Download Safety and efficacy of Photorefractive Keratectomy (PRK) for myopia

ARTICLE
Safety and efficacy of Photorefractive
Keratectomy (PRK) for myopia using a new
corneal epithelium debridement technique
Rafael Bilbao-Calabuig, MD1; Felix Gonzalez-Lopez, MD1;
Miguel A. Calvo-Arrabal,MD1; Jose R Villada-Casaponsa, MD2; Jaime Beltrán, MD3
PURPOSE: To evaluate the clinical outcomes of photoreactive keratectomy (PRK) for myopia,
using a new combined, ethanol-assisted and blunt mechanical corneal epithelial peeling technique.
METHODS: In this prospective cases series, PRK was performed in myopic patients. A circular
cellulose cell sponge soaked with 20% ethanol solution was positioned over the central cornea
for 50 seconds. The adhesions between the epithelium and corneal stroma were loosened using a
Weck-Cel spear, and finally, central loosened corneal epithelium was easily lifted off in a circular
epitheliorhexis-like technique. Corneal photoablation was then performed using the usual
nomograms and protocols for myopic surface photoablation treatments. Manifest refraction,
uncorrected distance visual acuity (UDVA), and corrected distance visual acuity (CDVA) were
evaluated preoperatively and postoperatively, and adverse effects were also assessed.
RESULTS: The study enrolled 248 eyes of 144 consecutive patients. Mean and standard deviation
of preoperative manifest refraction spherical equivalent (MRSE) was −3.73 ± 1.49 D, and mean
preoperative cylinder −0.65 ± 0.71 D. After 6 months, mean decimal UDVA was 0.97 ± 0.08
and MRSE was −0.04 ± 0.33 D; postoperatively 96% of eyes had an MRSE within ±0.50 D
of emmetropia. Efficacy Index was 0.99 and Safety Index 1.02. Postoperative mean time for reepithelialization and contact lens removal was 5.1 ± 0.4 days, and no patient required more than
14 days of contact lens wear. No eye lost two or more lines of CDVA, or presented any significant
clinical complication. Only one eye required an enhancement procedure.
CONCLUSIONS: This new corneal epithelium debridement technique has been shown to be
safe and effective when correcting myopia with PRK.
J Emmetropia 2015; 3: 133-137
Photorefractive keratectomy (PRK) is less invasive than laser
in situ keratomileusis (LASIK), and seems to structurally
Submitted: 07/06/2015
Revised: 08/24/2015
Accepted: 08/27/2015
Clínica Baviera, Instituto Oftalmológico Europeo, Madrid, Spain
Clínica Baviera, Instituto Oftalmológico Europeo, Albacete, Spain
3
Clínica Baviera, Instituto Oftalmológico Europeo, Valencia, Spain
1
2
Financial disclosure: The authors have no commercial or proprietary
interest in the products mentioned herein.
Acknowledgements: Presented as an oral communication at the 32nd
Congress of the European Society of Cataract and Refractive Surgery
(ESCRS), London, September 2014. The authors thank Dr. Manuel
Romera (www.ilustracionmedica.es) for his collaboration in producing the
illustrations of the surgical procedure.
Corresponding Author: Rafael Bilbao-Calabuig
Clínica Baviera, Paseo Castellana, 20, Madrid 28046, Spain
E-mail: [email protected]
© 2015 SECOIR
Sociedad Española de Cirugía Ocular Implanto-Refractiva
weaken the cornea to a lesser degree. As a result, a trend
has emerged over the last decade favouring surface ablation
techniques1,2. Several modifications of the conventional
PRK procedure have been introduced in order to minimize
the disadvantages of the surface ablation techniques, namely
longer epithelial healing and visual recovery times, pain, and
corneal haze. These alternative methods modify the means
by which the corneal epithelium is removed prior to laser
photoablation. Mechanical debridement (using different
types of rotating brushes or scalpels), alcohol solution in
laser-assisted subepithelial keratomileusis (LASEK), excimer
laser in transepithelial PRK (t-PRK) and an epithelial
microkeratome in epi-LASIK, have been extensively used
to separate the corneal epithelium from the underlying
anterior stroma. We recently reported a technique to peel
off corneal epithelium prior to photoablation in surface
ablation laser surgery that combines both a chemical and
a blunt mechanical action while using very simple surgical
instruments3.
ISSN: 2171-4703
133
134
PRK FOR MYOPIA WITH A NEW CORNEAL EPITHELIUM DEBRIDEMENT TECHNIQUE
The aim of the present study was to assess the clinical
and refractive outcomes of PRK for myopia, using the
aforementioned corneal epithelial debridement technique.
MATERIALS AND METHODS
This prospective interventional case series comprised
144 consecutive patients (248 eyes) who had PRK
for myopia, treated for targeted emmetropia. It was
performed at the Clinica Baviera (Madrid, Spain) in
compliance with the tenets of Declaration of Helsinki,
and had full ethical approval from the Clinica Baviera
Institutional Ethics Committee. All patients provided
written informed consent after receiving a full
explanation of the procedure.
All patients were assessed preoperatively and
operated by one single experienced refractive surgeon
(RBC), between April 2011 and March 2013.
Inclusion criteria were aged over 18 years, and
stable myopic error less than 8.00 D of MRSE. The
exclusion criteria were: history of eye disease and ocular
abnormalities that would normally exclude the patient
from being a candidate for myopic PRK, previous ocular
surgeries, aged over 50 years, less than 470 microns in
central corneal pachymetry and preoperative CDVA
less than 0.6.
Before surgery, all patients had a complete ophthalmic
examination, which included: manifest and cycloplegic
refractions, keratometry, corneal topography (Orbscan
II, Bausch&Lomb, Rochester, NY, USA), ultrasound
corneal pachymetry, slitlamp microscopy, applanation
tonometry and binocular indirect ophthalmoscopy
through a dilated pupil.
The surgical technique has been extensively described
by the authors elsewhere (Figure 1)3.
Photoablation was performed using the Technolas
217 Z100 (Bausch&Lomb, Rochester, NY, USA)
excimer laser platform using our standard nomogram.
Following laser ablation, 0.02% mitomycin C (MMC)
was applied on the ablated stroma. The duration of
MMC application was 12 seconds when the depth
of central ablation was less than 65 microns, and 20
seconds if more than 65 microns. Eyes were then
thoroughly irrigated with 50 ml of chilled balanced salt
solution and a silicon hydrogel contact lens (Acuvue
Oasys, Johnson&Johnson Vision Care, Inc) was placed
over the cornea until complete re-epithelialization. Our
usual postoperative topical and oral analgesic regime
was applied in all patients3.
RESULTS
Of the 144 patients, 80 were women and 64 men. The
mean age (± standard deviation [SD]) was 32.73 ± 7.09
years (range 18 to 49). Pre-operatively, the mean
manifest refraction spherical equivalent (MRSE) was
−3.73 ± 1.49 D (range −1 to −7.12 D), mean refractive
cylinder –0.65 ± 0.71D (range 0 to −4 D) and mean
decimal best spectacle corrected distance visual acuity
(CDVA) 0.98 ± 0.06. Postoperatively, after a minimum
of 6 months follow-up (mean 185 ± 17 days), the mean
decimal uncorrected distance visual acuity (UDVA) was
0.97 ± 0.08 and MRSE was −0.04 ± 0.33 (range +0.85
to −0.82) (Table 1); 6 months postoperatively, 96% of
eyes had an MRSE within ± 0.50 D, and 99% were
within ± 1.00 D of emmetropia (Figure 2).The Efficacy
Index (mean postoperative UDVA/mean preoperative
CDVA) was 0.99 (Figure 3). Only one eye out of 248
(0.4%) required an enhancement procedure at the end
of follow-up. Postoperative mean time for complete
re-epithelialization and contact lens removal was
5.1 ± 0.4 days, and no patient required more than 14
days of contact lens wear. Eight eyes had transient grade
1 corneal haze. No eye lost 2 or more lines of CDVA,
or presented any significant clinical complication;
the Safety Index (mean postoperative CDVA/ mean
preoperative CDVA) was 1.02 (Figure 4).
No patient presented any intraoperative or early
postoperative complications, or required any other
technique to complete epithelial debridement. The
mean time for complete re-epithelialization and
contact lens removal was 4.3 ± 0.4 days, and no patient
required more than 14 days of contact lens wear. With
respect to the refractive results, we did not notice
any significant difference compared to our previous
epithelial debridement techniques, and no modification
in our previous laser nomograms was needed. No eye
presented corneal haze higher than grade 1 after 6
months of postoperative follow-up.
DISCUSSION
Pain, slow vision recovery, myopic regression and
haze have been extensively described as the adverse
effects related with conventional PRK. As mentioned
previously, several modifications of the initial PRK
technique have been introduced in order to minimize
these drawbacks. These include laser transepithelial
debridement, de-epithelialization with diluted alcohol,
epithelial mechanical scraping with scalpels or rotating
brushes, and later, the epi-LASIK technique4,5,6,7,8.
All these techniques have been found to be safe and
effective for treating a wide range of myopias and
myopic astigmatisms9. However, comparing the clinical
outcomes among them has been difficult due to the
variability in the surgical conditions and protocols10.
Controversy remains as regards the advantages and
disadvantages of each method, particularly regarding
postoperative pain, recovery of visual acuity, subepithelial scar formation, the toxic effect of alcohol, and
synergistic effect with MMC11,12,13.
JOURNAL OF EMMETROPIA - VOL 6, JULY-SEPTEMBER
PRK FOR MYOPIA WITH A NEW CORNEAL EPITHELIUM DEBRIDEMENT TECHNIQUE
135
Figure 1. Corneal epithelium debridement technique. A) An 8 mm circular Weck-Cel sponge soaked in 20% alcohol solution is positioned over
the central corneal surface for 50 seconds. B) If some solution leaks towards the periphery, it is dried with another Weck-Cel spear. C) Epithelial
adhesions are released by applying some pressure with circular movements over the central surface of the cornea. D, E and F) Central loosened corneal
epithelium is easily lifted off with the same Weck-Cel spear in a circular epitheliorhexis manner. G) The edges of the debrided area can be slightly
extended towards the corneal periphery with the Weck-Cel or a blunt spatula before laser photoablation, and the epithelial flap is discarded.
JOURNAL OF EMMETROPIA - VOL 6, APRIL-JUNE
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PRK FOR MYOPIA WITH A NEW CORNEAL EPITHELIUM DEBRIDEMENT TECHNIQUE
Figure 2. Achieved versus attempted MRSE correction.
EfficacyIndex:0.98
0.98
1
0.97
1
0.8
0.6
0.4
UDVA
CDVA
0.12
0.2
0
PREOP
6monthsPOSTOP
Figure 3. Changes in mean uncorrected and corrected visual acuity.
ChangesindecimallinesofCDVA
90%
78.48%
80%
70%
60%
50%
40%
30%
20%
10%
0%
21.02%
0.00%
0.00%
0.01%
Loss3or
more
Loss2
Loss1
No
change
Gain1
Figure 4. Changes in decimal lines of CDVA.
0.04%
0.00%
Gain2
Gain3or
more
Mechanical debridement is straightforward and
effective, but Bowman’s layer can be damaged, and a more
irregular anterior stromal surface and retained islands of
residual epithelium have been described. Moreover, the time
required for mechanical debridement is longer, and patients
generally experience more discomfort.
Alcohol-assisted removal is perhaps easier, faster and
more comfortable for both the patient and the surgeon14,15.
However, some pressure needs to be applied with the cone
over the ocular globe for 20-30 seconds, and the 20% ethanol
solution may sometimes spill towards the periphery of the
cornea, particularly after involuntary ocular movements when
the patient feels the pressure of the cone. The spilled solution
can damage the ocular surface epithelial cells, and often
produces pain and significant irritation of the conjunctiva.
In t-PRK, total epithelial removal using excimer laser is
difficult, and in some cases areas of Bowman´s membrane
can be unintentionally removed. This may lead to underor overcorrections in refractive results16. The Epi-LASIK
technique requires sophisticated surgical material, and
complications such as anterior corneal stromal damage or
optic neuropathy related to the suction process have been
described17.
In the technique described above, we combine the initial
chemical effect of the 20% ethanol solution, which loosens
the corneal epithelium, with a non-traumatic mechanical
effect produced by the circular movement of the cellulose
sponge and the later epithelial peeling. This procedure
combines the advantages of the two initial techniques while
minimizing their adverse effects. The diluted alcohol separates
the epithelium and corneal stroma, creating a smooth, regular
surface; however, in contrast to the conventional alcoholassisted technique, no pressure needs to be applied to the ocular
globe, and no spillage of the solution occurs, thus minimizing
patient discomfort and surgical trauma to the ocular surface.
The mechanical effect in this technique is produced by a blunt
sponge, thus rendering the use of sophisticated or potentially
traumatic surgical instruments unnecessary.
In our experience, contact with the circular cellulose
sponge is required for 50 seconds in order to easily loosen
Table 1: Refractive parameters before and after the procedure
Manifest refraction spherical
equivalent (D)
Manifest cylinder (D)
Manifest myopic refraction (D)
Manifest decimal corrected distance visual acuity (D)
Preoperatively
Postoperatively
−3.73 ± 1.49
(−7.12 to −1.00)
−0.65 ± 0.71
(0.00 to −4.00)
−2.97 ± 1.71
(−6.75 to −0.50)
0.98 ± 0.05
(1.20 to 0.55)
−0.04 ± 0.33
(+0.85 to −0.82)
−0.35 ± 0.22
(0.00 to −1.00)
+0.11 ± 0.32
(+0.75 to −0.75)
1 ± 0.04
(1.20 to 0.82)
Data given as mean ± standard deviation, with range in parentheses
JOURNAL OF EMMETROPIA - VOL 6, JULY-SEPTEMBER
PRK FOR MYOPIA WITH A NEW CORNEAL EPITHELIUM DEBRIDEMENT TECHNIQUE
corneal epithelium. When exposure time is shorter, removal of
the epithelium with the Weck-Cel sponge is often incomplete,
and the use of other rigid surgical instruments may be required
thereafter. No clinical adverse effects have been found with
this alcohol solution exposure time, which is longer than that
described in previous techniques. In addition, patient tolerance
is excellent, as no pressure is applied over the ocular globe. The
technique also allows for complete lifting of the epithelial flap,
which can be repositioned over the corneal stroma after laser
ablation, if the surgeon considers it appropriate.
In the current series, early refractive and anatomic
results are consistent with those in previous studies that
used different epithelial debridement techniques for myopic
PRK, showing excellent efficacy, predictability and safety
outcomes in eyes with low myopia18,19,20,21. Although this
was a case series without a control group, and a randomized
controlled study would have been a better option to
compare this epithelium debridement technique with those
previously described, this was not the purpose of our study.
Since it was first introduced in our clinic in 2011, most
of the surgeons in our group have progressively abandoned
their previous debridement methods, and have changed to
the above-described technique, which has now been very
extensively used in surface ablation photorefractive surgery;
the authors have also used this manoeuvre for epithelial
debridement in other surgical procedures, such as corneal
cross-linking or phototherapeutic keratectomy for anterior
corneal disorders, without any adverse effects or unexpected
corneal reactions.
In conclusion, this corneal epithelium debridement
technique combining a chemical and blunt mechanical
action has proven to be safe and effective when used for
myopic PRK. The minimization of the intraoperative ocular
surface damage and the reduction in patient discomfort has
allowed us to optimize our surgical performance with this
refractive procedure.
7.
8.
9.
10.
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13.
14.
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16.
17.
18.
REFERENCES:
1.
2.
3.
4.
5.
6.
Pop, M, Payette Y. Photorefractive keratectomy versus laser in
situ keratomileusis: a control matched study. Ophthalmology.
2000;107:251-7.
Hersh PS, Brint SF, Maloney RK, Durrie DS Gordon M,
Michelson MA.Photorefractive keratectomy versus laser in situ
keratomileusis for moderate to high myopia. A randomized
prospective study. Ophthalmology. 1998; 105:1512-22.
Bilbao-Calabuig R, González-López F, Villada-Casaponsa JR.
Combined ethanol-assisted and blunt mechanical corneal epithelial
peeling technique. J Emmetropia 2014;145-9.
Melki SA, Azar DT. LASIK complications: etiology, management
and prevention. Surv Ophthalmol. 2001;46:95-116.
Alio JL, Artola A, Claramonte PJ, et al. Complications of
Photorefractive keratectomy for myopia: two year follow-up of
3000 cases. J Cataract Refract Surg. 1998;24:619-26.
Pallikaris IG, Karoutis AD, Lydataky SE, Siganos DS. Rotating
brush for fast removal of corneal epithelium. J Refract Corneal
Surg. 1994;10:439-42.
19.
20.
21.
137
Camellin M. Laser epithelial keratomileusis for myopia. J Refract
Surg. 2003;19:666-70.
Pallikaris IG, Kalyvianaki MI, Katsanevaki VJ, Ginis HS. EpiLASIK: preliminary clinical results of an alternative surface ablation
procedure. J Cataract Refract Surg. 2005;31:879-85.
Campos M, Hertzog L, Wang XW, Fasano AP, Mc Donnell PJ.
Corneal surface after deepithelization using a sharp and a dull
instrument. Ophthalmic Surg. 1992;23:618-21.
Litwack S, Zadok D, García-de Quevedo V, Robledo N, Chayet
A. Laser-assisted subepithelial keratectomy for the correction of
myopia; a prospective comparative study.J Cataract Refract Surg.
2002;28:1330-3.
Johnson DG, Kezirian GM, George SP, Casebeer JC, Ashton J.
Removal of corneal epithelium with phototherapeutic technique
during multizone, multipass photorefractive keratectomy. J Refract
Surg. 1998;14:38-48.
Shah S, Doyle SJ, Chaterjee A, Williams BE, Ilango B. Comparison
of 18% ethanol and mechanical debridement for epithelial removal
before photorefractive keratectomy. J Refract Surg. 1998;14:S2124.
Kanitkar KD, Camp J, Humble H, Shen DJ, Wang MX. Pain
after epithelial removal by ethanol-assisted mechanical versus
transepithelial excimer laser debridement. J Refract Surg. 2000;
16:519-22.
Blake CR, Cervantes-Castañeda RA, Macias-Rodríguez
Y, Anzoulatous G, Anderson R, Chayet A. Comparison
of postoperative pain in patients following photorefractive
keratectomy versus advanced surface ablation. J Cataract Refract
Surg. 2005;31:1314-9.
Lee HK, Lee KS, Kim JK, Seo KR, Kim EK. Epithelial healing
and clinical outcomes in excimer laser photorefractive surgery
following three epithelial removal techniques: Mechanical, alcohol
and excimer laser. Am J Ophthalmol. 2005;139:56-63.
Ghoreishi M,Attarzadeh H, Tavakoli M, et al. Alcohol-assisted
versus mechanical epithelium removal in photorefractive
keratectomy. J Ophthalmic Vis Res. 2010;5:223-7.
Montezuma SR, Lessell S, Pineda R. Optic neuropathy after epiLASIK. J Refract Surg. 2008;24:204-8.
Einollahi B, Baradaran-Rafii A, Rezaei-Kanavi M, Eslani M,
Parchegani MR, Zare M, Feizi S, Karimian F. Mechanical versus
alcohol assisted epithelial debridement during photorefractive
keratectomy: a confocal microscopic clinical trial. J Refract Surg
2011;27:887-93.
Shortt AJ, Allan BD, Evans JR. Laser-assisted in-situ keratomileusis
(LASIK) versus photorefractive keratectomy (PRK) for myopia.
Cochrane Database Syst Rev. 2013; 31: CD005135.
Shojaei A, Ramezanzadeh M, Soleyman-Jahi S, Almasi-Nasrabadi
M, Rezazadeh P, Eslani M. Short-time mitomycin-C application
during photorefractive keratectomy in patients with low myopia. J
Cataract Refract Surg. 2013;39:197-203.
Sia RK, Coe CD, Edwards JD, Ryan DS, Bower KS. Visual
outcomes after Epi-LASIK and PRK for low and moderate
myopia. J Refract Surg. 2012;28:65-71.
JOURNAL OF EMMETROPIA - VOL 6, APRIL-JUNE
First author:
Rafael Bilbao-Calabuig, MD
Clínica Baviera
Madrid, Spain