Bullous Keratopathy and Fuch’s Corneal endothelial dystrophy
Bullous Keratopathy and Fuch’s Corneal endothelial dystrophy
FThe cornea is a transparent tissue at the front of the eye through which light travels. It is dome shaped, and is responsible for most of the focusing of light onto the retina. When the cornea becomes waterlogged for any reason, it is less transparent and the vision is reduced.
Fuch’s corneal endothelial dystrophy
4% of the population have this condition. It usually runs in families and is usually not important. It impacts the health of a single layer of cells on the internal lining of the cornea that are responsible for pumping fluid out of the cornea. They do not divide and those that you are born with are the ones you die with. It is this layer that is damaged when bullous keratopathy exists. The cell density of this layer reduces with age.
In Fuch’s the cells decay at a faster rate and after cataract surgery the curve is reset at a much lower level. It becomes important when Fuch’s patients undergo cataract surgery. It is important that it is identified before surgery and specific additional steps taken to minimise the impact on this single cell layer during cataract surgery. Sometimes it will be inevitable that the cornea will stop working after cataract surgery and here a combining cataract surgery and Corneal Transplantation may be the faster most reliable way to ensure visual rehabilitation.
Symptoms vary. In early disease patients may notice a fluctuation in their vision throughout the day, worse in the mornings. As the disease progresses, it takes longer for the vision to clear in the day. Finally, the cornea is permanently waterlogged, the vision reduced and the skin of the front of the eye is easily scratched leading to pain, light sensitivity and watering eyes.
So patients do not feel their vision is impacted even though tests confirm the vision is affected and they have marked water blisters and water logging of the front of their eyes on microscope examination. This is because the problem creeps up on them slowly. Once the waterlogging causes blistering (bullous keratopathy) then secondary scarring can limit the usefulness and final vision obtainable with the newer standard partial thickness transplant techniques.
How can these symptoms be controlled?
In the earlier stages of the disease hypertonic salt drops (Muro128) and even use of a hairdryer can improve the vision earlier in the morning. These treatments have no effect in moderate to late disease. Corneal grafting can offer some patients improvement in vision and comfort. In some although the drops improve the vision they may cause unacceptable irritation and redness causing the eye to become more inflamed and create a more hostile environment for any final corneal transplant.
What is a corneal graft?
A corneal graft for Fuch’s or bullous keratopathy is perceived as a tissue rather than an organ transplant. Tissue gifted from a donor and finally the grieving family of the donor. It is used to replace the defective cornea in the patient. A corneal graft for bullous keratopathy can be a full thickness graft (man-hole cover) or a partial thickness graft (wallpaper). A full thickness graft requires sutures for up to 2 years to keep the graft in place, and although compatible with the highest level of vision possible, is more often associated with large amounts of astigmatism which mean only about half of recipients will be correctable to 20/20 after the operation. Up to half of patients require contact lenses to get the best vision, or tolerate a lesser level of vision in spectacles. Furthermore, after sutures are removed the shape of the graft can change significantly. Incisions in the graft, laser to the graft surface and implants into the eye can all be helpful in maximising the final best corrected vision. The vision may require 3 yrs and 12-14 outpatient visits to stabilise and maximise the vision.
A partial thickness (posterior lamellar graft) requires no sutures in the graft itself and is stuck to the back of the patients own cornea using an air bubble and is able to remove the water-logging from the patients own cornea. The vision is not quite as good as with a full thickness graft but the majority of patients can expect to maintain driving vision if there is no other problem with the eye. The vision recovers much more rapidly (12 weeks) with about 60-80% of otherwise normal eyes having a best corrected vision within driving standards by 6 months. Additionally as the patients own cornea remains intact and there are no large wounds or sutures there is usually much less astigmatism distorting the vision. Typically 4-6 outpatient visits over 2 years are required.
Partial thickness grafting is rapidly becoming the new gold standard for patients with bullous keratopathy requiring a corneal graft. Common terms for this procedure depend on the exact technique performed; Descemet’s stripping endothelial keratoplasty ( DSEK / DSAEK ) or Descemet’s membrane endothelial keratoplasty ( DMEK ). It is however not the right operation for everybody. The surgeon will discuss with you what is the best option based on your individual needs.
What does the surgery involve?
With any corneal graft it is useful to think of this as a process and a journey rather than a one off surgical event. The surgery can be carried out under general anaesthesia or local anaesthesia with sedation. With a full thickness graft sutures are required. These may need to be adjusted within the first couple of months to reduce astigmatism and maximise the intermediate post-operative vision. Sutures are then removed around 18-24 months. A posterior lamellar graft (partial thickness) is held in position on the back of the patients own cornea initially by an air bubble for 20 minutes at the end of surgery while lying on your back. This air bubble needs to be repeated in up to 2-5% of cases to ensure the donor transplant remains attached.
What results may I expect?
The outcomes of corneal transplantation have been most extensively studied using data from the Australian Corneal Graft Registry. Broadly, these outcomes can be divided into two major groups: Visual outcomes and survival outcomes. Both groups depend very much on the condition of the eye prior to the graft being performed. Conditions which have resulted in inflammation, infection or blood vessels entering the eye e.g. herpes simplex infections are associated with worse outcomes than those which do not e.g. keratoconus. A prior blood transfusion and a failed previous graft are also recognised as risk factors (albeit lesser) for graft survival. Overall, approximately 60% of grafts are functional at 10 years (rising to >90% in the best cases).
Visual outcomes vary according to the reason for which the graft was performed. A patient with uncomplicated Fuchs’ dystrophy might expect to achieve 6/12 vision at 5 years about 50% of the time with a full thickness ( penetrating ) graft. These figures are a guide and assume no other ocular disease. It has been estimated that approximately 40% of patients would achieve their best possible vision following a full thickness corneal transplant by the use of a contact lens but a quarter-of those individuals cannot use one because of difficulties in the handling of the lens.
A study which looked at patient satisfaction following corneal transplantation found that overall, about 75% of patients were satisfied. Partial thickness corneal grafts are less likely to need contact lenses to maximize their vision however their visual potential is usually 1-2 lines less than with a full thickness graft but up to 15% can still expect to achieve 20/20 corrected vision in the longer term but between 60-80% can be corrected to within driving limits.
Are there any risks with the surgery?
All operations carry the risk of complications whether from the anaesthetic, surgical procedure, subsequent medical procedures (e.g. removal of stitches) or any drugs e.g. eye drops which need to be taken. Specifically, in the case of eye surgery in which a cut is made into the eye, there is a risk of infection or bleeding inside the eye which can cause a permanent worsening or (rarely) loss of vision. The risk of retinal detachment following a corneal transplant is estimated at about 2% (twice that for cataract surgery), and sight threatening infection about 1% (five times higher than for cataract surgery). The donor material is tested for HIV, Hepatitis and the presence of bacterial infection and is assessed for quality at the supplying Eye Bank.
There is always however, remains a risk that a transmissible disease may be passed from the donor to recipient although that risk is thought to be extremely small.
All transplant operations rely on the body’s own tendency to reject foreign tissue to be medically suppressed. There is always a risk of graft rejection. This runs at 15-30% for full thickness grafts.
Partial thickness grafts are more likely to dislodge inside the eye (1 in 10) within the first week of surgery and can usually be replaced with another air bubble easily. The extra tissue handling involved in a partial thickness graft and the need for repeat air bubbles means that the risk of early graft failure is slightly higher than with full thickness grafts. It is hard to be sure but about 1-5% (versus 1% with full thickness grafts).
The long term data for posterior lamellar grafts has not been published yet as this is a new operation however it seems that rejection rates of less then 1-3% can be expected. However unlike a full thickness graft a failed partial thickness graft is simply peeled off and another new graft inserted relatively easily. A DMEK is very thin and fragile. This type of transplant gives the best possible visual outcomes but also the highest rate of primary graft failure with some estimates for primary graft failure being as high as 1 in 3. This raises ethical issues regarding the commodification of donor material as well as the additional demands on a precious resource.