Eyeball Histology Flashcards
what are the structures shown here
what are these layers called
what are these layers called
what are these structures
what are these structures
what are these structures
what are these structures
what are these structures
what are the structures
what is occuring here
Artefactual retinal detachment
Slide 2: This low power image shows the layers/tunics of the wall of the eyeball (outer fibrous, middle vascular and inner nervous) in the area of the vitreous chamber. Note that the fibrous tunic (sclera) is significantly thicker than the vascular or nervous tunics – how does this relate to the function of the sclera?
The sclera is responsible for giving the eyeball shape and resisting the pressure from the content – therefore it is a thick, tough layer. Also provides attachment points for the extra-ocular muscles.
Slide 3: What structure, located within the choroid, is not present in the pig but is present in the other major domestic species? What is its function?
The Tapetum Lucidum – a reflective layer that reflects light back through the retina, increasing the stimulation of the receptor/neuroepithelial cells and therefore increasing the sensitivity of the eye in low light levels.
Which cranial nerve provides sensory innervation to the cornea?
This slide (medium power) shows the limbus of the fibrous tunic (the junction between the sclera and the cornea). Note the paler appearance to the cornea, and the more evenly organised structure to the cornea compared to the sclera.
Trigeminal (cranial nerve 5)
What is the importance of Descemet’s membrane when assessing corneal ulcers with fluoroscein?
This slide (high power) shows a section of the cornea (the anterior surface of the eye is to the top left of the image, with the anterior chamber to the bottom right). The anterior and posterior epithelia are labelled, as is Descemet’s membrane. The bulk of the cornea (the Substantia Propria) is comprised of carefully arranged layers of collagen fibres – this arrangement allows the cornea to be transparent).
Descemet’s membrane is the last barrier to complete perforation of the cornea – when fluorescein is applied, it will not adhere to Descemet’s membrane (but will adhere to the exposed substantia propria), resulting in a non-staining area in the centre of the ulcer. When seen, this non-staining centre indicates a corneal ulcer that is close to rupturing.
Other than the support and adapation of the lens, what is the other major function of the ciliary body and processes?
This high-power slide shows the ciliary body (part of the vascular tunic). The ciliary body and ciliary processes can be identified (the iris is seen at the top right of the image). Zonular fibres (not seen in this image) extend from the ciliary processes to suspend the lens and control its thickness and therefore focussing power.
Production of the aqueous humour that fills the anterior and posterior chambers of the eyeball.
How is the movement of the iris (and the size of the pupil) controlled?
This medium-power slide shows the iris (with the pupil to the left of the image). The posterior pigmented epithelium can be identified – this give the eye its colour. The iris contains smooth muscle (radial and circular fibres) which control the size of the pupil and regulate the amount of light entering the eye.
Pupillary constriction is stimulated by parasympathetic innervation (carried by the Oculomotor nerve (Cranial Nerve 3); Pupillary dilation is stimulated by sympathetic stimulation (originating from cranial thoracic segments of the spinal cord).
What condition can arise if the drainage angle is blocked or has a congenital malformation? What are the possible consequences of this condition?
This low-power image shows the iridocorneal angle (also called the filtration angle or drainage angle). The lens is not seen on this image, but would separate the posterior and vitreous chambers. Aqueous humour produced by the ciliary body is secreted into the posterior chamber, passes into the anterior chamber through the pupil and exits via the iridocorneal angle. The rate of drainage of aqueous humour should match the rate of production.
Glaucoma – an increase in intra-ocular pressure due to failure of aqueous humour to drain away from the eye. The eye will become swollen and (extremely) painful, and the increased pressure can lead to blindness.
Are neuroepithelial/receptor cells present throughout the retina?
This high-power image shows the layers of the retina.
Outer layer of pigmented epithelium prevents light reflecting back through the receptor cells and so increases acuity.
The receptor/neuroepithelial cells (Rods and Cones) detect the light and generate nerve impulses, which are passed via the bipolar ganglion cells to the multipolar ganglion cells and then via the nerve fibres to the optic nerve.
Close apposition between the retina and choroid (which is maintained by the vitreous body in the vitreous chamber) is vital to maintain the nutrient supply to the retina.
A detached retina can result in cell death and blindness.
A frequent artefact seen in histological sections of the eyeball is an apparent retinal detachment, resulting from the loss of the vitreous body when the eyeball is sectioned (see slide 9a – in this image the retina is detaching from the choroid (arrow) as a result of the sectioning of the eye).
No – they are not present over the optic disc (see Slides 10 and 11) and are also absent from the retina in the anterior 1/3 of the vitreous chamber (in the area of the ciliary body/iris) – light entering the pupil will not strike these areas and so receptor cells are not needed. The junction between the visual and non-visual parts of the retina is called the ora serrata.
what is a frequent artefact seen in histological sections of the eyeball
apparent retinal detachment, resulting from the loss of the vitreous body when the eyeball is sectioned (see slide 9a – in this image the retina is detaching from the choroid (arrow) as a result of the sectioning of the eye).
what are the structures shown
What other structures enter the eyeball alongside the optic nerve? Would you expect to see these structures on ophthalmoscopic examination?
This medium-power image shows the optic disc and origin of the optic nerve (Cranial Nerve 2) at the posterior end of the eyeball. The retina has detached from the choroid either side of the optic disc – this is a processing artefact. The retinal nerve fibres can be seen collecting together to leave the eye as the optic nerve.
Retinal arteries and veins – should be able to see these with an ophthalmoscope.
What muscle are these fibres from and what is its function?
From Orbicularis oculi – function is to close the palpebral fissure (close the eyelids/blink)
What structures can be found at the base of the cartilage of the 3rd eyelid?
Lacrimal glands – gland of the third eyelid or Nictitating/Nictitans gland (and a deeper gland seen in pigs and cattle).
what are the structures here
