Overview of Retrobulbar Block
The retrobulbar blockade, a type of anesthesia used during eye surgery, was first introduced by Herman Knapp in 1884. In the same year, Carl Koller performed a successful eye surgery using a cocaine-based anesthetic. Later in 1936, Atkinson outlined a method for performing the retrobulbar technique which became widely used. However, due to a high rate of side effects, this method became less popular over time. Since then, there have been many advances in anesthesia methods for eye surgery.
The retrobulbar blockade is considered a traditional go-to technique for numbness and muscle immobility during eye surgery. However, it does carry risks of serious, though rare, complications that can threaten sight or life. Because of this, some doctors have switched to newer techniques, such as peribulbar blockade and the Sub-Tenon block. These techniques are believed to have less severe side effects but provide the same levels of numbness and muscle immobility as the retrobulbar blockade. Nonetheless, some surgeons still prefer using local anesthesia for certain eye procedures.
Anatomy and Physiology of Retrobulbar Block
Understanding how the eye and the space around it, called the orbit, are structured is vital for making sense of how a particular type of anesthetic—called the retrobulbar block—works and any complications it might cause. The space inside the orbit can be divided into two sections. One section encloses fat, some nerves that control eye movement and sensation, and the artery that supplies the eye with blood. The other section contains more fat, a gland that makes tears, another eye-controlling nerve, and some branches of the main nerve that controls sensation in the face.
The eye sockets, or orbits, aren’t perfectly pyramid-shaped; instead, they have curved, irregular walls punctuated by gaps and holes. The height, width, and depth of these orbits can vary, but typically, the depth is between 42 to 54 mm, which is why it isn’t recommended to use needles longer than 38 mm for this kind of anesthesia. The inner wall of the orbit is thin, and right behind it, there’s a sinus. Very rarely, if the needle goes through this thin wall, it could lead to a pocket of pus (abscess) or an infection (cellulitis).
The eyeball itself has a diameter of about 25 mm and sits at the front of the orbit. This size is important because it impacts the effectiveness of the anesthesia. Nearsighted people, whose eyes are slightly bigger, carry a higher risk of damage if the needle goes too far. Also, the presence of outpouching of weak eye tissue, known as staphylomas, can increase the risk of damage.
The rotation of the eye is controlled by six muscles. The tendons of four of these muscles join to form a ring, creating a spacious area filled with fat. This area is perfect for injecting the anesthetic. Most of the muscles are controlled by a nerve called the oculomotor nerve. A facial nerve controls the muscle that is responsible for blinking, and it often needs to be numbed as well to prevent blinking during surgery. The sensation of the eye is primarily controlled by the trigeminal nerve and its branches. However, only parts of those branches are affected by this type of anesthesia.
The blood supply to the eye and the muscles is primarily the ophthalmic artery, which tends to lean more towards one side: the top-right corner of the eye. Therefore, it is prudent to avoid this area when administering the anesthetic. The eyeball and these muscles are also surrounded by a capsule of connective tissue. Injecting anesthetic into the space around this capsule helps to numb the muscles and nerves of the eye.
Imaging studies have been done on the distribution of the anesthetic in the space around the eye. They found that the anesthetic spread intensely within the inner part of the eye socket, surrounding the nerve that connects to the brain.
One thing to keep in mind is that anesthetics used for eye surgery can momentarily increase eye pressure because of the volume of liquid injected around the eye. Applying digital pressure to reduce bleeding or enhance the spread of anesthesia isn’t recommended as it can sharply increase eye pressure, sometimes causing bleeding in the front chamber of the eye. If certain, specialized balloon devices are used to apply pressure, they should not exceed a preset limit.
There’s also something called the Oculocardiac reflex to be aware of. This is a mechanism where pressure on the eye—specifically the muscles controlling eye movements—could slow the heart rate, potentially causing skipped beats or even a temporary stop in heartbeat. This occurs because stimulation of the eye muscles send signals to the brain to slow down the heart’s activity.
Why do People Need Retrobulbar Block
The retrobulbar blockade is a technique that doctors use to make the eye numb and inactive for certain types of eye surgery. It’s used when the operation is expected to take less than two hours. A retrobulbar blockade is most commonly used for different types of eye surgeries, like:
1. Cataract surgery: This is when the eye’s lens – which has become cloudy due to cataracts – is removed and replaced with an artificial one.
2. Corneal transplant or Keratoplasty: Here, a damaged or diseased cornea – the eye’s clear, front surface – is replaced with healthy tissue from a donor.
3. Vitrectomy: In this surgery, the vitreous gel that fills the back of the eye is removed and replaced.
4. Tube shunt placement: Here, an artificial channel is implanted to help drain excess fluid from the eyes, often in cases of glaucoma.
5. Enucleation or Evisceration of the eyeball: These are surgeries to remove all or part of the eyeball. These are generally performed to attack advanced cancer, or to relieve pain in a blind and painful eye.
6. Cyclodestructive procedures: Processes for advanced glaucoma that aim to lower the pressure within the eye by decreasing the production of eye fluid.
In summary, a retrobulbar blockade is a valuable tool for assisting in a range of different eye surgeries. It’s a way to keep the eye still and pain-free during the operation.
When a Person Should Avoid Retrobulbar Block
Your eye doctor may need to perform a procedure called a retrobulbar block, which is a type of local anesthesia for the eye. But sometimes, there might be certain reasons due to which they cannot do this procedure. Here are a few:
Absolute reasons include:
- If you refuse the retrobulbar block.
- If you’re allergic to the local anesthetic medication.
- If there’s a local infection in or around your eye area.
- If your eyes move uncontrollably, a condition known as nystagmus.
Relative reasons could include:
- Open eye injury
- Presence of blood vessel tumors within the eye socket.
- If you had a previous surgery to fix a detached retina, known as scleral buckling.
- Eyes that are highly nearsighted, specifically if your eye is longer than 26 millimeters, with or without a bulge in the retina due to extreme nearsightedness.
- An eye condition associated with thyroid disease, known as thyroid-associated orbitopathy.
- If your blood tends to bleed excessively or is not clotting properly, technically termed ‘bleeding diathesis’
- If you’re currently taking medication to prevent blood clotting.
- Having severe difficulty in breathing while lying flat, known as orthopnea.
- If you have psychiatric disorders that are not well-controlled or inability to cooperate with the procedure.
- If you only have vision in one eye.
Equipment used for Retrobulbar Block
If you’re undergoing a medical procedure, your doctors might give you Sedation. This means they will use certain medications to help you relax or fall asleep during the procedure. This might involve:
* Using a needle to create an ‘intravenous access’, or a way to deliver medication directly into your blood vessels.
* Giving you a medication called Midazolam, typically between 1 to 2mg. This medication can make you feel sleepy and relaxed.
* Administering a medication known as Fentanyl, usually between 50 to 100 micrograms. Fentanyl is a pain killer.
* Monitoring you according to the American Society of Anesthesiology (ASA) basic guidelines. This means they’ll closely watch your blood pressure, oxygen levels, carbon dioxide levels, and heart rate, usually with a blood pressure cuff, a device on your finger (pulse oximetry), a monitor that checks the carbon dioxide in your breath (capnography), and an electrocardiogram machine that monitors your heart.
If your doctor does a Retrobulbar Block, it is a form of anesthesia often used for eye surgery. You might expect the doctors to:
* Clean your eye with a Povidone-iodine 5% ophthalmic preparation. This is a type of antiseptic that kills bacteria to prevent infection.
* Give you anesthetic eye drops (specifically, proparacaine hydrochloride 0.5%), to numb your eye.
* Use gauze, a type of soft fabric, to clean or cover your eye.
* Use a syringe (5 mL to 10 mL) to inject the local anesthetic.
* Use a sharp needle (23 to 25 gauge; length 30 to 38mm) to administer the anesthesia.
Another technique for eye anesthesia is the Peribulbar Block. Like the retrobulbar block, this involves injecting a local anesthetic into your eye area. For this procedure, they’ll use a different needle (25 to 27 gauge, length 15 to 25mm), and they might also use something called a ‘Honan balloon’. This balloon can help to spread the anesthetic evenly through your eye area.
Lastly, a Sub-Tenon Block is another type of anesthesia used in eye surgery. The procedure is done using a Sub-Tenon cannula (a small medical tube) 19 gauge; length 25mm with a flat, curved tip. However, this is outside our discussion today.
Who is needed to perform Retrobulbar Block?
A retrobulbar block is a specific kind of anesthesia technique that only experts should do. This means doctors like anesthesiologists (who are trained to give medications that make you not feel pain or put you to sleep) and ophthalmologists (eye doctors) usually do it. It’s really helpful if a nurse, who knows a lot about anesthesia too, is there to help. They can give you medications to help you relax.
Preparing for Retrobulbar Block
Before having eye surgery, it’s important to have a full check-up. This includes a look at your current health condition, a physical exam, and a special test to see how your airway is working. Your doctor will also look at your past test results, particularly those related to the size of your eye and how quickly your blood clots. They will also need to know what medicines you are taking right now, especially any painkillers or blood thinners.
While eye surgery is generally safe and complications are rare, the doctor who gives the anesthesia will explain any possible risks. They will also take steps to ensure these risks are kept to a minimum. There’s no fixed rule on how to handle blood thinners in eye surgery, but most doctors follow the guidelines set out by the American Society of Regional Anesthesia in 2018. These guidelines offer advice on managing blood thinning medication in patients having certain types of blocks, which are injections that numb part of your body.
Lastly, the surgery should happen in a place with the right equipment to safely monitor your health and handle any emergencies. This gear includes tools to check your blood pressure, measure the amount of oxygen in your blood, monitor your heart activity, and track the amount of carbon dioxide you’re breathing out.
How is Retrobulbar Block performed
The choice of a local anesthetic, a drug that causes loss of feeling or numbness, relies on how fast the drug starts working (onset) and how long it lasts (duration of action). Normally, a combination of drugs that work quickly and last longer is preferred. Lidocaine, a common anesthetic, should never be used in concentrations over 2% to avoid muscle toxicity, which is when the drug harms muscles.
Some doctors might also use hyaluronidase, a substance that helps anesthetics spread through the tissue more quickly and can lessen muscle toxicity. The safe dosage is 50 IU for each milliliter of local anesthetic. Epinephrine, a hormone that can increase the duration of numbness, was previously used. However, due to the risk of vasoconstriction (narrowing of blood vessels) and consequent retinal ischemia (decreased blood flow to the retina), along with the availability of long-lasting anesthetics, its usage has become less common recently.
Two techniques are commonly used for administering the anesthetic: the Retrobulbar and Peribulbar techniques.
Retrobulbar Technique:
This technique starts by applying two drops of local anaesthetic to the eye, then the area around the eye is cleaned. The injection point is chosen around the lower part of the eye socket. The patient is asked to look straight ahead, to avoid potential injuries. While one hand is used to lift the eye and avoid direct trauma from the needle, the other hand is used to insert the needle following a certain path and depth, which can be identified by specific sensations (known as pops). Then, slowly, 3-5 mL of local anesthetic is injected, and after 5 minutes, the movement of the eye is checked.
Peribulbar Technique:
This procedure is similar to the Retrobulbar technique, with a few key differences. After inserting the needle, 6-8 mL of local anesthetic is injected. A second injection is needed because a specific muscle may not be affected by just one injection. The depth of this second injection should be less than 25mm to avoid potential damage to the optic nerve. After the injection, 3-5 mL of local anesthetic is injected. After 10 to 15 minutes of infiltration, the movement of the eye is checked.
Possible Complications of Retrobulbar Block
Problems arising from local anesthesia used in eye surgery are uncommon, but can sometimes risk the patient’s sight or even life. However, life-threatening situations are extremely rare, happening only in about 3.4 out of every 10,000 cases. These issues are often linked with a type of anesthesia called a retrobulbar block. Evidence shows that the usage of a different method, called a peribulbar technique with shorter needles, has a lower chance of causing bad reactions.
Retrobulbar hemorrhage, which is bleeding behind the eye, is one possible complication. This can occur in 0.04% to 1.7% cases when retrobulbar blocks are used. As the needle goes in deeper, blood vessels become more crowded, raising the risk of poking one. If an artery is punctured, symptoms such as sudden eye bulging, vision loss, severe pain, and increased eye pressure may appear. This is a medical emergency that might require urgent eye specialist procedures. If the bleeding comes from a vein, the symptoms often show up later and are usually less severe.
Injury to the ocular globe – the eyeball – is another rare but possible issue. The likelihood of this occurring varies, but having a longer eyeball or a bulge in the back of the eye could increase the risk. The usage of a retrobulbar block raises the risk of perforation (a hole) in the eyeball by 30 times. Symptoms might include pain where the medicine was injected and sudden vision loss. If eyeball puncture is suspected, attempting to move the eye can confirm it – if the needle is blocking movement, the eye won’t respond as expected.
Optic nerve damage and muscle injuries around the eye can also happen, but are also very rare. If the needle used is longer than 31mm, there’s a higher chance of optic nerve injury. Anesthesia injected directly into the eye muscles can cause issues such as misaligned eyes, eyelid drooping and double vision. Too much anesthesia, or highly concentrated solutions, can also harm the eye muscles.
In very rare cases (0.3% to 0.8%), the anesthesia might spread to the central nervous system and affect the brain, leading to symptoms like ear ringing, vision loss, slurred speech, shaking, excitability, and seizures. In such cases, patients will need immediate medical attention and might require intensive care.
What Else Should I Know About Retrobulbar Block?
In the past, the retrobulbar block, a type of local anesthesia used specifically for the eyes, was widely used by doctors. This technique could numb the eye quickly to provide relief from pain and stillness (akinesia) for certain procedures. However, its popularity has dropped due to the introduction of newer techniques that can achieve similar results but with less risk of complications.
Yet, it’s important to remember the potential benefits of the retrobulbar block. Notably, it can provide fast relief from pain and stillness, which may be more effective compared to other techniques. Additionally, any type of regional anesthesia comes with risks associated with the specific area of the body where it is applied. Therefore, understanding the basic anatomy of the area around the eye (the orbital space) is key to understanding these possible risks.
