ENDOPHTHALMITIS

Prompt aggressive treatment with intravitreal antibiotics, corticosteroids and vitrectomy appear to provide the best outcomes in eyes with endophthalmitis, Lars Wagenfeld MD told the 13th EURETINA Congress in Hamburg. “The treatment of endophthalmitis in general consists of three components. First is the administration of sufficient drugs to inactivate the infective organism. Second is anti-inflammatory therapy to reduce the inflammatory response and third is the mechanical elimination of the pathogenic microorganisms and pus,” said Dr Wagenfeld, University Hospital Hamburg-Eppendorf, Hamburg, Germany.

Anterior segment with hypopyon in a case of endophthalmitis

He emphasised that it is critically important to start treatment of endophthalmitis immediately after diagnosis. However, just before administering antibiotics, samples should be taken from the vitreous and the anterior chamber. When performing a vitrectomy, a vitreous cutter is the best tool for obtaining the samples. In hospitals without the facilities for vitrectomy, a vitrector will usually suffice.

Vitreous taps deliver the highest rate of positive results. The positive rates for anterior chamber taps are not as high. In the Endophthalmitis Vitrectomy Study, the anterior chamber was the only means by which microorganisms could be identified in around four per cent of cases. Surface swabs are not helpful in identifying the infecting organism, he noted.

Gram-staining the sample obtained can give a quick but not very specific indication of the pathogen in most cases. Polymerase chain reaction (PCR) is very precise and highly sensitive and can identify the causative microorganism in around 90 per cent of cases. It also works well in culture-negative cases, which account for 30 to 60 per cent of cases. Nonetheless a positive culture is the gold standard because it enables microbiologic sensitivity testing. The microorganisms most frequently identified in cases of endophthalmitis are Gram-positive bacteria, followed by some Gram-negative species and fungi.

Current ESCRS guidelines recommended administering antibiotics intravitreally and systemically. Systemic antibiotics reduce the osmotic gradient and therefore reduce the flow of the antibiotic out of the eye and prolong the half-life of the antibiotic in the eye. The antibiotics of first choice in cases of endophthalmitis are vancomycin and ceftazidime or another thirdgeneration cephalosporin. In case of any contraindication of those agents, alternatives include combinations of ciprofloxacin and cilastin or imipenem.

The use of corticosteroids is more controversial. The rationale for using them in cases of endophthalmitis is that they will reduce the inflammation that occurs in response to the toxins that bacteria release when they die. They limit tissue destruction and lower the toxic effects of cytokines. Research indicates that intraocular application of dexamethasone can diminish the inflammation. However, reports from clinical and laboratory studies have yielded contradictory findings regarding the effect of corticosteroids on salvaging visual acuity in such cases. The best route of administration is also debated. The alternatives are intravitreal, systemic, conjunctival or topical administration. The ESCRS recommend the intravitreal route, although in the Endophthalmitis Vitrectomy Study patients received the agent systemically.

The last part of the treatment of endophthalmitis is the mechanical elimination of pus and detritus from the eye. Vitrectomy offers the advantage of providing more material to use in identifying the pathogenic microorganisms involved. In addition the removal of pus reduces the bacterial load and the amount of inflammatory mediators and toxins.

The endophthalmitis vitrectomy study showed that in severe cases, where the retina is completely obscured and the visual acuity is light perception or less, vitrectomy reduces the risk of a severe vision loss by 50 per cent and increases by three-fold the chance of achieving a visual acuity of 20/40 or better. In less severe cases, where the larger retinal vessels are visible and the vitreous cavity is not filled with pus, vitrectomy had no significant effect on mean visual acuity, although it reduced the incidence of severe vision loss from 15 per cent to eight per cent.

“Surgical techniques have evolved since the publication of the Endophthalmitis Vitrectomy Study back in 1995. Today there are an increasing number of reports showing that a complete vitrectomy gives better results than previously reported in less severe cases,” he said.