refractive surgery Flashcards
prevalence of myopia in UK
15-20%
complications from radial keratotomy
- glare from incisions
- reduced contrast sensitivity
- diurnal variation
- hyperopic drift
- weakened globe
what is radial keratotomy?
cuts in the cornea to flatten the cornea
the amount of cuts depends on the amount of myopia present
what does this image show??
radial keratotomy
when was laser refractive surgery first suggested?
1980s
what was the first use of laser in ophthalmology?
photo-coagulation for DR - 1960s
what does this image show?
smooth calcific band keratopathy - LASER CAN GET RI OF SUPERFICIAL SCARS LIKE THIS !!
what does -OTOMY mean??
taking tissue away
what does PRK stand for?
photo refractive keratectomy
limitations of PRK
- INDIVIDUAL WOULD HEALING VARIATION
- small diameter ablation zones
- single pass treatments = aberration
- poor beam homogeneity
- edge-profile sub-optimal
what is a small ablation zone?
central 4mm which could be treated (initially - now we can treat the whole cornea)
leaves a haze in the centre
what happens if you cannot treat the whole cornea?
positive spherical aberration (HALOS)
major complications of PRK
- regression
- anterior stromal haze
- aberrations (halos)
- night vision problems
- loss of BCVA
- loss of contrast sensitivity
regression in PRK
start at -10
get PRK
be +4.00 ish
regress back to myopia (roughly -4.00)
why was LASIK introduceD?
to stop anterior haze (would be inside the cornea)
what does LASIK stand for?
Laser
ASisted
In-situ
Keratomileusis
advanatges of LASIK
- virtually no haze or scarring
- rapid recovery
- more accurate/predictable
- extended range (-10 to +5)
- virtually painless
- both eyes treated at same time
- re-treatment is relatively easy
how does LASIK work?
- slicer which produces a very thin flap (1/5th the thickness of the cornea)
- flap is lifted
- UV light from the laser (works at 193nm) - PX CANNOT SEE THE BEAM
- px fixates on a flashing red light
what is waveScan?
scans the wavefront
tells you if they have any aberrations (sph, cyl, coma etc)
when wavescan is scanning, how does it work?
uses a flying spot laser (laser scanning spot)
different sizes
what is the aim of WaveScan?
tries to create the perfect cornea shape to get minimum point spread function
why is iris registration/recognition v important?
need to line up the cornea properly otherwise you could make their aberrations worse
what form of refractive surgery is the gold standard
LASIK
when is lasik an NHS treatment?
- myopia after cataract surgery
- treating corneal graft astigmatism
- severe disability (motoneurone disease, parkinsons, stroke patientts, friedreichs ataxia) - UNABLE TO WEAR GLASSES
what are the 5 main refractive groups
- simple myopia
- astigmatic myopia
- hyperopia
- astigmatic hyperopia
- mixed astigmatism
why do you need to analyse YOUR laser results (not just generic from the manual)
need to determine if the laser is under or over correcting your patients
if the laser is under or over correcting your patients, what do you do?
need to adjust the laser output
e.g. if laser is producing results at 85% of full correction, you need to boost the laser by 15% to get full correctin
in a high prescription, do you use LASIK or LASEK?
LASEK
what are the factors that need to be assessed of refractive surgical techniques
SAFETY
efficacy
stability
cost
predictability
pre-operative complications of LASIK
patient selection/suitability
patient counselling
realistic expectations
refractive aims (e.g. monovision)
operative complications of LASIK
poor preparations
sterility issues
equipment related
technique related
flap complications THERE ARE SOOOOOOOO MANY but not sure we need to know this 100%
- partial flap (obstruction/suction break)
- buttonholes + thin flaps (steep corneas)
- macerated flap
- free flap (cap - flat corneas, low IOP)
- no flap (loss of suction)
- epithelial defects
how does careful preparation and technique avoid flap complication in LASIK?
drapes, good exposure, vacuum
good centration, copious irrigation
chayet sponge
mask hinge (e.g buratto guard)
how does repositioning the flap avoid flap complication in LASIK?
vidaurri cannula
adequate irrigation
align para-radial marks
dry edge of flap gently (and wait)
why does a macerated flap occur?
due to a faulty blade
post-op complications of lasik
- flap macro and micro striae
- debris
- displaced flaps
- corneal surface problems
- DRY EYE
- DLK - diffuse lamellar keratits
- infective keratitis
- epithelial ingrowth
why do striae occur in LASIK?
meibomian secretions get under the flap
what is the most common post-op complication of LASIK?
dry eye disease (30% of px’s)
what problems does epithelial ingrowth cause?
optical problems
melting - keratolysis
FB sensation
why does dry eye disease occur post LASIK?
damaged corneal nerves cutting back on the positive feedback to the lacrimal gland
how do you manage dry eye disease with laser?
pre-op screening/exclusion
preservative free tear film supplements
punctum plugs
sodium hyaluronate
cyclosporin A
autologous serum
what are the residual refractive error and quality of vision complications of LASIK
under or over correction
induced cylinder
irregular astigmatism
halo/glare/ghosting/scatter
why would you do LASIK retreatment?
fine tuning
what is DLK? diffuse lamellar keratitis
white granular cells in peripheral infiltrate (under the flap)
what is corneal ectasia?
we have made the cornea too thin (THINK OF IT LIKE INDUCED KERATOCONUS)
who is more likely to get corneal ectasia?
high myopes (ofc) and ppl with thin corneas
how do you prevent post-LASIK ectasia?
ensure normal topography
flap thickness, pachymetry
limit ablation to 80 micron
maximum -8.00 D
which laser is used to make a corneal flap?
femtosecond photodisruption
how does femtosecond photodisruption work?
a pulse of laser energy is focused to a precise location inside the conrea. (1 micron)
a microplasma is created vaporizing 1 micron of cornea tissue
vaporization creates an expanding bubble of gas & water seperating the corneal lamellae
which kinds of px’s ar emore likelyto have unrealistic expectations?
IT people
architects/surveyors
licence applicants
night drivers
bare questions
low myopic presbyopes
30 y/o accompanied by mum
px who talk you round to the statistics they would like to hear
“but it will be okay for me - wont it??”
