11. Choroid

Choroid characteristics

• Very vascular

• Located between the sclera and retina

• extends from the optic nerve head to the

Choroid layers from external to internal

• Suprachoroid

• Stroma

• choriocapillaris

• Bruch’s membrane

• RPE

Suprachoroid lamina

• posterior lamina fusca or epichoroid are old names for it

• contains numerous melanocytes

• site of smooth muscle stars

• small space

What is found in the suprachoroid lamina?

• Nerves and blood vessels

• contains the perichoroidal or suprachoroidal space

• contains diagonal collagen fibrous sheets

• fastens the choroid to the sclera

Why are the collagen fibrous sheets diagonal in the suprachoroid?

To accomodate for changes in thickness within the choroid stroma

Stroma of choroid

Widest layer and is the vessel layer.
Composed of connective tissue, fibroblasts, APCs, and melanocytes
Blood vessels are arranged in layers

Layers of blood vessels in the choroid stroma

Haller’s Layer, more external and larger (3)

Sattler’s layer, more internal and smaller (4)

Choriocapillaris

Single layer of anastamosing fenestrated capillaries.
Has a discontinuous basement membrane.
Capillaries have a wider lumen (3-4 times)

Pericytes

wrap around the capillary and are involved with blood flow & communicate with endothelium of blood vessel

Choriocapillaries is densest where?

Foveal region

Where is high arteriole to venule ratio? What benefit does this ratio have?

In the macula and peripapillary area. It is more resistant to eschemic event due to high number of arterioles.

Where is low arteriole to venule ratio? What benefit does this ratio have?

In the equitorial and peripheral areas. It is more resistant to ischemic events due to high number of venules.

Bruch’s Membrane Composition

• Basement membrane of choriocaillaris

• Outer collagenous zone

• elastic layher

• inner collagen zone

• basement membrane of retinal pigment epithelium

Where does Bruch’s membrane taper?

In pars plana

What is the neural retina continuous with?

Non-pigmented ciliary epithelium

Innervation of the Choroid

both divisions of autonomic nervous system.
Sympathetic is for vasoconstrictgion.
parasympathetic is for vasodilation ish
Some autoregulation

Function of choroid

• absorbs stray light

• thermoregulation

• removes wastes

• blood supply to part of the retina (photoreceptors highly metabloic)

Degeneration of Bruch’s membrane

Drusen

Drusen

• nodule outer to RPE basement membrane

• collection of BM-like material in inner collagenous zone

• seen as a yellow-white dot with ophthalmoscope

• Occurs in older individuals

• does not cause vision loss, but increases risk of AMD

Age related maculoar degeneration (AMD)

• common cause of blindness in western countries

• pathology associated with both the choroid and the retina

• can involve drusen deposition, RPE atrophy, vision loss

• can involve neovascularization

Types of AMD

• geographic atrophy AMD

• wet AMD

Geographic atrophy AMD

Substancial loss of RPE due to poor nutrient exchange

wet AMD

neovascularization from hypoxic event. Blood is toxic to neurons and kills the retinas

Tapetum lucidum

Present in the stroma (sattler’s layer). Various in color, size, reflective material.

Tapetum lucidum function

Increase sensitivity to light in dark environments by reflecting certain wavelengths back to retina.
cats have light detection threshold 7x lower than humans
feline tapetum reflects 130x more light than humans