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ORIGINAL ARTICLE OPEN ACCESS
Journal of the College of Physicians and Surgeons Pakistan 2024, Vol. 34(01): 42-47
42
Refractive Outcome of Femtosecond Assisted Laser in situ
Keratomileusis in 1564 cases of Myopia and Compound
Myopic Astigmatism
Sadia Humayun1, Mazhar Ishaq2, Aisha Fawad1 and Sabahat Arzoo1
1Refractive Surgical Department, Armed Forces Institute of Ophthalmology, National University of Medical Sciences, Rawalpindi,
Pakistan
2The Eye Consultants, Rawalpindi, Pakistan
ABSTRACT
Objective: To determine the outcomes of Femtosecond Assisted Laser in situ Keratomileusis (Femto LASIK) on eyes with myopia and
compound myopic astigmatism in terms of efficacy, safety, accuracy, predictability, and stability of the procedure.
Study Design: Quasi-experimental study.
Place and Duration of the Study: Refractive Surgical Department, Armed Forces Institute of Ophthalmology (AFIO), Rawalpindi,
Pakistan, from January 2014 to August 2019.
Methodology: Participants aged 18 years and above with upto -12D (dioptre of myopia, underwent preoperative detailed work-up
with history, ocular examination, subjective refraction and assessment on topography, tomography, and aberrometry. Suitable candi-
dates underwent Femto LASIK and were re-evaluated at 1st postoperative day, end of 1st week, 1 month, 3 months, 6 months and
1 year. Results were analysed and represented in form of standard graphs for refractive surgery.
Results: Postoperative UDVA (uncorrected distance visual acuity) of 20/40 was achieved in 99% of patients. Efficacy index was 1.02
+ 0.15. Safety index was 1.04 + 0.199. None of the patients lost more than one line in postoperative CDVA (corrected distance visual
acuity) when compared to preoperative CDVA. All the eyes (100%) were accurately treated within +1.0 DS of intended spherical equi-
valent (SEQ) range. Mean SEQ showed stability with 1% eyes recorded to have more than 0.5D change or more over 12 months.
Conclusion: Femto LASIK is an effective, safe, accurate, predictable, and stable procedure for correction of myopia and compound
myopic astigmatism.
Key Words: Femtosecond, Laser in situ Keratomileusis, Refractive surgery, Myopia, Compound myopic astigmatism, Uncorrected
distance visual acuity.
How to cite this article: Humayun S, Ishaq M, Fawad A, Arzoo S. Refractive Outcome of Femtosecond Assisted Laser in situ Kera-
tomileusis in 1564 cases of Myopia and Compound Myopic Astigmatism. J Coll Physicians Surg Pak 2024; 34(01):42-47.
INTRODUCTION
An array of surgical techniques exists which treat corneal shape
with the help of lasers in order to cure refractive errors. These
procedures aim to correct refractive errors and thus, relieve
patients of their dependency on glasses and contact lenses.
LASIK, first done in Europe in 1989 and first approved by FDA in
1995,1 is one of the most commonly performed and established
procedure amongst a list of refractive surgeries.2
It is estimated
that around 20-25 million eyes have been treated since the US
FDA approval of LASIK and around 700,000 procedures are
performed annually.3-5
Correspondence to: Dr. Sadia Humayun, Refractive Surg-
ical Department, Armed Forces Institute of Ophthal-
mology, National University of Medical Sciences,
Rawalpindi, Pakistan
E-mail: sadia.humayun@yahoo.com
.....................................................
Received: March 25, 2023; Revised: June 19, 2023;
Accepted: November 21, 2023
DOI: https://doi.org/10.29271/jcpsp.2024.01.42
Like any other surgical procedure, it has its limitations, precau-
tions, and adverse effects, but overall consensus remains that
more than 90% patients feel satisfied and happy with their postop-
erative results.6 The procedure, its protocols, the enigma of under-
standing the appropriateness of an individual for LASIK, its effects
on vision and patient’s lives are constantly undergoing active
research worldwide and require input of data from all quarters.
In Pakistan, LASIK is widely popular with both surgeons and
patients. Despite extensive refractive surgery practice in the
country, there is a lack of scientific data that represents the perfor-
mance of this procedure and its outcomes on Pakistani population
specifically in the form of standardised graphs.
It is imperative to present the major side-effects of the procedure
and the outcomes of Femto LASIK for myopia and compound
myopic astigmatism in the form of standard graphs used for
presenting the outcomes of refractive surgery.7,8 These graphs
are considered a standard for clear communication between
readers and researchers for quick comparative analysis between
different studies as well as different procedures pertaining to
refractive surgery.
Sadia Humayun, Mazhar Ishaq, Aisha Fawad and Sabahat Arzoo
Journal of the College of Physicians and Surgeons Pakistan 2024, Vol. 34(01): 42-47 43
The objective of this study was to present outcomes of Femtose-
cond Assisted Laser in situ Keratomileusis (Femto LASIK) on
eyes with myopia and compound myopic astigmatism in terms
of efficacy, safety, accuracy, predictability, and stability of the
procedure.
METHODOLOGY
It was a quasi-experimental study carried out at the Armed
Forces Institute of Ophthalmology, Rawalpindi, Pakistan
between January 2014 to August 2019. An approval from the
Hospital Ethical Review Committee, AFIO, Rawalpindi was
sought. A total of 1564 eyes were recruited over this duration
through purposive sampling. Informed consents were taken
from patients who fulfilled the criteria and were treated by
either of the two surgeons, both having similar surgical tech-
nique and protocol. Patients over the age of 18 years, having
myopia or compound myopic astigmatism up to -12D, esti-
mated postoperative flat K value more than 34D, residual
stromal bed of 280 microns or more and percentage of tissue
altered <40% were recruited. Those with recent changes in
refraction, pregnancy, lactation, any underlying systemic or
ocular conditions like glaucoma, cataract, dry eye or ocular
surface disease, suspicion of Keratoconus, previously done
ocular or refractive surgery were excluded from this study.
Contact lens-wearers were advised to discontinue for a period
of one to two weeks and then, were reassessed. Thorough
assessment of all individuals was carried out preoperatively. It
included careful history and meticulous examination of uncor-
rected distance visual acuity (UDVA), subjective or corrected
distance visual acuity (CDVA) and cycloplegic refraction,
intraocular pressure measurement, anterior and posterior
segment examinations on slit lamp, dry eye testing. All individ-
uals were analysed on a set of diagnostics including Tomog-
raphy (Wavelight Oculyzer II), Topography and Pupillometry
(Wavelight Topolyzer Verio), and Aberrometery (Wavelight
Analyzer). Finally, each individual was comprehensively anal-
ysed for suitability to undergo the procedure. Those found suit-
able were explained the benefits, possible side-effects, proce-
dure details, postoperative care, and follow-up requirements.
Written consent was taken from each patient as per the stan-
dard routine of the hospital as well as consent for use of their clin-
ical data for the purpose of research.
Patients’ subjective refraction was validated on the day of
surgery and the data were entered into the planner of the
excimer laser machine, targeting emmetropia with Wavefront
Optimized ablation profile. An optical zone of 6-6.5 mm and abla-
tion zone of 9mm were maintained for all the patients. Flap thick-
ness was kept between 100-120 microns depending on the avail-
ability of residual stromal tissue which was kept more than 280
microns under all circumstances.
Preoperatively, patients were instilled with 0.5% Proparacaine
Hydrochloride drops as topical anaesthesia. Periocular skin was
prepared with 7.5% Betadine antiseptic solution and positioned
under the microscope of FS 200 Femtosecond laser (Wavelight
GmBH Erlangen, Germany). Sterile drape and lid speculum were
placed. Ocular surface was rinsed with balanced salt solution to
get rid of debris and Meibomian gland secretions. Laser was then
docked and centration was confirmed on the screen. Once proper
centration and immobilisation of eye were achieved, laser was
fired to get the intrastromal and sidecut and then docking was
released. The same procedure was followed for the other eye and
patient was shifted to a position under the microscope of EX 500
Excimer laser (Wavelight GmBH Erlangen, Germany). Flap was
lifted with the help of a spatula and reflected against the hinge to
expose the stromal bed. Fixation was achieved and ablation was
performed under pupil tracking while protecting the hinge. The
bed was irrigated with the balanced salt solution and flap was
gently stroked back in its position. Speculum was carefully
removed. Patients were prescribed 0.5% Moxifloxacin,
Tobramycin plus Dexamethasone combination and lubricant
eye drops for every 2 hours for the first day. After that,
Moxifloxacin was given 8 hourly for one week and Tobramycin
plus Dexamethasone eye drops were given 8 hourly for two
weeks. Lubricants were prescribed 4 hourly after the first day
and gradually tapered over 6 months. Patients were called for a
follow-up after one day, one week, one month, three months, six
months, and a year. Patients' uncorrected, best corrected
vision, ocular examination, topography, and tomography were
recorded. Efficacy was when postoperative UDVA was compared
to preoperative CDVA (efficacy index is postoperative UDVA /
preoperative CDVA).1 Safety of procedure was judged by
comparing preoperative and postoperative CDVA (Safety index
is postop CDVA/ preop CDVA).9 Target induced astigmatism (TIA)
is the change in astigmatism (magnitude and axis) intended by
the surgery whereas surgically induced astigmatism (SIA) is the
amount of astigmatic change (magnitude and axis), that the
surgery actually induced.10
Statistical analysis was performed on MS Excel 2013. Preopera-
tive readings were compared to post-operative ones using
paired sample t-test, and p-value <0.05 was considered to be
significant. The categorical variables were expressed as counts
and percentages, and continuous variables were expressed as
mean and SD.
RESULTS
A total of 1564 eyes were recruited for the study, amongst which
34.8% were males and 65.2% were females, amounting to 544
and 1020 of the total sample, respectively. The study groups’
mean age was calculated to be 25.99 + 6.04 years.
Mean preoperative UDVA, CDVA, and spherical equivalent
(SEQ) which is the algebraic sum of sphere and half of cylinder,
were recorded and compared with mean postoperative values
(Table I).
At 12 months, 1552 eyes, i.e. 99% of the sample achieved equal
or better than 20/40 postoperative UDVA. Around 1536 eyes
(98%) achieved 20/30 postoperative UDVA (Figure 1A). To begin
with, all the study patients did not have 20/20 preoperative
CDVA. Around 82% participants had CDVA of 20/20 preopera-
tively. In comparison, postoperative UDVA was 20/20 in 84% of
cases. Efficacy index was calculated to be 1.02 + 0.15.
Femto LASIK in myopia
Journal of the College of Physicians and Surgeons Pakistan 2024, Vol. 34(01): 42-47
44
Figure 1: Standard graphs for refractive surgery outcomes. (A) Efficacy profile (postoperative UDVA vs. preoperative CDVA), (B) Safety profile
(change in CDVA in form of loss or gain of lines), (C) Predictability profile (intended vs. achieved spherical equivalent), (D) Accuracy profile
(percentage of patients within + 1.00 D), (E) Refractive astigmatism (percentage of patients within + 1.00 D), (F) Stability profile (change in
mean SE over time), (G) Refractive astigmatism, (H) Target induced astigmatism vs. surgically induced astigmatism, (I) Refractive astigmatism
Angle of Error.
Sadia Humayun, Mazhar Ishaq, Aisha Fawad and Sabahat Arzoo
Journal of the College of Physicians and Surgeons Pakistan 2024, Vol. 34(01): 42-47 45
Table I: Visual and refractive outcomes (Mean, SD, and Paired Two-Sample t-test).
Parameter Preop mean
(M±SD)
Postop mean (M±SD) p-value (two-tail)
1 month 6 months 1 year Preoperative
vs. 1 month
Preoperative
vs. 6 months
Preoperative
vs. 1 year
6 months
vs. 1 year
UDVA (LogMAR) 1.215 ±
0.353
0.031 +
0.078
0.023 ±
0.066
0.024 +
0.068
<0.001 <0.001 <0.001 0.002
SEQ (D) -4.421 ±
2.169
0.033 +
0.093
-2.166 +
1.075
-0.037 +
0.144
<0.001 <0.001 <0.001 <0.001
CDVA (LogMAR) 0.030 +
0.081
0.023 +
0.067
0.018 +
0.060
0.018 +
0.058
<0.001 <0.001 <0.001 0.309
UDVA: Uncorrected distance visual acuity, CDVA: Corrected distance visual acuity, SEQ: Spherical equivalent, D: Dioptre, SD: Standard deviation, Preop:
Preoperative, Postop: Postoperative.
Preoperative CDVA was compared with postoperative UDVA
in each case in terms of loss or gain of lines. About 95.5%
(1493) achieved either the same or better UDVA after one
year of the procedure (Figure 1B). Around 99.7% partici-
pants had postoperative UDVA within 1 line of preoperative
CDVA.
Any loss of lines postoperatively was considered against
safety of the procedure. Out of 1564 eyes, 0.8% of partici-
pants (13) experienced loss of one line in postoperative
CDVA (Figure 1C). Rest of the 99.2% (1551) of cases either
experienced better or the same corrected visual acuity as
preoperative CDVA. None of the eyes had more than one
loss of line. Safety index remained more than 1, that is 1.04
+ 0.199.
Comparison of intended and achieved SEQ was carried out
to see how predictable the results were at 12 months. In
Figure 1D, the scattergram shows that all the achieved
points fell within the +1D intended SEQ range.
The accuracy profile in Figure 1E revealed that 99.6% (1557)
of eyes were accurately treated within +0.5D of the
intended SEQ target.
Mean SEQ at different times (preop, 1 month, 3 months, 6
months, and 12 months) was recorded to see the stability of
results. Postoperatively, the SEQ remained essentially
stable. Around 1% (15) of eyes were recorded to show a
change of more than 0.5D over a span of 11 months (from 1
month to 12 months postoperatively).
In this study, the target was to achieve emmetropia. Postop-
erative astigmatism was recorded. In 1 year, 99.2% of eyes
were within 0.5D astigmatism. All the eyes (100%) had post-
operative astigmatism within 0.75D.
When compared, 99.9% of SIA points were within +1D of
TIA range. Only one of the points fell outside the purple (+1
D) lines in Figure 1H scattergram. Angle of error is the angle
described by the vectors of achieved (SIA) versus intended
(TIA) correction.10 In Figure 1I, 97.7% (1528) of treated eyes
had Angle of Error within +5 degrees and 99.6% (1558) had
Angle of Error within +15 degrees.
Adverse effects encountered postoperatively included ecta-
sia in two patients. Diffuse lamellar keratitis (Grade 1) had
to be managed in 12 patients and pressure-induced stromal
keratitis in one patient; both conditions were treated medi-
cally and brought under control with no effect on the final
visual outcome. Around 43 patients were steroid respon-
ders.
DISCUSSION
Femto LASIK has gained popularity as well as trust of both
surgeons and patients for the treatment of myopia.11 In this
study, the prime aim was to produce and publish refractive
results of this procedure as per the standard requirements.
Efficacy, safety, predictability, and accuracy of results were
compared with other similar studies.
The efficacy at 12 months was 99% of participants achieving
equal or better than 20/40 postoperative UDVA. A total of
84% had 20/20 postoperative UDVA (when only 82% had
20/20 CDVA before the procedure).
A study by Chua et al. carried out primarily on Asian eyes
revealed that efficacy remained >99% reaching 20/40 UDVA
or better and around 70% reaching 20/20 mark after 18
years of follow-up. They had reported efficacy index of 0.9112
as compared to the efficacy index of 1.02 + 0.15 in this
study.
A study by Kim et al. reported similar results on Korean popu-
lation despite the difference in follow up duration when
compared to the current study. They reported 96.3% of
patients achieving 20/40 and 69.9% achieving 20/20 UDVA
at the end of three months.13 The same study reported
efficacy index of 0.95 at the end of 3 years duration postop-
eratively.
There remains a solid concern for developing corneal ectasia
after LASIK despite its excellent efficacy.14 Two participants
showed signs of ectasia, one eye in one participant and both
eyes in the second participant despite all normal scans and
parameters during one year follow-up period. Both under-
went immediate collagen cross-linking and are still under
observation.
Tabacaru and Stanca conducted one-year study on cases of
myopia treated with Femto LASIK and concluded that none
of their patients experienced loss of lines in CDVA postopera-
tively.15 In contrast to this study, the present authors encoun-
Femto LASIK in myopia
Journal of the College of Physicians and Surgeons Pakistan 2024, Vol. 34(01): 42-47
46
tered 0.8% of participants who lost up to one line when
preoperative CDVA was compared with postoperative CDVA.
This difference can be attributed to major dissimilarity in the
sample size of the two studies (60 vs. 1564 eyes).
Another study conducted by Shehadah et al. performed
Wavefront Optimized LASIK on 326 (myopic and myopic
astigmatic) eyes and concluded that none of their partici-
pants lost any lines of CDVA at 12 months.16
On the contrary, a study carried out by Brar et al. performed
Femto LASIK on 328 myopic eyes on two different machines.
At 12 months, both groups had 1% and 3% of participants
who encountered loss of 1 line in CDVA.9 Safety index how-
ever remained more than one. Another study using similar
platforms of femtosecond and excimer laser concluded that
86% of their myopic patients either had same or better
CDVA and 14% experienced loss of 1 line at 1-year follow-
up. None of their patients had loss of two lines or more.17
Predictability is evaluated by comparing attempted versus
achieved spherical equivalent. Similar to this study’s obser-
vation, a study by Agarwal et al. also concluded 100% of
participants achieving intended spherical equivalent within
+1.0 DS range.18 FDA trials and Singapore National Eye
Centre trial had reported achievement of 90 and 94% within
the target spherical equivalent, respectively.12 The same
studies reported 72 and 70% of participants within +0.5 DS
of intended spherical equivalent as compared to the present
study where 99.6% of the patients were treated accurately
within this range.
A study compared outcomes of LASIK in 6.0 and 6.5-mm
optical zone myopic cases and concluded that 11 out of
2664 (1332 in each group) patients were either over
corrected or under corrected when SIA and TIA were plotted
in comparison.19 Mean Angle of Error was 1.1 + 18.5 for 6.0
mm group and 0.5 + 17.2 for 6.5 mm group. In this study,
only one patient was recorded out of +1.0D range, thus,
showing better astigmatic results. Also, arithmetic and abso-
lute mean Angle of Error concluded in this study were 0.0 +
3.1 and 0.4 + 3.0, respectively. The duration of follow-up
was same for both the studies. However, the sample size
was double the size of this study. Another study by Khalifa et
al. was carried out to compare astigmatic outcomes of Wave-
front Guided and Wavefront Optimized LASIK on 220 eyes.20
They reported mean Angle of Error for low and moderate
myopia as -0.04 + 0.87 and -1.15 + 12.36 respectively, at 6
months follow-up. Thus, the results of current study proved
to be better in terms of correction of astigmatism.
The main strength of this study was a large-sized sample.
However, the quality of vision after this procedure needs to
be explored to ascertain its exact effect on patients’ quality
of life.
CONCLUSION
Femto LASIK is an effective, safe, accurate, predictable, and
stable procedure for eyes with myopia and compound
myopic astigmatism.
ETHICAL APPROVAL:
An approval was granted by the Hospital Ethical Review
Committee, AFIO, Rawalpindi, on 1 January 2014.
PATIENTS’ CONSENT:
Informed, written consents were taken from patients for
both the treatment and publication of the data.
COMPETING INTEREST:
None of the authors had any conflict of interest to declare.
AUTHORS’ CONTRIBUTION:
SH: Conception and design of the work, data analysis.
MI: Final approval of the manuscript, data interpretation.
AF: Drafting of the work.
SA: Data acquisition.
All authors approved the final version of the manuscript to
be published.
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