Subconjunctival gentamicin prophylaxis against postoperative endophthalmitis in the rabbit.

An experimental aphakic rabbit model was employed in order to evaluate the correlation of the clinical course of postoperative endophthalmitis and the ability to recover microorganisms in the postoperative time period, the ocular antibiotic penetration of gentamicin, and the value of antibiotic prophylaxis. 2. Staphylococcus aureus is far more pathogenic organism than Staphylococcus epidermidis. A concentration of 5,000 organisms resulted in an 88% infection rate whereas 50,000 organisms and greater resulted in 100% infection rate after extracapsular cataract extraction. 3. Staphylococcus aureus could be isolated from the eyes demonstrating infection following cataract extraction for 2 days (3 days in one case) and then could no longer be recovered despite the persistance of intraocular inflammation. 4. The infection which appeared in animals receiving 5,000 organisms of Staphylococcus aureus after peripheral iridectomy was significantly milder than that which occurred following cataract extraction. In addition, the microorganisms could only be isolated on the first postoperative day. 5. When 20 mg of gentamicin sulfate was administered subconjunctivally following the post-cataract extraction or post-iridectomy administration of the 5,000 organisms of Staphylococcus aureus, none of the eyes developed clinical signs of endophthalmitis nor could bacteria be recovered. 6. Subconjunctivally administered gentamicin sulfate rapidly penetrated into the aphakic rabbit eye; 75-100 mug/ml appears in the aqueous humor at 1 hour and persists in bactericidal concentrations for at least 4 hours in both the treated and contralateral eyes. 7. Antimicrobial (subconjlnctival gentamicin sulfate 20 mg/prophylaxis at the time of surgery in the experimental animal significantly reduced the incidence of experimental postoperative bacterial endophthalmitis.