The subdivisions of these terms at first reading appear complicated, but prove simple enough on closer study, indicating only the direction of the turning or tendency to turn. For instance: Esophoria signifies _inward_ tendency. Exophoria signifies _outward_ tendency. Hyperphoria signifies _upward_ tendency. Hypophoria signifies _downward_ tendency. Cyclophoria signifies _tendency_ to torsion. Esotropia signifies _inward_ turning. Exotropia signifies _outward_ turning. Hypertropia signifies _upward_ turning. Hypotropia signifies _downward_ turning. Cyclotropia signifies _actual_ torsion. Combinations are describable in similar terms. A tendency of the right eye to turn up and inward, is a “right hyperesophoria”; the left eye to turn down and out, a “left hyperexophoria,” etc. Tendencies of both eyes together are denoted by the terms which follow: Anaphoria signifies an _upward_ tendency. Kataphoria signifies a _downward_ tendency. Dextrophoria signifies a _right_ tendency. Laevophoria signifies a _left_ tendency. CHAPTER XVII SYMPTOMS OF HETEROPHORIA These depend on the kind of error present as well as the degree and widely vary. In general, they may be said to fall into three classes—(1) defective vision, (2) pain of greater or less degree—(3) reflex symptoms. _Defective Vision._ The first class may be present, even though each eye has a normal visual acuity; since, even when compensation is very good, the brain gets the impression of two objects, nearly, though not quite fused; and vision may be considerably worse with both eyes together than with either eye singly. When compensation is considerably impaired, the diplopia becomes more and more persistent, till the brain finally makes choice of one image as more satisfactory, entirely suppressing the other. Visual acuity may not suffer in either eye; but vision being no longer binocular, everything is seen in the flat, the judgments of depth and distance being regularly more or less defective. While this is a tremendous disadvantage in many occupations, people gradually and not infrequently become accustomed to these visual defects and are not conscious of the handicap. _Pain._ It is quite different with the second set of symptoms, which are always accompanied with pain. In fact, the character of the subjective symptoms in refractive errors and muscular imbalance is so similar that it is practically impossible to differentiate in many cases.