vision Flashcards
Identify AND describe the THREE tunics (layers) of the eyeball
- Fibrous tunic (outer layer)
- Vascular tunic (middle layer)
- Reina (inner layer)
What does the fibrous tunic contain?
the cornea: a transparent layer that covers the iris and the curved shape that helps focus light onto the retina (refraction). Function: refracts 75% of light for focus
Sclera: “white” of the eye, provides shape and support of the eyeball and covers the entire eyeball except the cornea.
What does the vascular tunic contain?
Choroid: Melanocytes produce melanin to absorb scattered light within the eyeball and maintain a clear sharp image, is highly vascular, blood vessels provide nutrients to retina
Ciliary body: Ciliary processes (secrete aqueous humor) and Ciliary muscle (smooth muscle that alters shape of lens which is essential for focus (accommodation).
Iris: Colored portion of eye, color is determined by the amount of melanin, contains circular and radial smooth muscles, function is to regulate amount of light entering eye by changing diameter of the pupil
Pupil: Hole in the center of the iris and where light enters the eye
What does the retina contain?
- Photoreceptors - rods and cones
- Optic disc - site where the optic nerve exits the eyeball
- Retinal blood supply
- central retinal artery and central retinal vein
-Macula lutea - exact center of the posterior retina
Fovea centralis - center of the macula lutea (contains only cones and area of highest visual acuity)
State the functions of Rods
Rods - disturbed around periphery of the retina and specialized for black and white vision, shapes and movement, contains 120 million rod cells in each eye
State the functions of Cones?
Cones - sharp colored vision, six million in each eye and central fovea densely packed region (sharpest resolution)
Identify AND describe the functions for the Cavities and Chambers in the interior of the eyeball
Anterior Cavity - Anterior to the lens, has two chambers:
Anterior chamber - between the cornea and iris
Posterior chamber - between iris and lens is filled with aqueous humor which nourishes the lens and cornea
Posterior Cavity - lies between the lens and retina, contains the vitreous body, a jellylike substance that maintains the shape of the eye (intraocular pressure is the pressure in the eye produced by aqueous humor and vitreous body, it helps maintain the shape of the eye). Vitreal floaters are debris that float in the visual field.
Name the THREE cranial nerves involved with movement of the extrinsic eye muscles
- Oculomotor (lll)
- Abducens (VI)
- Trochlear (IV)
Describe each of the FOUR major processes of image formation: REFRACTION
Involves bending of light rays by cornea and lens to focus an image on the retina (central fovea)
Describe each of the FOUR major processes of image formation: ACCOMMODATION
involves changing the shape of the lens to focus light rays on the retina
Describe each of the FOUR major processes of image formation: PUPIL CONSTRICTION/DILATION
The smooth muscle of the iris controls the amount of light entering the eye and helps prevent scattering of light
Describe each of the FOUR major processes of image formation: CONVERGENCE
Medial movement of the eyes to keep both eyes focusing on an object.
State the role of the hypothalamus and midbrain in the visual pathway
Visual information in optic nerve travels to:
Hypothalamus to establish sleep patterns based upon circadian rhythms of light and darkness.
Midbrain which has some visual reflex centers that control movement of the head, eyes and trunk in response to visual changes.
Identify and describe the effects of aging on the eye and vision.
- Sharpness of vision decreases, colour and depth perception are reduced
- Retinal damage can result in macular degeneration
3.Decreased tear production resulting in dry eyes
4.Eyelids lose elasticity and less adipose tissue in the orbits give the appearance of sunken eyes.
State the changes to the visual structures which occur with ageing AND how this alters the formation of visual images.
- Lens: loses some of its elasticity and transparency resulting in cataracts
- Sclera: thickens and changes color
-Iris: fades or develops irregular pigments, muscles weaken causing slower pupillary reactions resulting in slower adaption to darkened areas. SO increased risk of falls.
