By Maggie Jeffries, MD

One of the challenges that high volume cataract surgery centers face is how to balance efficiency with cost control both for the center and the anesthesia group. 
Our high-volume surgeons will perform approximately 18-25 surgeries in two operating rooms during a 5-hour surgical block of time. This requires patients to arrive early so that they can be moved through the check-in and pre-surgical process as efficiently as possible so that 3-5 patients are in preoperative beds at any one time. Many times, this means patients will wait in the waiting room or in their preoperative beds for longer than they find acceptable especially if an unanticipated complication, such as a vitrectomy, occurs. This was indeed the problem when we took over a cataract center in 2013. Patients would be sitting in their beds constantly interrupting nurses and anesthesia providers about when was their turn, sometimes escalating into anger.  

As a group, we decided we could do better. We also had the challenge of staffing costs associated with “flip” rooms in a market of ever decreasing reimbursements. And thus, was the introduction of preoperative anxiolytic medications into our practice. 

We initially settled on use of diazepam 10mg PO given to patients by the preoperative nurse.  Exclusion criteria were patients who require assistance to ambulate, wheelchair bound, liver failure, and allergy to diazepam.  Patients of Asian descent received diazepam 5mg.  The preoperative nurse administers the medication per our standing orders after consents are signed, NPO is confirmed and an initial set of vital signs are taken.  They all receive in-services regarding exclusion criteria and dosing modification strategies.   When scheduled for an eye block, patients still received diazepam preoperatively.

Why diazepam?
Diazepam 5mg PO is commonly used by ophthalmologists for Lasik surgery with good results.  Most of our high-volume surgeons also use the femtosecond laser in conjunction with cataract surgery which requires the patient to be awake, relaxed and cooperative – similar to what they need during Lasik.  Diazepam also has mild muscle relaxant properties, helping our patients with arthritis and other orthopedic issues be more comfortably in the flat position. As with all benzodiazepines, there is often a beneficial element of amnesia.  Many patients fall into a light sleep but are easily arousable and their vital signs remain stable. 

As part of this process change, we tracked how much additional medications patients received in the OR and patient satisfaction.  The overall mood of our patients in the preoperative holding area went from anxious and frustrated to quiet and serene.  Our nurses and doctors also reported better satisfaction as the patients were not only more comfortable in the preoperative holding area but in the OR as well. 

Because patients were already somewhat relaxed, nurses could take a patient back to the OR and get them ready in anticipation of the surgeon/anesthesia team coming from finishing the prior OR. This enabled us to further increase our efficiency by staffing both ORs with the same CRNA (we work in a team model) – they would essentially follow the surgeon from room to room. Furthermore, many of our patients didn’t require additional medications in the OR after receiving diazepam which drove down the cost of anesthetic medications as diazepam is less expensive than midazolam and fentanyl. During drug shortages that involved both midazolam and fentanyl, we found our practice unaffected as our use of such medications is minimal. 

There are many other preoperative medications that we have added to our arsenal over time.
When given preoperatively, benzonatate (Tessalon) perles are fantastic in decreasing coughing and tramadol works to decrease postoperative pain when anticipated after particular surgeries (i.e. glaucoma procedures). There are also the standard medications used for the prevention of postoperative issues such as ketorolac, ondansetron, dexamethasone.

More recently, we have added the use of the MKO melt at two of our centers.  The MKO melt is a sublingual formulation of midazolam 3mg, ketamine 25mg and ondansetron 2mg.  Most patients typically require 1-2 melts and we have found that only about 15-20% of those patients will require additional IV medications in the OR.  This medication has a cost factor and at one of our centers we have specific criteria for its use such as young, high anxiety and co-existing psychiatric conditions.  At our other center, where the majority of patients are scheduled for the Lensx femtosecond laser, we use the MKO melt on all patients unless the medication is contraindicated.

In summary, we were able to greatly increase our efficiency and control staffing costs from the addition of preoperative anxiolytic medication before eye surgery.

By George Dumas, MD

In this edition of the newsletter, we are pleased to present articles by OAS members Sue Wolf, PA-C, and Derek Sakata, MD. 

With the ever increasing cost of healthcare and surgery, there is a push to perform more procedures at ambulatory facilities and reduce unnecessary testing. However, some preoperative testing may be indicated and some procedures are best performed in the traditional hospital environment.  It will always be important to have patients “optimized” before surgery. At my institution, there is tremendous pressure to move cases that have been traditionally performed in the hospital setting to lower acuity facilities. 

Ms. Wolf will explore the utility of preoperative testing and its consequences.  Dr. Sakata will present ASC guidelines and suitability of surgery in settings with fewer resources. 

We are always open to newsletter suggestions and hope that the updated format of OASIS provides an enhanced reading experience. I know that you will enjoy reading this latest edition of OASIS.

George A. Dumas MD
Editor, OASIS

Caption: Sample of an algorithm used to screen and manage surgical patients at risk for OSA, from Open Access: Preoperative testing and risk assessment: perspectives on patient selection in ambulatory anesthetic procedures)

By Susan Wolf, PA-C

Over the years, there has been much discussion and debate regarding the need for preoperative testing for patients undergoing ophthalmic surgery. The rationales for performing preoperative testing have been varied. Arguments have been made that these tests help predict patient risk for postoperative complications, help screen for unknown abnormalities, establish baseline values and provide the ordering practitioner, medico-legal protection. Numerous studies now involving well over one million patients have been performed. The results of these studies have overwhelmingly reached the same conclusion: the surgical and medical outcome of patients are statistically negligible, regardless of whether or not patients receive preoperative labs, ECGs, or in many cases, even echocardiograms or stress tests. 

The shift now is to focus on Clinical Practice Guidelines (CPGs) to identify high-risk patients, use Risk Assessment Tools to asses the patient's current health status and comorbidities, optimize these high-risk patients and to choose wisely when ordering tests. To achieve this, Perioperative Optimization has become an emerging specialty. 

Centers for Perioperative Optimization (CPOs) staffed by anesthesiologists, PAs and NPs familiar with CPGs and familiar with Risk Assessment Tools have been proven to decrease cost of testing, decrease cancellations/delays and decrease adverse perioperative events. Factors considered, in addition to the patient's health, are: type of surgery, type of anesthesia; patient comorbidities such as CHF and PAH; and, OR setting (freestanding clinic versus tertiary center). Based on a patient's Risk Assessment score, the COP practitioners can decide if a patient needs further evaluation by a specialist or any further testing such as echo, stress test, PFTs, etc. 

Commonly used Risk Assessment Tools: 

• American Society of Anesthesiologist ASA Physical Status Classification: assesses patient physical status based on their health and co-morbidities 
• The Revised Cardiac Risk Index (RCRI): uses six independent predictors and assigns a complications' risk percentage
• Pulmonary Arterial Hypertension (PAH) Classification: assesses patient risk based on degree and cause of pulmonary hypertension 
• Functional Capacity Assessment Tools: uses METS; metaboloic equivalent; a measure of exercisse intensity based on oxygen consumption or energy expended
• New York Heart Association (NYHA) Classes: assesses patient's functional capacity and assigns a risk classification
• CHAD2DS2 Vascular Score: uses eight risk factors to assess patient risk for stroke

One last thought -- it is predicted in 2020 that 3.3 million Medicare patients will undergo cataract surgery and 4.4 million patients in 2030. Using today's average cost of $175.00 for preoperative evaluation (H&P/CBC/BMP, ECG) by 2030, testing will cost approximately $770,000,000. And this is only for one type of ophthalmic surgery!). Using clinical practice guidelines and Risk Assessment Tools, it is estimated that only one out of five patients undergoing ophthalmic surgery benefit from preoperative testing. This would save over $616,000,000 in unnecessary testing in addition to saving patients from increased pain, inconvenience and anxiety.

by Derek Sakata, MD, and Patrick Bakke, MD

Anesthesia is Easy!

When working with our students, I half kiddingly say, “One only needs to accomplish four goals to become a safe and board-certified anesthetist.”

After absorbing their hopeful but quizzical expressions, I state that everything they do is about protecting the patient. First, protect the patient from the surgeon/proceduralist. Although the patient is receiving therapeutic care, we all know there are any number of risks associated with the procedure. Second, protect the patient from us, the anesthetist. We all know that any one of our medications can cause patient demise if dosed incorrectly and combinations of medications can have even more acute deleterious effects. Third, protect the patient from themselves. All of us have experienced patients with such severe comorbidities that they run the risk of acute deterioration in pre-op before they even receive medications from us or undergo the procedure! The fourth is ascertaining their risks with each of the three and then the combination of these.  Upon recitation of this fourth goal, the countenances of my enthusiastic protégés become a bit more flummoxed.

Your Island

As many of us practicing anesthetists know, there is a balance between what types of cases we do, what types of patients qualify and the combination of both of these together.

Balancing these goals is particularly important for ambulatory surgery centers (ASC) in which a majority, if not all, of the cases are elective and the centers are usually devoid of advanced resources to care for the complex maladies of some challenging patient populations.  Additionally, these maladies may be pre-existing and/or explode when fanned by the insults associated with our procedures and/or our anesthetic management.

It is in consideration of these issues, our Senior Nursing Ambulatory Surgery Director, Selena Young, MBA, BSN, RN, CASC explains, “In ambulatory surgery centers, we are not there to diagnose issues during surgery. The diagnosis should already have been made and we are there to treat.” 

Our Surgical Services Nurse Manager Brent Klev, MBA, BSN, RN, summarizes, “When faced with medically complex patients, sometimes you just don’t let them on your island.” 

I like both of these statements because they generally dictate not only how we discern which patients we choose but also how we decide on their treatment. 

Welcome to ASC Island

Many, if not all of us, are challenged by what patients to allow in our ASCs. Top of mind are, of course, airway and respiration and having necessary knowledge, ability and resources to handle routine and emergency issues in the care of our patients. At the University of Utah, we have come up with evidence-based guidelines to guide our decisions in selecting and caring for our ASC patients.  Specifically, we have come up with body mass index inclusion metrics and pediatric guidelines.

In our Ophthalmic Anesthesia Society (OAS) board discussions, we have discussed the benefits of sharing our evidence-based guidelines that many of us have written to create discussion and generate consensus on what patients we specifically think can be safely cared for in our centers.  We look forward to increased and ongoing dialogue and collaboration to optimally and more uniformly care for all of our patients. Aloha and Mahalo!

Are there any evidence-based guidelines you'd like to share? Add them to the comments below!

Dear colleagues, 

First, a warm welcome to all OAS members. I am honored to lead the Society in the coming year. My hope is that my tenure will promote greater interaction between members creating an environment fertile for constructive discussion, resulting in improved care and outcomes for our surgical population.

Our 2018 Annual Meeting was undoubtedly a resounding success. The comments received in response to our post-meeting survey indicate that delegates appreciated the admixture of didactic lectures, pro-con debates, focus groups and workshops. A special word of thanks to my meeting co-chairs, Tina Tran and Chris Bender for the time and effort they devoted in preparing for this memorable event. CME certificates for the 2018 Annual Meeting will be distributed shortly. I thank you for your patience in accepting the delay in their release.

The vitality of an organization can be measured by growth in its membership. In this respect, our Society has been ailing of late because our annual renewals have been waning. A primary goal of my tenure is to grow our membership. My introductory appeal this year is for each and every one of you to please make a concerted effort in promoting our organization among your ophthalmic surgery colleagues, no matter the discipline. Essentially, OAS is a collaborative venture between anesthesiologists, nurse anesthetists, ophthalmologists and allied professionals involved in the care of eye surgery patients. And, annual membership renewal notices will be distributed early in the new year, so kindly replenish your subscription in a timely fashion.

Aside from routine rotation of the Executive, the composition of the Board is soon to be transformed such that we will include the Head of the Scientific Panel and an at-large position, reserved for a member from no specified discipline. In anticipation of accepted ratification to our Articles of Association, I am delighted to welcome Drs. George Dumas, Derek Sakata and Jefferson Doyle to the reconstituted Board. In addition, Sue Wolf will join the Board in the at-large portfolio.

Plans for the 2019 Annual Meeting scheduled to be held in Chicago from September 13-15 are already under way. The organizing committee comprises myself, Zhuan Fang and Chris Bender. For this meeting we hope to attract more international speakers in order to create an interactive learning experience to broaden our ideas and perspectives on ophthalmic anesthesia techniques and case management. Suggestions about changes in the meeting format are welcome and can be forwarded to any member of the organizing committee. The Annual Meeting is our single opportunity to maximize the benefit of national inter-collegial interaction so diarize now and let’s make it a resounding success!

Finally, thank you for your continued and loyal membership. I am always available via email (hpalte@miami.edu) to accept ideas or address inquiries, so don’t remain a stranger!

Best regards,

Howard Howard, MD

An October study published in Investigative Ophthalmology & Visual Science, demonstrated that lens epithelial cells produce specific inflammatory cytokines following cataract extraction and lens injury. This response could be responsible for cataract surgery complications including posterior capsular opacification (PCO). 

In an article published by the University of Delaware in November, “Eye research targets scar tissue that forms after surgery,” researcher and study author, Melinda Duncan, PhD, explained, “Some cells always remain behind after surgery, and that can form scar tissue, which isn’t transparent.” 

Duncan, whose research is funded by the NIH, believes the team has discovered molecules responsible for formation of PCO. More targeted therapy, other than general anti-inflammatory eye drops prescribed after cataract surgery, will hopefully result from this research.

“Normally in the eye, lens cells are completely walled off from the immune system and have no resemblance to immune cells. It turns out that an injury to the lens, such as surgery, changes that.  The data really surprised us because this was completely unknown before.”

The Ophthalmic Anesthesia Society has been a significant part of my academic, clinical, and personal life. I attended my first OAS scientific meeting several years ago and was fascinated by the comradery and collaboration between anesthesiologists, ophthalmologists, CRNAs, and other clinical providers. Everyone was encouraged to contribute, to share innovations, and to join this organization of fiercely dedicated members. Several members have not missed a meeting since its conception over 30 years ago!

I was welcomed in with strong handshakes and warm smiles. Members listened to my ideas and invited me to become more involved by giving presentations, becoming editor of the OASIS newsletter, becoming chair of the Scientific Advisory Panel, becoming co-chair of the annual meetings, becoming a valued member of the Scientific Advisory Board, and so much more. I always look forward to the annual scientific meetings. I walk away with new ideas and additional knowledge that continue to impact my practice. In additional to the presentations, interactive sessions, focus group discussions, and ophthalmic block workshops, it is a time to reconnect with friends. An annual family reunion. Through the years, we have gotten to know each other’s significant others, family, children, and grandchildren. We congratulate each other on our successes and build long lasting friendships and collaborations. We expand our influence every year and our impact continues to grow.

I am truly humbled and honored for these opportunities. I am grateful to all OAS members and appreciate all that you have done to support me. My career has flourished due to your support. I became chief of Wilmer Eye Institute at Johns Hopkins Hospital, chair of several committees for the American Society of Anesthesiologists (ASA), chair of several committees for the Society of Education in Anesthesiology (SEA), and chair of several committees for the Institute of Excellence in Education (IEE). I have been invited to give talks at several national and international societies. I aspire to represent you and OAS well in every aspect.

I want to give the deepest appreciation to my mentors, Dr. Ric Rivers, Dr. Zhuang Fang, and Dr. Steve Gayer. They have stood behind me every step of the way and encouraged me during times when I felt most overwhelmed. My successes and the success of OAS are a tribute to you all. 

I want to thank Dr. George Dumas for inviting me to share my story with you. I look forward to many successful years ahead. I am excited to be a part of the new year lead by Dr. Howard Palte!

-- Tina Tran, MD
Chief of Anesthesia for the Wilmer Eye Institute
Johns Hopkins School of Medicine

OAS Member, Dr. Maggie Jeffries, was interviewed by EyeWorld reporters this October. She discussed her recent MKO melt study, which was also presented at the 32nd Annual OAS Scientific Meeting this fall.

The study included 611 patients. It was Institutional Review Boards (IRB) approved. The patient were randomized to receive either an MKO melt, valium alone (10 mg), or valium with tramadol and ondansetron. Then her team tracked how much medication the patients needed for pain, anxiety, or both. 

To learn more, watch the interview at ewreplay.org. 

Written by Cagri Besirli, MD, PhD, Department of Ophthalmology and Visual Sciences (University of Michigan)

Intravitreal treatment has been transformative, saving vision for millions of

 patients. The success of anti-VEGF drugs, aging population, diabetes epidemic, and increasing indications have led to a dramatic growth in the number of injections performed, increasing from less than 50,000 a year in the early 2000s to an estimated 6 million injections in 2017.

Current methods of pharmacologic ocular anesthesia used prior to intravitreal injections have several drawbacks, including the need for two patient encounters (the first to administer anesthesia and the second 5-15 minutes later after anesthesia has had time to work), corneal toxicity with blurred vision, and increased rate of hemorrhage seen with subconjunctival lidocaine. In addition, there is concern that certain forms of anesthesia, particularly lidocaine gel and viscous lidocaine drops, may result in suboptimal antiseptic access to the ocular surface, which could theoretically increase the risk of endophthalmitis.

Administering an intravitreal injection safely requires a multi-step process. The anesthesia step is the longest phase and creates a bottleneck in intravitreal injection workflow. Therefore, there is an unmet need for a rapid, non-invasive anesthesia for intraocular injections.  With this in mind, we developed focal cooling as a novel method of non-pharmacologic anesthesia to improve the patient experience. To provide focal cooling on the ocular surface, we designed a portable, battery operated device with a single-use, sterile tip that rapidly cools the ocular surface within 10-20 seconds, temporarily halting nerve conduction. There is a wealth of literature showing that nerve conduction is stopped between 0-8 C, and the temperatures chosen for this study were done based on thermal modeling that showed the ability to achieve this temperature range in the sclera prior to an intravitreal injection.  

To assess the safety and feasibility of focal cooling for ocular anesthesia, we performed a first-in-human feasibility trial.  This was a single center, randomized, unmasked controlled trial that compared non-pharmacologic, ultra-rapid focal cooling to lidocaine-based standard of care anesthesia.  The study included patients older than 18 years of age with a diagnosis of exudative age-related macular degeneration or diabetic macular edema requiring bilateral anti-VEGF therapy.  One eye of each patient was randomized to the focal cooling treatment arm and the fellow eye was randomized to topical lidocaine (lidocaine gel or lidocaine-soaked cotton tipped applicators).  The primary pain outcome was patient reported pain at the time of injection.  The secondary pain outcome was post injection pain measured 4 hours post treatment.

The visual analog scale was used to measure injection and post-injection pain. We found effective pain control in the focal cooling groups, with increasing pain control with colder temperatures and longer treatment duration.  Similar to injection pain, post-injection pain after non-pharmacologic anesthesia was similar to standard of care.  This first-in-human study showed that focal cooling reduced the time patients spent waiting for the injection procedure by approximately 4.5 minutes, which represented a statistically significant improvement, and one that has considerable benefit for patient care.

The first-in-human trial shows that rapid, non-pharmacological anesthesia via focal cooling has the potential to transform the way intravitreal injections are delivered, dramatically improving the patient experience. This technology has now been exclusively licensed to iRenix Medical, with additional development and commercialization planned in the near future. 

Written by Howard Palte, MD, Bascom Palmer Eye Institute (University of Miami)

Today, more than 6 million patients in the USA receive long-term therapy for the prevention of thromboembolism from atrial fibrillation, mechanical heart valves and deep vein thrombosis. Patients undergoing eye surgery are often elderly, have significant comorbidity and receive antiplatelet or anticoagulant therapy. These medications may predispose eye surgery patients to risk of hemorrhagic complications either during the administration of regional anesthesia or intra-orbital intervention. The anesthesia provider is faced with the dilemma of balancing the risk of orbital hemorrhage against the peril of a catastrophic outcome associated with cessation of anticoagulation therapy. In this respect, an appreciation of the pharmacology of the newer anticoagulant agents is key in the management of eye surgery patients.

Heparin and Vitamin K Antagonists

Unfractionated heparin and warfarin have been available for more than half a century but impose limitations, such as slow onset of action, interaction with food and drugs, and narrow therapeutic window. Also, Vitamin K antagonists (VKA) have unreliable efficacy and demand routine coagulation monitoring and dose adjustment to maintain the international normalized ration (INR) in the target range. In addition, the slow onset of action means that many patients require perioperative bridging therapy with a rapidly acting agent (e.g. heparin).

Newer Antithrombotic Agents

In addressing these deficiencies, research development has centered on newer oral agents that inhibit two key serine proteases in the coagulation cascade:

1. Thrombin (FIIa)

2. Activated factor X (FXa).

Thrombin (FIIa) plays a central role in coagulation and clot formation by converting fibrinogen to fibrin and feedback activation of factors V, VIII and XI (see Fig. 1).

Factor Xa is a logical target because it is located at the junction of the extrinsic and intrinsic pathways. FXa inhibition attenuates thrombin formation preventing the conversion of fibrinogen to fibrin (see Fig.1).

Figure 1. Newer anticoagulants and their targets in the coagulation pathway (adapted from: Erikson et al. Novel Oral Factor Xa and Thrombin Inhibitors)

Advantages of the new oral anticoagulants over VKA include rapid onset of action and few food interactions. However, the greatest clinical benefit of these new oral anticoagulants is their predictable efficacy in attaining a desired level of anticoagulation, thus obviating the need for routine monitoring.

Thrombin (FII) Inhibitor

1.      Dabigatran (Pradaxa) - direct thrombin inhibitor, oral bioavailability 6%, dose once or twice daily, half-life (t1/2) 12 hours, no inhibition cytochrome P-450 (CYP).

Factor Xa (FXa) Inhibitors

1.      Rivaroxaban (Xarelto)  -  bioavailability 80%, administered once or twice daily, t1/2 12 hours, potent inhibitor CYP3A4.

2.      Apixaban (Eliquis) – bioavailability 66%, dose twice daily, t1/2 12 hours, potent inhibitor CYP3A4.

3.      Edoxaban (Lixiana) – bioavailability 50%, dose once daily, t1/2 10 hours, potent inhibitor CYP3A4.

Bleeding Risks of Ophthalmic Surgery During Continuation Antithrombotic Therapy

The predominant concern surrounding continuation of antithrombotic therapy is the risk of hemorrhage with placement of an ophthalmic block or during surgery. Block-induced hemorrhage can have devastating consequences leading to compressive hematoma, retinal ischemia and loss of vision. However, the main risk factor for periorbital hemorrhage is arterial fragility rather than hemostatic disorders. These devastating complications can be minimized by adopting single injection techniques, short needles (<25G and <25 mm), limited depth of needle insertion, minimal angulation, and injection in the vascular-poor infero-temporal quadrant.

Cataract Surgery

In most centers phacoemulsification surgery is performed under either topical anesthesia alone or with intracameral preservative-free supplementation. A meta-analysis of 11 studies found that patients who continued oral anticoagulants had an increased bleeding risk but these were insignificant (subconjunctival) and self-limiting.

Vitreoretinal Surgery

In recent years there have been a number of studies addressing continued antithrombotic therapy in patients undergoing vitreoretinal surgery. An observational study of 822 patients identified five risk factors for bleeding; male sex, smoking history of proliferative diabetic retinopathy, glaucoma and anticoagulant use. Although anticoagulants were associated with increased risk of intraorbital hemorrhage there were no serious sequela, need for re-operation or surgical failures. Posterior segment surgery is commonly performed under regional anesthesia but the incidence of retrobulbar hemorrhage following an ophthalmic block is exceptionally low. There is no evidence-based data to substantiate that regional ophthalmic anesthesia amplifies risk for retrobulbar hemorrhage.

Glaucoma Surgery

Two recent studies reported a higher incidence of hemorrhage during or after cutaneous surgery in patients on antithrombotic therapy but without serious consequence. For oculoplastic procedures, the incidence is also very low; one American survey found an incidence of 1:2000.

Conclusion

There are no randomized controlled trials that directly compare the rate of thromboembolic events associated with anticoagulant discontinuation against periorbital hemorrhage secondary to ongoing therapy. Severe sight-threatening block-related hemorrhagic complications are rare. Therefore routine cataract, glaucoma, vitreoretinal and oculoplastic procedures appear to be safe in patients on antiplatelet and vitamin K antagonists, as long as the INR is within therapeutic range. On balance there is insufficient data to substantiate firm recommendations for the newer antithrombotic agents (rivaroxaban, dabigatran, apixaban) but clinical experience supports continuation of therapy.

Prudence dictates assessment on an individual basis, and on occasion, liaison between the anesthesia provider and cardiologist or neurologist. Ultimately, management decisions in regard to perioperative anticoagulation rely on best clinical judgement.

Suggested Reading:

1.      Management of antithrombotic therapies in patients scheduled for eye surgery. Bonhomme et al. European Journal Anaesthesiology. 2013.

2.      Novel oral factor Xa and thrombin inhibitors in the management of thromboembolism. Eriksson et al. Annual Review Medicine. 2011.

3.      Ophthalmic patients on antithrombotic drugs: a review and guide to perioperative management. K-L Kong et al. British Journal Ophthalmology.2015.

4.      Peri-operative management of ophthalmic patients taking antithrombotic therapy. Lip et al. International Journal of Clinical Practice. 2011.

5.      The use of perioperative antithrombotics in posterior segment ocular surgery. McClellan et al. American Journal Ophthalmology. 2014.