The lesions of the external ear are mainly those of the skin and are reported with the integumentary system. This INHAND document serves as a framework that can be used for the harmonization of diagnostic criteria of otic lesions in laboratory rats and mice. well mainly because lesions induced by exposure to test materials, are included. Although some diagnoses have synonyms offered, these terms may not be appropriate as histologic diagnoses in toxicity studies (i.e., coloboma and synechia). The nomenclature recommended here is generally descriptive rather than diagnostic. I. Nonproliferative and Proliferative Lesions of the Rat and Mouse Vision Histological processing of the eye The eye and optic nerve are included on the core list of tissues recommended by the Society of Toxicologic Pathology for histologic examination in nonclinical repeat-dose toxicity and carcinogenicity studies. The perfect vision section for a routine rodent toxicity study is usually a superior-inferior sagittal section, passing through the optic nerve head, with proper orientation and free of artifacts. Cornea should be free of clefts or folds, and corneal endothelial cells should not be vacuolated. Shattering or vacuolation of the lens should be avoided, and the lens should be correctly oriented PKN1 in the globe, with the epithelium facing the cornea. Artifactual retinal separation or vacuolation is usually a common problem, and evaluation of photoreceptors demands sections no greater than 5 m in thickness. Specialized ocular studies may require a different sectioning protocol, depending on the route of administration (systemic, topical intravitreal, sub-Tenon), the nature of the test article (aqueous answer, viscous depot, slow-release capsule, stem cells, subretinal device), or as a result of unusual ophthalmoscopic findings. Pathologists should be involved in determining the best protocol for a particular study. PND-1186 PND-1186 The genesis of a good ocular section begins at necropsy. Rough handling of the eye at enucleation can induce retinal separation and optic nerve PND-1186 artifacts. The optic nerve should be transected at the level of the orbit to maximize the available nerve tissue. Extraocular tissues, including glands, should be trimmed off the globe prior to fixation to optimize the fixation of the retina and avoid separation; this also allows better visualization of the landmarks for subsequent trimming. Incision of the globe prior to fixation will compromise the architecture of the retina due to the reduced pressure inside the globe. Similarly, injection of fixative into the globe is not recommended, and is not necessary for rodent eyes. If orientation is critical, consider using tissue marking fluid or a suture to identify landmarks or the 12?oclock position at time of collection, as landmarks are more difficult to see in a fixed globe. Left and right eyes should be clearly differentiated to allow correlation with clinical findings. A variety of fixatives PND-1186 may be used. Perfusion fixation frequently results in artifactual spaces in the retina, and immersion fixation is probably a better option for rodent eyes. Ensure PND-1186 that the eye is usually immersed in a sufficiently large volume of fixative (at least 10x the volume of the eye) as rapidly as possible to prevent autolytic change in the retina. Submersion in 10% formalin is frequently used in toxicology studies, but retinal preservation is usually often compromised. Davidsons answer gives better retinal fixation than 10% formalin, but prolonged exposure will result in artifacts associated with hardening of the lens, and clefting and pseudoedematous changes in the cornea. Rodent eyes should remain in Davidsons answer for 24 hours (no more than 48 hours). For best results, eyes should be transferred directly to ethanol around the tissue processor; consider washing and transferring to ethanol if a short delay (up to 10 days) is usually anticipated, but longer term archival of eyes warrants transfer to 10% formalin. Davidsons fixation is usually associated with artifactual vacuolation in the optic nerve due to the ethanol content, and thus a small section should be collected for fixation in 10% formalin for cross-section examination. Davidsons fixation is compatible with immunohistochemistry techniques for many antigens, and morphology is usually superior to that obtained with formalin fixation, but it is usually not suitable for electron microscopy evaluation. Fixation with solutions made up of glutaraldehyde (e.g. Karnovskys answer) is suitable if electron microscopy is usually planned (Ramos et al. 2011). To improve results, submerge the globe in the fixative for 2 hours to allow initial firming of the globe and then cut a.