Photoablation

Question 1

excimer laser - wavelengths and photochemically

Answer 1

193-nm argon-fluoride (ArF)

Question 2

excimer laser - in which methods

Answer 2

PRK, LASEK, epi-LASIK

Question 3

LASIK - short definition

Answer 3

In LASIK, the excimer laser ablation is performed under a lamellar flap that is created with either a mechanical microkeratome or a femtosecond laser

Question 4

What does excimer on molecular level

Answer 4

A single 193-nm photon has sufficient energy to directly break carbon–carbon and carbon–nitrogen bonds that form the peptide backbone of the corneal collagen molecules. Excimer laser radiation ruptures the collagen polymer into small fragments

Question 5

PRK - good for

Answer 5

irregular or thin corneas; epithelial basement membrane dystrophy, previous corneal surgery, such as PKP and RK; and treatment of some LASIK flap complications, such as incomplete or buttonholed flaps

Question 6

Surface Ablation vs LASIK

Answer 6

eliminates the potential for stromal flap–related complications and may have a decreased incidence of postoperative dry eye as compared to LASIK. Corneal haze, the major risk of PRK, decreased markedly with the use of adjunctive mitomycin C; subsequently, the use of PRK for higher levels of myopia has increased

Question 7

When Wavefront-guided is inappropriate

Answer 7

after cataract surgery, particularly with multifocal intraocular lenses

Question 8

Topography-guided systems

Answer 8

use corneal topography data to create ablation profiles that treat existing corneal shape irregularities and optimize corneal curvature. In the treatment of corneas with irregular surfaces, such as those with small or decentered optical zones from prior excimer ablations, LASIK flap complications, or post-RK corneal irregularities

Question 9

Is keloid contraindication for surface ablation or LASIK?

Answer 9

No

Question 10

Postoperative dry eye due to corneal denervation is more common with

Answer 10

LASIK than with surface ablation

Question 11

Corneas steeper than 48.00 D are more likely to

Answer 11

have thin flaps or frank buttonholes (central perforation of the flap) with procedures using mechanical microkeratomes

Question 12

Corneas flatter than 40.00 D are more likely to

Answer 12

have smaller-diameter flaps and are at increased risk for creation of a free cap due to transection of the hinge with mechanical microkeratomes. These problems may be reduced by using a smaller or larger suction ring

Question 13

estimate the postoperative keratometry

Answer 13

flattening of 0.80 D for every diopter of myopia treated and a steepening of 1.00 D for every diopter of hyperopia treated

Question 14

which layers are exposed in 1) surface ablation and 2) LASIK

Answer 14

Bowman layer for surface ablation and the midstroma for LASIK

Question 15

Manifest or cycloplegic refraction is more accurate determining cylinder axis and amount?

Answer 15

manifest refraction

Question 16

What is blend zone?

Answer 16

The blend zone is an area of peripheral asphericity designed to reduce the possible undesirable effects of an abrupt transition from the optical zone to the untreated cornea. A prolate blend zone reduces the risk of glare and halo after excimer laser photoablation

Question 17

Epithelial debridement techniques for surface ablation. The epithelium can be removed with

Answer 17

sharp blade, blunt spatula, rotary corneal brush, application of 20% absolute alcohol to the corneal surface for 10–45 seconds, mechanical microkeratome with an epi-LASIK blade, transepithelial ablation from the excimer laser

Question 18

LASEK

Answer 18

goal is to preserve the patient’s epithelium. loosens the epithelium with 20% alcohol for 20 seconds and folds back an intact sheet of epithelium

Question 19

Epi-LASIK

Answer 19

epithelial flap is fashioned with a microkeratome fitted with a blunt epikeratome and a thin applanation plate that mechanically separates the epithelium

Question 20

Suction ring dimention

Answer 20

The thicker the vertical dimension of the suction ring and the smaller the diameter of the ring opening, the less the cornea will protrude, and hence a smaller-diameter flap will be produced.

Question 21

Advantages of femtosecond

Answer 21

more customizable flap, size and thickness of flap less dependent on corneal contour, centration easier to control, epithelial defects on flap are rare, less risk of free cap and buttonhole, more reliable flap thickness, hemorrhage from limbal vessels less likely, ability to re-treat immediately if incomplete femtosecond laser ablation

Question 22

Disadvantages of femtosecond

Answer 22

longer suction time, more flap manipulation, opaque bubble layer interfere with excimer ablation, bubbles in the AC may interfere with tracking and registration, increased overall treatment time, difficulty lifting flap after 6 months, increased risk of transient light sensitivity, increased cost, delayed photosensitivity or good acuity plus photosensitivity, which may require prolonged topical corticosteroid therapy

Question 23

How quick heals the epithelium after surface ablation?

Answer 23

4-7 days

Question 24

Why corticosteroids after surface ablation?

Answer 24

modulate postoperative wound healing, reduce anterior stromal haze, and decrease regression of the refractive effect remains controversial. Patients who received mitomycin C at the time of surgery have a reduced risk of haze formation and thus may have a shorter duration of corticosteroid use.

Question 25

Ablation area for hyperopic

Answer 25

large ablation area is required for hyperopic treatments. Most studies have employed hyperopic treatment zones with transition zones out to 9.0–9.5 mm.

Question 26

The period from surgery to postoperative stabilization is longer in myopic or hyperopic

Answer 26

hyperopic

Question 27

advantage of LASIK over surface ablation

Answer 27

refractive stability generally occurs earlier, allowing earlier enhancements, typically within the first 3 months after LASIK

Question 28

How long to wait before an enhancement surface ablation is undertaken

Answer 28

the ongoing activation of keratocytes and the risk of haze after enhancement usually require a wait of 3–6 months before an enhancement surface ablation is undertaken

Question 29

More often re-treatment surface ablation for which refractive error

Answer 29

higher for hyperopia and for high astigmatism than for other indications

Question 30

Higher re-treatment rates in surface ablation

Answer 30

Rates of re-treatment are higher for higher initial correction, residual astigmatism, and patients older than 40 years

Question 31

Surface ablation after LASIK

Answer 31

Surface ablation performed on a LASIK flap carries an increased risk of haze formation and irregular astigmatism, but it is an appealing alternative when the RSB is insufficient for further ablation; when the LASIK was performed by another surgeon and the flap thickness, or RSB, is not known; or with conditions such as a buttonhole or incomplete flap.