are administered. The implant remains suspended within the eye at the surgical incision site overlying the pars plana. Correct placement should be verified with indirect ophthalmoscopy while the patient is still on the operating room table.

The Ganciclovir Implant Study for CMV retinitis demonstrated the efficacy of utilizing ganciclovir implants to treat CMV retinitis [20]. Progression in that study was primarily due to depletion of active drug from the implant and not to the development of viral resistance to ganciclovir. Patients may therefore require the serial placement of multiple implants. Subsequent implants may be placed adjacent to the preexisting implant(s).

37.4.2 Acute Retinal Necrosis

VZV, HSV-1 and HSV-2, and CMV have all been implicated as causes of ARN. Acyclovir is very effective against herpes zoster but not as effective against CMV. Intravenous acyclovir (1500 mg/m2/day in three divided doses over 10–14 days) is the standard initial treatment for patients with ARN. Oral acyclovir is then employed for variably prolonged periods. Retinal lesions typically dissipate 4–5 days after therapy initiation, which decreases the risk of subsequent development of bilateral acute retinal necrosis (BARN). Palay et al. [21] showed that only 13% of acyclovir-treated patients developed BARN, compared with 70% of untreated patients. Thankfully, most immunocompetent patients with ARN respond to intravenous acyclovir.

In cases of ARN caused by HSV, oral corticosteroids at dosages of 40–60 mg/day may be introduced to limit the inflammatory response following 24–48 hours of antiviral treatment. However, some patients may be infected with HSV strains resistant to conventional therapy; in such patients, intravitreal antiviral therapy may be introduced to improve visual prognosis [22]. Some patients with ARN caused by HSV benefit from intravitreal ganciclovir injection (200 μg/0.05 ml) and intravenous foscarnet (1200 μg/0.05 ml, administered every other day for four doses).

In cases of ARN caused by VZV, brivudine and valganciclovir have shown good results. Valganciclovir is a valyl ester prodrug of ganciclovir, with proven efficacy similar to that of intravenous ganciclovir. Famciclovir has also been used.

In cancer patients, we favor an aggressive multidrug approach and usually start with combination therapy consisting of intravenous acyclovir and ganciclovir. A recent pilot study demonstrated complete resolution of ARN in all patients treated with oral antiviral drugs (valacyclovir and famciclovir) [18]. Low-dose aspirin has been used as an adjuvant antithrombotic treatment, since the majority of patients have occlusive retinal vasculitis. Systemic and topical corticosteroids have also been used to potentiate anti-inflammatory treatment and attempt to minimize optic nerve and retinal vessel damage [23].

Since rhegmatogenous retinal detachment occurs in up to 75% of eyes affected by ARN, therapy for advanced disease focuses on preventing or treating this important sight-threatening complication. If rhegmatogenous retinal detachment does occur, surgical repair may be necessary [23].