the visual field for technicians
DESCRIPTION
Visual Field for Technicians.TRANSCRIPT
Dwight Thibodeaux, OD
THE VISUAL FIELD
VISUAL FIELDS
Localized measurement of visual perception using manual or automated methods to determine normal status or to evaluate and track an ocular or neurological disease state.
NORMAL FIELDS
• Visual Field - Roughly 140 degrees monocularly and just over 180 degrees binocularly
• Field of Gaze – Over 200 deg
• Field of View – Over 300 deg
COMMON METHODS OF FIELDS TESTING
• Confrontation –gross target movement - in from periphery
• Manual kinetic central fields – Tangent screen, Autoplot
• Microperimetry – Amsler Grid, automated units
• Manual kinetic widefield perimetry – Goldmann
• Automated static perimetry – Computer algorithm, tester independent
Humphries HFA and FDT/Matrix
Haag-Streit Octopus
Oculus and others
HISTORICAL FIELD TESTS
CONFRONTATION FIELD TESTING
Technique
Targets
GOLDMANN KINETIC FIELD TESTER
GOLDMANN KINETIC PERIMETRY
OCTOPUS AND OCULUS
ZEISS/HUMPHRIES
HUMPHRIES
FIELD ANALYZER (HFA)
FDT and MATRIX
TEST STRATEGIES
• Suprathreshold – usually full field - 60 degrees
• 24 degree central field 24-2
• 30 degree central 30-2
• 10 degree 10-2
SUPRATHRESHOLD
• Targets set at moderate brightness
(above threshold) with wide field • Either seen or not seen• Useful for lid/ptosis evaluation• Two field tests, taped and untaped
THRESHOLDING
• First stimuli presented in each of the 4 quadrants
• Lowered by 3-4 Db until not seen and vise versa
• Moves to different area and repeats process
• Cloverleaf pattern in poor pt.
management and cooperation
SITA / SITA FAST (HFA)
Swedish Interactive Thresholding Algorithm
SITA 50% faster than standard, but 90% accuracy
SITA FAST 70% faster, 80% as accurate
FDT/FDP
• Frequency Doubling Technology (Perimetry)
• For early detection of glaucoma
• Resistant to blur (Rx) and pupil size effects
MATRIX FDT
• Hybrid of FDT and SAP
• Even more sensitive to early glaucoma defects
• Too hypersensitive for neuro field testing and poor for
tracking glaucoma progression
• Best for glaucoma suspects / pre-perimetric glaucoma
SWAP – SHORT WAVELENGTH AUTO PERIMETRY
• Yellow background and large blue stimulus on HFA
• Catches early defects in pre-perimetric glaucoma
• Very time consuming and sensitive to media opacities
• Matrix now more commonly used
30-2 VS 24-2
• 30-2 = 76 test locations
Most accurate, 0.2 sec.
stimulus vs. 0.25 sec
latency for eye movements
• 24-2 = 54 test locations
Used for the difficult patient
HFA 10-2
• 10 deg. central field for macular toxicity and end stage glaucoma or RP
• Plaquenil – hydroxychloroquine
• OCT of macula also part of new protocol
MICROPERIMETRY
• Amsler Grid
• Automated
WHAT FIELD IS INDICATED?
• Glaucoma suspect or pre-perimetric pt.• Established glaucoma patient with field loss• Neuro patient• Ptosis patient• High risk meds patient
GLAUCOMA SUSPECT
• Minimal or no nerve head cupping – Matrix/FDT
• Obvious nerve damage – SITA Standard 30-2
• Difficult patient w/ damage– SITA Fast 24-2
ESTABLISHED GLAUCOMA
• SITA Standard 30-2
• Difficult / older patient
SITA Fast 24-2
NEURO FIELDS
• SITA Fast 30-2• Used for unexplained
vision loss or
neuro signs• Matrix oversensitive
PTOSIS OR BLEPHAROCHALASIS
• Suprathreshold automated or kinetic fields
• Wider field to catch more peripheral defects
HIGH RISK MEDSSITA 10-2
• For subtle central defects from retinal toxicity
INTERPRETATION
• Quality measures and errors
• Plots
• Glaucoma Hemifield Test
• Global indices
QUALITY MEASURES
• Fixation losses – targets blind spot, need <15%, ? misaligned
• False positives – positive response when no target is shown, need < 20%
• False negatives – <33%
• Gaze tracker - camera notes eye movement
COMMON ARTIFACTS AND ERRORS
• Ptosis
• Prominent brows
• Lens holder positioning—ring scotoma
• Patient positioning—high FL, ring scotoma
• False positives based on patient expectations of stimulus timing
GREY SCALE PLOT
• Quickly identifies overall depressions
• Good for patient education
• No comparison for age related normals
• No adjustment for media opacities
• Under represents shallow gen. depression and overemphasizes midperipheral non-significant defects
TOTAL DEVIATION PLOT
• Graph and numeric representation
• Compared to age-matched normals
PATTERN DEVIATION PLOT
• Probably the most important data
• Takes total deviation and filters out overall depression (cataracts)
• Looks for focal damaged areas pertinent to glaucoma
GLOBAL INDICES
• Mean Deviation (MD)
• Positive Standard Deviation (PSD)
• Glaucoma Hemifield Test (GHT)
GLOBAL INDICES
• Single number representations of the visual field
• Overall guidelines to help assess the field
• Probability values when numbers reach significant levels
MEAN DEVIATION (MD)
• Overall level of sensitivity compared to age-matched normals
• Not corrected for generalized depression from media opacities
• Important for following diffuse loss in glaucoma
• MD of -2.00 or worse is suspicious
• Mild damage at <-6
• Moderate at -6 to-12 severe >-12
PATTERN STANDARD DEVIATION (PSD)
• Sensitive measurement of localized loss
• Especially useful in glaucoma evaluation/progression
• The higher the number, the greater the loss
GLAUCOMA HEMIFIELD TESTGHT
• Compares top and bottom half of field
• General reduction in sensitivity
• Abnormally high sensitivity
• ONL – difference not found in 99% of patients without glaucoma
• Borderline – difference not found in 97% of normals
VISUAL FUNCTION INDEX (VFI) AND PROGRESSION ANALYSIS
Seen in newer units
VFI similar in meaning to MD but easier to conceptualize--100% is normal
75-80% is approaching significant loss = -6 or worse on MD
COMMON GLAUCOMA SCOTOMAS
• Arcuate
• Nasal step
• Temporal wedge
• Localized paracentral
• Generalized depression
ARCUATE OR NERVE FIBER BUNDLE DEFECT
NASAL STEP
LOCALIZED PARACENTRAL SCOTOMAS
SECTOR OR WEDGE DEFECTS
GENERALIZED DEPRESSION
FUNCTIONAL VISION LOSS
• Most common in young girls
• Emotional trauma
• Also called hysterical fields
• Spiral and variable in nature
• Treat with education of parents and counseling
NEURO FIELDS
Unilateral – usually involves the retina or optic nerve
Bilateral – involves both nerves or the optic chiasm/tract/brain
Homonymous – alike, same side on both eyes
Heteronomous – different, opposite sides
Congruous – symmetric in both eyes
Hemianopia – defect respects vertical midline
MRI CHIASM
HOMONYMOUS
• Hemianopsia – homonymous, congruous, points to cerebral cortex lesion such as stroke
• Quadranopsia or sectoranopsia– cerebral cortex (congruous) or lateral geniculate nucleus
HETERONOMOUS
Hemianopsia- bitemporal, congruous- points to chiasmal lesion such as a pituitary tumor
Quadranopsia- very rare, points to different area of chiasm
BINOCULAR FIELDS
ALTITUDINAL
• Almost always unilateral
• Associated with AION – stroke at the optic disc
CENTRAL SCOTOMA
• More commonly unilateral
as in:
optic neuritis
macular degeneration
early AION, cerebro-vascular
blood loss
retinal dystrophy
Bilateral – toxic, nutritional, heriditary optic neuropathy and
maculopathy
QUESTIONS? [email protected]