CAROLINE J. MACEWEN
Directorate of Opthalmology, Ninewells Hospital and Medical School, Dundee, U.K.
Approximately half of all patients who present to an eye casualty department do so because of ocular trauma. In Scotland, the cumulative incidence of ocular trauma requiring admission is 8.14 per 100 000 of the population annually. Over 10% of these people will lose useful vision in the injured eye. This review discusses the mechanisms of ocular trauma, its management and potential outcomes, and the changing trends in the pattern of ocular injuries.
Keywords: ocular trauma, management
J.R.Coll.Surg.Edinb., 44, October 1999, 317-23
Ocular trauma, once described as the ‘neglected disorder’1, has recently been highlighted as a major cause of visual morbidity. Annually, over 2.5 million Americans suffer an eye injury, and globally more than half a million blinding injuries occur every year. World-wide, there are approximately 1.6 million people blind from eye injuries, 2.3 million bilaterally visually impaired and 19 million with unilateral visual loss; this being the commonest cause of unilateral blindness today.2 The age distribution for the occurrence of serious ocular trauma is bi-modal, with the maximum incidence in young adults and a second peak in the elderly.3,4 Both hospital and population based studies indicate a large preponderance of injuries affecting males.5,6,7 So, in addition to the impact on affected individuals there are profound social implications regarding the lost productivity by young men and requirement of caring facilities and rehabilitation for the elderly. The overall financial costs can only be an estimate but direct and indirect costs taken together are known to run into hundreds of millions of dollars annually.8 Developing countries carry the largest burden, yet are the least able to afford the costs.9,10
Approximately half of all patients who present to an eye casualty department do so because of ocular trauma.11,12 The spectrum of injuries ranges from very mild, non-sight threatening to extremely serious with potentially blinding consequences. As expected, the majority of injuries are minor, affecting the peri-orbital structures or the ocular surface such as corneal abrasions or superficial corneal foreign bodies. Only 2-3% of all eye injuries require hospital admission6,11 and it is this small minority of cases that are of interest with regard to management and outcome, and therefore have attracted most attention. Currently, in Scotland, the cumulative incidence of ocular trauma requiring hospital admission is 8.14 per 100 000 of the population annually.13 Over 10% of these people will lose useful vision in the injured eye.
Serious eye injuries involving the orbit or intra-ocular structures are usually classified into those caused by blunt objects, large sharp objects, small flying particles or burns. The type and extent of damage sustained by a traumatised eye depends on both the mechanism and force of the injury. Penetrating injuries, whether due to large or small objects, are known to carry a poorer prognosis than contusional injuries. However, considerable disruption of the globe may occur with severe blunt trauma which causes tearing of intra-ocular structures and diffuse changes secondary to energy absorption by the tissues.
Blunt Injuries
A direct blow to the eye and surrounding tissues causes a blunt, contusional injury. This may result in a spectrum of injuries ranging from a simple ‘black eye’ to severe intra-ocular disruption, including rupture of the globe. When the eye is struck, it is compressed antero-posteriorly and correspond-ingly stretched in the equatorial plane which causes a combination of contusional and tearing damage, resulting in a well recognised pattern of injuries (Figure 1). The increase in intra-orbital pressure may result in a blow out fracture as the floor of the orbit decompresses into the maxillary antrum (Figure 2). This is a rare but important type of facial fracture, that may result in damage to the inferior rectus muscle and orbital septae, causing restriction in eye movements and diplopia, both of which are difficult to treat effectively.
Figure 1: Blunt trauma to the eye results in a well recognised pattern of injury
Figure 2: Radiograph of blow out fracture to the left orbit, with inferior orbital contents herniating into the maxillary antrum (arrow)
When the eye is struck, the cornea is flattened and the intra-ocular pressure rises rapidly. The anterior chamber is compressed and the pupil is forced to dilate rapidly which may tear areas of the sphincter pupillae, causing traumatic mydriasis. The aqueous humour is forced peripherally, leading to damage to the drainage angle which, if extensive enough predisposes to glaucoma at a later date. There is tension on the peripheral iris which may disinsert from its root (iridodialysis; see Figure 3). Bleeding from any of these areas of the highly vascular iris causes a hyphaema, and the hyphaema is the hallmark of severe intra-ocular blunt trauma. Most hyphaemas absorb spontaneously within 2-6 days of the injury and the prognosis of an uncomplicated hyphaema is excellent. Rarely, increased intra-ocular pressure and/or secondary haemorrhage 3-5 days later may complicate the bleed and result in corneal or optic nerve damage. The importance of a hyphaema is that its presence indicates that the eye has suffered a significant injury, and structures within the anterior and posterior segments are likely to be damaged, which may require prophylactic treatment. A full ocular assessment is, therefore, mandatory, paying particular attention to the intra-ocular pressure, structures within the drainage angle, clarity and stability of the lens, the posterior pole and the peripheral retina.
Figure 3: Iridodialysis: the iris has become separated from its root, causing a peripheral cleft at the limbal region
A concussional cataract is an acute lens opacity, which may disappear in the days following a blunt injury. Alternatively, it may be progressive requiring surgical removal. The supporting lens zonules may partially or completely rupture, causing a lens subluxation or complete dislocation, respectively. The lens usually dislocates posteriorly into the vitreous cavity, but may be found in the anterior chamber where, because of constraints in space, it is likely to cause damage and, therefore, needs to be removed.
In the posterior segment, the vitreous humour is firmly attached in the region of the anterior retina, and stress on this area causes disinsertion of the peripheral retina (retinal dialysis), which will result in a retinal detachment (Figure 4) if not treated prophylactically. Stretching of the vascular choroid causes a choroidal rupture which appears as sub-retinal blood; this gradually clears to reveal an arcuate choroidal scar. Unfortunately, this has a predilection for the macular region, with loss of central acuity. Retinal oedema and haemorrhage, usually over a localised area, are seen as commotio retina. The photoreceptors and underlying retinal pigment epithelium may be irreversibly damaged and, depending on the part of the retina affected, may result in loss of acuity or field of vision. Any damage in the posterior segment may result in vitreous haemorrhage, usually due to a uveal tract rupture, a retinal blood vessel injury, a retinal tear or a scleral rupture. Full thickness globe ruptures usually occur at the corneo-scleral limbus, under the insertion of one of the rectus muscles or around the entrance of the optic nerve posteriorly. There is often loss of the lens and prolapse of the uvea and vitreous at the time of the injury.
Figure 4: Peripheral retinal tear: the retina is rolled over to expose the underlying choroid
There is a specific type of localised trauma, caused by air gun pellets. These strike the eye, but have insufficient momentum to penetrate the globe. They cause an intense force over a small area on the scleral surface, causing a rupture of the underlying choroid and retina. Shock waves from the impact site lead to distant damage, with vitreous and sub-retinal haemorrhage and damage to the photo-receptors.
Penetrating Injuries
Penetrating injuries, overall, carry a poorer prognosis than blunt injuries, although the extent of damage depends on where and how far the object enters the eye. Wounds that are isolated to the cornea, may not penetrate the anterior segment structures and, if small, may self seal with little visual morbidity, especially if they are off the visual axis. The iris may plug the wound, resulting in an irregular pupil (Figure 5). Larger or more complex corneal wounds require closure resulting in scarring, which itself may be visually disabling. Penetrating injuries of the anterior segment may involve the anterior capsule of the lens, causing a localised or, more commonly, a diffuse lenticular opacity. As part of the protective reflex, the eye rotates upwards as it closes (Bell’s phenomenon), and penetrating injuries are often situated inferiorly in the sclera. The vast majority of such scleral and corneo-scleral wounds involve underlying structures, and prolapsed iris or choroid need to be replaced or removed prior to closure of the wound. Posterior wounds involve the retina, and the development of vitreo-retinal traction and scarring in the period after the injury are important factors in the development of complex retinal detachments.
Figure 5: An irregular pupil: the iris has plugged the small corneal wound
Intra-ocular foreign bodies
Foreign bodies that enter the eye may cause damage in two ways: 1) they may cause structural damage to the intra-ocular contents as they enter and pass through the eye; and 2) they may cause toxicity to tissues as they degrade or oxidise, if not removed rapidly. Most particles that have sufficient momentum to penetrate the cornea decelerate within the anterior chamber and can be seen sitting on the iris, although some may fall down into the inferior drainage angle, making localisation difficult. A deeper wound may penetrate the lens capsule resulting in cataract formation over the ensuing days to weeks. Foreign bodies that enter the posterior segment may remain suspended in the vitreous or may strike the retina causing bleeding or formation of a retinal tear. Through and through penetration of the eye is rare except in cases of gun shot wounds. In such cases the energy and shock waves dissipated within the eye causes disruption of the contents.
Inert, non toxic, sterile materials such as plastic and glass are well tolerated within the eye, but most intra-ocular foreign bodies occur from metal striking metal. The majority of these are magnetic, and particles containing iron oxidise to set up an inflammatory reaction within the eye (siderosis). Vegetable matter may also induce a severe response with endophthalmitis. Therefore, it is vital that these foreign bodies are removed without delay and in order to plan removal, the composition and location of the material are important. Localisation may be straightforward on clinical examination, but there are inaccessible parts of the eye that require special lenses or radiological investigations.
It is not uncommon for small particles to enter the eye via an entry site that is very difficult to identify, even with the assistance of slit lamp magnification. Damage to the intra-ocular contents may also be undetectable at the time of injury. This is a potential medico-legal minefield for accident and emergency departments. An eye with even the slightest suspicion of an injury of a penetrating foreign body must be radio-graphed or fully examined by an ophthalmologist in order to exclude or locate the material.
Burns
Burns to the eye caused by strong acids or alkalis are amongst the most urgent of ophthalmic emergencies. The outcome of any chemical burn depends on the concentration and pH of the offending agent and duration of exposure. Alkalis, in particular, cause severe injuries, as they damage cells and penetrate the tissues rapidly. Acid injuries tend to be less severe, as they remain confined to the ocular surface. Mild burns result in loss of the corneal and conjunctival epithelium, which is usually fully recoverable. More severe injuries cause ischaemic damage to the limbal area, which affects the epithelial stem cells that are vital for subsequent epithelialisation and, hence, recovery of the eye. At the initial examination valuable information can be obtained regarding the severity and, thus, prognosis of the injury by evaluating the amount of epithelial loss, the degree of limbal ischaemia and the haziness of the cornea.
Following the injury, re-epithelialisation commences, although this may be hampered or prevented by either loss of epithelial stem cells in the limbal region or persistent inflammation. Re-epithelialisation is vital to prevent excessive collagenase activity which leads to progressive corneal thinning and ultimately to perforation if the eye. Even if the epithelialisation does take place, the vision may be reduced due to tear and mucin deficiencies, corneal opacification and vascularisation, collagen shrinkage, cataract formation and necrotic peripheral retinopathy.
The prognosis for severely injured eyes has improved with the development of advanced microsurgical techniques and better understanding of tissue reaction to trauma from which surgical and medical protocols have been derived. In addition, better methods of visual rehabilitation have improved the final visual function.
In the immediate period after the injury, the rapidity with which treatment is instituted may have an important effect on the final result. This is most pronounced in chemical burns where every second may count. Immediate, copious irrigation of the affected eye with water at the time of the incident may improve the prognosis considerably. Speed is also vital in penetrating injuries where measures to prevent secondary further loss of intra-ocular tissues from the eye are required. Control of raised intra-ocular pressure after blunt trauma reduces the patient’s pain and prevents secondary corneal and optic nerve damage.
An open eye should be repaired as soon as feasible, and closure of a rupture or penetrating wound should always be attempted, even in an apparently disrupted eye, as it is impossible to give an accurate prognosis at the time of the injury. Even in irreversibly damaged eyes it is psychologically easier for the patient to accept the loss of an eye some days after the initial injury, and primary closure should always be attempted. The development of sympathetic ophthalmia in the other eye has always been a concern with penetrating injuries, but this possibility is not a good reason to remove an eye. Sympathetic ophthalmia is a bilateral granulomatous inflammatory response to a full thickness perforating injury in one eye. It is extremely rare and is now considered to be a treatable condition using steroids and cytotoxic agents.
Because a smooth, transparent, regular cornea is so important in the formation of a clear retinal image, the accurate micro-scopic repair of corneal wounds is essential. Corneal laceration repair aims to restore the integrity of the globe, but at the same time minimise scarring and prevent distortion of the wound which would induce unwanted astigmatism. The development of atraumatic needles and inert mono-filament suture materials have helped to achieve these goals, and an effective primary repair prevents the complication of further scarring from a secondary procedure. Any iris tissue which is adherent should be removed from the wound, as this delays healing and distorts the wound. An intact iris lens diaphragm should be retained, if possible, as this improves the final visual outcome. If the lens capsule is damaged, then the lens will almost inevitably have to be extracted. This can be carried out at the time of the primary repair or as a secondary procedure, depending on the extent of damage and facilities available. Small breaches in the anterior capsule may be left for a short while, but gross disruption will result in inflammation if left, and requires immediate removal of the lens. Extraction through the injury site is usually impossible and a second incision has to be fashioned. Small incision cataract surgery using phaco-emulsification means that the lens can be broken up and removed with minimal further disruption to the eye.
Scleral lacerations or ruptures require primary closure as soon after the injury as possible, in order to restore normal anatomical relationships and reform the collapsed eye without incarceration of uveal tract or vitreous in the wound. This should allow orderly wound healing without the complications of abnormal fibrocellular repair, which would hinder any further surgical procedures. Secondary procedures to repair damaged intra-ocular structures are commonly required after these injuries, but appropriate immediate management is imperative in order to stabilise the eye and leave it in an optimum state for the next step in treatment.
A major advance in the management of all forms of posterior segment trauma has been the development of the three port pars plana vitrectomy. This is a closed ocular procedure that allows successful clearance of persistent intra-ocular blood, extraction of intra-ocular foreign bodies and repair or removal of damaged intra-ocular tissues while maintaining an inflated globe. The eye is entered via three 20 gauge sclerotomies in the pars plana; one for an infusion cannula, one for an intra-ocular light and the other for a variety of standard gauge instruments, such as cutters, forceps and magnets (Figure 6). The surgical procedure is visualised through the dilated pupil and a contact lens, which can be sutured to the eye allowing a three dimensional view of the internal eye. The vitreous cavity is cleared using a suction/cutting device, and this may involve removal of blood and the division of vitreo-retinal scar tissue. If the lens is damaged or unstable, it can either be fragmented and removed through the vitrectomy port, or floated into the anterior chamber with heavy liquids and removed via a larger incision. Traumatic retinal detachments can be flattened with the assistance of intra-ocular gases or perfluorcarbon heavy liquids, which allow isolation and treat-ment of the responsible retinal tears with intra-ocular laser delivery systems or external cryotherapy. Long acting expanding gases (SF6, C3F8) or silicone oil can be left inside the eye at the end of the vitrectomy in order to tamponade the tears for prolonged periods of time.
Figure 6: Vitrectomy: a closed intra-ocular procedure
Immediate vitrectomy, as a primary procedure for the removal of an intra-ocular foreign body, is the treatment of choice, in order to rapidly remove any toxic or infected material and to repair any associated damage. Otherwise vitrectomy should not be considered until 10-14 days after a blunt injury or following the primary repair of a laceration as this allows time for choroidal effusions to settle and a posterior vitreous detachment to develop, both of which ensure a safer, more effective procedure.
Extensive clinical and laboratory based research into the response of the eye to chemical burns has led to the formulation of clear medical protocols which promote the re-epithelialisation of the ocular surface and reduce the incidence and extent of corneal and scleral melting. These involve the use of collagenase inhibitors, free radical scavengers, topical antibiotics, steroids and ocular hypotensives being introduced and withdrawn at strategic times following the burn.14 The long term results of serious ocular burns remain disappointing as the whole ocular environment is destroyed, although attempts to re-populate the corneal epithelium are encouraging using epithelial stem-cell transplantation, which may improve the ocular surface.15
Regarding rehabilitation of injured eyes, various methods of correcting optical abnormalities, which were previously insuperable, are now commonplace. Large diameter rigid contact lenses with flexibility and high permeability are extremely valuable in restoring the irregular corneal surface, which is vital for good acuity. Excimer laser photo-therapeutic keratectomy can also be used to permanently alter the shape of the cornea and remove scars. Small foldable intra-ocular lens may be inserted via tiny incisions into eyes which have retained supporting capsule and, even if all supporting structures have been removed at the time of the injury, replacement of the lens is possible. Complex methods of suturing specially constructed large diameter lens implants into the sulcus have been devised to minimise further incisions and restore vision to the aphakic eye.
CHANGING TRENDS IN THE PATTERN OF OCULAR INJURIES
The causes of ocular trauma have changed continuously over the course of this century in the UK. The introduction of effective preventative strategies and changes in work practices and lifestyle have led to fewer injuries; there has also been an evolution in the type of injury which means that those sustained are less severe in type and nature than previously. Almost 100 years ago more than 70% of all serious injuries occurred in the workplace.16 With heavy industry and no knowledge of protective devices industrial accidents were common. The type of injury sustained was usually a metallic intra-ocular foreign body and the prognosis for vision was poor. Appropriate standards for eye protection were introduced and decline of heavy industry further reduced this cause and type of injury. The road traffic accident took over as the most common cause of serious injury in the 1960s and 1970s, with car occupants suffering penetrating injuries due to windscreen glass.17 These were often bilateral and commonly blinding. The introduction of laminated windscreens and the seat belt law virtually eliminated this problem.18 Sport and leisure activities became the main source of serious eye injuries in the 1980s with sports associated eye injuries becoming responsible for most cases of hospitalised eye trauma.6,19,20 These injuries were mostly blunt in nature, which meant a better prognosis than the previously more common intra-ocular foreign bodies and penetrating trauma. Recognition of this led to the introduction of preventative strategies and protective devices which meet a British standard (at least for some sports). The home is now the most common location for an eye injury of sufficient severity to warrant hospital admission.4 The home has long been recognised as an important area for other types of injury to occur, and the increasingly large elderly population has made this even more likely.
In the past, children were identified as suffering a disproportionate amount of serious ocular trauma, with more penetrating injuries and a poorer visual outcome than adults.5 Recently, the pattern of paediatric ocular trauma has been shown to have changed with fewer, less severe injuries, which have a better outcome than their adult counterparts.21 The reasons for this are not entirely clear, but effective prevention in the form of better supervision of children is the most likely explanation.
While eye injuries remain a cause for concern, fewer, less severe injuries, due to socio-economic change and effective preventative strategies, combined with modern surgical and medical management have led to an improvement in the over-all outcome in countries that have these means at their disposal.
Copyright date: 20th August 1999
Correspondence: Dr CJ MacEwen, Directorate of Ophthalmology, Ninewells Hospital and Medical School, Dundee DD1 9SY, UK
©1999 The Royal College of Surgeons of Edinburgh, J.R.Coll.Surg.Edinb.,44; 5: 317-23