Unit 1 - Vision PDF

Unit 1 - Vision Devin Mott PT, DPT Objectives Recall the layers of the eye Differentiate between cone and rod cells Describe the visual pathway Describe the pupillary light reflex Distinguish between sympathetic and parasympathetic effects on the eye Sense of Sight The eye ha...

Unit 1 - Vision Devin Mott PT, DPT Objectives Recall the layers of the eye Differentiate between cone and rod cells Describe the visual pathway Describe the pupillary light reflex Distinguish between sympathetic and parasympathetic effects on the eye Sense of Sight The eye has many similarities to an older-type film camera. The light rays from the image you view pass through the pupil, and then through the lens, where they are focused on the retina (photoreceptors). The iris allows the right amount of light to enter the eye for proper focusing. Anatomy Overview Orbital Region Eyeball Cones vs Rods Innervation Orbital Region (External Structure) Made up of: ○ Face around eye ○ Lacrimal Apparatus Eyelids: ○ Protects ○ Spreads lacrimal fluid Lacrimal Apparatus: ○ Lacrimal Gland ○ Lacrimal Canaliculi ○ Nasolacrimal Duct External Structures of the Eye (1 of 5) The orbit is a cone-shaped cavity formed by the skull that houses and protects the eyeball. ○ This cavity is padded with fatty tissue that acts as a cushion to prevent injury. Six short muscles connect the eyeball to the orbit, and allow rotary movement so you can see in all directions. External Structures of the Eye (2 of 5) The eyelids close over the eye to protect it from light, foreign particles, or impact injury. Eyelashes in the eyelid help to prevent large particles from entering the eye. External Structures of the Eye (3 of 5) The eyelids also contain sebaceous glands that secrete oil to keep the eyelids soft and pliant, and make the eyelashes slightly sticky to trap particles. External Structures of the Eye (4 of 5) The conjunctiva is a membrane over the surface of the eyeball that acts as a protective covering for the exposed surface. The lacrimal apparatus produces and stores tears and contains the lacrimal gland and its corresponding ducts. External Structures of the Eye (5 of 5) The lacrimal gland produces tears, spread by blinking, for cleaning and lubrication. ○ Tears act as an antiseptic. Internal Structures of the Eye (1 of 2) The globe-shaped eyeball is the organ of vision and is separated into two chambers of fluid that help to protect the eye. Internal Structures of the Eye (2 of 2) The fluids of the eye are called humors. ○ Aqueous humor is watery and bathes the iris, pupil, and lens and fills the anterior and posterior chambers. ○ Vitreous humor is a clear jelly-like fluid that occupies the entire cavity behind the lens. ○ The eye has three layers: sclera, cornea, retina Eye (Internal) Three Layers: ○ Fibrous Layer ○ Vascular Layer ○ Inner Layer Fibrous Layer Sclera: tough opaque part of eye ○ Provides attachment site for both the intrinsic and extrinsic muscles Cornea: transparent part of the eye ○ Contains 6 layers Vascular Layer Choroid ○ Blood supply to the eye Ciliary Body ○ Ciliary Muscles ○ Ciliary Processes ○ Ciliary Zonule Iris ○ Pupil Pupil ○ Sphincter Pupillae ○ Dilator Pupillae Layers of the Eye: The Choroid (1 of 3) Highly vascularized, pigmented middle layer that provides nourishment to the eye ○ Iris: colored portion that controls the opening (pupil) where light passes into the eye ○ Iris: a sphincter that in low light relaxes, allowing the pupil to dilate so more light can enter Layers of the Eye: The Choroid (2 of 3) Located behind the pupil is the lens, which is surrounded by ciliary muscles. These muscles can alter the shape of the lens, making it thinner or thicker to allow the incoming light rays to focus on the retina. Layers of the Eye: The Choroid (3 of 3) This process is called accommodation, which basically combines changes in the size of the pupil and the lens curvature to make sure the image converges in the same place on the retina and therefore is properly focused. Near vs Far Vision Lens Shape Shape of lens controlled by ciliary muscle Inner Layer Retina: ○ Pigmented Layer Prevent light scattering Phagocytic Activity ○ Neural Layer Photoreceptors Cones Rods Bipolar Cells Ganglion Cells Layers of the Eye: The Retina (1 of 4) The retina is a delicate membrane that continues posteriorly and joins the optic nerve. The retina contains two types of light sensing receptors called rods and cones. The rods are active in dim light and do not perceive color, while the cones are active in bright light and do perceive color. Layers of the Eye: The Retina (2 of 4) These receptors contain photopigments that cause a chemical change when light hits them, causing impulses to be sent to the optic nerve. Layers of the Eye: The Retina (3 of 4) The information is then sent to the brain, where the impulse is interpreted, in the visual cortex of the occipital lobe, and we “see” the object. Layers of the Eye: The Retina (4 of 4) In summary, light rays enter the eye and pass through the cornea, aqueous humor, pupil, lens, and vitreous humor and are focused on the retina. Here the photoreceptors in the retina cause an impulse to be sent to the optic nerve (Cranial Nerve II), which carries it to the occipital lobe of the brain for the interpretation we call vision. See Table 11–1 in the textbook. Cones and Rods Cones Rods ○ Bright light ○ Dim Light ○ Color Vision ○ Peripheral Vision ○ One cone per ganglia ○ Many Rods converge on one ganglion These receptors contain photopigments that cause a chemical change when light hits them, causing impulses to be sent to the optic nerve. Perception of Vision Eye Movements Muscular Overview ○ Extraocular Four Recti Muscles Two Obliques Levator Palpebrae ○ Intraocular ciliary muscle sphincter pupillae dilator pupillae. Extraocular Movements Visual Pathway Most fibers of optic tract terminate in lateral geniculate body (located in the thalamus) Axons are relayed to occipital lobe for visual processing ○ The temporal radiations (Meyer’s loop) are fibers that relay information from the contralateral superior visual field. ○ The parietal radiations (Baum’s loop) are fibers that carry information from the contralateral inferior visual field Visual Pathway Pupillary Reflex Normal Pathway: ○ Light enters via CNII (afferent path) ○ Parasympathetic response via CNIII (efferent pathway) Discussion How does the structure and function of the eye contribute to our perception of the visual world, and how do visual stimuli undergo processing in the brain to create our perception of sight?