Ortho-K (night lenses) Flashcards
1
Q
Describe the corneal changes that happen with ortho-k lenses?
A
- Epithelial Change:
o Not really using NaFl with these lenses – as wearing lens with eye closed not open
o Open eye is a crude assessment – did they get it in w/o a bubble?
o Topography will you the fine fit of the eye
o Suction forces – tear vortex forces
o ~20 micron change with epithelium
Limited to a thickness – if lower Rx then thickness changes over a larger area
Higher Rx – smaller tx zone px will get
o All changes are epithelial – not changing anything about stroma (structural layer of eye)
o See them on day 1 and then see them 2 wks later – most of change happens over weekend – takes while for epithelium to remember
If take lens away will just resolve back to how it was
Easier to manage pxs at 2 wks as often they can fix their own problems
2
Q
What are the correction ranges of ortho-k lenses?
A
- Optimum:
o -5.00 SE
o Vision good
o No OR specs - Published:
o -6.00 Sph
o -1.50 Cyl
o TZ on Visual Axis
o Vision acceptable
o P/time OR Specs - Custom:
o Unlimited Sph
o Unlimited Cyl
o TZ on Visual Axis
o Vision Acceptable
o F/P/time OR specs
BVS of -5.00 max
Higher Rx or higher astigmatism – will have residual
Non-standard range – expect glasses for night time driving possibly
3
Q
What are the correction limits of ortho-k lenses?
A
- Standard Rx Range:
o Myopia up to -5.00 can anticipate full correction
o Astigmatism up to -1.25 residual cyl is usually tolerated well - Non-standard Range:
o >-5.00DS or >-1.25 may provide binocular 20/happy VA, OR specs should be anticipated when full VA is appreciated (night driving)
3
Q
Describe safety and ortho-k lenses?
A
- Corneas don’t change in long-term wearers and through adult-life
- Corneas don’t change – if good baseline map then wont change – only time it changes is if px has keratoconus
- Changing epithelial cells & not stroma
o Changing epithelial cells doesn’t cause much damage
4
Q
What is the CL risk of sleeping in lenses?
A
- Stated as no. of incidences of microbial keratitis
- In 10,000 px years
- 5.3/10,000 years – 5.3 infections would occur if 10,000 pxs wore lenses for 1 yr
- Same as daily wear soft lenses
Sleeping in lenses is continuous wear – tell px the stats & they decide on the risk – if see 10,000 pxs then 5 will get infection
4
Q
What assessments and discussions would need to take place to determine a good candidate for ortho-k lenses?
A
- Ocular exam:
o No ectasia, recurrent erosions (20yrs ago may be fine, but if thin/weak epithelium avoid), infection or inflammation, smooth conjunctival - Topography:
o Exclude any ectasia
o Anticipate decentred TZ
o HVID - Behaviour:
o Sleeps more than 5hours per night (to keep topped up)
o Sleep masks not suitable – putting pressure on lids can affect lens
o Will comply with lens handling & care – can get them in at night & can manage with them in, then can take them out during day
5
Q
Describe topography and ortho-k?
A
- mm = D on the map
- Tangential – tangent will track each point on cornea picks up tear blobs, dry patches
- Axial – goes through visual axis
- Screen px with tangential – to make sure normal
- Axial scale then gets normalised
o Cropping scale so it fits that particular cornea - Cannot normalise tangential
- Higher Rx need to measure decentration as if sitting off then px may get glare, poorer quality of vision
6
Q
Who is suitable for orth0-k lenses?
A
- General CL suitability
- Px able to follow good practice
- No active infection or anterior eye inflammation
- No disease, injury, abnormality of cornea, conjunctiva or lid
- No severe dry eye/corneal hyposensitivity
- No known adverse reaction to CL or care solution
7
Q
What are the tips for insertion and removal of ortho-k lenses?
A
- Wash hands
- Get px to tranfer lenses into lens case
- Before applying 1st lens instill topical anaesthetic
o Allow px to learn undistracted
They are not then affected by comfort & can focus on how to get lenses in
o Good 1st impression
o 4x less drop out
Roll lid up & push against orbit bone – key to getting lens in
8
Q
What should you do at ortho-k aftercare?
A
- Px remove lenses when waking
- Discuss wear & vision
- Visions, Rx & Acuities
- Slit lamp
- Topography
- Schedule follow up
9
Q
What should be doen at follow up of ortho-k lenses?
A
- Clinical support supply
o SE (BVS) refraction
o Full Rx
o Corneal stain image or details
o Topography (pdf/export) - Give Videos to px to watch – on scotlens.com
o Teach one technique – tell px not to deviate from this technique – if they do not follow & practice technique then they will never learn it properly
10
Q
How does treatment zone affect axial length? Myopia management and ortho-k?
A
Myopia Management:
Options: time spent outdoors, specs, day lenses, night lenses
Peripheral defocus – theory (see Myopia Management CLs)
* Small TZ slows AL
* Small TZ can reduce VA
* Small TZ can induce High Order Aberrations
* Adult correction TZ size now increasing >6.00mm
Spherical aberration reduces axial length
Worse you make the px’s vision with aberrations – the slower the AL seems to grow
11
Q
What affects spherical aberrations (SA) (ortho-k)?
A
- Optic zone diameter
o Reduces the TZ size
o Reduce to 5.00mm
o May impact on VA - Treatment Zone Decentration TZD
o Bullseye up to 0.5mm from visual axis
o >0.52mm higher SA, better MC - Power Distribution in TZ
o Rx high Rx greater increase in SA
o Jessen Factor will affect Rx correction
Optical aberrations correlate well with corneal aberrations – can get this info from topographer
If increase in spherical aberration is 0.8 then in slower growth of axial length category
Can make treatment zone (TZ) size smaller – it also matters where the TZ is e.g. decentred increases spherical aberrations
12
Q
What are the main things to remember for ortho-k lenses?
A
- Optimum correction for any CL wearer <-5.00
- ‘Freedom’ ‘naturally good vision’
- No contact lens dryness
- Myopia control
- 68% px prefer night lenses to SCL
