Patients usually know when a foreign body has gone into their eye and the history is clear-cut -but not always. Occasionally, the complaint is simply a red sore eye, which might have been present for some time. Spotting these corneal foreign bodies is really lesson number one in ocular examination. It involves employing the important basic principles of examining the anterior segment of the eye. Most foreign bodies can be seen without the use of the slit-lamp microscope if the eye is examined carefully and with a focused beam of light. Figure 6.8 demonstrates the great advantage of the focused beam, and, in fact, this principle is used in slit-lamp microscopy. If the foreign body has been present for any length of time, there will be a ring of ciliary injection around the cornea
caused by the dilatation of the deeper episcleral capillaries, which lie near the corneal margin. Ciliary injection is a sure warning sign of corneal or intraocular pathology.
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