11- Vitreous Body

A set of flashcards covering key concepts about the vitreous body and its functions in the eye.

What is the size of the vitreous chamber in a newborn eye?

10.5 mm

What is the size of the vitreous chamber in an adult eye?

16.5 mm

What is the water content of the vitreous body?

98%

What provides the vitreous body its gel-like consistency?

Collagen & glycosaminoglycans (GAGs)

Which type of collagen makes up the majority of the vitreous body?

75% type II collagen

Which type of collagen makes up some of the vitreous body?

10% type 5 and type 11

At age 18, what percentage of the vitreous is liquefied?

20%

At age 80, what percentage of the vitreous is liquefied?

50% or more

Explain embryology and primary vitreous?

The optic cup is occupied by the lens vesicle —> The cup grows —> the space is filled with fibrillar material secreted by embryonic retina —> The Hyaloid artery penetrates, and more fibrillar material from the blood vessel cell wall fills the space —> the mass in the end is called the primary vitreous

What forms the secondary vitreous?

Increase in size of the vitreous cavity and regression of the hyaloid vascular system.

What is tertiary vitreous?

Suspensory fibrils developed from fibrillary material are called zonules

What is cloquet’s canal?

A tube of primary vitreous surrounded by secondary vitreous running from the retrolental space to the optic nerve.

What is the vitreous base?

A three-dimensional zone extending from 2 mm anterior to 3 mm posterior to the ora serrata.

Which of the following is not a place that vitreous cortex attached firmly to internal limiting membrane?

Ora serrata

What prevents us from seeing the internal limiting membrane well with the naked eye?

It is very thin, only 1-3 microns thick.

Which of the following constituents is not greater in blood compared to vitreous body?

Ascorbate

What happens to glucose levels in a diabetic eye compared to a healthy eye?

It is 2x higher in the vitreous.

What is the Maillard reaction?

Insoluble proteins produced by a covalent bond between an amino group and glucose cause increasing molecular weight of the vitreous collagen with age

What is Weiss ring?

The firm attachment of the vitreous cortex that has moved away from the ILM at the optic disc.

Why does vitrectomy improve visual acuity in diabetic macular edema patients?

• The outward active transport increases and decreases passive permeability/leakiness. Also, removing the vitreous allows the leaky material to leave the retina, improving the patient’s VA

  • Also improves the preretinal oxygen tension, so neovascularization & edema decrease

Explain why the diffusion barrier of vitreous plays an important role?

1. Substances liberated from the ant segment have difficulty reaching high concentrations in the posterior part of eye

2. Vitreous gel also prevents topically administered substances from reaching the retina and optic nerve

Why is there a regression of neovascularization of retina and macular edema after vitrectomy?

1. Exchange between the anterior and posterior part of eye is fast and easy

2. Pre-retina oxygen tension transport increases

How does vitreous serve as a metabolic buffer?

1. Glucose and glycogen can supplement the metabolism of the retina

2. Vitamin C is present in high concentrations and acts a reservoir of antioxidants

Name one disadvantage of vitrectomy in an eye with neovascularization.

It can cause vaso-proliferative factors to move to the anterior pole.

Name pathological conditions in vitreous that hinders in path of light?

All of the above

Name pathological conditions in vitreous that hinders in path of light?

All of the above

What is the shape of the vitreous?

Spherical, except for the concave anterior end (lens)

What is the cortex of the vitreous?

The outermost part

What is the vitreoretinal interface?

The outer part of the cortex, including the retina's internal limiting membrane (ILM) and anchoring fibrils of the vitreous body.

What does the ILM consist of?

Mainly type IV collagen & proteoglycans (considered basal lamina of the Mueller cells)

Which of the following constituents is not in greater concentration in the vitreous compared to blood?

Potassium

What is the biophysical aspect of the vitreous?

Its gel structure acts as a barrier against movement of solutes.

How do substances move through the vitreous?

Through diffusion and bulk flow.

What bulk flow a result of? What molecules move due to this gradient?

Pressure gradient from the anterior to posterior pole of the eye; Large, high molecular weight substances (no effect on low molecular weight substances)

What can be used as tracer substance through diffusion?

Fluorescein

What is the main aging change in the vitreous?

Liquefaction/synchysis primarily in the center & get replaced with aqueous lacunae

What happens to vitreous collagen molecular weight with age?

It increases due to new covalent cross-links.

Which of the following is not the main aspects of vitreous physiology?

Active production of aqueous humor for intraocular pressure regulation

What is the function of the vitreous supporting the retina?

It helps prevent large retinal detachment and absorbs external forces.

What is considered an ocular emergency regarding retinal detachment?

Macula on retinal detachment, as the macula can still be saved.

What characterizes a posterior vitreous detachment (PVD)?

Degeneration causing the cortex to sink to the center, leading to floaters.

What is posterior vitreous detachment (PVD)?

Large central region degeneration which causes a collapse —> cortex sinks to the center of the vitreous body —> leads to floaters (considered normal aging phenomena)

What is the first step in a rhegmatogenous retinal detachment?

Retinal tear resulting from strong attachment between posterior cortex and ILM

What are signs of a PVD?

Flashing lights, sudden onset floaters, and decreased visual field.

What leads to macular edema formation?

Increased passive permeability and decreased outward active transport.