Download Clinical assessment of defocus curves after Excimer Laser

ARTICLE
Clinical assessment of defocus curves after Excimer Laser
presbyopia surgery using aspheric ablation profiles
Marta Romero-Domínguez, MD1; Alfredo Castillo-Gómez, MD, PhD1;
David Carmona-González, OD1; Carlos Palomino Bautista, MD1
PURPOSE: To assess binocular visual acuity (VA) through the evaluation of defocus curves
in patients who underwent correction of spherical aberration and micro-monovision using
PRESBYOND Laser Blended Vision (Carl Zeiss Meditec).
SETTING: Universidad Europea de Madrid, Madrid, Spain.
METHODS: A prospective study of 80 eyes from 40 patients that underwent PresbyLASIK
surgery. Patients were divided into 2 groups according to their preoperative spherical
equivalent (SE): group I (range +0.5 to +3 diopters (D) and group II (range −0.75 to −5.5 D).
Refractive changes, uncorrected distance and near VA (UDVA and UNVA, respectively),
and independence from glasses were assessed.
RESULTS: Mean age of patients was 47.75 ± 4.38 years. Defocus curve of group I showed
pre- and post-operative UDVA of 0 logMAR, while intermediate visual acuity (IVA) at
67 cm was 0.10 to 0.09 logMAR, and at 33 cm VA increased from 0.47 to 0.41 logMAR.
Pre- and post-operate UDVA in group II was 0 logMAR, while for IVA it decreased from
0.06 to 0.11 logMAR, and at 33 cm it decreased from 0.34 to 0.44 logMAR.
Independence from distance spectacles was achieved by 100% of patients in both groups,
whilst 91.4% of group I and 61.7% of group II achieved independence from near spectacles.
CONCLUSION: PresbyLASIK treatment is effective for both myopic and hyperopic
patients because it reduces presbyopia symptoms and corrects distance refractive error in the
same procedure, thus offering greater independence from spectacles. Defocus curves provide
a useful method to assess visual capability after refractive surgery.
J Emmetropia 2016; 1: 39-45
Presbyopia is a reduction in the focusing power of
the eye, which loses the ability to focus on near objects.
It is estimated that presbyopia currently affects around
1 million adults worldwide. As the world population
becomes older, presbyopia prevalence will increase. By
2030, the world population aged 40 years or over is
expected to increase by up to 41%1-2.
Monovision was initially used in optometry as
a means to adapt contact lens for the treatment of
presbyopia3 (the original term used was “single vision”).
Submitted: 10/13/2015
Revised: 1/28/2016
Accepted: 2/17/2016
1
Hospital Universitario Quirónsalud, Madrid, Spain.
Financial Disclosure: The authors declare no conflict of interest. No
financial support was received for this study.
Corresponding Author: Marta Romero-Domínguez
Calle Diego de Velazquez 1. 28223 Pozuelo de Alarcón. Spain
E-mail: [email protected]
© 2016 SECOIR
Sociedad Española de Cirugía Ocular Implanto-Refractiva
In the 1980s, as a result of advances in crystalline surgery,
combined vision became more common as a means to
improve both distance and near and intermediate vision
for patients who underwent cataract surgery or refractive
lensectomy. With the incorporation of excimer laser
technology to ophthalmology in the 1990s, multifocal
profiles started to be developed to correct presbyopia4.
Monovision, with or without modification of corneal
asphericity5, was also incorporated as a treatment option
for presbyopia (LASIK-monovision or Blended Vision6).
There are also other techniques for the correction of
presbyopia: multifocal lens, accommodating lens,
femtosecond laser7 or intracorneal implant8,9.
Defocus curves are graphic tools that assess visual
performance after refractive surgery by measuring VA at
varying distances with 2 peaks of optimum acuity: 1 at
the distance focal point and the other at the near focus.
They are mostly used in refractive corneal surgery to
correct presbyopia, in contact lens fittings (multifocal),
to calculate amplitude of accommodation10 or in the
implantation of multifocal intraocular lens11-13.
ISSN: 2171-4703
39
40
DEFOCUS CURVES AFTER PRESBYOPIA SURGERY
We present an observational, prospective study to
evaluate defocus curves before and after presbyopia
treatment with Excimer laser that included correction
of spherical aberration and micro-monovision.
METHODS
The prospective study included 80 eyes of 40
patients between 40 and 55 years of age who underwent
presbyopia corrective surgery with MEL-80 excimer
laser (Presbyond, Carl Zeiss Meditec, Jena, Germany) at
the Hospital Universitario Quirón in Madrid, between
January and December 2014.
The study followed the principles outlined in the
Declaration of Helsinki.
Prior to surgery, all participants signed an informed
consent form outlining the risks, complications and
surgical technique used.
The inclusion criteria were: between 40 and 55 years
of age, manifest symptoms of presbyopia and absence
of cataract. The exclusion criteria included: altered
topography, contraindicated for LASIK treatment,
clouding of the crystalline lens, absence of symptoms
of presbyopia, corneal disease, glaucoma, retinopathy
or macular degeneration, previous history of ocular
inflammation, and previous corneal or intraocular
surgery.
Patients were divided into 2 groups according to
their preoperative spherical equivalent (SE): group I
(range +0.5 to +3 diopters [D]) and group II
(range −0.75 to −5.5 D).
Preoperative workup consisted of a complete
ophthalmic exam that included: binocular best
uncorrected distance visual acuity (UDVA),
binocular corrected near visual acuity (CNVA),
binocular uncorrected near visual acuity (UNVA),
autokeratometer measurements (TopCon Corporation,
Tokyo Japan), subjective and cyclopegic refraction,
applanation tonometry, slit lamp exam, funduscopy
with pupil dilated, corneal topography (Pentacam
Oculus, Germany), ultrasonic pachymetry (DGH
Technology, Inc., United States), ocular dominance
test, anisometropia tolerance test using test frames,
and CRS-MASTER with H-S aberrometer (Wasca
Analyzer), iris registration and corneal anterior surface
topographer (ATLAS 9000).
Motor ocular dominance was determined using
the hole-in-card test. Sensory ocular dominance was
determined using the plus 1 D test or swinging-plus
test (can also be used for near eyes). These tests were
followed by an anisometropia tolerance test using
test frames. The correct prescription was set on the
dominant eye, while the non-dominant eye in myopic
patients was undercorrected within a range of 0.75 D
and 1.5 D, and overcorrected within the same range in
hyperopic patients. Testing started with the minimum
possible overcorrection (0.75 D) in the non-dominant
eye (having already set the correct ranking for the
dominant eye). The test must always be binocular. The
adaptation of the patient is checked after a period of
20-30 minutes. Graduation in the non-dominant eye
is gradually increased to a maximum of 1.5 D, until
comfortable binocular distance and near vision was
achieved.
Binocular defocus curves, constructed using vergence
ranges between −5.00 D and +3.00 D spherical, in 0.50 D
steps, were obtained for all patients preoperatively and
6 months after surgery.
Three points were analyzed on the defocus curves:
1 corresponding to the infinite or distance vision (DV),
1 at 67 cm for intermediate visual acuity (IVA) and B
1 at 33 cm for near vision (NV).
MEL-80 excimer laser (Presbyond) has a complex
wavefront guided laser ablation profile that expands the
depth of focus available to each eye. So, while adaptation
is similar to micro-monovision, the expanded depth
of field achieves a wider range of focus, thus reducing
dependence on spectacles as far as possible. Surgical
planning with the system includes inputting the
functional age of the patient’s eye (this refers to the
patient’s actual amplitude of accommodation). The
system calculates and programs the spherical aberration
(SA) (in Malacara nomenclature14) to be corrected
taking into account each patient’s preoperative SE:
a) in hyperopic patients: the same SA obtained by
the aberrometer; b) in myopic patients: programmed
according to the patient’s preoperative SE to a maximum
of −0.8 (this is the maximum value that can be applied).
The aberration correction is bilateral and symmetrical,
together with the residual myopia previously calculated.
Follow-up examinations were set at 1 day, 1 week
and 1, 3 and 6 months after surgery. The following were
assessed: binocular UDVA, BCDVA, CNVA, UNVA,
dominant and non-dominant eye refraction, defocus
curves and topography. A slit lamp exam was also
carried out.
Results are expressed as mean ± standard deviation.
Data were analyzed using IBM SPSS Statistics for
Windows, Version 21.0 (Armonk, NY: IBM Corp.).
The Wilconxon test was used to compare pre- and postoperative data for each group, and to assess the relevance
of pre- and post-surgery differences within each group.
The non-parametric Mann-Whitney U test was used to
compare the differences between 2 independent groups.
Statistical significance was set at a p-value of less than
0.05.
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DEFOCUS CURVES AFTER PRESBYOPIA SURGERY
Table 1. Demographic characteristics and preoperative data.
Parameter
Patients (n)
Age, years (mean ± SD)
Sex (male / female)
Eyes (n)
Preoperative spherical equivalent (D)
Value
40
47.75 ± 4.38
16 / 24
80
Group I
Group II
mean ± SD
range
mean ± SD
range
1.31 ± 0.83
+0.50 to +3
−3.46 ± 1.37
−1 to −5.50
mean ± SD
range
mean ± SD
range
−0.98 ± 1.32
−0.25 to −4.50
−1.01 ± 0.51
0.25 to −2.50
42.68 ± 1.75
44.12 ± 1.91
Preoperative cylinder (D)
Group I
Group II
Preop keratometry. k1 (D ± SD)
Preop keratometry. k2 (D ± SD)
Overcorrected nondominant eye
Eyes (n)
+0.75 D
+1 D
+1.25 D
+1.75 D
12
32
16
20
n= sample size, SD= standard deviation.
Table 2. Comparison of pre- and postoperative spherical equivalent (SE).
Mean ± SD (range)
GROUP I
GROUP II
PRE-OP SE
POST-OP SE
(dominant eye)
POST-OP SE
(non-dominant eye)
1.31 ± 0.83
(+0.50 to +3)
−3.46 ± 1.37
(−1 to −5.50)
0.17 ± 0.56
(0.75 to −1)
−0.14 ± 0.23
(0.13 to −0.88)
−0.89 ± 0.18
(−0.23 to −1.03)
−1.05 ± 0.35
(−0.75 to −1.63)
SE = spherical equivalent; OP = operative.
RESULTS
A total of 80 eyes of 40 patients were operated.
Average age was 47.75 ± 4.38 years (range 41-55).
There were 24 women (60%) and 16 men (40%). The
mean preoperative SE of group I was +1.31 ± 0.83 D
(range +0.5 D to +3 D), while that of group II was
−3.46 ± 1.37 D (range −1 D to −5.50 D). Mean
preoperative astigmatism of group I was −0.98 ± 1.32 D
(range −0.25 D to 4.50 D) and that of group II was
−1.01 ± 0.51 D (range 0.25 D to −2.50 D). Mean
preoperative astigmatism axis of group I was
91.92 ± 45.49 (range 5° to 170°) and that of group II
was 88.70 ± 47.77 (range 10° to 170°).
Overcorrection of patients’ non-dominant eyes was
as follows: 6 patients (15%) tolerated an overcorrection
of 0.75 D, 16 (40%) tolerated 1 D, 8 (20%) tolerated
1.25 D, and 10 (25%) tolerated 1.50 D (Table 1).
The mean postoperative SE of group I was
+0.17 ± 0.56 D (range 0.75 D to −1 D) in dominant
eye and −0.89 ± 0.18 D (range −0.23 D to −1.03 D)
in non-dominant eye, while that of group II was
−0.14 ± 0.23 D (range +0.13 D to −0.88 D) in dominant
eye and −1.05 ± 0.35 D (range −0.75 D to −1.63 D)
in non-dominant eye (Table 2). Mean astigmatism
at 6 months was −0.62 ± −0.40 D (range −0.25 D to −1.25 D)
in group I, and −0.49 ± 0.27 D (range 0.12 D to −0.75 D)
in group II. Mean postoperative astigmatism axis of
group I was 96.69 ± 37.81 (range 25° to 170°) and that
of group II was 111.16 ± 50.32 (range 33° to −180°).
At 6 months after surgery in group I, 12 eyes had againstthe-rule astigmatism (corrector cylinder between 80° and
100°) and only 1 eye with-the-rule astigmatism (170°).
In group II, 10 eyes had against-the-rule astigmatism
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DEFOCUS CURVES AFTER PRESBYOPIA SURGERY
Table 3. Visual acuity (logMAR) obtained preoperatively and at 6 months after surgery.
PREOPERATIVE UDVA
POSTOPERATIVE UDVA
DISTANCE
GROUP I
GROUP II
GROUP I
GROUP II
p-value*
Infinite
0.00 ± 0.00
0.00 ± 0.00
0.00 ± 0.00
0.00 ± 0.00
-
2m
0.01 ± 0.01
0.00 ± 0.00
0.00 ± 0.00
0.00 ± 0.01
-
1m
0.03 ± 0.06
0.01 ± 0.01
0.03 ± 0.03
0.04 ± 0.04
-
67 cm
0.10 ± 0.14
0.06 ± 0.06
0.09 ± 0.04
0.11 ± 0.06
0.012
50 cm
0.20 ± 0.21
0.14 ± 0.12
0.19 ± 0.06
0.19 ± 0.09
-
40 cm
0.32 ± 0.24
0.22 ± 0.21
0.30 ± 0.12
0.34 ± 0.11
-
33 cm
0.47 ± 0.26
0.34 ± 0.29
0.41 ± 0.13
0.44 ± 0.19
0.023
29 cm
0.63 ± 0.25
0.45 ± 0.29
0.59 ± 0.20
0.55 ± 0.22
-
25 cm
0.82 ± 0.19
0.57 ± 0.30
0.71 ± 0.21
0.74 ± 0.28
-
22 cm
0.93 ± 0.23
0.66 ± 0.38
0.83 ± 0.15
0.88 ± 0.24
-
20 cm
1.08 ± 0.18
0.78 ± 0.35
0.97 ± 0.16
1.07 ± 0.18
0.011
UDVA = binocular best uncorrected distance visual acuity. Values given as mean ± standard deviation; *p-value indicated when
significant differences present.
Postop
Preop
1.00
0.80
0.60
0.40
0.20
Postop
Visual Acuity (logMAR)
Preop
1.20
0.80
0.60
0.40
0.20
0.00
-5
-4.5
-4
-3.5
-3
-2.5
-2
-1.5
20 cm 22 cm 25 cm 29 cm 33 cm 40 cm 50 cm 67 cm
-1
1m
-0.5
2m
-0.20
0
ь
1.00
Visual Acuity (logMAR)
1.20
0.00
-5
-4.5
-4
-3.5
-3
-2.5
-2
-1.5
20 cm 22 cm 25 cm 29 cm 33 cm 40 cm 50 cm 67 cm
-1
1m
-0.5
2m
-0.20
0
ь
Figure 1. Pre and postoperative defocus curves in group 1.
Figure 2. Pre and postoperative defocus curves in group 2.
(corrector cylinder between 65° and 105°) and 6 eyes
with-the-rule astigmatism (corrector cylinder between
155° and 180°).
Residual myopia in the non-dominant eyes was
higher in group II (−1.05 ± 0.35 D) than in group I
(−0.89 ± 0.18 D).
The preoperative SA obtained using OSA nomenclature
(Optical Society of America) for a 6 mm pupil in group I
was 0.22; at 6 months it was 0.04. In group II, SA changed
from 0.14 to 0.18 at 6 months.
Three points were analyzed on each defocus curve:
1 corresponding to the infinite or distance vision (DV),
1 at 67 cm for intermediate visual acuity (IVA), and
1 at 33 cm for near vision (NV) (Table 3).
Defocus curves of group I showed pre- and postoperative UDVA of 0 log of the minimum angle of
resolution (logMAR) (20/20), while for IVA at 67 cm it
changed from 0.10 to 0.09 logMAR (20/32 to 20/25),
and at 33 cm VA increased from 0.47 to 0.41 logMAR
(20/60 to 20/50) (Figure 1).
Pre- and post-operate UDVA in group II was 0 logMAR
(20/20), while for IVA at 67 cm it decreased from 0.06 to
0.11 logMAR (20/25), and at 33 cm, it decreased from
0.34 to 0.44 logMAR (20/45 to 20/55) (Figure 2).
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DEFOCUS CURVES AFTER PRESBYOPIA SURGERY
Postoperative defocus curve of group I showed an
overall improvement across the range of distances from
2 m to 20 cm, with the most significant improvement
observed at 25 cm (29.89%) and the least significant
observed at 2 m (1.35%). This is because preoperative
VA was maintained at practically the same value. UDVA
of 0 logMAR was maintained, while for IVA at 67 cm
there was a 15.69% improvement, and for NV at 33 cm
a 15.69% improvement was observed.
Postoperative defocus curve of group II showed an
overall decrease in vision across the range of distances
from 2 m to 20 cm, though maintaining a postoperative
distance VA of 0 logMAR.
The most significant change in postoperative VA
was observed at 20 cm, with VA decreasing an average
of 39.77% (0.78 to 1.07 logMAR) (p = 0.011).
VA decreased postoperatively an average of 11.49% at
67 cm (0.06 to 0.11 logMAR) (p = 0.012) and 20.65%
at 33 cm (0.34 to 0.44 logMAR) (p = 0.023).
None of the operated eyes required a second
intervention to modify the refractive results obtained.
There were no complications during or after any of
the surgeries performed. All of the patients (100%)
in both groups achieved complete independence from
distance spectacles, while 91.4% of patients in group
I and 61.7% of patients in group II achieved complete
independence from near spectacles.
DISCUSSION
Defocus curves are a graphic tool used to evaluate
a patient’s visual performance at various distances in
order to establish a connection between those distances
and visual acuity. As mentioned above, they are an
excellent way of assessing range of vision after surgical
procedures, mainly after presbyopia corrective surgery.
Most studies that use spherical lenses to construct
defocus curves employ ranges between −5 D and +3 D
spherical, although many different ranges are described
in the literature13,15. The step size may vary from 0.25 D
to 0.75 D or higher. However, increasing the step size
may distort the results and affect their validity16. Thus,
a step size of 0.50 D or 0.75 D across vergence ranges
is generally preferred. Our study used 0.50 D steps and
vergence ranges between −5 D and +3 D.
Points discussed in the defocus curves differ between
authors13,17. For intermediate visual acuity, the distance
varies from 63, 64 or 67 cm. For near vision, the
distance varies from 33 to 40 cm. We analyzed 1 point
at 67 cm for intermediate visual acuity, and 1 at 33 cm
for near vision. These points are the most widely used
in the literature.
According to the refractive results obtained,
emmetropia was almost achieved in all dominant eyes,
43
with a postoperative SE of 0.17 ± 0.56 D in group I and
−0.14 ± 0.23 D in group II. These results coincide with
those reported by other authors, such as Baudu et al.18,
who achieved a postoperative SE of +0.17 ± 0.34 D in
the dominant eye.
Pre-programming the correction of spherical
aberration during surgery is also important when
aiming to achieve successful refractive outcomes, since
it extends depth of focus by increasing the axial defocus
range. The higher the spherical aberration induced,
the greater the depth of focus generated, although
sensibility to contrast will be affected as a result.
Consequently, adherence to the nomograms provided
by the manufacturer is essential in order to avoid
unexpected results.
After LASIK surgery, increased higher-order
aberrations, primarily, an increase of SA, and to a lesser
extent, coma or astigmatism, irregularities induced by
treatment or ablationn offset pattern are observed. This
increase in SA is directly related to loss of compensation
between the SA of the cornea and crystalline lens.
The corneal photoablation generates a quasi-spherical
cornea and even oblate (Q > 0). The myopic correction
induces positive SA, and the hyperopic induces negative
SA19. Some studies have demonstrated that negative
SA correlated well with improved near performance20.
The vertical coma and other aberrations could hinder
near visual acuity and patient satisfaction. Decentered
ablations on SA could reduce the effectiveness of
aspheric shape design and induce coma.
With the modification of the SA-inducing
treatment used, we reduced SA in hyperopic eyes
(0.2 to 0.04), while the increase in myopic eyes was
less significant (from 0.14 to 0.18) than if they were
treated without control of SA, in which case the
increase in myopic eyes after surgery would be much
greater. Reinstein et al.21, in emmetropic patients,
achieved a change in SA from 0.14 to −0.08 (in OSA),
much more striking than that obtained in our study
in either group; however, the study was conducted in
emmetropic patients.
We found some differences in inclusion age between
ours and previous studies. Luger et al.22 included
patients within an age range of 51 ± 3, while the
average age in Reinstein’s21 study was 55, with an age
range of 44 and 65 (in another study by Reinstein23,
average age was 56, with range of 44 and 66). The
age range in Falcon24 et al. was between 42 and 69.
In contrast, the age range in our study was inferior to
that in other published studies, with an average age
of 47.75 ± 4.38 and an age range of 41 to 55. This
difference could have affected the postoperative results
obtained, since near and intermediate VA is normally
higher in younger patients.
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DEFOCUS CURVES AFTER PRESBYOPIA SURGERY
Regarding the refractive outcomes obtained with
the surgical procedure, in Reinstein et al.25, 100% of
patients achieved 20/20 or better binocular UDVA and
96% achieved binocular UNVA of J2. In Luger’s22
study, 93% of patients achieved 20/20 or better
binocular UDVA and 90% achieved J2 or better
UNVA; 7% of patients lost 2 lines of CDVA. In Falcon
et al.24, 91.1% of patients achieved a binocular distance
vision of 20/20 or better, and 86.7% achieved a near
vision of J1. In our study, 100% of patients achieved a
UDVA of 20/20, while 33.3% of group I and 20% of
group II achieved a UNVA of J4 or better. Therefore,
the near vision outcomes in our study are lower than
those reported by other authors.
Some differences between the 2 study groups were
observed in terms of defocus curves. Vergences range
from 0 to +3 is not specified because there is no change
in either pre- and postoperative focusing results in
vergences −5 to 0. Both groups had a preoperative
UDVA of 0 logMAR, which was maintained
postoperatively. Some differences were observed between
groups for all the other distances, although these are not
statistically significant for any of the distances measured
(p > 0.05). Before surgery, Group II achieved a higher
VA in distances ranging from 1 m to 40 cm and from
25 to 20 cm. Preoperative UDVA at 67 cm was 0.10
in group I and 0.06 in group II. Similarly, VA at 33 cm
was 0.47 in group I and 0.3 in group II. These results
affected the near and intermediate visual outcomes
after surgery, as group II did not achieve the same
improvement percentages as group I, because the latter
had higher initial visual acuities.
Luger et al.22, in their evaluation of defocus curves,
reported that patients with a mean initial SE of
−1.08 ± 2.62 D and 0.52 ± 0.42 D astigmatism achieved
a mean gain of 2 lines of near vision at 33 cm (−3 D), no
changes at 67 cm, and lost half a Snellen line of distance
vision. Our defocus curves show that patients in group
I gained VA in the 40-20 cm range after surgery, with
no changes in distance vision. Patients in group II did
not experience any changes in distance vision either, but
lost VA in the 29-20 cm range. Surgical outcomes were
more satisfactory in group I, though only with regard
to intermediate and near VA. This discrepancy may
be explained by the fact that myopic patients usually
maintain excellent VA at these distances.
With regard to against-the-rule astigmatism, the
curvature of greater power is near the horizontal
meridian, between the meridians of 30° to 150°, so
that the corrector cylinder is between 60° to 120°. This
astigmatism generates an increased depth of focus,
improving near vision26. Due to this factor, 12 eyes of
group I and 10 eyes of group II received additional help
in near vision.
All patients in both groups achieved complete
independence from distance spectacles after surgery.
Independence from near spectacles was achieved by
91.4% of patients in group I and 61.7% in group II,
showing that a correct near VA can be maintained for
most tasks, while glasses are only needed to carry out
certain tasks.
In conclusion, the results obtained in our study
demonstrate that corneal ablation decreases presbyopia
symptoms and corrects distance refraction in a single
surgical procedure, thus offering patients greater
independence from glasses in their daily lives.
Studies with larger sample sizes and a longer
postoperative monitoring period are needed to assess
refractive stability over time.
Defocus curves are useful tools to evaluate visual
performance after refractive surgery.
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JOURNAL OF EMMETROPIA - VOL 7, JANUARY-MARCH
First author:
Marta Romero-Domínguez, MD
Hospital Universitario Quirónsalud,
Madrid, Spain.