Refractive

Question 1

A corrective lens has the power -5.00 +1.00 x 45. If it is worn 5 cm closer to the eye, what must the prescription become in order to have the same effect?

  A. -5.00 +0.66 x 45
  B. -5.00 -0.66 x 45
  C. -4.00 +0.66 x 45
  D. -4.00 -0.66 x 45

Answer 1

The prescription can be expressed by its two principal meridians: -4.00 x 45 and -5.00 x 135.

The first meridian has a far point of 1/4 = 25 cm; the second meridian has a far point of 1/5 = 20 cm.

Adding 5 cm to each of these far points requires that the principal meridian powers become:

1/30 cm = -3.33 x 45 and

1/25 cm = -4.00 x 135

Recombining the two meridians:

-4.00 +0.66 x 45.

Question 2

Post LASIK K measurement (contact lens method)

Answer 2

Base curve of RGP (in D) + RGP Power + over refraction - SE of MRX without RGP (See OQ #47; 2/10/13 (3) #47; or 3/3/10 (20) #30)

Question 3

Post-LASIK K measurement (historical method)

Answer 3

Post-op K = Pre-op K + pre-op SE of MRX - post-op SE of MRX

Question 4

Post-LASIK K measurement (topography method)

Answer 4

K power from topo reduced by a specified amount

Question 5

Munnerlyn’s formula

Answer 5

ablation depth (in microns) = [(ablation zone in mm)^2 * diopter of myopia to be corrected]/3

Question 6

Medications associated with poor healing after LASIK/PRK

a) Epithelial
b) Stromal

Answer 6

a) HRT, antihistamines, sumatriptan

b) Accutane

Question 7

DLK Staging and Treatment

Answer 7

I: Faint peripheral infiltrates –> topical steroids
II: Central faint infiltrates –> topical steroids
III: Dense central infiltrates –> lift flap, irrigate
IV: Dense central infiltrates c flap melting –> lift flap, irrigate

Question 8

What is the ideal IOL to implant in the following situations:

1) s/p myopic LASIK
2) s/p hyperopic LASIK
3) s/p low hyperopic LASIK

Answer 8

1) Aspheric IOL with negative spherical aberration (Alcon SN60wf or AMO ZCB00) –> most sensitive to decentration
2) Aspheric IOL with positive spherical aberration (Alcon SA60AT or Alcon MA60AC)
3) Consider aspheric neutral lens (B&L LI6180) –> least sensitive to decentration

Question 9

Meds associated with poor stromal healing and epithelial healing

Answer 9

Stromal: amiodarone, accutane

Epithelial: antihistamine, sumatriptan, HRT