Eye Teaming (Vergence)

Eye teaming refers to the eyes making accurate inward (convergence) and outward (divergence) movements together, based on the distance of an object to see a single image.

The most common symptom of a breakdown in eye teaming skills is double vision, which can occur in the distance or at near.

Eye teaming (vergence) problems are classified as:

Convergence Insufficiency - the eyes are unable to cross together when looking at a near object and begin to drift outwards. Here the brain perceives the object to be further away than it actually is.

Convergence Excess - the eyes cross too much when trying to look at a near object. Here the brain perceives the object to be closer than it actually is.

Divergence Insufficiency - the eyes are unable to relax and move outward together to look at something in the distance. The brain perceives the object to be closer than it actually is.

Divergence Excess - the eyes relax and move outwards too much when looking in the distance. The brain perceives the object as being further away than it actually is.

Eye Focusing (Accommodation)

Eye focusing (accommodation) is the ability of the internal lens of the eyes to keep an object clear by expanding or relaxing to focus at different distances.

The 'normal range' for accommodation measurements vary with age, i.e. the younger the patient the better their accommodation skills should be. This means they are able to maintain clear vision at a close range for a long period of time. Most adults begin to lose this ability after 40 years old (known as Presbyopia), resulting in the need for reading glasses.

The most common symptom of a breakdown in eye focusing skills is intermittent blurry vision that resolves with a blink or after a period of resting the eyes from intense focusing.

Eye focusing (accommodation) problems are classified as:

Accommodative Insufficiency - the internal lens is unable to expand to the level that corresponds to their age, resulting in blurry vision at near particularly with prolonged near work.

Accommodative Fatigue - normal (age appropriate) results are achieved on initial measurements, but on repetition the internal lens begins to fatigue and is unable to sustain the same level of accommodation. Producing worse results over a short period of time.

Accommodative Infacility - the eyes have difficulty quickly changing their focus between a distant and near target and back. This often results in blurry distance vision after long periods of near work.

Eye Tracking (Ocular Motility)

Ocular Motility involves the 6 external muscles around each eye working equally to move the eyes into different positions (up, down, left right, and 4 corners). Problems with ocular motility can occur following nerve palsies or caused by mechanical restrictions of the muscles to move (e.g. trapped muscles).

Eye Tracking, describes the eye movements that allows a person to fix their eyes on an object and smoothly follow it as it moves, or follow a sentence on a page from left to right. Eye tracking also includes eye-hand coordination skills.

Eye tracking skills are particularly important in sports such as football, soccer and tennis.

Symptoms of a breakdown in eye tracking include:

Skipping over words when reading,
Re-reading words or lines unintentionally,
Over-reliance on finger or ruler to keep place while reading (in children), and
Excessive head movements during desk work.

Eye Tracking skills are made up of 3 components:

Fixation - keeping the eyes steady without looking away from a target/object.
Saccades - accurate jumps between objects without overshooting or undershooting.
Pursuits - the ability of the eyes to remain fixated on a target/object as it moves.