Clinical results of arcuate incisions to correct astigmatism - Buzard.info

Clinical results of arcuate incisions
to correct astigmatism
Kurt A. Buzard, MD, Eduardo Laranjeira, MD,
Bradley R. Fundingsland, BS
ABSTRACT
Purpose: To evaluate the effectiveness of arcuate incisions for correcting congenital,
post-cataract, post-radial keratotomy, and post-trapezoidal keratotomy
astigmatism.
Setting: Buzard Eye Institute, Las Vegas, Nevada.
Methods: In this retrospective study, 46 eyes of 29 patients had arcuate incisions to
correct astigmatism. The average age of patients was 52 years.
Results: Mean preoperative astigmatism was 3.51 ± 1.57 D (keratometric) and 3.41 ±
1.44 D (manifest). Mean preoperative uncorrected visual acuity was 20/80, ranging
from 20/30 to 20/400. Thirty eyes had a pair of 45-degree arcuate incisions, 10 eyes
had a pair of 60-degree arcuate incisions, and 6 eyes had a pair of 90-degree
arcuate incisions. Mean follow-up was 6 months. Mean postoperative astigmatism
was 1.46 ± 1.07 D (keratometric) and 1.05 ± 0.94 D (manifest), with a reduction of
astigmatism in all operated eyes. Mean postoperative uncorrected visual acuity
was 20/32, ranging from 20/20 to 20/60. The analysis of the vector astigmatic
change showed that only two patients were overcorrected after the procedure.
Conclusion: The predictability and safety of arcuate incisions are reflected in these
results. J Cataract Refract Surg 1996; 22:1062-1069
The common view is that astigmatism can be easily
corrected with spectacles or contact lenses. However,
even when corrected by these devices, it may cause
off-axis blur, eye strain, glare, and visual field restriction.
Surgical correction of astigmatism has been attempted
since the last century. Transverse keratotomy
From the Buzard Eye Institute Las Vegas, Nevada (Buzard, Laranjeira,
Fundingsland), Hospital do Servidor Publico Estadual, Department of
Ophthalmology, %o Paulo, Brazil (Laranjeira), Department of Surgery-Division
of Ophthalmology, University of Nevada, Reno (Buzard),
and Department of Ophthalmology, Tulane University Medical Center,
New Orleans, Louisiana (Buzard).
The authors have no Proprietary or financial interests in any of the devices
described.
Reprint requests to Kurt Buzard, MD, 6020 Spring Mountain Road,
Las Vegas, Nevada 89102.
was suggested by Snellen 1in 1869. Lans2 and Sato3
investigated the concept of relaxing incisions. In the
1970s, Trutman and Swinger* introduced and popularized
the use of cornea1 relaxing incisions and corneal
wedge resection to correct postkeratoplasty astigmatism.
In 1982, Ruiz described trapezoidal keratotomy,5 which
was explored in a cadaver eye study performed by Lavery
and Lindstrom.’ This study indicated that a simple pair
of transverse incisions appeared to provide a considerable
percentage of the effect of the full Ruiz procedure.
Many authors7-‘* have described potential complications
of trapezoidal keratotomy, such as microperforations
and macroperforations, large postoperative axis
shifts, glare, overcorrections, and wound dehiscence.
The main disadvantage is the excessive number of incisions
in a limited area of the cornea, with subsequent
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XRCUATE INCISIONS FOR ASTIGMATISM
cornea1 instability. The same problem has been observed
with other modalities of astigmatic surgery, such as the
“I,” procedure’ ’ and the Binder” procedure.
Arcuate incisions have become popular as a means
of correcting moderate and large amounts of astigmatism.
Arcuate incisions were first performed to correct
astigmatism after penetrating keratoplasty. In 1985,
Tchah et al.‘” ’introduced the bowrie procedure, which
involves a four-incision radial keratotomy (RK) connected
at the limbus by two arcuate incisions straddling
the steep axis. This procedure was abandoned because of
wound healing problems and block lift in the area in
which the radial and arcuate incisions connect. The corneal
topographic changes induced by arcuate incisions
were first investigated in eye-bank eyes by Tripoli and
coauthors.14 The first systematic use of arcuate incisions
to correct congenital astigmatism was by Merlin, who
investigated incisions ranging from 100 to 160 degrees
and optical zones ranging from 5 to 7 mm. He found
progressive diminished effect as the optical zone was
shifted from 5 to 7 mm. The effect on spherical equivalent
was null for 100 degree incisions and produced
larger hyperopic effects as the incision length increased
to 160 degrees. Duffey et al.16 performed a cadaver eye
study to evaluate the effectiveness of arcuate incisions
and found that longer paired arcuate incisions produced
a predictable cornea1 flattening in the meridian centered
over the incisions and a smaller cornea1 steepening
90 degrees away, making the procedure ideal for mixed
astigmatism.
This study presents the clinical results of arcuate
incisions performed to correct congenital, post-cataract,
post-RK, and post-trapezoidal kcratotomy astigmatism,
using the Buzard nomogram.17,1x Few clinical studies of
the effectiveness and predictability of astigmatic surgery
have been published.‘9-2’ We describe a method that
uses shorter and more shallow incisions in the first procedurc.
This approach tends to avoid the serious problem
of overcorrection while allowing for additional
correction on follow-up visits, if necessary.
Subjects and Methods
Forty-six eyes of 23 patients (17 men and
I2 women) had arcuate incisions to correct astigmatism.
The surgeries were performed between October
1991 and November 1993. The average age of the patients
was 52 years (range 23 to 90 years). The patients
had four categories of astigmatism: congenital (28 eyes),
post-cataract (15 eyes), post-RK (2 eyes), and post-trapezoidal
keratotomy (1 eye). The mean time of astigmatic
surgery after cataract extraction was 12 months (range
3 to 36 months). The two cases of arcuate incisions after
RK and the only case after trapezoidal keratotomy were
performed 5 years after the original procedure.
All procedures were performed by one surgeon
(K.A.B.). Twenty-three were performed in the operating
room and the other 23, at the slitlamp. All enhancement
procedures were performed at the slitlamp. Keratometry,
photokeratometry, and computed cornea1 topography
were performed on all eyes at all preoperative and
postoperative visits.
Just prior to surgery, the eye was marked at the 12,
6,3, and 9 o’clock limbal positions with a skin marker or
needle to prevent surgical problems with eye torsion at
the time of the surgery. All cases were performed with
topical anesthesia (tetracaine). Pachymetry was done at
the locations contemplated for the incisions and the
knife was set at 80% of the thinnest reading. A locking
lid speculum was used to secure the lids, and an aximeter
was used for patient fixation. The steep axis was verified
by aligning a Mendez gauge with the previously placed
major marks. The arcuatc incisions were marked with
the specialized Buzard/Friedlander astigmatic arcuatc
markers after they were dipped in methylene blue. The
eye was stahilized using a ring fixation without teeth (a
Buzard/Thornton ring).
Two arcuatc incisions were performed at a 7.0 mm
optical zone in all cases. Thirty patients had a pair of
45-degree arcuate incisions, 10 had a pair of 60-degree
arcuate incisions, and 6 had a pair of 90-degree arcuate
incisions. All surgeries were planned using the Buzard
arcuate nomogram (Figure 1), placing incisions in the
steep axis. In cases of doubt between two incision
lengths, the smaller was chosen. The refraction was expressed
in plus cylinder and the surgery performed on
the plus cylinder axis. The incisions were made with a
front-cutting motion of the knife, using the vertical cutting
edge of the diamond. In cases of previous RK, the
incisions were “jumped” or placed between the radial
incisions. A Thornton 15-degree trifaceted diamond
knife was used to perform the incisions. A disposable
contact lens was placed on the eye after the procedure
and removed that night by the patient. Postoperatively,

ARCUATE INCISIONS FOR ASTIGMATISM
AGE
DEGREE
OF ARC
I
; 1gj .~~~~I~~~~,~!~,,
Figure 1.
(Buzard) Buzard nomogram for arcuate incisions at a 7.0 mm optical zone.
the patient used antibiotic-steroid drops four times a
day and artificial tears every hour while awake.
Postoperatively, the undercorrecred eyes were
treated by making the incisions deeper and/or longer
with enhancement surgery. Twenty-three eyes (50%)
had enhancement procedures: 9 had one, 9 had two, and
5 had three. The number of reoperations was higher
with longer arcuate incisions. Twelve eyes (40%) with
45-degree atcuate incisions and 6 (60%) with 60-
degree arcuate incisions had enhancements, but 5 of
the 6 eyes (83%) with 9O-degree atcuate incisions had
reoperations.
Results
Mean follow-up after surgery was 6 months (range
2 to 24 months). There was a reduction of both keratometric
and manifest astigmatism in all eyes. The mean
preoperative keratometric astigmatism was 3.5 1 ±
1.57 diopters (D) (range 1.37 to 8.75 D) and the mean
manifest astigmatism, 3.41 ± 1.44 D (range 1.25 to
7.75 D). Before enhancement surgery, the mean postoperative
keratometric astigmatism was 1.91 ± 1.60 D
(range 0.37 to 9.50 D) and the mean postoperative manifest
astigmatism, 1.30 ± 1 .OO D (range 0.00 to 5.50 D).
After enhancement surgery, the mean postoperative
keratometric astigmatism was 1.46 ± 1.07 D (range
0.37 to 6.87 D) (Figure 2) and the mean postoperative
manifest astigmatism, 1.05 ± 0.94 D (range 0.00 to
3.00 D) (Figure 3).
Analysis of the change in astigmatism achieved by
the incisions shows that more astigmatism is corrected
with longer incisions. At last follow-up, the mean
change in keratometric astigmatism for the 45-, 60-, and
90-degree arcuate incisions was 1.66 ± 0.64 D, 2.69 ±
1.24 D, and 2.83 ± 1.04 D, respectively.
0
0 2 4 6 8 10
Preoperative Keratometric Astigmatism (D)
--
Figure 2. (Buzard) Preoperative and postoperative keratometric
astigmatism.
The mean difference between preoperative and final
postoperative keratometric axis was 12.3 ± 16.6 degrees
(Figure 4), and the mean difference between preoperative
and final postoperative manifest axis, 10.7 ±
9.38 degrees [Figure 5). Two patients had axis changes
greater than 25 degrees: one had an axis shift of 5 1 keratometric
degrees and 50 manifest degrees after a pair of
9O-degree arcuate incisions; the other had an axis shift of
105 degrees (keratometric and manifest) after a pair of
GO-degree arcuate incisions. Analysis of the vector astigmatic
change (Figure 6) shows that these two patients
(4%) were the only cases of overcorrection in this series.
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ARCUATE INCISIONS FOR ASTIGMATISM
200
9
g8
0
0 I 2 3 4 5 6 7 8 9 10
Preoperative Manifest Astigmatism (D)
0
0 50 100 150 200
Preoperative Manifest Axis (degrees)
Figure 3.
astigmatism.
(Buzard) Preoperative and postoperative manifest
Figure 5.
(Buzard) Preoperative and postoperative manifest
I-
-
0 50 100 150 200
Preoperative Keratometric Axis (degrees)
-
0 2 4 6 8 10
Preoperative Keratometric Astigmatism (D)
(Buzard) Preoperative and postoperative keratomet-
Figure 4.
ric axis.
Figure 6. (Buzard) Vector astigmatic change. The patients to
the right of the dark line are undercorrected and the patients to the
left of the dark line are overcorrected.
Vector astigmatic change was analyzed using the Holladay/Gravy/Koch
formula.22 Roth cases were complicated
by problems of wound dehiscence.
The average uncorrected visual acuity at last follow-up
was 20/32 (range 20/20 to 20/60) (Figure 7).
Postoperatively before enhancement surgery, 3 1 eyes
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ARCUATF, INCISIONS FOR ASTIGMATISM
0
0 0.2 0.4 0.6 0.8 I 1.2
Preoperative Uncorrected Visual Acuity
-6
-6 -4 -2 0 2 4 6
Preoperative Spherical Equivalent (D)
J
Figure 7. (Buzard) Preoperative and postoperative uncorrected
visual acuity. The results are expressed in decimals to
facilitate the confection of the graph.
Figure 8.
equivalent.
(Buzard) Preoperative and postoperative spherical
(67%) had 20/40 or better acuity. At last follow-up after
enhancements, 35 (76%) had 20/40 or better. None of
the eyes had a decrease of uncorrected visual acuity after
surgery. The best corrected visual acuity remained the
same or improved in all eyes.
The mean preoperative spherical equivalent was
-0.09 ± 1.60 D (range -2.50 to +4.25 D) and the
mean postoperative spherical equivalent at last followup,
-0.27 ± 1.30 D (range -3.00 to +2.50 D) (Figure
8). The mean preoperative keratometrywas 43.65 ±
1.60 D (range 38.18 to 47.43 D) and the mean keratometry
after surgery, 43.75 ± 1.80 D (range 38.31 to
47.93 D) (Figure 9). The mean ratio of corneal flattening
in the steep meridian to steepening in the flat meridian
(F/S ratio) was 0.97 ± 0.9 (range 0.16 to 3.84).
With 45-degree arcuate incisions the ratio was 1.05 ±
0.8. With 60- and 9O-degree arcuate incisions, the
F/S ratio was 0.81 ± 0.4 and 0.70 ± 0.3, respectively.
Three patients had steepening of both steep and flat
meridians, and three other patients had flattening of
both meridians.
Two cases of wound dehiscence were observed.
These patients were treated by suturing the wound
with 11-O polyester fiber (Mersilene@) interrupted
sutures. Final outcome data on these cases are
presented after suture correction. We had no other
complications such as microperforations and macroperforations,
infection, or vascularization of the
incisions.
Discussion
Astigmatism represents a refractive error that should
be analyzed separately from myopia and hyperopia.
Ruzard and coauthors” have demonstrated that manifest
refraction often underestimates true keratometric
astigmatism. In a related study, Lakshminarayanan et
aL2* found that a tilted or displaced intraocular lens
induced a maximum astigmatism of 0.50 D. These studies
support our opinion that most astigmatism in the
human optical system resides in the cornea and that,
therefore, astigmatic surgery should bc based on keratometry,
computed cornea1 topography, or both, instead
of on manifest refraction, In cases in which there is a
significant difference between manifest and keratometric
astigmatism, it is often better to avoid the surgery,
which may lead to a complex cross-cylinder effect, creating
an astigmatic error at an entirely new axis. 17
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ARCUATE INCISIONS FOR ASTIGMATISM
I
Figure g.
keratometty.
36
36 38 40 42 44 46 48 50
Preoperative Mean Keratometry (D)
(Buzard) Preoperative and postoperative mean
Astigmatic surgery is distinguished from RK in
many ways. In RK, the length of the incisions and optical
zone are linked (i.e., the longer the incision, the
smaller the optical zone), making nomograms very similar.
In astigmatic keratotomy, incision length and optical
zone are unlinked, resulting in many different
nomograms to correct similar amounts of astigmatism.
In a recent article 14 experts were asked to give their
opinion about correcting astigmatism after cataract surgery.
Each proposed a different approach, including
transverse incisions, wedge resection, and resuturing the
wound.
Arcuate incisions have the potential for greater effect
because the chord length is the same as straight
transverse incisions, but the actual length is about 10%
longer on the curve.” Moreover, the length of the incision
is equidistant from the center of the cornea, cutting
through tissue of approximately equal thickness.5’17 Arcuate
incisions are, however, more difficult to perform.
To avoid irregularities, the incision must be performed
slowly and with a continuous movement, following the
curved marks. Hanna et a1.27 have developed an arcuate
keratome for performing the incisions with a more uniform
and accurate depth. A multiple-puncture technique
has been proposed;l’ it consists of successively
deeper incisions to connect multiple punctures when
creating arcuate incisions.
Hanna and coauthors28 have found that at an optical
zone of 7.0 mm, arcuate transverse incisions show
maximal effect at 100 degrees. Because of the potential
for cornea1 instability and lack of additional effect, we do
not recommend performing arcuate incisions over
100 degrees in length. Another important issue is the
incision depth. We believe transverse incisions, whether
straight or atcuate, should aim for significantly less than
100% of the thinnest paracentral corneal thickness to
avoid the possibility of cornea1 instability, wound gape,
and overcorrection. In this study we aimed for 80%
depth, which could be deepened later if necessary. Finally,
the effect of astigmatic incisions is dependent on
age and increases 15% per decade according to the
Buzard nomogram and 0.36 D per decade according to
Price et aL2’ One wound dehiscence case in this series
consisted of a 7O-year-old man with post-cataract astigmatism.
He had a pair of 90-degree arcuate incisions and
had an axis shift of 50 degrees, with wound dehiscence,
which was corrected in the postoperative period with
suturing. Although pilocarpine has been discussed as
treatment for overcorrections associated with RK,30 it
has been observed to worsen astigmatic overcorrections.
Because of this case and the findings of the Buzard and
Price nomograms, we suggest arcuate incisions be limited
to 60 degrees in length in patients older than
60 years.
This conservative approach of short, shallow incisions,
followed by enhancement if necessary, showed
encouraging results and safety when compared with related
studies. A reduction in astigmatism was observed
in all operated eyes. The effectiveness of the procedure
was reflected through the achievement of 20/40 ot better
uncorrected visual acuity in 35 eyes (76%) at last
follow-up (Figure 7). In a study of 142 eyes, Price et a1.29
achieved a mean postoperative refractive cylinder of
1.22 ± 0.85 D, whereas we achieved 1.30 ± 1.00 D
before any enhancement surgery and 1.05 ± 0.94 D
after enhancements.
With this technique, the majority of patients
showed a tendency toward undercorrection. Undercorrection
can be managed by enhancing the original surgical
procedure-making the incisions deeper, longer,
or both-which can be performed at the slitlamp. These
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ARCUATE INCISIONS FOR ASTIGMATISM
enhancements differ from traditional reopcrations in
that no new incisions are made. This enhancement philosophy
follows that of the RK “tickle”13 in which incisions
are reopened or lengthened for postoperative
precision and to avoid overcorrections. Our results demonstrate
that the enhancement procedures correct an
additional 12% of keratometric astigmatism and an additional
7% of manifest astigmatism without additional
complications.
Overcorrection is a much more serious problem. It
leads to diminished best corrected vision, glare, diurnal
variation, and wound dchisccnce. A new set of incisions
in the opposing axis must be made to correct significant
overcorrections. Analysis of the vector astigmatic change
in this study revealed two patients (4%) with overcorrections
(Figure 6). The overcorrections were due to the
two large axis shifts of 50 and 105 degrees, complicated
by wound dehiscence problems. This 4% incidence is
lower than the 18% reported by Price et a1.29 and 19%
reported by Neumann and coauthors.“z In addition, the
mean coupling ratio of 0.97 (F/S) demonstrates less flattening
than the 1.47 ratio reported by Duffey et al.,33
the 1.0 reported by Merlin,15 and the 2.0 reported by
Lundergan and Rowsey.“*
Arcuate incisions couple in a more unpredictable manner,
preserving spherical equivalent in some cases and making
the patient more myopic or hyperopic in other cases
(Figures 8 and 9). At a 7.0 optical zone with longer arcuate
incisions (60 and 90 degrees), there is a tendency to make
the cornea slightly steeper, which is supported by coupling
ratio data in this and other studies. 28S34 For this reason, we
recommend that astigmatic corrections larger rhan 3.00 D
be performed prior to RK to determine the actual spherical
correction needed after astigmatic surgery.
In summary, arcuatc incisions may be an effective
treatment of astigmatic patients who do not have satisfactory
results with spectacles or contact lenses. A conservative
approach, making the incisions shallow and short, and
deepening or extended later, eliminates a large amount of
corneal astigmatism and tends to avoid the number of overcorrections
observed with other techniques.
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