Laser burn intensity and the risk for choroidal neovascularization in the CNVPT fellow eye study

Objective: To explore the relationship between laser burn intensity and the subsequent risk for development of choroidal neovascularization (CNV) in e yes assigned to the treatment group of the Fellow Eye Study (FES) of the Ch oroidal Neovascularization Prevention Trial (CNVPT), using computerized met hods for laser burn quantitation, and to examine the association between la ser burn intensity and (1) drusen reduction and (2) visual acuity. Methods: Color fundus images before and immediately after laser treatment in the CN VPT FES were available for 53 of 59 eyes. Prelaser and postlaser treatment images were analyzed using custom-developed computer software, allowing for laser burn identification and quantitation. As measures of laser burn inte nsity, we derived integrated burn rating (IBR) (the integral of the normali zed intensity difference divided by the burn pixels), and the maximum burn intensity (MAX). We identified CNV using fluorescein angiography. A Cox pro portional hazards model was fit to the time to development of CNV. Baseline and 6-month color photographs were used to determine reduction in drusen. Visual acuity was measured using a standardized protocol. Results: The IBR and MAX spanned 4.5 logarithm units. After adjusting for smelting history a nd predominant drusen size, the risk ratio for CNV per logarithm unit of in creasing laser burn intensity for each measure was 2.0 (P=.05) for MAX and 1.7 (P=.07) for IBR. When patients were divided into high- and low-intensit y treatment groups of equal size, the high-intensity group had more drusen reduction (57% vs 32%; P=.14). There was no effect of laser intensity on ch ange in visual acuity at 6 months. Conclusion: Higher-intensity prophylacti c laser applications appear to be associated with a greater risk for develo pment of CNV and with more extensive drusen reduction.