Incisional Techniques Flashcards
Radial incisions - where flattening
in both the meridian of the incision and the one 90° away
Tangential (arcuate or linear) - where flattening
in the meridian of the incision and steepening in the meridian 90° (may be equal to or less than the magnitude of the decrease in the primary meridian)
coupling
flattening in the meridian of the incision and steepening in the meridian 90° away
How deep should be the incision
85%–90% deep
In older effect is lower or grater
greater
Collagen Shrinkage - what temperature
58°–76°C
Thermokeratoplasty and conductive keratoplasty - where
in the midperiphery to cause local collagen contraction with concurrent central corneal steepening
Photoablation - laser energy sufficient to break
4 eV per photon or greater
Argon-fluoride (ArF) lasers - wavelength
193 nm with 6.4 eV per photon
Argon-fluoride (ArF) lasers - advantages
high energy per photon, very low tissue penetrance, capable of great precision
femtosecond laser - usage
creating flaps for LASIK and for the SMILE procedure, channels for intrastromal ring segments and for lamellar keratoplasty and PKP
femtosecond laser - wavelength
1053-nm infrared beam
femtosecond laser - phenomenon
photodisruption, a process by which tissue is transformed into plasma, and the subsequent high pressure and temperature generated lead to rapid tissue expansion and formation of microscopic cavities within the corneal stroma
Ho:YAG laser - wavelength
2.13 μm
Ho:YAG laser - phenomenon
Photothermal effects with a wavelength of 2.13 μm into the anterior stroma
Photothermal effects - for whom
low hyperopia
How to reduce glare, halos, and regression with Photoablation
optical zone should be 6 mm or larger
Ablation - which layers
Bowman layer and the anterior stroma
LASIK - which layers
stromal bed
Flaps thickness
80 - 180 μm
Broad-beam lasers
larger-diameter 7 mm, slower repetition, high energy, require a small number of pulses to ablate
Scanning-slit lasers
narrow-slit, improving the smoothness, allowing for larger-diameter ablation zones
Flying spot lasers
smaller-diameter beams (approximately 0.5–2.0 mm), higher repetition rate, majority of today’s lasers
Most common aberrations follwing myopic corrections
spherical aberration and coma
Wavefront-optimized laser ablation
taking the curvature of the cornea into account and increasing the number of peripheral pulses
wavefront-guided
slower, expense of the aberrometer, treat both lower-order and higher-order, pupil-tracking system, treatment of highly aberrated eyes, such as eyes with previous RK or PKP
greater tendency toward haze formation
deeper ablations, increased surface irregularity, and prolonged absence of the epithelium
What drugs are contraindicated
Isotretinoin, amiodarone, sumatriptan for PRK and LASIK. hormone replacement therapy or antihistamines for PRK
Tangential keratotomy and AK - where is incision
at the 7-mm optical zone
Tangential keratotomy - use
was used in the past in combination with RK to correct myopic astigmatism
AK and LRI - use
AK - post-keratoplasty astigmatism. AK and LRI - astigmatism during or after cataract surgery and IOL implantation, as well as after refractive surgery procedures such as LASIK and PRK
When there is a coupling ratio greater than 1.0 - what occurs
hyperopic shift occurs
Long, straight, and tangential incisions tend to induce a coupling ratio
greater than 1.0
When a correction is less than 2.00 D of astigmatism, the coupling ratio is
typically 1.0
when a correction is greater than 2.00 D of astigmatism, the coupling ratio tends to be
greater than 1.0
AR or LRI change spherical equivalent?
no
LRI - how deep incisions ?
600 μm depth, or 50 μm less than the thinnest pachymetry measurement at the limbus
What can happen when moving from an upright to a supine position
15° of cyclotorsion can occur
Where to make AK after KP?
in the graft or in the graft–host junction. . When AK incisions are made in the host, the effect is significantly reduced
Irregular astigmatism is more common after AK or LRI?
more common with AKs
