Myopia OT #12 Flashcards
Where are light rays focused in myopia? Which type of image is produced?
Parallel light rays are focused in front of the retina which results in a blurred retinal image.
How does a minus lens work in regard to the focal points?
The second focal point of the correcting lens should coincide with the far point of the eye
What are possible effects of a high myopic refractive error?
Glaucoma, Cataracts, retinal detachment, maculopathy
How many adults are myopic in the US from 1999-2004?
41.6%
What will happen by 2050?
Half the word will my myopic with 1 billion having high myopia (>6D)
What percentage of high myopia will develop retinal disease?
70%
What are the global economic burdens of myopia and what will it increase to in 2050?
$478 billion by 2050 it will be $1.2 Trillion
What is emmetropization?
Newborns are hyperopic but this refractive error decreases during infancy and early childhood
What is a leptokurtotic distribution?
Emmetropization with a high peak from -2 -> +4
This occurs in 6-8 years old
Which type of curve do newborns have?
Normal Distribution from -7 -> +11
What grows during the first three years of life?
Cornea, Ant. Chamber depth, crystalline lens, axial length
What needs to happen if you have a long axial length in order to be an emmetrope?
You need less corneal or crystalline lens power (flatter curvature)
What is the anomalous component of myopia?
Axial length especially increased vitreous chamber depth
How many chromosomes have been identified for high myopia?
4
What is the heritability index of myopia for twins?
80%
What is the greatest risk factor of myopia?
Two myopic parents
What are possible risk factors for myopia?
- Environment
- Diet
- Near work
- Intelligence
- Stress
- Lack of outdoor activities
What is accommodation?
Change in the shape of the crystalline lens which increases the refractive power of the eye thus bringing near object into focus
What happens if the increase in power of the eye is maintained when viewing a distant target?
The image of the distant target will lie in front of the retina but far point is the point conjugate with the retina of the UNACCOMMODATED eye
What is associated with a 1D increase in myopia?
67% increase in myopic maculopathy
What happens if you slow myopia by 1D?
Reduces the risk of the patient having maculopathy by 40%
Why does each diopter of myopia matter?
- Less visual disability when uncorrected
- Better option for surgical myopia correcting
- Reduced risk of blindness associated with lower levels of myopia
What is the greatest myopia related risk?
Myopic Maculopathy which is irreversible vision loss AKA Myopic Macular Degeneration
What do individuals with high myopia have increased risks of?
- Posterior Staphyloma
- Chorioretinal and RPE atrophy
- Lacquer Cracks
- Macular Hemorrhage
- Choroidal neovascularization
- Myopic Macular Hole
Do 6-7 year olds or 11-12 year olds progress faster for myopia?
6-7yo are 2x faster for refraction and axial elongation
Do girls or boys progress faster for myopia?
Girls are 10% faster
How much faster are children with 2 myopic parents likely to get myopia?
30-40% faster than kids with no myopic parents
How much quicker do Asian children in Asian progress for myopia than US children?
50% faster
What are myopia treatments?
- Lenses ( SV, bifocal, PALs, myopia control lenses)
- Contacts (SV, multifocal, Ortho-K)
- Refractive Surgery
- Atropine
Can environment influence the axial length of the eye and if so, how?
Yes, via “Hyperopia retinal defocus”
Which type of defocus do minus lens create?
Hyperopic Retinal Defocus -> Increased axial growth
Which type of defocus do plus lens create?
Myopia retinal defocus -> reducing axial growth
Do bifocals slow myopia progression? What if prisms are added to them?
Yes, they help in 2014 the were 31% effective and prism bifocals were 34% effective
- The lenses slowed the refractive change and slowed axial length growth more than single vision
Do PALs slow myopia progression?
The difference between single vision and PALs was 0.20D
They help but bifocals are better
Which type of patient would PALs work best with? What is their approximate reduction in myopia?
In patients with larger lags of accommodation and esophoria at near
- 0.8D reduction in myopia
What are the effects of a large dose of atropine?
They slow myopia the most but have large “rebound” effects
Is there a significant difference in axial length between a placebo and 0.01% atropine?
NO
Is there a difference in spherical equivalent between a placebo and 0.01% atropine?
YES
What are the effects of a peripheral refraction?
Visual signals from the peripheral retina can impact emmetropization at the fovea and possibly the development of refractive error
It is best to eliminate hyperopia retina defocus in the periphery than centrally
What is the ideal myopia correction?
PERIPHERY
What are Essilor Stellest Lens? And how much do they slow myopia progression?
Aspherical Lenslets for myopia control
SAL - Slightly Aspherical Lenslets
HAL (best)- Highly aspherical Lenslets
67% slower
What does a Hoya DIMS lens do? And how much do they slow myopia progression?
Add more plus in the periphery to causes peripheral myopic defocus
52% slower
What does ortho K do?
Central Flattening via peripheral steepening -> leads to relative peripheral myopia
What does LASIK do?
Refractive surgery that flattens the central corneal making it less myopia and slows myopic progression
Corneal reshaping and peripheral refraction
What do multifocal CLs do?
Plus power in the near that way rays passing through that zone are focused in front of the retina for myopia retinal defocus
Which are the top 2 methods for myopia control?
Atropine and Ortho-K
What does sunlight exposure do for myopia?
54% lower risk of myopia progression if >11hrs outdoors/ week
40mins outdoor time/ day lead to 23% reduction in incidence of myopia
What are the possible mechanisms of sunlight’s effect on myopia?
Less accommodation outdoors
Pupil constriction outdoors
Dopamine is released which inhibits eye growth
What is the leading cause of visual loss throughout the world?
Myopia
Has there been proof that near work is associated with increased risk of myopia?
NO
What are risks that are associated with higher risks of myopia?
Myopic parents and higher IQ
What are the types of refractive surgery?
Radial Keratometry
Photorefractive Keratometry
LASEK- Laser assisted epithelial keratomileusis
LASIK- Laser in situ keratomileusis
Problems with RK?
> 12D corneal astigmatism
What happens in PRK?
Laser is used to reshape the cornea
- The corneal epithelium is removed with a blade or rotary brush -> new epithelium grows back over the corneal surface
What happens in LASEK?
Similar to PRK except tissue is moved aside to allow the laser to reshape the stromal bed and the replaced
What happens in LASIK?
Laser is used to create an epithelial flap which is then retracted -> exposed stromal bed is removed -> flap repositioned
What are complications of refractive surgery?
Reduced BCVA
Reduced contrast sensitivity
Reduced corneal sensitivity
Need reading glasses
Increased Dry Eye
Reduced Night vision
Starbursts and halos around lights
Thinner cornea
What percentage of nerves remain after refractive surgery (years later)?
<60%
