W8 - special sense P2 the eye Flashcards
(17 cards)
Briefly describe the bony orbits
The eye is the organ of vision and consists of the eyeball and optic nerve.
The bony orbit contains the eye and its accessory visual structures.
The orbits are bilateral bony cavities in the facial skeleton.
The orbit is pyramidal-shaped, having the base directed anteriorly and the apex pointing posteriorly and medially.
Identify the four walls of the bony orbit: superior, inferior, lateral, and medial.
The apex of the orbit contains the optic canal, transmitting the optic nerve (CN II).
The orbit has also two fissures (slit-like openings): the superior and inferior orbital fissures. These are used by nerves and vessels to pass into and from the orbit.
Briefly describe the accessory structures of the eye
The accessory structures of the eye are the eyebrows, eyelashes, eyelids, extrinsic muscles that move the eyeballs and lacrimal apparatus.
The eyelids and eyelashes help protect the eyeballs from foreign objects and direct sunlight.
Blinking helps spreads lubricating secretions over the eyeballs.
Lacriminal Apparatus
Tear system
It includes a group of glands, ducts and canals that produce and drain the lacrimal fluid (tears) from the orbit into the nasal cavity.
The location of the lacrimal gland in the upper lateral corner of the orbit and the direction of the tear flow towards the medial corner, where tears are collected and delivered into the duct (nasolacrimal duct), which opens on the floor of the nasal cavity.
Tears
Extraocular Muscles
Six extrinsic eye muscles move the eyeball right, left, up, down, and diagonally.
Three pairs of cranial nerves are dedicated to the extraocular muscles (CN III, IV and VI).
Superior, medial, lateral and inferior rectus
Superior and inferior oblique
fibrous layer (fibrous tunic)
The external layer that consists of two parts:
Anterior cornea
Transparent fibrous coat that covers the coloured iris. It is curved and helps focus light rays onto the retina.
Posterior sclera
white of the eye, is a coat of dense connective tissue that covers all the entire eyeball except the cornea. It gives shape to the eyeball, makes it more rigid and protects its inner parts.
An epithelial layer called the conjunctiva covers the sclera, but not the cornea, and lines the inner surface of the eyelids. Inflammation of conjunctiva is called conjunctivitis.
vascular layer (vascular tunic)
consists of the choroid, ciliary body, and iris
Choroid
Thin membrane that lines most of the internal surface of the sclera.
It contains many blood vessels.
It also contains melanocytes that produce the pigment melanin, which causes this layer to appear dark brown in colour.
Melanin absorbs stray light rays, which prevents reflection and scattering of the light within the eyeball.
Ciliary body + Lens
iris
Retina
It lines the posterior three-quarters of the eyeball and is the beginning of the visual pathway.
The internal layer that consists of a pigmented layer and a neural layer
Neural layer
multilayered outgrowth of the brain. It includes the three distinct layers of retinal neurons – the photoreceptor layers, the bipolar cell layer, and the ganglion cell layer.
Pigmented layer
A sheet of melanin-containing epithelial cells located between the choroid and the neural part of the retina. The melanin in the pigmental layer helps to absorb stray light rays.
Photoreceptors & Vision Types
Rods: Allow vision in dim light and shades of grey (e.g., moonlight).
Cones: Allow colour vision and acute vision in brighter light.
Loss of cones = Legal blindness.
Loss of rods = Night blindness (difficulty seeing in dim light).
Colour-blindness: Loss or deficiency in one of the cone types.
Fovea Centralis: Area of highest visual acuity, densely packed with cones.
Rods: Most concentrated in the periphery of the retina, absent in fovea.
Visual Pathway & Ophthalmoscopy
Photoreceptor info flows to bipolar cells, then to ganglion cells.
Ganglion cell axons form the optic nerve, exit at the optic disc (blind spot).
Ophthalmoscopy: Examines the retina, optic disc, choroid, and blood vessels in the eye’s posterior part (fundus).
Name the two segments of the eye and state their significance
Interocular pressure
Briefly describe the visual pathway to the brain
After stimulation by light, the rods and cones trigger electrical signals that create a cascade of events associated with the visual pathway
Because of crossing at the optic chiasm, the right side of the brain receives signals from both eyes for interpretation of visual sensations from the left side of an object, and the left side of the brain receives signals from both eyes for interpretation of visual sensations from the right side of an object.
Steps of visual pathway to the brain
