Anesthesia in Ophthalmic Surgery — MCQs
Premedication is prescribed to – a) Allay anxiety b) Make the patient asleep before coming for operation c) Reduce the dose of induction agents d) Produce amnesia
Which pre-operative investigation is recommended before surgical procedures in a patient on warfarin therapy?
Retrobulbar injection of xylocaine blocks all of the following except:
A patient aged 28 years, was given epidural anesthesia with 15 ml of 1.5% Lignocaine with adrenaline for hernia surgery. He developed hypotension, respiratory arrest and became unconscious within 3 minutes, most probable cause will be:-
Local anaesthetic usually used for retrobulbar block -
What is the maximum dose of plain lignocaine (in mg) for adults?
A 5 year old healthy child is undergoing strabismus surgery with a Laryngeal mask airway in place. Thirty minutes into the procedure, his heart rate is 60 bpm, blood pressure is 90/60 mmHg, and oximeter shows 98% saturation. The next step in management is
The type of iridectomy shown in the image is:
Which one of the following is a branch of the first part of the maxillary artery?
Identify the ophthalmic instrument used for measuring heterophoria and heterotropia.
Anesthesia in Ophthalmic Surgery Indian Medical PG Practice Questions and MCQs
Question 1: Premedication is prescribed to – a) Allay anxiety b) Make the patient asleep before coming for operation c) Reduce the dose of induction agents d) Produce amnesia
- A. Reduce the dose of induction agents
- B. Allay anxiety (Correct Answer)
- C. Produce amnesia
- D. Make the patient asleep before coming for operation
Explanation: ***Allay anxiety*** - Premedication frequently includes anxiolytic agents like **benzodiazepines** to calm the patient before surgery. - Reducing anxiety helps in achieving a smoother induction of anesthesia and can improve the patient's overall experience. *Reduce the dose of induction agents* - While some premedication agents like **opioids** or sedatives can have an anesthetic-sparing effect, this is a secondary benefit, not the primary goal. - The main aim is patient comfort and psychological preparation, not primarily dose reduction. *Produce amnesia* - Amnesia, particularly **anterograde amnesia**, is a desirable side effect of some premedication drugs like **midazolam**. - However, it's a consequence of the anxiolytic effect rather than the sole or primary reason for prescribing premedication. *Make the patient asleep before coming for operation* - While some premedication agents can cause **somnolence** or light sleep, the goal is not to have the patient fully asleep before entering the operating room. - The primary aim is to make the patient relaxed and comfortable, not unconscious.
Question 2: Which pre-operative investigation is recommended before surgical procedures in a patient on warfarin therapy?
- A. International Normalized Ratio (INR) (Correct Answer)
- B. Partial Thromboplastin Time (PTT)
- C. Clotting Time
- D. Differential Count
Explanation: ***International Normalized Ratio (INR)*** - The **INR** is specifically used to monitor the effectiveness of **warfarin** therapy, as it standardizes the prothrombin time (PT) for variations in thromboplastin reagents. - Before surgery, an INR measurement helps assess the patient's **coagulation status** and guides decisions on temporary cessation or bridging therapy to minimize bleeding risk. *Partial Thromboplastin Time (PTT)* - **PTT** primarily measures the **intrinsic and common pathways** of coagulation and is used to monitor **heparin** therapy, not warfarin. - While prolonged in some bleeding disorders, it is not the standard test for assessing warfarin's anticoagulant effect. *Clotting Time* - **Clotting time** is a very general and less precise measure of overall coagulation that is **rarely used** in modern clinical practice due to its low sensitivity and specificity. - It does not offer sufficient detail or standardization to guide pre-operative management for patients on warfarin. *Differential Count* - A **differential count** measures the different types of **white blood cells** within a blood sample and is used to diagnose infections, inflammatory conditions, or hematologic disorders. - It provides no information about a patient's coagulation status or the effects of anticoagulant medications like warfarin.
Question 3: Retrobulbar injection of xylocaine blocks all of the following except:
- A. 3rd cranial nerve
- B. 4th cranial nerve (Correct Answer)
- C. 6th cranial nerve
- D. Ciliary nerves and ciliary ganglion
Explanation: ***4th cranial nerve*** - The **trochlear nerve (CN IV)** innervates the **superior oblique muscle** and has a unique superior and anterior course in the orbit, making it less accessible to retrobulbar injections. - Its location relative to the muscle cone and globe means a retrobulbar injection, which typically aims to block nerves within the muscle cone, often misses it. *3rd cranial nerve* - The **oculomotor nerve (CN III)** supplies most of the extraocular muscles and travels within the **muscle cone**, where retrobulbar anesthetic is deposited. - It is reliably blocked by a retrobulbar injection, causing akinesia of the muscles it innervates. *6th cranial nerve* - The **abducens nerve (CN VI)** innervates the **lateral rectus muscle** and is located within the **muscle cone**, making it susceptible to retrobulbar block. - Anesthetic diffusion within the cone effectively blocks this nerve, leading to paralysis of the lateral rectus. *Ciliary nerves and ciliary ganglion* - The **short ciliary nerves** and **ciliary ganglion** are located in the retrobulbar space, typically within the muscle cone or close to it. - Anesthetic solution injected retrobulbarly readily diffuses to these structures, blocking sensory input from the cornea and iris, as well as parasympathetic innervation to the pupil and ciliary body.
Question 4: A patient aged 28 years, was given epidural anesthesia with 15 ml of 1.5% Lignocaine with adrenaline for hernia surgery. He developed hypotension, respiratory arrest and became unconscious within 3 minutes, most probable cause will be:-
- A. High spinal block
- B. Intravascular injection of Lignocaine (Correct Answer)
- C. Anaphylaxis to lignocaine
- D. Total spinal block
Explanation: ***Intravascular injection of Lignocaine*** - Rapid onset (within 3 minutes) of **hypotension**, **respiratory arrest**, and **unconsciousness** after an epidural injection strongly indicates systemic toxicity from intravascular local anesthetic injection. - The large volume (15 mL) and concentration (1.5%) of lignocaine, especially with adrenaline, when injected directly into the bloodstream, can quickly lead to **central nervous system (CNS) depression** and cardiovascular collapse. *High spinal block* - A **high spinal block** typically results from a local anesthetic spreading too high in the intrathecal space, leading to widespread sympathetic blockade and paralysis of respiratory muscles. - While it causes hypotension and respiratory depression, the rapid onset and immediate unconsciousness, without prior signs of extensive motor block ascending, make intravascular injection a more probable cause for such acute and severe symptoms. *Anaphylaxis to lignocaine* - Anaphylaxis to local anesthetics is rare and would typically present with **urticaria**, **angioedema**, **bronchospasm**, and widespread erythema, which are not described. - While anaphylaxis can cause hypotension and cardiovascular collapse, the rapid onset of CNS depression leading to unconsciousness is more characteristic of local anesthetic systemic toxicity. *Total spinal block* - A **total spinal block** occurs when a local anesthetic meant for the epidural space accidentally enters the subarachnoid space and diffuses extensively. - This results in profound **hypotension**, **bradycardia**, and **apnea** due to high sympathetic and somatic nerve blockade; however, unconsciousness typically ensues after significant hypotension and hypoperfusion, not as immediately and severely as seen with direct intravascular injection of a toxic dose.
Question 5: Local anaesthetic usually used for retrobulbar block -
- A. Prilocaine
- B. Bupivacaine (Correct Answer)
- C. Tetracaine
- D. Procaine
Explanation: ***Bupivacaine*** - **Bupivacaine** is a long-acting local anaesthetic commonly chosen for retrobulbar blocks due to its prolonged duration of action, providing extended pain relief and akinesia. - Its slower onset compared to some other agents is often acceptable for ophthalmic procedures where prolonged block is more critical than rapid onset. *Prilocaine* - **Prilocaine** is an intermediate-acting local anaesthetic, generally having a shorter duration of action than bupivacaine, making it less ideal for procedures requiring sustained blockade. - High doses of prilocaine are associated with the risk of **methemoglobinemia**, which is a significant consideration in its use. *Tetracaine* - **Tetracaine** is primarily used as a topical anaesthetic, particularly for surface anaesthesia of the eye (e.g., prior to drops or contact lens insertion). - It is not typically used for injection in retrobulbar blocks due to its high systemic toxicity when administered via injection and its short duration of action. *Procaine* - **Procaine** is a short-acting ester-type local anaesthetic with a rapid onset but very brief duration of action. - Its short duration makes it unsuitable for retrobulbar blocks where prolonged akinesia and anaesthesia are desired for the surgical procedure.
Question 6: What is the maximum dose of plain lignocaine (in mg) for adults?
- A. 300 (Correct Answer)
- B. 500
- C. 700
- D. 1000
Explanation: ***300 mg*** - The maximum recommended dose of **plain lidocaine** (without epinephrine) for adults is typically **300 mg** or 4.5 mg/kg, whichever is less. - Exceeding this dose can increase the risk of **systemic toxicity**, including central nervous system and cardiovascular effects. *500 mg* - This dose is generally considered the maximum for **lidocaine with epinephrine** in adults, as **epinephrine** causes vasoconstriction and delays systemic absorption of lidocaine. - For **plain lidocaine**, 500 mg would be an overdose and significantly increase the risk of toxicity. *700 mg* - This is well above the recommended maximum dose for both plain lidocaine and lidocaine with epinephrine, posing a **severe risk of toxicity**. - Such a high dose could lead to **seizures**, cardiac arrhythmias, and even **cardiac arrest**. *1000 mg* - This dose is extremely dangerous and far exceeds any recommended maximum for lidocaine, regardless of whether it contains epinephrine. - Administration of 1000 mg of lidocaine would almost certainly result in **severe and potentially fatal toxicity**.
Question 7: A 5 year old healthy child is undergoing strabismus surgery with a Laryngeal mask airway in place. Thirty minutes into the procedure, his heart rate is 60 bpm, blood pressure is 90/60 mmHg, and oximeter shows 98% saturation. The next step in management is
- A. Replace the LMA with endotracheal tube
- B. Nothing, this is normal for this child
- C. Inform surgeon, administer atropine (Correct Answer)
- D. Increase FiO2 to 1.0
Explanation: ***Inform surgeon, administer atropine*** - **Oculocardiac reflex** is a common complication during strabismus surgery, characterized by bradycardia, hypotension, and arrhythmias. The significant drop in heart rate (60 bpm in a 5-year-old child) and mild hypotension suggest this reflex. - The standard management for an oculocardiac reflex involves informing the surgeon to temporarily cease manipulation of the extraocular muscles and administering an **anticholinergic drug** like atropine to counteract the vagal stimulation. *Replace the LMA with endotracheal tube* - The patient's oxygen saturation of 98% indicates adequate ventilation and oxygenation with the LMA, so there is no immediate need for **airway intervention**. - Replacing the LMA with an endotracheal tube is a more invasive procedure and would not directly address the underlying cause of bradycardia, which is likely due to the oculocardiac reflex. *Nothing, this is normal for this child* - A heart rate of 60 bpm is **significantly low** for a 5-year-old child under anesthesia, as the expected heart rate for this age group is typically much higher (around 80-120 bpm). - Ignoring this bradycardia could lead to further compromise in **cardiac output** and tissue perfusion if not addressed promptly. *Increase FiO2 to 1.0* - The current oxygen saturation of 98% indicates **adequate oxygenation**, so increasing the FiO2 would not address the bradycardia or hypotension. - While maintaining good oxygenation is important, this step would not resolve the primary issue of an **oculocardiac reflex** causing vagal stimulation.
Question 8: The type of iridectomy shown in the image is:
- A. Peripheral basal iridectomy (Correct Answer)
- B. Sector iridectomy
- C. Button-hole iridectomy
- D. Complete iridectomy
Explanation: ***Peripheral basal iridectomy*** - The image clearly depicts an iris with a small, circular opening located at its **periphery**, specifically at the base near the ciliary body. - This type of opening is characteristic of a **peripheral basal iridectomy**, which creates an alternative pathway for aqueous humor flow to relieve pupillary block, often associated with angle-closure glaucoma. *Sector iridectomy* - A **sector iridectomy** involves removing a full-thickness, wedge-shaped section of the iris that extends from the pupillary margin to the iris root, creating a keyhole-shaped pupil. - The image does not show a wedge-shaped defect extending to the pupil. *Button-hole iridectomy* - A **button-hole iridectomy** is typically a small, central opening in the iris that is completely surrounded by iris tissue, often performed for optical purposes. - The image shows a peripheral opening, not a central one. *Complete iridectomy* - A **complete iridectomy** implies the removal of the entire iris, or at least a very large portion, which would result in a highly enlarged and distorted pupil. - The image shows a small, localized opening, not extensive iris removal.
Question 9: Which one of the following is a branch of the first part of the maxillary artery?
- A. Middle meningeal
- B. Inferior alveolar
- C. Anterior ethmoidal
- D. Anterior tympanic (Correct Answer)
Explanation: ***Anterior tympanic*** - This artery arises from the **first part** (mandibular part) of the maxillary artery. - It supplies structures within the **tympanic cavity**, including the inner surface of the tympanic membrane. - Among the options listed, this is a **classic branch** consistently mentioned in anatomy texts. *Anterior ethmoidal* - This artery is a branch of the **ophthalmic artery**, which itself is a branch of the internal carotid artery, **not the maxillary artery**. - It supplies the **ethmoid air cells**, frontal sinus, and nasal cavity. - This is the **definitively incorrect option** as it does not arise from the maxillary artery at all. *Middle meningeal* - This artery **also arises from the first part** (mandibular part) of the maxillary artery. - It is a significant artery that supplies the **dura mater** and cranial bones. - While anatomically correct, **anterior tympanic** is the more specific answer being tested in this context. *Inferior alveolar* - This artery **also arises from the first part** (mandibular part) of the maxillary artery. - It descends to supply the **mandible**, its teeth, and the lower lip and chin. - While anatomically correct, it is not the best answer in this specific question context.
Question 10: Identify the ophthalmic instrument used for measuring heterophoria and heterotropia.
- A. Maddox rod (Correct Answer)
- B. Maddox wing
- C. Maddox glass
- D. Red glasses
Explanation: ***Maddox rod*** - A **Maddox rod** consists of a series of parallel cylindrical lenses that converts a point source of light into a line, forcing the patient to dissociate the images seen by each eye. - This dissociation allows for the measurement of **heterophoria** (latent deviation) and **heterotropia** (manifest deviation or strabismus) by observing the position of the perceived line relative to a fixation light. *Maddox wing* - The Maddox wing is used to measure **heterophoria at near**, typically at 33 cm. - It presents separate images to each eye (a scale and arrows) and does not involve the principle of converting a point source to a line. *Maddox glass* - The term **Maddox glass** is not a standard ophthalmic instrument. - It might colloquially refer to a Maddox rod or a similar device, but it lacks the specific definition of the other options. *Red glasses* - **Red glasses** (or red filter) are used in various ophthalmic tests, often to create dissociation between the eyes or to test for suppression. - They do not, however, convert a point source of light into a line for the precise measurement of ocular deviation in the same way a Maddox rod does.
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