Long-Term Excimer Laser Enhancements: Myopic PRK Following Myopic LASIK Jonathan M. Davidorf, M.D.Davidorf Eye GroupLos Angeles, CA

ASCRS Annual SymposiumSan Diego, CAMarch, 2011

Financial Interest Disclosure

The author has no financial interest in any of the devices or techniques used in this study

Purpose

•To study the predictability and safety of myopic PRK in eyes previously treated with myopic LASIK.

Background

Three main options for performing laser vision enhancements following myopic lasik

1. Flap re-lift2. flap re-cut3. PRK

Options for LASIK Enhancements

Benefits Concerns

Flap Re-Cut Quick recovery; accurate

Flap complications; difficult with intralase

Flap Re-Lift Quick recovery; accurate

Flap depth/dimensions (particularly if initial treatment performed elsewhere); epithelial ingrowth (reports that incidence higher if initial treatment 3+ years prior1)

PRK Size/depth of initial flap irrelevant

predictability; haze; recovery

Concerns About Epithelial Ingrowth

The reported incidence of epithelial ingrowth ranges significantly in the literature1-5. Some authors have reported that there is a lower incidence of epithelial ingrowth in femtosecond laser created flaps compared to microkeratome created flaps3. At a minimum, patients with epithelial ingrowth need to be followed more closely (to identify progression) than non-epithelial ingrowth patients. The extra visits alone can become an inconvenience and source of concern for patients (even in the cases in which the epithelial ingrowth does not require intervention). If the epithelial ingrowth becomes significant (progression, visually significant, foreign body sensation), it must be treated, constituting additional, from the patient’s perspective, unanticipated inconvenience: office visits, procedures, risks.

Concerns About Epithelial Ingrowth

On the other hand, PRK is almost always inconvenient. Whether discussing the visual recovery or postoperative pain, there is little debate that uncomplicated LASIK (initial treatment or enhancement) provides, from the patient’s perspective, an easier postoperative process than uncomplicated PRK. However, the recovery with PRK is fairly predictable and easy to counsel. The surgeon and patient must decide between one procedure that carries with it the known downside of a slow recovery (PRK) and another that carries with it the somewhat difficult to predict complication of epithelial ingrowth.

The incidence of epithelial ingrowth has been shown to rise when the initial LASIK procedure had been performed three or more years prior.2,5 After reading recent such reports, we began using the three year mark as a guideline for recommending PRK to patients requesting enhancement of their initial LASIK procedure.

Concerns about PRK following LASIK

Apart from the visual recovery and postoperative pain, anticipated concerns of predictability arise when contemplating PRK following LASIK. For example, can epithelial hyperplasia impact the refractive outcome when the thickened area of epithelium is removed? In the case of prior myopic lasik, a hyperplastic central epithelial disk, if removed, could induce a hyperopic shift on its own, without any laser treatment being applied.

Additionally, the risk of corneal haze always exists with PRK and has been reported to be an increased problem with post-LASIK eyes.6 However, intraoperative application of Mitomycin C may offset that risk somewhat.

Methods

•Ongoing prospective study

Inclusion criteria: • eyes with a history of myopic LASIK

performed more than three years prior• Eyes with myopia, with or without

astigmatism

Methods

•PRK with EtOH epithelial debridement •B&L Technolas Excimer Laser (PlanoScan

software)•Post-laser 12 second application of 0.02%

mitomycin C

Demographics

•16 eyes of 15 patients•Mean follow-up 4.6 months (1 to 12

months)•Mean preoperative manifest refraction

spherical equivalent: -1.37 + 0.69 D (-0.63 to -2.88 D)

•Mean preoperative refractive cylinder:-0.78 + 0.55 D (-0.50 to -1.75 D)

ResultsMRSE Cylinder

Pre-op -1.37 + 0.69 D(-0.63 to -2.88 D)

-0.78 + 0.55 D(-0.50 to -1.75 D)

1 M 0.27 + 0.33 D(-0.13 to +0.75 D)

-0.47 + 0.36 D(0 to -1.25 D)

3 M -0.17 + 0.25 D(-0.50 to +0.13 D)

-0.39 + 0.32 D(0 to -0.75 D)

Uncorrected Visual Acuity at 1 Month

20/20+ 20/25+ 20/40+ < 20/2000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0%

8%

46%

8%

69%

92% 92%

Pre-op1M Postop

Best Spectacle Corrected Vision•All eyes 20/20 or better pre- and

postoperatively•No eyes lost or gained lines of BSCVA.

Haze

•No eyes developed visually significant corneal haze

Predictability

-3.50 -3.00 -2.50 -2.00 -1.50 -1.00 -0.50 0.00

-3.50

-3.00

-2.50

-2.00

-1.50

-1.00

-0.50

0.00

f(x) = 0.8139377162323 x − 0.185212403561225R² = 0.702517056800121

M-PRK over M-LASIK Entered vs. Achieved MRSE

Achieved MRSE (D)

En

tere

d M

RS

E (

D)

Predictability

•100% within 0.75D of target•69% within 0.50D of target

Discussion

While firm conclusions cannot be drawn from this small series of treated eyes, the data suggests that PRK for low myopia and astigmatism is a predictable and safe means for treating eyes with a remote history of myopic LASIK. The refractive outcomes parallel the published data on myopic LASIK enhancements performed with flap re-lifting.1,4 Concerns of poor predictability owing to variable epithelial thicknesses, and safety concerns, including the possibility of corneal haze or disruption of the prior LASIK flap did not manifest as problems in this current series of eyes.

DiscussionOnly one patient in this series had a bilateral treatment. Since this cohort comprised primarily patients with relatively low levels of refractive error, desiring treatment in only one eye, the patients would be expected to function reasonably well with the untreated eye while waiting for the treated eye to achieve good functional vision. With only one eye being treated, the recovery inconveniences of PRK are lessened compared to a bilateral simultaneous or bilateral sequential treatment. It is noteworthy that all of the treated eyes attained a good visual outcome by the one month visit.

Conclusions

In light of the published data on the incidence of epithelial ingrowth, combined with our encouraging preliminary data, we are continuing to recommend PRK for prior LASIK patients considering enhancement if their initial last LASIK procedure was performed over three years previously. Ultimately, longer term follow-up on a larger series of eyes is needed before firm guidelines and conclusions can be drawn.

References1. Brahma A, McGhee CNJ, Craig JP, Brown AD, Weed KH, McGhee J, Brown R. Safety

and predictability of laser in situ keratomileusis enhancement by flap reelevation in high myopia. Journal of Cataract & Refractive Surgery . April 2001 (Vol. 27, Issue 4, Pages 593-603)

2. Caster A, Friess DW, Schwendeman FJ. Incidence of epithelial ingrowth in primary and retreatment laser in situ keratomileusis. Journal of Cataract & Refractive Surgery. January 2010 (Vol. 36, Issue 1, Pages 97-101)

3. Hyunseok Ahn H, Jin-Kook Kim, Chang Kook Kim, Gyu Heon Han, Kyoung Yul Seo, Eung Kweon Kim, Tae-im Kim. Comparison of laser in situ keratomileusis flaps created by 3 femtosecond lasers and a microkeratome. Journal of Cataract & Refractive Surgery. February 2011 (Vol. 37, Issue 2, Pages 349-357)

4. Rubinfeld RS , Hardten DR, Donnenfeld EO, SteinRM, Koch DD, Speaker MG, Frucht-Pery, Kameen JA, Negvesky GJ. To lift or recut: Changing trends in LASIK enhancement . Journal of Cataract & Refractive Surgery . December 2003 (Vol. 29, Issue 12, Pages 2306-2317)

5. Waring , GO.; Durrie, DS.; Stahl, JE.; Schwendeman, FJ. Natural History of Epithelial Ingrowth After Lift Flap Enhancement Procedures for LASIK: Prospective Single-Center Evaluation. Abstract number 413055 presented at the American Society of Cataract and Refractive Surgery Annual Symposium, 2008.

6. Liu A, Manche EE. Visually significant haze after retreatment with photorefractive keratectomy with mitomycin-C following laser in situ keratomileusis . Journal of Cataract & Refractive Surgery . September 2010 (Vol. 36, Issue 9, Pages 1599-1601)