perimetry BY Dr.Ricky


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Seminar on Assessment of Visual field. Automated Perimetry.:

Seminar on Assessment of Visual field. Automated Perimetry. Dr. Ricky Mittal.

Slide 2:

What is the normal visual field? Traquair-“island of vision surrounded by the sea of darkness.” 3 dimensional- strategies that are the foundation of all perimetric examinations. X-Y axis, Z axis. Kinetic perimetry: extent along X-Y axis. Static perimetry: differential light sensitivity ,altitude of the hill of vision along vertical z axis.

Slide 3:

Extent of visual field, XY axis:

Basic terminologies::

Basic terminologies : Threshold : Physiological capacity to detect a stimulus at a given location, that stimulus intensity that has a 50%probability of being seen. Apostilbs : Absolute units of light intensity. Luminance of test target. 1 asb=.3183 candela/m 2 Decibels : Relative scale, created by manufacturers. Attenuation of light by neutral density filters. 1dB=1/10 log units of attenuation of max. stimulus. Measures sensitivity at each point.0to40dB.

Sensitivity Vs threshold: :

Sensitivity Vs threshold: Inverse relationship. In automated perimetry, threshold is recorded in the inverted decibel scale, and dimmer targets have higher decibel values. Therefore, threshold in decibels is directly proprotional to retinal sensitivity .

Apostilbs Vs decibels: :

Apostilbs Vs decibels : Lumininance of test targets is measured in an absolute unit, apostilbs. Decibel is a relative scale created by manufacturers of automated perimeters to measure sensitivity. Inverted logarithmic scale with 0dB=brightest stimulus. Not standardized.

Slide 7:

Total deviation :difference between patient’s threshold measured and value expected in age matched normals.

Global indices: :

Global indices : Mean deviation : mean difference between sensitivities of age matched normals and subject. Highlights overall depression, dB, STATPAC, p value. Indicated as: -ve in Humphrey. +ve in Octopus. Pattern standard deviation : this is a measure of degree to which the shape of patients field differ from normal, extent of focal loss as a single value. PSD can be normal when there is a diffuse loss.

Slide 9:

primarily reflects retinal condition. excludes conditions affecting the overall field. PSD: small value-normal field or diffuse loss. scotoma -clearly abnormal. advanced -PSD starts decreasing if many threshold values near 0dB.

Slide 10:

SF : Intratest test variability, threshold at 10 predetermined points, twice. SD – SF indicator of patient’s consistency, pathology. 1-2.5dB. CPSD : extent of focal loss in the visual field, taking short term fluctuations in account i.e. which is not caused by SF. Probability analyses : symbolic represenation. Statistical probability of a threshold value measured at a point that exists in age-matched normals. Darker the symbol lower the probability. Comparison on a point by point basis. Cataract, ref.error excluded. Retinal condition.

Glaucoma hemifield test: :

Glaucoma hemifield test: Compares five zones (along the nerve fibre bundles) in the upper field with their mirror images in the lower field. A very good determinant of the presence of glaucomatous damage on a single field. Does not analyze temporal nerve fibre bundle defects.

Slide 12:

Inference: Outside normal limits. <1%,0.5%. Borderline. 3% Abnormally low sensitivity. 5% Abnormal high sensitivity. higher than 99.5% Within normal limits.

Basics of the Humphrey field analyser::

Basics of the Humphrey field analyser: Projection type automated static perimeter. Most popular, consistency of basic hardware, constant upgradation of the software on the basis of clinical feedback from the ophthalmologists. The machine: Viewing distance-33cms. Background illumination-31.5asb. Static mode, newer models - kinetic.

Slide 14:

Stimulus size: Goldman stimulus size(1to5) Stimulus duration:0.2 second. Fixation monitor : Heijl Krakau blind spot technique, gaze monitoring.

Slide 15:

Data storage. STATPAC: computerised statistical package Comparison of patients results with age matched normal data. Patients own baseline with follow up data. Newer HFA series: database of stable glaucoma patients for glaucoma change probability analysis.

Interpretation of visual field: :

Interpretation of visual field: Recognise artifacts: Reliability. Assessment of damage .

Slide 17:

Baseline visual field exam : 2 fields – min. baseline. 1 st field-Central 30-2 threshold 2 nd -central 30-2 threshold within 1 to 2 months. Provided: Consistent ,no learning effect. <2dB (MD). If 1 st field constricted or depressed: Obtain 10-2 threshold test. Retest with size5 stimulus(64mm 2 ). Or combine.

Artifacts :

Artifacts Lid. Lens rim-too far or the eye is not centered. Refractive error. Learning effect. Pupillary size. Rapid fatigue.

Reliability: :

Reliability: False positives-tendency of the patient to press the trigger not in response to seeing a stimulus but at random, either as a response to an audible cue or due to the expectation of the stimulus. Ratio of such responses to the number of FP catch trials done. >33%FP rate is flagged with a double XX. Low reliability.

False negative::

False negative : False negative responses are failure of the patient to respond to stimulus 9 dB more intense than the previously determined threshold at that point due to patient inattention or fatigue. Reason may be a tired patient. A high FN rate may or may not be reliable. Cloverleaf defect due to high FN.

Fixation losses::

Fixation losses: Not all fixation losses represent true loss of fixation. High fixation loss may indicate, centre of blind spot was slightly mislocated. If FP, FN rates and STF are low, then the high FL can be discounted. If two baseline fields are similar it can again be discounted. Mislocation of the blind spot. Macular disease.

Short term fluctuations: :

Short term fluctuations: Testing option, shows variability of patients response over a single test period. low ( ≤2dB) SF- good reproducibilty high (≥ 3dB) SF-poor reproducibility

Minimum Criteria for Diagnosing Acquired Glaucoma::

Minimum Criteria for Diagnosing Acquired Glaucoma : A Glaucoma Hemifield Test outside normal limits on at least two fields. or A cluster of three or more non edge points in a location typical for glaucoma, all of which are depressed on the PD plot at p <5% level and one of which is depressed at p <1%level on two consecutive fields. or A CPSD that occurs in less than <5% of normal fields on two consecutive fields.

Slide 33:

Early defect : Neither extensive nor near fixation. Mean deviation index (MD) –better than -6dB. On PD plot: 1.<25%(18) points are below 5% level. 2.< 10 points below 1% level. Central 5°-no points having less than 15dB sensitivity.

Slide 37:

Moderate defect : MD<-12dB. 1.PD-<50%( 37) points < 5% and < 20 points <1%. Central 5°-no points with 0dB. Only one hemifield may have a point in central 5° with <15dB sensitivity.

Slide 41:

Severe defect : Any of the following: 1.MD plot >-12dB 2.PDplot: >37 points depressed below<5%. >20 points depressed below 1%. Any point in central 5°has sensitivity of 0dB. Central 5°-points <15dB in both hemispheres .

Recognition of progressive damage: :

Recognition of progressive damage : defect. 2.deepening of pre exisiting defect. 3.expansion of pre existing defect. 4.entire field develops decreased sensitivity.

How would u approach?:

How would u approach ? Compare baseline field to each individual field Study the entire series.

Compare with baseline field::

Compare with baseline field : 1.For a new defect in previously normal area . Cluster of 3 or or more non edge points each of which declines by 5 or >5dB. 2.For deepening of pre existing defect . A cluster of 3 or more non edge points, each of which declines by 10 or>10dB. 3.Generalized depression : Decline of all points by 3dB.

Glaucoma change probability programme: :

Glaucoma change probability programme: Point by point probability of any change in baseline field and new field. defect : 3 or more non-edge points each of which, p<5%,on two consecutive fields. 2.deepening of pre existing defect : part of a scotoma, cluster, p<5%. 3. expansion : Within 15 ° of field-2 previous normal points. Outside 15° of field-3 previously normal points depressed with p,5%.

Slide 49:

Generalized depression : Decline in MD, p<1%.

References: :

References : Illustrated Automated Static Perimetry G.R.Reddy. Testing of the Field of Vision-Douglas R.Anderson. Clinical Decisions in Glaucoma-Elizabeth Hodapp,Richard K.Parrish,Doughlas R.Anderson. Visual Field Examination-A.K.Gupta ,Reena M.Chaudhary,Charu Tandon.

Slide 51:

. Thank you .