Ophthalmologic Anesthesia - Structure, Preoperative Evaluation, Indications, Complications.

Introduction

Nowadays, many ophthalmic surgeries are being performed based on ophthalmologic anesthesia used in the surgeries. The technique used to perform ophthalmologic anesthesia also plays an essential role in surgery as the method used is individualized based on the needs of the patient, the nature, and the extent of eye surgery. The goal of anesthesia during surgery is to focus on patient safety. It provides a patient with a pain-free experience and forms a surgical procedure to work coordinately with fellow members.

What Is Ophthalmologic Anesthesia?

Anesthesia is used in surgeries related to eye function, structure, or eye disease. Surgeries of the eye require anesthesia to comfort the patient in terms of pain. Anesthesia used in these surgeries is local or topical and regional anesthesia. Lidocaine, 2 percent, and Bupivacaine, 0.5 percent, are usually used. Techniques used to give anesthesia, like Akinetic and non-akinetic, also play an essential role in ophthalmic surgeries. Techniques depending on the patient's requirements and safety are used.

What Is Present Inside an Eye?

The structure of an eye has many different muscles and nerve supplies. An eye contains:

• Orbit - The orbit is an irregular four-sided pyramid having a medial wall, a lateral wall, a roof, and a floor. The medial walls of each orbit are toward the nasal cavity and parallel to each other. The lateral walls of each orbit are perpendicular to each other—a roof towards an eyebrow.

• Globe - The globe is present in the anterior part of the orbital cavity, closer to the roof than the floor and nearer to the lateral wall than the medial wall. It has three outer layers containing cornea and sclera in one; iris, ciliary body, and choroid in the second; retina in the last layer. The globe has a large posterior segment containing the optic nerve and retina and a small anterior segment. The axial length of the globe is 24mm, but larger (26 mm) in myopic and shorter (<20 mm) in hypermetropia.

• Muscles of the Eye - Extraocular muscles control the globe movements by rectus muscles (inferior, lateral, medial, superior) and oblique muscles (superior and inferior). These muscles form an incomplete cone.

• Nerve Supply - Within the cone, optic nerve, oculomotor nerve, abducens nerve (nerves from the brain), ciliary ganglion with nerves, and blood vessels are present. The trochlear nerve is present outside the cone. These different nerves supply different muscles of the eyes.

What Is the Preoperative Evaluation for Ophthalmic Anesthesia?

The important aspects of being considered in ophthalmologic anesthesia are:

• Physical examination of the patient with detailed history.

• Previous history of ophthalmic surgery.

• The axial length of the eye of the patient.

• Presence of any staphyloma.

• Relationship between the globe and eye.

• Whether the patient has glaucoma or not.

• B-scan echography.

• Blood sugar and blood pressure should be under control.

• Patients for cataract surgery should go for antiplatelets and diopter power circulation.

• The patient should receive oxygen 2 liter/min by nasal catheters.

• The patient's oxygen levels and blood pressure is checked before giving anesthesia.

What Are the Techniques for Anesthesia Administration?

The doctor follows a few techniques to insert anesthesia in ophthalmic cases. The techniques are:

• Sub-Tenon's Nerve Block:

• Surgical technique with a blunt cannula.

• Non-surgical technique with a blunt cannula.

• Non-surgical technique with a sharp needle.

• Improvised cannula technique.

• Retrobulbar Anesthesia:

• Classical technique.

• Modern techniques.

• Peribulbar Anesthesia: It involves the orbit with anesthesia being deposited in the orbicularis oculi muscle. It blocks the ciliary nerves, oculomotor nerve, and trochlear nerve.

What Is Retrobulbar Anesthesia?

• Retrobulbar anesthesia is a technique in which a small volume of anesthetic is injected inside the muscular cone.

• The doctor uses this technique earlier in time. This technique damages the globe's structures, so it requires technique modification. This technique is also called Atkinson.

• During this technique, the patient is asked to look up and down. The needle is inserted into the skin at the lateral and medial orbital edge junction. The needle is moved to the apex of the orbit, and an anesthesia solution of 2 to 4 ml is injected. And an additional nerve block to stop the blinking of the eyelid is required.

• Altogether, it is still not so suitable as an additional facial block requirement, and globe damage makes it risky too.

What Is Sub-Tenon's Nerve Block?

This technique is an alternative to the retrobulbar technique. After the topical anesthesia is used, the bulbar conjunctiva is handled with forceps. Small scissors create openings in the conjunctiva and tenon's capsule. A plastic cannula is inserted into the space to allow injection. Little modifications have been made to this technique. The modifications are:

• Non-surgicalTechnique With Blunt Cannula - This technique uses a blunt cannula and prevents the conjunctiva (white part of the eye) from cutting as it gives a scar on the conjunctiva.

• Non-surgicalTechnique With Sharp Needle - This technique uses a sharp bevel needle between the conjunctiva and the globe. The needle is shifted slightly medially and posteriorly, and anesthesia is injected in large quantities.

• ImprovisedCannula Technique - This technique uses a short intravenous cannula to inject anesthesia.

Which Is the Better Technique for Ophthalmologic Anesthesia?

The peribulbar and retrobulbar have the same effect on injecting the anesthesia. But the risks in cases of retrobulbar are more, so out of these two, peribulbar is better. The best among the three-technique is the sub tenon's nerve block which provides more safety to the patients with less complication.

What Are the Indications and Complications of Ophthalmologic Anesthesia?

Indications:

• Cataract surgery.

• Corneal surgery.

• Refractive surgery.

• Glaucoma surgery.

• Oculoplastic surgery.

• Extraocular muscle surgery.

• Vitreoretinal surgery.

• Open-globe surgery.

• Ophthalmic oncology.

Complications:

Complications Related to the Eye:

• Globe perforation (outer surfaces of the eye are disrupted by trauma).

• Retrobulbar hemorrhage (accumulation of blood in the retrobulbar space).

• Optic nerve damage (the optic nerve of the eye gets damaged).

• Subconjunctival edema (presence of fluid in the conjunctival).

• Venous hemorrhage (blood gets accumulated in the vein).

• Decreased visual acuity (decreased ability to see).

• Myotoxicity (side effect of statin therapy).

Systemic Complications:

• Seizures.

• Respiratory or cardiac arrest.

• Pulmonary edema.

• Allergic reactions.

Conclusion

Ophthalmic anesthesia is used in eye surgeries to give a pain-free experience to patients. The surgeries include retinal, corneal, cataract, and optic nerve surgery. Various techniques inject anesthesia into the eye. However, using the sub-tenon's nerve block and its modification significantly improves surgery results. In addition, sub-tenon is safer than retrobulbar and peribulbar, which risk the patients.