Author reply
Authors: Susan Lightman, Chun Lau, Tom Missotten, Joel Salzmann
Journal: Ophthalmology (2008)

We thank Drs Kim and Lo for their comments and in response offer the following comments. Regarding the use of intravenous acyclovir—we and others are now switching to oral valacyclovir for the management of patients with acute retinal necrosis, but our study was undertaken previous to the general availability of valacyclovir. Oral acyclovir does not achieve a therapeutic level within the eye, whereas intravenous acyclovir does, which is why we used it intravenously for at least a week for the patients. Oral valacyclovir at a dose of 2 g thrice daily achieves a level of penetration to the CNS similar to that of the intravenous acyclovir dose we all use, 10 mg/kg thrice daily1Eksborg S. Pal N. Kalin M. et al.Pharmacokinetics of acyclovir in immunocompromized children with leukopenia and mucositis after chemotherapy: can intravenous acyclovir be substituted by oral valacyclovir?.Med Pediatr Oncol. 2002; 38: 240-246Crossref PubMed Scopus (23) Google Scholar, 2Guex-Crosier Y. Meylan P.R. High dosage of oral valaciclovir as an alternative treatment of varicella zoster acute retinal necrosis syndrome.Eye. 2006; 20: 247Crossref PubMed Scopus (15) Google Scholar—its advantage is not that it achieves higher levels, but that it can be given orally to achieve the same levels, and hence, hospital admission and intravenous access are not essential. Whether we always need to give this full dose or whether, as suggested by others, 1 g thrice daily is enough3Emerson G.G. Smith J.R. Wilson D.J. et al.Primary treatment of acute retinal necrosis with oral antiviral therapy.Ophthalmology. 2006; 113: 2259-2261Abstract Full Text Full Text PDF PubMed Scopus (67) Google Scholar is not known and whether different doses are required for an aggressive versus indolent clinical picture is also not known. We use the higher dose of 2 g thrice daily in most patients now, as it is well tolerated and is the oral equivalent dose needed to achieve the effective therapeutic level achieved previously by the intravenous route. It is known that repeated intravitreal injections increase the risk of associated complications such as iatrogenic retinal detachment (RD) and infectious endophthalmitis. Furthermore, the concurrent use of 2 effective antiviral agents in immunocompetent patients is not cost-efficient. We therefore did not use the repeated intravitreal foscarnet injections (in cases without optic nerve or CNS involvement) in combination with oral valacyclovir, as proposed by Drs Kim and Lo, but will switch to foscarnet as the second antiviral agent when the first agent failed. We always do a vitreous rather than an aqueous tap for the sample for polymerase chain reaction (PCR) in these patients for 2 reasons: (1) it has been shown that different viruses can be identified by PCR in the aqueous and vitreous,4Mitchell S.M. Fox J.D. Aqueous and vitreous humor samples for the diagnosis of cytomegalovirus retinitis.Am J Ophthalmol. 1995; 120: 252-253Abstract Full Text PDF PubMed Scopus (17) Google Scholar and (2) intravitreal treatment, when used, can be given through the same needle when the sample has been taken. This avoids the need for 2 injections for the patient. We reported a difference in the RD rate between those who had received prophylactic laser and those who did not. Media opacity is not the only cause of significantly reduced visual acuity in these patients, and involvement of the macula or optic neuropathy is common. It is important that, if laser photocoagulation is to be given, it is done posterior to the involved retinal edge—we aim to leave a gap of at least 100 μm from the edge of involved retina to the site of the applied laser burn where possible to ensure, as well as we can, that we are not lasering involved retina. To our knowledge, we have not had an RD secondary to a laser-induced hole in the retina. In eyes where there is too much vitritis for us to ensure that adequate barrier laser has been applied, we now ask our vitreoretinal colleagues to undertake a vitrectomy and put adequate endolaser on for us. Acute Retinal NecrosisOphthalmologyVol. 115Issue 6PreviewWe read with great interest the article by Lau et al in the April 2007 issue on the subject of acute retinal necrosis (ARN).1 The authors performed a retrospective review of 27 eyes with ARN that were treated with intravenous acyclovir and underwent confirmatory testing with vitreous biopsy. The authors concluded that prompt diagnostic testing should be performed and that prophylactic laser retinopexy reduced the incidence of retinal detachment (RD). Although we commend the authors for their efforts, we have reservations regarding this later conclusion. Full-Text PDF