Embryology of Eye — MCQs
The following ocular structure is not derived from surface ectoderm –
Which of the following cell types is neuroectodermal in origin?
At 30 days of intrauterine life, what is the expected developmental milestone?
The normal growth of the human eye includes all except
Which of the following is a specific sign of albinism?
What is the diagnosis if a patient can only see 3 green dots on the Worth 4 Dot test?
What is the yoke muscle of the right lateral rectus?
Identify the ophthalmic instrument used for measuring heterophoria and heterotropia.
All of the following statements are true regarding cavernous sinus thrombosis EXCEPT:
Bilateral inter nuclear ophthalmoplegia is pathognomonic of-
Embryology of Eye Indian Medical PG Practice Questions and MCQs
Question 1: The following ocular structure is not derived from surface ectoderm –
- A. Epithelium of lacrimal glands
- B. Crystalline lens
- C. Sclera (Correct Answer)
- D. Corneal epithelium
Explanation: **Sclera** - The **sclera** develops from the **neural crest cells**, which differentiate into mesenchymal tissue around the optic cup, forming the fibrous coats of the eye [1]. - It is part of the **fibrous tunic** of the eye, along with the cornea, and provides structural support. *Epithelium of lacrimal glands* - The **epithelium of lacrimal glands** originates from the **surface ectoderm** through invaginations and subsequent differentiation. - These glands are responsible for producing the **watery component of tears**. *Crystalline lens* - The **crystalline lens** also develops from the **surface ectoderm**, specifically from the lens placode, which invaginates to form the lens vesicle. - It is crucial for **focusing light** onto the retina. *Corneal epithelium* - The **corneal epithelium** is derived from the **surface ectoderm** and forms the outermost layer of the cornea [1]. - It provides a **protective barrier** and helps maintain the smooth refractive surface of the cornea [1].
Question 2: Which of the following cell types is neuroectodermal in origin?
- A. Smooth muscle cells (Correct Answer)
- B. Skeletal muscle cells
- C. Endothelial cells
- D. Cardiac muscle cells
Explanation: ***Smooth muscle cells*** - This is the **correct answer** based on a **specific exception**: smooth muscle cells of the **iris dilator and sphincter muscles** and the **ciliary muscle** in the eye are derived from **neuroectoderm** (specifically from the **optic cup**, an outgrowth of the neural tube). - **Important note:** The vast majority of smooth muscle in the body is of **mesodermal origin** (e.g., in blood vessels, GI tract, respiratory tract). This question tests knowledge of this **notable embryological exception**. - In the context of the given options, this is the only cell type with any neuroectodermal component. *Skeletal muscle cells* - Skeletal muscle cells are entirely derived from the **paraxial mesoderm**, specifically from **somites** (myotome portion). - They form the voluntary muscles of the body and are **never** of neuroectodermal origin. *Endothelial cells* - Endothelial cells lining blood vessels and lymphatic vessels are derived from the **mesoderm** (specifically from **angioblasts**). - They are part of the cardiovascular system and are **entirely mesodermal** in origin. *Cardiac muscle cells* - Cardiac muscle cells are derived from the **splanchnic mesoderm** (lateral plate mesoderm). - The heart musculature is **entirely mesodermal** with no neuroectodermal contribution. **Clinical Pearl:** Classic neuroectodermal derivatives include neurons, glial cells (astrocytes, oligodendrocytes), ependymal cells, and neural crest derivatives (Schwann cells, melanocytes, chromaffin cells). The smooth muscle of the iris represents an important exception to the general rule that smooth muscle is mesodermal.
Question 3: At 30 days of intrauterine life, what is the expected developmental milestone?
- A. Optic vesicle appears (Correct Answer)
- B. Heart starts beating
- C. Cerebellum develops
- D. Pinna appears
Explanation: Optic vesicle appears - The **optic vesicle** is an outpocketing from the diencephalon that appears around **day 22-28** of development. - At approximately **30 days** (end of 4th week/early 5th week), the optic vesicle is actively present and beginning to invaginate to form the optic cup. - Among the given options, this represents the developmental structure most characteristically associated with the **late 4th week/30-day timeframe** in embryology milestones. *Heart starts beating* - The primitive heart tube begins to beat around **day 22-23** of gestation. - By 30 days, the heart has already been beating for over a week, making this an earlier milestone rather than one expected "at" 30 days. *Cerebellum develops* - The cerebellum develops later, primarily during the **second and third months** (weeks 8-12) of gestation as the metencephalon differentiates. - Major cerebellar development occurs well after 30 days. *Pinna appears* - The external ear (pinna) begins forming around the **sixth week** (~42 days) from six auricular hillocks.
Question 4: The normal growth of the human eye includes all except
- A. Dramatic decrease in lens power in first one year
- B. A 4 mm increase in axial length in first 6 months of life
- C. An increase in corneal power in first 6 months (Correct Answer)
- D. A corneal diameter of 10.5 mm at birth, 12mm by age 2
Explanation: ***An increase in corneal power in first 6 months*** - Normal physiological development of the human eye involves a **decrease in corneal power** during the first 6 months of life. This emmetropization process helps the eye achieve a clearer focus as it grows. - An increase in corneal power would typically lead to **myopic shifts** or other refractive errors if not compensated by other ocular changes. *Dramatic decrease in lens power in first one year* - The human lens is highly positive at birth (around +34.50 D) and undergoes a significant physiological decrease in power during the **first year of life** as part of the emmetropization process. - This reduction in lens power, coupled with the increase in axial length, helps the eye achieve **emmetropia** (normal refractive state). *A 4 mm increase in axial length in first 6 months of life* - The eye undergoes rapid growth after birth, with the axial length increasing significantly, particularly in the **first 6 months of life**. - A 4 mm increase in axial length during this period is an expected part of **normal ocular development** contributing to emmetropization. *A corneal diameter of 10.5 mm at birth, 12mm by age 2* - The average corneal diameter at birth is approximately **9.0 mm to 10.5 mm**, rapidly increasing to about 11.5 mm by age 1 and reaching its adult size of around **12 mm by age 2** to 3 years. - This growth in corneal diameter is a normal part of ocular development and contributes to the overall enlargement of the eye globe.
Question 5: Which of the following is a specific sign of albinism?
- A. Iris transillumination (Correct Answer)
- B. Sensitivity to light (photophobia)
- C. Involuntary eye movements (nystagmus)
- D. Decreased visual acuity
Explanation: ***Iris transillumination*** - This is a highly **specific sign** of albinism, resulting from the severe reduction or absence of pigment in the iris. - When light shines through the pupil, it passes through the unpigmented iris, creating a visible red reflex, indicating the lack of pigment that normally blocks the light. *Sensitivity to light (photophobia)* - While common in albinism due to the lack of pigment in the iris and retina allowing more light to enter the eye, **photophobia is not specific** to albinism. - It can be a symptom of various other ocular conditions like uveitis, corneal abrasions, or migraines. *Involuntary eye movements (nystagmus)* - **Nystagmus is frequently associated with albinism** due to foveal hypoplasia and impaired visual development but is **not specific**. - It can also be caused by neurological disorders, inner ear problems, or other ocular conditions. *Decreased visual acuity* - **Reduced vision is a characteristic feature of albinism** resulting from foveal hypoplasia and abnormal optic nerve pathways, but it is **not specific** to the condition. - Numerous eye conditions, such as refractive errors, cataracts, and retinal diseases, can lead to decreased visual acuity.
Question 6: What is the diagnosis if a patient can only see 3 green dots on the Worth 4 Dot test?
- A. Right eye suppression (Correct Answer)
- B. Crossed diplopia
- C. Uncrossed diplopia
- D. Left eye suppression
Explanation: ***Right eye suppression*** - Seeing **three green dots** exclusively indicates that the patient is only perceiving input from the **left eye**. - In the Worth 4 Dot test, the **left eye** (viewing through a green filter) sees **three green dots**: the white dot at the top (which appears green through the filter) plus the two lateral green dots. - The **right eye** (viewing through a red filter) normally sees **two red dots**: the white dot at the top (which appears red) plus the red dot at the bottom. - Since the patient sees only **three green dots**, the visual input from the **right eye is being suppressed**. *Crossed diplopia* - **Crossed diplopia** (heteronymous diplopia) occurs when the image from the right eye is perceived to the left of the image from the left eye. - This typically occurs with **exotropia** (divergent strabismus) and would result in seeing **five or more dots** (patient perceives both eyes' images but misaligned), not just three green. *Uncrossed diplopia* - **Uncrossed diplopia** (homonymous diplopia) occurs when the image from the right eye is perceived to the right of the image from the left eye. - This is usually associated with **esotropia** (convergent strabismus) and would also lead to the perception of **five or more dots** (both eyes' images perceived but misaligned), not only three green dots. *Left eye suppression* - If there were **left eye suppression**, the patient would see **two red dots** from the right eye only (the white dot appearing red plus the red dot at the bottom). - Seeing **three green dots** confirms the **left eye input is dominant** and the **right eye is suppressed**.
Question 7: What is the yoke muscle of the right lateral rectus?
- A. Lt medial rectus (Correct Answer)
- B. Lt superior rectus
- C. Lt lateral rectus
- D. Lt inferior oblique
Explanation: ***Lt medial rectus*** - Yoke muscles are pairs of muscles in opposite eyes that produce **conjugate eye movements**, meaning they cause both eyes to move in the same direction. - When the **right lateral rectus** abducts (moves outward) the right eye, the **left medial rectus** adducts (moves inward) the left eye, both eyes gaze to the right. *Lt superior rectus* - The left superior rectus is primarily responsible for **elevation** and **intorsion** of the left eye. - It works synergistically with the right **inferior oblique** for upward gaze. *Lt lateral rectus* - The left lateral rectus is the primary muscle for **abduction** (moving outward) of the left eye. - It is not a yoke muscle for the right lateral rectus, as both perform similar actions in their respective eyes. *Lt inferior oblique* - The left inferior oblique primarily causes **extorsion**, **elevation**, and **abduction** of the left eye. - It works with the right superior rectus for upward gaze.
Question 8: 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.
Question 9: All of the following statements are true regarding cavernous sinus thrombosis EXCEPT:
- A. Loss of jaw jerk (Correct Answer)
- B. Loss of sensation around the eye
- C. Sphenoid sinusitis is the most common cause
- D. Inferior ophthalmic vein can spread infection from dangerous area of face
Explanation: ***Loss of jaw jerk*** - The **jaw jerk reflex** is mediated by the **trigeminal nerve (V3)** and its mesencephalic nucleus, which lies within the brainstem, superior to the cavernous sinus. - Cavernous sinus thrombosis primarily affects structures passing *through* or *adjacent* to the sinus, predominantly **cranial nerves III, IV, V1, V2, and VI**, but typically does not directly impact the brainstem structures responsible for the jaw jerk reflex in its localized progression. *Inferior ophthalmic vein can spread infection from dangerous area of face* - The **inferior ophthalmic vein** drains into the **cavernous sinus**, providing a direct route for infection from the **"dangerous area" of the face** (e.g., upper lip, nose, medial canthus). - This venous connection allows pathogens to enter the cavernous sinus and cause **thrombosis**. *Sphenoid sinusitis is the most common cause* - **Sphenoid sinusitis** is a common cause of **cavernous sinus thrombosis** due to the close anatomical proximity of the sphenoid sinuses to the cavernous sinuses. - Inflammation and infection in the sphenoid sinus can easily spread directly into the adjacent cavernous sinus. *Loss of sensation around the eye* - The **ophthalmic division (V1)** of the trigeminal nerve passes through the **cavernous sinus** and provides sensation to the forehead, upper eyelid, and **area around the eye**. - Compression or involvement of V1 due to thrombosis can result in **sensory deficits** in this distribution.
Question 10: Bilateral inter nuclear ophthalmoplegia is pathognomonic of-
- A. Pontine haemorrhage
- B. Lateral medullary syndrome
- C. Multiple sclerosis (Correct Answer)
- D. Pontine glioma
Explanation: Bilateral internuclear ophthalmoplegia (INO) is highly suggestive of multiple sclerosis due to demyelination in the medial longitudinal fasciculus (MLF) on both sides. INO results from a lesion in the MLF, which coordinates conjugate eye movements, leading to impaired adduction on attempted lateral gaze and nystagmus of the abducting eye. *Pontine haemorrhage* - A pontine haemorrhage typically causes a more widespread neurological deficit, including coma, quadriplegia, and pinpoint pupils, rather than isolated INO. - While it can affect the brainstem, primary findings are usually related to mass effect and destruction of vital centers. *Lateral medullary syndrome* - Also known as Wallenberg syndrome, lateral medullary syndrome is caused by infarction of the posterior inferior cerebellar artery (PICA) and presents with vestibular symptoms, ataxia, dysphagia, and contralateral loss of pain and temperature sensation. - It does not directly cause bilateral internuclear ophthalmoplegia as its primary clinical feature. *Pontine glioma* - A pontine glioma is a brain tumor that can affect various cranial nerves and tracts within the pons. - While it can cause some ophthalmoplegia, bilateral internuclear ophthalmoplegia is not its specific or pathognomonic presentation; the clinical picture is usually more diverse and progressive.
Want unlimited practice?
Get full access to all questions, explanations, and performance tracking.
Start For Free