Fundamentals of hfa perimetry

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  • Fundamentals of hfa perimetry

    1. 1. 1 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement
    2. 2. 2 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement There are three International Standards of measurement for Perimetry: ASBASB dBdB FT/LFT/L
    3. 3. 3 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement ASBASB AApopoSStiltilBB 0 (Dimmest) – 10,000 (Brightest) A measurement of light, dealing with the brightness of the surface of the bowl International StandardInternational Standard
    4. 4. 4 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement FT/LFT/L Foot LambertFoot Lambert HFA Range 0 (dimmest) – 929 (Brightest) FT/L Higher number = Brighter light International StandardInternational Standard
    5. 5. 5 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement dBdB DecibelDecibel HFA Range 0.1 dB (Brightest) – 51dB (Dimmest) Higher number = Dimmer Spot International StandardInternational Standard
    6. 6. 6 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement International Standards Comparison Dimmest Brightest 0 ASB 10,000 ASB 0 FT/L 929 FT/L 51 dB 0.1 dB
    7. 7. 7 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement All Perimeters use the same standards These standards are based on the Goldmann Perimeter ASB ASB ASB ASB ASBASB ASB ASB ASB ASB FT/LFT/L FT/LFT/L FT/LFT/L FT/L FT/L FT/L FT/L FT/L FT/L dBdB dBdB dBdB dBdB dBdB dBdB
    8. 8. 8 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement The Goldmann Perimeter, which defined the Standards of Perimetry. These standards are still in use today.
    9. 9. 9 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement The standards of Perimetry are:  Spot IntensitySpot Intensity  Background IlluminationBackground Illumination  Spot DurationSpot Duration  Spot SizeSpot Size  Spot SpeedSpot Speed
    10. 10. 10 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Background Illumination  The standard value is 31.5 ASB.The standard value is 31.5 ASB.  The illumination in the bowl must remainThe illumination in the bowl must remain constant throughout the test.constant throughout the test.
    11. 11. 11 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Why 31.5 ASB?  Originally used by Goldmann Perimeter  Adopted as standard by International Peremetric Society (International Council of Ophthalmology 1979)  Approximates minimum level for photopic or daylight vision  Photopic vision relies on retinal cone function instead of rods  Cones – Object Contrast Rods – Absolute Brightness  Small changes in pupil size or clarity of media do not have an effect on Contrast, so have little effect on test results.
    12. 12. 12 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Spot IntensitySpot Intensity  Glass Wedge/Film WedgeGlass Wedge/Film Wedge  The Spot intensity is controlled by filter wheelsThe Spot intensity is controlled by filter wheels  The spot intensity is directly related to theThe spot intensity is directly related to the bowl intensity.bowl intensity.
    13. 13. 13 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Spot Size  Size V spot is the largestSize V spot is the largest  The size of the spot can be size I,II,III,IV,or VThe size of the spot can be size I,II,III,IV,or V  The default spot size is size IIIThe default spot size is size III Mr. DefaultMr. Default to you!to you!
    14. 14. 14 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Spot size 3 is .43 degrees Spot Size is smaller in the HFA II bowl than in the HFA I, because the bowl radius is smaller.
    15. 15. 15 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Spot Duration  The default time duration is 200mSThe default time duration is 200mS (milliseconds) + or – 10mS(milliseconds) + or – 10mS  How long the spot is displayedHow long the spot is displayed  Duration can be changed to 500 mS for olderDuration can be changed to 500 mS for older patients.patients.
    16. 16. 16 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement The principle of temporal summation holds that for very short durations, the visibility of a stimulus increases with duration; when a stimulus lasts more than about 0.5 seconds, on the other hand, its visibility is basically independent of duration. 200 ms – long enough for visibility to not be affected by small variations in duration. But less than … 250 ms – latency for voluntary eye movement
    17. 17. 17 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Spot Speed  This only applies toThis only applies to KineticKinetic testing.testing.  How fast the spot movesHow fast the spot moves  Default speed for the HFA is 4 degrees per second.Default speed for the HFA is 4 degrees per second.
    18. 18. 18 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Goldmann vs. Humphrey Parameters Goldmann HumphreyGoldmann Humphrey Spot Size I,II,III,IV, V I,II,III,IV,VSpot Size I,II,III,IV, V I,II,III,IV,V (V is the largest) (V is the largest)(V is the largest) (V is the largest) Filters 1,2,3,4 Glass WedgeFilters 1,2,3,4 Glass Wedge (4 is the brightest) Film Wedge(4 is the brightest) Film Wedge a,b,c,d,ea,b,c,d,e (e is the brightest)(e is the brightest)
    19. 19. 19 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Kinetic Testing Single intensity; Moving Target A light spot (Stimulus) is introduced along a particular meridian, following a straight line until a patient response (sees the light spot) is indicated. MeridianMeridian Patient ResponsePatient Response
    20. 20. 20 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Static Testing Varies the intensity of the spot over the entire Hill of Vision. Patient does not see the spot move. The spots are projected at different positions on the bowl, but the instrument will return to the spots at different intensities. Variable Intensity; Stationary Target
    21. 21. 21 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement The “Island” of Vision AA StaticStatic test on atest on a normal eye willnormal eye will produce a patternproduce a pattern similar to the one atsimilar to the one at right.right. DimDim BrightBright Blind SpotBlind Spot FoveaFovea NasalNasal TemporalTemporal
    22. 22. 22 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Scotomas There are two types ofThere are two types of ScotomasScotomas:: Definition: A defect on the Retina. An area or spot onDefinition: A defect on the Retina. An area or spot on the Retina that is not as sensitive to light as it shouldthe Retina that is not as sensitive to light as it should be.be. 1.1. RelativeRelative – An area or spot on the Retina that– An area or spot on the Retina that can detect light,detect light, but not as good as when compared to a normal eye at that samebut not as good as when compared to a normal eye at that same spot.spot. 2. Absolute – An area or spot on the Retina that cannot detect light, no matter how bright it is.
    23. 23. 23 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Scotoma Is this Scotoma RelativeIs this Scotoma Relative or Absolute?or Absolute? Relative!!Relative!! BlindspotBlindspot
    24. 24. 24 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Hey man, like, ALL myHey man, like, ALL my relatives are Scotomas!relatives are Scotomas! Absolutely!!!Absolutely!!! Can you dig it??!!Can you dig it??!! Cool!!Cool!!
    25. 25. 25 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement The Blind spot exhibits the same characteristics as an ________ ________? AbsoluteAbsolute Scotoma!Scotoma!
    26. 26. 26 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Thresholding and Bracketing What is thresholding? Threshold (or Threshold Level) is the minimum amount of light that the eye can detect at a particular point on the retina. Bracketing is the process of determining the Threshold value.
    27. 27. 27 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Thresholding by Bracketing For our purposes, we will assume that the instrument begins the threshold test with a spot of 36db. The spot or stimulus is presented at a particular spot on the bowl to see if there is a patient response. 0 dB36 dB55 dB Indicates a negative (did not see) responseIndicates a negative (did not see) response Indicates a positive (did see) responseIndicates a positive (did see) response DimmerDimmer BrighterBrighter
    28. 28. 28 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Thresholding by Bracketing The patient did not respond, indicating that he/she did NOT see the spot. The instrument will now introduce a spot of 32dB (a 4dB change) at the exact same location. 0 dB0 dB36 dB36 dB55 dB55 dB Indicates a negative (did not see) responseIndicates a negative (did not see) response Indicates a positive (did see) responseIndicates a positive (did see) response 32 dB32 dB DimmerDimmer BrighterBrighter
    29. 29. 29 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Thresholding by Bracketing The patient responded positively, indicating that he/she DID see the spot. The instrument will now introduce a spot at the same exact position, at a brightness of 34dB. (A 2dB change) 00 dBdB 36 dB 55 dB Indicates a negative (did not see) response Indicates a positive (did see) response 32 dB DimmerDimmer BrighterBrighter 34 dB
    30. 30. 30 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Once again, the patient did not see the spot. The instrument has determined by BRACKETING that the threshold for this spot is 32dB. (NOTE: Some tests may closer define the threshold by testing at 1 dB steps.) 0 dB 36 dB 55 dB Indicates a negative (did not see) response Indicates a positive (did see) response 32 dB DimmerDimmer BrighterBrighter 34 dB34 dB Thresholding by Bracketing
    31. 31. 31 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement What happens when you start a test? 1. One spot in each1. One spot in each quadrant will bequadrant will be bracketed to determinebracketed to determine the Threshold level.the Threshold level. At the same time, theAt the same time, the location of the Blindlocation of the Blind Spot will be determined.Spot will be determined. Bracketing begins at 24dBBracketing begins at 24dB Blindspot
    32. 32. 32 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement What happens when you start a test? 2. Once the threshold value for a spot in each quadrant has been found, an Expected Hill of Vision is determined. DimmerDimmer Expected “Hill of Vision” 36dB (CEN)36dB (CEN)
    33. 33. 33 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement The “CEN” is defined asThe “CEN” is defined as the Central ReferenceCentral Reference LevelLevel, or the, or the ExpectedExpected Foveal SensitivityFoveal Sensitivity, or the, or the Expected FovealExpected Foveal Threshold.Threshold. Expected “Hill of Vision” DimmerDimmer 36dB (CEN)) What happens when you start a test?
    34. 34. 34 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement What happens when you start a test? 3. As the test is run, the patients “Actual” readings are plotted. Expected “Hill of Vision”Expected “Hill of Vision” DimmerDimmer 36dB36dB Actual Patient plotsActual Patient plots Blind Spot
    35. 35. 35 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Types of Tests 1. Screening Tests – A QUICK overview of the patient’s field of vision. Most screening tests tell only if the patient did or did not see the spot. In general, screening tests do not quantify. That is, they do not determine how bad a scotoma is. Now you see it……..Now you see it…….. Now you don’t!!!!!!!!!Now you don’t!!!!!!!!!
    36. 36. 36 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Types of Tests 2.2. Threshold TestsThreshold Tests –– QuantifiesQuantifies each spot. That is, it finds the thresholdeach spot. That is, it finds the threshold level. Determines how bad the scotoma is by calculating thelevel. Determines how bad the scotoma is by calculating the exactexact lightlight level the patient can see at a particular spot on the Retina.level the patient can see at a particular spot on the Retina. I don’t see it… I don’t see it… Now I see it!!!!! Now I see it!!!!!
    37. 37. 37 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement  Short Wavelength Automated Perimetry (SWAP)  Blue Goldmann Size 5 Stimulus on bright Yellow background  Yellow Background reduces responsiveness of the red and green cone system  Blue Stimuli are seen primarily by the Blue Cone System  SWAP can detect progression of field loss earlier in patients than standard White on White perimetry  SWAP eliminates the redundancy in the visual system by reducing responsiveness from non blue cones and the rod system
    38. 38. 38 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Reliability Factors After a Field Test has been completed, aAfter a Field Test has been completed, a determination must be made if the test is accuratedetermination must be made if the test is accurate and therefore reliable. Several Reliabilityand therefore reliable. Several Reliability Indicators appear on the test printout:Indicators appear on the test printout:  Fixation LossesFixation Losses  False Negative ErrorsFalse Negative Errors  False Positive ErrorsFalse Positive Errors  Gaze TrackingGaze Tracking
    39. 39. 39 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Fixation Losses During the test, the patient is told to Fixate (Stare) at a central LED. The instrument records the number of times that the patient lost this fixation and reports it on the printout. Excessive fixation losses can render a test invalid.
    40. 40. 40 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Fixation Monitoring The HFA uses two systems for measuring patient fixation: the standard Heijl-Krakau blind- spot monitoring and the IR Gaze Tracking System. Both methods can be used, either together or alone, or they can both be turned off, as required.
    41. 41. 41 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Heijl-Krakau Blind Spot Monitoring
    42. 42. 42 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Gaze Tracking Location of Corneal Reflex Marker Corneal Reflex marker Location Digitized and Stored in Memory
    43. 43. 43 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement The direction of a patient's gaze is determined in two steps: 1. A reflex marker is established on the corneal surface. 2. The location of the pupil center is determined. Gaze Tracking
    44. 44. 44 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Gaze Tracking Gaze tracking is initialized in the following manner when a selected test is first started: The patient is asked to fixate on the central illumination LED. Gaze tracking turns on the reflex gaze IR LED located just under the diamond fixation pattern and turns off eye illumination briefly . Light from the LED is reflected off the cornea, and back to the IR sensitive camera.
    45. 45. 45 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Gaze Tracking The majority of the cornea appears black except for the reflected spot. This image is digitized and stored in memory. The reflected spot is referred to as the reflex marker. Because the corneal surface is rounded, the reflex marker will move very little even if the patient's eye rotates, and thus the marker becomes a (relatively) stationary reference point.
    46. 46. 46 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Gaze Tracking Next, the system locates the pupil center by illuminating the entire eye with the two IR LEDs located either in the bottom of the bowl, or in the trial lens holder (when in the raised position). The iris appears bright with a dark pupil. This image is also digitized and stored in memory. It is the relationship between the location of the reflex marker on the cornea and the location of the pupil center that determines fixation.
    47. 47. 47 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Gaze Tracking During a test, each time a spot is projected into the bowl, the locations of the reflex marker and the center of the pupil are compared to the initial images stored in memory. If the patient is fixating correctly, the positional relationship between the reflex marker and the pupil center will be the same as that of the stored images. If the patient is off fixation, the positional relationship between the reflex marker and the pupil center will be different. The greater the misalignment, the higher the mark on the Gaze Graph.
    48. 48. 48 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Gaze Tracking Determining the Pupil Center Patient Fixating – Corneal Reflex Marker and Pupil in Proper Relationship Patient Not Fixating – Corneal Reflex Marker and Pupil Not in Proper Relationship
    49. 49. 49 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Gaze Tracking Gaze Graph Upward spikes indicate that the patient has lost fixation; • a spike that reaches the top horizontal line (or higher) indicates 10 degrees (or more) off fixation; • a spike that extends halfway to the top line indicates 5 degrees off fixation. P Downward spikes indicate as follows: • a short spike downward indicates that the gaze at that time cannot be determined by the software. • a long spike downward indicates that the patient blinked at the time fixation was checked. The absence of marks on the graph indicates proper fixation.
    50. 50. 50 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Gaze Tracking
    51. 51. 51 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Gaze Tracking
    52. 52. 52 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement Gaze Tracking
    53. 53. 53 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement False Negative Errors Let us say that aLet us say that a StimulusStimulus (Spot) is presented at(Spot) is presented at 26dB26dB,, and the patient responds that the spot was seen.and the patient responds that the spot was seen. Later in the same test, at the same location, a brighterLater in the same test, at the same location, a brighter spot, sayspot, say 22dB22dB, is presented, and the patient does not, is presented, and the patient does not respond, that is, the patient does not see the spot.respond, that is, the patient does not see the spot. ““Yessir, I see it!”Yessir, I see it!” ““Nosir, I didn’t see that one!”Nosir, I didn’t see that one!”
    54. 54. 54 Humphrey Field Analyzer II/IIi Fundamentals of Perimetry Measurement False Positive Errors The patient responds that a spot of light was seenThe patient responds that a spot of light was seen when none was presented. This sometimes canwhen none was presented. This sometimes can occur when the motors move on the Humphreyoccur when the motors move on the Humphrey Field Analyzer, or a patient gets into a rhythm andField Analyzer, or a patient gets into a rhythm and anticipates spots.anticipates spots. SpotsSpots

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