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Visual field examination
- 2. VISUAL FIELD • That part of environment wherein a steadily fixating eye can detect visual stimulus. • BASIS - presence of Photoreceptors and corresponding visual pathways up to the periphery of retina away from point of fixation i e fovea.
- 4. Physiological basis DIFFERENTIAL LIGHT SENSITIVITY Basis of most modern visual field examination methods TRAQUAIR – “HILL OF VISION IN THE SEA OF DARKNESS
- 5. PHYSIOLOGICAL BLIND SPOT • Corresponding to optic nerve head • 15 deg temporal to point of fixation • Span – 5 deg horizontal x 7 deg vertical • Two thirds below the horizontal meridian
- 6. FACTORS affecting visual field • Apparent size of spot • Distance from eye • Duration of stimulus • Background illumination • Stimulus intensity • Contrast • Colour • Patient factors Light / dark adaptation Vision Refractive status Education , attentiveness, cooperation
- 7. • SCOTOMA : focal region of abnormally decreased sensitivity surrounded by an area of normal sensitivity ABSOLUTE RELATIVE POSITIVE NEGATIVE • DEPRESSION : is an area of reduced sensitivity without a surrounding area of normal sensitivity appears as denting of isopters.
- 8. Different field defects • Generalized depression (both peripheral and central contraction) e g cataract • Peripheral Contraction – retinitis pigmentosa • Temporal contraction – age • Hemifield defect : B/L - Hemianopias homonymous heteronymous • Altitudinal defect
- 9. Normal arrangement of nerve fibers
- 10. Glaucomatous field defects • Barring of blind spot • Nasal step • Seidel scotoma • paracentral scotoma • Bjerrum scotoma • Arcuate • Ring – double arcuate
- 11. • Split fixation
- 12. Visual field examinations Confrontation test Kinetic perimetry Static perimetry ARC PERIMETERS eg LISTER‟s PERIMETER BJERRUM’s SCREEN ( CAMPIMETRY) GOLDMANN’s PERIMETER
- 13. CONFRONTATION • Patient and examiner at same level • Compares the visual field of eye of patient with opposite eye of the examiner in a plane perpendicular to line of gaze
- 14. Kinetic perimetry • Test object of particular size and intensity • non seeing area to seeing area • 3 – 5 deg per sec • Repeated every 15 – 30 deg • ISOPTER (Groenouw) marking • 2 D map of the hill of vision
- 15. STATIC • The location, size and duration of stimulus is kept constant and the luminance is gradually increased until seen • Actual estimation of sensitivity (THRESHOLD ) of each point
- 16. AMSLER GRID • For Central 10 deg ( static ) • Other eye occluded • Near correction given • Chart at held 28-30 • 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
- 17. Standard automated perimetry HUMPHREY FIELD ANALYZER OCTOPUS • STATIC perimetry • Measurement of threshold values
- 18. ADVANTAGES • Subjective • More sensitive to subtle field defects • Reproducibility • Retests abnormal points automatically • Gives reliability parameters like fixation monitoring – HEIJL KRAKAU method Gaze tracking
- 19. Apostilbs(asb) : absolute units of light intensity 1 asb is equal to 0.3183 cd/m2 Decibels (dB) are the relative units Depends on degree of attenuation 1 decibel=1/10 log unit of attenuation of maximum available stimulus
- 20. • WHITE ON WHITE • BACKGROUND ILLUMINATION - 31.5 asb • STIMULUS SIZE – GOLDMANN - III • DURATION OF SPOT EXPOSURE 0.2s
- 21. PROGRAMS / PATTERNS 30-2 24-2 10-2 MACULAR 30-1, 24-1 Peripheral 60-4 Estermann test – for binocular 120 deg field
- 23. 30-2 vs 24-2
- 24. 10-2 & 30-2
- 26. STRATEGIES • SUPRATHRESHOLD • FULL THRESHOLD • SWEDISH INTERACTIVE TESTING ALGORITHM (SITA)
- 28. FULL THRESHOLD BRACKETING STRATEGY( staircase) – GOLD STANDARD FASTPAC Estimation of SHORT TERM FLUCTATIONS at 10 prefixed points
- 31. SWEDISH INTERACTIVE TESTING ALGORITHM (SITA) SITA algorithm developed for the Humphrey perimeter uses a complex mathematical model to estimate threshold values for each point based on responses to stimuli presented at that location, as well as information gathered from nearby locations
- 32. How it is different? Calculations of to False POSITIVE errors and False NEGATIVE errors in Percentage Does not Calculate Short term-Fluctuation Single Crossing of seeing and non seeing zones Calculations are done after the test, so there is less fatigue for the patient
- 33. • SITA STANDARD ( Bracketing strategy based) • SITA FAST ( FASTPAC based) • SITA FASTER Analyzes patients response and responds accordingly Decreases overall no of stimuli presented, hence test duration Paces the test according to patients speed Doesn‟t estimate Short term Fluctuations
- 34. • 24-2 sita faster – 2min
- 35. Pre-requisites • Selection of adequate test • Proper environment • Comfortable sitting position • Visual acuity >3/60 • Adequate size of pupil >3mm • Proper explanation – running of demonstration • Age >18 years
- 36. 8 Zones
- 37. Zone 1 Patient data • Name, DOB, eye • Vision, refraction, • Pupil diameter Test data • Date and time • Program and strategy • Background illumination • Test size, color
- 38. ZONE 2 : RELIABILITY INDICES Fixation monitor • Fixation target • Test duration • Reliability indices Fixation losses ( Heijl Krakau) <20 % Gaze tracking False positives < 33% False negatives < 33 % Foveal threshold
- 39. FP FN
- 40. ZONE 3 : GREY SCALE • Based on actual threshold values at each location • General identification • Patient information
- 41. ZONE 4 :TOTAL DEVIATION PLOT • Numerical plot – indicates by how much decibels is each point depressed compared to mean value in normal population of similar age • Probability plot- grey scale indicates the probability of occurrence of the deviation in normal population Generalized depression due to media opacities, refractive error, miosis may hamper appearance of a pattern
- 42. ZONE 5 : PATTERN DEVIATION PLOT • Selection of the 7th best sensitivity point for ex. If it is -5, add +5 to all the deviations. The new resultant deviations will form the Pattern deviation numerical Plot. • Numerical - calculated by adjustment for generalized depression or elevation of visual field • Thus brings out pattern • Probability plot
- 43. ZONE 6 : GLOBAL INDICES • MEAN DEVIATION : average loss of sensitivity from normal age matched population along with probability calculated from total deviation plot • PATTERN STANDARD DEVIATION : measures irregularity by summing the absolute value of the difference between the threshold value for each point and the average visual field sensitivity. PSD= normal value for each point + MD • SHORT TERM FLUCTUATIONS • CORRECTED PATTERN STANDARD DEVIATION
- 44. ZONE 7 : GLAUCOMA HEMIFIELD TEST • PLAIN ENGLISH LANGUAGE MESSAGE • Comparison of 5 clusters of points in superior hemifield with mirror images in inferior hemifield.
- 45. GHT 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
- 46. VFI • Visual field index (VFI) is a single number that summarizes each patient’s visual field status as a percentage of the normal age-corrected sensitivity. • Rate of ganglion cell loss. • Derived from the pattern deviation plot • Ranges between 0-100%
- 47. Zone 8: RAW DATA
- 48. ANDERSON and PATELLA CRITERIA • 3 or more congruous, non edge points in typical arcuate area on 30-2 program depressed @ p< 5 % with at least one point @ p<1 % •PSD / CPSD @ p< 5% •GHT – outside normal limits
- 49. CLASSIFICATION
- 52. SHORT WAVELENGTH AUTOMATED PERIMETERY • “BLUE ON YELLOW” • detects glaucomatous defects 3-5 years earlier than SAP • high fluctuation rates
- 53. FREQUENCY DOUBLING PERIMETRY • Based on frequency doubling illusion • Test stimulus – series of white and black bands flickering at 25 Hz ( low spatial frequency & high temporal frequency) • Detects damage to Magnocellular Ganglion cells
- 54. RANDOM DOT MOTION PERIMETRY Patient has to tell direction in which dots are moving HIGH PASS RESOLUTION PERIMETRY Test resolution and not mere threshold detection
- 57. ARTEFACTS • OBSTRUCTION RIM ARTEFACTS PTOSIS MEDIA OPACITIES • MIOSIS • REFRACTION ARTEFACTS • High power plus and minus lenses
- 61. PTOSIS