- ORH is not a disease in itself but the manifestation of a craniofacial deformity that may be present in a variety of craniofacial conditions
Telecanthus (pseudo-hypertelorism):Distance between the inner canthi more than two standard deviations above the mean (objective); or, apparently increased distance between the inner canthi
The term hypertelorism means an increased distance between two body parts. Greg applied it for the eyes and termed it as “ocular hypertelorism” in 1924 to signify widely placed eyes. He used interpupillary distance (IPD) to record its presence. However, Tessier noted that IPD could be increased because of exophoria alone without any bony abnormality of the orbit. He, therefore, proposed the term “orbital hypertelorism” (ORH), wherein there is true lateralisation of the whole of the bony orbit in a way that the distance between the lateral canthus and auditory meatus is shortened.
- Inner canthal distance (ICD): Distance between two medial canthi measured at the level of posterior lacrimal crest.
- Outer canthal distance (OCD): Between the two lateral canthi.
- Interpupillary distance (IPD): Distance between the two mid-pupillary regions in the front gaze