Kahook Dual Blade
Kahook Dual Blade (KDB) Glaucoma Operation
A surgical procedure designed to help reduce intraocular pressure, commonly known as KDB.
This page gives you information that will help you decide whether to have
glaucoma surgery. You might want to discuss it with a relative or carer.
Before you have the operation, you will be asked to sign a consent form and
so it is important that you understand the information in this leaflet before
you decide to have surgery.
Introduction
Glaucoma is usually treated with medication in the form of eye drops to lower the pressure in the eye called the intraocular pressure (IOP).
If medication is not effective at lowering the IOP, not well tolerated or you are struggling to instil I the drops, then the KDB operation may be of value for you in lowering / controlling the IOP particularly if you also require cataract surgery.
What is the KDB Operation?
Under normal conditions, fluid produced within the eye (by the cilary body) known as aqueous humour is drained away by an area in the drainage angle in the front portion of the eye called the trabecular meshwork (figure 1 – black arrow). The trabecular meshwork (TM)which extends 360 degrees around the front portion of the eye, works like an active pump to move the aqueous humour into the drainage canal (Schlemn’s canal) from which the fluid drains away into the collector channels & finally the blood circulation of the eye (episcleral veins) (Figure 1 ).
In glaucoma/raised IOP the function of the trabecular meshwork is impaired such that it has reduced or inability to pump aqueous humour into the Schlemn’s canal. As a result, aqueous humour cannot escape & builds up in the front chamber of the eye causing raised IOP (figure 1 – red arrow). The KDB operation works by physically removing about four clock hours (sometimes 3 to 5) of trabecular meshwork tissue to allow aqueous humor to flow freely into the Schlemn’s canal and
beyond. To remove the trabecular mesh work tissue a special blade called a KDB blade is used. The operation is usually combined with cataract surgery
but can be performed on its own. When combined with cataract surgery, the cataract is removed, then an artificial lens is implanted following which the KDB operation is performed.
The operation is usually performed under local anaesthetic (LA) whereby anaesthetic medication is administered around the eye to numb the eye and prevent you from moving your eye during the operation. The administration may cause mild discomfort or a pressure sensation when it is delivered, however, this sensation will quickly disappear. If you feel nervous our anaesthetist can also administer medication through the vein to make you “sleepy” but you will still be conscious and aware of your surroundings.
The LA will be then be given around the eye to anesthetise it. Occasionally we perform the operation under general anaesthesia (GA) where you are asleep for the duration of the surgery.
Due to the associated risks, you must inform your consultant prior to surgery if you a retaking ANY blood-thinning medication.
What are the benefits of the KDB operation?
When combined with cataract surgery, the operation allows us to both remove your cataract and combine this with an operation to lower your eye pressure and/or a number of glaucoma medications or both.
A number of studies have now been published showing the success of the KDB procedure at 12 months after the operation. The largest of these trials(reference 1) showed that 71 % of patients had either a 20% reduction in the IOP or reduction in one glaucoma drop or both.
In a smaller study (reference 2), 58% of eyes achieved an equal to or greater than 20% reduction in IOP with 64% of eyes achieving a reduction in the number of glaucoma drops by 1 or more. In a subgroup analysis, patients with a preparation higher IOP (greater than 16.SmHg) achieved a 40% reduction in the IOP and 100% of eyes met the success criteria of greater than or equal to 20% reduction in the IOP from baseline.
Despite the above, longer term data on the success of this procedure is awaited.
What are the risks of the KDB operation?
- Hyphema (bleeding into the front chamber of the eye) -has been reported to occur in 17% of eyes within the first week following surgery. The hyphema usually has no bearing on your vision however can cause high IOP and or blurred vision. lfhyphema does occur, it can take up to 2 weeks (average 7 days) to clear on its own. Rarely (0.5%) if the hyphema does not clear and the IOP remains sustainable high you may need surgery to clear this away (reference 1 ). It has been shown that if you are on blood thinning medications (anti-coagulants) you have a higher risk of hyphema (approximately 24%} compared to not being on this medication ( 14%). Therefore, please inform you consultant prior to surgery if you are taking ANY blood thinning medication.
- High /OP (defined as a rise greater than 1 0mmHg above base line preoperation IOP)- has been reported to occur in about 11 % and usually occurs within the first 2 weeks after surgery and is more likely to occur in patients with a hyphema.
- Damage to the iris (coloured part of the eye) or cornea (clear window of the eye)- these are rare complications and can occur during the procedure itself. If they occur it can cause glare which you either adaptto with time (damage to the iris) or settle with time (damage to the cornea).
- Loss of vision - in a about 1 :1000 patients due to infection or bleeding.
After the Operation
- Stop all glaucoma drops in the operated eye ONLY (continue your drops in the un-operated eye as normal).
- Wear the plastic shield provided at night for 10 days.
- Do not rub or apply pressure to the eye.
- Avoid strenuous activity- sports, heavy lifting etc for 2 weeks.
Your vision may be blurred for up to 2-3 weeks following the surgery and this is quite normal particularly when combined with cataract surgery.
For the majority of patients, the eye will appear red/bloodshot for 2-3 weeks following surgery however, this will all settle down.
Post operation Drops/ medication
- Anti-biotic drop (commonly Chloramphenicol) - which should be used 4times a day for a total of 14days.
- Steroid drop (Dexamethasone) - to reduce inflammation after surgery. This is usually prescribed initially 4-6 times a day.
- Pilocarpine 2% drops - to keep the Schlemn’s canal open and lower the eye pressure. This is to be used 4times a day. The main side effect of these drops is that they can cause brow ache/ headache and reduce your night vision. if you experience headaches, you can take paracetamol regularly until it settles.
- Acetazolamide tablets - These are often prescribed at 1 tablet (250mg) 3 times a day for 3 to 5 days to lower the eye pressure in the early period after the surgery. Side effects include: tiredness, drowsiness, pins and needles around the mouth, hands and feet and altered appetite/taste.
Please note, only one drop should be instilled at a time and a minimum of 5 minutes gap should be left between drops.
Below is the typical schedule of drop reduction following surgery.
Follow-up after the operation
On the day of surgery, depending or whether or not you have glaucoma and if you do, its severity, we may see you BEFOREY OU GO HOME to check your IOP.
The nursing team will be informed if we need to see you before discharge.
All patients are then seen 1 week following surgery and then 6 to 8 weeks following surgery.
If you have had combined cataract surgery and the KDB procedure, at 5-6 weeks after your operation, please see your optician for a glasses prescription test (refraction) and bring the paper copy to your next clinic appointment.
It is very important that if you do not receive your appointment to be seen as
above, you contact your consultant’s secretary without delay.
References
1. EG Sieck et al. Outcomes of Kahook Dual Blade Goniotomywith and without Phacoemulsification Cataract Extraction. Ophthalmology Glaucoma 2018;1 :75-81.
2. Dorairraj et al. 12-Month Outcomes of Goniotomy Performed Using the Ka hook Dual Blade Combined with Cataract Surgery in Eyes with Medically Treated Glaucoma. Adv Ther2018;35:1460-1469
