Week 11 Flashcards
What consequences are there for high myopia
Glaucoma
RD
Myopic maculopathy
Mechanisms to delay myopia onset
Spending time outdoors decreases risk of becoming myopic
Less time on screens
Mechanisms to control myopia progression- what drugs ?
1% atropine - has side effects: blurred near vision, hypersensitivity reactions and rebound on cessation (myopia can come back)
Low concentrations of atropine are less effective but can reduce side effects
What cls are used to control myopia progression
Soft Multifocal (MF) Cls
(Misight)
Concentric design (centre distance) with 4 optical zones.
Slows down distance focus- defocusing controls axial elongation.
2 correction zones (refractive correction)
2 treatment zones (+2.00D: myopic defocus)
Control myopia by ↓ peripheral hyperopic → myopic defocus
Myopic defocus controls axial elongation
How to fit misight lenses
Select lens power based on child’s distance refraction.
Astigmatism less than or equal to 0.75D try sph cls
Astigmatism more than or equal to 1.00D sph cls with over specs to compensate for the astigmatism
DD cls - no solution needed
Daily wear use upto 14 hours a day
What is orthokeratology
Creates a multifocal cornea
Technique used to reduce refractive error temporarily
Lens worn during night while sleeping
Px removes lenses when awake and does not need to wear specs or cls during the day for good vision
Retainers cls must be worn every night to maintain OK effect
What does a successful OK depend on
Lid forces
Duration of lens wear
Type of fitting
Corneal rheology of the px
Fun fact of OK
1990’s - Reverse geometry ; high dk material, corneal topography
Corneal topography is mandatory
Describe the reverse geometry lens
There’s 3 zones:
1. Base curve (Treatment zone) (centre)- flatter than centre of cornea. Chosen based on myopia of px (for vision)
2. Secondary reverse curve - more curved than average corneal periphery. Provides stability
3. Alignment with mid peripheral cornea- parallel to the peripheral cornea. Provides stability
Fun fact of OK
Corneal epithelium shape changes during treatment
What is the range of myopia does it go upto for OK ? How many days for results to be seen ?
Corrects med-low myopia upto -6D and astigmatism upto -1.75D WTR with no age restriction
Smaller zone required for higher rxs
Around 3-5 days for myopia below -3D
Around 7-10 days for myopia upto -6D
Advantages of OK
Good unaided vision for most of the day
Non surgical
Reversible
No pain
Treats both eyes
CL fitting techniques have minimal risk problems
No corneal haze
Disadvantages of OK
Only treat low - medium degrees of myopia
Several visits required over first few months
Retainer CLs necessary to prevent corneal regression
Precise reduction can’t be guaranteed
Careful compliance necessary for best results
Indications of OK
Young, early myopes
Myopia upto -4.5D
Low degrees of astigmatism <1.50D WTR
Sport
Vocational use
Occasional specs wear
High corneal e values over 0.50
Contraindications of OK
Myopia >-4.5D
WTR astigmatism >1.25D
Where astigmatism extends beyond central cornea
ATR astigmatism
Significant residual astigmatism
Large pupils
Loose lids
Keratoconus or irregular corneas
Unrealistic expectations
