Microanatomy of Eye

Question 1

What are the layers of the eyeball?

Answer 1

Outer - sclera + cornea
Uvea (vascular) - choroid, ciliary body, iris
Retina

Question 2

Describe the sclera + cornea layer

Answer 2

• Sclera is tough, dense CT - opaque + white
• Cornea is transparent
• Limbus (boundary between) - zone of transition of epithelium of conjunctiva + cornea
• Protects inner structures
• Determines shape of eyeball along with intraocular fluid

Question 3

Describe the uvea

Answer 3

• vascular layer (BV to supply retina)
• pigmented to light proof eye + reduce reflection of light
• compromises choroid, ciliary body + processes, iris
• Ant portion contains smooth muscle of ciliary body and dilator + constrictor of iris (controls how much light passes through pupil)
• Ciliary body muscle regulates the tension of suspensory ligaments of lens

Question 4

Describe the retina

Answer 4

• Outer pigmented layer + inner retinal layer
• Post 2/3 is light sensitive + contains photoreceptor neurons - rods + cones
• Ant 1/3 not light sensitive + separated from post portion by ora serrata (regulation of nutrients from BV in choroid to retina)
• derived from neuroectoderm
• sensory retina made of 9 layers of diff cell types
• function to convert light to nerve signals

Question 5

What are the four cell groups found in the sensory retina?

Answer 5

Photoreceptor neurons (rods + cones)
Conducting neurons (bipolar + ganglion cells)
Association neurons (horizontal + amacrine cells)
Neuroglial cells (Muller cells)

Question 6

What are the 9 layers of the retina?

Answer 6

Inner limiting membrane
nerve fibre layer
ganglion cell layer
inner plexiform layer
inner nuclear layer
outer plexiform layer
outer nuclear layer
external limiting membrane 
Photoreceptors

Question 7

What is the fovea?

Answer 7

Point of greatest visual acuity

Question 8

What is the macula?

Answer 8

Provides sharp, straight ahead vision + colour vision

Question 9

What are the transparent components of the eye?

Answer 9

Cornea (avascular)
Aqueous humour - ant to lens, watery fluid similar to CSF, produced by ciliary processes
Lens (avascular) - focus light
Vitreous humour - post to lens, hydrated gel, mostly hyaluronic acid + some collagen

Question 10

What are the layers of the cornea?

Answer 10

• SSNK epithelium (numerous free nerve endings, potent wound healing, continuous with conjunctiva at limbus)
• Bowman’s layer (basement membrane, damage leads to scar formation + loss of visual acuity)
• Stroma (parallel arrangement of collagen fibrils into lamellae gives transparency)
• Descemet’s membrane
• Corneal endothelium

Question 11

Describe the parts of the iris + its features

Answer 11

• delineates ant + post chambers
• heavily pigmented
• blocks light except at pupil
• fibroblasts + melanocytes (ant)
• stroma containing BVs + melanocytes
• pupil dilator muscle
• pigmented epithelium

Question 12

Describe the ciliary body

Answer 12

• Aqueous humour produced by epithelium lining ciliary processes
• Aqueous passes from post to ant chamber and drains through canal of Schlemm (corneroscleral junction)
• Contraction of ciliary muscle causes relaxation of lens

Question 13

What can a blockage in the trabecular meshwork in base of cornea cause?

Answer 13

• usually drains fluid from anterior chamber
• blockage leads to rise in intraocular pressure (glaucoma)
• damage to retina
• pressure on optic nerve
• blindness

Question 14

Describe the lens

Answer 14

• Avascular
• Outer capsule of type IV collagen
• layer of cuboidal epithelium on anterior face only
• centre of tightly packed anucleate cells packed with transparent proteins (crystallins) to from lens fibres

Question 15

What do rods and cones perceive?

Answer 15

Rods - light intensity

Cones - colour

Question 16

Where are the rods + cones distributed?

Answer 16

Cones concentrated in fovea
Rods concentrated at periphery of retina
Between fovea + periphery there is a mixture