Vitreous and Choroid (Q3) Flashcards
Which layers is the choroid in between?
Sclera and RPE
Where is the choroid at its thickest (~383microns or 0.2mm)?
Thickest at the posterior pole due to needing a good blood supply for the large number of photoreceptors there
Where is the choroid at its thinnest (~277microns or 0.1mm)?
Thinnest at the ora serrata (where it extends up to from the optic nerve)
The suprachoroidal space is continuous with… ?
the supraciliary space
Sensory retina is continuous with which parts of the uvea?
Iris posterior epithelium + non-pigmented ciliary epithelium + sensory retina = continuous
RPE/Bruch’s membrane is continuous with which parts of the uvea?
Iris anterior epithelium + pigmented ciliary epithelium + RPE/Bruch’s membrane = continuous
What are the attachment sites of the uvea to the sclera?
Scleral spur, vortex veins, optic nerve
What are the functions of the choroid?
Provide nutrients to the retina and removes wastes, absorbs excess light, passageway for vessels and nerves, with vascular supply to the macula
What are the layers of the choroid?
- suprachoroidal lamina (outermost)
- choroidal stroma
- choriocapillaris
- Bruch’s membrane (innermost)
The suprachoroidal space is a passageway for which structures?
long posterior ciliary arteries (LPCAs) and long posterior ciliary nerves (LPCNs)
What is the name of the layer of the choroid that contains components of both sclera (collagen fibers, fibroblasts) and choroidal stroma (melanocytes)?
Suprachoroid Lamina - contains components of BOTH choroid and sclera, it does not belong exclusively to the choroid
What components are in the choroidal stroma?
loose connective tissue, containing blood vessels, nerves, melanocytes (dense melanin granules), fibroblasts, macrophages, lymphocytes, and mast cells
What are the 2 vascular layers of the choroidal stroma?
Haller’s layer (large vessels, more posterior) and Satler’s layer (smaller vessels that branch to form a capillary bed, more anterior)
Where does the venous blood supply of the choroid drain through?
Vortex veins
What is the name of the layer of anastomosing, fenestrated capillaries that provides blood to the outer retina called?
Choriocapillaris
inner retina has its own blood supply
Where is the choriocapillaris the densest?
at the macula, to supply the large number of photoreceptors there
What is the name of the cells that surround capillary walls and provide local regulation of blood flow?
Pericytes (can be damaged by diabetes)
What are the five layers of Bruch’s membrane?
- basement membrane of the choriocapillaris
- outer collagenous zone
- elastic layer
- inner collagenous zone
- basement membrane of the RPE
What happens to the choroid with age?
Bruch’s membrane increases in thickness and drusen accumulate
Choriocapillaris decreases in thickness
overall choroid thickness decreases
What is drusen and how does it affect ocular health?
drusen are yellow deposits, containing cellular debris and cause elevation of the RPE, damaging photoreceptors above and not allowing metabolites to transport properly
What are the types and signs of Age-Related Macular Degeneration?
- Dry (non-exudative) - drusen, pigmentary change, atrophy
- Wet (exudative) - fluid/hemorrhage
symptoms are reduced central vision, metamorphopsia and scotoma
What is a chorioretinal coloboma?
Choroidal defect due to improper formation during embryological development
What is a choroidal nevus?
An accumulation of atypical, benign melanocytes, fairly common, size and location should be documented and monitored for any changes
What is the most common primary intraocular tumour in adults?
Choroidal melanoma (80% of uveal melanomas), malignant, metastatic especially to the liver, and usually unilateral
What are choroidal folds and what causes them?
Alternating bands seen usually in the posterior pole, asymptomatic usually, caused by tumour, hypotony, papilledema, or is idiopathic. Bands are seen because of the amount of RPE cells in crests and troughs of the folds
What is the outermost layer of the retina?
Retinal Pigment Epithelium (RPE). Classified as part of the retina since it arises from neuroectoderm like the rest of the retinal layers. The apical side faces photoreceptors, basal side faces Bruch’s membrane of choroid
What is the shape of the cells of the RPE and how are they different at the macula?
Single layer of hexagonal epithelial cells, apical side has microvilli, and in the macular region the cells are taller and more pigmented
Which layers does RD usually happen between?
between RPE and photoreceptors because there is loose adhesion due to embryological development
How are RPE cells linked to each other?
Strongly linked with zonula occludens, zonula adherens, desmosomes, and gap junctions which form the blood-retinal-barrier
What is ocular albinism and what does it include?
a genetic disorder of melanin synthesis, can be just ocular or oculocutaneous also affecting skin and hair. Signs/symptoms include nystagmus, reduced VA, photophobia, loss of RPE resulting in lack of pigment in fundus
What is lipofuscin?
incomplete phagocytosed particles, accumulates in RPE and can result in disease such as Best’s or adult vitelliform macular dystrophy, or Stargardt’s
What are the boundaries of the vitreous chamber of the eye?
lens (posterior surface), retrozonular portion of posterior chamber, ciliary body’s pars plana, retina and optic disc,
patellar/hyaloid fossa
What is the volume and composition of the vitreous humor?
4ml (80% of globe), * 98.5-99.7% water, type II collagen, hyaluronic acid, soluble proteins, salts and ascorbate.
Fibroblasts (mostly in vitreous base) synthesize collagen fibrils
What is the function of hyaluronic acid (GAG) in the vitreous?
HA is a hydrophilic molecule that maintains fibril spacing, creating the gel structure.
Hyalocytes (mostly in vitreous cortex) may function to produce HA but is not scientifically confirmed, may have phagocytic action as well
What are the functions of vitreous humor?
Physical support, shock absorber, passageway for particles, storage of metabolites for lens, transmits and refracts light, and provides UV protection
What is liquefaction in vitreous?
The vitreous changes with age from a homogenous gel earlier in life, to become more liquid-like centrally, shrinking, displacing collagen and forming floaters
By age ~75 vitreous is 50/50 liquid to gel. Volume doesn’t change, just composition
Why are floaters seen and what can be done?
The collagen fibrils floating that form during vitreal changes create shadows on the retina and are most bothersome the closer they are to the retina. Not really any treatment, besides invasive lasers or vitrectomy
What is Shafer’s sign?
aka Tobacco dust. vitreal strands seen in the anterior vitreous with RPE (red) cells floating, usually indicative of retinal compromise/break, and should be checked for when a patient complains of flashes and floaters
Where is the strongest attachment for the vitreous?
Strongest attachment at the vitreous base located at the ora serrata, vitreal fibers embed in the basement membrane of the non-pigmented ciliary epithelium and ILM, most dense area of collagen, but common site of RD due to changes in vitreous with age
How does the vitreous attach to the lens?
there is a ring-like attachment between the posterior lens and the anterior vitreous, formed by the hyaloideocapsular ligament (of Weiger) or retrolenticular ligament, with the retrolental space (Berger’s space) within
Where does PVD happen and what is the associated sign called?
Posterior vitreous detachment occurs at the edge of the optic disc resulting in a Weiss Ring. May be asymptomatic or have new flashes or floaters
What are the complications of PVD and what is the risk?
95% of PVD are uncomplicated, but complications can include retinal or disc hemorrhage when the vitreous pulls on a blood vessel and breaks it, vitreal hemorrhage, retinal tear or detachment
What is vitreomacular traction?
traction of the vitreous at the macula, can be treated with protease or vitrectomy, can cause a macular hole
What is the weakest attachment site for the vitreous?
retinal blood vessels, vitreous detachment results in retinal hemorrhage
What are the zones of the vitreous?
- vitreous cortex (tightly packed collagen)
- intermediate zone (unbranched fibers running anterior/posteriorly)
- center zone (contains least amount of collagen - Cloquets canal)
What is Cloquet’s canal?
aka hyaloid channel or retrolental tract, S-shaped, within the central zone of the vitreous, former site of the hyaloid artery system formed during embryological development. Posterior end of Cloquet’s canal near the optic disc is called the area of Martegiani
What is a Mittendorf dot?
embryological remnant, a small, circular opacity on the posterior lens capsule, representing the anterior attachment of the hyaloid artery (benign finding)
What is Bergmeister’s papillae?
Embryological remnant, glial tissue on the optic disc, represents the posterior attachment of the hyaloid artery (benign finding)
What are epicapsular stars?
Embryological remnant, gold flecks located on the anterior lens capsule, remnants of the connection between the tunica vasculosa lentis and the posterior hyaloid artery (benign finding)
What is asteroid hyalosis?
common degenerative process, calcium-pyrophosphate globules collect within the vitreous varying in density, generally unilateral and asymptomatic (benign finding)
What are the primary associations and symptoms of vitreous hemorrhage?
blood in the vitreous chamber, associated with PVD, or PDR (proliferative diabetic retinopathy) or ocular trauma. Symptoms include sudden, painless vision loss or mild haze, new-onset floaters, red tint to vision (less common)
What are Moore’s Lightning Streaks?
Momentary, vertical, lightning-type streaks (phosphenes) seen on temporal side due to sudden head movements in the dark (vitreous hits the retina, usually when older and vitreous is more loose)
What are anti-VEGF injections for?
RPE secretes VEGF into the choroid but when the balance is disrupted and secreted into the retina it can cause new blood vessel growth and leakage, the injections are to stop this growth
(PDR, wet AMD, macular edema, etc.)
choroidal neovascular membrane (CNVM)
results from a break in Bruch’s membrane that can occur in a variety of conditions, and associate with angioid streaks
angioid streaks
result from damage to the elastic layer of Bruch’s membrane, remember PEPSI for the associated conditions
PEPSI (associated conditions for angioid streaks)
Pseudoxanthoma elasticum
Ehlers-Danlos syndrome
Paget’s disease
Sickle cell disease
Idiopathic
What are the vitreal attachment sites from strongest to weakest?
Vitreous base -> posterior lens -> optic disc -> macula -> retinal vessels
What is the patellar fossa?
a depression in the anterior vitreous caused by the posterior lens
vitreous cortex
outer region of the vitreous adjacent to the retina, extends to the ora. Consists of high density gel filled with collagen fibrils, cells, proteins, and a mucopolysaccharide filler substance. Divided into anterior and posterior regions by the vitreous base
Anterior hyaloid region of the vitreous cortex
extends from the vitreous base anteriorly to attach to the lens. includes the patellar fossa, hyaloideocapsular ligament of Weigner, and Berger’s space
Posterior hyaloid region of the vitreous cortex
begins at the posterior edge of the vitreous base and extends posteriorly to the optic disc
Hyaloideocapsular ligament of Weigner
strong circular adhesion between the anterior vitreous, posterior zonules, and the posterior capsule of the lens
Berger’s space
a potential space between the anterior hyaloid and the posterior lens capsule that is located in the central area of non-adhesion within the circular hyaloideocapsular ligament.
