Input-Processing-Output, How to Think About the Visual System

Vision is fascinating.  It is one of those rare things which even casual observation makes people pause and wonder.  We use our visual system effortlessly but we are well aware it is exceedingly complex.  Even eye doctors break it down into specific sections and focus on area.  There are retinal specialists, developmental specialists,  low vision specialists, and others.  Each of these focuses on only one part but they require a working knowledge of the full system.

This is how I like to break up the system. And it is important to realize each step affects the next.

Input →     Processing →      Output

This model is used for many things in life, for instance, how to make the body of a car.  We buy steel from a company (input); in our factory we weld it together and shape a body (processing).  We now have a car body to sell (output).

With vision, light enters the eyes and hits the retina creating electrical signals from rods and cones (input).  The brain then uses that raw data and processes it into useful tools, for instance, an unconscious layout of the room surrounding someone, and words from a page (processing).  Finally we use those tools to better function within our world; we can now walk across the room without walking into a coffee table or read a page and find meaning (output).
 

Input

These are two big input questions that any eye doctor checks.

• Is the eye healthy?

• Can it see clearly?
   

A developmental optometrist asks a few more input questions.

• How well do the eyes see together?

• How long can they see clearly?

• Do they see one single or double?

• Can the eyes shift focus from distance to up close without strain?
   

Processing

Processing asks questions about how the brain takes the information from the eyes and uses it.

• Can the black letters be extracted from a white page?

• Are those letters combined into words?

• If we see a car in the distance and it is half covered by a tree are we still able to identify it and mentally fill in the missing portions?
   

Output

This is the part that everyone understands.

• How well do they perform in school/work?

• Can they read fluidly?

• Do they understand what they read?
   

Using this model it is easier to understand where the break downs in the system can take place and how to treat them.

“Dodge”

William Dodge Perry, OD