RISK FACTORS FOR PSEUDOPHAKIC ENDOPHTHALMITIS

Much of the time it is not known why certain patients are more prone to developing pseudophakic endophthalmitis when the vast majority of others do not, noted Terrence O'Brien MD, Bascom Palmer Eye institute, University of Miami Miller school of Medicine, at the UKisCRs XXXV Congress. he said that a more detailed understanding of the interactions between pathogen and host is needed to more efficiently treat endophthalmitis and improve visual outcome. For example, certain pre-existing diseases such as diabetes are known to increase risk, as are a number of preoperative issues.

'so there are host factors, organism factors and perhaps most importantly, in what is least well understood, is the interaction between the host and the organism and the cause. 'There is a paradox in that there is a significant number of microbes that are positive from anterior chamber taps recovered at the time of uncomplicated cataract surgery and yet the infrequency of endophthalmitis certainly suggests the potency of the ocular immune response to control invasion by a limited number of avirulent microorganisms,' he explained. Discussing endophthalmitis risk factors, Prof O'Brien listed systemic immunosuppression, operative preparations, intraoperative complications such as vitreous loss, perioperative factors such as surface bacteria, wound leak or inferior wound placement, and chronic blepharitis.

he cited the results from a Us study, which showed that a high percentage of routine cataract patients operated on in the community had positive cultures from both the lid and conjunctiva, especially Gram positive species. 'however, what was most alarming was that nearly 50 per cent of the Staph. epidermidis isolates were methicillin resistant, and nearly 30 per cent of staph. aureus were MRsA.' The question that now arises is which bacteria are the principal cause of pathogenesis. Clearly there are concerns about growing antimicrobial resistance, he commented, confirming that there is concern in the Us over the inappropriate use of topical antibiotics, which is 'perhaps selecting out resistant strains which are more virulent than conventional strains of bacteria'.

Outlining the results of animal research, he said S. epidermidis tends to produce a mild non-cavitary response with little tissue damage, accounting for relatively good prognosis. S. aureus is the more virulent ocular pathogen with the putative virulence factors being adhesions, cytolytic toxins, and proteolytic enzymes that are controlled by a system of global transcriptional regulators called staphylococcal accessory regulator (sar) and accessory gene regulator (agr). Prof O'Brien said further research has shown that globally regulated toxins, particularly the alpha-toxin, are key virulence factors in s. aureus endophthalmitis.

'Thus perhaps if we could arrest s. aureus toxin production by inactivating the global regulatory systems during the early stages of infection this may be a more viable therapy option than simply targeting the individual toxins alone.' he concluded that successful endophthalmitis treatment is dependent on the rapid and aggressive recognition of the bacteria and referral for diagnosis and treatment, but treatment and outcomes will improve in the future if a more detailed understanding of the interactions between the pathogen and the host is achieved.