Refractive

Question 1

In LASIK, how does the myopic correction change the post-operative K’s? Hyperopic?

Answer 1

1. 0.8 X every Diopter corrected (e.g. 2 diopter corrected make the post-op K’s 1.6 flatter2. 1 X every diopter corrected for hyperopia

Question 2

In general, what is the accepted post-op K’s in LASIK?

Answer 2

34-50 (to flat can risk free cap, to steep can risk K buttons)

Question 3

Multifocal lens Restore and Tecnis are both what type of lens? (refracting or diffracting)?

Answer 3

Diffracting

Question 4

The natural cornea is prolate or oblate?

Answer 4

prolate (steeper at center and flatter at periphery)

Question 5

For monovision, which eye is usually set for near? What is the target refraction often?

Answer 5

The non-dominant is set for near and the target is often -1.5 to -1.75. “mini monovision” is -0.75

Question 6

The RSB (residual stromal bed) should not be less than what number?

Answer 6

250 microns

Question 7

What are the two refractive errors that are common in patients having undergone RK?

Answer 7

1. diurnal fluctuation2. Hyperopic shift (ave about 1.0 D)

Question 8

LRI’s tend to induce no change in spherical equivalence and a net coupling of 1.0. However, straight keratotomies tend to induce what?

Answer 8

a hyperopic shift (they have a positive coupling factor)

Question 9

Keratophakia

Answer 9

A high plus powered lens is placed intrastromally to correct high hyperopia or aphakia. Now obsolete.

Question 10

Epikeratoplasty

Answer 10

homoplastic (living transplant) placed onto bowmans layer of the host. No reshaping of the cornea. Basically a contact lens placed into the cornea. Obsolete.

Question 11

Spherical aberration is what type of higher order abberation?

Answer 11

4th order

Question 12

Which type of higher order abberation is more visually significant?

Answer 12

spherical abberation

Question 13

What is the difference between tracking and registration in laser treatment?

Answer 13

tracking follows the pupil, registration the iris

Question 14

For the same amount of correction, does a hyperope or a myope take longer to have stable vision following refractive surgery?

Answer 14

hyperopes

Question 15

What is the most common cause of interstial keratitis following LASIK?

Answer 15

Staph A and other gram positives

Question 16

INTACS is ideal for what type of patient

Answer 16

low myopic keratoconus patient

Question 17

What is a distinguishing exam finding that can often distinguish interstitial keratits from DLK in a post refractive patient?

Answer 17

DLK is usually contained under the flap and IK can spreak past the flap border.

Question 18

When does Pressure-induced stromal keratoapthy usually manifest post-LASIK?

Answer 18

About 10-14 days

Question 19

What is the treatment for pressure induced stromal keratopathy?

Answer 19

Rapid taper off corticosteroid

Question 20

What is the optimal temperature to induce collagen shrinkage in cornea when performing conductive keratoplasty?

Answer 20

65 degrees celcius +/- 10 degrees

Question 21

Conductive keratoplasty can be used for what type of refractive error?

Answer 21

low hyperopes

Question 22

How is corneal cross linking performed?

Answer 22

1. Epithelium is denuded2. Riboflavin administered X 30 minutues3. UVA light administered X 30 minutes with continued riboflavin instillation

Question 23

What does bioptics mean in refractive surgery?

Answer 23

combining refractive surgery and intraocular surgery sequentially

Question 24

ND:YAG uses photodisruption like what other laser used in refractive surgery?

Answer 24

femtosecond

Question 25

When calculating power for two piggy backs, how much power should be added to the combined power so as to compensate for posterior shift of the more posterior IOL?

Answer 25

+1.50 to +2.50

Question 26

Does Restore or Tecnis multifocals have harder time with reading in dark?

Answer 26

Restore because the diffraction component is only 3.6mm

Question 27

In regards to higher order abberrations, what is rms value is considered normal?

Answer 27

Less than 0.3 um

Question 28

What is the normal q value for asphericity of the human cornea?

Answer 28

-0.26, negative value means it is a prolate cornea, i.e. Steeper centrally

Question 29

A myopic patient that had overcorrection from PRK/LASIK can be helped to induce myopia by doing what?

Answer 29

Going off steroids