Australian and New Zealand Journal of Ophthalmology (1998) 26, 3

Editorial

The conundrum of endophthalmitis

Every ophthalmologist knows the face of endophthalmitis and its potential devastation. In this issue of the journal, Morlet et al. 1 report the results of the Australia-wide survey. The response rate was a remarkable 89% and this illustrates the importance of this condition to us all.

The conundrum of the clinical prevention of endoph- thalmitis is that it is uncommon (approximately 1/1000 cases). Prospective clinical trials with enough patient numbers to achieve statistical power exist only from devel- oping countries.2 This has questionable applicability t o developed countries. Therefore, clinicians must indirectly draw from a variety of source knowledge to construct their own prevention protocols.

Much is known about endophthalmitis after cataract surgery. Clinical and laboratory work offer the following. Microbiological and genetic fingerprinting techniques have shown that the bacteria causing postoperative endoph- thalmitis are those of the external eye.3 During surgery, the fluids that wash over the external eye are able t o enter the eye.4 At the end of a cataract procedure, the aqueous is culture positive for external eye bacteria in 2 9 4 3 % of cases.4,5 In rabbits, an infective load of 1000 colony forming units (c.f.u.) or more will result in clinical endophthalmitis.6 Fewer bacteria will not cause disease. In primates, the minimum infective load is 10 000 c.f.u.7 Therefore, clinical endophthalmitis will be manifest i f some critical number of bacteria are left in the eye at the end of surgery and are able to overwhelm the host defences.

The epidemiological approach is able t o offer risk factors for disease. In the case control study by Menikoff et a/.,* the key factors were vitreous loss (risk ratio of 13.7) and polypropylene haptics (risk ratio of 4.5). T h e epidemiologi- cal study by Morlet et al.1 shows that endophthalmitis is less common if a surgeon has been practising for more than 20 years o r if the practitioner performs more than 300 cases per year. However, there was little difference between the large

range of current clinical approaches t o prevention. Somewhere in this conundrum there are ill-defined factors that appear more important than the use of antibiotics and antiseptics. These relate t o surgical experience and surgical volumes. This begs questions as t o the biological mecha- nisms at play. W h e n they are better defined, we may be able t o devise clinical strategies t o better prevent this most awful of complications.

REFERENCES 1 .

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Morlet N, Gataus B, Coroneo M. Patterns of peri-operative prophylaxis for cataract surgery: A survey of Australian oph- thalmologists. Aust. N.Z. J. Opbtbalmol. 1998; 26: 5-12. Christy NE, Sommer A. Antibiotic prophylaxis of postopera- tive endophthalmitis. Ann Opbtbalmol. 1979, 1 1 : 1261-5. Speaker MG, Milch FAr Shah MK, Eisner W, Kreiswirth BN. Role of external flora in the pathogenesis of acute postopera- tive endophthalmitis. Opbtbalmology 1991; 98: 639-50. Sherwood DR, Rich WJ, Jacob JS, Hart RJ, Fairchild YL. Bacterial contamination on intraocular and extraocular fluids during extracapsular cataract extraction. Eye 1989; 3: 308-12. Dickey JB, Thompson KD, Jay WM. Anterior chamber aspi- rate cultures after uncomplicated cataract surgery. Am. J. Opbtbalmol. 1991, I 12: 278-82. Beyer TL, Sharma D, Vogler G, O'Donnell FE Jr. Protective barrier effect on the posterior lens capsule in exogenous bac- terial endophthalmitis: An experimental pseudophakic primate study. J . Am. Intraocular Implant. SOC. 1984: 9: 293-6. Records RE, lwen PC. Experimental bacterial endophthalmitis following extracapsular lens extraction. Exp. Eye Res. 1989; 49: 729-37. Menikoff JA, Speaker MG, Marmor M, Raskin EM. A case- control study of risk factors for post-operative endophthal- mitis. Opbtbalmology 1991; 98: 1761-8.

MJ Elder, MD, FRACS, FRACO Christchurch Hospital

New Zealand