nemoci-sympt/OCNI/presbyopia/zhorusujici-vyvolavajici-rizikove-faktory
A decrease in the permeability of aquaporin zero (AQP-0)
- As a possible cause for presbyopia
- Decrease in the permeability of aquaporin zero found in lab analysis
- Major intrinsic protein (MIP)
- Fluid flow exists inside the avascular lens
- Enters and leaves the lens during the accommodation process [17]
- Aquaporin zero
- Abundant in the membrane of the fiber cells [17]
- Volume change due to fluid traversing the surface of the lens occurs during accommodation
- We present the hypothesis that increasing the permeability of AQP-0 would facilitate accommodation
- It is possible to visualize and measure the fluid volume lost during un-accommodation
- Determine if the fluid is lost across the anterior, posterior or both surfaces [17]
- Age-related loss in lens water permeability
- Could reduce fluid fluxes during the shape changes of accommodation potentially contributing to presbyopia [17]
Axial length
- Increased significantly with accommodation
- Mean corrected increase in axial length of 2±18 um
- 8±16 um observed at 3.00 and 4.50 D [14]
- Magnitude of accommodative change in axial length was not dependent on refractive error classification
- Significant reduction in the magnitude and variance of axial length change
- Evident after 43 to 44 years of age [14]
- Negative association between transient increase in axial length and age
- In combination with reduced variance after age 43 to 44 years
- Consistent with a significant increase in posterior ocular rigidity
- May be influential in the development of presbyopia [14]
- Lower accommodative amplitudes and gains
Změny viscoelastic properties of the lens capsule and lens matrix
- Pokles elasticity and leverage
- Provided by posterior, anterior and tensile fibre systems [24]
- Ability to expand and increase refractive power is lost by age
- Elasticity of the lens capsule decreases by half between youth and 60 years of age
- Reduced capsular elasticity alone cannot explain presbyopia
- Only diminished capacity to change curvature [25]
Zvětšení objemu čočky
- Lidská čočka roste celý život
- Po 40. roce života vede tento růst ke ztrátě pružnosti pouzdra čočky [4]
Změna tahu v závěsném aparátu čočky
- Deterioration in structure and function of a number of inter-related tissues
- Changes in crystalline lens dimensions with age
- Associated change in geometry of zonular attachments
- Suggests that the longitudinal muscle fibers of the ciliary muscle contract during accommodation
- Placing more tension on the equatorial zonules
- While relaxing the anterior and posterior zonules
- This force distribution causes an increase in the equatorial diameter of the lens
- Decreasing the peripheral volume while increasing the central volume [24]
- Under this theory, presbyopia occurs because of the increasing equatorial diameter of the aging lens
- Once the lens diameter reaches a critical size, usually during the fifth decade of life
- Resting tension on the zonules is significantly reduced [24]
- Geometric theories
- Changes in the geometry of the zonular attachments to the lens [25]
- Geometric disorder
- Only attributed to changes in the size and volume of the lens
- Zonular tension is increased during accommodation in young subjects in contrast with the classic Helmholtz's theory, as we described above
- Schachar and colleagues 8 believes that presbyopia results from a decrease in zonular tension caused by the normal growth of the crystalline lens with age
- Equatorial diameter increases at approximately 0.02 mm/year
- Distance between the ciliary muscle and the equator of the lens decreases throughout life
- Effective force that the ciliary muscle can apply to the lens equator is reduced in a linear fashion with age
- Amplitude of accommodation decreases linearly with age resulting in presbyopia [25]
- Surgical expansion of the sclera surrounding the ciliary body
- Can restore accommodation as a remedy for presbyopia
- Implantation of a plastic ring or arches of plastic in the sclera surrounding the ciliary body
- To increase the space between the ciliary body and the lens equator
- Efficacy of scleral expansion surgery was not completely determined [25]
- Location of the zonulo-lenticular attachments relative to the lens equator and the ciliary muscle
- Changes with age as lens increases in size
- Changing its curvatures [25]
Skleroza čočky
- Sclerosis of the crystalline lens as the cause of presbyopia
- Inability of the lens capsule to mold the hardened lens substance into the accommodated form
- Accommodative loss - changes in the elastic properties of the lens [20]
- Crystalline lenses beyond 58 years of age
- Would not change focal length when increasing and decreasing radial stretching forces were applied through the ciliary body-zonular complex [20]
- Různé studie - různé výsledky a teorie
- Young's Modulus of Elasticity of the lens varies with age
- Polar elasticity and equatorial elasticity
- At birth
- 0·75 × 103 and 0·85 × 103 Nm-2
- At 63 years of age
- Both are equal to 3 × 103 Nm-2 [29]
- proteins slowly denature throughout life
- Change from clear to a yellow color
- Causing blurry vision
- Glare with night driving [30]
Tuhost čočky x tah kapsuly
- Lens and capsule-based theories
- Changes in the elasticity and compliance of the lens and capsule
- Lens substance houses restoring forces
- Tend to maintain it in the unaccommodated form
- Predominate in presbyopia
- Antagonized by capsular elasticity
- Young eye, elastic capsular forces are dominant [25]
- Residual stresses between the lens and capsule [25]
Colagen crosslinks
- High blood sugar and other molecules in the fluids can react with proteins
- Chemical bonds called crosslinks
- Crosslinks act like molecular “handcuffs,”
- Two neighboring proteins that were previously able to move independently
- And binding them together
- Impairing their function [31]
- Crosslinking of strands of the protein collagen
- Prevents them from spreading apart from one another to accommodate - tuhost cév
- More and more strands of collagen become crosslinked together over time
- The blood vessels to become ever more rigid
- Gradual rise in systolic blood pressure with age [31]
- Cushioning effect provided by free-moving collagen
- Blood pulses are damaging to the structures of organs that filter our blood [31]
Elastická kolagenní vlákna - ztráty
- proteins responsible for the elasticity - podobná regulace ?????
- Artery wall
- Transparency of the lens of the eye
- High tensile strength of the ligaments... [31]
Liquefaction of the vitreous
- Presbyopia is associated with
- Occur at about the same point in the human lifespan
- Does not explain why the age-related decline in accommodative amplitude begins so early in life [28]
Age-related changes in the muscle fibers surrounding the lens
- Age-related changes in ciliary muscle (CM) morphology and contractility have variously reported
- That CM weakens
- Or strengthens with age
- Two groups of eyes-40 eyes of 40 healthy volunteers mean age of 28.1?±?5.8 years
- 40 eyes of 40 healthy volunteers with a mean age of 56.6?±?7.3 years
- Evaluate relaxed CM tone
- PCM was calculated as the difference between the change in mean anterior chamber depth (ACD) and lens thickness (LT) before and after cycloplegia
- PCM for relaxed CM tone was
- 0.04±0.04 mm in pre-presbyopic participants
- 0.06±0.03 mm in presbyopic ones [15]
- When relaxed, CM tone does not diminish with presbyopia according to changes in anterior chamber parameters due to cycloplegia [15]
- Extralenticular theories
- Changes in the ciliary muscle and choroid [20]
- Ciliary muscle
- Capable of providing the same magnitude of force in presbyopic as in pre-presbyopic eyes
- Impedance cyclography - measure ciliary muscle contraction
- It remains normal up to the age of 60 years
- Ability of the ciliary muscle to alter its configuration in response to topical cholinomimetic drugs or electrical stimulation of the Edinger-Westphal nucleus
- Clearly declines with age 30-32 [20]
- Distance from the ciliary body to the zonular insertion onto the lens
- Does not change with increasing age [20]
Mydriáza
- Stavy a léky, které působí mydriázu - roztažení zornice mohou zhoršovat schopnost zaostřit na blízko
- Adrenalin, stres např.
- Cycloplegia
- More effective in young eyes than old
- Onset of cycloplegia to be more rapid in early presbyopes than nonpresbyopes [25]
Job that requires a lot of close-up work
- Higher risk of premature age-related long sight [26]
Preexiting hypermetropia
- Higher risk of premature age-related long sight [26]
Sclera
- Undergoes scleral sclerosis as well as metabolic physiological stress
- Loss of elasticity
- More rigid sclera elicits compression and loading stresses upon underlying structures
- Specifically those related to accommodative function
- Increased ocular rigidity affects other tissues as well, including
- Ocular blood flow through the
- Sclera
- Optic nerve [20]
- Correlated to the pathogenesis of
- Macular degeneration
- Other age-related eye diseases
- Ocular rigidity
- May not only impact the loss of visual accommodation
- May have more extensive clinical significance
- Sclera becomes less deformable during accommodation in the nasal area with age
- Models suggest up to 2 diopters that might be contributed by extralenticular structures [20]
- Laser anterior cilary excision
- Primary mechanism of action is to decrease scleral resistive forces
- In order to restore accommodative ability in the aging eye
- By increasing resultant ciliary muscle constriction [20]
- Laser anterior ciliary excision
- Appears to be a safe procedure for the restoration of accommodation in aging adults
- Changing the biomechanical properties in the sclera
- Appears in this IRB monitored pilot study to improve dynamic accommodative range for both intermediate and near vision [20]
- Further investigation must be performed to further assess efficacy and long-term stability [20]
Tabaco smoke
- Exposure induced lens hardening
- Causes presbyopia in humans
- Rats exposed to tabaco smoke can be used as a presbyopia model [28]
UV light
- People who live and work in a hot climate with lots of ultraviolet sunlight exposure
- Higher risk of premature age-related long sight [26]
Loss of flexibility of the lens and surrounding structures
- Vitreal-zonular complex stiffens with age
- Losing its elasticity
- Age-related changes in these structures and their biomechanical interactions with the ciliary-lens complex
- May contribute to presbyopia
- Changes in extralenticular structures which may have an impact on the loss of accommodation
- Sclera
- Choroid
- All ocular tissues are made of collagen
- Are impacted like all other connective tissues by age
- Ocular rigidity has been correlated with age
Nápady - vařim z vody a z neznalosti - co by kdyby k dohledání
- Zvětšení objemu oka / tahu na akomodační a závěsný aprát čočky
- Může to být jeden z fakturů ? Jsem zvědavá, zda objevím něco, co bude podporovat tuto možnost. )
- Například zvýšeným nitroočním tlakema pomalými degenerativními změnami s oslabením vaziva sklivce / prozánětlivým stavem / nějakým deficitem - a zvětšení obvodu sklery - oka
- Jako například dilatace aorty a následná chlopenní insuficience
- Jenže zde zrovna v úrovni akomodačního a závěsného aparátu čočky
- V literatuře spíše nalézám argumenty pro to, že tohle je nesmysl a naopak zvětšní obvody oka by mohlo pomoct zvýšit tah na tuhou čočku při akomodaci
- Hypoosmolární prostředí v oku
- Degenerace závěsného aparátu čočky
- Degenerace akomodační inervace - co třeba neuropatie - deficity vitamínů řady B ap. a porucha koncových kapilár ?
- Nadměrná aktivita nějakého enzymu, který syntetizuje vodíkové můstky mezi kolagenními vlákny čočky ?
- Ztenčení / oploštění rohovky - degenerací/zánětem/nedostatkem bílkovin - riziko pak i pro laserové op a vznik keratokonu
