Ocular surgery may be performed under topical, local or general anesthesia. Local anaesthesia is more preferred because it is economical, easy to perform and the risk involved is less. Local anaesthesia has a rapid onset of action and provides a dilated pupil with low intraocular pressure.
Susruta Samhita has evidences of use of anaesthesia for ocular surgeries. Inhalational anaesthesia was used for this purpose.[citation needed] Egyptian surgeons used carotid compression to produce transient ischemia during eye surgery to reduce the perception of pain.[citation needed] In 1884, Karl Koller used cocaine for ocular surgery.[citation needed] The same year, Herman Knapp used cocaine for retrobulbar block.[citation needed] In 1914, van Lint achieved orbicularis akinesia by local injection.[citation needed]
Surface anaesthesia is given by instillation of 2.5 ml xylocaine. One drop of xylocaine instilled four times after every 4 minutes will produce conjunctival and corneal anaesthesia. Paracaine, tetracaine, bupivacaine, lidocaine etc. may also be used in place of xylocaine.[1] Cataract surgery by phacoemulsification is frequently performed under surface anaesthesia. Facial nerve, which supplies the orbicularis oculi muscle, is blocked in addition for intraocular surgeries. Topical anaesthesia is known to cause endothelial and epithelial toxicity, allergy and surface keratopathy.[citation needed]
There are four types of facial block : van Lint's block, Atkinson block, O' Brien block and Nadbath block.
This technique was first practiced by Herman Knapp in 1884. Here, 2% xylocaine is introduced into the muscle cone behind the eyeball. The injection is usually given through the inferior fornix of the skin of the outer part of the lower lid when the eye is in primary gaze. The ciliary nerves, ciliary ganglion, oculomotor nerve and abducens nerve are anesthetized in retrobulbar block.[2] As a result, global akinesia, anaesthesia and analgesia are produced. The superior oblique muscle, which is outside the muscle cone, is not usually paralyzed. The complications of retrobulbar block are globe perforation, optic nerve injury, retrobulbar haemorrhage and extraocular muscle palsy. Retrobulbar anaesthesia is contraindicated in posterior staphyloma, high axial myopia and enophthalmos.[4]
This technique was first applied by Davis. In peribulbar block, local anaesthetic is injected to the peripheral spaces of the orbit. The anaesthetic diffuses into the muscle cone and eyelids, causing global and orbicularis akinesia and anaesthesia. After injection, orbital compression is applied for around 15 minutes.[clarification needed][4]
Nearly all ocular surgeries viz keratoplasty, cataract extraction, glaucoma surgery, iridectomy, strabismus,[5] retinal detachment surgery etc. can be done under regional anaesthesia. Conjunctiva, globe and orbicularis can be paralysed using a combination of surface anaesthesia, facial anaesthesia and retrobulbar block.[1] The advantage is that it produces less post-operative restlessness. It has less post-operative lung complications and less bleeding.[2]
General anaesthesia is preferred for ocular surgeries in anxious adults, psychiatric patients, infants and children.[5] It is also indicated in perforating ocular injuries and major surgeries like exenteration. During the surgery, it has to be ensured that no carbon dioxide retention occurs. If this occurs, the choroid swells up and ocular contents may prolapse as soon as the eye is opened. The advantages of general anaesthesia is that it produces complete akinesia, controlled intraocular pressure and safe operating environment. It is the safest option for bilateral surgery. The complications of general anaesthesia are laryngospasm, hypotension, hypercarbia, respiratory depression and cardiac arrhythmia.