Comparative quantification of focal and diffuse visual field loss by the SPARK Precision threshold algorithm and SITA.

PURPOSE: The aims of this paper were to examine focal and diffuse visual field loss in terms of threshold agreement between the widely used SITA Standard Humphrey Field Analyser (HFA) threshold algorithm with the SPARK Precision algorithm (Oculus Twinfield 2). METHODS: A total of 39 treated glaucoma patients (34 primary open angle and 5 primary angle closure glaucoma) and 31 cataract patients without glaucoma were tested in succession with the Oculus Twinfield 2 (Oculus Optikgeräte GmbH, Wetzlar, Germany) using the SPARK Precision algorithm and with the HFA 3 (Carl Zeiss Meditec, Dublin, CA) using the 30-2 SITA Standard algorithm. RESULTS: SPARK Precision required around half the testing time of SITA Standard. There was a good correlation between the MS of the two threshold algorithms but MD and PSD were significantly less severe with SPARK Precision in both glaucoma (focal field loss) and cataract (diffuse field loss) groups (p < 0.001). There was poor agreement for all global indices (MS, MD and PSD) between the two algorithms and there was a significant proportional bias of MD in the glaucoma group and PSD in both glaucoma and cataract groups. The pointwise sensitivity analysis yielded higher threshold estimates in SPARK Precision than in SITA Standard in the nasal field. Classification of glaucoma severity using AGIS was significantly lower with SPARK Precision compared to SITA Standard (p < 0.001). CONCLUSION: SITA renders deeper defects than SPARK. Compared to the SITA Standard threshold algorithm, SPARK Precision cannot quantify early glaucomatous field loss. This may be due to the mathematical linear interpolation of threshold sensitivity or deeper scotomas due to the plateau effect caused by the reduced dynamic range of the Twinfield 2 perimeter. Although not of clinical significance in early glaucoma, the plateau effect may hinder the long-term follow-up of patients during disease progression.

The influences of stimulus wavelength and eccentricity on short-wavelength pathway isolation in automated perimetry.

The aim of the study was to determine whether the suggested stimulus and background parameters employed in commercially available short-wavelength sensitive perimetry (SWAP) are clinically appropriate. Threshold versus intensity curves were measured using a modified Humphrey Field Analyser. The reduction in background luminance was achieved using aperture stops in order to avoid changes in the chromaticity of the background. Short-wavelength thresholds were determined for 440, 450 and 460 nm stimuli and were corrected for pre-receptoral absorption. Short-wavelength sensitive pathway isolation was approximately 1.5 log units and decreased with increases in eccentricity and in stimulus wavelength. It would seem that the use of a 450 nm narrowband stimulus filter would offer a compromise between both the physiological requirements and the physical properties of the stimulus. Such an approach would reduce some of the inherent between-subject normal variability associated with SWAP.

Statistical aspects of the normal visual field in short-wavelength automated perimetry.

PURPOSE: To determine the intraindividual and interindividual characteristics of normal sensitivity derived by short-wavelength automated perimetry (SWAP) as a function of threshold algorithm. To determine also the influence of ocular media absorption on the magnitude of the interindividual variation in normal sensitivity, and hence the confidence limits, derived by SWAP. METHODS: The sample comprised 51 normal subjects, stratified for age by decade (mean age, 55.5 years; range, 24-83 years) and experienced in white-on-white (W-W) perimetry and SWAP. One randomly assigned eye of each subject was examined on three occasions with Program 30-2 of the 640 Humphrey Field Analyzer using the Full Threshold and FASTPAC strategies for SWAP and W-W perimetries. Ocular media absorption (OMA) was assessed by the difference in scotopic sensitivity to stimuli of 410 and 560 nm. RESULTS: The group mean examination time (P < 0.001) was greater for SWAP than for W-W perimetry for both the Full Threshold (15.0% longer) and FASTPAC strategies (16.8% longer). The gradient of the age-decline in Mean Sensitivity for SWAP was approximately 25% less steep when corrected for OMA than when uncorrected. The interindividual normal variability, expressed as the coefficient of variation, for SWAP without correction for OMA was 2.7 times greater (range 2.0-3.9), and with correction 1.9 times greater (range 1.4-2.9), than that for W-W perimetry. CONCLUSIONS: The increased interindividual normal variability of SWAP, exacerbated by the lack of correction for OMA, currently limits the utility of SWAP in that the reduction in sensitivity required to indicate abnormality was proportionately greater than for W-W perimetry.