![]() In most vertebrates and some molluscs, the eye allows light to enter and project onto a light-sensitive layer of cells known as the retina. The last common ancestor of animals possessed the biochemical toolkit necessary for vision, and more advanced eyes have evolved in 96% of animal species in six of the ~35 main phyla. The first proto-eyes evolved among animals 600 million years ago about the time of the Cambrian explosion. In other organisms, particularly prey animals, eyes are located to maximise the field of view, such as in rabbits and horses, which have monocular vision. The visual fields of many organisms, especially predators, involve large areas of binocular vision for depth perception. From more complex eyes, retinal photosensitive ganglion cells send signals along the retinohypothalamic tract to the suprachiasmatic nuclei to effect circadian adjustment and to the pretectal area to control the pupillary light reflex.Ĭomplex eyes distinguish shapes and colours. The most simple eyes, pit eyes, are eye-spots which may be set into a pit to reduce the angle of light that enters and affects the eye-spot, to allow the organism to deduce the angle of incoming light. ![]() Image-resolving eyes are present in molluscs, chordates and arthropods. Eyes with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system. In higher organisms, the eye is a complex optical system which collects light from the surrounding environment, regulates its intensity through a diaphragm, focuses it through an adjustable assembly of lenses to form an image, converts this image into a set of electrical signals, and transmits these signals to the brain through complex neural pathways that connect the eye via the optic nerve to the visual cortex and other areas of the brain. Eyes detect light and convert it into electro-chemical impulses in neurons (neurones). They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. If you’ve been wanting to dissect a cow or sheep eye, this would be the time to do it! Science supply stores sell preserved eyes, but you can sometimes find fresh ones if you live near a butcher shop and you ask in advance so they know to save one.Eyes are organs of the visual system. Some people really like dissecting things. ![]() Here is one you can print out and put on the wall: Activity 62-3: Dissect an eye (VERY OPTIONAL) I am not recommending or endorsing any of these websites, just posting the ones that have the most user-friendly eye tests. Usually the tests are posted on websites where companies are selling eyeglasses and contacts. Various tests include acuity (testing if you can see very small letters), astigmatism (imperfections in the shape of your cornea), light sensitivity, and the color blind test. However, the online eye tests are fun to take and they can let you know about eye issues you might not have been aware of. They tell you to go to an eye doctor for official diagnosis. Of course, the tests will first tell you that you can’t rely on these tests for accurate diagnosis of eye problems. You can find online eye exams that you can do on your computer. But here is a quick link you can use: Activity 62-2: Give yourself an eye exam ![]() The patterns and directions for this model are posted in the freedownloads on this website. Sample of final drawing 62 2) ACTIVITIES Activity 62-1: Make a paper model of the eye The next lesson will do more “physiology” which is now those parts work. “Anatomy” means learning what the parts look like and what they are called. In this drawing we will learn all the major parts of the eye. ![]()
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