John M. Wild

Serial examination of the normal visual field using Octopus automated projection perimetry Evidence for a learning effect

Abstract. The influence of prior perimetric experience on the magnitude of both differential sensitivity and the short and long term fluctuations remains unclear, and confounds accurate interpretation of visual field data obtained by computer‐assisted perimetry. The purpose of the experiment was to identify and quantify any influence of training on the automated perimetric response. The full field of the right eye of 10 clinically normal, naive subjects was examined on 8 occasions with Octopus Program 21 (target size 3) on days 1–5 inclusive, 15, 16 and 44. Sensitivity increased with serial examination in 8 subjects. By dividing the field into zones, it was demonstrated that the learning effect was greatest in the superior field and for eccentricities beyond 30°.

Long-term follow-up of baseline learning and fatigue effects in the automated perimetry of glaucoma and ocular hypertensive patients

Abstract. The detection of change in the visual field is confounded by factors associated with the patient response. Sixteen patients who had previously undergone a training regime in automated perimetry over a short time period were followed up to evaluate the longer term learning and fatigue effects. The patients, all attending a glaucoma clinic, were originally naive to automated perimetry. The training period had comprised examination of the right followed by that of the left eye with the Humphrey Field Analyser 630 on each of 3 successive days and again after an interval of 12 days. The follow‐up study comprised two examinations on 2 successive days after a follow‐up period of between 5 and 15 months (mean 8.7 months). The learning effects present over the initial training period were not observed at the follow‐up whilst the fatigue effects in the fellow eye were still apparent.

Pointwise Univariate Linear Regression of Perimetric Sensitivity Against Follow-up Time in Glaucoma

PURPOSE The authors compared pointwise univariate linear regression (ULR) of sensitivity against follow-up as an indicator of visual field progression with that of the corresponding ULR of mean deviation (MD) and with the Glaucoma Change Probability (GCP) analysis. The authors determined the influence of the number and sequence of prior examinations on the slope of the pointwise function. METHODS Univariate linear regression was undertaken at each stimulus location on the arbitrarily assigned left eyes of 38 patients with glaucoma examined with the Humphrey Field Analyzer Programs 30-2 or 24-2 (stimulus size III, Humphrey Instruments Inc, San Leandro, CA). The mean age was 59.0 years (standard deviation [SD] = 12.9), the mean number of fields per patients was 12.0 (SD = 2.8), and the mean duration of follow-up was 6.0 years (SD = 1.6). RESULTS Four patients showed statistically significant MD slopes. Of the 34 patients exhibiting a nonsignificant MD slope, 15 exhibited clusters of at least two contiguous progressing locations. Less than half of these locations were designated as progressing by GCP. The GCP detected less than one third of the locations considered progressing by ULR for the last six fields in the series: this was attributed to the nonlinear nature of the decline in sensitivity. CONCLUSIONS The degree of agreement between the outcomes of ULR and GCP was dependent on the quality of the collected data, the magnitude of the baseline sensitivity, the extent and type of the subsequent visual field progression, and the position of the fields within the examination series. Good agreement was illustrated at those locations where the deterioration fell outside the limits of expected variability in stable glaucoma.

Evaluation of FASTPAC, a New Strategy for Threshold Estimation with the Humphrey Field Analyzer, in a Glaucomatous Population

PURPOSE A new fast strategy for the estimation of threshold, FASTPAC, has been introduced for the Humphrey Field Analyzer. The aim of this study is to evaluate the performance, in a glaucomatous population, of FASTPAC compared with the standard full-threshold 4-2-decibel (dB) double-staircase strategy. METHODS The sample consisted of 30 glaucoma patients experienced in automated perimetry, ranging in age from 26 to 84 years. One eye of each patient was examined with both strategies using program 24-2, target size III. The order of strategy was randomized for each patient. The results were analyzed using analysis of covariance for a two-period crossover trial. Mean deviation, pattern standard deviation, short-term fluctuation, corrected pattern standard deviation, number of stimulus presentations, and examination time were analyzed separately; test sequence and severity of field loss were considered as between subject factors and age as a covariate. RESULTS The FASTPAC algorithm demonstrated a 36% saving in examination time (P < 0.001), a lower mean deviation (0.91 dB) (P < 0.001), and a greater short-term fluctuation (0.64 dB) (P = 0.008). The differences in mean deviation (P = 0.015) and short-term fluctuation (P = 0.033) became greater with an increase in age. As the severity of the field loss increased, the short-term fluctuation increased (P = 0.043), and examination time was increased for the FASTPAC strategy, while it became shorter for the standard full-threshold strategy (P = 0.033). CONCLUSIONS The FASTPAC strategy reduced the examination time but exhibited a decreased estimate of field severity and a greater intra-test variance.

Time-related Variation in Normal Automated Static Perimetry

The effects of phase of eye test and order of eye examined were investigated in 38 normal subjects using a customized 30-point central threshold program of the Humphrey Field Analyzer 640. This program, designed to be completed within 5 minutes, was successively repeated three times for each eye (i.e., three phases for each eye) at two visits separated by an interval of approximately 2 weeks. Both global and pointwise group mean sensitivity decreased in a time-related manner, deterioration being greater for the second eye at each visit, for both 200 ms and 100 ms stimulus durations.

Alterations in the shape of the automated perimetric profile arising from cataract

The attenuation of the perimetric response arising from cataract was investigated and related to the degree of cataract quantified by glare sensitivity. Visual fields were measured with the Octopus and Dicon automated perimeters out to an eccentricity of 30°. Nuclear and non-nuclear cataracts differed in their effect on the perimetric profile. Non-nuclear cataracts exhibited the same qualitative characteristics as a model developed in previous studies, whereby the overall pattern of perimetric attenuation was dependent upon target configuration. For these subjects, perimetric sensitivity was depressed to a greater extent at an eccentricity of 30° compared with fixation when measured with the large projected stimuli, whereas the reverse was true when sensitivity was measured with the small LED stimuli. Conversely, nuclear cataracts depressed perimetric sensitivity to a greater extent at the fovea compared with more peripheral regions for both the large projected and small LED stimuli.

SOME STATISTICAL CONCEPTS IN THE ANALYSIS OF VISION AND VISUAL ACUITY

Abstract— As conventionally recorded, visual acuity data constitute an ordinal scale of measurement. An investigation of four different clinical samples shows that visual acuity is not normally distributed amongst these populations. Furthermore, acuity is often measured on charts which, by the inherent restriction of the stimulus size, have the effect of truncating the upper limit of the scale producing, in statistical terms, an incomplete distribution. The distribution of acuity for each sample is found to be adequately described in terms of the equation: F(x) =Axα(T‐x)β, where F(x) is the cumulative distribution of the statistical population, T is the truncation level (known), x is the Snellen decimal acuity (known) and A, α and β are parameters. Alternative analytical procedures based upon this model, which overcome these limitations, are discussed.

Evaluation of FASTPAC: a new strategy for threshold estimation with the Humphrey field analyser

A new strategy for threshold estimation, FASTPAC, has been introduced for the Humphrey Field Analyser with the aim of improving the efficiency of visual field examination without loss of accuracy. FASTPAC was compared to the standard 4-2 double staircase strategy in 98 normal volunteers (age 23-83 years). One eye of each subject was examined with both strategies on two visits using Program 30-2. The order of strategy was randomised. FASTPAC examination time was 43% faster than the standard algorithm, but the mean sensitivities were similar. Short-term fluctuation was 24% higher with FASTPAC (P<0.001). Most parameters were adversely affected by increasing age. FASTPAC offers a valid alternative to the standard strategy in the examination of suspected normal fields and should always be considered as an alternative to the threshold-related screening strategies. The performance of the algorithm in the identification of field loss and in areas of reduced sensitivity awaits further study.

Induced intraocular light scatter and the sensitivity gradient of the normal visual field

The influence of intraocular light scatter on the perimetric sensitivity profile of the normal eye was investigated using a series of light-scattering cells containing 0.01%, 0.02% and 0.025% concentrations of 500 nm diameter latex beads. The degree of induced intraocular light scatter was quantified by measuring contrast sensitivity using the Nicolet CS2000 system in the presence and absence of both wide- and narrow-angle glare light. Perimetric sensitivity out to an eccentricity of 30° was assessed, using the Octopus 201 and the Dicon AP3000 automated perimeters, with the three light-scatter cells and in the cell-free control condition. The results for both functions were expressed as the difference between the control response and that recorded under the particular experimental condition. Perimetric attenuation increased with increase in intraocular light scatter; the extent of the attenuation varied with stimulus type, bowl luminance and eccentricity

Baseline alterations in blue-on-yellow normal perimetric sensitivity

Abstract• BackgroundThe extent of any learning and fatigue effects in blue-on-yellow (B-Y) perimetry is unknown. The within- and between-eye changes in B-Y normal sensitivity at a single visit and between visits was investigated as a function of previous experience in white-on-white (W-W) perimetry and of subject age.• MethodsSixty-one normal subjects — 22 young (range 20–34 years) and 39 elderly (range 51–80 years) — assigned to one of four groups based upon perimetric experience and age underwent B-Y perimetry on four separate occasions using Program 30-2 of a modified Humphrey Field Analyser 640. Perimetry was performed for both eyes on three consecutive days and again one week later. Global, hemifield and annular mean sensitivities and global short-term fluctuation were calculated for each eye at each visit.• ResultsMean sensitivity was higher in the first eye examined and increased over the 3 days. The increase in mean sensitivity was similar for each eye and was independent of perimetric experience and age. Short-term fluctuation decreased over the 3 days, regardless of eye and experience, but was more pronounced for the younger age group. The extent of all improvements varied considerably between subjects.• ConclusionsImprovements in B-Y perimetric performance occured as the familiarity with the test increased, regardless of previous W-W experience. Failure to account for such improvement could reduce the efficiency of B-Y perimentry.