The Visual System Flashcards
What are the layers of the layer?
Fibrous layer
Vascular layer
Neural layer
What is the fibrous layer of the eye?
Contains the cornea and sclera, formed of collagen fibres.
What is the cornea?
Fibrous layer overlying the iris, responsible for focussing the light rays to the back of the eye in the retina, innervated by the trigeminal nerve.
What is the sclera?
Tough fibrous layer over the majority of the eye, innervated by the ophthalmic nerve which protects the eye. This is where the extra-ocular muscles attach.
What is the uvea?
Vascular layer of the eye which contains the
Iris
Ciliary body
Choroid plexus, a layer of connective tissue with the blood vessels of the eye from branches of the ophthalmic artery, ciliary muscles and suspensory ligaments.
What is the ciliary body?
Structure in the urea layer that is an extension of the iris. It produces aqueous humour for the anterior eye cavity, to nourish the lens and the cornea and keep the eye round and rigid.
It also has the ciliary muscle that have processes to connect to the pupils via suspensory ligaments for controlling the size of the pupil for light entry to the retina.
Where does the aqueous humour drain?
Aqueous humour travels through the trabecular mesh work and leaves via the canal of Schlemm, through the anterior ciliary veins.
What is the neural layer of the eye?
Contains a light sensitive layer of tissue called the retina which is connected to the optic nerve and contains the optic disc.
What is the blood supply to the retina?
Outer layer and retinal epithelium photoreceptors is supplied by the innermost layer of the choroid via choriocapillaris..
Inner layer is supplied by central retinal artery.
What is the optic disc?
Round spot on the retina where the axons of the retinal ganglion pass through to the optic nerve.
What is the iris?
Coloured part of the eye which contains:
Circular muscle formed by the sphincter pupillae under parasympathetic control.
Radial muscle formed by the dilator pupillae under sympathetic control.
What is the pupil?
Opening in the centre of the iris where light enters the eye. The diameter of this is controlled by the suspensory ligaments, ciliary muscles and muscles of the iris.
What is the fovea?
Pit in the retina which contains only cone photoreceptors, and has the highest visual acuity and resolution. This is located in the macula.
What is the lens?
Responsible for focussing light towards the retina, which is able to change shape via the accommodation reflex for focussing on close and distant objects.
What is the anterior cavity of the eye?
Located between the cornea and iris, filled with aqueous nutrient rich fluid produced by the ciliary body.This fluid nourishes the lens and cornea which maintains ocular pressure and drains into the Schlemm canal, held open by the trabecular mesh work.
What is the posterior cavity of the eye?
Located between the iris and the lens, filled with vitrous fluid to maintain eye shape and attachment to the retina and vision clarity.
What is the optic chiasm?
Crossing over of the optic nerves from each eye in the base of the hypothalamus, by the nasal field of vision. This is why the vision in the left eye is partially controlled by the right hemisphere.
Which muscles are present in the iris?
Dilator pupillae which causes dilation of the iris, under sympathetic control and forms radial muscle.
Sphincter pupillae which causes constriction of the iris, under parasympathetic control and forms circular muscle.
Which muscles are involved in pupillary constriction?
Sphincter papillae and ciliary muscle which contract due to parasympathetic innnervation via the Edinger-Westphal nucleus.
Which muscles are involved in pupillary dilation?
Dilator pupillae due to sympathetic innervation.
What is the accommodation?
To focus on a near or distant object, the lens will change shape.
How does the eye focus on distant objects?
Light enters in a parallel angle so lens should be unfocused. Ciliary muscle is relaxed, suspensory ligaments are now tight and cause constriction of the pupil, so less light enters. Each eye must be divergent and turn outwards.
How does the light focus on close objects?
Light rays enter at a divergent angle, so lens needs to increase focusing power by becoming short and curved. Ciliary muscle will contract to change lens shape as suspensory ligaments loosen and eyes converge and turn inwards.
What is the accommodation reflex?
Co-ordinated change in the eye from far away to focus on a near object consisting of:
Convergence via medial rectus muscle
Constriction/miosis through Edinger-Westphalia nucleus parasympathetic innervation
Contraction of the lens torn fatter and more Convex