BS - Lens Structure & Metabolism 2 - Week 5 Flashcards
What is the most common cause of treatable blindness globally?
Cataracts
Name the four types of cataracts (by the area it affects), and its rarity.
Nuclear cataract (common) Cortical cataract (most common) Anterior subcapsular (rare) Posterior subcapsular (rare)
Define iatrogenic.
A condition caused by medical intervention.
Describe steroid-induced iatrogenic cataracts, and the area it affects.
Occurs after long term, high dose steroid therapy.
Affects the posterior subcapsular region.
What are the three main mechanisms that are altered in steroid cataracts?
Lens metabolism
Protein formation
Growth factor imbalance
How are steroids believed to affect the lens metabolism and DNA synthesis?
- Increase glucose levels
- Decrease ATP levels
- Decreased Na+K+ATPase activity
- Increased DNA synthesis
How are steroids believed to affect the formation of lens proteins? How is this believed to contrivute to cataracts, and what bond is involved?
Binding of steroids to lens proteins creates a steroid-protein adduct.
This increases agglutination via disulphide bonds between adducts.
How are steroids believed to affect the balance of ocular growth factors? Name the two factors involved and which is likely responsible for catactous-like changes. Describe what happens to their levels with and without steroids.
The two main factors are FGF-2 and TGF-β.
TGF-β is involved with steroid action.
With steroids, FGF-2 levels decrease significantly.
TGF-β levels are not significantly affected by steroids, leading to an imbalance of FGF-2 and TGF-β.
TGF-β was found to cause cataractous-like changes to the eye.
How are steroids believed to impact the migration of epithelial cells?
Due to altered cell migration and differentiation, cells migrate posteriorly, however they no longer differentiate.
Undifferentated cells migrate to the posterior pole, and clump there, forming a posterior subcapsular cataract.
How much more likely are diabetics likely to get cataracts?
5 fold increase to risk.
What 3 factors lead to diabetic cataract?
Altered osmolarity
Oxidative stress
Glycation
Describe posterior capsular opacification occurs, and the population it most occurs in. How is it treated?
Occurs after a cataract surgery, a complication.
Occurs most in younger patients.
Treated with a YAG laser, creating a hole for light.
What are 3 risks of YAG laser treatment for posterior capsular opacification?
Raised IOP
Cystoid macular oedema
Retinal detachment
What causes posterior capsular opacification?
Results from lens epithelial cells differentiating into mesenchymal cells, and expressing excess fibrous material.
Which growth factor is suggested to cause posterior capsular opacification?
TGF-β.
