Special Senses: Vision Flashcards
___ % of the body’s sensory receptors are in the eyes.
70
What is the function of eyebrows?
Eyebrows - overlie the supraorbital margins; shade the eye from sunlight and prevent perspiration from reaching the eye
Define, know the function of, and be ready to label: palpebrae, palpebral fissure, medial commissure, lateral commissure, lacrimal caruncle, tarsal plate, tarsal gland, and conjunctiva.
Eyelids (Palpebrae): thin, skin-covered folds that protect the eye anteriorly
Palpebral Fissure: separation between eyelids
Medial + Lateral Commissures: corners of the eyes
Lacrimal Caruncle: raised structure in medial commissure; oil + sweat glands
Tarsal Plates: supporting connective tissue for the eyelids; anchor points for orbicularis oculi and levator palpebrae superioris
Tarsal Glands: lubricating glands associated with the tarsal plates – when inflamed, causes a sty!
Conjunctiva: transparent mucus membrane that produces a lubricating mucus secretion
Differentiate palpebral and bulbar conjunctiva. What is the conjunctival sac?
Palpebral Conjunctiva: membrane on the interior of the eyelids
Bulbar Conjunctiva: membrane that covers the white of the eyes – contains small blood vessels
Conjunctival Sac: space between the palpebral and bulbar conjunctiva – the area where a contact lens rests
Be ready to identify the lacrimal gland in the picture.
What is contained within tears?
a dilute, saline solution containing mucus, antibodies, and lysozyme
What pathway do tears travel?
Blinking spreads tears toward the medial commissure – they enter the paired lacrimal canaliculi via the lacrimal puncta
Tears drain into the lacrimal sac and the nasolacrimal duct
Duct enters the nasal cavity
Know the 6 extrinsic eye muscles. In which direction does each of them move the eye?
table on slide 9
What is strabismus?
What are the 2 humors of the eye? In which compartment would you find each of them? What causes glaucoma?
Aqueous humor (Anterior)
Vitreous humor (Posterior)
…
What are the 2 regions of the fibrous layer of the eye?
sclera + cornea
What are the functions of the sclera? How about the cornea?
Sclera: opaque posterior region
- Protects and shapes the eyeball
- Anchors the extrinsic eye muscles
- Posteriorly, where the optic nerve exits, the sclera is continuous with the dura mater of the brain
Cornea: transparent, anterior 1/6 of the fibrous layer
- Forms a clear window – allows light to enter, bends light
- Both sides are covered with epithelium – the outer surface is protected from abrasions, the inner surface helps to maintain clarity
- Contains many pain receptors – responsible for blinking and tearing reflexes
The vascular layer of the eye is also called the: ________.
uvea
What are the 3 regions of the vascular layer?
choroid, ciliary body, and iris
What is the function of the choroid? The ciliary body? The iris?
Choroid: posterior portion of the uvea
- Supplies blood to all layers of the eyeball
- Brown pigment absorbs light to prevent scattering and visual confusion
Ciliary Body: anterior portion
- Thickened ring of tissue surrounding the lens
Iris: most anterior portion of the vascular layer
- colored part of the eye
- lies between the cornea and the lens – continuous with the ciliary body posteriorly
Know the location and role of the: ciliary muscles, ciliary processes, ciliary zonule, and pupil.
Consists of smooth muscle bundles – ciliary muscles – that control the shape of the lens
Capillaries of the ciliary processes secrete fluid of the anterior segment of the eyeball
Ciliary Zonule (suspensory ligament): extends from the ciliary processes to the lens – holds the lens in position
Pupil: round, central opening that regulates the amount of light entering the eye
What 2 muscles make up the iris? How do they work to control the size of the pupil?
Sphincter pupillae + dilator pupillae
For close vision and in bright light, sphincter pupillae contracts and the pupil constricts
Controlled by parasympathetic fibers!
For distant vision and in dim light, dilator pupillae contracts and the pupil dilates
Controlled by sympathetic fibers!
Where does the retina originate from? What are its two layers?
Retina: very delicate 2-layered membrane, originates from an extension of the brain
Contains millions of photoreceptor cells that transduce light energy, neurons, + glial cells
Outer Layer: pigmented layer
Inner Layer: neural layer
What is the function of the pigmented layer of the retina?
Pigmented Layer of the Retina: single-cell thick lining; next to the choroid; extends anteriorly to cover the ciliary body + iris
The pigmented layer absorbs light/prevents scattering, phagocytizes photoreceptor cell fragments, and stores vitamin A.
What 3 types of neurons make up the neuronal layer of the retina?
photoreceptors, bipolar cells, and ganglion cells
How do signals pass between these different types of neurons (in what direction)?
Signals are produced in response to light and spread from the photoreceptors to the bipolar cells to the ganglion cells
Which of these 3 types produces action potentials?
ganglion cells
Axons of the ganglion cells become the _____________________.
optic nerve
What is the optic disc? Why it is our blind spot?
Optic Disc: the site where the optic nerve leaves the eye; this site lacks photoreceptors so it is referred to as the “blind spot”
About how many photoreceptors are in each retina?
The retina has a quarter-billion photoreceptors
What are the two varieties of photoreceptors? What does each variety specialize in?
Rods and cones
Rods: dim-light and peripheral vision receptors
- More sensitive to light than cones
- No color vision or sharp images
- Mostly located in the periphery of the retina
Cones: bright-light receptors
- Provide high-resolution, color vision
What is the macula lutea? The fovea centralis? What kind of photoreceptors can you find there?
Macula Lutea: oval region located lateral to the blind spot of each eye – contains mostly cones
Fovea Centralis: tiny pit in the center of the macula lutea – contains all cones
The goal of eye movement is to provide the fovea centralis with images of different parts of the visual field
What is the lens? Where can you find it? What is its function?
Lens: a biconvex, transparent, flexible, and avascular structure
Located just posterior to the iris and held in place by the ciliary zonule
The lens changes its shape to precisely focus light on the retina
What protein can you find in lens fibers? Why does the lens become less elastic with age?
Lens Fibers: form the bulk of the lens; filled with a transparent protein called crystallin – no organelles, no nuclei
Lens fibers are continually added – the lens becomes more dense, more convex, and less elastic with age
What is a cataract?
clouding of the lens that causes visual distortion; can be genetic or a result of diabetes mellitus or a result of various exposures
What is refraction? What causes it?
Refraction: bending of light rays
When light travels in a given medium, its speed is constant
When light passes from 1 transparent medium to another medium with a different density, the speed of light changes and refraction occurs
What is the pathway of light entering the eye? Where is light refracted along this pathway?
Because lenses are curved, light hits them at an angle, and they can refract light
Convex lenses bend light so that its rays converge at a focal point
In general, the more convex a lens is, the more the light bends, and the shorter the distance will be between the lens and the focal point
What structure of the eye has the most refractory power? What structure of the eye can accommodate?
The majority of refractory power is in the cornea, but the cornea cannot change its shape and therefore cannot change focus
The lens CAN adjust its curvature to allow for fine focusing – distant and close vision!
What’s the average far point for vision? The average near point?
Far Point of Vision: distance beyond which no change in lens shape (accommodation) is needed for focusing
~20 feet for the healthy eye
What shape does the lens take for distance vision? For close vision? Know how this is caused by the ciliary muscle!
Ciliary muscles are completely relaxed in distant vision – this causes pull on the ciliary zonule, and the lens is stretched flat
What 3 steps are required for effective close vision?
- Accommodation of the Lens: changing the shape of the lens to increase refraction
Near Point: closest point on which the eye can focus – about 4 inches in a healthy eye
- Constriction of the Pupils: prevents most divergent light rays from entering the eye – mediated by the parasympathetic system
- Convergence of the Eyeballs: medial rotation of the eyeballs causes convergence of the eyes towards the object being viewed
What is presbyopia? Myopia? Hyperopia? Astigmatism?
Presbyopia: loss of accommodation < age 50
Myopia (Nearsightedness)
Eyeball is too long – the focal point is in front of the retina
A concave lens moves the focal point back – distance glasses
Hyperopia (Farsightedness)
- Eyeball is too short – the focal point is behind the retina
- A convex lens moves the focal point forward – reading glasses
Astigmatism: unequal curvatures in different parts of the cornea or lens
- Special glasses or laser surgery can correct
