The Eye Students PDF

Ch 14 - Sensory Perception (EYE) Molly’s mother first noticed that she problems with her vision when Molly was a baby. When Molly was breastfeeding, she would often focus her gaze on lights in the room. Molly would also rub and press on her eyes frequently. Molly was taken to the doctor where she...

Ch 14 - Sensory Perception (EYE) Molly’s mother first noticed that she problems with her vision when Molly was a baby. When Molly was breastfeeding, she would often focus her gaze on lights in the room. Molly would also rub and press on her eyes frequently. Molly was taken to the doctor where she was given a battery of vision tests. 1. Response to light. An infant will blink in response to a bright light. Molly did not respond to a bright light. The Snellen Eye chart is used to diagnose vision acuity. Why might this test be difficult to administer to Molly? 2. Pupil response. The pupil is an opening that allows light into the eye. Pupils will DILATE in darkness and constrict in bright light. - Molly’s pupils were slow to respond to a bright light shined on them. 3. Ability to follow a target. Infants will be able to follow a toy or other item they are interested in. Molly could not track a toy. 4. Ability to navigate obstacles. Molly would frequently bump into chairs and trip over objects on the floor. What other methods could be used to test a The doctor ordered additional tests, including a baby’s vision? genetic test to identify some types of hereditary blindness. Molly was diagnosed with Leber Congenital Amaurosis (LCE) Molly inherited two defective copies of the RPE65 gene. Each of her parents had one defective copy. (Recessive) A a What are the chances that A two parents who carried the defective gene would have a child with LCE? a The Structure of the Eye and Accessory Organs EYELID - Covers and protects the eye, thin skin Skin will not protect you from intense radiation, that’s why we use special goggles in a tanning bed EYELASHES - fine hairs that function to protect the eyes from dust and debris. Trichiasis - inversion of the eyelashes, which can irritate the eye CONJUNCTIVA is a covering around the eye and under the eyelids. PINK EYE - also known as CONJUNCTIVITIS (from bacteria, very contagious) Extrinsic Eye Muscles - move the eye 5 1 3 4 6 2 LACRIMAL GLANDS produce tears, which drain into the nasal cavity via the LACRIMAL DUCT. TEARS function is to moisten and lubricate the eye surface, and it has enzymes that kill bacteria. CANALICULI! Outer Tunic of the Eye Cornea - transparent dome that focuses light Cornea transplants can be done to replace damaged or diseased corneas. Your corneas can be donated if you have signed on to be an organ donor. Keratoconus is an eye condition in which the normally round cornea thins, causing a cone-like bulge to develop. Source: NPR http://n.pr/1a1oSx6 Outer Tunic of the Eye Sclera – continuation of cornea, going toward the back of the eye (white of the eye) Unlike other primates, human beings have eyes with a distinct color contrast between the white sclera and the colored iris. The cooperative eye hypothesis is a proposed explanation for the appearance of the human eye. It suggests that the eye's distinctive visible characteristics evolved to make it easier for humans to follow another's gaze while communicating. Why do dogs have white sclera? Outer Tunic of the Eye Optic Disk Optic Nerve – exits at optic disk and transmits information from the eye to occipital lobe of the brain. During Prohibition, methanol poisoning was the main cause of blindness. Wood Inflammation of the optic nerve can alcohol or “spirits” cause optic neuritis, or sudden vision contained a chemical loss. It is common in those with multiple that would damage the sclerosis. optic nerve. Vision loss may not be permanent. Middle Tunic of the Eye Choroid – contains blood vessels Ciliary Body – holds the lens in place Lens – focusing Iris – colored portion of the eye Pupil – opening for light to enter Aqueous humor – liquid surrounding the lens Eye Color Melanin is a brownish pigment that adds color to your hair, eyes, and skin. Caucasian babies are born with very little melanin in the eyes, so they appear blue. When exposed to sunlight, melanin levels rise and the eyes can change color. Brown is the world’s most common eye color. Heterochromia - one eye is a different color than the other Mila Kunis PUPILS - dilate or constrict to adjust light entering eye Fun Fact: - When you are looking at someone you love, your pupils dilate, and they do the same when you are looking at someone you hate. What causes red-eye? The flash on a camera is bright enough to cause a reflection off of the retina -- what you see is the red color from the blood vessels. Many cameras have a "red eye reduction" feature. In these cameras, the flash goes off twice -- once right before the picture is taken, and then again to actually take the picture. The first flash causes people's pupils to contract, reducing "red eye" Inner Tunic Retina - visual receptor cells Fovea Centralis - region of the sharpest vision, also called the macula Optic Disc – where nerve fibers leave the eye, creating the blind spot Vitreous Humor – supports internal parts, fluid within the eye BLIND SPOT (optic disk) The region where the optic nerve and blood vessels goes in and out of the eye has no photoreceptors = BLIND SPOT. Hold your hands out at 45° and that’s the location of the blind spot. You can still see your hands because the other eye sees it. Close your right eye and look for your right hand and you’ll find the blind spot. The Retina - has PHOTORECEPTORS, which are sensors for light. In LCA, the RPE65 protein is expressed in the photoreceptor cells. The mutated form of this gene causes the cells to die, resulting in blindness. Rods = monochromatic (b&w) Cones = color vision RPE65 expressed in epithelium R.O.Y.G.B.I.V Rainbows are seen after rain because light is passing through water droplets. This separates the white light into the individual colors of the spectrum Humans have three different color sensitive cone cells (red, green, blue). Dogs only have yellow and blue. Stare at the 3 dots over her nose for 20 seconds. Then look at the wall or ceiling.  Vitreous Humor Fovea Centralis (macula) = the center of focus Aqueous Humor How Does the Eye Work? Accommodation = Lens changes shape to facilitate focusing. Images are then projected to the back of the eye (focal points). The lens reverses the image (objects are seen upside-down) Zonules of Zinn - connect ciliary body to lens - can change the shape of the lens - also called suspensory ligaments Information from retina passes through the optic nerve, crosses at the chiasma, and is sent to the occipital lobe of the brain. The brain is responsible for interpreting those images. We have difficulty interpreting images that are upside down Which one is the real mona lisa? Problems with the Eyes Cataracts - Clouding of the lens leads to a clinical condition known as CATARACTS. Treatment is to remove the lens and replace it with an artificial one, called an intraocular lens (IOL) Problems with the IRIS and PUPIL The function is to constrict or dilate the pupil (opening) to allow light in. Therefore, it regulates the amount of light passing to the visual receptors of the eye. ANIRIDIA = a condition where a person is born without an iris Onchocerciasis, also known as river blindness, is a disease caused by infection by a parasitic worm. Symptoms include severe itching, bumps under the skin, and blindness. Color Blindness A genetic trait that affects boys more than girls. The location of the gene is on the X chromosome. FLOATERS occur when the vitreous substance clumps and casts shadows on the retina. Floaters don’t actually move, the eye just tries to track them. Retinal Detachment A retinal detachment occurs when the retina is pulled away from its normal position. Blindness can occur if it is not treated right away. Symptoms flashing lights; new floaters; a shadow in the periphery of your field of vision; a gray curtain moving across your field of vision. Glaucoma -pressure from vitreous humor damages the optic nerve and can lead to blindness. Can be managed with medication. Hyperopia = farsightedness You can see distant objects fine, but close objects appear blurry Presbyopia is the loss of ability to see close objects or small print, age-related. Myopia = nearsightedness You can see near objects fine, but distant objects appear blurry ASTIGMATISM is when the cornea has an irregular shape. Part of the field of view is out of focus. Most vision problems are treated with glasses or contact lenses. Both change the focal point of the light entering the eye. Surgery is also an option Gene Therapy may also be an option for some types of blindness. In 2010, the FDA approved gene therapy for Leber Amaurosis. Molly’s Story ~17 min ciliary body vitreous humor fovea centralis iris pupil aqueous humor optic nerve cornea sclera retina optic disk suspensory ligaments choroid lens