D - Ocular Ageing - Week 1 Flashcards
List 4 extrinsic factors that contribute to ageing pathology
Nutrition
Radiation (UV)
Stress
Smoking
Describe the pathogenesis of nuclear cataracts. Explain how the main symptoms of nuclear cataracts arise (2)
Nuclear fibres compact with age, increasing the density of the nucleus.
- The denser tissue leads to a higher refractive index = myopic shift.
- compaction leads to development of reflective crystallin deposits = glare
Describe how the increased density of the nucleus affects oxygen transport in nuclear cataracts (3)
Increased tissue density from nuclear compaction creates a “tissue density border” (= barrier for transport), resulting in:
- less oxygen flowing to the nucleus
- increased oxidative stress (from O2 pooling/accumulating at edge of nucleus inside)
- reduced antioxidant access to the nucleus
Describe how UV exposure affects a lens with nuclear cataract
Light (UV) exposure of oxygen generates free-radicals, which the lens proteins react with, causing protein cross-linking in the lens.
What does protein cross-linking of the lens lead to?
Nuclear cataract development.
Why does UV lead to cataract formation in a denser nucleus?
Because with a denser nucleus, the tissue density border prevents antioxidants getting in, meaning antioxidants can’t remove the free-radicals that get formed when the oxygen at the nucleus edge reacts with UV
How do antioxidants (such as glutathione/GSH, the one used for the lens) remove free-radicals?
They donate an electron to them to make them more stable/less reactive
Briefly outline the 3 key pathological changes that can happen in cortical cataracts
Fibre cell degeneration, liquefaction, and fragmentation
Describe the pathogenesis of cortical cataracts.
UV light exposure leads to fragmentation of the lens fibres, which release protein and break off into globules.
Describe the pathogenesis behind the progression of cortical cataracts into hypermature cortical cataracts (2)
As the cataract progresses, globules and denatured proteins accumulate in a “cleft”, leading to formation of a water diffusion gradient.
- This gradient attracts water to the lens fibre/cell in the cortex: resulting in the lens absorbing fluid and swelling up.
This process is known as “cortical liquefaction”
What is a cleft? (in relation to cortical cataract)
it literally just means the space between where the lens fibre has broken apart
What happens to the nucleus of the lens in a hyper-mature cortical cataract?
Eventually, the globules/abnormal protein replaces the entire cortex, resulting in complete liquefication of the cortex.
- The nucleus then sinks, by gravity, inferiorly
What does the lens look like in a hypermature cortical cataract?
A milk-filed sac.
How can cortical liquefication affect the appearance of the capsule in cortical cataracts?
If the fluid is small enough, it can escape through the intact capsule, resulting in a smaller-than-normal lens with a wrinkled capsule.
i.e. the capsule has wrinkles in it. (not always, obv)
How do globules form in a cortical cataract?
Fibres comprise a bi-lipid membrane layer which gets broken by UV. Sulphydryl bond crosslinking of lens proteins gives infolding, rounding and aggregation.
Thus causing the formation of globules.
What does the anterior and posterior lens sutures look like?
anterior: Y
posterior: upside-down Y
