VSA is the first order of concern in an assessment of visual function, and follows immediately after the comprehensive general health and eye health examination and history.
Assessing VSA in young children is an effective means of screening for dyslexia even before the child begins to read. VSA problems in adults is most often missed, even during normal eye exams. ‘Mysterious’ aches in the head, neck and shoulders often result from troubled signal acquisition. Most reading problems also have associated VSA issues; sometimes the VSA problem is a result of the reading problem, sometime it is the cause.
VSA elements can be measured by various means including using hand tools, and also with a fine motor measurement device such as the ‘Visagraph’, which we employ in our clinic.
The elements of visual signal acquisition are:
- 1. Vergence: Movement of the eyes together, in opposing directions, either divergence, or convergence.
- 2. Duction movements: These are movements of the eyes in tandem, looking up or down.
- 3. Binocular coordination: Movement of the eyes together to target an object/signal. Includes
- A. Saccades: Small ‘jump’ movements from one target to another, or as a sequence of targets such as letters/words on a page.
- B. Pursuits: Smooth movements of both eyes as they track a moving object.
- 4. Accommodation:Focusing on a target, and maintaining focus. Focusing must be quick, balanced between the eyes, and it must be able to change from near to far and back again with ease.
- 5. Target acquisition and Fixation: Use of peripheral vision to guide the eyes and head towards a target, then maintaining fixation on the target for as long as required – this might be for a fraction of a second, or it might be several minutes.
- 6. Varied distinct perceptual elements: Spatial organization, object perception, visual memory, visual thinking, allocation of visual attention, and the ability to integrate visual information with other sensory and output modalities.
Our VSA is guided by Visual Signal Processing (VSP), and VSP in turn is determined by signals acquired by VSA.