Visual Field Defects (VFD) - Diagnosis & Interpretation - PDF

Visual fields are a useful tool in diagnosing multiple conditions & in monitoring progression. Examples: ​ Glaucoma management (OCTs, VF must correlate to make glaucoma diagnosis) ​ Diagnosis & management of neurological disease (common CC: HAs) ​ Diagnosis & management of retinal disease...

Visual fields are a useful tool in diagnosing multiple conditions & in monitoring progression. Examples: ​ Glaucoma management (OCTs, VF must correlate to make glaucoma diagnosis) ​ Diagnosis & management of neurological disease (common CC: HAs) ​ Diagnosis & management of retinal disease (ex: ARMD -> take home Amsler Grid) ​ Certification of visual function in patients w/ visual disabilities (low vision such as RP) Screening visual fields (i.e. CVF) can uncover several visual field defects, but the diagnostic capacity is far superior with threshold field test ​ Keep in mind that some patients are not ideal for automated visual fields Depression: areas of reduced sensitivity without a surrounding area of normal sensitivity (cataracts, uncorrected RE), can be something but less of what they should ​ VF general depression is most commonly seen w/ cataracts but can also arise from uncorrected refractive error or miosis Scotoma: visual field defect (VFD) surrounded by normal visual field ​ Localized defects can be further described by size, depth, and location to help w/ the diagnosis ​ Absolute (sees nothing/black) vs Relative (somewhat dimmer) VF defects ​ Absolute scotomas are when a stimulus is presented at maximum brightness and is not seen ​ Relative scotomas is an area where a stimulus with low luminance cannot be seen, but larger or brighter stimulus can be seen ​ Types of VF Defects 1.​ Glaucomatous visual field loss -> follow specific pattern 2.​ Neurological visual field loss 3.​ Retinal visual field loss Neurological VFD ​ Respect the vertical meridian (abrupt stop @ vertical midline) ​ Most commonly hemianopic ​ Majority present in the central 30° of the visual field ○​ May initially not notice completely Retinal Visual Field Loss ​ Defects are often deep, w/ steep borders & highly reproducible -> similar & DNI ​ Affected area of retina is opposite to the visual field defect ○​ Ex: superior temporal RD = inferior nasal VFD Glaucomatous VFD ​ Glaucomatous visual field defects first occur in the nasal or in the arcuate region (Bjerrum area) ○​ These may extend from the blind spot, around the macular region, ending abruptly at the horizontal meridian nasally ○​ Usually occurs first in the Bjerrum areas of the upper and lower hemifields ○​ Early glaucomatous defects take the form of relative scotomas or small regions of decreased sensitivity. ​ Tend to respect the horizontal meridian ○​ Nasal steps ○​ Significant horizontal meridian sensitivity differences ​ Visual fields most commonly performed are to evaluate de central 24° or 30° ​ A homogenous reduction of sensitivity alone is almost never from glaucoma ○​ Media opacity such as cataracts or miosis ​ Types of Perimeters ​ 30-2 pattern: tests 76 points on the central 30° field w/ a grid pattern 6° degrees apart -> symmetrical ​ 24-2 pattern: tests 54 points on the central 24° field, except nasally where it extends to 30° ○​ More testing points nasally ○​ Fav* ​ 10-2 pattern: test the central 10° using a grid of test points spaced every 2° ○​ End-stage glaucoma & maculopathies (hydroxychloroquine standard) Full Threshold Strategy (FT) ​ A suprathreshold stimulus is presented at each location based on the threshold values from prior points ​ The intensity is then decreased until the stimulus can no longer be identified, then it is increased again until it can first be seen ○​ The threshold value is the last stimulus seen ​ Longer test time Swedish Interactive Threshold Algorithm (SITA) ​ SITA Standard: offers high accuracy and short test time (50% less than standard HVF test)- pt takes 7-11 min. per eye ○​ In SITA standard (SS), only small differences are acceptable, it is going to continue to measure those points again, which may take longer ​ SITA Fast (SF): a very fast threshold test w/ sensitivity similar to Full Threshold Tests ○​ More variability is allowed between repeated measurements, which allows for a faster test ○​ Reduces the threshold test time to 3-5 min. w/o sacrificing accuracy (70% less test time) ​ SITA Faster: ~2 min. per eye, does not use false negatives which gives us the reliability of pt; done “to get out of the way” Esterman Binocular Field ​ We care about their full VF view, not monocular ​ Patient’s who gone through stroke, etc. ​ Enough VF to drive and get their license back ​ Horizontally +/- 75 degrees ​ Superior 35 degrees ​ Inferior 55 degrees Stimulus ​ Standard automated perimetry: uses white stimulus on white background and will detect a VFD when about 40% of the RGC have been lost ​ Short-wavelength automated perimetry (SWAP): selectively measures the short blue wavelength by projecting a blue stimulus on a yellow background ○​ SWAP has been found to be more effective at early glaucoma damage, up to 5 years earlier ​ The intensity in a Humphrey Field Analyzer (HFA) ranges from 10,000 to 0.1 apostilbs (abs) ​ Apostilbs relates to luminance of a given test target being projected onto the interior of the white bowl ○​ These values in apostilbs are converted to logarithms and then to decibels, because these numerical values are smaller, easier to work with and give the same results ​ 10,000 apostilbs is given a value of (0) zero, meaning zero retinal sensitivity ○​ This target has the highest intensity if unable to see this it is considered an absolute scotoma (blind). Target Size ​ Target size is identified in roman numerals ​ HFA typically uses a target size Goldmann III (4 mm^2) and varies the target brightness ○​ The stimulus size can be changed to be larger or smaller ​ Goldmann V used for severely disturbed fields such as RP ​ Goldmann 0 used for clinical research- no use in clinical practice ​ Interpretation ​ Fixation Losses (FL): they occur when the patient reports seeing a stimulus in the area marked as the physiological blind spot ○​ Calculated: # of times the patient reported seeing stimulus in the BS / total # of presentations in the BS ○​ If the patient responds, it is assumed that the patient lost fixation and/or the blind spot is no longer in the original location ​ Could also be examiner error: not patching the contralateral eye or placing the patch in the wrong eye ○​ Fixation losses >20% indicates poor patient reliability ○​ If FL are happening, verify: ​ Patient’s gaze: drifted from fixation, so stimulus falls on a seeing part of the retina ​ Location of the blind spot: if it is mapped out incorrect ​ Patient readjusted head position after the BS had been plotted ​ False Positive Rate (False POS errors): ○​ “Trigger Happy” patient ○​ A high (>15-20%) false positive rate indicates an unreliable field ​ High FP rate is the MOST devastating when it comes to interpretation ○​ High FP rates will be accompanied by: ​ Suprathreshold levels ​ Mean deviation (MD) with a high (+) value ​ High fixation losses ​ Patchy loss on the grayscale ​ White scotoma: white areas in the grayscale indicating impossibly high threshold levels ​ Pattern deviation is worse than the total deviation ​ False Negatives (False Neg Error): ○​ When a stimulus is presented on a point that already has been seen and the patient does not report seeing it ​ This may indicate the patient is fatigued or falling asleep, has changed personal criteria for response or may be a true indicator of actual field loss where sensitivities are variable ○​ Greater than 15-20% means poor patient reliability ○​ In a normal field, a high FN rate results from patient inconsistency in responses ○​ In an abnormal field, a high FN rate occurs because there is highly variable visibility during the test in abnormal regions. ​ Tracking System (Gaze Monitor)  ○​ Helps determine the exact instance when a patient closes their eyelids (excluding blinks) or makes a saccadic deviation from fixation ○​ Deviation upward: gaze was not on the fixation target ​ The magnitude of the deflection indicates the extent of the errant fixation ○​ Large deviation downwards indicates a blink (longer than expected) ​ Small downward deviations indicate that the computer cannot tell the direction of the patient’s gaze ○​ A pattern which resembles a “city skyline” indicates a dubious fixation reliability ○​ ​ Interpretation ○​ Short-term fluctuations: ​ Tell us if the patient is consistent ​ A point is tested twice during a given test period; the difference should be less than 3dB ​ If abnormal (greater than 3dB): ​ Inattentive patient or ​ Patient with a disease visual system ​ Low Fluctuation: