Vision

Vision

1. What are the basics of vision?

   • It captures the light at the front of the eye and projects detailed images of the world into the retina, which is found in the back of the eye
   • The light captured is transduced into neural signals
   • The eye is moved by extra ocullar muscles.

2. What is the anatomy of an eye?

   • Retina: A layer of neurons in the back of the eye onto which detailed images of the external world are projected
     • Bipolar cells: Interneurons in the retina that receive information from rods and cones and pass it to retinal ganglion cells
     • Ganglion cells: Cells in the retina whose axons form the optic nerve
     • Fovea: The central portion of the retina. It is packed with the highest density of photoreceptors (specifically a high density of cones) and is the center of our gaze
   • Cornea: The transparent outer layer of the eye whose curvature is fixed. It bends light rays and is primarily responsible for forming the image on the retina
   • Lens: A structure in the eye that helps focus an image on the retina. It changes shape, controlled by ciliary muscles, to fine-tune the image on the retina, a process called accommodation
   • Ciliary muscles: Muscles that control the shape of the lens inside the eye, focusing an image on the retin
   • Photoreceptors: Neural cells in the retina that respond to light
     • They continuously release neurotransmitters, releasing less in the light (hyperpolarized) and more in the dark (depolarized)
     • Rods: Photoreceptor cells most active at low levels of light. They are involved in the scotopic system, which operates at low light levels. Rods are very sensitive but insensitive to color
       • Scotopic system: system in retina that operates at low levels of light
     • Cones: Photoreceptor cells responsible for color vision. They are involved in the photopic system, which operates at high light levels. Cones show sensitivity to color and involve less convergence compared to rods
       • Photopic system: system in the retina that operates at high levels of light
     • Photopigments are special receptor molecules in the rods and cones that capture light
       • Opsins: photopigment that responds to photonic energy
   • Optic nerve (CN II): A collection of ganglion cell axons that extend from the retina to the brain
   • Pupil: An opening formed by the iris that allows light to enter the eye. Its size changes to deal with a large range of light intensities
     • Dilation (opening) of the pupil is controlled by the sympathetic division of the autonomic nervous system
     • Constriction (closing) of the pupil is controlled by the parasympathetic division of the autonomic nervous system
   • Iris: A circular structure of the eye that provides an opening to form the pupil

3. Myopia: Inability to focus the retinal image of objects that are far away. Develops if eyeball is too long → cornea and lens focus image in front of the retina rather than on it

4. What is the order of the process of light capture?

   • Photoreceptors
     • Bipolar cells
       • Ganglion cells
         • Optic nerve