Corneal transplantation, also known as
corneal grafting, is a surgical procedure where a damaged or diseased
corneaThe cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...
is replaced by donated corneal tissue (the graft) in its entirety (penetrating keratoplasty) or in part (lamellar keratoplasty). The graft has been removed from a recently deceased individual with no known diseases or other factors that may affect the viability of the donated tissue or the health of the recipient. The cornea is the transparent front part of the
eyeThe human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
that covers the
irisThe iris is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupils and thus the amount of light reaching the retina. "Eye color" is the color of the iris, which can be green, blue, or brown. In some cases it can be hazel , grey, violet, or even pink...
,
pupilThe pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...
and
anterior chamberThe anterior chamber is the fluid-filled space inside the eye between the iris and the cornea's innermost surface, the endothelium. Aqueous humor is the fluid that fills the anterior chamber. Hyphema and glaucoma are two main pathologies in this area. In hyphema, blood fills the anterior chamber...
. The surgical procedure is performed by
ophthalmologistsOphthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems...
, medical doctors who specialize in eyes, and is often done on an outpatient basis. Donors can be of any age as was
Janis BabsonJanis Anne Babson was a 10 year old Canadian child, who gained posthumous fame through the donation of her eyes for cornea transplants...
, who donated her eyes at age 10.
Indications
Indications for corneal transplantation include the following:
- Optical: To improve visual acuity by replacing the opaque or distorted host tissue by clear healthy donor tissue. The most common indication in this category is pseudophakic bullous keratopathy, followed by keratoconus
Keratoconus , is a degenerative disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape than its normal gradual curve....
, corneal degeneration, keratoglobusKeratoglobus , is a degenerative non-inflammatory disorder of the eye in which structural changes within the cornea cause it to become extremely thin and change to a more globular shape than its normal gradual curve...
and dystrophyCorneal dystrophy is a group of disorders, characterised by a noninflammatory, inherited, bilateral opacity of the transparent front part of the eye called the cornea.The distrophies could be subdivided based on specie affected:...
, as well as scarring due to keratitisKeratitis is a condition in which the eye's cornea, the front part of the eye, becomes inflamed. The condition is often marked by moderate to intense pain and usually involves impaired eyesight.-Types:...
and traumaTrauma refers to "a body wound or shock produced by sudden physical injury, as from violence or accident." It can also be described as "a physical wound or injury, such as a fracture or blow." Major trauma can result in secondary complications such as circulatory shock, respiratory failure and death...
.
- Tectonic/reconstructive: To preserve corneal anatomy and integrity in patients with stromal thinning and descemetoceles, or to reconstruct the anatomy of the eye, e.g. after corneal perforation
Corneal Perforation is an anomaly in the cornea resulting from damage to the corneal surface. A corneal perforation means that the cornea has been penetrated, thus leaving the cornea damaged....
.
- Therapeutic: To remove inflamed corneal tissue unresponsive to treatment by antibiotic
An antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...
s or anti-virals.
- Cosmetic: To improve the appearance of patients with corneal scars that have given a whitish or opaque hue to the cornea.
Pre-operative examination
In most instances, the
patientA patient is any recipient of healthcare services. The patient is most often ill or injured and in need of treatment by a physician, advanced practice registered nurse, veterinarian, or other health care provider....
will meet with their ophthalmologist for an examination in the weeks or months preceding the surgery. During the exam, the ophthalmologist will examine the eye and diagnose the condition. The doctor will then discuss the condition with the patient, including the different treatment options available. The doctor will also discuss the risks and benefits of the various options. If the patient elects to proceed with the surgery, the doctor will have the patient sign an
informed consentInformed consent is a phrase often used in law to indicate that the consent a person gives meets certain minimum standards. As a literal matter, in the absence of fraud, it is redundant. An informed consent can be said to have been given based upon a clear appreciation and understanding of the...
form. The doctor might also perform a physical examination and order lab tests, such as blood work, X-rays, or an EKG.
The surgery date and time will also be set, and the patient will be told where the surgery will take place. The surgery only takes place when the best corresponding donor tissue is found. This can take weeks and months.
Procedure
On the day of the
surgerySurgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...
, the patient arrives to either a
hospitalA hospital is a health care institution providing patient treatment by specialized staff and equipment. Hospitals often, but not always, provide for inpatient care or longer-term patient stays....
or an outpatient surgery center, where the procedure will be performed. The patient is given a brief physical examination by the surgical team and is taken to the
operating roomAn operating theater was a non-sterile, tiered theater or amphitheater in which students and other spectators could watch surgeons perform surgery...
. In the OR, the patient lies down on an operating table and is either given general anesthesia, or
local anesthesiaLocal anesthesia is any technique to induce the absence of sensation in part of the body, generally for the aim of inducing local analgesia, that is, local insensitivity to pain, although other local senses may be affected as well. It allows patients to undergo surgical and dental procedures with...
and a
sedativeA sedative or tranquilizer is a substance that induces sedation by reducing irritability or excitement....
.
With anesthesia induced, the surgical team prepares the eye to be operated on and drapes the face around the eye. An eyelid
speculumThe term speculum, Latin for "mirror", and its plural specula, may refer to:* Speculum , a medical tool used for examining body cavities* Speculum , a journal of medieval studies published by the Medieval Academy of America...
is placed to keep the lids open, and some lubrication is placed on the eye to prevent drying. In children, a metal ring is stitched to the
scleraThe sclera , also known as the white or white of the eye, is the opaque , fibrous, protective, outer layer of the eye containing collagen and elastic fiber. In the development of the embryo, the sclera is derived from the neural crest...
which will provide support of the sclera during the procedure.
Penetrating keratoplasty
A trephine (a circular cutting device) is then placed over the cornea and is used by the surgeon to cut the host cornea, which removes a circular disc of the patient cornea. The trephine is then removed and the surgeon cuts a circular
graftGrafting refers to a surgical procedure to move tissue from one site to another on the body, or from another person, without bringing its own blood supply with it. Instead, a new blood supply grows in after it is placed. A similar technique where tissue is transferred with the blood supply intact...
(a "button") from the donor cornea. Once this is done, the surgeon returns to the patient's eye and removes the host cornea.
The donor cornea is then brought into the surgical field and maneuvered into place with
forcepsForceps or forcipes are a handheld, hinged instrument used for grasping and holding objects. Forceps are used when fingers are too large to grasp small objects or when many objects need to be held at one time while the hands are used to perform a task. The term 'forceps' is used almost exclusively...
. Once in place, the surgeon will fasten the cornea to the eye with a running stitch (as used in the upper image above) or a multiple interrupted stitches (as in the lower image). The surgeon then reforming the
anterior chamberThe anterior chamber is the fluid-filled space inside the eye between the iris and the cornea's innermost surface, the endothelium. Aqueous humor is the fluid that fills the anterior chamber. Hyphema and glaucoma are two main pathologies in this area. In hyphema, blood fills the anterior chamber...
with a sterile solution injected by a
cannulaA cannula or canula is a tube that can be inserted into the body, often for the delivery or removal of fluid or for the gathering of data...
, then testing that it's watertight by placing a dye on the wound exterior.
AntibioticAn antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...
eyedrops placed, the eye is patched, and the patient is taken to a recovery area while the effects of the anesthesia wear off. The patient typically goes home following this and sees the doctor the following day for the first post operative appointment.
Lamellar keratoplasty
This procedure consists in leaving just the patient's own Descemet membrane and endothelium, while transplanting approximately 95% of the cornea. The great advantage of this technique is the virtually "no rejection" post-op. The main disadvantage is that the visual acuity is not as sharp as it is with the full cornea transplantation penetrating keratoplasty). The final visual acuity is usually around 20/40.
Risks
While the cornea is
avascularThe blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
, there is still a potential for some blood loss, usually from suturing the metal ring to the sclera. Any blood loss is typically less than 2 ml (1.80001800018E-10 imp fl oz).
There is also a risk of
infectionAn infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
. Since the cornea has no blood vessels (it takes its nutrients from the aqueous humor) it heals much more slowly than a cut on the skin. While the
woundA wound is a type of injury in which skin is torn, cut or punctured , or where blunt force trauma causes a contusion . In pathology, it specifically refers to a sharp injury which damages the dermis of the skin.-Open:...
is healing, it is possible that it might become infected by various microorganisms. This risk is minimized by antibiotic prophylaxis (using antibiotic eyedrops, even when no infection exists).
Graft failure can occur at any time after the cornea has been transplanted, even years or decades later. The causes can vary, though it is usually due to new injury or illness. Treatment can be either medical or surgical, depending on the individual case. An early, technical cause of failure, may be an excessively tight stitch
cheesewiringIn medicine the term cheesewiring describes any process in which cells or intercellular matrix are dissected either by the material being pressed through a taut element , or by the tension of a taut element pulling through...
through the sclera.
Prognosis
When the primary purpose of a cornea transplant is to improve visual acuity, the prognosis is dependent upon whether the rest of the eye is healthy. If it is, then it should be possible to recover normal vision.
History
The first cornea transplant was performed in 1905 by
Eduard ZirmEduard Konrad Zirm was an ophthalmologist who performed the first successful human tissue transplant on 7 December 1905....
(Olomouc Eye Clinic, now
Czech RepublicThe Czech Republic is a landlocked country in Central Europe. The country is bordered by Poland to the northeast, Slovakia to the east, Austria to the south, and Germany to the west and northwest....
), making it one of the first types of transplant surgery successfully performed. Another pioneer of the operation was
Ramon CastroviejoRamón Castroviejo Briones was a famous Spanish and American eye surgeon remembered for his achievements in corneal transplantation.-Biography:Born in Logroño, Spain he received his medical education at the University of Madrid...
. Russian eye surgeon Vladimir Filatov's attempts at tranplanting cornea started with the first try in 1912 and were continued, gradually improving until at 6 May 1931 he successfully grafted a patient using corneal tissue from a deceased person. He widely reported of another transplant in 1936, disclosing his technique in full detail. In 1936, Castroviejo did a first transplantation in an advanced case of
keratoconusKeratoconus , is a degenerative disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape than its normal gradual curve....
, achieving significant improvement in patient's vision.
Advances in operating microscopes enabled surgeons to have a more magnified view of the surgical field, while advances in
materials scienceMaterials science is an interdisciplinary field applying the properties of matter to various areas of science and engineering. This scientific field investigates the relationship between the structure of materials at atomic or molecular scales and their macroscopic properties. It incorporates...
enabled them to use sutures finer than a human hair.
Instrumental in the success of cornea transplants were the establishment of
eye bankEye banks retrieve and store eyes for cornea transplants and research. US eye banks provide tissue for about 46,000 cornea transplants a year to treat conditions such as keratoconus and cornea scarring. The cornea is not the only part of the eye that can currently undergo transplantation. The...
s. These are organizations located throughout the world to coordinate the distribution of donated corneas to surgeons, as well as providing eyes for research. Some eye banks also distribute other
anatomical giftsOrgan donation is the donation of biological tissue or an organ of the human body, from a living or dead person to a living recipient in need of a transplantation. Transplantable organs and tissues are removed in a surgical procedure following a determination, based on the donor's medical and...
.
Boston keratoprosthesis
The
Boston keratoprosthesisThe Boston Keratoprosthesis is a collar button design keratoprosthesis or artificial cornea. It is composed of a front plate with a stem, which houses the optical portion of the device, a back plate and a titanium locking c-ring. It is available in type I and type II formats...
is the most widely used synthetic cornea to date with over 900 procedures performed worldwide in 2008. The Boston KPro was developed at the Massachusetts Eye and Ear Infirmary under the leadership of Claes Dohlman, MD, PhD.
AlphaCor
In cases where there have been several graft failures or the risk for keratoplasty is high, synthetic corneas can substitute successfully for donor corneas. Such a device contains a peripheral skirt and a transparent central region. These two parts are connected on a molecular level by an
interpenetrating polymer networkAn Interpenetrating polymer network is a polymer comprising two or more networks which are at least partially interlaced on a polymer scale but not covalently bonded to each other...
, made from
poly-2-hydroxyethyl methacrylatePoly is a polymer that forms a hydrogel in water. It was invented by Drahoslav Lim for use in soft contact lenses. Copolymers of pHEMA are still widely used today....
(pHEMA). AlphaCor is an FDA-approved type of synthetic cornea measuring 7.0 mm in diameter and 0.5 mm in thickness. The main advantages of synthetic corneas are that they are biocompatible, and the network between the parts and the device prevents complications that could arise at their interface. The probability of retention in one large study was estimated at 62% at 2 years follow-up.
Osteo-Odonto-Keratoprosthesis
In a very rare and complex multi-step surgical procedure, employed to help the most disabled patients, a lamina of the patient's tooth is grafted into the eye, with an artificial lens installed in the transplanted piece.
Phototherapeutic keratectomy (PTK)
Diseases that only affect the surface of the cornea can be treated with an operation called phototherapeutic keratectomy. With the precision of an excimer laser and a modulating agent coating the eye, irregularities on the surface can be removed. However, in most of the cases where corneal transplantation is recommended, PTK would not be effective.
Intrastromal corneal ring segments
The implants manufactured under the trade name Intacs are the only patented intrastromal corneal implant that has US FDA approval and European CE Mark for both Myopia and Keratoconus. There are over one-hundred clinical articles at
http://www.pubmed.com for clinical reference (search for Intacs and they all are arranged in chronological order) and are a well documented clinical solution for treating keratoconus. Another version of intrastromal cornea ring segments is manufactured under the trade name KeraRing and is available in South America and Europe.
With this procedure, the implants are placed in the stroma to reshape the cornea into a more natural shape. In mild myopia, this corrects a patients vision. In keratoconus, the goal is to reshape the cornea to where contact lens intolerant patients are able to achieve functional vision with contact lenses or glasses. Although, surgical procedure don't carry a guarantee, one clinically proven benefit of Intacs is that they can be safely removed and the cornea returns to its pre-operative state. Future treatment options are not affected.
Contact lenses
In the early stages and up to the more advanced stages of keratoconus, contact lenses are often used to improve vision. Contact lenses improve visual acuity of the majority of the keratoconus patients. The majority of the patients need to use hard contact lenses. Only 10 to 20% will need cornea tranplantion during their lifetimes due to progression of the disease.
High speed lasers
Blades are being replaced by high speed lasers in order to make surgical incisions more precise. These improved incisions allow the cornea to heal more quickly and the sutures to be removed sooner. The cornea heals more strongly than with standard blade operations. Not only does this dramatically improve visual recovery and healing, it also allows the possibility for improvement in visual outcomes.
Since 2004,
Amnitrans Eyebank in Rotterdam, The Netherlands, provides donor corneas pre-cut for advanced keratoplasty procedures, such as DSEK, DSAEK, FS-DSEK and DMEK. In 2007, Seattle-based
SightLife, one of the leading corneal tissue banks in the world, introduced a process for the preparation of donated corneal tissue using a Femtosecond Laser. This process is known as
Custom Corneal Tissue.
DSEK/DSAEK/DMEK
Endothelial keratoplasty (EK) has been introduced by Melles et al. in 1998. Today there are three forms of EK. Deep Lamellar Endothelial Keratoplasty (DLEK) in which the posterior part of the recipient cornea is replaced by donor tissue. Descemet's Stripping (Automated) Endothelial Keratoplasty (DSEK/DSAEK) in which the diseased
Descemet's membraneDescemet's membrane is the basement membrane that lies between the corneal proper substance, also called stroma, and the endothelial layer of the cornea. It is composed of a different kind of collagen than the stroma. The endothelial layer is located at the posterior of the cornea...
is removed and replaced by a healthy donor posterior transplant. The transplant tissue can be prepared by a surgeon's hand or ordered already prepared for surgery.
Ocular Systems Inc. was the first organization to deliver prepared grafts for surgery in 2005. DSEK/DSAEK uses only a small incision that is either self-sealing or may be closed with a few sutures. The small incision offers several benefits over traditional methods of corneal transplant such as Penetrating Keratoplasty. Because the procedure is less invasive, DSAEK leaves the eye much stronger and less prone to injury than full-thickness transplants. New medical devices such as the EndoSaver (patent pending) are designed to ease process of inserting endothelial tissue into the cornea. Additionally, DSAEK has a more rapid rate of visual recovery. Vision is typically restored in one to six months rather than one to two years. Descemet Membrane Endothelial Keratoplasty (DMEK)] is the most recent EK technique in which an isolated Descemet membrane is transplanted. The DMEK procedure combines the anatomical benefits of DSEK/DSAEK with visual rehabilitation to 20/40 or better in 90% of cases and 20/25 or better in 60% of cases within the first three months. In the UK (2010) the only surgeon offering DMEK procedure under the auspices of the National Health Service is Mr. Ewan Craig of the Royal Shrewsbury Hospital.
Not all patients with diseased corneas are candidates for endothelial keratoplasty. These procedures correct corneal endothelial failure, but are not able to correct corneal scarring, thinning, or surface irregularity. There is currently very little data on long-term survival of DMEK grafts.
Stem cells
There is a bioengineering technique that uses stem cells to create corneas or part of corneas that can be transplanted into the eyes. Corneal stem cells are removed from a healthy cornea. They are collected and, through laboratory procedures, made into five to ten layers of cells that can be stitched into a patient’s eye. The stem cells are placed into the area where the damaged cornea tissue has been removed. This is a good alternative for those that cannot gain vision through regular cornea transplants. A new development, announced by the University of Cincinnati Medical School in May 2007, would use bone marrow stem cells to regrow the cornea and its cells. This technique, which proved successful in mouse trials, would be of use to those suffering from inherited genetic degenerative conditions of the cornea, especially if other means like a transplant aren't feasible. It works better than a transplant because these stem cells keep their ability to differentiate and replicate,
and so keep the disease from recurring, longer and better.
Biosynthetic corneas
On 25 August 2010 investigators from Canada and Sweden reported results from the first 10 people in the world treated with the biosynthetic corneas. Two years after having the corneas implanted, six of the 10 patients had improved vision. Nine of the 10 experienced cell and nerve regeneration, meaning that corneal cells and nerves grew into the implant. To make the material, the researchers placed a human gene that regulates the natural production of collagen into specially programmed yeast cells. They then molded the resulting material into the shape of a cornea. This research shows the potential for these bioengineered corneas but the outcomes in this study were not nearly as good as those achieved with human donor corneas. This may become an excellent technique, but right now it is still in the prototype stage and not ready for clinical use. The results were published in the journal Science Translational Medicine.
Epidemiology and economics
Corneal transplant is one of the most common transplant procedures. Although approximately 100,000 procedures are performed worldwide each year, some estimates report that 10,000,000 people are affected by various disorders that would benefit from corneal transplantation.
http://www.asmr.org.au/news/CS.pdf
In
AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, approximately 1,500 grafts are performed each year.
http://www.asmr.org.au/news/CS.pdf According to the
NHS Blood and TransplantNHS Blood and Transplant is a special health authority of the English National Health Service .It was established on 1 October 2005 to take over the responsibilities of two separate NHS agencies: UK Transplant , founded by Dr. Geoffrey Tovey in 1972, and the National Blood Service...
, over 2,300 corneal transplant procedures are performed each year in the
United KingdomThe United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
.
http://www.uktransplant.org.uk/ukt/statistics/transplant_activity_report/current_activity_reports.jsp/ukt/tx_activity_report_2005_uk_complete-v2.pdf Between April 1, 2005 and March 31, 2006, 2,503 people received corneal transplants in the UK.
http://www.uktransplant.org.uk/ukt/statistics/statistics.jsp
In the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
, the cost is usually covered in part by Medicare and health insurers. Reimbursement depends on your personal healthcare provider. Usually 80% of the cost will be covered by your agency. Those on Medicare will be reimbursed up to $1,200 while the remainder is left up to the patient. The average cost of the procedure ranges from $7,500 to $11,000.
In 2005, there were about 32,840 corneal transplant recipients. The estimated first year billed charges per patient, including medications, was $19,100. There were a larger number of transplants for patients over 65 than under, 18,000 compared to 14,840. There were 41,652 corneal transplants performed in the United States in 2008.
In
SwedenSweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
, corneal transplants are paid by taxes. Every year about six hundred of these operations are performed.
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