Flashcards in Epidemiology Deck (33)
what is refractive error determined by
1. optical components of the eye
2. axial length
-determined primarily by the post chamber
what is too long in the eye that causes myopia
what is with the rule
K: more power in the vertical meridian
Rx: axis 180 + or - 30 (if minus cyl)
for against the rule
K: more power in the horizontal meridian
R: axis 90 + or - 30 (if minus cyl)
what is oblique (least comon)
K: meridians > 30 away from 90 or 180
Rx: axis 30-60 or 120-150
what is anisometropia
different refractive error btwn the two eyes
what is presbyopia, what changes?
-onset at what age
changes in the crystalline lens occur w/ again => lose ability to accomodate
-onset around 40 years
what is primary refractive error
-etiology is multifactoria (visual input, genes, environment)
-more refractive errors are primary
-we focus on today
what is secondary refractive error
-we can identify a specific cause
-often deviate from what is predicted by epidemiology and natural history
-disease, pharmacological, mechanical process that changes axial length or refracting power of cornea or lens
what is epidemiology
the study of the patterns, cuases, and effects of health and disease conditoins in defined populations
-natural history, changes or progression of conditoin over time
uncorrected refractive error is a leading cause of what?
-how many indiv affected worldwide
-how many children
-accounts for how many % visual impairments
correctable visual impairment worldwide
- 98-200 million indiv affected worldwide
- ~13 million children 5-15 y/o are affected worldwide
-accounts for 5.3% of visual impariments in the US
myopia has high increasing prevalence
-in the US
-pop of East Asia
-differences in prevalence with what?
> 25% in US
> 80% some populations of East Asia
-w/ race, gender, age, geographic location, rural/cities
what are the risk factors for vision-threatening conditions
myopic degeneration is what cause of vision impairment?
glaucoma, retinal detachment, maculopathy, retinoapthy
-2nd cause of vision impairment in HK
hyperopia affects how many % of children at 1 year old?
infants w/ high hyperopia are up to how many times more likely to develop strabismus by 4 years of age?
-how many times more likely to have reduced visual acuity
-what is the leading cause of amblyopia
anisometropic hyperopia (~2/3 of children w/ strabismus or amblyopia have > 1.00D of anisometropia)
what is needed for emmetropization
ability of the eye to adjust its growth during development to acheive emmetropia
-optical componenets balance axial length
visually guided, active process that uses visual feedback to regulate eye growth (genetic and environmental factors)
what is the mean refraction for normal full term infants
when is astigmatism greatest
during first 6 mos and decreases thereafter
>1.00 of astig is common in infants and toddlers
axis is quite variable
mild anisometropia of what is common in infants?
likely to presisnt into childhood if anisometropia is what?
in premature infants, what are they more liekely to have
retinopathy of prematurity and myopia (high), astig and anisometropia
-emme tends to be disrupted if low birth birth weight
what is the mean for toddlers and preschoolers (3-5 yrs)
mean is slightly hyperopic
when does astig decrease most significantly
during the first 2 years and stabilizes by 3-4 years
-shifts in axis are common
at age 5-6:
around 80% have how much of astig?
transition to waht?
0.25D of astig
-transition to mostly emmetropic (+-.75)
-80% btwn 0.50 and 3.00
at age 6-20
-what do some develop
-what stablizes or decreases
-if < 0.75 hyperopic at 6 eras, what happens
-if > 1.0 hyperopic at 6 years, what happens
remian hyperopic for life
-astig stable in hyperopes
-may revert to infantile astig in myopes; asit stabilizes when myopia stabilizes
what does myopia typically progress by each year in childhood myopia
-the earlier the onset.....
-0.50D per year
-progession more rapid during school months
the higher amount of myopic reached
when is refractive error usually stable
what are the two forms that young adult (18-20 years) onsent myopia progression can take
1. further progression of juvenile onset myopia
2. new incidence of low myopia
around 25-60 years rx is stable w/ the following exceptions...
age ~25 years: hyperopia stable, but more becomes 'absolute' or 'manifest' due to decreasing ability to acommodate
-pseudomyopia will decrease
age 40+ years
-absolute presbyopia by ~65 years
at ~ 60 years of age you may have stable refractive error or ...
changes in refractive error that are secondary to nuclear sclerosis of the crystallin lens
-seondary refractive errors: myopic shift-second sight bc pt can see at near more easily (senile myopia)
-increase in ATR astig in some indiv