in fewer than 1% of normal subjects. Border line – It is displayed whenever at least one zone pair differs by an amount found in fewer than 3% but more than 1% of normal subjects. General reduction in sensitivity / Abnormally high sensitivity : These messages are presented whenever even the best test point locations are either so low or so high as to be at levels seen in fewer than 0.5% of normal subjects. Within normal limit .- if none of the above conditions

42. Interpretation of Visual field printout.

43. VISUAL FIELD SEVERITY GRADING SYSTEM as proposed by Hodapp, Anderson, and Parrish . Stag e 1 : E arl y Defec t : Mean deviation (MD) ≤ –6.00 dB and at least one of the following : On pattern deviation plot, <25% of the points depressed below the 5% level and less than 15% depressed below 1% level. No point within central 5 ˚ with sensitivity <15dB.

44. Stage 2: Moderate Defect : MD of –6.01 to –12.00 dB and at least one of the following : On pattern deviation plot, greater than or equal to 25% but fewer than 50% of points depressed below the 5% level, and greater than or equal to 15% but fewer than 25% of points depressed below 1% level At least 1 point within central 5° with sensitivity of < 15 dB but no point within central 5° with sensitivity of < 0 dB Only 1 hemifield containing a point with sensitivity < 15 dB within 5° of fixation

45. Stage 3: Advanced Defect : MD of –12.01 dB to –20.00 dB and at least one of the following : On pattern deviation plot, greater than or equal to 50% but fewer than 75% of points depressed below the 5% level and greater than or equal to 25% but fewer than 50% of points depressed below 1% level Any point within central 5° with sensitivity of < 0 dB Both hemifields containing a point(s) with sensitivity < 15 dB within 5° of fixation

46. Stage 4: Severe Defect : MD of –20.00 dB and at least one of the following : A) On pattern deviation plot, greater than or equal to 75% of points depressed below the 5% level and greater than or equal to 50% of points depressed below 1% level B )At least 50% of points within central 5° with sensitivity of < 0 dB C )Both hemifields containing greater than 50% of points with sensitivity < 15 dB within 5° of fixation

47. Stage 5: End-Stage Disease - Unable to perform Humphrey visual fields in “worst eye” due to central scotoma or “worst eye” visual acuity of 6/60 or worse due to primary open-angle glaucoma. “Best eye” may be any stage

48. Par a cen t ra l scotoma

49. Nasal step scotoma

50. Arcuate scotoma

51. Severe Defect

52. Measurement of visual field progression

53. GLAUCOMA PROGRESSION ANALYSIS Helps to identify and quantify visual field progression. Includes: Event Analysis & Trend Analysis Event analysis assess whether there has been any statistically significant worsening in the visual field . Trend analysis’s goal is to quantify any observed rate of change.

54. GPA SUMMARY REPORT Preferred report for use in glaucoma management.Includes- Two baseline fields An event analysis of the most recent test. 3)A trend analysis of all available tests.

55. GPA Event Analysis GPA provides a plain language event analysis called GPA Alert which displays either of the following 2 messages: Possible Progression Likely Progression When three or more When the same three or test points show more significantly statistically significant deteriorated test points deterioration on two appear in atleast three consecutive follow up consecutive follow-up examinations. tests.

56. GPA change probability maps use triangle symbols to highlight statistically significant deterioration from a baseline consisting of the average of two chosen tests.Each follow up is compared to baseline and : OPEN TRIANGLES :indicate test point locations with deterioration that is statistically significant at the 5% level. HALF BLACK TRIANGLES :indicate test point locations that have shown statistically significant deterioration in two consecutive follow-up examinations. FILLED IN BLACK TRIANGLES :Designate locations where such deterioration has been observed in three or more consecutive tests.

57. GPA TREND ANALYSIS The goal of trend analysis is to quantify how quickly each patient is changing and thereby identify patients who are progressing at rates that threaten to cause considerable visual disability within the patient’s expected lifetime. Here we estimate the rate of progression using linear regression analysis of the Visual Field Index(VFI) over time.

58. VISUAL FIELD INDEX (VFI) It is the enhancement of Mean Deviation(MD) that is designed to be less affected by cataract and is more sensitive to changes near the centre of field so as to better co-relate with ganglion cell loss. VFI is thus a single number that summarizes each patients visual field status as a % of normal age corrected sensitivity. VFI of 100% implies completely normal visual field and VFI of 0% implies a perimetrically blind visual field.

59. The overview printout: sequential series of upto 16 visual fields (grey scale, measured thresholds, TD & PD) of same patient on a single sheet of paper.

60. SELECTIVE PERIMETRY There are thought to be three subtypes of retinal ganglion cells that connect the retina to the lateral geniculate nucleus (LGN): The most numerous of these three subtypes, the midget ganglion cells, connect to the parvocellular layer of the LGN. The parasol cells, which comprise about 10% of the ganglion cell population, project to the magnocellular layers of the LGN. The blue-yellow ganglion cells, or B-Y cells, project to the koniocellular layers of the LGN.

61. SHORT WAVELENGTH AUTOMATED PERIMETRY(SWAP ) Also known as “Blue on yellow perimetry”. It selectively tests the B-Y ganglion cells that project to the koniocellular layers of the LGN. Sensitivity to blue light (mediated by blue cone photoreceptors) is adversely affected relatively early in glaucoma. SWAP is mostly being used currently to test patients who have suspicious optic discs but normal SAP fields LIMITATIONS- Lengthy test Longer learning curve Influence of nuclear sclerosis Higher test variability. No clinical utility in moderate-advanced glaucoma

62. FREQUENCY DOUBLING CONTRAST TEST(FDT) FDT relies on what is known as the frequency doubling illusion. It selectively tests cells in the magnocellular pathway(thought to be damaged first in glaucoma), perhaps allowing earlier glaucoma diagnosis than white-on-white perimetry.