Abstract:
We assessed the effect of dividing attention on visual field sensitivity using the SITA interactive algorithm running on a Humphrey Field Analyzer (HFA) combined with asynchronous tasks running at fixation, in patients with glaucoma and an age–matched control group.
One eye of 14 patients with glaucoma (mean age 68.9±7.86yrs) and 14 healthy control subjects (72.43±6.2yrs; p=0.08) was assessed using the 30–2 SITA Standard program running on an HFA Series VII (model 740i). Standard visual fields (SF) were compared with the fields recorded when subjects, in addition to performing the field task, also had to respond to targets presented at fixation using a second hand–held button (modified field MF). Threshold data was averaged across each of four regions, from the central four macula points, to the 20º to 30º region.
Using a mixed factor ANOVA with group (glaucoma vs. controls) treated as a between subjects factor and field region (x4) and field type (x2) as within subjects factors, we found both a significant difference between the groups (F1,26=19.1, p<0.0001), and significant differences in both field region and field type (region F3,24=33.82, p<0.0001; type F1,26=34.26, p<0.0001). As a group, the glaucoma subjects were more variable than the controls when tasks were combined; some glaucoma subjects exhibited a marked depression in MF sensitivity far greater than anything observed in the controls. The two groups had comparable response times for the central detection task (glaucoma 603±56msec vs. control 584±63msec; F1,52=0.05; p=0.8) when this was run alone.
The effect of dividing attention reduced visual field sensitivity in patients with glaucoma to a greater extent than in controls. However, glaucoma patients were also more variable. It remains to be seen if the greater depression in sensitivity observed in the glaucoma patients is indicative of actual damage not detected by standard visual fields, or predictive of future damage. This would suggest central compensation for glaucomatous damage.