The aim of treatment is, of course, to remove the foreign body completely. Sometimes this is not as easy as it might seem, especially when a hot metal particle lies embedded in a "rust ring". In instances when it is clear that much digging is going to be needed, it can be prudent to leave the rust ring for 24 h, after which it becomes easier to remove. The procedure for removing a foreign body should be as follows: the patient lies down on a couch or dental chair and one or two drops of proparacaine hydrochloride 0.5% (Ophthaine) or a similar local anaesthetic are instilled onto the affected eye. A good light on a stand is needed, preferably one with a focused beam and the eyelids are held open with a speculum (Figure 6.9). The doctor will also usually require some optical aid in the form of special magnifying spectacles, for example "Bishop Harman's glasses" or the slit-lamp. Many foreign bodies can be easily removed with a cotton-wool bud (particularly those lodged under the upper lid), but otherwise at the slit-lamp a 25-gauge orange needle angled nearly perpendicular to the plane of the iris can be used to lift off the foreign body. When the foreign body is more deeply embedded, a battery-powered handheld blunt-tipped drill can be used to clean any rust deposits that remain, again under the careful control of the slit-lamp microscope.
Once the foreign body has been removed, an antibiotic drop is placed in the eye and the lids are then splinted together by means of a firm pad. There is no doubt that the corneal epithelium heals more quickly if the eyelids are splinted in this way. It is usually advisable to see the patient the following day if possible to make sure that all is well, and if the damaged spot on the cornea is no longer staining with fluor-escein, the pad can be left off. Antibiotic drops should be continued at least three times daily for a few days after the cornea has healed. The visual acuity of the patient should always be checked before final discharge.
There are one or two factors that should always be borne in mind when treating patients with corneal foreign bodies: in most instances, healing takes place without any problem but, rarely, the vision can be permanently impaired by scarring. Also, on rare occasions, the site of corneal damage becomes infected and if
neglected, the infection can enter the eye and cause endophthalmitis, with total blindness of the affected eye. This is a well-recognised tragedy, which should never happen in an age of antibiotics. Of course,if the eye has been perforated, endophthalmitis is a frequent sequel in the absence of antibiotic treatment. One only has to examine old hospital case notes from the pre-antibiotic era to obtain proof of this.
It is important to remember that a perforating injury of the eye is a surgical emergency. Any doubt about the possibility of a perforating injury of the cornea can usually be resolved by examining it carefully with the slit-lamp microscope. One other factor to bear in mind is the possibility of a retained intraocular foreign body. Sometimes the patient can be quite unaware of such an injury and this might mislead the doctor into underestimating the serious nature of the problem. The answer for the doctor is "when in doubt, X-ray", especially when a hammer and chisel or high-speed drill have been used. A retained intraocular foreign body might not set up an inflammatory reaction or irreversible degenerative changes until several weeks or even months have elapsed (Figure 6.10).
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