visual field examination

VISUAL FIELD EXAMINATIONAND

INTERPRETATION OF AUTOMATED PERIMETRY IN GLAUCOMA

DR PAAVAN KALRA

DEPARTMENT OF OPHTHALMOLOGYS P MEDICAL COLLEGE

BIKANER

VISUAL FIELD• That part of environment wherein a steadily fixating eye can

detect visual stimulus.

• BASIS - presence of Photoreceptors and corresponding visual pathways upto the periphery of retina away from point of fixation i e fovea.

• IMPORTANCE – Reflects topographic sensitivity of various foci on retina and corresponding visual apparatus.

Resolution – Acuity

differential light sensitivity and contrast

colour

flicker

motion

PHYSIOLOGICAL BASIS

VISUAL ACUITY

DIFFERENTIAL LIGHT SENSITIVITY

Basis of most modern visual field examination methods

TRAQUAIR – “HILL OF VISION IN THE SEA OF DARKNESS”

FACTORS

Apparent size of spot – real size

-- distance from eye

Duration of stimulus

Background illumination

Stimulus intensity

Contrast

Colour

Patient factors

Light / dark adaptation

Vision

Refractive status

Education , attentiveness, cooperation

Stereoscopic field

PHYSIOLOGICAL BLIND SPOT

Corresponding to optic nerve head

15 deg temporal to point of fixation

Span – 5 deg horizontal

-- 7 deg vertical

Two thirds below the horizontal meridian

COLOUR FIELD

• Point at which passing from periphery to centre, the colour first becomes evident

• Peripheral to the limit, the object is perceptible but appears grey

• First red and green are used followed by blue and yellow

• Extent of field for objects of same size and intensity

white > yellow > blue > red > green

VISUAL FIELD DEFECTS

• SCOTOMA : focal region of abnormally decreased sensitivity surrounded by an area of normal sensitivity

ABSOLUTERELATIVE

POSITIVE

NEGATIVE

• DEPRESSION : is an area of reduced sensitivity without a surrounding area of normal sensitivity

appears as denting of isopters

• 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

• Central scotoma• Pericentral • Centrocaecal scotoma

• Arcuate scotomas

Seidel scotoma

paracentral scotoma

Bjerrum scotoma• Nasal step• Ring – double arcuate• Split fixation• Barring of blind spot

EXAMINATION METHODOLOGY

KINETIC• Test object of particular size and intensity is passed from

non seeing area to seeing area along a particular meridian at the rate of 3 – 5 deg per sec

• Repeated every 15 – 30 deg• To find points in the visual field of equal sensitivities –

ISOPTER (Groenouw) marking• Intensity and size of stimulus is varied to mark various

isopters• Thus 2 D Contour map of the hill of vision is made• Extent of scotomas and blind spot marked from inside

out

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 is made out• SUPRA THRESHOLD stimulus used for screening

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IMPORTANT :

one eye is tested at a time, other is occluded

fixation of the patient has to be steady and is monitored throughout the test

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CLINICAL METHODS GROSS DEFECTS

PROJECTION OF LIGHT

In patients with very poor vision –> HM + to PL +

e g dense cataracts

-dark room, other eye occluded

-patients are constantly instructed to look straight to avoid tendency to deviate eye towards light source

-light shown onto 4 quadrants from 30-50 cm and switched on and off

-Patient tells about the direction of light source

Accurate in all quad

Inaccurate in some quad

Inaccurate in all quad

HAND IDENTIFICATION

Other eye is occluded

Patient fixates on the nose of examiner

Examiner keeps both hands on either side of eye 50 cm away

One hand absent or indistinct – hemianopic defect

Either palms or fingers of both hands missing / faint – altitudinal defect

FINGER COUNTING

Varying no of fingers are held in each quadrant, 1 m and 45 deg from fixation

If unable to count, fingers are brought closer to fixation, until patient sees (kinetic)

RED DESATURATION

Can be confirmed kinetically

Patient has to indicate when color appears to change

Can also be used to compare the two eyes in case of optic neuropathy

CONFRONTATION(kinetic)

Patient’s 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

Red pin is particularly useful for neurological cases

GROSS PERIMETRY (kinetic)

Follows facial contour

AMSLER GRIDFor Central 10 deg ( static )

Other eye occluded

Near correction given

Chart at held 28-30 cm – each small square subtends angle of 1 deg

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

EQUIPMENTS

PERIMETRY

Examination and quantification of visual field by using stimulus of various sizes, intensities and colours

ARC PERIMETERS eg LISTER’s PERIMETER

• Only kinetic• Peripheral charting

BJERRUM’s SCREEN ( CAMPIMETRY)

• Patient sits at 1 or 2 m from flat screen• Kinetic and static• For central 30 deg only• Done under subdued lighting

GOLDMANN’s PERIMETER

• Bowl type• Standardization• Both kinetic and static• Peripheral as well as central

AUTOMATED PERIMETRYstandard automated perimetry

HUMPHREY FIELD ANALYZER

OCTOPUS

• STATIC perimetry

• Measurement of threshold values

• STATPAC (HFA)- Comparison to normative data

• Inbuilt program for analysis – diagnosis and progression

ADVANTAGES• Removal of examiner variability• More sensitive to subtle field defects• Reproducibility• Retests abnormal points automatically• Gives reliability parameters like

fixation monitoring – HEIJL KRAKAU method

Gaze tracking

False positive

False negative

SHORT COMINGS• EXPENSIVE• Learning curves• Difficult to follow by older debilitated patients especially

neurological problems• Not infallible – only 1 % of field is actually examined• Diagnosis and management decisions based on

correlation with other clinical findings

A well performed tangent screen examination is better than poorly carried out automated perimetry

In neurological patients, clinical methods may be the only possible assessment techniques

• WHITE ON WHITE

• BACKGROUND ILLUMINATION - 31.5 asb

• STIMULUS SIZE – GOLDMANN - III

• DURATION OF SPOT EXPOSURE 0.2s

PROGRAMS / PATTERNS

30-2 – gold standard

24-2

10-2

MACULAR

Nasal step program – additional 12 locations upto 50 deg nasal

peripheral 60 and 60-4 prog

Estermann test – for binocular 120 deg field

MACULA PROGRAM :16 locations within the central 5° with 2° spacing. Each location is tested three times

STRATEGIES

SUPRATHRESHOLD – screening

Fixed suprathreshold

contour suprathreshold

3 zone suprathreshold

FULL THRESHOLD

BRACKETING STRATEGY( staircase) – GOLD STANDARD

FASTPAC

Estimation of SHORT TERM FLUCTATIONS at 10 prefixed points

SWEDISH INTERACTIVE TESTING ALGORITHM (SITA)

SITA STANDARD ( Bracketing strategy based)

SITA FAST ( FASTPAC based)

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

• Selection of adequate test• Proper environment• Comfortable sitting position• Adequate size of pupil >3mm• Adequate Near correction• Proper explanation – running of demonstration• Reassurance – not all points will be seen

- test can be paused by keeping the response button pressed

Patient data• Name, DOB, eye• Vision, refraction,• Pupil diameter

Test data• Date and time• Program and strategy• Background

illumination• Test size, color,

duration, interval

ZONE 1 : REPRODUCIBILITY

ZONE 2 : RELIABILITY• Fixation monitor• Fixation target – central, small diamond,

large diamond, bottom LED• Test duration

• Reliability indices

Fixation losses ( Heijl Krakau) <20 %

Gaze tracking

False positives < 33%

(trigger happy)

False negatives < 33 %

Foveal threshold

ZONE 3 : GREY SCALE

• Based on actual threshold values at each location• General identification• Patient information

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

ZONE 5 : PATTERN DEVIATION PLOT

• Numerical - calculated by adjustment for generalized depression or elevation of visual field

• Thus brings out pattern• Probability plot • Significance - ANDERSON’S CRITERIA

ZONE 6 : GLOBAL INDICESsingle numbers to denote whole field

• MEAN DEVIATION : average loss of sensitivity from normal age matched population along with probability

calculated from total deviation plot

• PATTERN STANDARD DEVIATION : range over which change of sensitivity at all the points has occurred, along with probability

compensates for effect of generalized depression or elevation of field on mean deviation value

local defects affect PSD > MD

• SHORT TERM FLUCTUATIONS• CORRECTED PATTERN STANDARD DEVIATION

ZONE 7 : GLAUCOMA HEMIFIELD TEST

• PLAIN ENGLISH LANGUAGE MESSAGE

• Comparison of 5 clusters of points in superior hemifield with mirror images in inferior hemifield

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

ANDERSON and PATELLA CRITERIA

• 3 or more congrous ‘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

Must be demonstrated on 2 field tests

CLINICAL CORRELATION : MUST

DISC and NERVE FIBRE LAYER

OVERVIEW

CHANGE ANALYSIS

GLAUCOMA PROGRESSION ANALYSIS

ARTEFACTS• OBSTRUCTION

RIM ARTEFACTS

PTOSIS

MEDIA OPACITIES

ANGIOSCOTOMA

• MIOSIS

• REFRACTION ARTEFACTS• High power plus and minus lenses

NEWER METHODS

SHORT WAVELENGTH AUTOMATED PERIMETERY

“BLUE ON YELLOW”

detects glaucomatous defects 3-5 years earlier than SAP

high fluctuation rates

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 frequncy)

Detects damage to Magnocellular Ganglion cells

C – 20 17 points – screening

N – 30 19 points – diagnosis n management

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

THANK YOU