Visual Field Testing in Glaucoma & Maculopathies

• Visual fields are useful for diagnosing multiple conditions and monitoring their progression.

Examples of Visual Field Use

• Glaucoma management requires OCT and VF correlation for diagnosis.

• Diagnosis and management of neurological diseases is another example.

• Diagnosis and management of retinal diseases, such as ARMD, where patients may use an Amsler grid at home

• Certification of visual function for patients with visual disabilities like low vision or RP

• Screening visual fields can reveal defects, but threshold field tests are more diagnostically capable.

• Automated visual fields aren't suitable for every patient.

Depression

• Defined as areas of reduced sensitivity without surrounding normal sensitivity.
• Cataracts and uncorrected refractive errors can cause this.
• It means that the eye can see something, but less than it should
• VF general depression is most common in cataracts.
• Can also result from uncorrected refractive error or miosis.

Scotoma

• This is a visual field defect surrounded by normal vision
• Localized defects are described by size, depth, and location for diagnostic purposes.
• Absolute scotomas are areas where nothing is seen (black).
• Relative scotomas are areas where vision is dimmer.

VF Defects

• Absolute scotomas: Stimuli at maximum brightness aren't visible.
• Relative scotomas: Low luminance stimuli can't be seen, but larger or brighter stimuli can be seen.

Types of VF Defects

• Glaucomatous VF loss follows a specific pattern.
• Neurological VF loss
• Retinal VF loss

Neurological VFD

• Respects the vertical meridian, stopping abruptly at the midline.
• Most commonly hemianopic
• Majority present in the central 30° of the visual field
• May not be completely noticeable initially

Retinal Visual Field Loss

• Defects are often deep with steep borders and highly reproducible, similar to "similar & DNI"
• The affected area of the retina is opposite the VF defect.
• Example: superior temporal RD results in an inferior nasal VFD.

Glaucomatous VFD

• Defects first occur in the nasal or arcuate region (Bjerrum area).
• May extend from the blind spot to the macular region, ending abruptly at the horizontal meridian nasally.
• Typically occurs first in the Bjerrum areas of the upper and lower hemifields.
• Early glaucomatous defects present as relative scotomas or small regions of decreased sensitivity.
• Tends to respect the horizontal meridian, showing nasal steps.
• Significant horizontal meridian sensitivity differences can be an indicator
• Visual fields are commonly performed to evaluate the central 24° or 30°.
• A homogenous reduction of sensitivity alone is almost never from glaucoma.
• Media opacity like cataracts or miosis can cause this

Types of Perimeters

• 30-2 Pattern: Tests 76 points in the central 30° field with a symmetrical 6° grid pattern
• 24-2 Pattern: Tests 54 points in the central 24° field, extends nasally to 30°, with more testing points nasally
• 10-2 Pattern: Tests the central 10° with 2° spaced test points; standard for end-stage glaucoma & maculopathies

Full Threshold Strategy (FT)

• A suprathreshold stimulus is presented based on previous threshold values.
• Intensity decreases until the stimulus disappears, then increases until it's seen again.
• 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); takes 7-11 minutes per eye.
• Very small differences are acceptable; re-measurement may occur, lengthening the test.
• SITA Fast (SF): Is a fast threshold test with similar sensitivity to FT
• Allows for more variability between repeated measurements for faster testing.
• Reduces threshold test time to 3-5 minutes without sacrificing accuracy (70% less time).
• SITA Faster: Takes about 2 minutes per eye; increases patient reliability by not using false negatives.

Esterman Binocular Field

• Assesses the full VF view, not monocular vision.
• Relevant for patients who have had a stroke, etc.
• Determines if sufficient VF to drive and obtain a license.
• Horizontal range: +/- 75 degrees.
• Superior range: 35 degrees.
• Inferior range: 55 degrees.

Stimulus

• Standard automated perimetry uses a white stimulus on a white background for detecting VFD, when about 40% of the RGC have been lost
• Short-wavelength automated perimetry (SWAP) measures blue wavelength with a blue stimulus on a yellow background.
• SWAP is more effective at detecting early glaucoma damage, up to 5 years earlier.
• Intensity in a Humphrey Field Analyzer (HFA) ranges from 10,000 to 0.1 apostilbs (abs).
• Apostilbs relate to a test target's luminance projected onto the white bowl's interior.
• Apostilb values are converted to logarithms, then decibels, for easier use with smaller numbers.
• 10,000 apostilbs is given a value of (0), indicating zero retinal sensitivity.
• This target has the highest intensity and if it cannot be seen, it is considered an absolute scotoma (blind).

Target Size

• Target size is identified using roman numerals.
• HFA typically uses Goldmann III (4 mm²) but varies the target brightness.
• The stimulus size can be changed to be larger or smaller as needed
• Goldmann V is used for severely disturbed fields such as RP
• Goldmann o used for clinical research, not clinical practice

Interpretation: Fixation Losses (FL)

• Occur when a patient reports seeing a stimulus in the physiological blind spot area.
• Calculated as the number of times stimulus reported in the blind spot divided by total presentations.
• If the patient responds, it's assumed they lost fixation and/or the blind spot isn't in the original location.
• Could also be examiner error: not patching the contralateral eye or placing the patch incorrectly.
• Fixation losses over 20% indicate poor patient reliability.
• Verify if FL are happening:
  • 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 incorrectly, 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)

• Results when a stimulus is presented at a point that's already been seen, yet the patient doesn't report it.

  • May indicate patient fatigue, sleepiness, changed response criteria, or 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) to help determine the instance a patient closes their eyelids and makes deviation

• Deviation upward indicates 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 dubious fixation reliability

• Short-term fluctuations tell us if the patient is consistent.

  • A point is tested twice during a test period
  • If abnormal (greater than 3dB): Inattentive patient or Patient with a disease visual system

• Low Fluctuation: <1.5dB

• Normal Fluctuation: 1.5-2dB

• Medium Fluctuation: more than 2 but less than 3dB

• High Fluctuation: over 3dB

• Raw data is threshold sensitivity values in decibels

• Grayscale displays interpolated raw dataIs a direct representation of the absolute threshold levels in raw data field

• The darker the zone, the less sensitive the area

• This doesn't provide information about the depth of the scotoma.

• Total deviation (TD) represents the difference in dB between the patient results and age-corrected normal values.

• Pattern Deviation (PD) corrects for overall sensitivity of the field by removing generalized depressions to identify localized abnormalities.

• Pattern deviation flags areas that deviate significantly from normal, correcting first for any overall change in the height of the hill of vision.

• The instrument assumes than an overall depression in the hill of vision is secondary to opacities in the media or miosis.

• Pattern Deviation allows to follow over the years after media opacities develop. It will factor out the depression caused by a cataract

• Is an excellent determinant of the depth of the scotoma

• Island of Vision

• Looks at pattern deviation taking away generalized loss

• Probability (p) values indicate the frequency of the tested value occurring in a normal age-matched population.

• Deviations are shown if the threshold is worse than the bottom 5% of normal for that age

• Interpretation of the data leads to next bullet point

More Interpretation

• The finding of an abnormal point is not sufficient to conclude that a field is abnormal
• Abnormality of a field as a whole must be judged on the basis of finding sufficient abnormality in a cluster of points in a pattern that is typical of the associated clinical findings
• A single statistically significant point may not be clinically significant, but a group of connected points that all reach statistical significance is unlikely to be normal
• A cluster of three or more connected points on the same side of the horizontal meridian that all reach statistical significance, with at least one of the points reaching the p<1% significance level, is diagnostic of glaucomatous visual field if the defect is repeatable

Global Indices

• Mean Deviation (MD): Represents the overall depression (-) or elevation (+) of the VF with scotomas or depression compared to an age-matched normal.
  • A positive (+) number indicates that the average sensitivity is above the normal for age
  • A negative (-) number indicates that the average sensitivity is below the average age-matched normal
  • Signifies the overall severity of the field loss, interpreting the severity of the field loss at individual locations and the area of the field involved

Pattern Standard Deviation (PSD)

• Expressed in dB, PSD indicates the smoothness of the hill of vision.

  • If there is VF loss, it determines how evenly the visual loss is spread across the field

• This is a weighted average of the pattern deviation

  • If the averaged amount that each point in the field deviates from the expected value after it has been adjusted for a general depression or suprasensitivity

• This is a measure of how different points are from one another within the field

• A high PSD indicates isolated depression in the normal hill of vision or variability in the patients' responses

• Any value of 2dB or greater will have a (P) indicating the significance of the deviation.

• Minimally influenced by cataracts

• If PSD is outside the normal range, the probability that such a value could exist in a normal population is given.

• Corrected Pattern Standard Deviation (CPSD): This is a calculated measure in dB of how much the total shape of the patient's hill of vision deviates from the shape of the normal hill of vision after adjustment.

• Glaucoma Hemifield Test (GHT): In glaucoma, the upper and lower hemispheres of the field are significantly different

• For GHT, points in the five smaller zones get grouped together (above and below the horizontal meridian) for testing

• Used probability values are used instead of threshold values

• The mirror images are compared to one another

GHT Interpretations

• 1. GHT outside normal limits (ONL): A score assigned to each member of mirror image zones based on percentile deviation from normal. A message will appear if:
  • The difference between the mirror image zones can be seen in

Explore visual field testing techniques. Understand patterns for assessing glaucoma and maculopathies like those from hydroxychloroquine. Learn about common defects, areas evaluated, and test parameters.