Gaze-related changes tied to navigation problems in AMD
By David Douglas
Greater pupil diameter and fixation counts seen in patients with age-related macular degeneration (AMD) who were watching video clips of passage through a building may help shed more light on navigational difficulties, according to new research.
As Dr. Peter Aspinall told Reuters Health by email, "The study has highlighted eye tracking differences between people with AMD and a control group in a simulated walk through a building. These differences (i.e. higher values in fixation count and pupil diameter in the AMD group) are related to perceived difficulty and search efficiency during the journey."
Earlier studies have shown that fixation count is negatively correlated with search efficiency, which in turn is tied to uncertainty regarding objects, Dr. Aspinall of Heriot-Watt University in Edinburgh and colleagues note in the British Journal of Ophthalmology, online May 15.
Gaze behavior has been studied extensively in normally sighted people, they add. However, navigational behavior has been difficult to study in standardized settings and little has been published on such behavior in AMD.
To investigate further, the researchers simulated a walking journey through a university building using video projection. The clips deliberately contained segments previously shown to cause problems during navigation, such as colored lights and surfaces lacking contrast or causing glare. Segments of each clip were graded as easy or difficult by 12 patients with AMD and six experts in the field of environmental design and vision.
The team then went on to monitor responses in 34 patients with bilateral AMD and 23 controls using automated eye tracking. Visual acuity, fixation count, fixation duration and pupil diameter were recorded as were comments on difficulties encountered en route.
Compared with controls, the AMD group had significantly greater pupil diameters in both easy and difficult segments. Fixation counts were also significantly higher in the AMD group during difficult segments.
The differences in both pupil diameter and fixation count correlated with the subject's visual acuity.
The researchers point out that among shortcomings in applying the findings to the real world is that the aim of the study was to investigate eye movements and pupil dilation; the effect of motor function and other sensory inputs was not assessed.
"At this stage," concluded Dr. Aspinall, "it is difficult to assess their consequences for navigational strategy or environmental design. However, the findings do provide additional markers for assessing the functional efficacy of current navigational intervention therapies for people with AMD."
Dr. Andrew Rabinowitz, a Phoenix, Arizona-based ophthalmologist not involved in the new research, said it "represents an initial foray into degree and expression of the functional vision loss in this most threatening of diseases."
"To date, there are only a few ways to describe the functional losses associated with AMD," Dr. Rabinowitz told Reuters Health by email. "This study attempts to identify and describe novel and objective markers of the functional compromise seen in patients with AMD."
Br J Ophthalmol 2014.
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