Effects of Aging Flashcards
Which elaborate systems support the ocular surface?
nervous-, vascular-, immune-, and endocrine-systems
What is the effect of aging that can be viewed on the external eye?
- Loss of skin elasticity & muscle tone - basically wrinkling
- Enophthalmos (posterior displacement of the globe)
- Ptosis (drooping eyelid)
- Ectropion (lower eyelid sags outwards)
- Epiphora (excessive watering)
How is the tear film affects by aging?
- Lacrimal gland secretion diminishes → reduced tear production (Roetth, 1953)
- Change in tear constitution → increased demand required as we age
The number of actively secreting meibomian glands decreases, and only half the glands are active at age 80 compared to age 20 (Norn, 1987)
The result is lipid insufficiency and/or poor lipid spreading, leading to a discontinuous film → increased tear film evaporation in older eyes (Guillon & Maissa, 2010)
Overall result: A reduction in tear volume [Dry eyes]
What happens to lacrimal drainage as we age?
Lacrimal drainage declines with age.
This is thought to be a compensatory mechanism for the lack of tear production in the first place
How is the cornea affected by aging?
The most important and clinically relevant change in the cornea with age is the loss of corneal endothelial cells
As endothelial cells do not divide, with age there is a decrease in cell density. Also an increase in the variability of size (polymegathism) and shape (pleomorphism)
Which of the following sections are of a young corneal endothelium?
A- Young Corneal Endothelium
B - Old corneal Endothelium
As endothelial cells do not divide, with age there is a decrease in cell density. Also an increase in the variability of size (polymegathism) and shape (pleomorphism)
What is the function of corneal endothelium cells and why are they vital in maintaining transparency?
Corneal endothelial cells are vital for maintaining corneal transparency to light because they provide a barrier function and pump water, stopping it from accumulating in the corneal stoma from the anterior chamber
→ fluid accumulation leads to corneal oedema and loss of corneal transparency (e.g., bullous keratopathy)
What occurs to pupil size as we age?
It decreases (known as senile miosis).
What could be possible causes of senile miosis?
ØLoss of sympathetic innervation (iris dilator muscle is sympathetically innervated)?
ØDegeneration of the radial dilatator muscle?
ØIncreased rigidity of iris blood vessels?
Why is senile miosis speculated to be a compensatory mechanism?
Optical aberrations increase with pupil size, and are heightened in older age thus reducing pupil size would do well to counteract this
True or False- Overtime the lens changes colour to become more yellow
True
Why does the lens yellow overtime and what are the advantages and disadvantages of this?
Over time the lens accumulates pigments – various chemicals that frequently have a yellowish tint.
The benefit of these are that they are protective for the back of the eye since yellow pigments block UV rays very effectively.
The disadvantage is→ decreased short-wave transmission so colour vision slightly affected
What happens to the structure of the lens overtime concerning proteins?
Soluble crystallin proteins become unstable (probably due to UV exposure) and form insoluble protein aggregates (fancy way of saying insoluble protein clumps)
→ This causes reduced transparency and increased scatter (because remember the regularity of the lens is what allows for as much transmission of light through as possible).
What are flurophores?
Flurophores are components that absorb light in one wavelength and re-emit it at another (usually a longer) wavelength.
[They are the basis for glow in the dark things]
What do we mean by fluorescence of the lens increases overtime and what does this mean for vision?
The number of fluorophores in the lens increases overtime- Fluorophores aggregate with age
Within the lens, fluorophores excited by UV light emit visible (blue/green) light ( which produce “straylight” inside the eye).
For vision this causes an intraocular veiling glare and reduces the contrast of the retinal image - it is particularly problematic for night driving
Why do wavefront aberrations increase as we age?
Normally the way the eye works is we have Equal-and-opposite aberrations in the lens which help to compensate for aberrations in the cornea
Corneal aberrations remain constant with age
But the ability of the lens to compensate is gradually lost, so whole-eye aberrations increase
How do increased wavefront aberrations with age affect vision?
Reduced acquity (as we have poorer image formation)
What is accommodation?
Accommodation is the ability of the eye to change its power (focal length) to bring objects of interest at different distances into focus
How is accommodation achieved?
In humans, accommodation to near objects is achieved by relaxing the zonule fibres, making the lens wider and more rounded.
What is the amplitude of accommodation?
The majority of refractive power (~45D) is provided by the cornea
But if the refractive power of the emmetropic eye was fixed, only objects at optical infinity (the Far Point) would be seen clearly.
The amplitude of accommodation is the change in refractive power afforded by accommodation.
How does amplitude of accomodation vary with age?
Adolescents generally have 12-16D (and infants as much as 30D !)
However, this declines by 0.2D/year until ~50 years, where most eyes no longer have the 2.5D necessary to read at arms length (40cm)
What is presbyopia?
An inability to focus on objects at near
It is where ampltiude of accommodation has declined so much that most eyes no longer have the 2.5D necessary to read at arms length (40cm)
Why does presbyopia occur?
Aqueous Humour
What cavity does it fill?
What is its function?
What is it produced by?
Where is it drained through?
Aqueous humour fills the anterior cavity,
It is important for providing nutrition (e.g., to the cornea, lens, etc.), immunity, and maintaining intraocular pressure (re: glaucoma lecture).
It is continually produced by the ciliary processes.
Aqueous humour is drained through the trabecular meshwork (canal of Schlemm) and a uveoscleral pathway (recent estimates suggest each contributes ~50% to total outflow.
What happens to the rate of aqueous drainage with age and why?
Due to an increase in the number and thickness of collagen fibres, a thickening of the elastic fibres, and as a result a reduced space between muscle bundles
→ which leads to a reduction of uveoscleral aqueous outflow
[A reduction in trabecular outflow may also contribute to the total decrease in aqueous outflow, though that is now disputed]
What happens to the rate of aqueous production as we age?
Aqueous production decreases
[This is thought to be another compensatory mechanism to account for the rate of drainage decreasing - hence why we don’t naturally get high IOP/glaucoma with age]
Which cavity does vitreous humour fill?
The posterior cavity
How does vitreous humour change as we age?
Vitreous humour is gelatinous and made up of a network of collagen fibrils which make it gel like.
Overtime these collagen fibres degrade. Thus the vitreous becomes watery and unstructured, and the fibres holding the surrounding membrane to the retina can break.
What can liquefaction (becoming water like) of the vitreous humour cause?
Increased risk of posterior vitreous detachment
Floaters
What are three examples of changes that occur to the retina as a result of aging?
Loss of ganglia (thinning of the RNFL- retinal nerve fibre layer)
Loss of photoreceptors
RPE dysfunction
Why are retinal ganglion cells important?
Retinal ganglia cells (RFCs) are crucial for the encoding and transmission photoreceptor responses to the brain
What happens to the number of retinal ganglion cells as we age?
They decline -With age RGCs are lost at a rate of 0.3% to 0.6%/year
What happens to the number of cones as we age?
The number of cones does not change significantly with age - so nothing
What happens to the number of rods as we age?
The number of rods decreases significantly.
If the number of rods decreases with age why do we not have gaps on the retina where the dead rods were?
The inner segments of the remaining rods expand, to fill any empty spaces (no “gaps” in the mosaic)
What are the functions of the retinal pigment epithelium?
It transports nutrients into and removal of waste products from photoreceptor cells
enables retinoid transport and regeneration,
and performs phagocytosis of photoreceptor outer segments.
[Left to their own devices photoreceptors would just keep growing and as a result the RPE basically eats/trims the photoreceptor if it gets too big]
What signs of aging can be seen in the RPE in old age?
We can see signs of aging on the RPE as well including but not limited to, an aggregation of lipofuscin- the waste product of photoreceptor phagocytosis.
What is a notable effect of aging on the RPE?
One notable consequence of increasing RPE dysfunction is that the rate of rhodopsin regeneration decreases with age (i.e., impaired dark adaptation)
→ Which leads to difficulty seeing at night (scotopic vision)
How do structural chnages of the eye with age affect vision? What gets worse?
LITERALLY EVERYTHING
Absolute luminance sensitivity
Dark adaptation
Visual acuity
Contrast sensitivity
Temporal resolution
Colour vision
Visual fields (peripheral vision)
Near vision (accommodation)
Etc.
What structural chnages is a loss of light sensitivity in old age related to?
Decreased pupil size (senile miosis)
Increased lens opacity
- Reduced N of rods (& ganglia)
- Impaired rhodopsin regeneration (RPE dysfunction)
- Etc.
What structural changes with old age is a loss of visual acuity related to?
Increased intraocular scatter
Increased aberration
Reduced retinal illuminance due to senile miosis & increased lens density
Etc.
How can a decline in visual function with age affect quality of life?
It can result in:
Reduced mobility - no night driving
Increased falls - decrease in visual acuity
Increased road traffic accidents
Loneliness
Depression
Inability to perform important everyday tasks
Etc.
