Download 12-Month Study Results of Eyes that Underwent Standard and

12-Month Study Results of Eyes that Underwent Standard and Wavefront-Guided High Myopic PRK
David R. Edmison, MD
Medical Director, Focus Eye Centre, Ottawa, Canada
Background
Higher levels of myopia require special consideration before proceeding with photorefractive
keratectomy (PRK). Careful attention to pachymetry (corneal thickness), keratometry (surface contours)
and Pentacam topography (anterior and posterior elevations) are necessary to ensure the corneas are
thick enough, steep enough and there is no evidence of keratoconus. Levels of myopia higher than -7.00
D require the use of Mitomycin C (MMC) prophylactically during the laser vision correction procedure to
help minimize the risk of corneal haze formation and regression.
The following are key clinical pearls for successful PRK:







Provide good pain management
Prophylactically use fourth-generation fluoroquinolones
Keep the eye cold with balanced salt solution, drops, and ice packs
Use MMC 0.02%
Reassure patients that visual acuity will improve for 6 months postoperatively
Use UV protection, vitamin C, and serum tears
Manage ocular surface disorders
Surface ablation complications include epithelial healing; infiltrates and ulcers; haze and regression; and
irregular astigmatism.
Study Objectives and Methods
In this retrospective, nonrandomized, single-center study, PRK was performed with CustomVue (WGA)
or Standard (STD) protocols. Patient demographics can be seen below.
WGA PRK eyes were treated with Iris Registration, and the epithelium was removed with Amoils brush.
The epithelial defect in these eyes was 8 to 9 mm. In STD PRK eyes, the laser was used to perform a
transepithelial removal, and the epithelial defect in these eyes was 6 to 7 mm. The laser room was
controlled for temperature and humidity, and MMC 0.02% was applied for 20 seconds.
To mechanically remove the epithelium with a brush, in the case of a WGA procedure, both the cornea
and brush are moistened. Amoils brushes are available in 6.5-mm and 9-mm sizes. The brush is a fast,
effective and safe way to remove the epithelium. Alternatively, the epithelium can be removed with a
laser.
Preoperatively, the WGA PRK eyes underwent a wavescan cluster (median of three wavescans) and a
nomogram adjustment. The STD PRK eyes underwent a best manifest refraction and a nomogram
adjustment. Acular LS 0.4% was used four times daily for the 48 hours before surgery. Artificial tears
were used frequently preoperatively if there were signs of dryness, and Zymar 0.3% was used four times
daily prophylactically.
Postoperatively, a bandage contact lens was used until complete re-epithelialization (approximately 2 to
3 days for STD PRK eyes and 3 to 4 days for WGA PRK eyes). Patients used Zymar 0.3% four times a day
for 7 days, as well as lubricants four times a day. Acular LS 0.4% was used four times a day for the first
24 hours postop. Artificial tears were used frequently, and a few drops of Tetracaine or diluted
anesthetic were used for irritation. Fluorometholone (FML) 0.1% four times daily was started after
complete re-epithelialization and was tapered over 2 months. Vitamin C 500 mg twice daily was also
given to all patients.
After the defect was completely healed, the bandage contact lens was removed. To remove the lens,
first, use lubricants to hydrate the lens. If the patient is a squeezer, use topical anesthetic. Slide the lens
to the side and off of the corneal. If the lens is fixed, lubricate. Re-check the eye at the slit-lamp to
ensure that there is no defect. If a defect occurs, the eye can be patched for a few hours.
If the patient experiences severe pain and the bandage contact lens is still in place and the eye is quiet,
the lens is often dry and tight. In these cases, increase lubrication and use a drop of Tetracaine 0.5%. If
there is mild iritis, dilate the pupil. If these methods do not work, remove the bandage contact lens and
replace with a looser lens or pressure patch.
Results
Below are the average spherical equivalent over time, average sphere over time, and average cylinder
over time.
At 1-month postoperatively, there were 214 eyes evaluated: 166 in the WGA PRK group and 48 in the
STD PRK group. At the 3-month evaluation, there were 154 eyes in the WGA PRK group and 46 eyes in
the STD PRK group.
At 6-months postoperatively, there were 124 eyes in the WGA PRK group and 40 eyes in the STD PRK
group. At 1-year postoperatively, there were 98 eyes in the WGA PRK group and 38 eyes in the STD PRK
group.
Below are uncorrected visual acuity results at all time points.
At 6-months postoperatively, 74% of eyes in the WGA PRK group and 68% of eyes in the STD PRK group
had no haze, and 24% of eyes in the WGA PRK group and 30% of eyes in the STD PRK group had 0.5+
haze. Two percent of eyes in both PRK groups had 1+ haze, and no eyes in either PRK group had more
significant amounts of haze.
Enhancements are considered 6 months postoperatively if the refraction is stable. Those who
underwent WGA PRK had a 21.0% enhancement rate, and those who underwent STD PRK had an 11.9%
enhancement rate. In contrast, the enhancement rate for low myopia is approximately 3%.
In summary, in the WGA PRK group, mean spherical equivalent is -0.24 D at 1 year with 81% ±0.5 D and
94% ±1.00 D. In the STD PRK group, mean spherical equivalent is plano at 1 year with 74% ±0.5 D and
95% ±1.00 D. Haze is relatively equal in both groups.