SLIDE 200 retina and cornea (of dog). 015 Histology of Eye & Ear development Objectives: At the end of this practical you should be able to : 1. Recognise and describe a section of neural retina, identifying areas of histogenesis with lamination/stratification and the adjacent choroid and scleral layers. 2. Recognise and describe a section of cornea, distinguishing areas of limbus-like character, as well as Descemet’s and Bowman’s membranes. 3. Be able to describe and recognise various stages in the development of optic vesicles, the differentiation of the optic cup, lens and adjacent structures, including : developing ciliary body and anterior and posterior chambers of the eye. 4. Distinguish between otic vesicles at various stages of their development and their spatial relationship with portions of the pharynx and developing cochlea in histological section. 1 EYE SLIDE 200 retina and cornea (of dog). Draw a low power sketch of this section identify the position and label: Cornea. Non- neural retina. Anterior chamber. Iris. Neural retina. Posterior chamber. Ciliary apparatus. Choroid. Cavity of vitreous humor. Corneal limbus. Sclera. Through examination observe whether different areas of the retina exhibits neural (thicker) and non neural (thinner) organisation approaching the iris. Q 1. In terms of retinal function, what might engender this structural distinction? Q 2. The function of the cornea is to?

Using higher magnification, examine the neural retina in more detail and draw a ‘full depth’ sketch of a small portion of this area to illustrate its very pronounced stratification/lamination and label the different zones. Cavity of vitreous humor Inner limiting membrane. Nerve fibre layer. Ganglion cell layer. Inner plexiform layer. Inner nuclear layer. Outer plexiform layer. Outer nuclear layer. Outer limiting membrane. Layer of rods and cones. Pigmented epithelium. Choroid layer. Scleral layer. sclera Note the arrangement of the choroid and scleral layers. Having located the cornea at low magnification, examine this at high magnification. Five layers can be identified in the cornea : 1. anterior epithelium 2. anterior sub-epithelial membrane (lamina) 3. stroma 4. posterior limiting membrane (Descemet’s) 5. posterior epithelium (corneal endothelium) Highlight the cellularity and the and the extent and organisation of the extracellular matrix in these compartments. Q 3. What type is the anterior epithelium? Q 4. What type is the posterior epithelium? Q 5. What is the corneal limbus? Note the lack of vasculature in the cornea proper.

2 DEVELOPING EYE SLIDE 11 (Coronal section through head at the level of the diencephalon and developing eyes) Examine this slide at low magnification and without drawing, identify the developing eye. Also note the location and organisation of the developing brain, nasal cavity and eye-lids. At high magnification, draw and label a region encompassing the equator of the lens, cornea, iris, retina, ciliary body and if possible anterior and posterior chambers of the eye. See if your section includes a cut through the optic nerve. Note the thickening of the retinal cell layer and the spatial differentiation of the lens fibre cells and epithelium. Care should be taken to distinguish between eye chambers and ‘space artefacts caused by the fixing and sectioning of the material. The surrounding lens capsule is composed of basal lamina and collagen fibres. The cuboidal epithelial cells on the anterior surface have their bases facing the lens capsule and their apices facing the lens fibres. At the equator of the lens the cells elongate and differentiate into lens fibres forming the body of the lens. These run in an anterior-posterior direction. The fully differentiated fibres are hexagonal in cross section and have lost their nucleus and most cell organelles. An examination of a variety of these sections will demonstrate the progressive development of the optic vesicle and perhaps its intimate association with the initial stages of lens formation and its continuity with the lateral diencephalon. If so highlight the organisation of these structures. Q 6. How is the diameter of the lens controlled?

Green Labelled slide set for eye 3 Green Labelled slide set for eye Examine one of the green labelled sections showing the early stages of eye development. Identify, with annotated notes providing your reasons, the degree of its development. 4 Green Labelled slide set for ear These sections demonstrate various stages of otic (ear) vesicle development and its association to other developing structures. Examine one of these slides and identify and draw the relationship between the developing otic vesicle and the pharynx. If possible try to identify the pharyngeal pouches and the visceral arches. Care should be taken to accommodate the possibility that at this stage of development, the prominent flexure of the head region can result in your section going through both hind brain and fore brain and sometimes also, the spinal cord. In your drawing, specify the orientation of the otic vesicle and regions of the primordial cochlea development and the semicircular duct development. Where possible, label the pharynx, otic vesicle, developing cochlea and 1st and 2nd visceral arches.