Crystalline Lens Flashcards
What is the location of the crystalline lens? What shape is it?
Biconvex structure located posterior to the iris and pupil and anterior to the vitreous body
What is the space called that the lens sits in in the posterior chamber?
Circumlental space
Which surface is steeper? So which one has the larger radius of curvature?
- posterior surface is steeper (5-8mm radius of curvature)
- anterior surface is flatter (8-14mm radius of curvature)
Where are the poles located? What are they connected by?
-the anterior and posterior poles are located at the center of their respective curvatures and are connected by the Axis of the lens
What is the lens diameter at birth? In adults?
Diameter at birth is 6.5mm, in adults it is 10mm
What is the thickness of the lens in unaccommodated state?
4mm thick
At what rate does the diameter change in adulthood? Thickness?
- diameter does not change in the adult lens
- thickness increases 0.02mm/year
What is the equator of the lens? Why is it important?
- the most peripheral edge
- germanitive zone: where cell proliferation occurs
Why doesn’t the diameter of the lens increase in adulthood?
Because it would make the circumlental space smaller and press on the ciliary body.
-that’s why it only increases in thickness
If you could describe the lens as a veggie, which one would it be?
Onion
What causes cataracts?
- normal. Its impossible to not get cataracts
- cells are proliferating in the inside and becoming more compacted
Does the iris rest on the anterior surface of the lens?
Yessssssssssssssss. You wanna be careful of a relative pupillary block that could increase the pressure in the anterior chamber and prevent flow of aqueous
How many diopters does the lens account for of the total power of the eye?
15-20 of the total 60
By age 40, what is the power of the lens, by age 60?
40: 8D
60: 1-2D
Tell me about the lens index of refraction
- non uniform due to the distribution of crystallins
- 1.36 peripherally
- 1.4 centrally
- higher index of refraction centrally and posteriorly
What is the purpose of the zonules? Where do they attach?
- suspensory apparatus that keeps the lens in place
- from the nonpigmented epithelium of the pars plicata
What is the distance between the equator of the lens are the pars plicata? Why is that important?
- 0.5mm
- important for the flow of aqueous between iris and the lens
What does Wieger’s ligament do?
It attaches the posterior surface of the lens to the vitreous body
-if you were to pull of the lens, you would also pull out the vitreous body
What is the patellar fossa?
Indent the lens makes in the anterior hyoid face of the vitreous body
What is Berger’s space?
Potential space between weiger’s ligament and the patellar fossa
What secretes the capsule anteriorly? Posteriorly?
Anterior: anterior lens epithelium
Posterior: lens fibers
Which part of the capsule is thicker?
Anterior! Because of the anterior epithelium is continuously secreting it! (20 microns) posterior is 3 microns
What is the lens capsule composed of?
Type 4 collagen!
NO ELASTIC FIBERS IN THE CAPSULE
Why is the lens capsule called “elastic capsule”?
-because the collagen is surrounded by glycoproteins that allow it to stretch, THERE ARE NO ELASTIC FIBERS
What are the two main functions of the lens capsule?
- Diffusion barrier freely permeable low-molecular weight compounds (allows nutrient from the aqueous to get through, but not bigger scarier things)
- Makes the lens pliable in to the pull zonules fibers during accommodation: lets lens change shape in response to tension of the zonules)
How much bigger is the anterior capsule by the age of 65?
1/3 larger
What is the zonules lamella?
Outermost layer of the lens capsule to which the zonules attach
What kind of cells make up the lens epithelium?
-it is a monolayer of cuboidal cells that stretch and turn columnar as they mover peripherally
What are the three functions of the lens epithelium?
- Proliferate throughout life at the germanitive zone at the equator to form lens fibers
- Centrally, it allows for exchange of ions and nutrients from aqueous to interior of the lens (at the lens fiber interface)
- Anterior epithelium secretes the anterior lens capsule
What constitutes the bulk of the lens?
The secondary lens fibers! (Crystallins)
What forms the lens fibers? Where do they originate?
- formed by epithelial cells stretching and becoming columnar at the equator
- originate at the equator and take on a meridional arrangement
What happens to the basal, apical, and nucleus portions of the secondary lens fiber as it moves centrally?
- Basal: creeps posteriorly around the posterior capsule
- Apical: begins to elongate as it is pushed centrally and situated itself under the anterior epithelium
- Nucleus: moves more anteriorly to form the lens bow and eventually disappears
What happens when the nucleus disappears?
Crystallins form
How long is a lens fiber?
10mm and U shaped
Where do the ends of fibers meet each other?
Sutures
What shape are the anterior sutures? Posterior?
Anterior-upright Y
Posterior-inverted Y
What kind of junctions are in lens fibers? Why?
Gap junctions. For communication and nutrient exchange
What is the epithelium-fiber interface?
- apex of anterior epithelium is in direct contact with apical parts of lens fibers
- gap junctions that allow exchange of nutrients
What is thought to give the lens a non uniform refractive index?
The non-uniform distribution of crystallins
Describe the embryonic nucleus
- earliest mass at center of the lens
- composed of primary lens fibers
- formed at 2 months gestation
- DOES NOT INCREASE IN SIZE
Describe the fetal nucleus
- formed 2 months before birth
- contains Y sutures
- DOES NOT INCREASE IN SIZE
Describe the adult nucleus
- fibers made between birth and sexual maturation
- INCREASE IN SIZE THROUGHOUT LIFE
- they sclerosis and become yellow with age
Describe the lens cortex
- newly formed fibers with nuclei
- surround adult nucleus
What is the most common complication of cataract surgery?
Posterior capsule opacification (occurs in 10-50%)
