Overview of Penetrating Keratoplasty
Penetrating keratoplasty (PKP), also known as optical penetrating keratoplasty (OPK), is a type of cornea transplant surgery. In this surgery, the doctor removes a damaged cornea from a patient’s eye and replaces it with a healthy one from a donor. This procedure was first successfully done by Eduard Konrad Zirm in 1905, on a patient who had suffered burns on both of his eyes.
Vladimir Petrovich Filatov, a renowned Russian eye doctor, is considered the pioneer of this type of surgery. He suggested that corneas from deceased individuals could be used for the transplant, which allowed many more people to benefit from the procedure.
The concept of cornea transplants has been around for quite some time. In 1813, K. Himly, a prominent figure in the field, suggested the idea of replacing a cloudy or damaged cornea with a clear one from another animal. This ground-breaking idea paved the way for the growth and development of corneal surgeries and transplants. The term “keratoplasty” comes from the work of F. Reisinger in 1824, who also proposed the idea of using animal corneas for human transplants.
Over the decades, there have been many advancements in this field. Various surgical instruments have been invented, techniques have been refined, and the understanding of potential complications, like graft rejection, has greatly improved. Even methods of preserving donor corneas have improved, thanks to the development of corneal storage media in 1974. More recent advancements include different types of keratoplasty performed by several prominent eye doctors, all contributing to enhancing the accuracy, safety, and outcomes of cornea transplant surgeries.
Anatomy and Physiology of Penetrating Keratoplasty
The cornea, the clear front surface of the eye, enjoys a unique characteristic: it’s somewhat ‘immune-privileged’. This means that it’s protected against certain immune system responses that happen elsewhere in the body. Three key features enable this special status: firstly, it lacks blood vessels; secondly, it also lacks lymphatic channels, which are often involved in the body’s immune response; and thirdly, something known as ‘anterior chamber-associated immune deviation’ or ACAID helps keep it immune balanced. These three elements play a crucial role in the success of keratoplasty, the medical term for a corneal transplant.
Why do People Need Penetrating Keratoplasty
Here are some conditions where you might need surgery on your cornea, the clear, protective layer at the front of your eye. The surgery is called keratoplasty, and it can restore vision, relieve pain, or repair damage to the cornea.
Conditions when you might need surgery:
1. Pseudophakic and aphakic bullous keratopathy: Problems with the cornea after certain eye surgeries
2. Corneal stromal dystrophies: A group of conditions that affects how clear the cornea is
3. Corneal endothelial dystrophies: Conditions that affect the cells on the innermost layer of the cornea
4. Corneal ectasia and congenital opacities: Conditions that affect the shape of the cornea or make it cloudy
5. Viral keratitis: Inflammation or infection of the cornea
6. Microbial keratitis or nutritional/chemical injuries: Infections or injuries to the cornea
7. Corneal degenerations: Aging changes to the cornea
8. Traumatic corneal scar or ulcerative keratitis: Scars or inflammation of the cornea caused by injury or other conditions
Possible types of the surgery include:
1. Tectonic: To maintain the round shape and integrity of the eye
2. Therapeutic/ reconstructive: To remove infection
3. Cosmetic: To remove cloudiness or other visible changes in the cornea
4. Optical: To restore vision
Some reasons why surgery might be particularly recommended include conditions like aphakic or pseudophakic bullous keratopathy, corneal scars, or diseases that change the cornea’s shape or clarity.
The success rate of this surgery can vary depending on the specific condition. For example, conditions like keratoconus, corneal dystrophy, and Fuchs dystrophy have high success rates above 90%. Other conditions like ocular pemphigoid, Steven Johnson syndrome, and congenital glaucoma have lower success rates, usually less than 50%. Your doctor can discuss this with you more based on your specific situation.
When a Person Should Avoid Penetrating Keratoplasty
There are several medical conditions related to the eyes. These include:
Severe dry eyes, which means the eyes do not produce enough tears to keep the eyes comfortably lubricated.
Steven Johnson syndrome, which is a severe skin reaction to medication or infection that can also affect the eyes.
Toxic epidermal necrolysis, another severe skin reaction that often starts with flu-like symptoms and a rash, and it can also affect the eyes.
Advanced ocular surface disease, which refers to several conditions that affect the surface of the eye and can cause discomfort or vision problems.
Anterior staphyloma, which is a condition where the front part of the eye bulges outward due to thinning of the eye wall.
Retinal detachment, when the layer at the back of the eye that senses light peels away from the layers it should be attached to.
Blepharitis, a common condition where the edges of the eyelids become red and swollen.
Meibomian gland disease, when the glands that produce oil for your tears get blocked or don’t work properly.
Acute conjunctivitis, more commonly known as pink eye, which is an infection or inflammation of the film that covers the white part of your eye.
Episcleritis, which is inflammation of the thin layer of tissue covering the white part of the eye.
Scleritis, which is a more serious inflammation that affects the white outer coating of the eye.
Corneal vascularization, which refers to the growth of blood vessels into more than two sections of the clear surface at the front of the eye, known as the cornea.
Equipment used for Penetrating Keratoplasty
Here is a list of tools and materials that your doctor might use during your eye procedure:
* Drape: a sterile cover used to keep the surgery area clean
* Povidone Iodine: a type of antiseptic used to kill bacteria and other microbes
* Artery forceps: a tool to control bleeding by closing off blood vessels
* Povidone iodine-soaked cotton balls: used for cleaning the area to prevent infection
* Clean cotton balls: used to clean or dry the area
* Lid speculum: an instrument to hold your eyelids open
* Side port blade-15 degree: a small surgical knife used to create tiny incisions
* MVR blade: a specific type of surgical blade used in eye surgery
* Conjunctival forceps: tool used to handle the conjunctiva, the clear tissue covering the eye
* Radial keratotomy marker: for marking the eye before certain procedures
* Scleral ring: a tool that helps to keep the eye stable and protected
* Trephine: a small instrument used to cut circular sections of tissue
* Conjunctival scissor: special scissors for cutting eye tissue
* Vannas scissors: small, precise scissors used in eye surgery
* Teflon block for graft trephination: used for cutting out precise samples of donor tissue
* 10-0 and 9-0 nylon sutures: Very fine threads for stitching up incisions after the procedure
* Suture holding forceps: Tool for holding the sutures during stitching
* Plain suture-tying forceps: Tool used to tie off the sutures
* Capsulotomy needle: cystitome: a sharp instrument for opening the lens capsule during cataract surgery
* Capsulotomy forceps: special forceps used during capsulotomy, a part of cataract surgery
* Sinskey hook: a sharp tool for manipulating eye tissues
* Simcoe cannula: for removing fluids or substances from the eye
* Intraocular lens: the artificial lens that replaces the eye’s natural lens in cataract surgery
* Automated anterior vitrectomy machine: a machine used to remove certain parts of the eye’s vitreous humor, if necessary through a surgical procedure.
Who is needed to perform Penetrating Keratoplasty?
An eye doctor known as an ophthalmic surgeon performs the operation. These doctors are specialists who have expertise in doing eye surgeries. Besides the surgeon, several other healthcare professionals are also involved in the surgery. These include a mid-level ophthalmic assistant who is trained in providing support to the surgeon during the operation.
The team also includes operating room nurses who help prepare you for the surgery and take care of you afterward, and a pharmacist who ensures you get the correct medications you need. Additionally, counseling nurses are there to help guide you through the process and answer any questions you might have.
There’s also an eye bank coordinator involved, who makes sure any necessary eye tissues for transplantation are ready. An eye bank-trained technician, skilled in preparing the eye tissues, is also part of the team. Other professionals like trained staff for enucleation, who assist in the removal process of the eye if necessary, are present as well.
Additionally, there’s a driver who ensures safe transport and sponsors who help fund the operation. An enucleation coordinator manages all the elements of this process to make sure everything runs smoothly.
All these people work together to keep you safe and comfortable during your eye surgery.
Preparing for Penetrating Keratoplasty
When doctors notice an issue with a person’s vision, they’ll firstly ask about their health history. Somebody might say that they’re having trouble seeing or that they have a white spot in their eye. The doctor also needs to know if there’s been any past eye infections, eye surgeries, issues with the retina, or long-lasting changes in the eye’s clarity. They will also want information about any eye injuries, infections, nutrient deficiencies, immune disorders affecting connective tissues, chronic diseases of the eye’s surface, or if a patient has ever had herpes of the eye. The doctor will also need to know about any other health conditions the person might have.
Doctors will run a few tests to understand what’s going on. These usually involve checking how well the person can see. Some people might have a test that involves reading letters from a chart, while others might have to look at a small hole while a bright light shines in their eye. If a person can’t do these tests, the doctor might use a special tool to look into their eye instead. Kids who can’t do the usual tests might have to do a different test that involves covering one eye, looking at a picture, or a test that uses a special card.
A doctor will usually examine the person’s eyes in more detail. With a special tool, they will look at the structures at the front of the person’s eye. The doctor may check for issues with the eyelashes growing abnormally, inflammation of the eye, drooping or turned-out eyelid, and signs of any eye infections. The whites of the eyes and the inside lining of the eyelids will be examined for any foreign objects, inflammation, or infection signs. The doctor will also look at the size, shape, and coloring of the cornea (the clear front part of the eye), check its feeling and any growth of small blood vessels into it. If the patient had transplantation previously, the health and size of the transplant and presence of stitches will be checked as well. Also, the physician will look at the space at the front of their eye, the iris, and the pupil. Patients with poor eyesight will need to know about their condition, whether they still have their natural eye lens (phakic), if they’re missing an eye lens (aphakic), or have an artificial lens replacing their natural one (pseudophakic).
The doctor will also need to look at the back of the person’s eye to rule out other eye conditions, for example, a condition that causes damage to the optic nerve called glaucoma. They will look at the optic disc, the area where blood vessels and nerves leave the eye, the macula which is responsible for seeing detail, and the nerve fibers that come from the retina. If the doctor can’t clearly see the back of the eye, they may use a special sound wave test to check for any inflammation, bleeding, changes in the optic nerve, or the retina detaching from the back of the eye.
Another test that might be done measures the pressure inside the eye. This can be done with a machine that puffs air into the eye, or some other tools if the puff test can’t be done. If those tools aren’t available, then the doctor will estimate the pressure by gently pressing on the eye.
Doctors may check if the person has dry eye by doing several tests to see the quality and amount of tears in their eyes. Then they might do some measurements to ensure the person’s eye is focusing light properly. In certain cases, a special tool remotely viewing the eye’s structures or measuring the curve on the front of the eye might be used. Another test might involve checking the thickness of the front part of the eye or using another tool to see the depth of the eye structures.
For patients undergoing a cornea transplant, the donor cornea needs to be stored properly for good results. Ideally, this should be done within 48 hours after it’s removed from the donor. It’s also important to have lots of healthy cells on the donated cornea. Lastly, diseases the donor might have had like rabies, certain brain disorders, HIV/AIDS, blood infections, systemic infections, eye tumors, and certain types of cancer can affect which corneas can be used for a transplant.
If a person has an infection on or near the eye, like in the eyelashes, this needs to be treated first. If there are small blood vessels growing into the cornea, these can sometimes be handled with eye drops, small electric currents, or lasers. Lastly, before the actual surgery, the eye pressure might need to be reduced in different ways, such as an IV fluid called mannitol or a pressure application tool. This can help lower the risk of serious complications during surgery, like loss of the gel-like substance that helps the eye keep its round shape or bleeding inside the eye.
How is Penetrating Keratoplasty performed
Your eyes will be prepared by cleaning it with a solution containing povidone-iodine. Then, a sheet that only exposes your eye will be placed over you before a special kind of device (lid speculum) is used to keep your eyelid open for the procedure.
For the next step, a small cut will be created and a medicine named pilocarpine will be injected if your lens is healthy and needs to be kept intact. However, if you also need to have a cataract removal, a different medicine named tropicamide will be used, before using a dye (trypan blue) and viscoelastic substance that helps the surgeon see and work inside the eye better.
Next, the center of your cornea (the front part of your eye) will be marked with blue ink as a guide. There are special instruments, such as a caliper or a hook with blue ink, we use to make this mark. The size of the marking is usually kept to about 7-7.5 mm, which is just right for most people. We then use a tool called a trephine to mark the cornea—towards 80% of the cornea’s depth (never 100% to avoid injury). Then, small cuts will be made to access the front part of the eye.
After this, a graft (tissue from a donor) will be prepared. This tissue will be carefully handled and cleaned to dry using a special type of forceps and sponge. The graft then gets placed on a block and a pressure is applied to make a punch. The size of the punch is calculated to be ideally 0.5 mm larger than your cornea (sometimes a bit more or less depending on individual cases). Different equipments might be used to make this punch, and its size will depend on multiple factors including your cornea’s size and whether or not you have an artificial lens implanted in your eye.
When placing the donor tissue onto your eye, special stitches are made to secure it in place. Four main stitches are placed at four corners, resembling a square. After this, different suture techniques can be used based on the specific needs of your eye.
These stitches are recommended especially for children and patients with unique conditions. One of the advantages of these stitches is that they can be removed individually if needed. The stitch shouldn’t cut through the full thickness of your cornea to avoid damaging the innermost layer of the cornea and causing leakage of the eye’s clear fluid.
After the surgery, you will be prescribed steroids and antibiotics. These will be used to control any inflammation or infection. Additionally, medications to lower the pressure in your eyes (antiglaucoma medications) might be needed. Then, drugs that help your pupil to become wide and relaxed (cycloplegics) could be used, but these need to be used with care. Last but not least, lubricants will be used to prevent any irritation caused by the stitches.
Possible Complications of Penetrating Keratoplasty
There could be problems that are encountered before, during and after eye surgery. These complications can range from mild to severe cases.
Before surgery, there might be issues like not enough pain relief or anesthesia, a forceful pressure in the eye which may cause part of the eye to move or come out or an incident where the lens of the eye comes out. There could also be a prolapse of the vitreous, which is the clear gel that fills the space between the lens and the retina of the eyeball, or a tear in the cornea which could occur because of the surgical process.
During the surgery, problems can develop with the white part of the eye, known as the sclera, or issues with the cornea, which is the clear front surface of the eye. Problems could also arise during the cutting of a circular piece from the cornea, if the cut is not centered, or not symmetrical, or ideal shape. Other issues that could arise during the operation include damage to the iris which is the colored part of the eye, dislocation of the lens, the transparent structure in the eye that focuses light rays onto the retina, which is the layer at the back of the eyeball. The surgery could also leave behind parts of the cornea’s inner lining, damage the cornea, or sew the iris into the wound.
After surgery, there might be early complications such as the surgical wound not healing properly, the shallow part at the front of the eye, known as the anterior chamber might also become shallow. Issues could also arise with the sutures or stitches such as looseness, infection and causing increased blood supply. Other notable issues can include various forms of infections, glaucoma which is an eye condition that leads to damage of the optic nerve, or abnormal attachments between the iris and other parts of the eye.
Later on after surgery, issues can include rejection or failure of the graft, which is the transplanting of cornea tissue, problems with the sutures, inflammation in the eye, accumulation of pus in the anterior chamber. Other complications that could arise include retinal detachment which is an emergency situation where the retina peels away from its underlying layer of support tissue, build-up of fluid in the macula, the part of the eye responsible for detailed central vision, or a disease that causes the cornea to degenerate.
What Else Should I Know About Penetrating Keratoplasty?
Optical penetrating keratoplasty (OPK) is a type of eye surgery that can significantly help improve vision in individuals who are visually impaired or blind. The recovery of your vision after this surgery happens gradually and usually takes about 3 or 4 months. OPK is commonly used to treat different corneal diseases, which are issues affecting the clear, dome-shaped surface on the front of your eye. Before undergoing OPK, it’s important that patients are made aware of their likely outcome.
To measure the success of the graft (the new cornea), doctors use a scale known as the R.P. Centre Grading of Graft Clarity:
– Level 0: The graft is completely opaque (can’t be seen through).
– Level 1: The cornea graft is very hazy, making it very hard to see the iris, lens, and initial part of your eye.
– Level 2: Though the graft appears hazy, the iris, lens, and initial part of your eye are visible but the details aren’t clear.
– Level 3: The graft is clear, but some parts of your iris and lens are slightly hidden.
– Level 4: The graft is clear and all parts of your eye (including the lens and anterior chamber) are completely visible.
A common dilemma faced by doctors post-operatively could be differentiating whether the wound from the surgical stitches is a result of an immune reaction (body fighting foreign substances) or an infection. Here are some key differences:
Immune Suture Infiltrate:
– Can only be located on the host’s side (your body’s original tissue)
– It usually presents as multiple small puncture wounds.
– There might be a break in the skin above the wound, but it’s not always present.
Infectious Suture Infiltrate:
– Can be found on either/both the graft or host side.
– Is typically a solitary wound.
– Usually, there’s a break in the skin above the wound.
