Histopathological assessments: Ocular

An extensive list of tissues associated with the eye (eyelids, lacrimal glands, draining lymph nodes, etc.) are collected into protocol-directed fixatives as part of the histopathology process. Tissues are identified as ‘left’ or ‘right’ and maintained separately throughout all processes to correlate possible microscopic findings to the dose administration. 

Alternatively, various sub-anatomic structures may be isolated from the eye via fresh or frozen tissue techniques for use in bioanalytical or other analyses. Modified Davidson’s fixative is the fixative of choice for histology; however, a variety of fixation methods may be recommended based on species, dose design, and the purpose of the study. 

For large animal species, which encompass the majority of ocular studies, a minimum of three slides are prepared for Hematoxylin and Eosin (H&E) staining at species specific and dose specific critical landmarks. As necessary, technical staff work with an ocular-focused anatomic pathologist to develop study-specific trimming planes for optimal histopathologic evaluation of the eye. 

Additional slides may be taken from paraffin blocks via serial sectioning or step sectioning to allow for additional H&E staining, immunohistochemistry or, to better demonstrate specific ocular components, other special staining protocols.