Navigating the world with sight loss

Tower Bridge photo showing loss of sight in the central field of vision
Photo copyright: Macular Society (figure 1)

It has been suggested the human eye is the most important sensory organ in our body, with 80% of all the impressions on our senses coming from the eye.

Many people fear blindness more than any other disability, yet finding our way around independently is something most of us take for granted.

We depend on our orientation and way finding skills to navigate our every day journeys – going to the shops, getting to work – being active and staying healthy in the process. But for people with sight loss, these every day journeys are daunting and challenging, particularly in the winter months when light levels are reduced.

The most common cause of sight loss – and blindness – in the developed world is advanced macular degeneration (AMD), a disease of the macula (the small spot near the middle of the retina, which is responsible for the central part of what we see) that affects approximately 500,000 people in the UK.

People with AMD experience loss of sight in the central field of vision as shown in figure 1 : straight lines may appear wavy, colours can appear faded, and they cannot fixate on the goal or object ahead in the same way as people with normal vision can. This makes for huge difficulties in navigating the world.

To investigate this further, a team of researchers at Heriot Watt University and VisonCentre3 Edinburgh simulated a walking journey through a university building using video projection. The clips deliberately contained attributes of the environment known to cause problems during navigation in people with AMD, such as colored lights and surfaces lacking contrast or causing glare.

We compared eye gaze and fixation patterns in 34 patients with AMD to 23 ‘controls’ i.e. normally sighted people of the same age using a mobile eye tracker. The eye tracker data produces images like the one below, showing the objects people with AMD fixate on; in this case, indicating high levels of eye fixation (the red) on lower level cues whilst navigating a doorway.

Fixation in advanced macular degeneration

Photo copyright: Chaham Alalouch

The data shows the environmental cues that help navigation in AMDs are walls, floors, and low-level items as opposed to the forwards goal – or central object – that normally sighted people use for navigation. Features our participants indicated causing problems include coloured lights, monochrome environments, surfaces causing glare (steel, glass), and lack of transition lighting when going from dark to light. You can read the full article here.

We believe our findings are an important new step in our understanding of the physical limitations of those with AMD. Hopefully it can help lead a way to develop new technologies and better design of our built environment to assist the day-to-day navigation for all with AMD.