Myopia and OrthoK Flashcards
What causes myopia?
Genetics: family history of myopia
Enviroment: Too much time doing near work (reading, compt) and less time spent outdoors
what are symptoms or myopia
blurry vision when looking far away
squinting
headaches and eyestrain
How do we measure myopia progression
-by the refractive error
-the length of the eye=axial length
-Myopic eyes tend to have a larger axial length
-the longer the eye, the higher the myopia
by 2050 what percent of the worlds population will be myopia?
50%
What is axial length and the length
the distance from the anterior surface of the cornea to the RPE
-16.8mm in infancy to about 23.6mm in adulthood
what is the normal max axial length elongation per year
0.2mm per year
-if the eye grows more than 0.2mm, there is a high risk of myopia progression
a change of 1.0mm is equal to how much of a diopter change
2-2.5D
how can we measure axial lenght?
-ultrasound or optical biometry
-creates a growth chart with normative axial length data that is used to assess risk
why is the axial length essential for?
-for measuring myopia risk. myopic progression and effectiveness of our myopia control measures
Higher levels of myopia increase the risk of..?
-retinal detachment
-glaucoma
-cataract
-holes in the macula
what is the key method they use in myopia control lenses
eliminate peripheral defocus
What does peripheral defocus do?
-creates a stimulus for the eye to grow longer during adolescence
-eye growth causes axial elongation or increased axial lenght
-leads to worsening myopia and eyehealth risks
why do we want to eliminate peripheral defocus
-aim to focus peripheral light rays in front of the retina (NOT BEHIND)
-creates a “slow down” signal for eye growth which reduces the progression
4 broad categories of myopia control treatments?
- specialized eyeglasses
- specialized contact lenses
- atropine eye drops
- environmental changes
specialized eyeglasses
-executive bifocals or PALS
-peripheral defocus lenses
~hoya miyosmart
~essilor stellest
3 main types of contact lenses used for myopia management
- multifocal CLs
~near power rings of the lens help focus peripheral light rays, slowing down eye growth - MiSight CLs
- Ortho-keratology
atropine eye drops
-the gtts dilate the pupils and temporarily freeze the focusing muscle inside the eye
~freezing the focusing muscles is believed to slow down eye growth
-drops used once a day at bedtime
side effects of low-dose concentration
-light sensitivity
-mild reduction in focusing ability
MiSight
-Dailiy disposable soft lenses (coopervision)
-dual-focus lens w. alternating distance correction and treatment zones
correction zones; pxs rx
treatment zones; +2D myopic defocus
-slow progression up to 59%
how long should you wear MiSight lenses for ?
minimum of 10 hours per day at least 6 days per week to get the max treatment effect
MiSight specifications
-power range from -0.50 to -7.00sphere
-no toric option
-no plano
what is OrthoK lenses
-speciallt designed GP lens worn ONLY during sleep that reshapes the cornea
-non surgical
-reversible
-by reshaping the cornea, ppl can have clear vision during the daytime w/o the need for gls or CLs
2 possible reasons to use orthoK
- correction of refractive error
~myopia
~astigmatism - myopia control
for orthoK lenses what is the ideal range of correction for myopia?
-0.50 to -4.50DS, up to -6 is possible
for orthoK lenses what is the ideal range for correction for astigmatism?
up to 1.5D of astigmatism for a spherical orthok lens, up to 3.50D for toric
ideal ages for orthoK lenses
6-35 years old
good candidate for OrthoK lenses
-low to moderate myopia and low amount of astig
-those that dont want to wear gls or CLs during the daytime especially ppl who are
-too young for refractive sx
-do not qualify for sx
-active in sports
-work in dusty/unhygenic enviroment
poor candidates for OrthoK lenses
-those with anterior segment eyeproblems
~keratoconus
~recurrent eye infections
~severe dry eyes or eye allergies
-those with erratic schedules or sleep patterns
-certain high refractive errors
~high myopes (>-6)
~high astig (>-3.5)
~hyperopes and presbyopes
recommended hours of screen time for 6-12 year old
2 hours daily
popularity of OrthoK
-specialized form of refractive correction that is less known
-limited amounts of providers to fit orthok
-lack of comfort/interest
-lack of accesses to appropriate technology
-cost barriers
-fitting fee, lens cost, solution costs = 500/year
risks of orthok
-infections (microbial keratitis)
-allergies
-injury to the ocular surface
-inflammatory reactions
can you have refractive sx after wearing orthok?
yes, but a px must wait until the cornea returns to its original shape
how does OrthoK correct visoin?
- ortho k are designed to float on top of the eyes tear film
- lenses apply water-based pressure to the epithelium
- the pressure causes the eipthelial cells to move from the centre of the cornea to the periperhy
- this movement of the corneal cells temporarily reshape the cornea and corrects refractive error
how long to get results
-after one night of wearing them, vision may be slightly improved
-optimum vision achieved in about 2 weeks
OrthiK lens care and maintenance
-hydrogen peroxide cleaner recommended
alternative: MPS approved for GP lenses
-years replacement
-same insertion and removal as scleral
2 most common orthok types
- corneal reshaping treatment - paragon
- vision shaping treatment -bausch and lomb
common characteristics of orthoK lenses
larger diameter (10-11mm)
small optic zone
a secondary (reverse)curve that is steeper than the BC radius
orthoK lens structure
BC-flattens the anterior cornea
Reverse curve- reshapes the corneal epithelium layer
Alignment curve- helps center the lens
Peripheral curve- encourages tear exchange and smooth removal of lens
