Comparative study of laser-induced choroidal neovascularization in rats by paraffin sections, frozen sections and high-resolution optical coherence tomography

The purpose of this study was to demonstrate the value of a quantitative study concerning experimental choroidal neovascularization (CNV) tissue by correlating the paraffin sections and frozen sections with optical coherence tomography (OCT) images. After OCT imaging was performed, four right eyes from the normal Brown Norway (BN) rats were made into paraffin sections and four left eyes were made into frozen sections. Laser photocoagulation was performed on the right eyes of the other 32 BN rats to induce CNV; these rats then were divided into two groups. After the OCT imaging was performed, four eyes were made into serial paraffin sections in Group A or frozen sections in Group B at 1 week after laser photocoagulation, and weekly for 4 weeks. A quantitative comparison of histopathological images and OCT images was performed. The thickness of the sensory retina and choroid of normal BN rats in paraffin sections was perceptibly less than that in the frozen sections, and the thickness of the sensory retina in the frozen sections was similar to that measured in the OCT images. The maximum thickness of the CNV tissue in the frozen sections was greater than that in the paraffin sections, but similar to that measured in the OCT images from week 1 to week 4. Only the frozen sections accurately matched the high-resolution OCT images because of the processing artifacts in the paraffin sections. In further quantitative studies on experimental CNV, the frozen sections may be more preferable if the thickness of the CNV tissue is to be measured and compared.