Lens Anatomy
This lens structure is the basement membrane for the lens epithelium and is thickest anteriorly.
What is the lens capsule?
This glycoprotein is the most abundant protein in the lens zonules.
What is fibrillin-1?
In terms of fluid transport in and out of the lens, name the lens location where fluid enters and where it leaves.
Enters vita anterior/posterior pole and exits at the equator.
Oxidative damage leads to oxidation of these proteins, which act as gap junctions for lens fluid/ion transport.
What are connexins?
If you’re asked about development of lens zonules, you should think about this type of vitreous.
What is tertiary vitreous?
Anterior displacement of the lens later in life increases the risk of forming this, which can lead to angle-closure glaucoma.
What is a pupillary block?
This is the site of origin for most lens zonules.
What is the basement membrane of non-pigmented ciliary epithelium of the pars plana?
This is the most common metabolic pathway that glucose will use within the lens.
What is anaerobic glycolysis (lactate)?
There is a “bidirectional relationship” between these two clinical findings.
*In other words, the presence of one may lead to the other*
What are cataracts and ocular inflammation?
SD mentions Marfan syndrome. You should immediately think of this clinical correlate.
What is lens subluxation (aka ectopia lentis)?
*Marfan = fibrillin-1 mutation (most common protein in zonules) causes displaced lens
What is the lens capsule?
This type of lens zonule acts as a fulcrum, connecting the anterior and posterior zonules back to the ciliary processes.
What are tension zonules?
Glutathione is an extremely important antioxidant in the lens. Name the three amino acids that must be present to produce glutathione.
What are glycine, cysteine, and glutamic acid (glutamate)?
This term is when a cataract breaks apart, releasing lens material into the aqueous fluid.
What is liquefaction of a hypermature cataract?
*May lead to lens-induced uveitis and/or phacolytic glaucoma*
This is the refractive index of the lens.
What is 1.408?
This portion of the lens contains fully-differentiated cells that lack organelles.
What is the lens nucleus?
This type of lens zonule acts as a shock absorber ensuring coordinated movement of the ciliary body, lens, and vitreous during accommodation.
What are vitreous/hyaloid zonules?
There are three molecules/ions that SD said definitely have a net INFLOW into the lens. What are they?
What are amino acids, glucose, and ascorbic acid?
A child has bilateral congenital cataracts. Genetic testing shows a mutation in a gap-junction gene. Which two types of protein may be involved?
What are connexins and aquaporins?
If you see something about a quiescent layer of the lens epithelium, that is immediately this region.
What is the central zone of the lens epithelium?
This protein is the most abundant macromolecule present in lens fibers.
What is crystallin?
Only made in epithelium! Requires organelles, so lens nucleus CANNOT make them.
According to Schachar’s theory of accommodation, name the type of zonules that relax and the zonules that contract during accommodation.
Relax: anterior and posterior zonules
Contract: Equatorial zonules
(Helmhotz theory: ALL zonules relax)
These are the two layers of the lens that do contain the enzyme needed to make reduced glutathione (antioxidant).
What are the lens epithelium and lens cortex?
*With age, we lose transporters required to get reduced glutathione into the nucleus. Leads to oxidative damage and crystalline precipitation = CATARACT!
A 45-year-old patient develops presbyopia and asks you for some reasons people get presbyopia. These are the possible explanations for presbyopia development.
What is:
Decreased flexibility of lens fibers?Decreased zonular tension from changes in anterior segment?Decreased elasticity of the lens capsule and/or *Bruch’s membrane?
*Remember: the choroid shifts anteriorly during accommodation, so stiffness of Bruch’s membrane makes this harder.
+100 BONUS POINTS: Name the mutated gene associated with this condition.
What are Congenital cataracts, neurological defects (ataxia, cognitive impairment), and tendon xanthomas (cholesterol nodules on limbs)
Gene: CYP27A1