Retinal And Vitreous Infections

6.1. Endophthalmitis

6.1.1. Epidemiology and Clinical Relevance

Postoperative endophthalmitis is the most significant retinal-vitreal infection encountered among the geriatric population. Endophthalmitis is defined as inflammation of the intraocular contents and develops as a result of microbial pathogens or chemical toxins gaining intraocular access. Although several etiologic mechanisms exist for the development of this infection (i.e., penetrating ocular trauma, or hematog-enous spread from another infectious site), postsurgical infection is the predominant mechanism among the elderly, who undergo the majority of intraocular surgery. Fortunately, it is a rare complication of intraocular surgery. The relative incidence of postoperative

Table 2

Incidence of Endophthalmitis Following Intraocular Surgery

Procedure

Incidence %

Cataract surgery Corneal transplantation surgery Glaucoma surgery Retinal-vitreous surgery

Adapted from refs. 14 and 15.

endophthalmitis for each of the commonly performed intraocular surgical procedures is listed in Table 2 (14,15).

Studies have shown that postoperative endophthalmitis is primarily caused by organisms that colonize the eyelids, conjunctiva, and nose, with 90% of culture-positive postoperative endophthalmitis cases caused by Gram-positive organisms, of which coagulase-negative staphylococci are the most common (16,17). The major host risk factors for the development of postoperative endophthalmitis include bacterial blepharitis, nasolacrimal duct infections, nasolacrimal duct obstruction, active nonocular infections, diabetes mellitus, and immunosuppression from any cause.

6.1.2. Clinical Manifestations

Postoperative endophthalmitis can manifest early or late in the postoperative period. Early postoperative endophthalmitis typically occurs within the first week after surgery. Patients will typically present complaining of severe ocular pain and decreased vision. On examination, these patients will show intraocular and periocular inflammation in excess of the normal postoperative inflammatory response. Depending on the severity of the infection, patients may also demonstrate frank purulence at the surgical wound site, purulent conjunctival discharge, or a hypopyon in the anterior chamber. It is important to note that most cases of endophthalmitis following cataract extraction occur early. In the Endophthalmitis Vitrectomy Study (EVS), for example, the median time to presentation was 6 d and about 80% of patients presented within 2 wk of cataract surgery (16).

Late or delayed-onset postoperative endophthalmitis can occur days to weeks and even years after surgery. The type of surgery appears to play a definite role in the development of these late infections, with glaucoma surgery being more frequently associated with late-onset postoperative endophthalmitis. Late infections can present very subtly or in a fulminant suppurative manner. The type of presentation is primarily determined by the virulence of the infecting organism. The subtle presentation of postoperative endophthalmitis is most commonly associated with postcataract surgery cases. This form of endophthalmitis usually manifests as persistent low-grade postoperative inflammation well beyond the expected time period for normal postoperative inflammation. Patients will complain of persistent photophobia and blurred vision. These patients will typically not manifest any signs of frank purulence and the eyes will often appear white and quiet. The etiologic mechanism underlying this form of endophthalmitis has been shown to be colonization of the intraocular lens implant by Propionibacterium acnes and coagulase-negative staphyloccocal species.

The fulminant presentation of late postoperative endophthalmitis is more frequently associated with streptococcal species and Gram-negative organisms, which cause the majority of late endophthalmitis. Glaucoma filtration surgery is the most frequently associated surgical procedure. Patients with this form of the disease will present in similar fashion to patients with acute postoperative endophthalmitis, i.e., severe pain, decreased vision, and marked intraocular and periocular inflammation. Given the strong association of late postoperative endophthalmitis with glaucoma filtration surgery, it is recommended that patients who have undergone glaucoma surgery and present with conjunctivitis be placed on topical antibiotic therapy immediately and referred to an ophthalmologist for a more in-depth evaluation.

6.1.3. Diagnostic Tests

The diagnosis of endophthalmitis is exclusively made clinically. Diagnostic needle taps of the anterior chamber or vitreous cavity may be performed to confirm the clinical diagnosis and identify the infecting organism.

6.1.4. Therapy

The prognosis for postoperative endophthalmitis is largely dependent on the virulence of the infecting organism and the length of time between the onset of infection and the initiation of therapy. The delicate intraocular structures cannot withstand prolonged exposure to destructive bacterial pathogens and inflammatory cells and therefore, early diagnosis and rapid therapy implementation are the keys to treatment success for this condition. The treatment of endophthalmitis involves intraocular antibiotic injections along with frequent application of topical fortified antibiotics and topical corticosteroids. The antibiotics most commonly used for intraocular injection are amikacin (400 ^g) and vancomycin (1 mg). In advanced cases, a vitrectomy is performed in conjunction with the above measures to debulk the infectious debris. One of the key findings of the EVS was that immediate vitrectomy was of use only in patients who presented with visual acuity of light perception or worse (16). Most retinal surgeons will also place patients on a short course of oral corticosteroids following vitrectomy. Diagnostic specimens of the aqueous and vitreous humors are obtained at the time of intraocular antibiotic injection or vitrectomy.

6.1.5. Prevention

Given the strong association with lid flora, patients with active blepharitis must be adequately treated prior to undergoing any form of ocular surgery. To further combat this problem ophthalmic surgeons instill preoperative prophylactic broad-spectrum antibiotics in the operative eye. In addition, some surgeons infuse antibiotics in the eye during surgery.

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