Explainers

Is Seeing Really Believing? – An Introduction to Sight and Vision


Part one of a series on vision

While working as a telephone triage nurse, I was confronted with callers complaining of problems relating to their vision. Some had chronic and degenerative health issues and some had acute and distressing symptoms. A woman called with a 36-hour history of complete vision loss in one eye. Helping a person who is suddenly without an essential function is a sobering experience, and as often happens when we are faced with circumstances we feel underprepared for, I wished in that moment that I had done more than squirm in my seat during university lectures about the anatomy of the eye and the neural pathways involved in perception.

I wished that I could conjure a mental picture of the process (as I can about cardiac circulation or an inflammatory response) to explain why she needed to attend her local emergency department. Without this ability to explain my thoughts, my advice seemed shallow, scary and based on an overwhelming sense that “I don’t know what it is, but it seems bad” (nobody wants to hear that from their healthcare provider!). I was determined to gain a better grounding in vision and visual perception, and now, you are the beneficiaries of my experience.

Vision is the overarching term used to describe the culmination of a number of complex processes that allow us to perceive the world and our place within it. It involves the lens of the eye directing light at the retina, which transforms light into electrical impulses. These impulses then travel along the optic nerve and neural pathways to the visual cortex in the brain where sensations such as depth and motion are organised and combined with prior knowledge and feature detection to create perception. Sounds confusing…

introduction to how vision works

For many who have normal vision, the complexity of the visual system is not often considered. We usually take for granted that what we perceive in the world around us is a true representation of objective reality. We understand the significance of what is before us and use this information to go about our business, trusting that the tall cylinder of wood we see is a tree, that the metal object in the kitchen will provide clean water, and that two flashes of light means that our car is safely locked.

But there are many factors that influence how we interpret the information collected by the eye and processed by the brain. How does the simplicity of light reflecting on the surface of an object become a perception that can affect our actions, memories and motivations? How can the disease processes of multiple sclerosis and diabetes both affect vision?

In the coming weeks I will be exploring the process of vision, from the lens of the eye to the visual cortex and everywhere in between. I will consider the impact of physiological as well as psychological factors on visual perception. My aim is to create a simple breakdown of a complicated process so that one day, when confronted with a situation like mine, your patient, client, health service recipient or indeed loved one, will feel informed and confident in the treatment and advice you are providing to them.

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