Continuing Education Activity

Intraocular foreign body (IOFB) is an accidental injury usually resulting from chisel hammering and firearm use. It is a serious ocular condition that can potentially cause permanent vision loss. To avoid the high morbidity associated with this condition, it must be promptly diagnosed and treated. This activity reviews the evaluation and treatment of an IOFB and highlights the role of the interprofessional team in evaluating and treating patients with this condition.

Objectives:

• Explain the pathophysiology and review the risk factors for IOFB.
• Summarize the typical presentation of a patient with IOFB.
• Describe the common physical findings in patients with IOFB.
• Review the management considerations for patients with IOFB.

Introduction

Ocular injuries are a major cause of blindness.[1] They continue to be a public health problem worldwide.[1][2]  Among these, intraocular foreign bodies (IOFB) are a major cause of morbidity in the young population.[3] IOFB associated ocular trauma is unique and requires skillful investigation with early treatment. IOFB is mostly metallic.[4] They are usually generated during chisel hammering, drilling, gunshot, or bomb blast. Manual laborers are at high risk.[5]

They can lodge in any part of the eye, either in the anterior or posterior segment. Since they are sharp and are generated at high speed, they mostly get lodged in the posterior segment. According to a study, about 2/3rd of IOFBs were found in the posterior segment.[6] With the advancement of surgical techniques, many eyes can be saved, and good final visual acuity can be achieved.[7] Visual prognosis depends upon multiple factors, including size, site, the composition of foreign body, inflammatory response, tissue damage, time since injury, and any associated endophthalmitis and retinal detachment.[8]

Etiology

Hammering is the most common mode of injury.[9] According to a study, the mechanism of injury was hammering in 43%, metal cutting in 19%, chiseling and drilling in 10%, gardening in 5%, fall from height in 5%, and unknown in 14% of cases.[9] Other modes are firearm and blast injuries that are common in war zones.[10]

Epidemiology

In the USA, the incidence of ocular injuries is 2.4 million cases.[9] IOFBs account for 17 to 41% of open globe injuries.[11][12] The majority of IOFBs occur in young working males.[13][14][15][16][17]. Home-related works account for only a minority (13%) of injuries.[6]

Workers and farmers are the two most common occupations because they are involved in hammering, drilling, chiseling, and shoveling. These activities generate more foreign bodies. The annual incidence rate of IOFBs is approximately 0.16 per 100,000 in the United Kingdom.[6] But only 0.77 to 6% of patients with an IOFB wear protective eyewear.[18][19][20] Thus, adequate safety measures at work should be taken.

Pathophysiology

Ocular injury caused by an IOFB depends on its velocity, size, nature, entry site, and impaction.[21] Small and sharp IOFB like iron chips cause a small and linear perforation at the entry site. Such perforations are easy to repair. Large, irregular projectiles like stone particles cause a ragged and large wound at the entry site. They cause significant tissue damage and are difficult to repair. IOFBs generated at high speed generally lodge in the posterior segment of the eyeball. They can also ricochet inside the eye, causing injuries at multiple sites.[14] 

Metallic foreign bodies are the most common type.[20] Iron and copper foreign bodies are highly reactive. Fe and Cu can cause metallosis.[22] They release metallic ions, which deposit in the various ocular tissues.

Ocular damage with iron foreign body results in siderosis bulbi. It is a pigmentary, degenerative process due to chronic retention of an iron IOFB.[23] The iron particles get deposited in structures of epithelial origin such as the cornea, lens, trabecular meshwork, iris, and retina. In the cornea, the pigments get deposited in the stroma or the endothelium.[24] In the iris, iron deposition is noted in the stroma and epithelium, leading to greenish-brown discoloration and iris heterochromia.[25]

The pupil may become fixed and dilated. The pupil may show denervation hypersensitivity.[26] Iron deposition causes pigmented trabecular meshwork and secondary open-angle glaucoma.[27] Cataracts may be seen with anterior subcapsular deposits. Siderosis affects the retinal pigment epithelium resulting in retinal degeneration.[28] 

An inflammatory reaction to a copper foreign body results in chalcosis.[29] The ocular fluid dissolves the metal, which gets deposited in the corneal stroma, Descemet membrane,  endothelium, anterior lens capsule, internal limiting membrane, and superficial retina.[30][31] The clinical manifestation depends upon the copper content. The copper content of more than 85% presents with supportive endophthalmitis and disseminated copper deposits.[29][32][33] Copper content less than 85% presents with localized copper deposits (chalcosis bulbi).[29] Iron ions are deposited intracellularly, and the deposition of copper ions is seen in basement membranes.

Organic foreign bodies such as animal hairs, insect parts, thorn, and vegetable matter are contaminated and cause fulminant endophthalmitis.[34] Foreign bodies such as glass and plastic are inert.[35] They are well-tolerated and do not cause any significant reaction.[36] In blast or firearm injuries, multiple splinters are generated, which can lodge in the various parts of the eye. They are more damaging and difficult to remove.[10] Foreign bodies entering through the cornea cause significant corneal scarring and may have a bad prognosis.[21]

Histopathology

Long-term retention of copper and iron foreign body can cause chalcosis and siderosis, respectively.[37] Histologically, Prussian blue stains the iron blue.[38] Blue staining can be seen in the epithelial structures and areas of scarred trabecular meshwork and scarred retina. On electron microscopy, intracellular sideromes can be seen in the corneal keratocytes, lens epithelium, and outer segments of the photoreceptors.[39] Copper deposits in the ocular tissue can be detected by staining with rhodanine, rubeanic acid, and alizarin blue stains.[29]

History and Physical

A detailed history is essential to know about the mechanism of injury and the nature of the foreign body. Trivial injuries are often difficult to detect. The patient presents with conjunctival congestion and blurring of vision or may be asymptomatic.[40] A careful history that something hit the eye often reveals the diagnosis of an IOFB. History should be taken whether one or both eyes were involved or not. Firearm and blast injuries generate multiple small splinters, which can cause bilateral injuries. Proper history and documentation are essential due to medicolegal issues and large monetary compensation in cases of missed intraocular foreign body.

A meticulous examination is very important. Presenting and best-corrected visual acuity should be recorded. Lids and eyebrows should be examined to look for external signs of injuries and small foreign bodies. Slit-lamp examination is a must. Careful examination should be done to look for conjunctival laceration, hemorrhage, and entry site of IOFB. Pigment under the conjunctiva may indicate uveal prolapse and possible entry site. Corneal perforation should be examined.

The extent of the defect and its location should be recorded. A Seidel test should be performed. Iris should be inspected for transillumination defects and heterochromia (usually seen in longstanding cases). The entry wound of the cornea and iris may help in localizing the foreign body. The lens should be evaluated for pigmentation, focal opacity, cataractous changes, capsule rupture, and phacodonesis.

Gonioscopy is done to look for trabecular pigmentation, scarring, and foreign body, especially in the inferior angle of the anterior chamber. Intraocular pressure should be noted. However, in an obvious open globe injury, any undue pressure on the globe should be avoided as it may lead to extrusion of intraocular contents. Most foreign bodies are located in the posterior segment.

Dilated fundus examination is essential. The retina should be inspected to locate the site of impaction of the foreign body. Often a fibrous capsule forms over it, and there may be surrounding pigmentary changes. Optic atrophy may be present in longstanding cases. In cases of media haze due to cataracts, vitreous hemorrhage, or endophthalmitis, the USG (ultrasonogram) B scan is done to locate the foreign body and measure the size.

Evaluation

Detection and localization of the IOFBs are essential. Anterior segment photography using a slit-lamp or fundus camera helps document the disease and may be helpful in counseling the patient about their clinical condition.

X-ray of orbits (anteroposterior and lateral view) can detect metallic foreign bodies but cannot detect radiolucent objects like wood or glass. It also reveals multiple metallic foreign bodies, if present. X-ray orbit with a limbal ring-rod sutured at the limbus and a proportionate geometric drawing can be used to localize an intraocular IOFB.[41] Another method is the Sweet localization technique which involves frontal and lateral projections.[42]

The patient's X-ray is taken with his eye at primary gaze. Then he is asked to look sideways, and again an X-ray is taken. If the foreign body is intraocular, it will rotate with eye movement. If it rotates in the same direction as the eye, then the IOFB is in the anterior segment. If it rotates in the opposite direction, then it is in the posterior segment.

USG B scan is a cheap and useful investigation to detect metallic foreign bodies. The metallic body appears as a hyperechoic structure with acoustic shadowing and a high spike on A-scan. Aluminum, steel, and bottle glass usually show a flashlight artifact, a focused and narrow ring-down artifact.[43] Lead, windshield glass, copper, and silver usually show a headlight artifact which is a broad and dense artifact.[43] 

Ultrasound has varied detection rates for a glass IOFB ranging from 24 to 97%.[44] A glass foreign body can appear as a hyperechoic lesion with a back shadow, or it can show a comet tail (reverberation) artifact.[45] The wooden foreign body usually appears as a hyperechoic structure, and dry wood may show faint reverberations.[43] A plastic foreign body can be of low echogenicity (spectacle) or high echogenicity (polyvinyl chloride, PVC).[43] An air bubble is hyperechoic on B-scan and produces a single-peaked 100% high spike on A-scan.[46] USG can also detect retinal detachment, vitreous hemorrhage, and vitreous exudates. However, the USG B scan should be avoided in an open globe as the pressure from the ultrasonic probe may further increase the damage and may cause extrusion of ocular contents. USG B scans can, however, be done safely after the repair of the open globe.

CT (computed tomography) scan can accurately detect the number, size, shape, and location of a foreign body.[47] A wooden foreign body has low attenuation with no artifact. A plastic IOFB has moderate attenuation with no artifact. A glass foreign body has high attenuation and no artifact. A metallic foreign body has high attenuation with a shadow artifact and a 'scatter' artifact around the object's edge.[43] The CT can give the exact relation of ocular coats with the IOFB, as IOFBs, which are deeply buried in the ocular coats, may be difficult or impossible to remove surgically.[14] 

MRI (magnetic resonance imaging) can detect organic and glass objects with greater sensitivity. MRI is contraindicated in the metallic foreign body as it can dislodge it and cause further damage.[48] 

Ultrasound biomicroscopy (UBM) can detect a foreign body at the angle of the anterior chamber, behind the iris, and ciliary body. UBM uses a 50 MHz frequency and has a penetration of 5mm, which allows for finer resolution.[49][50] As it requires contact, it should be avoided in open globe injuries. The 35 MHz probes can image deeper tissue, including the ciliary body and pars plana.

Anterior segment optical coherence tomography (AS-OCT) is a non-contact imaging modality and helps visualize the anterior segment IOFBs.[51] It has greater patient comfort and compliance than UBM. However, it has poor penetration across the pigmented layer of the iris. Thus IOFBs lying behind the iris might be missed.[52] 

Patients with long-standing iron IOFB present with siderosis. The full-field electroretinogram (ERG) is done to know the status of the photoreceptors' function. In the early stages, increased amplitude of a-wave and b-wave is present (supernormal response).[53] This is because the photoreceptors start recovering from the sudden insult.[54] Then a steady decrease is seen in the b-wave amplitude with a reduction in b: a wave amplitude ratio to less than 1.[53] In end-stage diseases, both waves are extinguished.[55] 

Patients with chalcosis show reduced b-wave amplitude on ERG. A hyper-normal b-wave is not observed. Then a steady decrease is seen in the b wave amplitude. An abnormal ERG  precedes the clinical findings in almost 50% of patients.[56] However, the ERG changes in chalcosis are less severe than in siderosis: ERG waves decrease to 50% and remain stable at that level for many years.[57] Preoperative ERG helps to prognosticate the cases after IOFB removal. Based on the ERG findings, the patient can be counseled about the chances of visual recovery after a successful surgery.[27]

Multifocal ERG may detect subclinical siderosis bulbi even if full-field ERG is normal.[58]

Treatment / Management

The goal of surgery is to prevent further damage and restore the ocular anatomy as far as possible. Functional restoration or visual gain is the secondary goal. The visual prognosis is usually guarded if retinal detachment or endophthalmitis is present. The IOFB should be localized on the CT scan, whether it is intraocular or extraocular or impacting the visual pathway or not.

The injured eye should be protected with a shield. During the examination, the eye should be gently handled. External pressure should be avoided as it may expel the intraocular contents. Tetanus toxoid (intramuscular) injection should be given. The contaminated part should be cleaned with a sterile solution, and small superficial foreign bodies should be removed in the absence of an open globe. Broad-spectrum intravenous antibiotics may be considered as prophylaxis against endophthalmitis. Endophthalmitis is a dreaded complication and is associated with 7 to 13% of IOFB cases.[59] Iron and copper foreign bodies should be removed as soon as possible as they are highly reactive. Stainless steel and aluminum may be better tolerated.[60] Organic matter and stone pieces are contaminated and have a high risk of endophthalmitis.[61] They should be removed as early as possible.

The position of the IOFB should be preoperatively localized in the anterior or posterior segment. The first step is the primary repair of the ocular coats (cornea and/or sclera) of the open globe. Meticulous closure of the perforation site is done first.[62] The anterior chamber should be formed, and the repaired wound should not leak at the conclusion of the surgery.

IOFB in the anterior chamber: The IOFB might be located in the anterior chamber. The perforation site should be inspected. Its extent should be noted. Iris or uveal tissue prolapse is ascertained. The corneal perforation should be repaired with 10-0 monofilament nylon sutures. Scleral perforation is repaired with a 6-0 or 7-0 polyglactin 910 suture. The anterior chamber should be formed with viscoelastic solutions. Any exudates or hyphema in the anterior chamber should be washed first. Small and mobile IOFB can be removed with viscoexpression or an intraocular magnet. If it is immobile due to surrounding fibrosis, then the IOFB should be removed with forceps. 

The IOFB should not be removed through the entry wound.[16] A separate incision should be made for its removal. The anterior chamber aspirate can be sent for microbiological evaluation if there is hypopyon or evidence of infection. A thorough anterior chamber wash should be done to remove all the debris. If the anterior lens capsule is ruptured, the cortical matter is washed. Gentle lens aspiration can be done, or the patient can be taken in second sitting for lens aspiration and intraocular lens implantation.

Intralenticular foreign body: IOFB might be impacted in the crystalline lens. The cataractous lens should be evaluated for the position of IOFB and posterior capsule tear.[63] If the IOFB is impacted in the posterior capsule or a large posterior capsular rent is present, then the whole cataractous lens should be taken out along with the IOFB.[64] Hydrodissection should be avoided as it might cause the posterior capsular tear to enlarge. This might then cause the lens or the IOFB to drop into the vitreous. Thus the possibility of posterior capsular tears should always be kept in mind when devising a surgical plan. If a preexisting posterior capsular tear is possible, a gentle aspiration and nucleus expression is done, and one should be prepared for anterior vitrectomy.[63]

Foreign body in the anterior chamber angle: A foreign body must be ruled out in the angle when not observed on initial examination. Gonioscopy should be done gently.[65] An imaging study should be performed to confirm the diagnosis. CT scan, UBM, and ASOCT help diagnose by accurately estimating the foreign body size and location.[66] The foreign body may be removed by an external approach using a large electromagnet or through an internal approach by forceps or intraocular magnets.[67]

Posterior segment IOFB: Accurate localization is necessary preoperatively. CT scan accurately localizes it in the ocular coat, anterior segment, posterior segment, or extraocular location.[68] Vitreous surgery provides excellent visualization and allows the removal of hemorrhage and exudates. Three standard scleral ports are made. Lensectomy is done if the lens is cataractous, or cataract surgery through the clear corneal/limbal/scleral incision may be performed. If possible, the anterior capsular rim should be preserved to enable a ciliary sulcus intraocular lens implantation. Then core vitrectomy is done. A posterior vitreous detachment is induced. The IOFB is localized. The adhesions and fibrous capsules around it are excised. It is mobilized and brought over the retinal surface. Its shape and size are determined. Accordingly, the decision is taken to remove it through the anterior or pars plana route. If the IOFB is large, it is better to remove it through the anterior route through a corneoscleral tunnel. A large IOFB requires a large pars plana incision which increases the chances of retinal incarceration, vitreous prolapse, and retinal detachment.[69] A small IOFB can be safely taken out through the pars plana. The IOFB, once freed from the surrounding adhesions, can be taken out with the help of an intraocular magnet or intravitreal forceps. PFCL (perfluorocarbon liquids) can be injected over the macula to protect it in the event of a fall of the IOFB in the process of extraction. 

The site of impaction should be laser barraged. The retinal periphery should be inspected for additional breaks. If retinal detachment is present, a complete vitrectomy should be done, followed by fluid air exchange, endolaser photocoagulation, and silicone oil tamponade. If the retina is attached, then the retinal break should be laser barraged. The scleral ports are closed tightly.

Differential Diagnosis

An IOFB is a clinical diagnosis. Sometimes trivial trauma is not reported by the patient. They present after a few years with signs of siderosis. This can resemble a retinal degenerative condition such as retinitis pigmentosa with pale disc and retinal pigmentary epithelial degeneration.[70] 

In chalcosis, the copper deposition will be seen near the limbus in the Descemet membrane, the Kayser-Fleischer ring similar to Wilson disease.[31][71][72][73] Sunflower cataracts may be present.[31] The vitreous may be opacified due to faint dust-like particles.[71] In these cases, a CT scan can detect a small IOFB. These findings will be absent in retinitis pigmentosa.

Sometimes, a fibrous tissue encasing an old retinal IOFB in the periphery can resemble a Toxocariasis granuloma. Ocular Toxocariasis is seen in young children with a history of close contact with a puppy.[74] A detailed history about the mode of injury often rules out this condition.

Prognosis

The prognosis of an IOFB depends upon multiple factors.[75]

• Timing of presentation: Early presentation and management have a good visual outcome. Patients presenting late develop siderosis (in case of iron foreign body/bodies) and have a poor prognosis.[76]
• Presenting visual acuity: If the presenting vision is good, then the final prognosis is generally good.[77][78]
• The extent of injury: Small perforation of the sclera has a good prognosis.[79] Central corneal perforation is associated with scarring in the visual axis and poor vision.[21]
• Location of the foreign body: Foreign body in the anterior segment has good visual outcome than the posterior segment IOFB.[80][4]
• Type of injury: Globe rupture and perforating injuries have a bad prognosis.[81]
• Associated features: The presence of an afferent pupillary defect, hyphema, vitreous hemorrhage, retinal detachment, proliferative vitreoretinopathy, or endophthalmitis has a bad visual outcome.

The prognosis of an IOFB can also be predicted with the help of an Ocular trauma score (OTS). It was proposed by Kuhn et al. in early 2000 to predict the final vision of an injured eye.[82] The variables used in the OTS are initial vision,  globe rupture, perforating injury, retinal detachment (RD), endophthalmitis, and afferent pupillary defect (APD). Each variable is given a score. The initial vision of NPL is given 60 points. Other scores include PL (perception of light)/HM (hand movements)- 70, 1/200 to 19/200- 80, 20/200 to 20/50- 90 and >=20/40- 100 points. Assigned scores for various various features include  globe rupture- -23, endophthalmitis- -17, perforating injury- -14, RD- -11, and APD- -10 points. All six scores are added to get a raw score. The conversion of raw scores into the OTS may predict the probability of final vision.[83]

Complications

Anterior segment injuries can cause corneal scarring, traumatic cataract, iris defect, hypopyon, hyphema, and open-angle glaucoma. IOFB in the posterior segment can cause endophthalmitis, retinal detachment, proliferative vitreoretinopathy, and phthisis bulbi.[84][81][85] Trauma to the optic nerve or siderosis can cause optic neuropathy. Sympathetic ophthalmitis[86] is seen in 0.5% to 2.0% of cases.[87]

The incidence of infectious endophthalmitis has been reported in 7 to 13% of IOFB cases.[59] The mean incidence is 6.8%.[88] A delay in managing more than 24 hours is associated with an increased risk of infectious endophthalmitis.[4] The risk of endophthalmitis in an IOFB has been reported to increase with age.[89] Early vitrectomy helps in gaining functional vision in 25 to 51% of patients.[12][88] In some cases, it helps in eye salvage without improvement of vision. The risk of phthisis should be explained in IOFB cases.[90]

Deterrence and Patient Education

As an IOFB can cause permanent vision loss, preventive measures must be taken by the patients.[81] The patients should be adequately counseled regarding the prognosis of IOFB and the importance of long-term follow-up.

Enhancing Healthcare Team Outcomes

Interprofessional communication can lead to better patient management. The patient will most often present to the primary clinician, and these professionals should be aware of the condition as it is treatable.

Prompt referral to an ophthalmologist is necessary. These patients can then be followed by their primary clinicians, and they should ensure compliance with treatment. The nursing staff will be the first in the department to come in contact with patients on follow-up. They can assess treatment progress, evaluate compliance with medication and lifestyle measures, and report any issues to the primary care clinician. This collaborative, interprofessional approach to care can ensure optimal patient outcomes.