Special senses vision
1 / 12

Special Senses: Vision - PowerPoint PPT Presentation

  • Uploaded on

Special Senses: Vision. The accessory structures of the Eye. Eyebrows Shade eyes from sunlight Prevent sweat in eyes Eyelids Lacrimal caruncle – sebecous and sweat glands “sandman” Reflex blinking every 3-7 seconds to prevent drying Eyelashes – nerve endings to trigger blink reflex

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation

PowerPoint Slideshow about ' Special Senses: Vision' - dalmar

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

The accessory structures of the eye
The accessory structures of the Eye

  • Eyebrows

    • Shade eyes from sunlight

    • Prevent sweat in eyes

  • Eyelids

    • Lacrimalcaruncle– sebecous and sweat glands “sandman”

    • Reflex blinking every 3-7 seconds to prevent drying

    • Eyelashes – nerve endings to trigger blink reflex

  • Conjunctiva

    • Transparent mucous membrane (lubricates eye)

    • Lines eyelids and white of eye

    • Very thin, lots of bv

  • Lacrimal Apparatus

    • Lacrimal gland – continually releases tears thru excretatory ducts, blinking spreads tears downward

    • Tears drain through paired openings called punctum , through the canaliculi into the lacrimalsac, ultimately draining into the nasal cavity via the nasal lacrimal duct

    • Tears – mucus, antibodies, and lysozyme (bacteria destroying enzyme!)

Internal eye structures
Internal Eye Structures

  • Sclera

    • tendon like “white” of eye

    • shapes eye and attaches to muscles

    • avascular

  • Cornea

    • Avascular

    • Window allows light into eye

    • Pain receptors

    • Can be transplanted w/no rejection!!

  • Aqueous Humor

    • Clear fluid, similar to blood plasma

    • Forms & drains continuously

  • Choroid

    • Vascular, dark brown (prevent light from scattering)

  • Ciliary body

    • Ciliary muscles – smooth muscle control lens shape

    • Cilaryzonule – ligamenrts hold lens in place

  • Iris

    • Smooth muscle possibly containing brown pigments

    • Pupil – round central opening

  • Lens

    • Biconvex, transparent, flexible structure

    • avascular

  • Vitreous Humor

    • Transmits light & maintains interocular pressure

    • Lasts a lifetime

  • Retina

Vision physiology
Vision Physiology

  • Objects have color b/c they absorb some wavelengths of light and reflects other w/in the visible spectrum

  • Refraction of light occurs when it meets the surface of a different medium at an oblique angle (the greater the angle, the greater the bending)

  • A convex lens will bend light so it converges at a focal point creating a “real image” – upside down and reversed

    (concave lenses diverge light)

Retina 3 layers
Retina – 3 layers:

  • Pigmented layer

    • Absorb light, prevent scattering

    • Phagocytes – remove damaged photoreceptors

    • Store vitamin A

  • Neural layer

    • 3 main types of neurons

      • Photoreceptors (millions)

        • Rods – dim light & peripheral vision receptors

        • Cones – color vision & high acuity

          • Macula –oval to blind spot (mostly cones)w/fovea centralis(only cones) in center

      • Bipolar cells

      • Ganglion cells – generate action potentials

        (and horizontal cells and amacrine cells help w/ visual processing)

    • Optic Nerve – ganglion cell axons

      • Optic disc – blind spot (lacks photoreceptors)


  • Detect photons between 700-400nm

  • Rods – presence or absence of photons and cannot discriminate wavelength (very sensitive)

  • Cones only function in bright light

    • Blue – pigments sensitive to blue light

    • Green

    • Red

  • Stimulation in various combinations creates perception of variety of colors

  • Colorblindness – 1+ cones absent or nonfunctional

  • Photoreception

    • Names rods and cones refer to shape of cell

    • Arrival of a photon alters membrane potential changing rate of neurotransmitter release

    • Discs contain visual pigments that absorb photons derived from rhodopsin (opsin protein varies w/type of photoreceptor + retinal made from Vit A)

    • Night Blindness due to insufficient vitamin A (converted from carotene) or functional photoreceptors

    Focusing of light on the retina
    Focusing of Light on the Retina

    • Emmetropic vision– normal (20ft)

      • Ciliary muscles are relaxed

      • Lens is at its thinnest (lowest refraction)

      • “Real Image” is projected upside down and backwards

    • Accomadation – for objects less than 20ft

      • Ciliary muscles contract

      • Lens bulges, increases refraction of lens

      • Near point of vision 4 inches (closer in children and increases w/age)

      • Pupils constrict, preventing divergent light from blurring vision

      • Convergence – medial rotation of eye balls

      • Prolonged periods cause eye strain

    Common vision problems
    Common Vision Problems

    • Myopia (nearsighted)

      • Object focused in front of retina (due to long eyeball)

      • Corrected w/concave lens or LASIK to flatten cornea

    • Hyperopia (farsighted)

      • Object focused behind retina (due to short eyeball)

      • Corrected w/convex lens

    • Astigmatism

      • Unequal curvature of lens and/or cornea causing blurred images

    Visual pathway
    Visual Pathway

    • Photoreceptor  bipolar cell  ganglion cell (converge to form optic nerve)… half nerve fibers cross at optic chiasma to opposite thalamic nucleus  brain stem (midbrain pupillary reflex centers) and cerebral cortex of occipital lobe

    • Collateral branches from optic tract to hypothalamus for circadian rhythms