Glaucoma and functional vision
Glaucoma and functional vision
In the thesis of Mehrdad Gazanchian was looked at how vision loss from glaucoma affects everyday life. Glaucoma is a common eye disease that slowly damages the optic nerve and leads to permanent vision field loss. The visual field is the part of the environment you can see while fixating on a fixed point.
Doctors have long believed that if one eye has a blind area in its visual field but the other eye can still see it (a so called non-overlapping visual field defect), the brain compensates and daily life is barely affected. Our research shows that this belief is often wrong.
We created a new way to measure this problem, called the Differential Visual Field. Using this method, we found that people non-overlapping visual field defects often have more difficulty in daily life compared to those without visual field defects. The problems are most noticeable in activities that involve movement and awareness of the surroundings. Examples include walking on uneven ground, crossing streets, and noticing objects coming from the side.
We also tested this in laboratory experiments. Even when vision from both eyes together looks normal, these blind areas reduce basic visual abilities. People become worse at seeing contrast, detecting movement, and recognizing shapes.
To better understand patterns of visual field loss, we analysed a very large dataset and identified 12 common patterns of binocular vision loss (visual field loss present when looking with both eyes simultaneously) in glaucoma. These patterns showed that the location of the visual field loss is important. For example, loss in the lower part of the visual field caused more problems with movement than loss in the upper part.
We then examined the common idea that damage near the centre of vision is worse for quality of life than damage in the periphery of the visual field. We found that this is not necessarily true. When overall visual field loss and visual sharpness are taken into account, then central damage is not automatically more harmful than other types of damage.
Finally, we studied three dimensional blind areas in front of or behind where a person is looking. We found the for most people with glaucoma, these blind areas do not cause major everyday problems.
In summary, this thesis shows that standard eye tests often miss important parts of how people actually see and function in real life. To give better and more personal care, doctors need tools that consider differences between the eyes and the pattern of vision loss, not just how much vision is lost overall.