Intraocular Fluid Cultures After Primary Pars Plana Vitrectomy Steven M. Cohen, M . D . , Jeffrey D . Benner, M . D . , Maurice B. Landers III, M.D., and Lawrence S. Morse, M . D . To determine what organisms enter the eye and remain in the eye after pars plana vitrectomy, vitreous cavity aspirates were cultured postoperatively. Two of 33 (6%) consecutive eyes undergoing primary pars plana vitrectomy had positive cultures. One sample grew a single colony of Staphylococcus epidermidis, the second grew two colonies of Acinetobacter Iwoffi. Neither of these eyes developed endophthalmitis. This study demonstrates that bacteria enter the eye at a low rate during pars plana vitrectomy and that the eye on which a vitrectomy has been performed is capable of clearing a low inoculum of bacteria.
rectomy might be more likely to cause endoph thalmitis than a similar inoculum of bacteria entering the eye during cataract extraction. Additionally, vitrectomies often last several hours and involve many instrument insertions into the eye. The duration of the procedure and using several instruments might increase the risk of introducing bacteria into the eye during the procedure. To ascertain what organisms enter the eye during pars plana vitrectomy, we cultured intraocular fluid from eyes at the con clusion of pars plana vitrectomy.
POSTOPERATIVE ENDOPHTHALMITIS often causes profound vision loss. 1,2 Recent reports showed that 29% to 43% of eyes undergoing uncompli cated cataract extraction with intraocular lens implantation have culture-positive anterior chamber aspirates at the conclusion of the oper ation. 3,4 Although no eyes in these studies de veloped endophthalmitis, other research has shown that bacteria introduced into the eye during an operation are the primary cause of postoperative endophthalmitis. 6 Bacteria introduced into the anterior chamber are less able to cause a clinically important infection than bacteria introduced into the vit reous cavity. 69 Therefore, a small inoculum of bacteria entering the eye during pars plana vit-
Thirty-three consecutive subjects undergo ing primary pars plana vitrectomy at the Uni versity of California, Davis, Medical Center were included in the study. Patients were ex cluded if they had had penetrating trauma or a ruptured globe; had evidence of local or sys temic infections at the time of surgery; or had previously undergone an anterior or posterior vitrectomy. The study was approved by the University of California, Davis, Human Sub jects Review Committee. The indications for vitrectomy were as fol lows: tractional macular detachments or vitre ous hemorrhage from proliferative diabetic retinopathy (14 patients); rhegmatogenous retinal detachments with proliferative vitreoretinopathy (12 patients); submacular hemorrhage in age-related macular degeneration (two pa tients); ectopia lentis from Marian's syndrome (two patients); vitreous hemorrhage in shaken infant syndrome (one patient); macular pucker (one patient); stage 5 retinopathy of prematuri ty (total retinal detachment) (one patient). The average age was 49 years. Of the 33 eyes under going surgery, 12 eyes had prior surgical proce dures. Eight eyes were pseudophakic and one eye was aphakic. All procedures were performed in the same operating room by two of us (L.S.M. or M.B.L.).
Accepted for publication Sept. 2, 1992. From the Department of Ophthalmology, University of California, Davis, Sacramento, California (Drs. Cohen, Benner, and Morse); and Center for Retina and Vitreous Surgery, Memphis, Tennessee (Dr. Landers). This study was presented at the Association for Research in Vision and Ophthalmology Annual Meeting, Sarasota, Florida, May 6, 1992. Reprint requests to Lawrence S. Morse, M.D., Depart ment of Ophthalmology, University of California, Davis, 1603 Alhambra Blvd., Sacramento, CA 95816.
Subjects and Methods
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No preoperative antibiotics were administered. All patients underwent the following identical skin preparation. The eyelids and surrounding skin were scrubbed with 5% povidone-iodine in concentric rings outward from the eyelids for three minutes. The eyelashes were cleaned sep arately with povidone-iodine on cotton-tipped swabs. One or two drops of 5% povidoneiodine was placed in the conjunctival fornix. The skin was then blotted dry with a sterile gauze sponge. The eyelids were opened by the surgical assistant with the wood end of a cot ton-tipped swab, and a clear plastic adhesive drape was placed over the eye. The drape was then incised over the globe and a wire eyelid speculum was used to tuck the edges of the drape around the eyelid margins and to main tain proper exposure. A standard three-port pars plana vitrectomy was performed on each patient. Before closing the sclerotomies, or before the fluid-gas ex change, 0.3 to 0.7 ml of fluid was removed from the mid vitreous cavity with a blunt 20-gauge cannula into a sterile tuberculin syringe. The syringe was capped and taken to the adjacent microbiology laboratory. Under sterile condi tions, the intraocular fluid was plated immedi ately on sheep-blood agar, chocolate agar, rose agar, MacConkey agar, and a drop was placed in thioglycolate broth. The first three plates were incubated at 35 C in 5% to 10% C0 2 . The MacConkey agar and thioglycolate broth were incubated at35 C in ambient air. Any colonies located outside of the area plated with intraoc ular fluid were considered contaminants. If no organisms were seen, plates were discarded after three days, and the thioglycolate broth was discarded after seven days. Cultured organ isms were identified both qualitatively and quantitatively by an experienced microbiologist.
Results Only two of 33 samples (6%) of intraocular fluid from the vitreous cavity were culturepositive. One sample grew a single colony of Staphylococcus epidermidis on blood agar. An other sample grew two colonies of Acinetobacter Iwoffi on chocolate agar. The average time between the beginning of vitrectomy and the aspiration of fluid for the culture was 117 minutes. The elapsed time for the two patients with positive cultures was 100
and 120 minutes. Both of these patients were diabetic. One had had no previous operation and one was pseudophakic.
Discussion Recent reports that 29% to 4 3 % of eyes had culture-positive anterior chamber fluid after routine cataract extraction suggest that contem porary ophthalmic operation is not absolutely sterile.3·4 In our patients, only two of 33 (6%) eyes had culture-positive intraocular fluid after vitrectomy. Each positive culture grew only one or two colonies of bacteria. Endophthalmitis after pars plana vitrectomy is rare, with an incidence of 0.05% to 0.14%. 1017 In a survey of 30,002 cases, Kattan and associ ates10 found the incidence of endophthalmitis after pars plana vitrectomy comparable to that after cataract extraction. 10 Despite the similar rates of endophthalmitis after cataract extrac tion, only 6% of eyes had culture-positive in traocular fluid after pars plana vitrectomy, compared to 29% to 43% of eyes that were culture-positive after cataract extraction. 3 · 4 Thus, even though bacteria remain in the eye much less often after pars plana vitrectomy than after cataract extraction, those bacteria that enter the vitreous cavity during vitrectomy may have a greater chance of producing en dophthalmitis. There are at least two possible reasons why bacteria would have a greater chance of causing endophthalmitis once they gain access to the vitreous cavity. First, animal studies have dem onstrated that in vivo, the vitreous is a better culture medium than the aqueous humor. In 1955, Maylath and Leopold 6 showed that the anterior chamber of rabbits was better able to overcome infections with small numbers of bac teria than the vitreous. This finding has been supported by human studies demonstrating that a communication with the vitreous cavity during anterior segment procedures confers a much greater risk of postoperative endophthal mitis.7"917 Secondly, both gentamicin and cephalosporins injected subconjunctivally do not penetrate well into the vitreous cavity.18·19 Therefore, subconjunctival injections adminis tered postoperatively would be more effective at eradicating intraocular bacteria after an ante rior segment procedure than after posterior segment cataract extraction. Although not as efficient as the anterior
Vol. 114, No. 6
Culture After Vitrectomy
c h a m b e r , the v i t r e o u s is c a p a b l e of o v e r c o m i n g i n v a d i n g bacteria. In a n intact eye, t h e v i t r e o u s is able to kill bacteria t h r o u g h i n f l a m m a t o r y related mechanisms. 2 0 · 2 1 A d d i t i o n a l l y , a l t h o u g h the v i t r e o u s is a n excellent c u l t u r e m e d i u m for bacteria, i n v a d i n g bacteria p r o b a b l y d o n o t sur vive a n d m u l t i p l y as well in t h e b a l a n c e d salt s o l u t i o n r e m a i n i n g in t h e eye after p a r s p l a n a vitrectomy. The lower i n c i d e n c e of c u l t u r e - p o s i t i v e i n t r a ocular fluid f o u n d in o u r p a t i e n t s is p r o b a b l y a t t r i b u t a b l e to differences in surgical t e c h n i q u e b e t w e e n p a r s p l a n a v i t r e c t o m y a n d cataract extraction. Pars p l a n a v i t r e c t o m y is p e r f o r m e d t h r o u g h several small i n c i s i o n s . The small inci sions may h e l p p r e v e n t bacteria from e n t e r i n g the eye. S h e r w o o d a n d associates 4 s h o w e d t h a t d u r i n g cataract e x t r a c t i o n , fluid is d r a w n i n t o the eye d u r i n g a s p i r a t i o n of t h e l e n s cortex a n d during intraocular lens insertion. During pars p l a n a v i t r e c t o m y a c o n t i n u o u s infusion of s o l u tion m a i n t a i n s p o s i t i v e p r e s s u r e w i t h i n t h e globe. The c o n s t a n t p r e s s u r e c a u s e s a n outflow of fluid w h e n incisions are m a d e a n d w h e n e v e r i n s t r u m e n t s are r e m o v e d from the eye. This o u t w a r d flux of i r r i g a t i n g s o l u t i o n d u r i n g p a r s p l a n a vitrectomy may p r e v e n t b a c t e r i a from e n t e r i n g the eye. F u r t h e r m o r e , the flow of solu tion t h r o u g h t h e eye m a y r e m o v e m o s t b a c t e r i a that gain e n t r y .
References 1. Olson, J. C , Flynn, H. W., Forster, R. K., and Culbertson, W. W.: Results in the treatment of post operative endophthalmitis. Ophthalmology 90:692, 1983. 2. Puliafito, C. A., Baker, A. S., Haaf, J., and Fos ter, C. S.: Infectious endophthalmitis. Ophthalmolo gy 89:921, 1982. 3. Dickey, J. B„ Thompson, K. D., and Jay, W. M.: Anterior chamber aspirate cultures after uncompli cated cataract surgery. Am. J. Ophthalmol. 112:278, 1991. 4. Sherwood, D. R., Rich, W. J., Jacom, J. S., Hart, R. J., and Fairchild, Y. L.: Bacterial contamination of intraocular and extraocular fluids during extracapsular cataract extraction. Eye 3:308, 1989. 5. Speaker, M. G., Milch, F. A., Shah, M. K., Eisner, W., and Kreisworth, B. N.: Role of external bacterial flora in the pathogenesis of acute postopera tive endophthalmitis. Ophthalmology 98:639, 1991. 6. Maylath, F. R., and Leopold, I. H.: Study of
699
experimental intraocular infection. Am. J. Ophthal mol. 98:1761, 1955. 7. Menikoff, J. A., Speaker, M. G., Marmor, M., and Raskin, E. M.: A case-control study of risk fac tors for postoperative endophthalmitis. Ophthalmol ogy 98:1761, 1991. 8. Beyer, T. L., O'Donnell, F. E., Goncalves, V., and Singh, R.: Role of the posterior capsule in the prevention of postoperative bacterial endophthalmi tis. Experimental primate studies and clinical impli cations. Br. J. Ophthalmol. 69:841, 1985. 9. Beyer, T. L., Vogler, G., Sharma, D., and O'Don nell, T. E.: Protective barrier effect of the posterior lens capsule in exogenous bacterial endophthalmitis. An experimental primate study. Invest. Ophthalmol. Vis. Sci. 25:108, 1984. 10. Kattan, H. M., Flynn, H. W., Pflugfelder, S. C., Robertson, C , and Forster, R. K.: Nosocomial en dophthalmitis survey. Ophthalmology 98:227, 1991. 11. Ho, P. C , and Tolentino, F. I.: Bacterial en dophthalmitis after closed vitrectomy. Arch. Oph thalmol. 102:207, 1984. 12. Blankenship, G. W.: Endophthalmitis aftei pars plana vitrectomy. Am. J. Ophthalmol. 84:815, 1977. 13. May, D. R., and Peyman, G. A.: Endophthal mitis after vitrectomy. Am. J. Ophthalmol. 81:520, 1976. 14. Michels, R. G.: Vitrectomy for macular pucker. Ophthalmology 91:1384, 1984. 15. Margherio, R. R., Morton, S. C , Trese, M. T., Murphy, P. L., Johnson, J., and Minor, L. A.: Remov al of epimacular membranes. Ophthalmology 92:1075, 1985. 16. Chong, L. P., de Juan, E., McCuen, B. W., and Landers, M. B.: Endophthalmitis in a silicone-oilfilled eye. Am. J. Ophthalmol. 102:660, 1986. 17. Speaker, M. D., and Menikoff, J. A.: Prophy laxis of endophthalmitis with topical povidone-iodine. Ophthalmology 98:1769, 1991. 18. Rubinstein, E., Goldfarb, J., Keren, G., Blu menthal, M., and Triester, G.: The penetration of gentamicin into the vitreous humor in man. Invest. Ophthalmol. Vis. Sci. 24:637, 1983. 19. Rubinstein, E., Triester, G., Avni, I., and Schwartzkopf, R.: The intravitreal penetration of cefotaxime in man following systemic and subconjunctival administrations. Ophthalmology 94:30, 1987. 20. Meredith, T. A., Trabeiski, A., Miller, M. J., Aguilar, E., and Wilson, L. A.: Spontaneous steriliza tion in experimental Staphylococcus epidermidis en dophthalmitis. Invest. Ophthalmol. Vis. Sci. 31:181, 1990. 21. Olarn, R. C , Aguilar, H. E., Wilson, L. A., Sawant, A., and Meredith, T. A.: Antibacterial effects of previously infected or inflamed vitreous. Invest. Ophthalmol. Vis. Sci. 31:2342, 1990.
rectomy might be more likely to cause endoph thalmitis than a similar inoculum of bacteria entering the eye during cataract extraction. Additionally, vitrectomies often last several hours and involve many instrument insertions into the eye. The duration of the procedure and using several instruments might increase the risk of introducing bacteria into the eye during the procedure. To ascertain what organisms enter the eye during pars plana vitrectomy, we cultured intraocular fluid from eyes at the con clusion of pars plana vitrectomy.
POSTOPERATIVE ENDOPHTHALMITIS often causes profound vision loss. 1,2 Recent reports showed that 29% to 43% of eyes undergoing uncompli cated cataract extraction with intraocular lens implantation have culture-positive anterior chamber aspirates at the conclusion of the oper ation. 3,4 Although no eyes in these studies de veloped endophthalmitis, other research has shown that bacteria introduced into the eye during an operation are the primary cause of postoperative endophthalmitis. 6 Bacteria introduced into the anterior chamber are less able to cause a clinically important infection than bacteria introduced into the vit reous cavity. 69 Therefore, a small inoculum of bacteria entering the eye during pars plana vit-
Thirty-three consecutive subjects undergo ing primary pars plana vitrectomy at the Uni versity of California, Davis, Medical Center were included in the study. Patients were ex cluded if they had had penetrating trauma or a ruptured globe; had evidence of local or sys temic infections at the time of surgery; or had previously undergone an anterior or posterior vitrectomy. The study was approved by the University of California, Davis, Human Sub jects Review Committee. The indications for vitrectomy were as fol lows: tractional macular detachments or vitre ous hemorrhage from proliferative diabetic retinopathy (14 patients); rhegmatogenous retinal detachments with proliferative vitreoretinopathy (12 patients); submacular hemorrhage in age-related macular degeneration (two pa tients); ectopia lentis from Marian's syndrome (two patients); vitreous hemorrhage in shaken infant syndrome (one patient); macular pucker (one patient); stage 5 retinopathy of prematuri ty (total retinal detachment) (one patient). The average age was 49 years. Of the 33 eyes under going surgery, 12 eyes had prior surgical proce dures. Eight eyes were pseudophakic and one eye was aphakic. All procedures were performed in the same operating room by two of us (L.S.M. or M.B.L.).
Accepted for publication Sept. 2, 1992. From the Department of Ophthalmology, University of California, Davis, Sacramento, California (Drs. Cohen, Benner, and Morse); and Center for Retina and Vitreous Surgery, Memphis, Tennessee (Dr. Landers). This study was presented at the Association for Research in Vision and Ophthalmology Annual Meeting, Sarasota, Florida, May 6, 1992. Reprint requests to Lawrence S. Morse, M.D., Depart ment of Ophthalmology, University of California, Davis, 1603 Alhambra Blvd., Sacramento, CA 95816.
Subjects and Methods
©AMERICAN JOURNAL OF OPHTHALMOLOGY 114:697-699, DECEMBER, 1992
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698
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No preoperative antibiotics were administered. All patients underwent the following identical skin preparation. The eyelids and surrounding skin were scrubbed with 5% povidone-iodine in concentric rings outward from the eyelids for three minutes. The eyelashes were cleaned sep arately with povidone-iodine on cotton-tipped swabs. One or two drops of 5% povidoneiodine was placed in the conjunctival fornix. The skin was then blotted dry with a sterile gauze sponge. The eyelids were opened by the surgical assistant with the wood end of a cot ton-tipped swab, and a clear plastic adhesive drape was placed over the eye. The drape was then incised over the globe and a wire eyelid speculum was used to tuck the edges of the drape around the eyelid margins and to main tain proper exposure. A standard three-port pars plana vitrectomy was performed on each patient. Before closing the sclerotomies, or before the fluid-gas ex change, 0.3 to 0.7 ml of fluid was removed from the mid vitreous cavity with a blunt 20-gauge cannula into a sterile tuberculin syringe. The syringe was capped and taken to the adjacent microbiology laboratory. Under sterile condi tions, the intraocular fluid was plated immedi ately on sheep-blood agar, chocolate agar, rose agar, MacConkey agar, and a drop was placed in thioglycolate broth. The first three plates were incubated at 35 C in 5% to 10% C0 2 . The MacConkey agar and thioglycolate broth were incubated at35 C in ambient air. Any colonies located outside of the area plated with intraoc ular fluid were considered contaminants. If no organisms were seen, plates were discarded after three days, and the thioglycolate broth was discarded after seven days. Cultured organ isms were identified both qualitatively and quantitatively by an experienced microbiologist.
Results Only two of 33 samples (6%) of intraocular fluid from the vitreous cavity were culturepositive. One sample grew a single colony of Staphylococcus epidermidis on blood agar. An other sample grew two colonies of Acinetobacter Iwoffi on chocolate agar. The average time between the beginning of vitrectomy and the aspiration of fluid for the culture was 117 minutes. The elapsed time for the two patients with positive cultures was 100
and 120 minutes. Both of these patients were diabetic. One had had no previous operation and one was pseudophakic.
Discussion Recent reports that 29% to 4 3 % of eyes had culture-positive anterior chamber fluid after routine cataract extraction suggest that contem porary ophthalmic operation is not absolutely sterile.3·4 In our patients, only two of 33 (6%) eyes had culture-positive intraocular fluid after vitrectomy. Each positive culture grew only one or two colonies of bacteria. Endophthalmitis after pars plana vitrectomy is rare, with an incidence of 0.05% to 0.14%. 1017 In a survey of 30,002 cases, Kattan and associ ates10 found the incidence of endophthalmitis after pars plana vitrectomy comparable to that after cataract extraction. 10 Despite the similar rates of endophthalmitis after cataract extrac tion, only 6% of eyes had culture-positive in traocular fluid after pars plana vitrectomy, compared to 29% to 43% of eyes that were culture-positive after cataract extraction. 3 · 4 Thus, even though bacteria remain in the eye much less often after pars plana vitrectomy than after cataract extraction, those bacteria that enter the vitreous cavity during vitrectomy may have a greater chance of producing en dophthalmitis. There are at least two possible reasons why bacteria would have a greater chance of causing endophthalmitis once they gain access to the vitreous cavity. First, animal studies have dem onstrated that in vivo, the vitreous is a better culture medium than the aqueous humor. In 1955, Maylath and Leopold 6 showed that the anterior chamber of rabbits was better able to overcome infections with small numbers of bac teria than the vitreous. This finding has been supported by human studies demonstrating that a communication with the vitreous cavity during anterior segment procedures confers a much greater risk of postoperative endophthal mitis.7"917 Secondly, both gentamicin and cephalosporins injected subconjunctivally do not penetrate well into the vitreous cavity.18·19 Therefore, subconjunctival injections adminis tered postoperatively would be more effective at eradicating intraocular bacteria after an ante rior segment procedure than after posterior segment cataract extraction. Although not as efficient as the anterior
Vol. 114, No. 6
Culture After Vitrectomy
c h a m b e r , the v i t r e o u s is c a p a b l e of o v e r c o m i n g i n v a d i n g bacteria. In a n intact eye, t h e v i t r e o u s is able to kill bacteria t h r o u g h i n f l a m m a t o r y related mechanisms. 2 0 · 2 1 A d d i t i o n a l l y , a l t h o u g h the v i t r e o u s is a n excellent c u l t u r e m e d i u m for bacteria, i n v a d i n g bacteria p r o b a b l y d o n o t sur vive a n d m u l t i p l y as well in t h e b a l a n c e d salt s o l u t i o n r e m a i n i n g in t h e eye after p a r s p l a n a vitrectomy. The lower i n c i d e n c e of c u l t u r e - p o s i t i v e i n t r a ocular fluid f o u n d in o u r p a t i e n t s is p r o b a b l y a t t r i b u t a b l e to differences in surgical t e c h n i q u e b e t w e e n p a r s p l a n a v i t r e c t o m y a n d cataract extraction. Pars p l a n a v i t r e c t o m y is p e r f o r m e d t h r o u g h several small i n c i s i o n s . The small inci sions may h e l p p r e v e n t bacteria from e n t e r i n g the eye. S h e r w o o d a n d associates 4 s h o w e d t h a t d u r i n g cataract e x t r a c t i o n , fluid is d r a w n i n t o the eye d u r i n g a s p i r a t i o n of t h e l e n s cortex a n d during intraocular lens insertion. During pars p l a n a v i t r e c t o m y a c o n t i n u o u s infusion of s o l u tion m a i n t a i n s p o s i t i v e p r e s s u r e w i t h i n t h e globe. The c o n s t a n t p r e s s u r e c a u s e s a n outflow of fluid w h e n incisions are m a d e a n d w h e n e v e r i n s t r u m e n t s are r e m o v e d from the eye. This o u t w a r d flux of i r r i g a t i n g s o l u t i o n d u r i n g p a r s p l a n a vitrectomy may p r e v e n t b a c t e r i a from e n t e r i n g the eye. F u r t h e r m o r e , the flow of solu tion t h r o u g h t h e eye m a y r e m o v e m o s t b a c t e r i a that gain e n t r y .
References 1. Olson, J. C , Flynn, H. W., Forster, R. K., and Culbertson, W. W.: Results in the treatment of post operative endophthalmitis. Ophthalmology 90:692, 1983. 2. Puliafito, C. A., Baker, A. S., Haaf, J., and Fos ter, C. S.: Infectious endophthalmitis. Ophthalmolo gy 89:921, 1982. 3. Dickey, J. B„ Thompson, K. D., and Jay, W. M.: Anterior chamber aspirate cultures after uncompli cated cataract surgery. Am. J. Ophthalmol. 112:278, 1991. 4. Sherwood, D. R., Rich, W. J., Jacom, J. S., Hart, R. J., and Fairchild, Y. L.: Bacterial contamination of intraocular and extraocular fluids during extracapsular cataract extraction. Eye 3:308, 1989. 5. Speaker, M. G., Milch, F. A., Shah, M. K., Eisner, W., and Kreisworth, B. N.: Role of external bacterial flora in the pathogenesis of acute postopera tive endophthalmitis. Ophthalmology 98:639, 1991. 6. Maylath, F. R., and Leopold, I. H.: Study of
699
experimental intraocular infection. Am. J. Ophthal mol. 98:1761, 1955. 7. Menikoff, J. A., Speaker, M. G., Marmor, M., and Raskin, E. M.: A case-control study of risk fac tors for postoperative endophthalmitis. Ophthalmol ogy 98:1761, 1991. 8. Beyer, T. L., O'Donnell, F. E., Goncalves, V., and Singh, R.: Role of the posterior capsule in the prevention of postoperative bacterial endophthalmi tis. Experimental primate studies and clinical impli cations. Br. J. Ophthalmol. 69:841, 1985. 9. Beyer, T. L., Vogler, G., Sharma, D., and O'Don nell, T. E.: Protective barrier effect of the posterior lens capsule in exogenous bacterial endophthalmitis. An experimental primate study. Invest. Ophthalmol. Vis. Sci. 25:108, 1984. 10. Kattan, H. M., Flynn, H. W., Pflugfelder, S. C., Robertson, C , and Forster, R. K.: Nosocomial en dophthalmitis survey. Ophthalmology 98:227, 1991. 11. Ho, P. C , and Tolentino, F. I.: Bacterial en dophthalmitis after closed vitrectomy. Arch. Oph thalmol. 102:207, 1984. 12. Blankenship, G. W.: Endophthalmitis aftei pars plana vitrectomy. Am. J. Ophthalmol. 84:815, 1977. 13. May, D. R., and Peyman, G. A.: Endophthal mitis after vitrectomy. Am. J. Ophthalmol. 81:520, 1976. 14. Michels, R. G.: Vitrectomy for macular pucker. Ophthalmology 91:1384, 1984. 15. Margherio, R. R., Morton, S. C , Trese, M. T., Murphy, P. L., Johnson, J., and Minor, L. A.: Remov al of epimacular membranes. Ophthalmology 92:1075, 1985. 16. Chong, L. P., de Juan, E., McCuen, B. W., and Landers, M. B.: Endophthalmitis in a silicone-oilfilled eye. Am. J. Ophthalmol. 102:660, 1986. 17. Speaker, M. D., and Menikoff, J. A.: Prophy laxis of endophthalmitis with topical povidone-iodine. Ophthalmology 98:1769, 1991. 18. Rubinstein, E., Goldfarb, J., Keren, G., Blu menthal, M., and Triester, G.: The penetration of gentamicin into the vitreous humor in man. Invest. Ophthalmol. Vis. Sci. 24:637, 1983. 19. Rubinstein, E., Triester, G., Avni, I., and Schwartzkopf, R.: The intravitreal penetration of cefotaxime in man following systemic and subconjunctival administrations. Ophthalmology 94:30, 1987. 20. Meredith, T. A., Trabeiski, A., Miller, M. J., Aguilar, E., and Wilson, L. A.: Spontaneous steriliza tion in experimental Staphylococcus epidermidis en dophthalmitis. Invest. Ophthalmol. Vis. Sci. 31:181, 1990. 21. Olarn, R. C , Aguilar, H. E., Wilson, L. A., Sawant, A., and Meredith, T. A.: Antibacterial effects of previously infected or inflamed vitreous. Invest. Ophthalmol. Vis. Sci. 31:2342, 1990.
