Compared to ARN, PORN may have a greater exclusivity to immunocompromised patients, whereas ARN occurs in immunocompetent and immunocompromised patients. PORN is further characterized by little or no vasculitis, less vitritis than ARN, and early posterior pole involvement.

Compared with progression of CMV retinitis, progression of PORN is markedly accelerated, with a typical absence of intraocular inflammation, vasculitis, or hemorrhage [3].

37.4 Treatment

37.4.1 CMV Retinitis

Treatment for CMV retinitis is complex, requiring collaboration between the ophthalmologist and the infectious disease specialist. Initial antiviral therapy must be individualized based on location and severity of lesions and can involve oral antiviral therapy or intravenous antiviral therapy in combination with intravitreal injection or implant for more sight-threatening lesions. Anti-CMV drugs are virostatic and cannot eliminate the pathogen, which is why, in an immunocompromised patient, the possibility of relapse or progression is important.

The first step is to improve the patient’s immune status, if possible. In some patients, particularly cancer patients (but not patients with AIDS), the discontinuation or reduction of immunosuppressive therapy may be sufficient to result in a cure. However, some patients develop active vitritis coinciding with the revitalization of their immune system. This has been described as immune recovery uveitis and should not be interpreted as a relapse [19].

Treatment of CMV retinitis includes an induction phase and a maintenance phase. Induction treatment is directed at halting progression of CMV retinitis lesions and typically lasts for 2–3 weeks. Maintenance therapy is directed at preventing reactivation of the CMV retinitis and generally needs to be maintained throughout the period of immunosuppression. Table 37.1 identifies Food and Drug Administration-approved medications for treatment of CMV retinitis, with appropriate induction and maintenance doses where applicable.

37.4.1.1 Intravitreal Injections

Only fomivirsen has been approved for intravitreal use although the off-label use of intravitreal ganciclovir and foscarnet is relatively common. The off-label use of intravitreal cidofovir has also been reported. However, both the Physician’s Desk Reference and the drug’s package insert specifically prohibit the intraocular use of this drug. Although not approved for initial therapy, fomivirsen is approved for use in patients who are unresponsive to or cannot tolerate other available treatments. The use of fomivirsen is contraindicated within 4 weeks of any use of cidofovir due to reported increased risk of ocular inflammation.

The use of the ganciclovir implant is generally felt to be superior to intravitreal injections in patients with sight-threatening lesions. It must also be stressed that implants and intravitreal injections provide local treatment only and that systemic therapy should be maintained in patients in whom these local treatments are employed. Intravitreal injections may be considered if there is a delay in obtaining a ganciclovir implant or operating room time for the implant procedure.

37.4.1.2 Ganciclovir Implant

One treatment option often used for the local treatment of CMV retinitis is the ganciclovir implant. The implant (Vitrasert, Bausch & Lomb Surgical Inc., Claremont, CA) is available in a 4.5-mg size and consists of a pellet of ganciclovir with a polymerized coating through which the drug is released at a rate of 1 μg/hour.

A careful examination of the retina, with scleral depression, is necessary prior to ganciclovir implant placement. Any tears or detachments must be repaired prior to placement of the device.

The implant has a long plastic strut that must be trimmed down to 2 mm. A small hole is fashioned in the strut with a 27-G needle. This hole must be centered on the strut and just under 0.5 mm from the strut’s leading edge. A double-armed suture is then passed through the hole. Various sutures have been used in reports on the surgical technique for ganciclovir implants. Both 8-0 nylon and 10-0 Prolene are acceptable, although other similar sutures may also be used. A sectoral conjunctival peritomy is then made in the inferotemporal quadrant. A microvitreoretinal blade is used to make a 5.5-mm sclerotomy parallel to and 4 mm posterior to the limbus over the pars plana. The sclerotomy should be centered at 6:30 in the right eye and 5:30 in the left eye. The implant is then inserted through the sclerotomy and is sutured to the sclera by passing one needle through the anterior edge of sclera and one needle through the posterior edge of sclera. Following this, the sclera is closed with 7.0 Vicryl sutures. After conjunctival closure, subconjunctival antibiotics and steroids