Incidence and distribution of refractive anomolies Flashcards
refractive error at birth
-skews towards hyperopia
What is the percentage of newborsn with myopia?
0-25%
why do infants shift towards emmetropia as they grow?
- due to eye growth
- skew towards myopia
- mostly within 1st year of life
emmetropization
the process in which refractive error shifts towards emmetropia
When does ocular development slow?
Ages 5-15
How much does the anterior chamber depth increase by?
0.10 to 0.20mm, slows by Aggies 5-15
How much does the vitreous chamber depth increase by?
- 1mm
- about 3D change for every 1mm
- slows by ages 5-15
How much does the axial length increase by?
- 1mm
- about 3D change
- slows by ages 5 to 15
What happens to the cornea throughout growth
Pretty much stable
What does the lens power do throughout growth?
- decreases by 2D
- lens thins but still grows new fibers
- slows by ages 5 to 15
What does hyperopia do with ocular growth?
- decrease about 1D
- slows by ages 5-15
When does emmetropization occur?
Age 5-15
Prevalence of myopia increases by how much during emmetropization
Increases by over 7 times to 15%
Juvenile-onset myopia increase
- About -0.50D per year during early teens
- from reduced ability of lens to compensate for the growth in axial length
When does myopia progression stop?
Around 14.6-15.3 years for females
Around 15-16.7 for males
-from eye not growing beyond age 13-14
Adult onset myopia
10% of population is myopic after teen years
-total myopic prevalence in adult population is about 25%
Both hyperopia and axial length increase…
Slow down at 5
Stops at 13-14
Factors that affect refractive error distribution
- age
- gender
- ethnicity
- geography
- diet
- time
- personality
- systemic conditions
- ocular diseases
What is the single most important determinant of distribution of refractive error in a given group?
Age
infants with myopia at birth
Very small portion
- neonatal myopia associated with prematurity
- astigmatism 1.00D cyl
When is low to moderate myopia first observed and progresses?
- age 6-8
- astigmatism decreases, ATR shift (from decrease in WTR corneal toricity> ATR lenticular toricity
Juvenile-onset myopia progression and cessation
- progression is 0.40D
- Cessation at age 14-15 females and 15-16 males
- lens can’t compensate for growing eye
About when does refractive error become stable?
High school
Adult onset of myopia and progression of pre-existing myopia
- prevalence is 25%
- decrease in prevalence of myopia in older age
Gender
-inconclusive
Ethnicity
- not enough data
- prevalence of myopia in Caucasian group twice as much as African American group
- across all groups: myopia develops primarily from excessive axial length
- different ocular component profiles for groups with low prevalence of myopia vs groups with high prevalence of myopia
Geography
- study results are confounded by other factors (diet, education)
- similar trends found in US ethnicity studies
Diet
- unclear
- ethical dilemma to alter nutritional needs of children
- Eskimos showed no difference in eating a regional diet vs 1 American meal per day
Time
- inconclusive
- overall trend: decrease in prevalence of myopia with increasing age in elderly range
Personality
-no strong data
What is myopia associated with (personality-wise)
- introversion
- inhibited disposition
- disinclination for motor activity and social leadership
What is hyperopia associated with (personality-wise)
- carefree
- impulsive
- hyperactive
- socially passive
Systemic conditions
- homocystinuria
- diabetes
Homocystinuria and refractive error distributions
- metabolism issue with the excretion of homocysteine in the urine and excesses of homocysteine and methionine in the blood
- fair hair and skin
- mental retardation
- Lens dislocation
- myopia
- light iridies
- hypotony (not enough eye pressure)
- retinal elevation
- cataract
Diabetes and refractive error distributions
-higher prevalence of myopia
-
Ocular diseases and refractive error distributions
- majority are associated with myopia
- clear visual input needed for normal emmetropization to occur and some diseases obscure clear vision
- congenital cataracts
- posterior polar and nuclear cataracts
- congenital ptosis ( astir increases after surgical correction)
- retrolental fibroplasia
- corneal opacification
- vitreous hemorrhage
- hemangioma (astir and myopia)
- Phylctenular keratitis (alters corneal curvature)
Ocular diseases associated with hyperopia
- involves fovea like development
- albinism (OCULAR!, systemic is myopic)
- maculopathies
- rod monochromacy (color defect)
Hereditary conditions associated with myopia
- achromatopsia
- nystagmus
- microcornea
- keratoconus
- Fabry’s disease (corneal and lenticular accumulation of glycosphingolipid)
- microphakia
- ectopia lentis
- coloboma
- choroideremia
- Gyrate atrophy
- fundus flavimaculatus
- retinitis pigmentosa
- progressive bifocal chorioretinal atrophy
- extensive myelination of the nerve fibers
- Wagner’s disease (membranous vitreous, arteriolar sheathing, choroidal sclerosis, cataract)
- vitreoretinopathy
- familial external ophthalmoplegia
Hereditary conditions associated with hyperopia
- Achromatopsia
- Nystagmus
- microphthalmia
Glaucoma and refractive error
-connected with myopia
Near-work theory of myopia
- prolonged reading (accommodation) increases IOP, driving the expansion of the eye by mechanical force
- related to glaucoma
Associated conditions with glaucoma and myopia
- genetics link- high prevalence of positive steroid response among myopia and glaucoma patients
- risk of OHTN appears to be higher in myopia than in emmetropes
- risk of open angle glaucoma and conversions of OHTN to glaucoma is higher in myopes than in emmetropes
ATR astigmatism and refractive error distribution
- pellucid marginal degeneration
- thins the inferior cornea and flattens the vertical corneal meridians
Based on consistent study results, these factors have a known affect on refractive error distributions
- age
- systemic conditions
- ocular diseases
These factors are found to be inconclusive on having a known refractive error association
- gender
- ethnicity
- geography
- diet
- time
- personality
Heredity and refractive error
- modes of inheritance: vary by study
- higher hertibilites in axial length and corneal power
Studies of twins show high heritability in:
- axial length
- corneal power
- refractive error
Near Work Theory
- Excessive reading during childhood causes abnormal eye growth , leading to myopia
- increase in myopia prevalence in first school-educated Eskimos
- decrease in myopia prevalence during WWII in Japan
- adult onset myopia in college populations
- excessive axial elongation and myopia is linked to schooling, studying, reading, and other near work
Intelligence
- myopes trend to have higher scores on tests of intelligence and cognitive ability and get better grades than other refractive error groups (even after factoring age trends)
- hyperopes tend to show poorer reading skills and other perceptual anomalies more frequently
Socioeconomic status
- myopes tend to be over represented among the higher socioeconomic strata and underrepresented among the lower income levels
- possibly due to connection between myopia, intelligence and education
What percentage of adults are myopic?
25%
Factors associated with refractive error
- hereditary
- near work
- intelligence
- socioeconomic
