Crystalline Lens Flashcards
Which side of the lens is flatter? Steeper?
Anterior side is flatter and posterior side is steeper.
Lens diameter at birth
6.5 mm
Lens diameter in an adult
Thickness?
10 mm
4 mm thick
Does the lens diameter increase with age?
No. But the thickness does. About 0.02 mm/yr
What is the most peripheral edge of the lens called? What happens here?
The equator of the lens, the marginal circumference of the lens.
This is where cell proliferation occurs
The Lens accounts for ___D of the total __D of the eye.
+15-20 D
+60 D
By age 40, what is the range of dioptric power reduced to? Why?
+8 D, hence onset of presbyopia
By age 60, what is the range of dioptric power reduced to?
+1 to 2 D
Why is there a non-uniform index of refraction in the lens?
Due to the non-uniform distribution of crystallin proteins in the lens fibers
Suspensory apparatus that holds the lens in place and attaches to the capsule of the lens
Lens zonules
How far is the lens equator from the ciliary processes of the pars plicata?
0.5 mm
Structure that attaches posterior surface of the lens to the vitreous body
Wieger’s ligament
Space between lens and vitreous
Berger’s space
The depression of the vitreous where the lens sits
Patellar fossa
3 parts of the crystalline lens
- Elastic capsule
- Lens epithelium
- Lens fibers
What acts as the basement membrane of the lens?
Elastic capsule
The elastic capsule is secreted by…
The anterior epithelium
There is no ____________ epithelium in the mature lens
Posterior
Where is the lens capsule the thickest?
Anteriorly, 20 microns
The lens capsule is in direct contact with :
The anterior lens epithelium
How thick is the posterior lens capsule?
3 microns thick.
There is no epithelium posteriorly, so the lens fibers secrete the posterior lens capsule
What allow the lens to stretch?
The collagen embedded within the glycoproteins and sulfate proteoglycans
–allows it to stretch up to 60% of its circumference without tearing
NO elastic fibers in the capsule.
What part of the capsule increases with age?
Anterior capsule, by 65 yrs old it will be 1/3 larger!
2 main functions of the lens capsule
- Diffusion barrier freely permeable low-molecular weight compounds
- Makes the lens pliable for zonular fibers in accommodation
Outermost layer of the lens capsule to which where to zonules will attach
Zonular lamella
What type of cells are the lens epithelium anteriorly? Equatorially? Posteriorly?
Anteriorly = monolayer of cuboidal cells
Equatorially = germanative zone, where proliferation occurs, cells stretch and become columnar shape
Posteriorly = there isn’t a posterior epithelium silly
What is the function of the lens epithelium at the equator? Everywhere else?
Proliferation, “germinative zone” to create lens fibers.
ALL of the lens epithelium secretes the lens capsule and transport of substances from aqueous humor to lens anterior.
Which type of fibers constitute the bulk of the lens?
Secondary lens fibers
Where do secondary lens fibers originate?
The equator, it will elongate as it is pushed towards the center. The nucleus will move anteriorly over time, and will eventually disappear. MAGIC
What happens to the lens fibers that lose their nuclei?
They detach from the capsule and are compacted on older fibers towards the center.
The ends of the lens fibers meet ends of lens fibers from the other side of the lens
Sutures
Why are Y sutures created?
The lens keeps increasing in size, and its lens fibers are unable to stretch the anteroposterior distance, so they compact into Y formations
Can cause problems, like sutural cataracts.
How do secondary lens fibers communicate with each other?
Gap junctions
Nutrient and ion exchange occurs here
Once fibers have lost their nuclei, the organelles of the fiber become specialized to form:
How much of the fiber do these make up?
Lens crystallins
40%
The non-uniform distribution if crystallins is thought to give the lens a _______________ ______________ ________.
Non-uniform refractive index
What are the 4 layers/divisions of the lens?
Not including the capsule.
- Embryonic nucleus
- Fetal nucleus
- Adult nucleus
- Lens cortex
Which layer of the lens is composed of primary lens fibers?
Embryonic nucleus
Which layer of the lens contains the Y-sutures?
Fetal nucleus
Which layer of the lens contains secondary fibers and increases with size?
Adult nucleus
Which layer of the lens becomes yellow with age?
Adult nucleus
Which layer of the lens contains newly formed fibers that contain nuclei? (And surrounds adult nucleus)
Lens cortex
If you have trouble driving at night, without any issues with reading, what type of cataract would you have?
Cortical cataract
Because large pupils will reveal the issues of a cataract in the cortex
What is ectopia lentis? When is it most common? (2 diseases)
Dislocation of the lens.
Common in Marfan’s syndrome, will dislocate UPWARD.
In homocysteinuria, lens will dislocate DOWNWARD.
If you have trouble reading, but not driving at night, what type of cataract will you have?
Posterior subcapsular cataract.
Small and in the middle, so small pupil reveal it.
Test where you check VAs and if they’re a candidate for cataract surgery
Brightness acuity test/cataract preoperative evaluation
What is retrobulbar block?
Where you inject an anesthetic transconjunctivally to numb the long cilary nerves
Saline solution that disconnects cortex from capsule
Hydrolineation
Process of breaking down the lens and auctioning pieces out
Phacoemulsification
What is the most common complication of cataract surgery?
Complete removal of ALL lens epithelial cells. Posterior lens capsule and a portion of the anterior capsule remain in place to support a posterior chamber lens. This will cause posterior capsular opacification.
10%-50% of patients.
What is pseudophakia?
Placement of IOL where lens was
