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What is the total volume of vitreous? And it accounts for what fraction of the volume of the eye?
3.9 mL, 2/3 volume of the eye.
Describe the water and solid composition of the vitreous?
99% water and 1% solids (such as proteins, hyaluronic acid, collagen filaments, albumin, hyalocytes, glucose, galactose, absorbic acid, etc).
In general, where is the vitreous attached?
- 1. Posterior lens surface: Weiger's ligament.
- 2. Retina: Vitreous Base (strongest)
- 3. Anterior and posterior hyaloid membrane covers the vitreal cortex.
- 4. ONH: weak attachment around the margin of ONH
- 5. Macula: weakest vitreal attachment.
What is Wieger's ligament? What role does age play?
This is where the vitreous attaches to the posterior lens surface. It is not a true ligament, and it WEAKENS WITH AGE!
What is the vitreous base? Where is is it located? How large is it (in DD).
It is the vitreal attachment to the retina (especially peripheral retina). It is located at the ora serrata and it extends anteriorly towards the pars plana and posteriorly towards the peripheral retina. It is approximately 1DD in width.
Describe the thickness of the vitreous base. Are breaks common here?
It is a very thickened area of the vitreous and has VERY strong attachments to the retina. Although retinal breaks and and degenerations are common along the posterior edge.
What structure divides the vitreal cortex into anterior and posterior portions?
What structures cover the vitreal cortex?
Anterior and posterior hyaloid membrane.
Describe the course of the anterior hyaloid membrane.
It begins at the ora and extends to the posterior capsule of the lens. It is attached to Wieger's ligament, and this attachment weakens with age.
Where is the second strongest attachment?
at the Optic nerve head, weaker than the attachment at the vitreous base.
Describe the vitreal attachment to the macula. Describe the strength of attachment. What if this became detached?
There is a 2-3 mm ring of vitreous attached to the macula, around the fovea. This attachment is stronger in youth and weakens with age. It is the weakest vitreal attachment and a break can result in a MACULAR HOLE!
What is cloquet's canal?
It is an S-shaped optically empty space that runs from the lens to the optic disc and represents atrophic primary vitreous.
Describe changes in cloquet's canal with age.
It becomes less visible as you get older. When you are born, it tends to be straight and with age-it takes on an S-shape.
Will the vitreous show up on a B-scan ultrasound? When is an ultrasound indicated?
- NORMAL vitreous is acoustically and radiologically empty or clear. However, if you get blood in the vitreous, or retina in the vitreous (with a detachment), this will show up on the B-scan ultrasound.
- An ultrasound is indicated when you suspect something is going on in retinal but vitreous is obscuring the view. The B-scan will go through the dense media (aka cataract).
What is a B-scan?
It consists of focused, short wavelength, acoustic waves. Measures tissue depth.
How does a youthful vitreous look?
avascular, acellular (if cells present, may be posterior uveitis), FINE collagen fibrils. You can see the vitreous move upon eye movements.
What are some vitreal features of a normal aging eye?
-hyaluronic acid molecules break down and release water
- Rheology-refers to the vitreous shifting from a gel-like to a more liquid-like vitreous
- Vitreal syneresis-when the vitreal base shrinks and collapses during PVD
- fibrillary degeneraiton -refers to the combination of liquefaction and syneresis
Describe liquefaction, rheology, and the shrinking of the cavity.
Hyaluronic acid macromolecules break down and release water (liquefaction-becomes more liquidy in late 30s to 40s). Collagen Fibrils will come together and aggregate (so you get thicker and wispier collagen fibrils). This results in rheology (which is a shift from gel-like to more liquid vitreous). There is a decline in collagen and hyaluronic acid concentration (so the vitreal cavity itself is shrinking--results in a decrease in viscosity and elasticity).
What are lacunae?
Optically empty spaces and clefts. They contain hyaluronic acid, but no collagen and the spaces appear black.
Describe the formation of a PVD?
As lacunae enlarge, they may empty into the space between the posterior hyaloid and ILM of the SR-this separation is called a PVD.
What is vitreal syneresis?
It is the shrinkage of the vitreal base with collapse during PVD.
What is fibrillary degeneration.
Liquefaction and syneresis.
In what population is PVD common, and is it something to be concerned about?
Common in patients that are beyond middle age and older. And it is usually benign, but can cause retinal breaks.
What are Sx of PVD?
- Flashes and Floaters.
- Flashes are acute and dissipate over time-occurs when the base is tugging and pulling on SR, may tear the retina resulting in flashes of lights (phosphenes).
- Floaters are acute and LONG standing-they have a well-defined shape and MOVE with fixation.
Can PVD result in retinal hemorrhages?
Yes, as the vitreous is collapsing, it may pull the retinal blood vessels-resulting in hemorrhages. It is essential to rule out blood in the retina when patient complains of NEWLY onset floaters.
What are floaters? What do they look like to patients?
Condesnation of vitreal fibers. They are particles of vitreous, blood and retina that are casting shadows on the retina. They look like ants/spiders with legs. Ask patient if the floaters move as you move your eyes--If the answer is yes, then it is a Weiss' Ring. Your brain will suppress these floaters-they will still be there but they won't bother you as much.
What is the pathogenesis of a PVD.
The lacuna filled with hyaluronic acid spearates the posterior hyaloid from the ILM.
Where does a PVD usually begin.
In the upper globe and it spreads towards the vitreous base and posterior down below the disc. The entire vitreous cortex may detach up to the vitreal base.
What is a Weiss' Ring?
It is a ring of vitreal attachment AROUND the disc- may tear loose and float forward towards the back of the lens.
Can there be detachment from the macula?
Yes, a small ring may arise as attachment to the macula separates but there is no name for this.
What do you look for clinically when examining the vitreous?
Look for Weiss' Ring. Look for optically empty space between a loose-veil like posterior membrane with direct focal illumination (inverted J) or wispy veil suspended in the vitreal cortex. Look for a small opacity temporal to the macula.
How do you distinguish Weiss' Ring from glial tissue?
Glial tissue is attached to the ONH. Weiss' is not attached, it is floating above the ONH.
How do you manage patients if you suspect a retinal tear?
Perform a full dilation and PERIPHERAL investigation for tears. BIO with scleral indentation.
What if no tears are detected?
F/U between 1-4 weeks, then another F/U 1 month later.
What are some complications from PVD?
Retinal tears and vitreal hemorrhages.
How do you differentiate between an incomplete vs complete PVD?
Complete: Vitreous completely separates from vitreous base. (no attachment to the retina)
Incomplete: There is still an attachment to the retina. There is continued tugging on the retina. Complications may arise.
How do you manage an asymptomatic patient with a COMPLETE PVD?
Normal REE annually.
What percentage of patients with a symptomatic PVD will develop retinal breaks? How should you mange these patients?
15-30%; Refer to a retinal specialist.
What if you see cells in the vitreous?
Assume that it is a tear unless proven otherwise.
What is a mittendorf's dot?
It is a benign finding-glial vascular remnant adherent upon posterior lens capsule. It is where the hyaloid vascular system was once attached.
What is Bergermeister's Papilla?
It is also a benign finding and it is residual glial tissue which has not regressed as hyaloid system has atrophied. It does not interfere with vision or visual functions. (review pictures)
What is asteroid hyalosis?
It is a benign, usually asymptomatic disease. There is NO predilection for race, but it is more common in patients with HT, diabetes, and atherosclerotic vascular disease.
What are the opacities in asteroid hyalosis composed of?
calcium phosphate complexes and complex phospholipids
How does it look like in clinic?
They are arranged in strands or seen as discrete bodies-without orderly arrangement. They are attached to vitreous fibrils and always return to original location in vitreous. They can interfere with visualization of fundus detail.
Is anterior or posterior AH easier to see?
Anterior AH is easier to see... bc the opacities will usually never sink to the bottom of the vitreous cavity.
What conditions cause vitreous hemorrhages?
They arise from retinal breaks from PVDs, retinal detachments, or ocular trauma, or proliferative retinopathy.
What are the main symptoms of vitreal hemorrhages?
Acute symptoms of decrease vision/floaters.
How does it affect the fundus.
Red, hazy dense opacification (blurry) of fundus
How do you manage a vitreal hemorrhage?
It should clear up on it's own. You should always expect a retinal break until proven otherwise. AVOID HEAVY LIFTING AND BENDING OVER. Conduct a B-scan utlrasound to rule out a retinal detachment.
WHAT IF VITREAL HEMORRHAGE DOES NOT CLEAR UP IN SEVERAL MONTHS?
Vitrectomy (removing vitreous and replacing with another gel like substance) can be considered. But blood clots should reabsorb on their own.
What is shaffer's sign AKA tobacco dusting
golden brown pigment granules in the anterior vitreous of phakic eyes: suggests retinal breaks. IF the sensory retina detaches, some of the RPE layer will be disrupted and pigment can be released into the vitreous.
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