Abdi Malik Musa1, James Richardson-May2, Joshua Adeyoju3
1Academic Foundation Year 1 Doctor, University Hospital Southampton, United Kingdom
2ST5 Ophthalmology Specialty Registrar, Ophthalmology Department, University Hospital Southampton, United Kingdom
3Foundation Year 2 Doctor, United Lincolnshire Hospitals NHS Trust, United Kingdom
Bacterial endophthalmitis describes inflammation of the vitreous secondary to bacterial colonisation. It is an ophthalmic emergency requiring prompt treatment to increase the chance of preserving sight and saving the eye. It is categorised as exogenous or endogenous in origin. Endogenous bacterial endophthalmitis is rare, resulting from the haematogenous spread of bacteria from systemic infection. Exogenous bacterial endophthalmitis, however, results from the introduction of bacteria from the ocular surface or an external source into the eye. This can occur post-operatively, following a penetrating ocular trauma, or after an intra-ocular procedure such as intravitreal injections.
The incidence rate of endophthalmitis following cataract surgery is approximately 0.14%. It is less common following intravitreal injections, which has an incidence rate of 0.06% (1, 2). Post-traumatic bacterial endophthalmitis has a higher incidence rate of up to 16.5% (3). However, given the large number of cataract surgeries performed globally, this is the leading cause of bacterial endophthalmitis. This article will focus on the recognition and management of post-operative bacterial endophthalmitis.
Pathophysiology and Risk Factors
Post-operative endophthalmitis can be acute or chronic, depending on whether the symptoms onset is within or after 6 weeks of the surgery. The most common causative organisms of acute post-operative bacterial endophthalmitis are Staphylococcus epidermidis, Staphylococcus aureus and Streptococci species (4). Chronic post-operative endophthalmitis is less common and is often caused by Propionibacterium acnes; Staphylococcus epidermidis and the fungus Candida parapsilosis are other notable causes (5). These are all commensals found on the ocular surface; conditions such as conjunctivitis, blepharitis, and nasolacrimal disease are therefore a risk factor for post-operative endophthalmitis as there is disruption of the normal ocular flora. Thus, good control of concurrent ocular surface disease is imperative prior to undertaking intraocular surgery, which should be delayed where possible to allow this to occur. Systemic conditions such as diabetes are also a risk factor, resulting in a state of relative immunosuppression which increases the risk of infection (6).
Signs and Symptoms
Symptoms of acute bacterial endophthalmitis typically begin within 7 days of surgery, with most presenting within 3-5 days (7). Onset within the first 24 hours is unusual and should prompt consideration of toxic anterior segment syndrome (TASS). The most common presenting complaint is blurred vision which may be accompanied by a red eye, pain, or photophobia (8).
On clinical examination, several signs may be present. Externally there may be lid swelling and conjunctival chemosis. Examination of the anterior chamber will show cell and flare, with a hypopyon often present; this is a layer of white blood cells that settle at the bottom of the anterior chamber, causing a fluid level. Fibrin, again a sign of significant inflammation, is often present. Corneal oedema can occur due to the inflammation and sometimes raised intraocular pressure; it can also result from endothelial failure post-operatively.
The red reflex may be blunted or absent and the fundal examination may be limited due to the anterior segment signs in addition to vitritis. In this case, an ultrasound may be required to assess the posterior pole; this will often show significant vitreous opacity from the inflammatory process, and it is important to assess for concurrent retinal detachment. Visual acuity should be accurately assessed and clearly documented as it prognosticates outcomes and thus influences the choice of intervention. Evidence of proptosis or restricted range of movements of the extraocular muscles suggests panophthalmitis, a severe complication of endophthalmitis where the infection and inflammation have spread to involve the surrounding orbital structures.
In chronic post-operative endophthalmitis, blurred vision is almost always present. However, pain is less likely to be a feature (5). The inflammation is milder, so some clinical signs, such as hypopyon, are sometimes absent. Where P. acnes is the causative organism, a white intracapsular plaque is often present (5).
Investigations and Diagnosis
Endophthalmitis is a clinical diagnosis based on the history, presenting symptoms and signs elicited from the examination. The diagnosis is confirmed by microbiological sampling. This is typically done via a “tap and inject” procedure, by taking a small sample of vitreous with a needle and syringe immediately before injecting intravitreal antibiotics. Ideally, this should be performed without delay to expedite diagnosis and commence treatment, to reduce damage from this destructive disease process. In cases where a vitrectomy is performed, a vitreous biopsy can be taken with the vitrector. An aqueous humour sample may also be obtained. These are sent for gram stain, microscopy, and culture. A positive culture is achieved in about 69% of cases, and so a negative culture does not exclude a diagnosis (8). Vitreous samples are more likely to yield a positive culture than aqueous samples (7). Where available a sample can be sent for a rapid polymerase chain reaction (PCR) testing which allows for faster and more accurate diagnosis (9).
Acute post-operative bacterial endophthalmitis is an ophthalmic emergency that requires prompt intervention on suspicion of the diagnosis. If the patient presents to an emergency department with blurred vision or pain post-operatively, it is important to involve an ophthalmologist early.
The mainstay of management in acute post-operative bacterial endophthalmitis is intravitreal antibiotics. Vancomycin plus amikacin or ceftazidime are the intravitreal antibiotics of choice, providing good coverage against the common causative organisms (10). They are given immediately following vitreous sampling to reduce delay. Some ophthalmologists choose to give adjunctive systemic antibiotic therapy, usually intravenous moxifloxacin. The Early Vitrectomy Study, a landmark trial assessing the treatment of acute exogenous endophthalmitis, found that adjunctive systemic antibiotics were not superior in improving visual acuity compared to intravitreal antibiotics alone; however, this study used intravenous ceftazidime and amikacin (8). Newer antibiotics, such as moxifloxacin, offer better intraocular penetration and so many clinicians will include them in their treatment plans (11).
The acute inflammatory response to the microbes results in irreversible damage to intraocular structures. This inflammation can be modulated using corticosteroids and they have been found to improve outcomes (8). In bacterial cases, topical corticosteroids are frequently used, and an oral form is usually introduced 24 hours after antibiotics have been given. The literature is divided on the benefits of intravitreal corticosteroids due to the risk of allowing a fungal infection to proliferate, and the effect it has on the elimination of vancomycin from the vitreous (12). If a fungal infection is suspected steroids should be avoided.
In those who present with visual acuity of light perception or less, early pars plana vitrectomy is recommended. In the Early Vitrectomy Study, this group were found to have a threefold increase of achieving 6/12 if they underwent early surgical intervention (8). It is theorised that this improves outcomes by reducing the inflammatory and infective burden. The study did not recommend early vitrectomy for patients with visual acuity better than light perception, who should be managed medically in the first instance. However, since the Early Vitrectomy study was undertaken, there have been significant advances in vitrectomy surgery. This is an area of ongoing research, but there is some evidence to support early vitrectomy in patients who have visual acuities better than light perception (13).
The patient will need to either attend daily as an outpatient or be admitted so that they can be monitored closely to assess clinical response. Repeat intravitreal antibiotics, systemic steroids or surgical intervention may be required if there is inadequate response. In addition, repeat or additional microbiological samples might be performed, and alternative diagnoses sought if there is no change in the clinical picture.
The management of chronic post-operative endophthalmitis is similar to that of the acute form. However, it will need to be tailored based on the causative organism. Bacterial causes can be managed using intravitreal antibiotics, adjusting the regime based on the sensitivity data once available. Cases caused by P. acnes have a higher risk of re-occurrence so may require vitrectomy plus total capsulectomy and removal of the intraocular lens (5, 14). Fungal causes are associated with poorer outcomes, and are often managed with a combination of vitrectomy, intravitreal antifungals such as amphotericin and a prolonged course of systemic antifungal drugs (15).
The visual prognosis of acute post-operative endophthalmitis is often poor. A best corrected visual acuity of 6/60 or better is achieved in 67% of eyes (16), and 28-53% of eyes achieve visual acuity of better than 6/12 (8, 17). Poorer visual outcomes are associated with increased virulence of the causative bacteria, and light perception vision at presentation. Visual loss occurs secondary to the formation of epiretinal membranes, retinal detachment, and macular oedema. Evisceration, a surgical procedure that removes the intraocular contents in treatment-resistant endophthalmitis or in a blind eye to improve cosmesis, is undertaken in 2-5% of cases (17, 18).
The risk of developing post-operative bacterial endophthalmitis has been reduced by treating patient risk factors prior to surgery and improvements in theatre practice such as the use of povidone-iodine to thoroughly clean eyelids. All post-operative patients must be advised what symptoms to be aware of and where to go if any of these develop. This safety-netting advice should result in earlier attendance, thus enabling earlier initiation of intervention.
Post-operative bacterial endophthalmitis is a rare but severe ophthalmic complication. Even with the early initiation of treatment prognosis is limited. While steps can be taken to reduce the chance of it occurring, it is important to remain vigilant when assessing post-operative patients. It is a clinical diagnosis that necessitates early investigation and prompt treatment to improve the chance of saving sight and the eye.
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