Myopia Flashcards
by 2050, how much of the world population is expected to have myopia
50% = 1 billion humans
what is the leading cause of visual loss worldwide
myopia
what is emmetropization
newborns are hyperopic, but their RE decreases during adolescents
In the first 3 years of life, which are the most dramatic growth of ocular components
cornea, AC depth, crystalline lens and axial length
how is emmetropia formed
the coordinated growth of ocular components
what is the most common cause of developed ametropia
increased vitreous depth - longer axial length
what is the greatest risk factor for myopia
two myopic parents
what are the possible risk factors to myopia
- diet
- near work
- intelligence
- stress
- lack of outdoor activities
what are the studies done upon near work and myopia that is not significant
- near work
- reading
- religious boys at school
- screens ( iphone est 2007, myopia rose before the time)
what is a possible theory associated with near work and myopia
increased screen time with less outdoor time
what is most common form of myopia
axial length myopia
if children spend more time outdoors then
Children w/ 2 myopic parents and spend more time outdoors = chances of developing myopia is lower (about 20%, compared to 60% to those who spend LESS time outdoors)
why does each diopter of myopia matter
- less visual disability when uncorrected
- better option and outcomes thru surgical myopia correction
- higher risk of blindness is assoc. w/ higher levels of myopia
higher myopes are at a greater risk of
- cataract
- glaucoma
- retinal detachment
the greatest myopia related cause of irreversible vision loss is
myopic macular degeneration
myopia progression is the following
- 6 to 7 yr olds progress 2x faster than 11-12yr old - refractively and axial length
- girls progress 10% faster than boys
- children w/ 2 myopic parents have onset 35% faster than 0 myopic parents
- children in Asia progress 50% faster than USA
can the environment influence the axial length of the eye
yes! hyperopic retinal defocus stimulates elongation
- the rays from distant object are focused posterior to R and then brain signals to elongate to eye to focus light on retina
what kind of defocus does myopic lenses create and how does it affect axial length
hyperopic retinal defocus - increased AL growth
what kind of defocus does hyperopic lenses create and how does it affect axial length
myopic retinal defocus - decreased AL
what is the significance of peripheral retina
visual signals from peripheral retina can impact emmetropization at fovea, possibly developed refractive error
how does the hoya DIMS lens work
forms myopic defocus peripherally to decreased axial growth
what is orhto K
- retainers for the eyeball
- continued wear overnight so pt doesnt have to wear lenses during daytime
- temp reduces myopia
what is the mechanism associated with ortho K
flat rigid lens > flattens central region of cornea > steepens peripheral cornea > leads to less power > increases radius
what happens with ortho K myopically
slows myopic progression
what is the main goal of refractive surgery
obtain myopic defocus
what is assoc w lasik
- laser forms epithelial flap
- remove epithelium and stroma
- reposition epithelial flap
- slows myopic progression
what occurs in multifocal CLs
adding plus power to the near region of lens will cause rays to pass through that zone to focus anteriorly of the retina
- thus myopic defocus
what are the 3 myopia controls and the significance
atropine, soft bifocal, ortho - K
all slow myopia progression to a degree, but doesn’t eliminate
what are the possible mechanisms assoc with time outside and reduced myopia
- less accommodation in outdoor environment
- pupil constriction in bright environments (pinhole effect of our eyes)
- sunlight exposure releases retinal transmitter (dopamine) > inhibits eye growth
what is radial keratometry
- series of cuts in 4, 8 or 10
- scar tissue unevenly heals > cataract > pulls on cornea > flattened cornea > decrease of myopia
- uneven healing > irregular and oblique astig
what is PRK
- laser used to reshape cornea
- corneal epithelium removed to reach stroma
what is lasik procedure
- same as PRK but the epithelium is moved aside so laser can reshape stromal bed
what the advantage oD LASIK
immediately better BVA
what are the complications to refractive surgery
- reduced BCVA (best corrected)
- red. contrast sensitivity
- red. corneal sensitivity
- reading glasses may be req
- increased dry eye
- reduced night vision
- halos around light during immediate months
- thinner cornea
what is the reduced corneal sensitivity from refractive surgery caused by
corneal nerve damage, will not all regenerate
does the axial length of the eye get changed during lasik
no, thus risk of retinal tears/ holes are still present
- the only take away is a thinner/flatter cornea > leads to higher risk of corneal perforation
