Eye

Overview of Layers

Tunica Fibrosa

• connective tissue layer
• outer connective tissue
• cornea
• sclera

Tunica Vasculosa

• connective tissue but rich in blood vessels
• choroid
• ciliary body
• stroma of iris

Tunica Nervosa

• derived from CNS
• retina
• posterior portion

Development

hallow out-pocket of diencephalon grows to overlying skin

optic cup tells skin to become lens

skin tells cup to keep invaginating

stalk will become optic nerve

Sclera

whites of eye

dense fibrous connective tissue

covers 5/6 of total surface area of eye

interrupted at back where optic nerve exits

• point is called lamina cribosa

functions

• structure
• protection
• site of muscle attachments

Cornea

11 mm diameter and 0.8 mm thick

essentially anterior most portion of sclera

layers

1. corneal epithelium

   1. outermost layer
   2. 5-6 layers of nonkeratinized stratified squamous epithelium
   3. free nerve endings

2. Bowman’s Membrane (basement)

   1. acellular

3. Substantia Propria (stroma)

   1. thickest layer

   2. keritocytes - specialized fibroblasts

      1. produce glycosaminoglycans

         1. rich in sulfates, hyaluronic acid, and ketaosulfates
         2. makes tissue very hydrated so clear and transparent

4. Descemet’s Layer/membrane

   1. basement membrane for next layer

5. Corneal endothelium

   1. low cuboidal epithelium

Tunica Vasculosa

blood vessels follow optic nerve

Choroid (plexus)

• vascular rich
• supply outer retina
• pigments
  • absorb light not absorbed by retina

Ciliary body

• just anterior to ora serrata
  • the line that separates the anterior and posterior chambers of the eye
• smooth muscle (ciliary muscle)
  • embedded in vasculature
  • attached to suspensory ligaments that are attached to lens
  • contraction causes lens to change shape
  • called accommodation
  • shifts image back to retina
• essentially stratified layering
  • top layer is non-pigmented
  • next layer is pigmented

Iris

• core of blood vessels
• 2 layers of pigmented cells
  • eye color has to do with what and how much pigment
  • eyes glow red in photos because of flash bouncing off blood vessels
• muscle
  • dilators run to outer edge from the pupil
  • sphincters make a circle around the pupil

Tapetum Lucidum

• Latin for bright carpet
  • why we see eyes glowing
• not found in humans but in mainly nocturnal animals, like cats and raccoons
• gives retina a second chance to absorb light
  • improves vision in low light conditions

Chambers

Anterior chamber

• everything in front of the iris
• aqueous humor
  • produced by ciliary body

Posterior Chamber

• everything lens to the back
• vitreous humor

Lens

covered in anterior epithelium cells

• cuboidal

equatorial cells

• from equator to blend with anterior epithelium
• very mitotic

lens fibers

• very clear cells
• cataracts are when these become cloudy
• surround lens nucleus

Tunica Nervosa (Neural Retina)

takes light photons and sends signals to brain

10 layers

1. Retinal pigmented epithelium (RPE)

   1. outermost layer
   2. represent outside of developing eye cup
   3. simple cuboidal epithelium
   4. separated the rest of the layers from the choroid
   5. nourishes retina and absorbs light

2. Photoreceptor outer segments

   1. outer portions of rods and cones

   2. cone opsin

      1. absorb red, blue, and green

   3. Rhodopsin

      1. for dark vision

3. Outer limiting membrane

4. outer nuclear

   1. cell bodies of rods and cones

5. Outer plexiform

   1. axons and dendrites

6. Inner Nuclear

   1. amacrine cells
   2. horizontal cells
   3. bipolar cells
   4. all of these are for relaying info between 2 cell layers

7. Inner plexiform

8. Ganglion Cells

   1. single layer
   2. cell dendrites leave to for optic nerve

9. Nerve fibers

   1. dendrites from ganglion cells
   2. Inner limiting membrane

• none of these are at the optic disk
  • what causes blind spot
  • instead has myelinated neurons

Macula

just lateral to optic disk

means spot

spot of central vision

center called fovea centralis

• just nuclei of outer nuclear layer and outer segment

lens concentrates all light to this

region of highest visual acuity

layers of neural retina thin at this spot

Pathology

myopia

• near sighted
• light hits behind macula
• corrected with a concave lens

hyperopia

• far sighted
• light focuses before macula
• correct with a convex lens

Glaucoma

• too much pressure in anterior chamber due to increase in aqueous humor
• can cause damage to neural retina
• measured by tap with a tiny stick like thing
  • used to be puff of air

Detached Retina

• layers 2-10 of neural retina pull away from RPE
• cause burst of light, blurry vision, and see not real specks
• due to thinning of eye cup with age