Basic Anatomy A
What percentage of the lens is water? What percentage is protein?
65-70% water
30-35% protein
Nasal-to-temporal diameter? Birth? Teenage years?
6.5 mm at birth
9 mm in teenage years
Orientation of apex and basal portion?
Hexagonal shape
Apex: just below lens epithelium
Basal: posterior lens capsule
4 weeks after fertilization
Why does the adult lens have no posterior lens epithelium?
Was used for primary lens fibers
What is an increase in dioptric power of the lens to focus light for near objects called?
Accommodation
Transparent envelope surrounding the entire lens?
Capsule
Where are mature lens fibers relative to new lens fibers?
Mature fibers are deeper in the lens than the new fibers
What are the 5 steps of lens development?
1. optic stalk and optic vesicle formation from forebrain
2. optic vesicle contacts overlying surface ectoderm
3. lens placode invaginates (lens pit), forms hollow sphere (lens vesicle)
4. posterior ep. cells of lens vesicle elongate anteriorly, fill hollow space
5. cells around equator elongate, form secondary lens fibers around embryonic nucleus by week 7
Secondary lens fibers
What are the enters of anterior and posterior surfaces called?
Poles
Connect ciliary body to lens capsule?
Suspensory Ligaments (zonules)
Border between the anterior epithelium and elongating fibers?
Epithelium-fiber interface
Neural ectoderm
What are the orientations of the anterior and posterior Y sutures?
What layer of the lens are the Y sutures found?
Anterior: Upright Y suture
Posterior: Inverted Y suture
Found in fetal nucleus
What is the largest circumference at the location between the poles called?
Equator
Orientation of apex and basal portions of lens epithelium?
Apex: points inward towards lens fibers
Basal: oriented towards capsule
Four layers of the lens? Inside to outside
Embryogenic nucleus - primary lens fibers
Fetal nucleus - formed before birth
Adult nucleus - birth to end of puberty
Lens cortex
What is induction?
The stimulated surface ectoderm thickens and differentiates in to lens epithelial cells. Called the lens placode
What forms from an error in lens fiber development?
Congenital cataract
Thickness of lens?
Increases by a small amount each year
What area contains epithelial cells just anterior to the equator that slowly undergo mitosis to become lens fibers?
Germinative zone
What are zones of discontinuity? What are they caused by?
Water, protein, and cholesterol content vary throughout the lens
Caused by differences in the physical properties of lens fibers and cells throughout the lens, from outer to deeper layers
What fibers are formed by the first group of cells to differentiate into lens fibers during embryonic development of embryonic nucleus?
Primary lens fibers
What is the shape between anterior and posterior lens fibers called?
Lens bow