Post-keratoplasty astigmatism management by relaxing incisions: a systematic review
Ho Wang Yin and Hoffart Eye and Vision
Post-keratoplasty astigmatism management by relaxing incisions: a systematic review
Gaëlle Ho Wang Yin 0 1 2 3 4
Louis Hoffart 1 4 5
0 Institut Fresnel UMR 7249, Aix Marseille Université , CNRS, Centrale Marseille, Domaine universitaire de Saint-Jérôme Avenue Escadrille Normandie Niemen, 13397 Marseille cedex 20 , France
1 Ophthalmology Department, Aix-Marseille University - APHM, Hôpital de la Timone , 264 rue Saint Pierre, 13 385 Marseille Cedex 5 , France
2 CERIMED, Aix-Marseille University
3 7 Boulevard Jean-Moulin , 13385 Marseille cedex 05 , France
4 Ophthalmology Department, Aix-Marseille University - APHM, Hôpital de la Timone , 264 rue Saint Pierre, 13 385 Marseille Cedex 5 , France
5 Ramsay Générale de Santé, Clinique Monticelli-Velodrome , Marseille , France
Postoperative visual acuity can be limited by post-keratoplasty astigmatism, even with a clear corneal graft. Astigmatism management can be performed by selective suture removal, adjustment of sutures, optical correction, photorefractive procedures, wedge resection, intra-ocular lens implantation, intracorneal ring segments, relaxing incisions with or without compression sutures and repeated keratoplasty. Relaxing incisions can be made in the graft, graft-host interface or host cornea. Despite the unpredictability of the method because the flat and steep meridians are usually not orthogonal after penetrating keratoplasty, with asymmetric power distribution, all the studies showed an overall reduction of refractive, keratometric or topographic astigmatism, ranging from 30% to 72% with manual or femtosecond-assisted techniques. Most patients with astigmatism higher than 6 diopters had residual cylinder less than or equal to 3 diopters, which can be treated by laser excimer ablation or secondary intraocular lens implantation.
Penetrating keratoplasty; Astigmatic keratotomy; Relaxing incisions; Femtosecond laser
The aim of penetrating keratoplasty (PK) is to improve a
patient’s postoperative vision. Despite a clear corneal
graft, visual acuity can be limited by astigmatism [
Based on several studies, 15-20% of patients may
develop 5 or more diopters (D) of post-keratoplasty
Post-keratoplasty astigmatism management can be
done before or after suture removal. If done before, it is
called suture-in post-keratoplasty astigmatism. In this
case, topography-guided suture manipulation, including
selective suture removal [
] guided by corneal
], or adjustment of sutures along the steep
meridian of astigmatism or adjustment of running
sutures are key factors for controlling astigmatism.
After suture removal, post-keratoplasty astigmatism
can be managed by optical correction such as contact
lenses or glasses [
], which can be compromised by
irregular astigmatism associated with high-order
]. Other astigmatism managements include
incisional keratotomy in the graft [
] or host cornea
, and photorefractive procedures such as
photorefractive keratectomy (PRK), laser in situ keratomileusis
(LASIK) or topography-guided excimer laser ablation
], compression sutures and a combination of
relaxing incisions and compression sutures (augmented
relaxing incisions) [
]. Wedge resection ,
intraocular lens (IOL) implantation [
] or intra-corneal ring
segments (ICRS) [
] can also be considered. As a last
resort, repeated keratoplasty [
] may be necessary.
The purpose of this review is to provide surgeon
updated information about post-keratoplasty
astigmatism management with arcuate keratotomy and to help
define a strategy for the correction of this
postkeratoplasty astigmatism. Questions we intend to answer
were: Is femtosecond laser-assisted relaxing incision
better than conventional relaxing incision for the
management of post-penetrating keratoplasty astigmatism?
Which nomogram and which length and depth should
we use for the correction?
A review on PubMed and Cochrane was performed,
analyzing all the publications from 1986 to 2017, concerning
the topic of post-keratoplasty astigmatism management
with keratotomies (keywords: arcuate keratotomy,
astigmatic keratotomy, penetrating keratoplasty,
postkeratoplasty astigmatism). Clinical trials, systematic
review, non-randomized prospective study and case
series of more than 6 patients, published in an English
language journal with an impact factor greater than or
equal to 2.0 were reviewed.
The corneal graft-host junction generally heals by 1 year
after transplantation and corneal surface stability is
generally achieved by 3 to 4 months after complete
suture removal [
]. Before any surgical astigmatism
management, a complete ophthalmologic examination
including manifest and objective refraction, keratometry,
and slit biomicroscopy should be performed to evaluate
the graft-host interface and clarity of the graft, corneal
topography, pachymetry, specular microscopy and
Etiology of astigmatism
Factors influencing post-penetrating keratoplasty
astigmatism involve the donor tissue and the host.
Infant donor corneas induce greater astigmatism than
adult donor tissues [
]. Non-uniform peripheral
changes in the donor tissue can affect the apposition
and healing between the host and donor tissue [
The severity of the underlying disorder (such as
keratoconus, keratoglobus or pellucid marginal
] also plays a role in post-penetrating
During surgery, trephination (oval or eccentric) [
graft size (large graft diameters induce less astigmatism
but are associated with a high risk for vascularization
and allograft rejection, small grafts are associated with
larger amounts of astigmatism) [
]; corneal thickness
and donor-recipient disparity [
]; a poor suturing
technique (single or double running sutures, interrupted
sutures, all 3 techniques are comparable) [
] are factors
involved in post-keratoplasty astigmatism. Time of
suture removal or adjustment [
] is also important.
Post-operative drugs, inflammation, corneal
vascularization, rejection and wound dehiscence
affect wound healing and may be associated with
Principles of relaxing incisions
Relaxing incisions can be made for patients with
keratometric astigmatism, 3 to 4 months after complete suture
]. The main principle of relaxing incisions is
to flatten the steep corneal meridian by one or two
incisions perpendicular to it. This flattens the steepest
meridian with reciprocal steepening of the meridian 90°
away, this effect is known as “coupling effect” [
length is related to the coupling ratio: a coupling ratio of
close to 1.0 is obtained with 30–90° incisions, which
should not change the resulting spherical equivalent.
Incisions less than 20° arc length have a coupling ratio
greater than 1.0 while those greater than 100° have a
coupling ratio less than 1.0. Relaxing incisions are made
under topical anesthesia, on both sides of the steepest
meridian, usually, with an arc length of 45° to 90°, and
can be done in the 7.0 mm optical zone for maximal
effect. The site and length are topography-guided [
arcuate incisions, each incision is at the same distance
from the visual axis to avoid uneven distribution of the
force on the corneal architecture and allows rapid visual
rehabilitation. Arcuate keratotomy can be made with or
without 10-0 nylon compression sutures, these are
added to achieve overcorrection of astigmatism in the
opposite meridian (90° away). Selective suture removal is
initiated 3 to 4 weeks later.
The site of arcuate keratotomy can either be in the
donor cornea or at the graft-host interface, or in the host
]. Incisions in the recipient corneas are not
recommended as it is believed that the scarring at the
graft-host junction changes the biomechanical state of
the cornea. The keratoplasty wound is supposed to form
a new limbus, blocking the effect of relaxing incisions in
the recipient cornea [
Relaxing incisions can be made manually (freehand with
a diamond knife [
] or mechanized with Hanna arcitome
]) or with femtosecond laser technology [
The optical zone, arc length and depth are determined
using nomograms. The effect of astigmatic correction
with astigmatic keratotomy increases with greater
incision depth, more central placement of the incisions,
increasing patient age [
] and longer arc length.
Nomograms used on patients with congenital
astigmatisms, such as the Lindstrom nomogram [
] do not
apply to post-penetrating keratoplasty patients. The
astigmatic effect of the incision is proportional to the
preoperative cylinder [
]. Typically, post-penetrating
keratoplasty arcuate keratotomy is made to a depth of
75% corneal thickness, and incisions are made at an
optical zone 1.0 mm central to the graft-host junction.
The Hanna nomogram is one of the most widely used
]. It is based on refractive astigmatism,
from 2.50 D to 15 D. The arcuate keratotomies are made
with an optical zone diameter ranging from 6.00–
6.75 mm, with an incision depth of 75% of corneal
pachymetry and an angular length from 60 to 80°.
The Nordan nomogram [
] is used by surgeons to
create paired symmetric incisions, 75–85% depth of the
thinnest measurement of the graft, and centered on the
steepest meridian axis as follows:
1.75–2.5 D of cylinder with 50° arc length,
2.75–3.3 D of cylinder with 57° arc length,
3.75–4.5 D of cylinder with 60° arc length,
5 D of astigmatism with 70° arc length.
Another nomogram, for beveled incisions, was
described by Cleary et al. [
]. These incisions, made at
a 135° angle centered on the axis of the astigmatism,
allowed for the anterior cornea to slide forward,
decreasing wound gape. Moreover, the beveled incisions can be
made at a 65–75% depth rather than 90%, with a
reported comparable reduction in astigmatism versus
traditional femtosecond laser-assisted arcuate
keratotomy (FSAK) incisions. Arc length at 8.0 mm optical
zone ranges from 60° to 85°.
The most recent nomogram was developed by Saint-Clair
]. It is a new nomogram for femtosecond laser astigmatic
keratotomy for astigmatism after keratoplasty, considering a
variety of incision-related factors and the degree of
preexisting astigmatism. Incision depth, arc length and optical
zone diameter depend on the pre-operative difference
between the steepest and the flattest keratometry values.
Manual versus femtosecond laser-assisted arcuate
Astigmatic keratotomy can be performed manually using
a handheld, fixed or adjustable depth diamond knife, or
mechanized like the Hanna arcitome. The diamond
blade is adjusted according to the proper nomogram.
FSAK improve arc length, depth and location precision
compared with manual and mechanized incision [
]. The surgeon can adjust location, depth and
centration of the incision using the intraoperative OCT of the
femtosecond laser platform.
FSAK is also associated with a lower risk of wound
dehiscence, epithelial down growth, infection, and
perforation or full-thickness corneal incisions [
results are summarized further.
Intrastromal astigmatic keratotomy
Intrastromal astigmatic keratotomy (ISAK) was
introduced for the treatment of low astigmatism. These
incisions are not opened anteriorly, decreasing the risk of
epithelial disruption, infection or wound dehiscence.
ISAK was successful for naturally occurring and
postcataract surgery astigmatism [
] and residual
astigmatism after refractive surgery [
Viswanathan & Kumar [
] treated a young
keratoconic patient with over 11 D of astigmatism in both eyes
after suture removal from bilateral penetrating
keratoplasties. Paired ISAK with a depth of 90%, 60 μm
anteriorly at a 90° side cut was made. At 4 months follow-up,
keratometric astigmatism was 4.1 D in the right eye and
1.12 D in the left eye, with a corresponding reduction of
65.5% and 89.42%, respectively.
Wetterstrand et al. [
] reported the results of
intrastromal relaxing incisions after penetrating keratoplasty of
16 patients. The incisions were made intra-stromally with a
length of 90°, depth of 90% of corneal thickness, diameter
zone of 6.0–7.0 mm, and a safe zone of 90 μm anteriorly.
Refractive cylinders decreased from 6.8 ± 2.2 D to 3.7 ± 1.7
D at 3 months follow-up, with only one bulge in the
temporal incision of one patient, treated with compression
suture. No other adverse effect was found. This technique
seems to be relatively safe and effective.
Loriaut et al. [
] described a novel technique,
combining deep ISAK performed under a LASIK flap, for the
treatment of high natural occurring and
postkeratoplasty astigmatism: deep intrastromal arcuate
keratotomy with in situ keratomileusis (DIAKIK).
The first step is ISAK made at a depth of 75% in eyes
with penetrating keratoplasty. A LASIK flap of 100 μm
was then made, lifted and ISAK were opened and the
flap replaced. Laser excimer ablation can be made
1 month after for the correction of residual ametropia,
after reopening of the flap.
This technique was performed in 9 patients. The mean
preoperative refractive cylinder was 6.11 ± 2.54 D, and
the post-operative cylinder was 2.85 ± 1.31 D. No
complications were reported. This technique affords
advantages of ISAK with a greater astigmatism correction, but
there are potential complications of the LASIK itself.
Main results are summarized in Table 1.
Arcuate keratotomy can be useful as it creates minimal
surface disruption, can treat nonorthogonal astigmatism,
and yields rapid visual recovery. This technique ensures
an optical zone of constant diameter and homogeneity
of depth over the entire length of the incision. Typically,
post-PK keratotomies are done to a depth of 75% to 80%
corneal thickness, and incisions are made at an optical
zone 1.0 mm central to the graft-host junction.
Three different incision locations were described: graft,
graft-host interface or host cornea. Refractive or
keratometric pre-operative cylinder was between 11 D and 6.1
D, and an overall reduction ranging from 30 to 72% was
8.8 ± 3.1
6.94 ± 2.11
9.02 ± 2.67
8.7 ± 2.4
8.84 ± 3
Depth = 50% to 66% CCT
Length = 60°
Depth and length variable
Manual relaxing incision
Depth = central corneal thickness
Length = 45°; 5 or 6 mm
from optical zone
Manual paired relaxing incision
Depth = 75% CCT
Length = not available
0.5 mm inside the
Manual paired relaxing
incision with Hanna arcitome
Depth = 75% thinnest pachymetry
Length = 60° to 80°
6 to 6.75 mm zone diameter
(Hanna nomogram [
Manual relaxing incision and
Depth = 480 μm
Length = 45°
Manual relaxing incision
Depth = 600 μm
Length = 60°; 6 mm from
Manual relaxing incision
Depth = 80% of peripheral
Length = 30° to 90°
9 to 10 mm zone diameter
Nonrandomized Manual relaxing incision
retrospective observational Depth = 80% of the thinnest
case series pachymetry on the meridian
Length = 35° to 90°
0.5 mm or 1 mm inside the
graft-host junction if >10 D
Hoffart et al., 2009 [
FS or Hanna arcitome
Depth = 75% thinnest pachymetry
Refractive (R) or
keratometric (K) cylinder
Graft-host 10.11 (K)
Graft or 6.18 ± 1.56
Graft-host 9.69 ± 3.51 (R) 3.92 ± 2.16
9.14 ± 4.38 (K) 3.59 ± 1.92
10.99 ± 4.26
3.33 ± 2.18
3.34 ± 1.96
3.2 ± 3.0
3.85 ± 1.95
3.94 ± 2.19 (K) 56 (K)
observed, with manual or femtosecond-assisted
techniques. Most of the patients with astigmatism higher
than 6 D had residual cylinder less or equal to 3 D,
which can be treated by laser excimer ablation, or
secondary IOL implantation.
In the reported studies, manual keratotomy seems
to have more complications (in particular wound
dehiscence) and poorer predictability than FSAK.
However, all studies had a high variability in
outcomes despite the use of a standardized method of
surgery. The unpredictability seems to be correlated
with many variables such as the value of the initial
cylinder, individual variability, alignment.
Individual variability responsible for limited
predictability is related to the variability in the distribution of
compressive forces and biomechanical constraints in the
corneal graft. Therefore, arcuate keratotomy after PK
necessitates its own nomogram, as the fibrotic rim
created at the graft-host junction has a different tension
than the natural limbus.
Under-correction and inter-individual variability can
be due to misalignment. This could be addressed by
preoperative limbal marking but the direct visualization
of the limbus can be masked by the suction ring during
the procedure. Also, a control of cyclotorsion can be
useful in this case. Femtosecond provides more depth
accuracy than manual keratotomy as we have a
preoperative view of the cornea thickness thanks to the
Unsuccessful correction and overcorrection can be
explained by the pattern of irregular astigmatism (the
flat and steep meridians are usually not orthogonal, with
asymmetric power distribution), which leads to
unpredictable correction. Some authors hypothesized that
using topography-guided placement of relaxing incision
can produce more predictable results, as shown by
vector analysis using Alpin’s methods [
39, 50, 51
Unpredictability can also be explained by the inherent
dynamic instability of such incisions over time.
It is possible that a smaller arc length would achieve
the intended effect on astigmatism or increasing the
angular length and reducing the optical zone diameter of
the incisions as Wilkins et al. [
A refinement in the treatment nomogram for
femtosecond laser-assisted AK for high astigmatism
after PK remains a major issue. Further prospective
studies with different length, depth and width
correlated with the pre-operative cylinder and optical zone
should be performed to define a new nomogram with
a higher predictability.
Manual procedures have some disadvantages: poor
predictability, overcorrection, corneal perforation, wound
dehiscence, and instability of corneal topography [
manual procedures, depth is usually set to 75–85%
depth of central corneal thickness (CCT), but
preoperative visualization of the corneal thickness is not
possible thereby increasing the risk of perforation and
overcorrection due to deep incisions. Deep incisions are
also associated with wound dehiscence. The suture of
the keratotomy can reduce dehiscence and
overcorrection, and can be used to treat micro-perforation. Poor
predictability with manual procedures is due to the
absence of standardized nomograms correlating the
amount of keratometric astigmatism with the extension
of the incisions. Nomogram for congenital astigmatism
cannot be applied for post-PK astigmatism [
newer and more precise nomogram should be studied.
FSAK is safer and more predictable than manual
procedures, but complications have also been described
(Table 1). Overcorrection or wound gaping can be
managed with compressive sutures. Infections are rare but
possible, keratitis and one case of endophthalmitis have
been reported. Topical post-operative antibioprophylaxis
should be sufficient [
]. Graft rejections have also been
reported, but topical corticosteroid for 1 month after the
surgery can be administered. Corneal perforation can
occur, even with per-operative OCT [
], but it is a very
No standard surgical procedure for performing arcuate
keratotomies for post-penetrating keratoplasties
astigmatism exists, due to its unpredictability. However, all the
studies show that patients with astigmatism higher than
6 D had residual cylinder less than or equal to 3 D,
which can be further treated by laser excimer ablation or
secondary IOL implantation.
Availability of data and materials
Data sharing is not applicable to this article as no datasets were generated
or analyzed during the current study.
LH and GH made substantial contributions to conception and design, and
interpretation of data of the review; have been involved in drafting the
manuscript or revising it critically for important intellectual content. All the
authors gave final approval of the version to be published.
Ethics approval and consent to participate
Consent for publication
The authors declare that they have no competing interests.
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