Physiological and anatomical protection from foreign bodies

A multitude of factors protects the eyeball. The lids and lashes prevent dust, sweat and small particles from entering the eye. The lacrimal gland serves the function of keeping the ocular surface moist and also washes out foreign bodies. Tears also contain lysozyme, which carries out antimicrobial activity. The conjunctiva protects the sclera, and the orbital bony rim protects the eye from mechanical trauma and foreign bodies. ([Figure 1])

Corneal foreign bodies and their implications

Sequence of events following a foreign body impaction

A sudden release of tears after a foreign body impaction causes a brief period of blindness associated with blepharospasm. Also, rubbing of eyes causes the foreign bodies to penetrate deeper layers which, on the other hand, would have been washed away.^[4] Once a foreign body is entrapped between the layers of the cornea, it triggers an inflammatory cascade and activation of white blood cells. These lead to congestion, corneal and lid oedema, chemosis, anterior chamber reaction. These are more prominent and early with organic foreign bodies like leaves, cow dung etc., due to infective foci. ([Figure 2]) A delay in intervention can result in necrosis of the tissue and lead to deleterious complications like endophthalmitis. Once an epithelial wound is formed, healing of the same is achieved by cell migration and proliferation. Small lesions that occupy less than 60 per cent of the total surface area heal rapidly within four days compared to defects occupying larger areas.^[5] Inert materials like glass, plastic etc., usually don't give rise to inflammatory reactions; finally, they get integrated into the cornea. Some surgeons prefer to leave them in situ unless there is profound irritation. But due to fibroblastic activation, the scar formed in the central cornea can be visually and cosmetically disabling for the patient. Rust which is left behind after removing ferrous foreign bodies, can lead to necrosis of the stroma.^[6] On the other hand, in the case of organic materials, there is a proliferation of giant cells and the formation of granulomas. The foreign body in such cases may act as a nidus for infective keratitis and may even flare up into endophthalmitis or panophthalmitis. ^[4]

Types of corneal foreign bodies

The common ocular foreign bodies include metal pieces, rust particles, glass pieces and organic matter. However, there are reports of unusual foreign bodies like one's own hair, caterpillar hair getting impacted. ^[7]  

Ocular foreign bodies can be classified based on the nature of foreign body into Organic and Inorganic type. Depending on the location of corneal foreign bodies, they can be divided into Superficial, Stromal or Deep.

Foreign bodies that are confined to the cornea's epithelium can be considered superficial foreign bodies ([Figure 3]a,b), and those embedded in the corneal stroma ([Figure 4]a) and below are considered deep ([Figure 5]a). Superficial ones are easily identified on slit-lamp and can be removed in the same sitting. In the case of deep foreign bodies, anterior segment optical coherence tomography before the procedure will benefit the surgeon in assessing the depth of penetration and planning the procedure accordingly. Jinagal et al. have reported a case of a plastic piece that was embedded in the superficial stroma. AS-OCT was used to assess the depth of impaction prior to removal with forceps. AS-OCT is particularly helpful in the case of pediatric age groups who are not able to provide a proper history.^[8] Caterpillar hair can give rise to ophthalmia nodosa, a type of severe nodular granulomatous iridocyclitis. ^[4]

Signs and Symptoms

The common symptoms are foreign body sensation, watering, redness, photophobia, blurred vision. Toddlers and children who are not able to communicate verbally or give a proper history might also be uncooperative for examination. They may show irritability and pain on closing the eyelid.^[9] Often, they can be asymptomatic also. The removal of a corneal foreign body is always carried out in an emergency setting.^[10] The type and circumstances of injury can give a clue regarding the possibility of globe penetration also. 

Investigations

Even though we can remove superficial corneal foreign bodies under an operating microscope or slit lamp, plain radiography of orbit, CT scan and occasionally MRI is indicated in cases of severe ocular injuries like blast injuries and perforating injuries. MRI is contraindicated in cases of suspected metal foreign bodies.^[11] A retained extraocular or intraocular foreign body can lead to ocular and adnexal inflammation and infection, hence the need for urgent removal. Inorganic foreign bodies are well tolerated; on the contrary vegetative foreign bodies act as a nidus for infection.^[12] Although, there are studies that show prolonged retained corneal foreign body without appreciable reaction. ^[13]

After taking a detailed history of the mode of injury, visual acuity, pupillary reflexes, intraocular pressure, extraocular movements should be noted. Slit-lamp evaluation and fundus examination should be carried out to locate the site of impaction.^[14] Double eversion of the eyelid should be carried out, and fornices should be examined under diffuse illumination. Objects like glass pieces and plastic bits are difficult to focus on due to their transparent nature. Hence, various techniques of illumination can be employed to identify the object. Making a slit section of the cornea is useful in assessing the depth of penetration of a foreign body, especially if the site of impaction is in the stroma. If the depth of entry could not be assessed under a slit lamp, it is always advised to remove the foreign body under an operating microscope to prevent inadvertent injury to surrounding tissue. Blind manipulation can also lead to the displacement of the foreign body into the anterior chamber.

Fluorescent staining is advocated to look for corneal abrasion and to check for Seidel's positive. On staining the traumtic area, washing out of the dye indicates aqueous leakage from the AC and should be repaired as early as possible. The anterior chamber should be assessed for hyphema, angle, cells or flare.^[10] Even though ocular pressure should be monitored, tonometry should be avoided in suspected penetrating injuries in patients with corneal defects and corneal infections.^[15] Foreign bodies that enter the eye can cause damage to the iris, lens, and can even reach the posterior segment in high-velocity injuries.

Since most of the injuries occur accidentally at the workplace, metallic foreign bodies are the most commonly encountered ones in the ER.^[16] The first step in emergency management is copious saline irrigation which can wash out any loose rust particles or dust lodged in the fornices and cul de sac.^[17] There are many techniques described for the removal of ferruginous foreign bodies. To alleviate the pain, one drop of local anaesthetic can be instilled in the eye. Loose particles present superficially can be removed using a cotton tip applicator moistened with a local anaesthetic agent. The tip can be gently rolled over the foreign body, which aids in its removal by lifting it off from the corneal surface.^[18] Another method of removing superficial corneal foreign body, especially rust ring, is by gently scraping the cornea and lifting the foreign body with the bevelled edge of a 25G needle attached to a tuberculin syringe.^[18] ([Figure 3]c) Metallic foreign bodies can give rise to the formation of rust rings if left beyond 12 hrs.^[19] Various studies have shown that if removal is delayed, in case of any material, especially deeply seated; it can later lead to scarring, which alters the quality of vision and increases the risk of infections.^[16] Debriding more than what is required can cause damage to Bowman's layer and deeper, which can result in irreversible scarring.^[20] Once the foreign body is removed, repeat saline irrigation and fluorescein test can be repeated to check corneal abrasions. Smaller corneal abrasions heal by themselves. Large abrasions caused by organic matter have higher chances of infection, and they should be followed up after 24hrs. The abrasions are treated with lubricant and antibiotic eye drops.^[21] Studies have shown that using an electric drill in removing the retained rust ring is superior to a manual drill in achieving a better outcome and less patient discomfort. ^[6]([Figure 3]d)

Organic foreign bodies can include insect parts, wooden chips, bamboo splinters, husk, caterpillar hair etc. which, if not removed urgently, can lead to reactive inflammation. They can also act as a nidus for infection.^[22] In 1950 a case was reported in which a patient had a retained grain particle embedded in the cornea for nearly 15 years. Although the patient was asymptomatic, corneal perforation with iris tissue incarceration was found upon removal of the foreign body. ^[23] 

In cases such as a deeply embedded foreign body, where surgical removal is imminent, fine-tipped forceps can be used to gently remove the object along its tract of entry. ([Figure 5]b) The procedure can be done under topical anaesthesia or under sedation in the case of pediatric patients. After removal, Seidel's test can be done if we suspect aqueous leakage. Sometimes, the foreign body can partially enter the anterior chamber, which needs very cautious surgical management. Yang has reported a case of a complicated deep foreign body that has entered the anterior chamber partially. A 6mm suture needle was passed beneath the foreign body so that the anterior opening of the wounds was everted.([Figure 5]c) This facilitated easy removal of the foreign body without any complications.([Figure 5]d) The use of a suture needle facilitated better light reflection, maintenance of the anterior chamber, easy removal of the foreign body, and better globe fixation. Also, it was less expensive and also helped in less endothelial cell loss because of less manoeuvring of the anterior chamber. ^[24] 

In their study on deep corneal foreign body removal, Duan and Yan havee used a needle hook as the surgical aid. They used a 40G needle to make a needle hook. Their study also advocates surgeons debride any necrotic corneal tissue, cut open the tunnel lodged with the foreign body with a keratome and scrape off the dead tissue so that further complications can be prevented. Once the inflamed stroma is denuded, the tunnel should be closed with intermittent sutures to prevent the incidence of infection.([Figure 5]e) The foreign body can also be sent for culture and sensitivity.^[25] Accidental injury with a pencil can lead to the deposition of graphite particles in the cornea. Philip et al. have documented graphite particles in the anterior stroma of a child three years after the injury. Since there was no deficit in vision and no evidence of inflammation, the child was kept under observation. ^[26] 

Polystyrene fragments have also been found in the mid stroma, presenting with glare complaints and a remarkably good visual acuity. The plastic piece containing polystyrene was embedded in the stroma for five years without causing vision loss. Since there was a foreseen possibility of lens damage while removing the foreign body and entering the anterior chamber, the surgeon preferred corneal transplantation.^[27] Although intracorneal cilia has shown to produce no reaction, a decrease in the endothelial cell count has been reported. The loss might be due to the mechanical effect or biochemical reaction caused by the cilia.^[28] Authors have also described caterpillar hair in the corneal stroma, which even penetrated the anterior chamber.([Figure 5]a) Since it is organic, associated inflammatory reactions and vitreous exudates were present but with unaffected visual acuity. AS-OCT was used to confirm the location of the hair, and the condition was managed by topical and oral steroids, cycloplegics and antibiotics. Later the patient was kept on low dose steroid after tapering the dose, although the final outcome after withdrawing steroids was not mentioned.^[29] The penetration of hair may be aided by its shape and structure, ocular movements and vascular pulsations. The granulomatous reaction which follows depends on the number of hair which has entered the eye.^[30] Intracorneal hair and cilia have been reported by other authors also. Using a Jeweler's forceps, microblade and 30gauge needle, hair trapped in the anterior stroma was successfully removed.^[31] Some surgeons prefer to leave the intrastromal hair in situ if the vision is unaffected and no active inflammation.^[32] Ocular trauma can also cause entrapment of cilia in the cornea and conjunctiva. In case of multiple lashes, the central ones can be removed through the epithelium while those on the limbus via a conjunctival peritomy. ^[33]

In case of foreign bodies like sugar cane or bamboo splinters, which are embedded in the anterior corneal stroma, blunt-tipped surgical forceps can be used to gently pinch and pull the splinter in the direction of the tunnel created.

Although corneal foreign bodies constitute the majority of cases being reported in the eye casualty, most of them do not hamper vision. Organic foreign bodies should be removed in the same sitting itself to prevent the incidence of infection. Suppose the pupillary area of the cornea is affected and the object is deeply buried in the stroma; in that case, it can affect the quality of vision due to stromal scarring and astigmatism.^[25] Once a foreign body is removed, treatment mainly consists of topical lubricants and antibiotics. In the case of larger corneal defects caused by the injury, eye ointments are preferred to eye drops since the former provides prolonged contact time and reduces friction caused by the lids.^[20] Topical anaesthetic agents should not be prescribed since it delays wound healing. Steroids are contraindicated in case of organic foreign bodies as they can flare up an occult fungal infection.^[34] Also, occupational health education is of utmost importance to prevent workplace hazards. Proper use of protective goggles and face shields, regular eye examinations, and timely intervention in case of an accident help maintain a good quality of vision and prevent further complications.

Role of suturing and tissue adhesive glue

A foreign body may leave a tissue defect depending on its size and velocity, which it hits the cornea. The primary aim is to maintain a clear cornea, remove the foreign material, and a fully formed anterior chamber.

How to proceed further with a corneal wound depends on the tissue loss and the depth of injury. In the case of self-sealed wounds, conservative management with prophylactic antibiotics and steroids is required if the size is less than 2mm. Applying a bandage contact lens will provide further wound stability.(Figure 4d) In case of large self-sealed wounds, the management options include suturing and tissue adhesive glue. Suturing is preferred in kids and patients who might unintentionally rub the eyes postoperatively.^[35] Although suturing can cause astigmatism in the future, the final decision depends on the wound integrity and a maintained anterior chamber. Partial-thickness lacerations tend to heal themselves without intervention.^[36] But if there is an associated flap, care should be taken to reposition it in place with partial-thickness sutures. For this, 10-0 nylon or 11-0 nylon sutures can be used. A flap that is not displaced can be managed by placing a bandage contact lens. A full-thickness corneal wound invariably requires suturing, and care should be taken to bury all the suture knots at the end of surgery. The depth of the suture should be 90 per cent of the total thickness.^[36] In case of bevelled edges, centration of the suture with respect to the posterior aspect of the wound will give better apposition of edges. If there is a loss of corneal tissue, the management depends upon the size of the defect. A small defect can be repaired by suturing with a foreseen complication like astigmatism, and a defect exceeding 5mm in diameter should be repaired by a patch graft. Tissue adhesive glues can manage defects of size up to 3mm. Fibrin glue provides better wound healing, but the plug formation takes a longer time than cyanoacrylate glue. In contrast, cyanoacrylate glue starts to polymerise immediately on exposure to air. Care should be taken to properly dry the cornea before applying cyanoacrylate glue. Glue is applied to the defect after all the necrotic tissues are removed and after confirming that there is no iris / foreign body at the wound site.^[37] Minimal tissue handling and avoiding suture bites in the visual axis are other measures to achieve better postoperative outcomes. ^[35] 

As small epithelial defects heal with adequate conservative management, the chances of fungal invasion into the stroma is infrequent in an immunocompetent individual. Topical fluoroquinolone, which has a broad spectrum of action against various microbes, will be adequate for proper coverage. Whereas in the case of larger wounds created by organic matter associated with tissue necrosis, a broad-spectrum antifungal like Natamycin 5 % can be added after sending the sample for fungal culture and sensitivity modifying the medication based on culture report.