a&p 1 (Vision) -lecture

• Lacrimal gland


  Produces and secretes tears (lacrimal secretion)
• Tear flow


  1. Tears enter the conjunctival sac via the excretory ducts of the lacrimal gland

  2. Tears flow down and across the eyeball

  3. Tears enter the lacrimal canaliculi at opening called lacrimal puncta

  4. Tears drain into the lacrimal sac

  5. From the lacrimal sac, tears empty via the nasolacrimal duct into the inferior meatus of the nasal cavity
• Conjunctiva


  Transparent mucous membrane that produces a lubricating mucous secretion
• Bulbar conjunctiva


  • A membrane that covers the White (sclera) of the eyes (not the cornea)
• Conjunctivitis


  Inflammation of the conjunctiva resulting in reddened, irritated eyes
• Pink eye


  Highly contagious conjunctival infection caused by bacteria or viruses
• Layers of the eyeball wall

  • Outer fibers layer
  • Middle vascular layer
  • Inner layer
• Humor


  Internal cavity filled with fluids
• Regions of the fibers layer

  • Sclera
  • Cornea
• Sclera


  • Opaque posterior region that protects and shapes eyeball
  • Anchors extrinsic eye muscle
  • Posteriorly, the optic nerve exits from the sclera
• Cornea


  • Transparent anterior ⅙ of fibers layer - forms a Clear Window that lets light enter the eye
  • Numerous pain receptors - blinking and tearing reflexes
  • High capacity for regeneration and repair
• Regions of the vascular layer

  • Choroid
  • Ciliary body
  • Iris
• Choroid region


  • The posterior portion supplies blood to all layers of the eyeball
  • Brown pigment absorbs light to prevent scattering of light, which would cause visual confusion
• Ciliary body


  • Anteriorly, the choroid becomes the ciliary body
  • Thickened ring of tissue surrounding the lens
  • Consist of smooth muscle bundles called ciliary muscles that control the shape of the lens
  • Ciliary zonules (suspensory ligaments) extend from ciliary processes to lens and hold the lens in position
• Iris


  • The colored part of the eye that lies between the cornea and leads continuous with the ciliary body
• Pupil


  • Central opening that regulates the amount of light entering the eye
  • Close vision in bright light causes sphincter pupillae (circular muscles) to contract in pupils to constrict; parasympathetic control
  • Distant vision and dim light cause dilator pupillae (radial muscles) to contract in pupils to dilate; sympathetic control
  • Changes in emotional state - pupils dilate when subject matter is appealing or requires problem-solving skills
• Components of the inner layer (retina)

  • Photoreceptor cells (rods and cones)
  • Neurons
  • Glial cells
  • Outer pigmented layer
  • Inner neural layer
• Outer pigmented layer of retina

  • Extends anteriorly single cell thick lining next to the choroid
  • Absorbs light and prevents its scattering
  • Phagocytizes photoreceptor cell fragments
• Neural layer of retina

  • Composed of three main types of neurons: photoreceptors, bipolar cells, ganglion cells
  • Ganglion cells' Axons exit the eye as optic nerve
• Optic disc


  • The site optic nerve leaves the eye
  • Lacks photoreceptors, referred to as blind spot
• Types of photoreceptors


  • Rods
  • Cones
• Rods


  • Dim light peripheral vision receptors
  • More numerous and more sensitive to light than cones
  • No color vision or sharp images
  • Number most significant at the periphery
• Cones


  • Vision receptors for bright light high-resolution color vision
• Macula lutea


  • Area at posterior pool lateral to blind spot
  • Contains mostly cones
• Fovea centralis


  • The tiny pit in the center of the macula lutea contains all cones, so it is a region with the best visual acuity
  • Eye movement allows us to focus in on objects so that fovea can pick it up
• Main types of neurons in neural layer

  • Photoreceptors
  • Bipolar cells
  • Ganglion cells
• Blind spot


  Located at the optic disc, lacks photoreceptors, referred to as blind spot
• Vitreous humor


  • Transmits light
  • Supports the posterior surface of the lens
  • Holds neural layer of the retina firmly against the pigmented layer
  • Contributes to intraocular pressure
  • Forms in the embryo and lasts a whole lifetime
• Chambers of the anterior segment

  • Anterior chamber - between cornea and iris
  • Posterior chamber - between iris and lens
• Aqueous humor


  • Plasma-like fluid continuously formed (unlike vitreous humor) by capillaries of ciliary processes
  • Supplies nutrients and oxygen mainly to the lens and cornea but also the retina and removes waste
• Retinal detachment


  • A condition where pigmented and neural layers separate (detach), allowing jelly-like vitreous humor to seep in between them
  • Can lead to permanent blindness
  • Usually happens when the retina is torn during a traumatic blow to the head or sudden stopping of the head during movement
• Glaucoma


  • Condition in which drainage of aqueous humor is blocked, causing fluid to back up and increase pressure within an eye
  • Pressure may increase to dangerous levels and compress the retina and optic nerve, leading to blindness
  • Late signs include seeing halos around lights and blurred vision
  • Detected by measuring intraocular pressure
  • Treated with eye drops, laser therapy or surgery
• Cataracts


  • Clouding of the lens
  • Consequences of aging, diabetes mellitus, heavy smoking, frequent exposure to intense sunlight
  • Some are congenital
  • Crystalline proteins clump
  • Lens can be replaced surgically with an artificial lens
• Visible light


  • Electromagnetic radiation that eyes respond to
  • Wavelengths between 400 to 700 nm
  • When visible light passes through the spectrum, it is broken up into bands or colors (rainbow)
  • Red wavelength is the longest and has the lowest energy, and violet is the shortest and has the most energy
  • Color that the eye perceives is a reflection of that wavelength
• Lens


  • Biconvex, transparent, flexible, and avascular
  • Changes shape to precisely focus light on the retina
  • Lens epithelium: anterior region of cuboidal cells that differentiate into lens fiber cells
  • Lens fibers: for the bulk of the lens and are filled with transparent protein crystalline
  • Lens fibers are continually added so the lens becomes more dense, convex, and less elastic with age
• Refraction


  Bending of light rays due to the change in the speed of light when it passes from one transparent medium to another, and the path of light is at an oblique angle
• Convex lens


  • Thicker in the center than at the edges
  • Bends light passing through it so that light converges at the focal point
  • The image formed at the focal point is upside down and reversed from left to right
• Concave lens


  • Thicker at the edges than in the center
  • Disperses light, preventing light from being focused
• The image formed at the focal point of a convex lens is upside down and reversed from left to right.
• Pathway of light entering the eye

  1. Cornea

  2. Aqueous humor

  3. Lens

  4. Vitreous humor

  5. The entire neural layer of the retina

  6. Photoreceptors