Definition Degree of protrusion of the eye (exophthalmos).
Landmarks The calibrated end of a Luedde exophthalmometer is held firmly against the lateral margin of the orbit. The long axis of the instrument is held parallel to the long axis of the eyeball. The examiner sights the anterior margin of the cornea through the calibrated scale and reads the distance in millimeters (Fig. 7.50).
Instruments A Luedde exophthalmometer; for details, see Gerber et al. (1972). A transparent calibrated ruler could be substituted.
Figure 7.49 Palpebral fissure inclination, both sexes, 6 to 18 years. From Farkas (1981), by permission.
Position Frankfort horizontal, with the facial profile in the vertical. The patient should be viewed from the side.
Remarks A Luedde ruler is easy to use and not frightening to children. Orbital protrusion will vary during puberty. Normal protrusion is between 13 and 22 mm for children and adults.
Pitfalls In the presence of ptosis, it may be difficult to estimate the anterior margin of the cornea.
Corneal Dimensions: Transverse Diameter Definition Transverse diameter of the cornea.
Landmarks Measure between the medial and lateral borders of the right iris, which for practical purposes represent the edges of the cornea. Repeat measurements on the left eye (Fig. 7.51a).
Instruments Spreading calipers, a transparent ruler, or tape-measure may be used.
Position The standard orientation of the head is the Frankfort horizontal.
Remarks The cornea is relatively large at birth and attains almost its adult size during the first and second years. Practically all its postnatal growth occurs in the second six months of life, although some increase in size may be evident up to the end of the second year. Although the eyeball as a whole increases its volume almost three times from birth to maturity, the corneal segment plays a relatively small part in this growth. The transverse diameter of the cornea increases roughly from 10 mm in the infant to a value slightly less than 12 mm in the adult. In the infant, values of less than 10 or more than 11 mm require further evaluation. Average values for the transverse diameter (external diameter of horizontal base) are found in Fig. 7.51b.
External diameter of horizontal base
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