Term
In what part of the conjunctiva are the lymphatics mainly found? |
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Definition
| Mostly in the bulbar conjunctiva |
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Term
| What are the functions of the conjunctiva? |
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Definition
1) physical barrier
2) nutritional metabolic support
3) Neutralize pathogens; very reactive to allergens
4) mucous production
5) Electrolyte and water secretion |
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Term
| What allows the stem cell to retain its original DNA while the new copy is passed along to the daughter cell? |
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Definition
| assymetric DNA segregation and low mitotic activity |
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Term
| How many layers are in the limbal epithelium? conjunctival epithelium? corneal epithelium? |
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Definition
limbal epithelium-10 cell layers thick
conjunctival epithelium-2-3 cell layers thick
corneal epithelium-5-7 cell layers thick |
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Term
| Can corneal cells repopulate by conjunctival transdifferentiation? |
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Definition
Yes but they cannot transdifferentiate into corneal epithelial cells as once thought. New corneal epithelial cells must come from stem cells if they are damaged. |
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Term
| When conjunctival cells repopulate the corneal epithelium, what are they always associated with? |
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Definition
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Term
| What two autoimmune diseases can cause loss of conjunctival and corneal epithelial cells? |
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Definition
1. Stevens Johnson syndrome
2. Ocular Cicatricial pemphigoid |
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Term
Can stem cell transplantation cure Stevens Johnson or ocular pemphigoid effects? |
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Definition
| No, Stem cell transplantation can create new epithelial cells but if you do not treat the underlying disease, these cells will be destroyed as well. |
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Term
| What does the tight binding of conjunctiva to the underlying orbital connective tissue by Tenon's capsule do? |
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Definition
| It stops conjunctival prolapse from occuring during eye movement, no bunching up of the redundantly layered conjunctiva. |
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Term
| What is the function of the sclera? |
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Definition
1. To provide structure for the eye
2. To maintain the eyes size and shape |
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Term
| What is the eye's protective outer coat? |
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Definition
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Term
| Which structure has more water content, cornea or sclera? |
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Definition
| The cornea is 78% water and the sclera is 70% water, so the corneal water content is slightly higher than the scleral water content. |
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Term
| What type of collagen fibers make up 75-80% of the dry weight of the sclera? |
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Definition
| Type I collage fibers, the most abundant type of collagen in the human body |
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Term
| What would happen if the scleral collagen fibrils were not interwoven but were a continuous parallel sheet? |
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Definition
| It'd be more like the cornea, weaker and more transparent. The strength and elasticity is due to the interwoven lamina and elastic fibers. |
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Term
| What is one potential effect of the lack of elasticity of the tissues of the eye? |
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Definition
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Term
| Rate the order of thickness of the sclera at the limbus, equator, and optic nerve. |
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Definition
Thickest to thinnest
1. optic nerve (.9-1.0 mm)
2. limbus (0.53 plus or minus 0.14 mm)
3. equator (0.39 plus or minus 0.17 mm) |
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Term
| How are corneal and scleral fibers different? |
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Definition
Scleral fibers are shorter, 10 times thicker, and interwoven |
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Term
| Where is amyloid P located in addition to being located in the elastin and elaunin fibers? |
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Definition
| The microfibrils of the lens zonules |
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Term
| What are the functions of amyloid P components in the sclera and the lens zonules ? |
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Definition
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Term
| What is the altering of proteoglycan synthesis rate involved in? |
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Definition
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Term
| How do proteoglycans help in hydration? |
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Definition
| The GAG molecules are negative and hydrophilic hence they help hydrate the sclera |
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Term
| Which proteoglycans are thought to be involved in axial length in the sclera? |
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Definition
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Term
| Which type of collagen fiber functions to resist tension in the sclera? |
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Definition
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Term
| Which collagen fibers function mainly to control fibril diameter and anchoring functions? |
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Definition
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Term
| What are four effects of aging on the sclera? |
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Definition
1) Progressive degeneration of collagen and elastin
2) Loss of glycosaminoglycans
3) Increase lipid content (sclera starts to look yellow)
4) Dehydration |
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Term
| How do drugs permeate the sclera? |
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Definition
| through the hydrophilic GAGS in the interfibrillar region |
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