D19 - The eyeball: tunics

Question 1

What does the visual organ consists of?

Answer 1

• Eyeball
• N. opticus
• Accessory organs
  
  • Corpus adiposum orbitae
  • Fascia bulbi
    
    • Preorbita
    • Fascia muscularis superficialis
    • Fascia muscularis profunda
  • Muscles of the eyeball
  • Eyelids (palpebrae)
    
    • Superior
    • Inferior
  • Gl. lacrimalis

Question 2

Define orbit

General knowledge

Answer 2

• The orbit is a cavity on the lateral surface of the skull
• Contains the eyeball
• Continous with fossa temporalis and fossa peterygopalatina

Question 3

Give the division of the interior of the eyeball

General knowledge, not directly linked to the topic

Answer 3

• The interior of the eyeball is divided into 3 chambers (camera bulbi):
  
  • Camera anteror (anterior chamber)
    
    • Between cornea and iris
    • Filled with aqueous humor
  • Camera posterior (posterior chamber)
    
    • ​Between iris, ciliary body and lens
    • Filled with aqueous humo
  • Camera viteria (viterous body)
    
    • Largest of the 3 chambers
    • Behind the lens
    • Surrounded by retina

Question 4

The eyeball

Give the tunics of the eyeball

Answer 4

• The wall of the eyeball is formed by 3 layers (tunicae), which enclose the interior of the eyeball

1. Tunica externa/fibrosa
   
   • ​Role: gives form and protects the eyeball
   • The only complete tunic
   • Consists of:
     
     • Sclera
     • Cornea
2. Tunica media/vasculosa
   
   • ​Consists of blood vessels and smooth muscles
   • Role:
     
     • Nutrition of the eyeball
     • Regulation of the shape of the lens and size of the pupil
   • Consists of:
     
     • Choroidea
     • Ciliary body
     • Iris
3. Tunica interna/nervosa
   
   • ​Consists of nervous tissue
   • Role: the layer most directly concerned with vision
     
     • Translation of visual stimuli into nerve impulses form interpretation by the brain
   • Consists of:
     
     • Nonvisual retina (pars caeca retina)
     • Optic part of retina (pars optica retinae)

Question 5

Tunics

Tunica externa/fibrosa

Answer 5

• Made up of very dense collagenous tissue
  
  • ​Resisting the internal pressure and gives the eye shape and stifness
• Consists of sclera and cornea which meet at the limbus
• Sclera:
  
  • Outer layer (together with cornea)
  • “white of the eye”
  • Pars perforata: ventral to the posterior pole, passes the fibers of n. opticus
  • It gives attachment to the tendons of the ocular muscles anterior to the equator
  • Vagina bulbi: posteriorly, except for the area taken up by the m. retractor bulbi, it is covered by a thin membrane that separates the corpus adiposum orbitae
  • Near the limbus the sclera is covered by conjuctiva, which furnishes connection to the inside of the lids
• Limbus cornea: the edge of the cornea where it is continous witht the sclera
• Cornea: ​​
  
  • Outer layer (together with sclera)
  • Avascular
  • Layers:
    
    • Epithelium
    • Lamina limitans anterior (acellular)
    • Substantia propria
    • Lamina limitans posterior (acellular)
    • Endothelium camerae anterioris
  • Cornea lack blood vessels
    
    • Nourished by diffusion from the interior of the eye
    • Nutrition: vessels of limbus → lacrimal fluid
  • Corneal reflex: free nerve endings from the n. ciliaris longus (of n. opthalmici); eye lids close when touching the cornea

Question 6

Tunics

Tunica media/vascularis

Answer 6

• Tunica vasculosa = uvea
• Interposed between sclera and retina
• Functions:
  
  • Blood supply
  • Suspension and regulation of shape of the lens
  • Regulation of the size of the pupil
  • Production of aqueous humor
• 3 zones in posterioanteroior sequence
  
  1. Choroidea
  2. Corpus cileare
  3. Iris

Question 7

Tunics

Tunica media/vascularis: choroidea

Answer 7

• ​​Vascular layer
• Envelopes the posterior part of the eyeball
• Tapedium lucidum:
  
  • Dorsal to optic papilla, in a half-moon shaped area
  • Has an additional reflective layer between the vascular and choroideocapillary layer
  • Avascular layer (ø sus)
  • Cellular (ca)
  • Fibrous (ru, eq)

Question 8

Tunics

Tunica media/vascularis: corpus ciliaris

Answer 8

• Thickened middle segment of tunica vascularis
• Between choridea and iris
• forms lateral borders of the posterior chamber
• Outer surface is covered by sclera
• Inner surface is covered by nonvisual part of retina
• Corpus ciliaris can be subdivided into:
  
  • Ciliary ring
  • Crown of ciliary body
    
    • ​Most prominant anterior portion
    • Contains processus ciliaris
• Lens is fixed in position by ciliary zonule
• M. ciliaris:
  
  • ​Smooth muscle
  • Action: accommodation
    
    • Enables the lens to change its shape to focus on near or distant objects
  • Innervation:
    
    • Parasympathetic from ggl. ciliaris (muscle contract)
    • Sympathetic innervation from plexus caroticus interna (muscle relaxes)
    • Sensory: V₁ → n. nasociliares → n. ciliare
• ​​Oculomotorius ??
• 1 motor nuclei ??
• Parasympathetic nuclei ??

Question 9

Tunics

Tunica media/vascularis: iris

Answer 9

• Thin ring of vascular tissue
• Suspended between the cornea and lens
• Attached at the periphery of the sclera (by ligg. pectinati) and corpus ciliaris
• Color of the iris determines the color of the eyes, depending on the number of pigmented cells present in the stroma
• Size of pupil: amount of light reaching the retina are regulated by the smooth muscles
  
  • M. sphincter pupillae
    
    • ​Close to pupillary margin
    • Parasympathetic fibers
  • M. dilator pupillae
    
    • ​Contraction → enlarges pupil
    • Sympathetic fibers
• Divides the space between the lens and cornea into:
  
  • Anterior chamber
  • Posterior chamber
• Both chambers are filed with aqueous humor
  
  • Circulation:
    
    1. Pupil
    2. Angulus iridocornealis
    3. Space of fontana
    4. Channels of schlemm
    5. Episcleral veins
• Consists of 3 layers:
  
  • Anterior epithelial layer
  • Middle layer
  • Posterior epithelial layer

Question 10

Tunics

Tunica interna/nervosa

Answer 10

Retina:

• ​Contains light-sensitive receptor cells
• No blood vessels
• Connected by n. opticus
• Outgrowth of diencephalon
• The retina can be divided into:
  
  • Non-visual retina (pars caeca retinae)
    
    • ​Ciliary part of retina (pars ciliaris retinae)
    • Iridial part of retina (pars iridica retinae)
  • Optic part of retina (pars optica retinae)
• Ora serrata: marks the border between non-visual retina and optic part of retina
• Discus n. optici: ​Blind spot where n. opticus enters
• Macula: Area of maximum optical resolution
• Non- visual retina: (optic part)
  
  • Pars ciliaris
  • Pars iridialis

Pars ceca retinae:

• ​Anterior part of eye

Pars optica retinae:

• ​Posterior to ora serrata
• Divided into:
  
  • Outer pigmented layer
  • Inner neural layer
• Layers:
  
  • Pigmented cells
  • Receptor cells:
    
    • ​Rods (black/white vision, night)
    • Cones (color vision, day)
  • Bipolar ganglion cells
  • Multipolar ganglion calles
• Transduction of stimulus: (tertiary receptor type)
  
  • Cell 1: rods and cones (sensing stimuli)
  • Cell 2: bipolar cells (transduction and transformation)
  • Cell 3: gangilon cells (affterent nerve)