Automated-perimetry - Brief review and basics
- 1. AUTOMATED PERIMETRY DR INDEEVAR V MISHRA MM JOSHI EYE HOSPITAL, HUBLI.
- 2. BASIC CONCEPTS • TRAQUAIR'S HAS DEFINED THE VISUAL FIELD AS BEEN A HILL ISLAND OF VISION IN A SEA OF DARKNESS TESTING ALONG X-Y AXES OF THIS 3 DIMENSIONAL AREA DETERMINES THE LOCATION IN THE VISUAL FIELD AND ALONG THE Z AXIS IDENTIFIES THE VISIBILITY THRESHOLD. • AUTOMATED PERIMETRY - " DIFFERENTIAL LIGHT THRESHOLD – ABILITY TO DIFFERENTIATE AN ILLUMINATED TARGET AGAINST AN ILLUMINATED BACKGROUND."
- 3. BASIC CONCEPTS --- CONTD THRESHOLD • LUMINANCE OF STIMULI THAT IS SEEN 50% OF TIMES IT IS PRESENTED • LOGARITHMIC UNIT DB ( DB PROP. 1 / BRIGHTNESS ) • BRACKETING STRATEGY ( 4 - 2 - 2 ALGORITHM ) • SUPRA THRESHOLD - 95 % CHANCE A STIMULUS IS SEEN. • INFRA THRESHOLD - 5% CHANCE A STIMULUS IS SEEN.
- 4. BASIC MACHINE DESIGN • ILLUMINATED HEMISPHERICAL BOWL 33 CM AWAY WITH TARGET OF FIXATION • STIMULI - SPOT OF LIGHT - LED / PROJECTION SYSTEM / COMP. VIDEO MONITOR • HFA - II ( 700 SERIES ) ASPHERICAL BOWL 30 CMS AWAY ,SMALLER ,MORE ERGONOMIC STIMULI IN PERIPHERY MORE CLOSER,
- 5. FIXATION CONTROL • CC TV MONITOR • HEIJL - KRAKAU BLIND SPOT METHOD • GAZE TRACKER • FULL TIME TWO VARIABLE GAZE MONITOR • IMAGE ANALYSIS • ERRORS - UPWARD / DOWNWARD • FIXATION CHECKED 100 % OF STIM. TIME • NO TESTING TIME FOR FIXATION CHECK
- 6. PARAMETERS RECOMMENDED FOR TESTING • FOVEAL FIXATION TARGET – SMALL AND LARGE DIAMOND WITH YELLOW LIGHTS. • GOLDMANN SIZE III TARGET FOR STIMULI & BLIND SPOT CHECK. IF EXCESSIVE FIXATION LOSS IT CAN BE DECREASED TO II OR I OR IF VISION LESS THAN 6/36 THAN IT CAN BE INCREASED TO V. • WHITE STIMULUS COLOUR • NORMAL TESTING SPEED. CAN BE SLOW DOWN IF PATIENT IS SLOW TO RESPONSE. • FOVEAL THRESHOLD - ON / OFF
- 7. THRESHOLD TESTS • CENTRAL 30-2 – 76 POINTS ARE TESTED . EACH POINT 6 DEG APART. STRADDLING THE HORIZONTAL AND VERTICAL AXIS SO THAT THE 2 INNER MOST TEST POINTS ARE 3 DEG FROM FIXATION POINT. • CENTRAL 24-2 – 56 POINTS ARE TESTED . AVOIDS RIM ARTIFACTS. • CENTRAL 10-2 – 68 POINTS SPACE 2 DEG APART. USEFUL IN ADVANCE DISEASE WITH SPILT FIXATION. • MACULAR THRESHOLD TEST – SQUARE GRID OF 16 POINTS EACH 2 DEG APART , WITH EACH POINT THRESHOLDED 3 TIMES.
- 8. 30 – 2 24 – 2 Macular threshold
- 9. INTERPRETATION FACTORS FOR CONSISTENCY IN TESTING • BEST REFRACTIVE CORRECTION USED. CONTACT LENS TO AVOID RIM ARTIFACTS. • PUPIL DIAMETER – AT LEAST 3.5 MM IN SIZE. • VISUAL ACUITY • DATE & TIME OF TESTING • AGE-FOR COMPARISON WITH NORMATIVE DATA • SHORT TERM FLUCTUATION-FLUCTUATION OCCURRING WITHIN THE TEST. SHOULD BE <3DB.
- 10. INTERPRETATION ----CONTD. FIXATION LOSSES: 10/12 XX FALSE POS ERRORS : 0/7 FALSE NEG ERRORS :0/6 TEST DURATION : 16:20
- 11. STATISTICAL GLOBAL INDICES • MD – MEAN DEVIATION – SENSITIVE TO TOTAL LOSS • PSD – PATTERN STANDARD DEVIATION – SENSITIVE TO LOCALIZED LOSS. • CPSD – CORRECTED PATTERN STANDARD DEVIATION – PSD CORRECTED FOR SHORT TERM FLUCTUATION. VERY SENSITIVE INDEX.
- 12. GLAUCOMA DEFECT WITH AUTOMATED PERIMETRY- ANDERSON'S CRITERIA • 3 OR MORE CONT.NON EDGE POINTS WITH >= 5 DB LOSS • 2 OR MORE CONT. NON EDGE POINTS WITH >=10 DB LOSS • DIFF. OF 10 DB ACROSS NASAL HOR. MERIDIAN AT 2 OR MORE ADJ. POINTS ( NASAL STEP.) • GHT - ONL • PSD PLOT - >= 3 PTS , P< 5% OF WHICH ONE < 1% • CPSD ( P <5% ) GHT ONL
- 13. SWAP • TESTS SUBSET OF GANGLIONS AFFECTED EARLIER & SELECTIVELY -- BLUE / YELLOW • REDUCES THE REDUNDANCY OF RESPONSIVENESS TO STIMULI • INTENSE YELLOW BACKGROUND - BLEACHES GREEN / RED CONES • BLUE STIM. ( 440NM ) - ISOLATES BLUE CONES • ADAPTATION - 3 MTS. ROOM ILLUMINATION - MINIMAL • STIMULUS SIZE & BS CHECK SIZE V • MEAN THRESHOLD VALUES LOWER THAN SAP - GRAY SCALE DARKER • STAT PAC PROBABILITY PLOTS MORE RELIABLE
- 14. SWAP -- CONTD • FIELD DEFECT PRECEDES SAP BY >= 3 YRS • ONCE ABNORMAL - REMAIN ABNORMAL ( NO RECOVERY OF DAMAGED BLUE CONES ) • NO ROLE IN ADVANCED POAG / ADVANCED LENTICULAR CHANGES / COLOUR VISION ABNORMALITIES • MOST USEFUL IN YOUNGER GLAUCOMA SUSPECTS, OHT , POAG WITH MILD TO MOD.DAMAGE • TIME CONSUMING - SITA OPTIMISED FOR SWAP / FAST PAC CAN BE USED