Re: Infectious endophthalmitis after intravitreal injection of antiangiogenic agents.

To the Editor: We read with great interest the article by Nagpal et al. In the article, the authors have prospectively compared the effects of 20-millisecond Pattern Scanning Laser (Pascal) with 200-millisecond single-spot, 532-nm, solid-state green laser (GLX) in nonproliferative and proliferative diabetic retinopathy. They claimed that Pascal panretinal photocoagulation (PRP) showed lesser collateral damage and was less painful for the patient compared with GLX. We would like to address several points in this study that may provide a more open interpretation of their findings to the journal readership. Currently, the standard laser pulse durations for PRP range from 20 milliseconds to 100 milliseconds. The use of 200-millisecond pulse laser appears rather excessive and not in keeping with current laser practice. Inevitably, the laser–tissue interactions and pain responses using 200-millisecond pulse laser will be considerably greater when compared with 20-millisecond PRP. ‘‘The Pascal and GLX systems showed average fluences of 191 and 40.33 J/cm, respectively. ’’ These data are clearly erroneous because shorter pulse duration will deliver a lower fluence compared with higher pulse durations. These data may be a typographic error as the abstract results conflict with the data presented in the article’s results section and Table 1. The authors report significant differences in fluence between Pascal and GLX; however, these data would appear inconsistent to readers and require clarification by the authors. A Mainster 165 PRP lens (magnification, 31.96) was used in the study, but there is no mention of adjusted laser spot size and fluence calculations by the authors. The current Pascal system has an integrated laser lens correction mode that will automatically adjust the fluence according to the laser lens used by the operator. This lens magnification factor requires clarification by the authors in order that these laser parameter data may clearly be interpreted. The fluence data presented by the authors would suggest that a 100-mm spot size was used for PRP, and the final 200-mm spot would be as a result of laser spot magnification. Otherwise, the reported fluence values should be corrected by 31.96 magnification, and this will produce lower fluence levels. GLX fluence range would be 33.1 J/cm to 66.3 J/cm (average, approximately 48 J/cm), and Pascal fluence range would be 6.6 J/cm to 16.6 J/cm (average, approximately 11 J/cm). The corrected fluence for 20-millisecond Pascal PRP would significantly be less than the authors’ report, and further clarification is required by Nagpal et al. To achieve threshold Grade 3 burns, the Pascal system required an average power of 630 mW (range 400–1000 mW), whereas the GLX needed 288 mW. The power used at 20-millisecond appears excessively high for threshold 20-millisecond PRP. The Pascal photocoagulator system was introduced to Manchester in 2006. We undertook a large retrospective evaluation of Pascal laser at Manchester Royal Eye Hospital and have recently published our experience using 20-millisecond to 30-millisecond Pascal PRP in proliferative diabetic retinopathy. On average, laser powers between 350 mW and 400 mW were required for 20-millisecond to 30-millisecond PRP, and levels of PRP power greater than 800 mW have not been encountered in our practice. There may be a higher risk of choroidal rupture and subretinal neovascularization using very high power at short pulse duration. The Manchester Pascal Study is a randomized clinical trial that evaluated the clinical effects of Pascal 20-millisecond versus 100-millisecond PRP (Archives of Ophthalmology 2010, in press). The laser powers used in our study were significantly lower than the Nagpal study, and we were able to demonstrate effective PRP responses using these lower laser power parameters. Furthermore, we performed 100-millisecond laser using much lower power settings than the Nagpal study, and so we would welcome the authors’ views on laser burn titration for PRP in their study. The authors report the changes in laser burn size over time. The laser burns in both groups increased up to 3 months, with doubling of the 200-millisecond burns and 1.5 times increase in average sizes of 20-millisecond burns. The expansion of 20-millisecond burns in this study is in contrast to the observations of laser–tissue interactions in animal studies. In the last few years, short-pulse laser burns have been found to progressively reduce in size, and this has been reported in vivo and in histopathologic work. We recently completed a randomized controlled trial of laser–tissue interactions, comparing 20-millisecond and 100-millisecond PRP burns. We observed a reduction in burn size using 20-millisecond laser lesions in the short-term. We presume that the enlargement of 20-millisecond burns in the study by Nagpal is related to the higher powers Supported in part by the Manchester Academic Health Sciences Centre (MAHSC) and NIHR Manchester Biomedical Research Centre. P.E. S. has received financial support from Optimedica Corporation.