Assessment of the Reliability of Standard Automated Perimetry in Regions of Glaucomatous Damage

Abstract

Purpose Visual field testing uses high contrast stimuli in areas of severe visual field loss. However, retinal ganglion cells saturate with high contrast stimuli, suggesting that the probability of detecting perimetric stimuli may not increase indefinitely as contrast increases. Driven by this concept, this study examines the lower limit of perimetric sensitivity for reliable testing by standard automated perimetry. Design Evaluation of diagnostic test. Participants 34 participants with moderate to severe glaucoma (Mean Deviation (MD) on their last clinic visit averaged −10.90dB, range −20.94dB to −3.38dB). 75 of the 136 locations tested had perimetric sensitivity ≤19dB. Methods Frequency of seeing curves were constructed at four non-adjacent visual field locations by the method of constant stimuli (MOCS), using 35 stimulus presentations at each of 7 contrasts. Locations were chosen a priori, and included at least two with glaucomatous damage but sensitivity ≥6dB. Cumulative Gaussian curves were fit to the data, first assuming a 5% false negative rate, and subsequently allowing the asymptotic maximum response probability to be a free parameter. Main Outcome Measures The strength of the relation (R2) between perimetric sensitivity (mean of last two clinic visits) and MOCS sensitivity (from the experiment), for all locations with perimetric sensitivity within ±4dB of each selected value, at 0.5dB intervals. Results Bins centered at sensitivities ≥19dB always had R2>0.1. All bins centered at sensitivities ≤15dB had R2<0.1, an indication that sensitivities are unreliable. No consistent conclusions could be drawn between 15–19dB. At 57 of the 81 locations with perimetric sensitivity <19dB, including 49 of the 63 locations ≤15dB, the fitted asymptotic maximum response probability was <80%, consistent with the hypothesis of response saturation. At 29 of these locations the asymptotic maximum was below 50%, and so contrast sensitivity (50% response rate) is undefined. Conclusions Clinical visual field testing may be unreliable when visual field locations have sensitivity below approximately 15–19dB, due to a reduction in the asymptotic maximum response probability. Researchers and clinicians may have difficulty detecting worsening sensitivity in these visual field locations and this difficulty may occur commonly in glaucoma patients with moderate to severe glaucomatous visual field loss.

The Effect of Stimulus Size on the Reliable Stimulus Range of Perimetry

“…12 Participants with moderate to severe primary open-angle glaucoma were recruited from a tertiary glaucoma clinic at Devers Eye Institute (Portland, OR). Inclusion criteria were a diagnosis of primary open-angle glaucoma as determined by each participant's clinician, and at least two nonadjacent visual field locations with sensitivities between 6 and 18 dB on both of their two most recent clinic visits (24-2 test pattern, size III stimulus, SITA Standard algorithm; Humphrey Field Analyzer [HFA]; Carl-Zeiss Meditec, Dublin, CA).…”

“…12 For example, the probability that participants responded to a 20,000% (2 dB) contrast in a deep visual field defect was typically only slightly higher than the probability that they would respond to a 2000% (12 dB) contrast at the same location (this small increase may reflect effects of light from the stimulus being scattered toward remaining areas of higher sensitivity). For locations with sensitivity worse than 15 to 19 dB (equivalent to contrasts of 1000%-400%), we found that the relation between sensitivity measures from FOS curves and those obtained from clinical perimetry had R 2 less than 0.1, indicating that the true sensitivity explained less than 10% of the observed variance.…”

“…In regions of severe glaucomatous damage, the observer's maximum response probability may be well below 100%, and even below 50%. 12 A testing algorithm would then be unable to quickly converge to the contrast to which the observer http://tvstjournal.org/doi/full/10.1167/tvst.4.2. 10 TVST j 2015 j Vol.…”

Combining optical coherence tomography with visual field data to rapidly detect disease progression in glaucoma: a diagnostic accuracy study

“…72 Many papers have described the large variability in VF measurements and the increasing variability as sensitivity declines. [7][8][9] Gardiner et al 73 found that sensitivity values below a cut-off value of between 15 and 19 dB are particularly unreliable and that values at these levels of sensitivity agree poorly with estimates obtained from 'frequency of seeing' curves. Gardiner et al 73 also discussed the concept that sensitivity values may not be truly defined at such low levels, as the retinal ganglion cells remaining cannot be stimulated sufficiently to produce a 50% response rate to stimuli, regardless of the intensity of the presentation.…”

“…[7][8][9] Gardiner et al 73 found that sensitivity values below a cut-off value of between 15 and 19 dB are particularly unreliable and that values at these levels of sensitivity agree poorly with estimates obtained from 'frequency of seeing' curves. Gardiner et al 73 also discussed the concept that sensitivity values may not be truly defined at such low levels, as the retinal ganglion cells remaining cannot be stimulated sufficiently to produce a 50% response rate to stimuli, regardless of the intensity of the presentation. Gardiner et al 74 found that the proportion of eyes identified as deteriorating was not decreased by truncating sensitivities at 10 dB (i.e.…”