How To Locate And Remove Ocular Foreign Bodies

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In the eyes, there are four common sites where foreign bodies can easily lodge and they include the following: subtarsal site, superficial site, intra-ocular site and retained intra-ocular site.

Subtarsal foreign bodies

Many small FBs will be washed out of the eye by the tears. Sometimes, however, the FB will become embedded in the subtarsal conjunctiva of the upper lid, which will cause pain on blinking and a vertical corneal abrasion. The area of abraded cornea, where the epithelium has been removed, will be seen as a disturbance of the corneal reflection. This can be viewed by installing fluorescein and viewing the eye under ultraviolet light. The upper lid must be everted if there FBs are to be located and removed. The healing of the epithelium may sometimes be incomplete, resulting in recurrent corneal erosions.

Superficial foreign bodies

An eye with a corneal FB usually shows marked vascular injection closest to its position. Ocular pain will be experienced but it will be difficult to localize. If the corneal FB has been present for a couple of days a grey ring of infiltration may occur around it and, on removal, a small, pitted ulcer will remain. It may leave a permanent scar, although this will generally only affect vision if it is over the centre of the cornea. FB embedded in the conjunctiva or sclera is often surrounded by hemorrhages.

Many foreign bodies are metallic, iron particles being the most common, followed by copper and aluminum. The softer metals (e.g. magnesium) are a less frequent cause of FBs left embedded in the eye will rapidly oxidize under the influence of the enzymes of the cornea and tears. This may set up a severe inflammation of the cornea or iris. The oxidation of steel is much faster than that of aluminum or magnesium and a rust ring may be apparent within a couple of hours. A rust deposit left in the cornea will partially dissolve and an iron stain will diffuse into stromal or sub-epithelial layers.

Intra-ocular foreign bodies

The possible presence of an intra-ocular foreign body (IOFB) should always be investigated, especially when the symptoms are a gush of fluid from the eye with blurring of vision. Small, hot FBs hitting the eye at great speed may penetrate the globe and actually seal their route of entry. As only a slight pain is experienced, it is essential not to miss an IOFB, as it may lead to loss of vision. Whenever the eye is perforated an X-ray should be taken to exclude the presence of a metallic IOFB. The classic signs of a perforating injury are a shallow anterior chamber, eccentricity of the pupil and prolapse of the iris. However, care must be taken in the following two cases:

1. A small conjunctival hemorrhage, while being the only clue may obscure deeper scleral laceration.
2. The eye appears normal but there is a history suggestive of an IOFB.

Recommended: Causes Of Perforating Eye Injury

The IOFB may have been stopped by the iris and then fallen down into the anterior chamber angle to be hidden from view. If an IOFB has penetrated through the vitreous, fibrous tissue will form along its path. The fibrous tissue may impair vision if it crosses over the visual axis and a vitrectomy may then be required to restore vision and/or to prevent tractional retinal detachment.

There are various methods of localizing IOFBs: X-rays techniques, ultrasonography, binocular indirect ophthalmoscopy and the use of a localizer, which employs electric induction currents. Ultrasonography can locate the position of non-metallic fragments, whereas X-ray show metallic FB positions. Ultrasonography traces the rebound of high frequency pulsations and by resulting patterns, the inside of the eye can be exposed. Once the IOFB has been located it can be removed.

Retained intra-ocular foreign bodies

Vegetable FBs may cause infections so severe that a purelent panophthalmitis may occur in only a few hours. Other FBs may be retained without noticeable reaction, e.g. gold, silver, platinium, glass and many plastics. Less well tolerated by the eye are lead, zinc, nickel and aluminium particles. These are often coated in an inert salt and later encapsulated by fibrous tissue coating, rendering them less toxic. The most dangerous IOFBs are iron and copper which cause siderosis and chalcosis respectively.

In siderosis the iron oxidizes and causes a slow, insidious intra-ocular reaction as it permeates most of the ocular tissues; this can lead to complete blindness. It is a late-occuring syndrome and the ferrous pigmentation causes a rusty coloration of the cornea, iris or lens. In addition, a series of chronic degenerative changes occur, which lead to pupil dilation because of atrophy of the sphincter pupillae, cataract and then retinal detachment and open angle glaucoma. These complications usually occur between two months and two years after injury and surgery is needed immediately after injury to remove the foreign body.

Pure copper will cause a rapid inflammation of the eye (chalcosis) and the eye may be lost if endopthalmitis occurs. Copper alloys (bronze and brass) may induce chronic degenerative processes by slow diffusion of the copper, which tends to be taken up by the limiting membranes of the eye. A green ring may develop in the peripheral cornea in descemet's membrane and a sunflower cataract in the anterior capsule of the lens is formed. It is not usually as essential to remove copper as iron IOFBs, as retained particles may not cause a significant loss of vision for many years.