Minimally Invasive Vitreous Surgery: 20 Gauge to 27 Gauge Shalabh Sinha
INDEX
×
Chapter Notes

Save Clear

Introduction and AnesthesiaCHAPTER 1

Shalabh Sinha
 
INTRODUCTION
Minimally invasive surgery, whether it is in general surgery, or orthopedics or cardiac surgery, is the universal choice for patients as well as surgeons. There is little doubt that lesser the surgical trauma, the faster is the recovery for the patient. The proof for ophthalmology lies in phacoemulsification for cataract removal, a revolutionary surgical step that has proved itself over time. Vitreous surgery has only followed suite. Various gauges of instrumentations have now become available for the vitreous surgeon, apart from the conventional 20 gauge. The vitreous surgeon must choose and evaluate the MIVS procedure that would become his/her choice for the treatment of various vitreoretinal diseases. No one gauge may be suited for all patients and all diseases. There is of course a learning curve that the surgeon must go through. For a surgeon who is well-versed with conventional 20 gauge vitrectomy, a 23 gauge system would be most ideal. 25 or 27 gauge vitrectomy system could be adopted later depending upon the indication, the machine one is using and the comfort of the vitreous surgeon.
 
Reasons for Choosing MIVS
 
In primary surgery
  1. Minimal conjunctival trauma—This is important in patients that already have a filtering bleb or who may need a glaucoma surgery at a later date.
  2. Less patient discomfort or pain.
  3. Faster visual rehabilitation—As there is less corneal astigmatism, and MIVS wounds heal quicker than conventional 20 gauge wounds.
 
In repeat surgery
  1. Conjunctival peritomy in a previously operated eye can cause significant bleeding.
  2. Scleral wounds remains healthy because no cautery is used. There are less chances of scleral necrosis or ectasia.2
 
Advantages of Cannula
  1. Protects the sclera and conjunctiva during intraoperative instrument exchanges.
  2. Minimal traction at the vitreous base, and hence reduction in sclerotomy related iatrogenic retinal breaks.
  3. Higher likelihood of a sealed/closed incision at completion of surgery.
  4. Silicone oil removal is easier with nonvalved cannula system, even passively.
  5. Ease of introducing instruments of appropriate gauge through the cannula, one does not have to search for the sclerotomy.
 
Advantages of Valves
  1. Valved cannulas provide stable intraoperative intraocular pressure.
  2. No fluid leak intraoperatively. This is valuable in eyes having undergone previous vitrectomy.
  3. Less turbulence inside the vitreous cavity especially during instrument removal or exchange.
  4. Least likelihood of vitreous or retinal incarceration into the cannula.
  5. Least likelihood of intraoperative choroidal detachment.
  6. Valved cannulas provide freedom from scleral plugs.
 
Misconceptions Regarding MIVS
It is faster than conventional 20 gauge surgery—False
While time was saved in not having to perform conjunctival peritomy, suturing the infusion cannula, or the sclerotomy and conjunctiva at completion of surgery, longer vitrectomy time balanced out time saved. This was with older generation cutters with reduced aspiration. Midlab cutter has a better aspiration rate than the older generation Alcon cutter. The new generation Alcon cutters have better aspiration rates and programmable duty cycle. It allows the surgeon to choose a particular mode such as “core vitrectomy” or “shave” depending upon where one is working.
Incisions need not be sutured—False
The threshold for placing a suture needs to be low. Any active leak must be addressed with placement of a suture. Sutures do not mean that the procedure has failed. It is what one does inside the eye that matters more with fine gauge instrumentation than the scleral suture.
Complicated cases cannot be done with MIVS—False
It is easier to perform surgery in tractional retinal detachment with narrow gauge instrumentation. The cutter becomes a multifunctional tool, making the use of scissors and forceps negligible. Bimanual membrane dissection can also be done using a suitable chandelier. 3
Patients requiring a buckle along with vitrectomy do not require the use of cannula—False
Valved cannulas provide all the benefits of using them as in a transconjunctival surgery. If silicone oil is used, there is minimal egress of silicone oil after removing the cannula. This ensures a complete fill.
Dropped nucleus or intraocular foreign body require a conventional 20 gauge vitrectomy—False
20 gauge valved cannula system is ideally suited for both the conditions for vitrectomy. A 23 gauge fragmatome needle is now available for dropped nuclei. One of the superior cannulas can be removed and the fragmatome needle can be passed through the same track to perform nucleus removal. The cannula can be placed back into the wound with a blunt insertor, and the procedure could be completed. For large foreign bodies in phakic or pseudophakic eyes one of the sclerotomies could be enlarged. If the patient is aphakic, a corneal tunnel incision could be fashioned for removal of the foreign body.
 
ANESTHESIA
The various modalities available for vitreoretinal surgery include local anesthesia and general anesthesia. Local anesthesia can be in the form of topical, sub-Tenon's, retrobulbar, peribulbar and parabulbar. The choice of the anesthesia must be based on the needs of the patient, the requirements of the surgeon and the skill of the anesthetic provider.1
 
Topical Anesthesia
Topical anesthesia is simple, quick and noninvasive.2 Similar to phacoemulsification, retinal surgeons have been looking to provide this modality to their patients. The first report of topical anesthesia for posterior vitrectomy was by Yepez et al using 4% lidocaine drops in 20 gauge vitrectomy along with perioperative sedation. Mild pain was perceived during making of sclerotomy, cautery and conjunctival closure.3 23, 25 and 27 gauge MIVS are less invasive than conventional 20 gauge vitreous surgery and are ideally suited for topical anesthesia. Raju et al reported that 25 gauge vitrectomy could be safely performed using topical anesthesia in their patients with vitreous hemorrhage, endophthalmitis and retained cortex. Pain was felt during insertion of the cannula, in most patients.4 Tang et al had a larger series of patients where they used topical anesthesia (Alcain) for their patients with macular disorders. 67.4% of patients tolerated the procedure well, but 28.3% required topical supplement during surgery and a further 4.3% required intravenous sedation.5 The major difference from cataract surgery is that the cannula passes through the uveal tissue in the pars plana. Penetration of the uveal tissue and movement of the cannula during surgery causes pain. Short duration of surgery combined with minimal manipulations may be the 4ideal candidates for topical anesthesia. Satyen et al have suggested surgeons calculate the expected duration of surgery and only those with least time be subjected to topical anesthesia using 23 gauge vitreous surgery.6 Theocharis et al have indicated that endolaser, scleral indentation and peribulbar anesthesia caused pain in their two year prospective study using topical 2% lidocaine drops and gel formulations. They have also found that 23 gauge MIVS was easier to perform than 25 gauge.7 Lidocaine gel formulations can provide a longer lasting anesthetic effect. The anesthetic gel must be placed after 5% or 10% povidone iodine has been instilled in the conjunctival cul-de-sac. Ehab et al compared 2% lidocaine gel to retrobulbar anesthesia for 23 gauge vitrectomy for macular disorders. They found that local anesthesia with 2% lidocaine gel was as effective as retrobulbar injection without the risks of IOP elevation prior to surgery. Lack of akinesia did not pose a problem and did not prevent a successful outcome.8
 
Sub-Tenon's Anesthesia
Sub-Tenon's anesthesia is found to be safe and effective for retinal surgery. It was initially used as a technique to augment the effect of retrobulbar anesthesia.9 Mark et al described it as an alternative technique to retrobulbar anesthesia. The authors used a 19 gauge blunt irrigating cannula to place anesthetic agent into the sub-Tenon's space, by opening the posterior Tenon's capsule. The technique was effective in 98% patients undergoing vitreoretinal surgery.10 Li et al evaluated patients with sub-Tenon's anesthesia for retinal surgery. Patients involved in longer duration of surgery and those with painful procedures such as scleral buckle and cryopexy needed supplementation either in the form of local or intravenous medication.11 The only problem with Sub-Tenon's anesthesia is increase in intraocular pressure and conjunctival chemosis. Chemosis may hamper placement of the microcannula. Hee et al studied the effect of volume used and found that 3–5 ml of anesthetic fluid was safe and effective. This was much less than the 11 ml of anesthetic solution used by Li et al. The authors also reported that posterior segment surgery lasting more than 3 hours or those requiring scleral buckling or cryopexy were more likely to require supplementation in the form of local anesthetic or intravenous sedation.12 Vip et al used 5 ml anesthetic agent injections into the sub-Tenon's space in two quadrants to provide better anesthesia than single quadrant injection.13 Sub-Tenon's anesthesia was found to be more effective than intravenous fentanyl in pediatric patients undergoing vitreo-retinal surgery. IV fentanyl group had more pain and required more ibuprofen postoperatively. The incidence of oculocardiac reflex was more in this group.14
Parabulbar anesthesia was described by Tarun Sharma et al. It comprised of a combination of orbicularis oculi injection, subconjunctival injection and sub-Tenon's irrigation. 69% patients did not require supplementation.15
5Needle-based and nonneedle cannula-based sub-Tenon's anesthesia has been described by various authors in the literature.16 A variety of rigid metallic cannulas and flexible cannulas have also been described. The choice is based on the surgeon and anesthetist preference.
Minor complications of sub-Tenons’ anesthesia include chemosis, subconjunctival hemorrhage, retained visual sensations. Major complications are orbital hemorrhage, retinal and choroidal vascular occlusion, optic neuropathy and postoperative diplopia.16 Globe perforation has been reported with sub-Tenon's anesthesia by Brett et al and they have pointed towards prior ophthalmic surgery, thinned sclera, excessive scarring as the various risk factors.17
 
Peribulbar Anesthesia
Peribulbar anesthesia is the more commonly employed procedure of local anesthesia for vitreoretinal surgery. The anesthetic agent is placed in the extraconal compartment in contrast to the retrobulbar technique where the drug is injected into the intraconal space. Peribulbar anesthesia is increasingly being adopted due to the major complications associated with retrobulbar anesthesia.
Peribulbar anesthesia for vitreoretinal surgery was described by Benedetti, et al.18 The most commonly used anesthetic agents are 2% lignocaine and 0.5% bupivacaine. Ropivacaine and levobupivacaine are two newer anesthetic agents. Hyaluronidase is universally used regardless of the anesthetic agent. Sharma et al described the use of pH adjusted alkalinized 0.5% bupivacaine and found that it produced a better quality of anesthesia in comparison to a nonalkalinized mixture of 2% lignocaine and 0.5% bupivacaine.19 Calenda et al used a mixture of bupivacaine 0.5%, lignocaine 2% and clonidine 1 mg/kg body weight and reported analgesia in 85% of patients. With sub-Tenon's supplemental infiltration the figure rose to 99% patients.20
Ropivacaine has also been used for peribulbar anesthesia in vitreoretinal surgery. Gioia et al evaluated 0.75% ropivacaine against a 1:1 combination of 2% lidocaine and 0.5% plain bupivacaine. 0.75% ropivacaine had similar onset of action and produced better postoperative analgesia.21 Preemptive analgesia with 0.75% ropivacaine in 5 ml dosage given before pars plana vitrectomy via peribulbar injection was found to produce less postoperative pain and discomfort.22 Another anesthetic agent 0.5% levobupivacaine, an S—enantiomer of racemic bupivacaine with limited cardio and neurotoxicity may be useful in elderly patients.23 Ghali evaluated 0.75% levobupivacaine versus 0.75% ropivacaine in peribulbar anesthesia in vitreoretinal surgery. 0.75% levobupivacaine was found to provide more effective peribulbar anesthesia and better postoperative analgesia than 0.75% ropivacaine.24
Retrobulbar anesthesia has however, not been completely abandoned. Aksu et al compared the efficacy of 0.5% levobupivacaine, 0.5% bupivacaine and 2% lidocaine for retrobulbar anesthesia in three different groups of patients 6undergoing vitreoretinal surgery.25 Combined retrobulbar and peribulbar anesthesia for vitreoretinal surgery has been reported using ropivacaine. The authors concluded excellent clinical efficacy as regards analgesia and muscle akinesia.26 Lim et al have reported successful use of retrobulbar anesthesia only in pars plana vitrectomy and transconjunctival sutureless vitrectomy.27
The length of the needle used is also important. The standard practice is to use a 31 mm needle for retrobulbar and a 25 mm needle for peribulbar anesthesia. But using long needles puts the patient at risk for developing complications. Some complications can cause serious enough to be sight and life-threatening. Raid et al used a 15 mm needle for peribulbar anesthesia for posterior segment surgery. The modification adopted was the application of digital compression around the hub of the needle using the thumb and index finger during injection of the anesthetic agent. This allowed the anesthetic solution to spread deeper into the orbit and obtain desired akinesia. The authors found comparable degree of akinesia, rate of supplementation and surgeon satisfaction as with the 25 mm needle without the risks of complications associated with long needles.28
Local anesthesia is safer than general anesthesia where traction on the rectus muscle is required, as in scleral buckle. Grover et al reported increased incidence of oculocardiac reflex with general anesthesia, than with local anesthesia.29
 
Sedation
Sedation is often required to improve the patient comfort during placement of local anesthetic block. Monitored anesthetic care is a term used for patients who undergo surgery under local anesthesia and intravenous sedation along with monitoring of vital signs by anesthetist.
Benzodiazepines such as midazolam, lorezopam and diazepam are the most widely used for sedation. The main effects of benzodiazepines are sedation, hypnosis, decreased anxiety, anterograde amnesia, centrally mediated muscle relaxation and anticonvulsant activity. In addition to their action on the central nervous system, benzodiazepines have a dose-dependent ventilatory depressant effect and they also cause a modest reduction in arterial blood pressure and an increase in heart rate as a result of a decrease of systemic vascular resistance. However caution must be exercised when combining midazolam with fentanyl or other opioids.30 It produces a potent drug interaction that places patients at a high risk for hypoxemia and apnea. Adequate precautions, including monitoring of patient oxygenation with pulse oximetry, the administration of supplemental oxygen, and the availability of persons skilled in airway management are recommended when benzodiazepines are administered in combination with opioids.31
Newer agents such as propofol and dexmedetomidine are considered safer than benzodiazepines. Propofol is an intravenous sedative hypnotic agent which rapidly and reliably causes loss of consciousness. It is also associated 7with a quick and ‘smooth’ recovery.32 Abdul et al used combination of propofol and remifentanil as a continuous infusion in patients undergoing vitreoretinal surgery under local anesthesia. The authors concluded that the combination of the two drugs given as a continuous infusion before the local anesthesia was associated with lesser incidence of patient movement, breakthrough pain or discomfort, hemodynamic stability and higher surgeon satisfaction.33 However propofol is both a cardiovascular and respiratory depressant. Dexmedetomidine is a potent α2 adrenoceptor agonist with sedative, anxiolytic and analgesic action following intravenous administration.34 Ashraf et al compared dexmedetomidine versus propofol for sedation in patients undergoing vitreoretinal surgery under sub-Tenon's anesthesia. The authors concluded that dexmedetomidine at similar sedation levels with propofol was associated with equivalent hemodynamic effects, maintaining an adequate respiratory function, similar time of discharge from PACU, better analgesic properties, similar surgeon's satisfaction, and higher patient's satisfaction.35 Both propofol and dexmedetomidine have also been used in general anesthesia. While propofol is used to induce anesthesia, dexmedetomidine is used as a supplement to isoflorane during vitreoretinal surgery.36
Snoring during vitreoretinal surgery under local anesthesia with anesthetist monitored sedation may be associated with sudden head movement. This is seen more in sedation with continuous infusion of propofol. The sudden head movement may result in complications during surgery.37
 
GENERAL ANESTHESIA
General anesthesia is preferred in children and patients in whom retrobulbar/peribulbar block is contraindicated, such as a high myope, or those with compromised ocular blood flow. General anesthesia is also used in patients who are expected to have a prolonged surgical time, or who fail to achieve adequate analgesia and akinesia with regional anesthesia. Care must be taken to ensure that the patient is fit for general anesthesia, by an evaluation by the anesthesiologist or physician. Combining general anesthesia with local anesthesia can reduce the dosage of potent general anesthetic agent. Early recovery from general anesthesia and prolonged postoperative analgesia is evident with this technique.38 This is advantageous in high risk patients especially the elderly. Another reason for combining peribulbar anesthesia with general anesthesia is in vitreoretinal surgery with scleral buckling. It is frequently associated with the oculocardiac reflex intraoperatively, as a result of traction on the rectus muscles. A high incidence of postoperative pain and postoperative nausea and vomiting are attributed to increased intraocular pressure due to expansion of the gas bubble or tight buckling or encirclage, when performed under general anesthesia. Insufficient akinesia resulting from partial blockade and patient discomfort during prolonged surgery involving scleral buckling are further limitations to the use of local anesthesia alone. 8The combination of general anesthesia and peribulbar anesthesia may reduce these drawbacks.39
 
DRESSING AND DRAPING
Standard conventional draping protocol is followed. After appropriate anesthesia, operative field along with eyelids and lashes are meticulously cleaned with antiseptic solution. Cutting of eyelashes is optional and should be left to surgeons’ discretion. Prior povidone-iodine (5%) instillation in the conjunctival sac (contact time of 5–10 minutes) and thorough scrubbing of the lid margins reduces the risks of bacterial contamination without adding to conjunctival or corneal toxicity. Use of 10% povidone-iodine was evaluated 5 minutes preoperatively and for painting the periocular skin. It was found to reduce the bacterial load in the conjunctiva.40 Though the study was done for patient undergoing cataract surgery, this is of great importance in MIVS which theoretically has an increased likelihood of developing postoperative endophthalmitis.
Disposable drapes with adhesive center must be used. The eyelashes need not be trimmed. The adhesive drape keeps them away from the surgical field. The speculum must give a wide exposure of the eye, but must not press upon the eye.
Since most MIVS procedures are done under peribulbar anesthesia, special attention must be paid to the airway. Most elderly patients find the drape claustrophobic. Also those with chronic obstructive pulmonary disease need to be put on a combination of air and oxygen so as to not have them panting or gasping for breath.
REFERENCES
  1. Charles S, Fanning GL. Anesthesia considerations for vitreoretinal surgery. Ophthalmol Clin North Am. 2006;19(2):239–43.
  1. Gayer S, Kumar CM. Ophthalmic regional anesthesia techniques, Minerva Anestesiologica. 2008;74(1–2):23–33.
  1. Yepez J, Cedeño de Yepez J, Arevalo JF. Topical anesthesia in posterior vitrectomy. Retina. 2000;20(1):41–5.
  1. Raju B, Raju NS, Raju AS. 25 gauge vitrectomy under topical anesthesia: A pilot study. Indian J Ophthalmol. 2006;54(3):185–8.
  1. Tang S, Lai P, Lai M, Zou Y, Li J, Li S. Topical anesthesia in transconjunctival sutureless 25 gauge vitrectomy for macular-based disorders. Ophthalmologica. 2007;221(1):65–8.
  1. Deka S, Bhattacharjee H, Barman MJ, Kalita K, Singh SK. No patch 23 gauge vitrectomy under topical anesthesia: A pilot study. Indian J Ophthalmol. 2011;59(2): 143–45.
  1. Theocharis IP, Alexandridou A, Tomic Z. A two year prospective study comparing lidocaine 2% jelly versus peribulbar anesthesia for 25G and 23G sutureless vitrectomy. Graefes Arch Clin Exp Ophthalmol. 2007;245(9):1253–8.
  1. Zakzouk E El, Emerah S, Shouman A, Raafat M, Bahy H. A prospective study. Comparing Lidocaine 2% Jelly versus retrobulbar anesthesia in 23 G Suturless Vitrectomy for Macular-Based Disorders: Efficacy and Intraocular Pressure. Life Science Journal. 2012;9(1):883–7.
  1. 9 Calvin E Mein, Harry W Flynn Jr, Augmentation of local anesthesia during retinal detachment surgery. Arch Ophthalmol. 1989;107;(7):1084.
  1. Mark A. Friedberg, Frank A. Spellman, A. Raymond Pilkerton, L. Edward Perraut, Jr, Robert F. Stephens. An alternative technique of local anesthesia for vitreoretinal surgery. Arch ophthalmol. 1991;109(11):1615–16.
  1. Li HK, Abouleish A, Grady J, Groeschel W, Gill KS. Sub-Tenon's injection for local anesthesia in posterior segment surgery. Ophthalmology. 2000;107(1):41–6.
  1. Hee Jin Sohn, Hyun Seung Moon, Dong Heun Nam, Hae Jung Paik. Effect of Volume Used in Sub-Tenon's anesthesia on efficacy and intraocular pressure in vitreoretinal surgery. Ophthalmologica. 2008;222:414–21.
  1. Gill VS, Presland AH, Lord JA, Bunce C, Xing W, Charteris DG. Two-quadrant high-volume sub-Tenon's anesthesia for vitrectomy: A randomised controlled trial. Br J Ophthalmol. 2012;96:189–92.
  1. Chhabra A, Sinha R, Subramaniam R, Chandra P, Narang D, Garg SP. Comparison of sub-Tenon's block with i.v. fentanyl for paediatric vitreoretinal surgery. Br J Anaesth. 2009;103(5):739–43.
  1. Sharma T, Gopal L, Parikh S, Shanmugam MP, Badrinath SS, Mukesh BN. Parabulbar anesthesia for primary vitreoretinal surgery. Ophthalmol. 1997;104(3):425–8.
  1. Kumar CM, Williamson S, Manickam B. A review of sub-Tenon's block: Current practice and recent development. Euro J Anaesthesiol. 2005;22(8):567–77.
  1. Brett J Frieman, Mark A Friedberg. Globe perforation associated with sub-Tenon's anesthesia. American Journal of Ophthalmol. 2001;131(4):520–1.
  1. Benedetti S, Agostini A. Peribulbar anesthesia in vitreoretinal surgery. Retina. 1994;14(3):277–80.
  1. Sharma T, Lingam G, Shanmugam, Mahesh P, Bhende, Pramod, et al. Comparison of pH adjusted bupivacaine with a mixture of non-ph-adjusted bupivacaine and lignocaine in primary vitreoretinal surgery. 2002;22(2):202–7.
  1. Calenda E, Quintyn JC, Brasseur G. Peribulbar anesthesia using a combination of lidocaine, bupivocaine and clonidine in vitreoretinal surgery. Indian J Ophthalmol. 2002;50(3):205–8.
  1. Gioia L, Prandi E, Codenotti M, Casati A, Fanelli G, Torri TM, et al. Peribulbar anesthesia with either 0.75% ropivacaine or a 2% lidocaine and 0.5% bupivacaine mixture for vitreoretinal surgery: A double-blinded study. Anesth Analg. 1999;89(3):739–42.
  1. Schönfeld CL, Hierneis S, Kampik A. Preemptive analgesia with ropivacaine for pars plana vitrectomy: Randomized controlled trial on efficacy and required dose. Retina. 2012;32(5):912–7.
  1. Pacella E, Collini S, Pacella F, Piraino DC, Santamaria V, Blasi RA De. Levobupivacaine vs racemic bupivacaine in peribulbar anesthesia: A randomized double blind study in ophthalmic surgery. Eur Rev Med Pharmacol Sc. 2010;14(6): 539–44.
  1. Ghali AM. The efficacy of 0.75% levobupivacaine versus 0.75% ropivacaine for peribulbar anesthesia in vitreoretinal surgery. Saudi J Anesth. 2012;6:1:22–26.
  1. Aksu R, Bicer C, Ozkiris A, Akin A, Bayram A, Boyaci A. Comparison of 0.5% levobupivacaine, 0.5% bupivacaine, and 2% lidocaine for retrobulbar anesthesia in vitreoretinal surgery. Eur J Ophthalmol. 2009;19(2):280–4.
  1. Seidenari P, Santin G, Milani P, David A. Peribulbar and retrobulbar combined anesthesia for vitreoretinal surgery using ropivacaine. Eur J Ophthalmol. 2006; 16(2):295–9.
  1. 10 Lim TH, Humayun MS, Yoon YH, Kwon YH, Kim JG. The efficacy of retrobulbar block anesthesia only in pars plana vitrectomy and transconjunctival sutureless vitrectomy. Ophthalmic Surg Lasers Imaging. 2008;39(3):191–5.
  1. W Riad, E Abboud1, E Al-Harthi, E Kahtani, N Ahmed. Superficial extraconal blockade for vitreoretinal surgery. Saudi J Anaesth. 2010;4(3):174–77.
  1. Grover VK, Bhardwaj N, Shobana N, Grewal SPS. Oculocardiac reflex during retinal surgery using peribulbar block and nitrous narcotic anesthesia. Ophthalmic Surgery and lasers. 1998;29:207–12.
  1. Olkkola KT, Ahonen J, Midazolam and Other Benzodiazepines, Modern Anesthetics, Handbook of Experimental Pharmacology. 2008;182,III:335–60.
  1. Bailey PL, Pace NL, Ashburn MA, Moll JW, East KA, Stanley TH. Frequent hypoxemia and apnea after sedation with midazolam and fentanyl. Anesthesiology. 1990;73(5):826–30.
  1. Fulton BR, Faulds D. Propofol. An update of its use in anaesthesia and conscious sedation. Drugs. 1995;50(3):513–19.
  1. Abdul Kader MM, Ghali AM. Combined use of remifentanil and propofol to limit patient movement during retinal detachment surgery under local anesthesia. Saudi J Anaesth. 2010;4(3):147–51.
  1. Bhana N, Goa KL, McClellan KJ. Dexmedetomidine. Drugs. 2000;59(2):263–8.
  1. Ghali A, Abdul Kader Mahfouz, Tapio Ihanamäki, Ashraf M. El Btarny. Dexmedetomidine versus propofol for sedation in patients undergoing vitreoretinal surgery under sub-Tenon's anaesthesia. Saudi J Anaesth. 2011;15(1):36–41.
  1. Lee YY, Wong SM, Hung CT. Dexmedetomidine infusion as a supplement to isoflurane anaesthesia for vitreoretinal surgery. Br J Anaesth. 2007;98(4):477–83.
  1. McCannel, Colin A, Olson, Eric J, Donaldson, Mark J, et al. Snoring is associated with unexpected patient head movement during monitored anaesthesia care vitreoretinal surgery. Retina.
  1. Koenig A, Weber H, Spitznas M. Combination of local anesthesia and intubation anesthesia in ophthalmic surgery—a gentle anesthetic technic for high risk patients. Anasth Intensivther Notfallmed. 1983;18(3):121–4.
  1. Ghali AM, Btarny AM El. The effect on outcome of peribulbar anaesthesia in conjunction with general anaesthesia for vitreoretinal surgery. Anaesthesia. 2010;65(3):249–53.
  1. Martin M, Nentwich, Mohammed Rajab, Christopher N, Ta, Lisa He, Martin Grueterich, et al. Application of 10% povidone iodine reduces conjunctival bacterial contamination rate in patients undergoing cataract surgery. Eur J Ophthalmol.. 2012;22(4):541–6.