Download Lamellar corneal surgery in 2016

with
Prof Charles McGhee
& A/Prof Dipika Patel
Series Editors
Lamellar corneal
surgery in 2016
MOHAMMED ZIAEI*, DIPIKA PATEL, CHARLES MCGHEE
Introduction
Full-thickness corneal transplantation is an
operation that deals with a wide variety of corneal
pathologies, but the procedure has not changed
significantly since Eduard Zirm successfully
performed the first penetrating keratoplasty (PK)
over a century ago. Lamellar keratoplasty revolves
around the concept of targeted replacement
of diseased corneal tissue and techniques have
evolved at an astonishing speed over the past 15
years. This article reviews some of the most recent
developments in this field.
Overview of lamellar surgery
Lamellar surgery includes anterior lamellar
keratoplasty (ALK) in which stromal tissue is
selectively replaced, and endothelial keratoplasty
(EK) which aims to replace damaged endothelial
tissue (Fig 1.).
Anterior lamellar keratoplasty
ALK has undergone a renaissance with the
dissemination of several new techniques since
Arthur von Hippel performed the first successful
anterior lamellar graft in 1886. This operation is
the procedure of choice for a variety of corneal
stromal disorders where the endothelium is
healthy such as ectasia, stromal dystrophies and
anterior stromal opacities. The modern version of
this surgery, deep anterior lamellar keratoplasty
(DALK), involves complete or near complete
removal of diseased stromal tissue and perhaps
the two most widely adopted techniques are
Anwar’s “Big Bubble” technique (Descemetic
DALK), and Melles’s “Closed manual dissection”
technique (pre-Descemetic DALK).
The major advantage of DALK surgery results
from the retention of healthy native endothelium
thereby eliminating endothelial allograft rejection,
although epithelial and stromal rejection are still
possible. Other advantages include a reduced
need for topical steroids (15% vs 75% still on
topical steroids after 12 months) and potential
for earlier suture removal. Several studies have
also shown that the visual quality with this form
of keratoplasty is comparable to that of PK. The
DALK procedure is also thought to be more cost
effective when compared to full thickness corneal
transplantation and reported to result in lower
endothelial cell loss 1-3.
In a recent meta-analysis whilst the proportion
of patients achieving best corrected visual acuity
≥ 6/12 did not differ statistically between DALK
and PK, the uncorrected and best corrected visual
acuity levels were significantly better for PK. The
DALK group however had a significantly lower
frequency of graft rejection than the PK group 3.
It is worthwhile noting that refractive error is a
significant barrier to functional vision with one
long term study reporting a mean refractive error of
-6.5 ± 1.7 D after pre-Descemetic DALK and -6.1 ± 1.8
D after Descemetic DALK4.
DALK does however have a steep learning curve
and is technically more challenging to perform
than PK. It is associated with unique potential
complications such as Descemet’s membrane
perforation, double anterior chamber (separation of
the donor stroma tissue from the host Descemet’s
membrane) and interface related issues. There are
also some challenges associated with performing
lamellar surgery in patients with a history of acute
corneal hydrops, in individuals with a pre-existing
split in Descemet’s membrane and patients with
advanced ectasia.
DALK makes up only 7% of corneal transplants
performed in New Zealand in 2015 (unpublished
data). This may reflect local population factors
such as advanced ectasia or late presentation of
patients. The low uptake of DALK could also be
due to the fact that whilst DALK has a number of
theoretical advantages over PK, long-term survival
of DALK performed for keratoconus has been
shown to be inferior to that of penetrating grafts in
the recent Australian graft registry study.
There have been some recent innovations in the
field of anterior lamellar keratoplasty. One novel
technique is that of femtosecond laser-assisted
anterior lamellar keratoplasty (FALK) in which
the depth of the recipient corneal pathology is
measured using anterior segment OCT (AS-OCT).
Subsequently the femtosecond laser is used to
create the lamellar cut in the recipient and donor
corneas and this depth can be adjusted based on
the extent of the corneal pathology. The recipient’s
scarred corneal tissue is then removed and replaced
with the healthy donor lenticule. The lenticule
can then be sutured into place or even retained by
applying a contact lens in a “sutureless” procedure.
Endothelial keratoplasty (EK)
Charles Tillet performed the first known successful
EK case in 1956 to treat corneal oedema. EK has since
transformed beyond recognition and is now the
procedure of choice for a variety of corneal endothelial
disorders such as Fuchs’ endothelial corneal dystrophy
and pseudophakic bullous keratopathy.
The two most widely adopted techniques are
Descemet stripping automated endothelial
keratoplasty (DSAEK) in which the Descemet’s
membrane endothelial complex is transplanted
Fig 1. Different types of keratoplasties (9).
(A) Penetrating keratoplasty. (B) Anterior lamellar keratoplasty. (C) Endothelial keratoplasty
22
NEW ZEALAND OPTICS October 2016
Fig 2. Anterior segment Optical Coherence Tomography (OCT) images of two patients who have undergone DSAEK.
Note that the graft is fully attached in the top image and partially detached (arrow) in the bottom image.
Fig 3. Anterior segment Optical Coherence Tomography (OCT) image of a patient following DMEK.
Note the focal area of donor detachment nasally (arrow).
with a sheet of stroma and Descemet’s membrane
(Fig 2.), and Descemet’s membrane endothelial
keratoplasty (DMEK) in which the Descemet’s
membrane endothelial complex is transplanted
in isolation and attached in a sutureless method
through air tamponade (Fig 3.).
Endothelial keratoplasty has replaced penetrating
keratoplasty as the preferred technique for treating
endothelial disease in the developed world, as
it offers numerous advantages compared to PK.
The most striking advantages of EK include the
predictability and rapidity of visual rehabilitation
associated with lower surgically-induced
astigmatism. These advantages have driven the
uptake of this technique. EK has also been shown
to be more cost effective than PK as it is associated
with fewer rejection episodes and requires less
intensive patient follow-up. Other advantages of EK
include the reduced need for topical corticosteroids
and a tectonically stronger eye.
In one large single centre study 50% of patients
reached a best corrected visual acuity of Snellen
6/12 or better, by four months following DMEK,
18 months following DSAEK, and more than 24
months following PK. A best-corrected visual
acuity of Snellen 6/7.5 or better at 24 months
postoperatively was reached in 53% after DMEK,
15% after DSAEK, and 10% after PK 6. However, in
another large study, 6/12 was achieved in 60.7% of
patients following DSAEK at three months, 71.0%
at six months, and 85.4% at 12 months7.
Disadvantages of EK include the technically
challenging nature of surgery, the need for special
instrumentation and its association with unique
potential complications such as graft dislocations
requiring re-bubbling (re-injection of air into the
anterior chamber), and interface related issues.
There are also some challenges with performing
EK in patients with a history of prolonged
endothelial dysfunction in which the stroma has
become scarred and in the presence of other ocular
co-pathology such as iris defects, aphakia and in
patients with a glaucoma drainage device.
EK is now the gold standard procedure for
endothelial disease comprising 31% of corneal
transplants performed in New Zealand in 2015
(unpublished data). However, whilst there are
a number of theoretical advantages over PK,
long term survival of EK performed for Fuchs’
endothelial dystrophy has been shown to be
inferior to that of penetrating grafts in the recent
Australian graft registry study5.
This has fuelled the interest in minimally
invasive procedures such as cultured human
corneal endothelial cell transplantation either
as a monolayer or by injection of cells into the
anterior chamber. Indeed we may soon see the
widespread use of medical therapy in patients
where topical treatment with Rho-associated
kinase (ROCK) inhibitors, a molecule that enhances
corneal endothelial survival, promotes cellular
proliferation, and has the potential to inhibit and
even reverse endothelial cell dysfunction8.
Conclusion
Penetrating keratoplasty has long been the standard
of care for treating eyes with corneal disease with
up to 95% long term success in keratoconus but
nonetheless, significant shortcomings. Noteworthy
barriers towards functional success include
prolonged refractive instability and high irregular
astigmatism. Advances in surgical instrumentation
and technique are improving keratoplasty outcomes
and it is widely believed that selective lamellar
keratoplasty is the future of corneal transplantation.
Advantages of lamellar surgery include a safer
surgical procedure, quicker visual recovery, less need
for topical steroids and a tectonically stronger eye.
However, there needs to be further innovation and
refining of current surgical techniques to improve
survival rates and long-term outcomes of lamellar
grafts. Until such time there will likely remain a
place for penetrating keratoplasty. ▀
References
1. Koo TS, Finkelstein E, Tan D, Mehta JS. Incremental costutility analysis of deep anterior lamellar keratoplasty
compared with penetrating keratoplasty for the treatment
of keratoconus. Am J Ophthalmol. 2011;152(1):40-7 e2.
2. Keane M, Coster D, Ziaei M, Williams K. Deep anterior
lamellar keratoplasty versus penetrating keratoplasty
for treating keratoconus. Cochrane Database Syst Rev.
2014;7:CD009700.
3. Chen G, Tzekov R, Li W, Jiang F, Mao S, Tong Y. Deep
Anterior Lamellar Keratoplasty Versus Penetrating
Keratoplasty: A Meta-Analysis of Randomized Controlled
Trials. Cornea. 2016;35(2):169-74.
4. Huang T, Hu Y, Gui M, Hou C, Zhang H. Comparison of
refractive outcomes in three corneal transplantation
techniques for keratoconus. Graefes Arch Clin Exp
Ophthalmol. 2015;253(11):1947-53.
5. Coster DJ, Lowe MT, Keane MC, Williams KA, Australian
Corneal Graft Registry C. A comparison of lamellar and
penetrating keratoplasty outcomes: a registry study.
Ophthalmology. 2014;121(5):979-87.
6. Heinzelmann S, Bohringer D, Eberwein P, Reinhard T,
Maier P. Outcomes of Descemet membrane endothelial
keratoplasty, Descemet stripping automated endothelial
keratoplasty and penetrating keratoplasty from a
single centre study. Graefes Arch Clin Exp Ophthalmol.
2016;254(3):515-22.
7. Khor WB, Han SB, Mehta JS, Tan DT. Descemet stripping
automated endothelial keratoplasty with a donor
insertion device: clinical results and complications in 100
eyes. Am J Ophthalmol. 2013;156(4):773-9.
8. Nakagawa H, Koizumi N, Okumura N, Suganami H,
Kinoshita S. Morphological Changes of Human Corneal
Endothelial Cells after Rho-Associated Kinase Inhibitor Eye
Drop (Ripasudil) Administration: A Prospective Open-Label
Clinical Study. PLoS One. 2015;10(9):e0136802.
9. Tan DT, Dart JK, Holland EJ, Kinoshita S. Corneal
transplantation. Lancet. 2012;379(9827):1749-61.
About the author
* Dr Mohammed Ziaei
completed his ophthalmic
training at Moorfields
Eye Hospital in London
and is currently in his
second year as a cornea
& anterior segment
fellow at the University of
Auckland.