In order to have good vision, the cornea must be healthy, clear and properly shaped. Any condition that jeopardizes this will likely distort vision. Regrettably, such conditions are not rare. In fact, corneal eye disease affects more than 10 million people worldwide and is the fourth most common cause of blindness.
To address these problems, tens of thousands of people in the United States alone will turn to some form of corneal transplant procedure in the hopes it will restore their vision or prevent it from getting worse. Unfortunately, a corneal transplant is rarely an end unto itself. Instead, most people will need a new prescription for vision correction following surgery.
Understanding Corneal Transplants
In it’s most basic form, a corneal transplant involves the removal of damaged or diseased corneal tissue so that it can be replaced with a healthy corneal graft. Transplant tissues are acquired from an organ donor via a local eye bank, similar to other organ transplants. Corneal transplants are relatively well-tolerated compared to other organ transplants, with over a 95% success rate of the procedure in the U.S. (add reference)
There are a number of different ways that a surgeon may perform a corneal transplant. The surgeon generally decides which procedure to use based on how much tissue will need to be removed.
When the majority of a patient’s cornea is diseased or scarred, a full-thickness penetrating keratoplasty (PK) may be selected. PK, which has been used for more than a century, involves the removal of all layers of the cornea before replacing the exposed section with a "button" made from donor tissue that is immediately sutured into place.
An alternative procedure, known as deep anterior lamellar keratoplasty (DALK), allows the patient to retain his or her corneal endothelium (innermost layer of the cornea) and replaces only the diseased surface cornea. However, as with PK, sutures are required and resulting post-operative challenges remain.
In recent years, doctors have developed a more selective tissue removal procedure, known as endothelial keratoplasty (EK), which can be used when a patient’s condition allows for more modest tissue removal. With EK, only the innermost back
layer of the cornea, called the endothelium, is stripped away. Another benefit of EK procedures is that they do not require sutures. Instead, the transplant is attached to the stroma through the use of an air bubble. This preserves structural integrity, reduces wound-healing problems, and eliminates suture-derived complications.
Descemet's Stripping Endothelial Keratoplasty, or DSEK, is the most common type of EK procedure. Others include Descemet's stripping automated endothelial keratoplasty (DSAEK) and Descemet's membrane endothelial keratoplasty (DMEK).
Post-Operative Visual Acuity Challenges
Although the goal of corneal surgery often involves visual restoration, transplant procedures are often the harbingers of astigmatism, anisometropia and other conditions that stand in the way of good optics, and thus good vision. For this reason, vision correction with glasses, contact lenses or additional surgery often is needed. However, it’s important to note that post-graft vision correction can take time since vision can fluctuate for many weeks or months following a transplant procedure. Also, the irregular topography of post-transplant corneas makes any chosen alternative more complex.
Practically speaking, if surgery results in large amounts of astigmatism, glasses will likely be ruled out as a viable option. Soft contact lenses likewise cannot adequately address irregular astigmatism and are therefore not often used.
If the transplant eye has fully healed and has only low to moderate levels of astigmatism, a patient may benefit from laser refractive surgery such as LASIK or PRK. However, graft rejection and wound dehiscence can result when higher prescriptions are attempted. For these and other reasons, gas permeable (GP) lenses are generally considered the gold standard of irregular cornea visual rehabilitation. Contact lenses are used by more than 50% of patients after successful penetrating keratoplasty to achieve better visual functions. Although contact lens fitting can be challenging, it has proven to be safe and effective following corneal transplant procedures. The type of contact lenses often chosen are either a gas permeable (GP) corneal lens design or a scleral GP lens design.
GP lenses act as the primary optical surface of the eye and mask corneal surface irregularities—both of which are beneficial in this population. For wearers who struggle with discomfort when wearing standard GP lenses, a scleral lens is often a good option to pursue.
How Scleral Lenses Can Help
Scleral lenses are becoming increasingly popular and are safe and effective in patients who have had a corneal transplant procedure. To begin, they don’t touch any part of the already fragile cornea. Instead, these large-diameter lenses vault over the cornea and rest on the white part of the eye, known as the sclera.
Scleral lenses also offer a fluid buffer that exists between the back of the lens and the front of the eye. Liquid fills this space and can help protect corneal tissue and create a smooth refractive surface. For this reason, and others, scleral lenses should be considered as lens of choice in eyes with complex corneal geometry, as their use may delay or prevent further surgical involvement.
If you’ve had a corneal transplant, consult you doctor about options that can meet your visual needs while avoiding further corneal damage.