Exophoria is a form of heterophoria

Heterophoria

Heterophoria is a type of eye condition in which the directions that the eyes are pointing are not consistent with each other. A person with two normal eyes has single vision because of the combined use of the sensory and motor systems. The motor system acts to point both eyes at the target of...

 in which there is a tendency of the eye

Human eye

The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...

s to deviate outward. During examination, when the eyes are dissociated by prisms, the visual axes will appear to diverge away from one another.

Prevalence

Exophoria is particularly common in infancy

Infant

A newborn or baby is the very young offspring of a human or other mammal. A newborn is an infant who is within hours, days, or up to a few weeks from birth. In medical contexts, newborn or neonate refers to an infant in the first 28 days after birth...

 and childhood

Childhood

Childhood is the age span ranging from birth to adolescence. In developmental psychology, childhood is divided up into the developmental stages of toddlerhood , early childhood , middle childhood , and adolescence .- Age ranges of childhood :The term childhood is non-specific and can imply a...

, and increases with age.

Cause

Exophoria can be caused by several factors, which include:

• Refractive errors - distance and near deviation
  Deviation
  Deviation may refer to:* Deviation , the difference between the value of an observation and the mean of the population in mathematics and statistics** Standard deviation, which is based on the square of the difference...
  
   approximately equal.
• Divergence excess - exodeviation is more than 15 dioptres greater for distance than near deviation.
• Convergence insufficiency
  Convergence insufficiency
  Convergence insufficiency or Convergence Disorder is a sensory and neuromuscular anomaly of the binocular vision system, characterized by an inability of the eyes to turn towards each other, or sustain convergence.-Symptoms:...
  
   - near exodeviation greater than distance deviation.

These can be due to nerve

Nerve

A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...

, muscle

Muscle

Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...

, or congenital problems, or due to mechanical anomalies. Unlike exotropia

Exotropia

Exotropia is a form of strabismus where the eyes are deviated outward. It is the opposite of esotropia. People with exotropia often experience crossed diplopia. Intermittent exotropia is a fairly common condition. "Sensory exotropia" occurs in the presence of poor vision...

, fusion is possible in this condition, causing diplopia

Diplopia

Diplopia, commonly known as double vision, is the simultaneous perception of two images of a single object that may be displaced horizontally, vertically, or diagonally in relation to each other...

to be uncommon.