Kinzer Flashcards
Refractive error at birth
- normal bell curve distribution
- skew towards hyperopia
- Myopia:0-25% in newborns
As infant grows…
- shift towards emmetropia
- due to growth of eye
- skew towards myopia
- within first year of life
Emmetropization
-process in which refractive errors shift towards emmetropia
Ocular development between 5-15
- development SLOWS
- anterior chamber depth INCREASES (3D)
- Vitreous chamber depth INCREASES(3D)
- Axial length INCREASES(3D)
- cornea is stable
- Lens power DECREASES 1-2D
Prevalence of myopia percentages
- 2% ages 7-8
- 15% at age 15
- total myopic prevalence: 25%
Juvenile-onset myopia
- increase 0.5D per year in teens
- reduced ability of lens to compensate for growth in axial length
- slows 13-14 for Female and 15-16 in Males
Adult-onset myopia
-10% of population is moyopic after teens
Age
- single most important determinant of distribution of refractive error
- small portion of myopes at birth
- infant myopia: premies
- astigmatism in infants: most are under 1D cyl
- ages 6-8-myopia first observed
- Astigmatism decreases: ATR shift
High school
-refractive error stable
Beaver-dam study
- decreases in prevalence of myopia in older age
- 40-80 see decrease
Gender
-trends in refractive error are inconclusive
Ethnicity
- not enough data to determine id there is a trend in refractive error
- other studies: asian>white>black
NHANES study
- compared white to black
- whites were 2 times more prevalent
Orinda longitudinal study
- kids 5-12
- different ocular components for groups with high prevalence and groups with low prevalence
Geography
- results are messed with from other factors
- similar trends found in US ethnicity studies
Diet
- results are unclear
- cannot ethically take things out of a kids diet
- Alaskan eskimos local food vs government= no conclusions
Time
- inconclusive for studies that focus on different decades
- different studies have different methods and differet characteristics of what determines “myopia”
- over all, decrease prevalence in older age
Myopia personality
- not strong data
- introversion
- no social leadership or activity
Hyperopia personality
- not strong data
- carefree
- impulsive
- hyperactive
Systemic/ocular conditions
-both effect development of the eye, so there will be an effect on refractive error
Hyperopic occular diseases
- albinism(ocular form)
- maculopathies
- rod monochromacy
- achromatopsia
- nystagmus
- microphthalmis(small eye)
Glaucoma Near work theory
prolonged reading=muscle contraction=increased eye pressure=elongate eye=myopia
Glaucoma Associated conditions theory
- genetic link: high prevalence for positive steroid responce=glaucoma and myopia
- risk of ocular hypertension is higher in myopes
- risk of developing glaucoma is higher in myopes
Against the rule astigmatism
- myopia
- pellucid marginal degeneration
- thins inferior cornea and flattens vertical corneal meridian
Factors that for sure have an effect on refractive error
- age
- ocular diseases
- systemic diseases
Factors that are inconclusive
- gender
- ethnicity
- geography
- time
- personality
- diet
Name the 4 factors associated with refractive error
- hereditary
- Near work Theory
- intelligence
- socioeconomic status
Hereditary factor
Parent/child
- axial length and corneal power
- 1 parent=0-20% chance
- 2 parents=30-40% chance
Twins
- axial length, corneal power, refractive error
- monozygotic twins are more similar
Near work theory factor
- excessive reading in childhood
- increase in myopia among educated eskimos
- decrease in myopia in WWII in Japan
- adult onset myopia in college
EXCESSIVE AXIAL LENGTH AND MYOPIA IS LINKED TO READING, SCHOOLING, STUDYING, AND NEAR WORK
Intelligence factor
- myopes have higher scores on tests of intelligence
- compared tests for same age group
- hyperopes read worse and perceptual anomalies are more frequent
Socioeconomic factor
- two large studies
- myopes more frequent in HIGH socioeconomic levels
- connection to intelligence and education
First month of life refractive error distribution of refractive error
from -10D of myopia to +5D of hyperopia
- Mean refracted error: -0.7D
- shift toward emmetropia with age
- decrease in ATR in first few years
- higher degree of of myopia in premature babies
Change in refraction in school aged years
- see most refractive changes
- linear change between 7 and 12 years old
- children who are myopic at age 5 will become MORE myopic
- children entering school with 0-+0.5D of hyperopia will become myopic
- children entering school with +0.5-+1,24D will be emmetropic at age 13
- children entering with +1.50D of hyperopia or more will still be hyperopic
Changes in hyperopes Vs myopes in school aged kids
- greatest changes in refractive error occur in myopes
- rate of progression is FASTER when a child crosses FROM hyperopia TO myopia`
Four types of myopia
- congenital:birth
- Youth-onset:school aged
- Early adult onset (late teens- 40s)
- Late adult onset (40 and up)
Youth-onset
- most common myopia
- 5-6 years prevalence: 2%
- 15-16 year prevalence: 20-25%
- onset for females is 2 years earlier than males
Ocular optical component in progression of myopia in school aged kids
- AXIAL ELONGATION continues into late teens
- increased vitreous chamber is more prevalent than increased anterior chamber depth
Ocular optical component in progression of hyperopia in school aged kids
- decrease in refractive power
- decrease in corneal lens and crystalline lens
- axial length stops at early teens
- experience changes, but they are all proportional
Myopic in comparison to emmetropes
- greater vitreous depth
- greater corneal power
- greater posterior crystalline lens radius
Females vs males
- shorter eyes
- steeper cornea
- more powerful crystalline lens
Factors that affect the rate of childhood myopia
- earlier the onset of myopia occurs, the greater the progression and faster
- more reading
- better readers
- more time inside
- higher IOP
- temporal crescents inside the eye
- near work
Why is a shorter reading distance associated with myopia?
-shorter distance=more accomodation=more axial length=more myopia
Childhood myopia and astigmatism
- children with ATR at 5-6 develop myopia more than kids with WTR
- once myopic, ATR do not have a greater progression
Myopic control
- medication
- rigid CL
- biofcals glasses
- progressive glasses
Medication control of myopia
Atropine and pirenzepine
- used in dilation
- knocks off focusing muscles
- affects development of retinal ganglion cells
- complete cyclo
- distortion from dilation
- possible allergies
- once you stop treatment, myopia ACCELERATES
Rigid CL myopic control
- flattens cornea(axial elongation continues)
- increases hyperopia
- Gas permeable CL are effective, but only when CL wearing is continued
Bifocals and progressives
- bifocals have line and progressives have intermediates
- reading add=less strain=less elongation=less myopia
- can also be used for vergence and accomodation problems
- rates of myopic progression are less in bifocals than single vision
- MOST EFFECTIVE FOR CHILDREN WITH ESOPHORIA AT NEAR. SHIFTS IS TO ORTHO/LOW EXO RANGE (changes postrure)
Refractive changes in young adulthood
- refractive errors stabilize
- some may have an onset of myopia(college)
- some have very small shift in hyperopic direction
Mean annual change in refractive error in young adults
- 20-34: -0.05D a year
- 35-53: +0.03D a year
Early Adult onset Myopia
- onset in 20-40 years
- prevalence for myopia increases from 20% at 20 years old to 30% at 40 years old
- progression rate is less in early adult than in youth-onset
Difference in Youth-onset and Early adult onset
- Youth-onset: before puberty
- Early-adult onset: after puberty
3 possibilities of myopia
- adult stabilization
- adult continuation
- adult acceleration
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
Myopia and corneal power
- adults with increases in myopia tend to have increases in corneal power
- still a decrease in crystalline lens power
Myopia progression and college
less than 10% of emmetropes and low hyperopes will develop myopia before age 40 in populations where subjects are not in college
- 20-40% of emmetropes and low hyperopes are likely to become myopic before age 40 when they go to college or are in the military
- unlikely for high hyperopes to be myopic even after college
overall trend in young adults
-emmetropes and low hyperopes shift towards myopia is LESS COMMON AND LESS IN AMOUNT than myopes
age different low hyperopes and early adult onset myopia
-17-18 year old low hyperopes are more likely to become myopic in near work situations than older low hyperopes
Astigmatism in young-adult
-overall shift to being WTR
Refractive changes from age 40 and up
- trend toward hyperopia
- refractive error increases in plus from 40-60 then DECREASES from 60 up
- +1.24D change over 24 years
- mean yearly rate change: +0.5D
Nuclear cataract
- age related nuclear cataracts give a shift to myopia
- some old people will notice they can read better so thats why
Astigmatism and Age 40 and up
-shift towards ATR
Emmetropization considerations
- peak of refractive error distributions occurs at emmetropia and low hyperopia
- coordinated growth of the eye AND some form of vision-dependent feedback system
Changes in ocular optical components
Separately: large changes in refractive error
Together: less changes in refractive error
Vitreous depth
-in childhood: increases which means myopic
Anterior chamber depth
-increases in children=myopia
Crystalline lens
power and thickness decrease for hyperopia
-posterior surface mostly involved in emmetropization
Vision dependent feeback system
- axial length changes based on vision input
- large refractive errors occur when eye does not have normal ocular imagery
- treatment of spectacles aids in emmetropization process and reduces amblyopia
High myopia eye things
- lid hemangiomas
- ptosis
- neonatal eyelid closure
- retinopathy of prematurity
Theories of myopic development
- etiology unknown
- genetic inheritance(+some lifestyle and environmental)
- near work
Primary theory for myopia
- near work theory
- accommodation increases IOP and leads to stretching of the posterior segment of the eye and axial longation
Mechanical forces on the sclera
-tension from extraocular muscles and IOP increase axial elongation
Retinal defocus
- defocus itself alters axial length
- not a mechanism of accommodation
Retinal biochemistry
-some molecules stop myopia and some induce it
theories of astigmatism
- eyelid tension steepens the vertical corneal meridian and causes WTR
- corneal WTR decreases when the eyelid is lifted
- increases when palpebral aperature is narrowed
- shift towards ATR in over 40 because decreased lid tension
