Development Of The Ametropias Flashcards
First month of life refractive error distribution range
-10D to +5D
Mean refractive error in the first month of life
-0.70D
ATR in the first few years of life
Decrease
What are premature infants more likely to have?
Higher degrees of myopia
-especially with very low birth weights
What kind of refractive error change between ages 6/7 to 11/12?
Linear
How much hyperopia will a 5/6 y/o have to still be hyperopia at age 13/14?
+1.50D
Majority of 5/6 year olds with refractive error of _______ to _______ will be emmetropic at age 13/14.
+1.50D
Most children entering school with refractive errors of _____ to ____ will be myopic at age 13/14
0 to +0.49D
Children who are myopic at age 5/6 will become…
More myopic
Among school aged children, what refractive error had the greatest change?
Myopes
When is refractive change fastest for school aged children?
When a child crosses from hyperopia into myopia
What are the 4 types of myopia?
- congenital
- youth onset
- early adult onset
- late adult onset
What is the most common type of myopia?
Youth onset
Youth onset myopia
- school age years
- most common type of myopia
- prevalence at 5 or 6 years of age: 2%
- prevalence at 15 or 16 years of age: 20-25%
- onset for females about 2 years earlier than males
Mean age of cessation of childhood myopia?
- 15.21 for females
- 16.66 for males
Once myopia appears in childhood, it increases until
Middle to late teens
What is responsible for myopia progression in childhood myopia?
Axial elongation
Refractive power decrease
Refractive power decrease in childhood myopia from…
Decrease in crystalline lens power and decrease in corneal power (hyperopia)
Axial length increases in childhood
Associated with normal growth of the eye in emetropic and hyperopic children, stops in early teens
Emmetropic children between 6 and 14 years old show:
- increase in axial length
- decrease in crystalline lens thickness
- decrease in crystalline power
Myopic vs emmetropic young adults
- greater vitreous depth
- greater corneal power
- greater posterior crystalline lens radius
School aged and young adult females vs males
- shorter eyes
- store corneas
- more powerful crystalline lens
The earlier in life the onset of myopia occurs
The greater the amount of myopia developed by late teens to early adulthood
Higher rate of childhood myopia progression is associated with
Earlier onset of myopia
Myopes vs nonmyopes
- spend more time reading and doing other forms of near work
- have occupations that require near work
- have better reading abilities
- have more years of education
Shorter reading distance associated with
- greater myopia progression
- the closer they read, the more myopia
Children with ATR at 5/6y develop myopia by age
13/14y vs those without astigmatism or WTR
Once myopic, ATR astigmats…
Do not have greater rates of childhood myopia progression
Associated with higher rates of childhood myopia progression
- earlier onset age and/or higher initial amount of myopia
- near-point esophoria
- temporal crescents and other myopic fundus changes
- higher IOP
- greater amount of time spent reading and doing near work
- less time spent on outdoor activities
Slowing of myopia with pharmaceuticals: Atropine
- daily
- effects the development of retinal ganglion cells
- unpopular bc
- completel cycloplegia
- photophobia from dilation
- possible allergic reaction
- myopia progression accelerates upon stopping treatment
Myopia control with pharmaceuticals: Pirenzepine
-similar to atropine
Myopia control with rigid lenses
- flattens cornea (while axial elongation continues)
- eye becomes more hyperopic
Myopes
+0.03D
Myopes
-0.42D
Effectiveness of RGP CLs
Effective in myopia control but only while CLs wear continued
Myopia control with bifocal lenses
- these lenses provide different refractive correction for distance and near
- can also be used for certain accommodation and vergence disorders
- rate of myopia progression lower than in single vision lens
- most effective in lower myopia progresssion rates for children with esophoria at near
What do bifocals best correct for children
Most effective in lowering myopia progression rates in children with esophoria at near
-want a near addition power to shift near phoria orthodox/low exo range
Myopia control with PALs
- same trend found as in bifocal specs
- rates of myopia progression about 0.2D less per year with PALs than with single vision lenses in esophoria
During school age years, astigmatism tends to…
Increase a small amount
In school age children, what kind of changes do you see in astigmatism?
Changes towards ATR more common than WTR
5/6 year olds more likely to become myopic with what type of astigmatism?
ATR
General trends for young adult hood
- refractive error stabilizes
- some onset of myopia
- some progression of myopia
- some have small shift in the hyperopic direction
Mean annual changes for 20-34 year olds
-0.05D/year
Mean annual changes in 35-43 year olds
+0.03D per year
Earaly adult onset myopia
20-40 years old
- based on physical maturity
- prevalence of myopia > 0.50D increased from about 20% at 20 years old to 30% at 40 years old
What can progress in young adulthood?
Youth onset myopia and early adult-onset myopia
-rate of early adult onset myopia progression
Adult stabilization
Childhood myopia progression is followed by stabilization of refractive error in young adulthood
Adult continuation
Childhood myopia progression followed by a general slower progression of myopia in young adulthood
Adult acceleration
Refractive change in the myopic direction accelerates in young adulthood
What is the percentage of emmetropes that will develop myopia before age 40 in populations where subjects are not in college?
10%
What percentage of emmetropes and low hyperopes are likely to become myopic before age 40 in populations where they go to college/military?
20-40%
In young adults, shift towards myopia by emmetropes and low hyperopes vs myopes
- less common
- lower in amount
College student with >+1.00D after 4 years of school?
Unlikely in either principal meridian to be myopic after 4 years
-if hyperopic, shift not so much in myopic progression
17/18y old low hyperopes vs older low hyperopes
More likely to become myopic in heavy near work situations
What kind of astigmatism is there a shift towards in young adulthood?
WTR
When does increase in plume occur to, and when does decrease
Increases in plus from 40 to mid 60, then decreases
Mean refractive error at 40 years old
+0.73D
Mean refractive error at 64 years old
+1.97D
Mean yearly rate change for ages 40 on
+.50D per year
Mean refractive error at 65 years old
+1.72D
Mean refractive error at 74 years old
+1.21 D
After age 45
- shift in hyperopic directions
- some myopes increase in myopia
- age related nuclear cataract causes shift towards myopia
Age related nuclear cataract
- after age 45
- shift towards myopia
- May be able to read better at first when they first start
Astigmatism trend in age 40 and on
- shift towards ATR
- mean change is 0.25DC per decade
Shift towards ATR ages 40-44
+0.27DC
Shift towards ATR over 80
-0.81DC
Prevalence of >0.25DC WTR 40-44
29%
Prevalence of > 0.25 WTR over 80
6.8%
Prevalence of > 0.25 DC ATR 40-44
9.5%
Prevalence of >0.25 DC ATR over 80
65.1%
Emmetropization
- the process to explain why there are more people with emmetropia and near emmetropia
- peak of refractive error distributions occurs at emmetropia and low hyperopia
- accounts for coordinated eye growth and some form of vision-dependent feedback system for ocular refractive development
If changes in ocular components occurred separately
Large changes in refractive error
If changes in ocular optical components occurred together
Less changes in refractive error
Emmetropization during childhood
- vitreous depth increases – myopia
- crystalline lens power and thickness decreases (hyperopia; posterior surface mostly involved with emmetropization)
- anterior chamber depth increases
Vision dependent feedback system
-axial length changes based on visual input
Axial length change based on visual input
Large refractive error occur when the eye does not have a normal ocular imagery
Axial length greater in
- neonatal eyelid closure
- juvenile corneal opacification
- congenital cataracts
High myopia can be caused by
- lid hemangiomas
- ptosis
- neonatal eyelid closure
- retrolental fibroplasia associated with retinopathy of prematurity
- vitreous hemorrhage in infants and children
What aids in emmetropization process and reduces amblyopia?
Treatment of spectacle correction
Amblyopia
Brain does not allow eye to see 20/40
Etiology
Unknown
Genetic inheritance
- some studies show that genetic inheritance and lifestyle and environment contribute to myopia
- other studies show that genetic inheritance is not a factor
Near work
-sustained accommodation increases IOP which leads to stretching of the posterior segment of the eye which leads to axial elongation
Mechanical forces on the sclera
Tension from extrocular muscles and IOP cause axial elongation
Retinal refocus
Defocus itself alters axial length (not the mechanism of accommodation)
Retinal biochemstry
- biochemical agents affect the function of retinal synapses
- some studies show that this stops myopia, others show that these molecules induce myopia
Etiology of astigmatism
- unknown
- eyelid tension theory
- high prevalence
Etiology of astigmatism eyelid tension
Eyelid tension steepens the vertical cornea meridian and causes WTR
What happens when the eyelids are lifted from the eye?
Corneal WTR astigmatism decreases
What happens when palpebral aperture is narrowed?
Corneal WTR astigmatism increases
What is the shift towards ATR in over 40 years of age due to?
Decreased lid tension
