Autonomic Drugs in Ophthalmology — MCQs
Ocular effects that include mydriasis are characteristic of which of the following drugs?
In head injury, unilateral dilatation of the pupil is seen due to?
Which of the following acts on the trabecular meshwork and increases aqueous outflow?
Which of the following drugs is a corticosteroid and not used for treating glaucoma?
Which intrinsic ocular muscle responsible for pupillary constriction is supplied by parasympathetic innervation?
Which is the shortest-acting mydriatic?
Mechanism of action of curare-like drugs?
Which sympathomimetic drug is primarily known to increase heart rate?
A lady presents with swelling of hands with shiny skin. She has a history of fracture radius and kept on POP cast for 4 weeks after which she develops this. Give the most likely diagnosis -
All of the following are true about neuroblastoma except -
Autonomic Drugs in Ophthalmology Indian Medical PG Practice Questions and MCQs
Question 1: Ocular effects that include mydriasis are characteristic of which of the following drugs?
- A. phenylephrine (alpha agonist) (Correct Answer)
- B. neostigmine (cholinesterase inhibitor)
- C. phentolamine (alpha blocker)
- D. mecamylamine (ganglionic blocker)
Explanation: ***phenylephrine (alpha agonist)*** - **Phenylephrine** is a direct-acting **alpha-1 adrenergic agonist** that causes contraction of the **pupillary dilator muscle**, leading to **mydriasis** (pupil dilation). [1] - It is frequently used clinically to dilate pupils for **ophthalmologic examinations** due to its selective action on alpha-1 receptors in the eye. [2] *neostigmine (cholinesterase inhibitor)* - **Neostigmine** inhibits acetylcholinesterase, increasing acetylcholine at the neuromuscular junction and muscarinic receptors. This leads to **miosis** (pupil constriction), not mydriasis. - Its ophthalmic use is primarily for treating **glaucoma** by improving aqueous humor outflow through cholinergic effects on the ciliary muscle. *phentolamine (alpha blocker)* - **Phentolamine** is a **non-selective alpha-adrenergic antagonist** that blocks both alpha-1 and alpha-2 receptors. - Alpha-1 receptor blockade in the eye would relax the pupillary dilator muscle, leading to **miosis** or prevention of mydriasis, not its induction. *mecamylamine (ganglionic blocker)* - **Mecamylamine** is a **ganglionic blocker** that antagonizes nicotinic receptors in both sympathetic and parasympathetic ganglia. - Blocking parasympathetic ganglia can cause some mydriasis, but ganglionic blockers have widespread, non-selective autonomic effects and are not primarily used for isolated mydriasis.
Question 2: In head injury, unilateral dilatation of the pupil is seen due to?
- A. Ophthalmic N. compression
- B. Trigeminal N. compression
- C. Oculomotor nerve compression (Correct Answer)
- D. None of the options
Explanation: Oculomotor nerve compression - Unilateral pupillary dilation, often referred to as a **blown pupil**, is a classic sign of **oculomotor nerve (CN III) compression** due to increased intracranial pressure, typically from a **herniating uncus** [1]. - The parasympathetic fibers responsible for pupillary constriction run on the superficial aspect of the oculomotor nerve and are thus vulnerable to extrinsic compression [1], [2]. *Ophthalmic N. compression* - The **ophthalmic nerve (CN V1)** is a sensory nerve responsible for sensation to the forehead, scalp, upper eyelid, and cornea, not pupillary control. - Compression of this nerve would cause **sensory deficits** in its distribution and potentially abolish the **corneal reflex**, but not pupillary dilation. *Trigeminal N. compression* - The **trigeminal nerve (CN V)** is primarily responsible for sensation to the face and motor control of the muscles of mastication. - Compression would lead to **facial numbness or pain** and **weakness in chewing**, with no direct impact on pupillary size. *None of the options* - This option is incorrect because oculomotor nerve compression is a well-established cause of unilateral pupillary dilation in head injuries [1].
Question 3: Which of the following acts on the trabecular meshwork and increases aqueous outflow?
- A. Timolol
- B. Pilocarpine (Correct Answer)
- C. Brimonidine
- D. Brinzolamide
Explanation: ***Pilocarpine*** - As a **muscarinic agonist**, pilocarpine contracts the **ciliary muscle**, which pulls on the scleral spur. - This action widens the spacing within the **trabecular meshwork**, increasing aqueous humor outflow. *Timolol* - Timolol is a **beta-blocker** that reduces the production of aqueous humor by the ciliary body. - It does not directly affect the structure or function of the trabecular meshwork to enhance outflow. *Brimonidine* - Brimonidine is an **alpha-2 adrenergic agonist** that reduces aqueous humor production and increases uveoscleral outflow. - It does not primarily act on the trabecular meshwork to facilitate outflow. *Brinzolamide* - Brinzolamide is a **carbonic anhydrase inhibitor** that decreases aqueous humor production by the ciliary body. - Its mechanism of action does not involve directly affecting the trabecular meshwork's outflow capacity.
Question 4: Which of the following drugs is a corticosteroid and not used for treating glaucoma?
- A. Prednisolone (Correct Answer)
- B. Dorzolamide
- C. Timolol
- D. Brimonidine
Explanation: ***Prednisolone*** - **Prednisolone** is a potent **corticosteroid** used to reduce inflammation. - While it has various therapeutic uses, **corticosteroids** can cause or worsen **glaucoma** by increasing intraocular pressure and are therefore generally avoided in its treatment. *Brimonidine* - **Brimonidine** is an **alpha-2 adrenergic agonist** used to treat **glaucoma** by reducing aqueous humor production and increasing uveoscleral outflow. - It is not a corticosteroid and directly targets **intraocular pressure (IOP)** reduction. *Dorzolamide* - **Dorzolamide** is a **carbonic anhydrase inhibitor** that effectively treats **glaucoma** by decreasing aqueous humor secretion. - It works by inhibiting the enzyme **carbonic anhydrase** in the ciliary body, and it is not a corticosteroid. *Timolol* - **Timolol** is a **non-selective beta-blocker** that lowers **intraocular pressure** by reducing the production of aqueous humor. - It is one of the most commonly prescribed drugs for **glaucoma** and is not a corticosteroid.
Question 5: Which intrinsic ocular muscle responsible for pupillary constriction is supplied by parasympathetic innervation?
- A. Constrictor pupillae (Correct Answer)
- B. Dilator pupillae
- C. Levator palpebrae superioris
- D. Ciliary muscle
Explanation: ***Constrictor pupillae*** - The **constrictor pupillae** (or **sphincter pupillae**) muscle is responsible for **miosis** (pupil constriction) and is innervated by **parasympathetic fibers** from the **oculomotor nerve (CN III)** via the **ciliary ganglion** [1]. - Stimulation of this muscle reduces the pupil size, which is a key part of the **light reflex** and **accommodation reflex** [1]. - This is the **only pupillary muscle** with parasympathetic innervation. *Ciliary muscle* - The **ciliary muscle** is involved in **accommodation**, altering the shape of the lens for focusing on near objects [1]. - While it also receives **parasympathetic innervation** from the ciliary ganglion, it does **not control pupil size**. - Its function is to change **lens curvature**, not pupillary diameter. *Levator palpebrae superioris* - This muscle is responsible for **elevating the upper eyelid**. - It is innervated by the **somatic motor fibers** of the **oculomotor nerve (CN III)**, not parasympathetic fibers. - It is **not an intrinsic ocular muscle** but rather an extraocular muscle. *Dilator pupillae* - The **dilator pupillae** muscle causes **mydriasis** (pupil dilation). - This muscle is innervated by **sympathetic fibers**, originating from the superior cervical ganglion, not parasympathetic fibers.
Question 6: Which is the shortest-acting mydriatic?
- A. Tropicamide (Correct Answer)
- B. Homatropine
- C. Atropine
- D. Cyclopentolate
Explanation: ***Tropicamide*** - It is an **anticholinergic drug** that produces **mydriasis** (pupil dilation) due to its blocking effect on **muscarinic receptors** in the iris sphincter muscle. - Tropicamide has the **shortest duration of action** among the listed mydriatic agents, typically lasting 4-6 hours. *Homatropine* - Homatropine is an **anticholinergic drug** with a longer duration of action than tropicamide, typically lasting 1-3 days. - It is commonly used for **cycloplegia** and mydriasis in ophthalmology, but not as the shortest-acting agent. *Atropine* - Atropine is a potent **anticholinergic drug** with the **longest duration of action**, causing mydriasis and cycloplegia that can last for 7-14 days. - Due to its prolonged effects, it is less commonly used for routine pupil dilation and more for therapeutic purposes like treating **anterior uveitis**. *Cyclopentolate* - Cyclopentolate is an **anticholinergic agent** that causes mydriasis and cycloplegia with a duration of action of approximately 6-24 hours. - While faster acting than atropine and homatropine, it is still longer-acting than tropicamide.
Question 7: Mechanism of action of curare-like drugs?
- A. Blocks ACh receptors (Correct Answer)
- B. Agonistic with ACh receptors
- C. Inhibits ACh synthesis
- D. Causes persistent depolarization
Explanation: ***Blocks ACh receptors*** - Curare-like drugs are **competitive antagonists** at the **nicotinic acetylcholine receptors (nAChRs)** found at the neuromuscular junction. - By binding to these receptors, they prevent acetylcholine (ACh) from binding and activating the receptors, thereby **inhibiting muscle contraction**. *Inhibits ACh synthesis* - Drugs that inhibit ACh synthesis typically target enzymes like **choline acetyltransferase**. - This mechanism would reduce the amount of ACh available, but curare acts directly at the *receptor level*. *Causes persistent depolarization* - This is the mechanism of action of **depolarizing neuromuscular blockers** like succinylcholine. - They initially activate the receptor, causing a brief depolarization, followed by a sustained depolarization that renders the muscle unresponsive. *Agonistic with ACh receptors* - An agonist binds to and activates a receptor, mimicking the effect of the natural ligand (acetylcholine in this case). - Curare-like drugs are **antagonists**; they bind to the receptor but do not activate it, instead blocking ACh binding.
Question 8: Which sympathomimetic drug is primarily known to increase heart rate?
- A. Isoprenaline (Correct Answer)
- B. Phenylephrine
- C. Noradrenaline
- D. Adrenaline
Explanation: ***Isoprenaline*** - **Isoprenaline** (isoproterenol) is a non-selective beta-adrenergic agonist, with a strong affinity for **β1 and β2 receptors** [1]. - Its activation of **β1 receptors** in the heart leads to a significant increase in **heart rate (positive chronotropy)** and contractility (positive inotropy) [1]. - It is the **most potent chronotropic agent** among sympathomimetics and is primarily known for increasing heart rate [2]. *Phenylephrine* - **Phenylephrine** is a selective **α1 adrenergic agonist** that causes vasoconstriction [4]. - It increases blood pressure but typically causes **reflex bradycardia** (decreased heart rate) due to baroreceptor activation. - Does NOT directly increase heart rate. *Noradrenaline* - **Noradrenaline** (norepinephrine) primarily acts on **α1 receptors** causing vasoconstriction, and to a lesser extent on **β1 receptors** [3]. - While it can stimulate β1 receptors, its predominant effect is to increase **mean arterial pressure** through vasoconstriction, often causing **reflex bradycardia** [3]. *Adrenaline* - **Adrenaline** (epinephrine) acts on **α1, β1, and β2 receptors** [4]. While it does increase heart rate via **β1 receptor** stimulation, it also causes significant **vasoconstriction** (via α1) and **vasodilation** (via β2). - Its cardiovascular effects are more complex and dose-dependent compared to isoprenaline's specific chronotropic action.
Question 9: A lady presents with swelling of hands with shiny skin. She has a history of fracture radius and kept on POP cast for 4 weeks after which she develops this. Give the most likely diagnosis -
- A. Malunion
- B. Rupture of external pollicis longus tendon
- C. Myositis ossification
- D. Reflex sympathetic dystrophy (Correct Answer)
Explanation: ***Reflex sympathetic dystrophy*** - This patient presents with **swelling of the hands**, **shiny skin**, and a history of trauma (fracture radius) followed by immobilization. These are classic symptoms of **Reflex Sympathetic Dystrophy (RSD)**, now known as **Complex Regional Pain Syndrome type I (CRPS I)**. - RSD is characterized by an exaggerated response of the **sympathetic nervous system** after an injury, leading to pain, swelling, trophic skin changes (shiny skin, hair changes), and often vasomotor instability. *Malunion* - **Malunion** refers to a fracture that has healed in an abnormal position, leading to cosmetic deformity or functional impairment. - While malunion can cause pain and some functional issues, it does not typically present with diffuse hand swelling and shiny skin as described. *Rupture of external pollicis longus tendon* - **Rupture of the extensor pollicis longus (EPL) tendon** can occur as a complication of a distal radius fracture, especially following non-union or sharp bone spicules. - This complication would primarily result in the inability to extend the **thumb at the interphalangeal joint**, not widespread hand swelling and shiny skin. *Myositis ossification* - **Myositis ossificans** is the heterotopic formation of bone in muscle or soft tissue, typically occurring after trauma. - It presents as a firm, painful mass in the muscle and can lead to restricted joint movement, but it does not cause the diffuse hand swelling and shiny skin characteristic of this case.
Question 10: All of the following are true about neuroblastoma except -
- A. Cafe au lait spots (Correct Answer)
- B. Opsoclonus
- C. Bone pain
- D. Diarrhea
Explanation: ***Cafe au lait spots*** - **Neuroblastoma** is a **neuroendocrine tumor** derived from **neural crest cells**, often leading to symptoms related to compression or metastasis, but not typically presenting with **cafe au lait spots**. - **Cafe au lait spots** are characteristic of **neurofibromatosis type 1**, a genetic disorder caused by mutations in the **neurofibromin gene (NF1)**, which is distinct from neuroblastoma. *Opsomyoclonus* - **Opsoclonus-myoclonus syndrome (OMS)**, an **autoimmune paraneoplastic syndrome**, is a known presentation of **neuroblastoma**, especially in younger children. - This syndrome is characterized by **rapid, irregular eye movements (opsoclonus)** and **sudden, jerky muscle contractions (myoclonus)**. *Bone pain* - **Neuroblastoma** commonly **metastasizes to bone** and **bone marrow**, particularly in advanced stages, causing significant **bone pain**. - The presence of bone pain often indicates widespread disease and can be a presenting symptom. *Diarrhea* - **Neuroblastoma** can secrete **vasoactive intestinal peptide (VIP)**, leading to **severe, watery diarrhea**. - This syndrome is known as **VIPoma syndrome** and is a potential paraneoplastic manifestation of neuroblastoma, particularly abdominal tumors.
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