Refractive surgery

Question 1

Radial keratometry

Answer 1

diamond blade make radial cuts deep into the cornea to flatten it. Visual probs common… Glare, starbursts at night, permanently weakened cornea

Question 2

Astigmatic Keratotomy (AK)

Answer 2

To correct high post-keratoplasty astigmatism and small degrees of pre-existing astigmatism at time of cataract surgery… placing arcuate peripheral incisions perpendicular to the steep axis of astigmatism

Question 3

Non-contact homium: YAG laser

Answer 3

Used to place radial “shrinkage” spots outside visual axis to steepen cornea (decreasing hyperopia).

Question 4

Conductive Keratoplasty (CK)

Answer 4

Uses a thin probe to deliver radio frequency current into stroma with less collateral damage/ regression. Effective, predictable, stable, safe, cheap, easy way to correct lower levels of hyperopia and manage presbyopia

Question 5

Laser photoablation

Answer 5

Excimer laser for correcting refractive error via PRK, Lasek, epi-lasik, and lasik. Argon-fluoride gas to emit UV pulses.

Question 6

Photorefractive Keratectomy (PRK)

Answer 6

FIrst commercially available form of laser vision correction; still commonly performed. Corneal epithelium removed mechanically. Excimer laser then photoablates anterior stroma to flatten or steepen cornea. Decreases curvature of cornea which reduces refractive error. (refractive errors from +3 to -6) Good for EBMD, or epithelial defect, because they will ablate away down to anterior stroma. Subepithelial haze caused by wound response… mitigated by mitomycin C.

Question 7

LASIK

Answer 7

Flap is created using microkeratome or femtosecond laser
Photoablation occurs deeper in the stroma.l (minimizes wound response/ haze)
Practically no discomfort!
Almost instant visual recovery
>6D of myopia and significant astigmatism are prone to haze
Complications:
Flap probs
diffuse lamellar keratitis (DLK)
epithelial ingrowth
Possibility of corneal ectasia

Question 8

Lasik and corneal thickness

Answer 8

REsidual corneal bed of 250 microns
Excimer laser removes about 12 micons of tissue for each D of correction.
SUM OF FLAP THICKNESS (100) + MIN STROMAL BED THICKNESS (250) + DESIRED TISSUE REMOVAL (12*D of correction) must be less than pt’s CCT

Question 9

LASEK

Answer 9

Alcohol used to loosen epithelium
Epithelial flap folded aside for photoablation and then rolled back into place. Similar to PRK with advantage of less discomfort and quicker visual recovery.

Question 10

Epi-LASIK

Answer 10

Epithelial flap created mechanically (using epi-microkeratome) No alcohol used so epithelial cells more viable and less toxicity to stroma

Question 11

Summary:
PRK
LASEK
EPI-LASIK
LASIK

Answer 11

PRK= epithelium removed entirely
LASEK= epithelial flap created with alcohol then elevated and repostioned. 
Epi-Lasik= epithelial flap created by epi-microkeratome and repositioned
Lasik= deeper flap (into anterior stroma) of epithelium/Bowman's layer/stroma created by microkeratome or laser and repositioned

Question 12

What surgery should be done for pt with <6D of myopia?

Answer 12

PRK

Question 13

WHat surgery is best for pt with 6-10D of myopia?

Answer 13

LASIK (less risk of haze) (more comfortable and convenient in short term but more compliations)

Question 14

Phakic Intraocular Lenses (pIOL)

Answer 14

Artificial lenses inserted into the eye can correct a greater range of refractive error than laser can.
Advantages: high refractive error
Reversible
High optical quality
preserves accommodation
Disadvantages: min of 3.2 mm AC depth (excludes high hyperopes)

Question 15

Refractive lens exchange

Answer 15

Essentially cataract surgery done for refractive benefit… not because of opacified lens
Non-presbyopic pts lose part or all of their accommodation..
High myopes at risk for RD

Question 16

Phakic IOL or RLE?

Answer 16

Phakic= safest, definitely preferred for non presbyopes
RLE= ONLY option for HIGH hyperopes
RLE= if expected to have cataract surgery soon

Question 17

List the summary of surgical options based on how much refractive error…
Thermal procedure
Photorefractive procedures
Intraoperative procedures

Answer 17

Thermal: Conductive Keratoplasty: low hyperopia
Photorefractive: surface ablations: +3 to -6
surface ablations with MMC: +5 to -8
LASIK: +5 to -10
Intraop: pIOL’s: 20+ hyperopia/myopia and astig up to 7.5
RLE: +20 hyperopia and 30 myopia