There are two main purposes of anesthesia for cataract surgery. The first is that the patient should not feel pain. This is the primary reason and is very important from the patients’ perspective. Ophthalmic surgeons call it ‘sensory anesthesia’.
The other important aspect of anesthesia in cataract surgery is that the eye should not move during surgery. The eye is supposed to be static so that the surgeon can visualize the tissues better and does not accidentally injure the delicate structures of the eye. Surgeons call it ‘motor anesthesia’ or akinesia.
Here is a brief account of all types of anesthesia used for cataract surgery:
Local anesthesia for cataract surgery
Local anesthesia has the advantage that it affects only the eye and tissues around it. The anesthesia does not require strict medical fitness as is required in general anesthesia. The patient is aware of the activities in the operation room and can communicate with the surgeon and other staff during the surgery.
The local anesthetic is injected behind the eye globe. The paralysis of extraocular muscles is good and the anesthetic effect is quicker but there is always a risk of optic nerve injury. Accidental anesthesia of brainstem with possible fatal consequences is possible because of the continuation of layers covering the optic nerve with those of the brain.
There is also a risk of eyeball perforation with the sharp needle. The extraocular muscles sometimes develop toxicity effects because of the local anesthetic drug.
In this technique, the local anesthetic is injected away from the optic nerve so that there is less risk of injury to optic nerve. Accidental anesthesia of brainstem is not possible with this technique.
The amount of injection is also more (about 6-10 milliliters).
Tenon’s capsule is a thin sheath or membrane covering the eyeball. Sub-Tenon’s block is given by injecting the local anesthetic into the space between Tenon’s capsule and the eyeball.
In order to avoid perforating the eyeball itself, a blunt-tipped cannula is used instead of a sharp needle.
Topical anesthesia for cataract surgery
Nearly two-third cataract surgeries in the United States and one-third cases in United Kingdom are performed under topical anesthesia.
Topical simply means that the anesthetic agent is applied on the surface of the eye just like an eye drop. The risk of eye injury with needle is not there. This is the main advantage of topical anesthesia over retrobulbar and peribulbar anesthesia. It may be combined with injection of an anesthetic agent under the conjunctiva or into the anterior chamber of the eye for better effect.
The purpose of topical anesthesia is to abolish the pain sensation but the patient can still move the eyes because the extraocular muscles are not paralyzed. To reduce the movement of the eye, the patient is asked to focus on the light of the operation microscope. This makes things easier for the surgeon, otherwise a moving eye can make the surgery difficult as mentioned earlier. It can also cause serious complications.
In general anesthesia the anesthetic agent acts on the brain and induces near-complete or complete loss of consciousness. For obvious reasons, all sensations are inhibited in the whole body including the eye.
This technique is used in children and some adult patients who are uncooperative because of various medical conditions such as Parkinsonism, mental retardation etc. The number of patients operated for cataract surgery under general anesthesia therefore is quite low.
If you are going to have cataract surgery done on your eye, your ophthalmologist has probably already informed you about which type of anesthesia will be used for your cataract surgery. If you are still not sure of this, you will most probably get topical anesthesia or peribulbar anesthesia which are most commonly used methods of anesthesia for cataract surgery.
You may also like to read:
- Risk Factors of Developing Cataract
- Future of Cataract Surgery
- Do You Need Glasses After Cataract Surgery?
- Floaters After Cataract Surgery
- Steroid Eye Drops After Cataract Surgery