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Visual field Analysis .ppt
- 1. 1 Dr. Md. Ashfakur Rahaman (Rayhan) D.O Student RpMC
- 2. Definition of Perimetry: Defined as Numeric, Graphical and Symbolic presentation of visual field.
- 3. Objectives: Identification and quantification of abnormal visual fields Longitudinal assessment to detect glaucomatous progression and measure rates of change.
- 4. The Visual Field: The visual field can be represented as a three- dimensional structure akin to a hill of increasing sensitivity.
- 5. THE NORMAL VISUAL FIELD : 50˚ SUPERIORLY 60˚ NASALLY 70˚ INFERIORLY 90˚ TEMPORALLY
- 7. Common terms used in V.F & Perimetry An isopter is a line connecting points of the same sensitivity, and on a two-dimensional isopter plot encloses an area within which a stimulus of a given strength is visible. When the field is represented as a hill, isopters resemble the contour lines on a map.
- 8. Cont…. A scotoma is an area of reduced (‘relative’) or total (‘absolute’) loss of vision surrounded by a seeing area. Luminance is the intensity or ‘brightness’ of a light stimulus, measured in apostilbs (asb).
- 9. Scotoma
- 10. Cont… Stimulus brightness: Apostilbe (Asb): Unit of intensity of light projected as stimulus. Decibel (dB): Unit of neutral density filters used to make stimulus dimmer. 0dB(withoutfilter)=10,000Asb (Humphrey) 10dB = 1/10th = 1000Asb 20dB = 1/100th = 100Asb etc. (10dB = 1Lu)
- 11. Cont… Threshold at a given location in the visual field is the brightness of a stimulus at which it can be detected by the subject. After the age of 20 years the sensitivity decreases by about 1 dB per 10 years.
- 12. Threshold
- 13. Cont… Background luminance: The retinal sensitivity at any location varies depending on background luminance. Rod photoreceptors are more sensitive in dim light. Cone photoreceptors are more sensitive in Bright light Peripheral retina more sensitive in proportion to the central retina.
- 14. Types of perimetry Kinetic Goldmann Lister Bjerrum s Screen Static Humphrey Octopus Henson
- 15. Automated Static Perimetry To find visual field sensitivity at pre-selected locations Presenting stimulus of known size and brightness known background for known amount of time. We measure differential light sensitivity or contrast sensitivity.
- 16. Testing algorithms Threshold Used for detailed assessment of the hill of vision By plotting the threshold luminance value at various locations
- 18. Cont… Suprathreshold Testing with stimuli of luminance above the expected normal threshold levels It enables testing to be carried out rapidly Reserved for screening.
- 19. Fast algorithms Introduced with shorter testing times, Providing efficiency benefits with little or no detriment to testing accuracy. SITA-Standard and SITA-Fast versions are available
- 20. Stimulus inteansity in decibel value 20 ∞ Retinal Sensitivity
- 22. Testing Protocols Most common ---- central 30-2 (76 points) or 24-2 (54 points), Neurological disease – 30-2 or 24-2, Small central scotoma – 10-2 (68 points) Peripheral – 60-4 Macula
- 23. 30-1 30-2
- 24. SITA (Swedish interactive threshold algorithm) Dramatic reduction of test time without sacrificing accuracy. More accurate choice of stimulus brightness. Complete use of patient information. Test pace completely determined by patient.
- 26. INTERPRETATIONS
- 27. Zone 1 Patient data & test data Zone 2 Foveal Therashold & Reliable indices 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
- 28. Zone 1 Patient data & test data Zone 2 Foveal Therashold & Reliable indices 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
- 31. Reliability indices B) False positive error rates : Should be < 33% Increased fixation loss value. C) False negative error rates : Should be < 33% ( No ‘xx’ for FN % in newer SITA strategy).
- 32. Reliability indices – a) Gaze stability – Heijl-Krakau blind spot method - Fixation loss should be <1/5th Gaze monitor Video monitoring
- 33. Single Field Printout:zone-3 Interpolated gray scale.(within green ring)
- 34. Total Deviation plots-zone-4 I . Numeric value in upper plot - diff. in dB between the patients test results and the age corrected normal values at each tested point in the visual Field. Value is abnormal -> if 5 dB less than normal . 2. Gray -scale symbols in lower plot -> translates values in upper plot, Darker the symbols, more the depth of defect.
- 35. Total deviation (from normal values for age) - Normal sensitivity range – larger peripherally than centrally and superiorly than inferiorly.
- 36. Pattern Deviation Is similar to total deviation Except that any generalised depression in the field caused by other factors such as lens opacities or miosis.
- 37. Pattern deviation :zone-5 Single most useful analysis For exposing localized defect masked by generalized depression or elevation Early field defect appear first in probability map Doesn’t come in very advanced field defects
- 39. P- Value Probability (Chance) - Chances of occurrence by chance expressed by 'P'. Ranges -> from '0' to I . P = 0, means no chance of an event happening or its occurrence is impossible e.g. Chances of survival after rabies are zero or nil . P = 1, means chances of an event happening are 100% e.g. death of any living being. P value -> Significant in 5% level, (95% confidence limit)
- 40. 40
- 41. Uniform total dev. plot depression but normal pattern dev. plot – Media opacity Normal total dev. but abnormal pattern dev.– trigger happy pt.
- 42. Statistical Analysis: zone; 6 Global indices : Mean deviation (M.D.) – Denote average severity of field loss. Pattern standard dev. (PSD) – It is the S.D. around M.D. ↑ PSD - ↑ focal defect.
- 43. Global indices: Short term fluctuation (SF) - Index of intra test measurement variability. Between 1-2.5 dB. Significance limited by small no. of points tested. High in inconsistency and in diseased area (not done in SITA). Corrected PSD (CPSD) - When SF removed from PSD.
- 44. 5 Zones in upper field compared with 5 mirror-image zones in lower field In 30-2 and 24-2 tests only Glaucoma hemifield test (GHT):zone-7
- 45. Glaucoma Hemifield Test (GHT) Five possible messages : Outside normal limits (one or more zone difference by P < 0.01) Borderline General reduction of sensitivity Abnormally high sensitivity Within normal limits
- 46. Visual Field Index(VFI) The VFI represents the entire visual field as a single percentage of normal Based largely on the pattern deviation; weighs central points more than peripheral ones. A full visual field has a VFI of 100%; perimetrically blind visual field has a VFI of 0%.
- 48. Overview - Minimum 4 field tests -- for evidence of progression. 6 or more -- for certainty.
- 49. Glaucoma Progression Analysis(GPA) Like GCP, but smarter Adjusts for cataract Deterioration from baseline at P<5% - ∆ Deterioration at same location, 2 consec. tests – Deterioration at same location, 3 consec. tests –▲
- 50. Artifact Edge artifact: Eye brow Lens rim
- 51. Artifact due to patient fatigue (clover leaf pattern)
- 53. 53 Stimulus – Blue (440 nm), Size V Background – Intense yellow Can detect presence and progression of glaucomatous V. F. change several years earlier than standard white on white auto perimetry (SAP).
- 55. 55
- 56. Microperimetry Microperimetry is a visual field test that measures retinal sensitivity and fixation behaviour in patients with macular disease and focal glaucoma involving the central visual field. 56
- 58. Cont... Goldmann size 3 stimuli are projected onto the central 9° of the fundus. A 4-2 staircase thresholding technique is used, Using this instrument normal retinal sensitivity is 18 dB.
- 59. Cont... Results are printed, together with reliability indices (fixation loss), probabilities, and retinal sensitivity values, Which are colour-coded. It can also be helpful in patients with early glaucoma, particularly when there is subtle change close to fixation.
- 61. Sources of error in perimetry Inexperienced or unskilled technician Incorrect patient details Miosis Lens opacities Uncorrected refractive error Spectacles rim artefact Ptosis Poor patient performance Inadequate retinal adaptation
- 62. 62