Cornea and Anterior Segment
Corneal Transplantation
What is corneal transplantation ?
Cornea is the clear, transparent structure in the front of the eye and along with Lens, it is responsible for focussing the light rays onto the nerve layer called Retina. Cornea is not a singe layer structure but it is a multilayered one. The transparency of the cornea can be affected due to various reasons. When the transparency and the resultant poor vision can not be restored by medical treatment , glasses or contact lenses corneal transplantation is the surgical option to improve vision. A cornea transplant (keratoplasty) is a surgical procedure to replace part of the cornea of the patient with that of corneal tissue from a donor. A cornea transplant is most often used to restore vision to a person who has a damaged cornea from various causes. A cornea transplant may also relieve pain or other signs and symptoms associated with diseases of the cornea. Through eye donation program corneal tissue is removed from donors after death. The donor cornea tissue is thoroughly screened for any communicable diseases and examined by an expert for quality assessment. A cornea transplant can restore vision, reduce pain and improve the appearance of a damaged or diseased cornea.
What are the different types of corneal transplantation?
With the advances in the field of Ophthalmology, it is now possible to remove only the affected layers of the cornea instead of replacing the entire, full thickness corneal tissue in selected patients. Avoiding a full thickness corneal transplantation reduces the complications and increase the survival rate of the graft. The various types of surgical procedures include
Penetrating keratoplasty (PKP)
In this procedure the entire cornea from the patient is removed and replaced with the donor cornea. It is done for patients who have disease involving most or all the corneal layers.
Endothelial keratoplasty (EK)
This procedure removes diseased tissue from the back corneal layers called the Endothelium and Descemet membrane. In a healthy cornea, these layers help to keep the cornea dry and prevents fluid accumulation. In conditions where the disease process involves these deeper layers, thy can be selectively removed and replaced with the donor corneal layers. There are two types of endothelial keratoplasty. The more common type, called Descemet Stripping Endothelial Keratoplasty (DSEK), uses donor tissue to replace about one-third of the cornea. A second type of procedure, called Descemet Membrane Endothelial Keratoplasty (DMEK), uses a much thinner layer of donor tissue.
Anterior lamellar keratoplasty (ALK).
This procedure removes diseased tissue from the front corneal layers, namely epithelium and the stroma, but leaves the back endothelial layer in place. This is suitable for patients who are having corneal problems involving only the front portion of the cornea like a superficial scar. Depending upon the thickness and depth of the tissue removed, the procedure can be Superficial Anterior Lamellar Keratoplasty (SALK) or Deep Anterior Lamellar Keratoplasty (DALK). The removed tissue is replaced with the corresponding layers of donor cornea and secured in place with fine sutures. The back layers of the cornea are not disturbed and left intact.
Who will benefit from a corneal transplantation?
There are a number of corneal conditions which cannot be treated with medication alone. The following is the list of conditions that may benefit from corneal transplantation to improve vision.
- Cornea scarring, caused by injury or infection
- Keratoconus- A condition in which the cornea gradually bulges out
- Clouding of the cornea
- Thinning of the cornea
- Swelling of the cornea
- Corneal ulcers not responding to medical treatment
- Complications caused by previous eye surgery
What are the risks associated with corneal transplantation ?
Cornea transplant is a relatively safe procedure. Still, it does carry a small risk of serious complications, such as:
- Eye infection following surgery as with any other intra ocular surgical procedures.
- Increased risk of cataract in some patients
- Pressure increase within the eyeball called Glaucoma
- Problems with the stitches used to secure the donor cornea. In endothelial keratoplasty there are no sutures used to secure the donor cornea unlike in PKP or DALK
- Rejection of the donor corneal graft can happen even years after the transplant surgery
How to proceed if any one of the above mentioned condition is present which needs corneal transplantation?
A complete pre op evaluation of both eyes is mandatory including visual acuity assessment, intra ocular pressure and examination under dilation to check the nerve fibre layer called retina and status of optic nerve. The risk factors are noted down and the consultant will discuss in detail about the surgical procedure, what to expect after the surgery, the post-operative medications, frequency of follow up visits etc. Patients are advised to get one of the family members during the discussion to clarify any doubts regarding the surgical procedure. All the surgeries are done under local anaesthesia except in children where general anaesthesia is preferred. After baseline blood examination and assessment by the Anaesthesiologist, the patient is kept in the waiting list for the transplantation procedure.
What you can expect on the day of surgery ?
- Patients are expected to come 2 hours prior to surgery for pre operative preparation
- All the surgeries are done under local anaesthesia. There will not be any pain during the surgery in any of the above mentioned procedure
- After the surgery eye patch is kept over operated the eye which will be removed on the next day
- Topical and oral medications are started from the first post operative day
What to expect in the post operative period ?
- Frequent follow up visits are mandatory in the next few weeks to make sure the cornea heals without any complications
- Risk of graft rejection continues for many years after surgery. For this reason patients are expected to see the doctor annually
- Vision improvement is usually gradual after corneal transplant procedure especially after penetrating keratoplasty(PKP)
- If sutures are placed as in PKP or DALK they will be removed after 6 months to 12 months
- Patients are clearly explained about the early symptoms of graft rejection so that they can report immediately to the surgical centre for early treatment
- Residual refractive errors can be corrected with glasses, contact lenses, refractive surgery once refraction stabilises few months after the surgery
- Patients who develop cataract later can undergo routine cataract surgery with intra ocular lens implantation
Keratoconus
About Keratoconus
Keratoconus is a condition in which the cornea becomes thin and bulges out gradually. Normal Cornea is smooth , dome shaped and transparent like a glass. When the smooth dome shaped normal corneal shape is altered, the vision gets distorted as the light rays are not focussed properly anymore. This leads to gradual blurring of vision. It usually affects both eyes but one eye may be more affected than the other. In addition to the change in the shape and progressive thinning of the cornea, the advanced cases may also develop scars in the cornea which may further reduce the vision.
Diagnosing Keratoconus
Usually Keratoconus starts around the age of puberty and gradually increases in severity till 25-30 years of age. Due to change in corneal shape the spectacle power changes more frequently. Diagnosis of this condition is based on assessment of vision and clinical examination. If Keratoconus is suspected after clinical examination, patient needs to undergo corneal imaging to confirm the clinical diagnosis.
Treatment of Keratoconus
Once diagnosed the treatment depends upon various factors like age of the patient, vision, severity of the condition, rate of progression etc. Corneal Collagen Cross linking (C3R) is a surgical procedure done under topical anaesthesia to arrest the progression of the disease. It is indicated for all patients with progressive disease. In the initial stages glasses or contact lenses give good results. Apart from regular RGP contact lenses, specialised lenses for Keratoconus like Rose-K lenses give excellent visual outcome in many patients. When the condition is very advanced or in patients with scarring, contact lens may not be suitable. In such patients surgical options are available to improve vision which include placing ring segments in the cornea or partial/full thickness corneal transplantation. Patients need to be on long term topical medications and need regular follow up after transplantation procedure. To prevent progressive vision loss and for a better visual outcome it is very important to diagnose this condition at an early stage itself.