Basic Sciences as Related to Eye — MCQs

A 67-year-old man presents with complaints of deteriorating vision. A form of glaucoma is diagnosed in which the aqueous humor does not drain properly into the scleral venous sinus at the iridoscleral angle of the eyeball. The aqueous fluid is secreted by the epithelium of the ciliary body directly into which of the following spaces?

Q164Medium

In a fracture of the optic canal, which pair of structures is most likely to be damaged?

Q165Easy

Where is the attachment of the vitreous strongest?

Q166Easy

What infection is called a stye?

Q167Easy

Dalén-Fuchs nodule is seen in which condition?

Q168Easy

Flexner-Wintersteiner rosettes in microscopy are seen in which condition?

Q169Easy

Inheritance of colour blindness is:

Q170Easy

A stye is an inflammation of which gland?

Basic Sciences as Related to Eye Indian Medical PG Practice Questions and MCQs

Question 161: Pars planitis is a form of which type of uveitis?

A. Anterior uveitis
B. Intermediate uveitis (Correct Answer)
C. Posterior uveitis
D. Pan uveitis

Explanation: The classification of uveitis is based on the primary anatomical site of inflammation, as defined by the **Standardization of Uveitis Nomenclature (SUN) Working Group**. **Why Intermediate Uveitis is correct:** Intermediate uveitis refers to inflammation where the primary site is the **vitreous** and the **pars plana** (the posterior part of the ciliary body). **Pars planitis** is a specific subset of intermediate uveitis characterized by the presence of "snowballs" (vitreous inflammatory aggregates) or "snowbanking" (exudates on the pars plana), occurring in the absence of an associated systemic disease (idiopathic). **Why other options are incorrect:** * **Anterior Uveitis:** Inflammation primarily involves the iris (iritis) and/or the anterior part of the ciliary body (iridocyclitis). * **Posterior Uveitis:** Inflammation involves the retina (retinitis) or choroid (choroiditis). * **Panuveitis:** Inflammation is generalized, involving the anterior chamber, vitreous, and retina/choroid simultaneously. **High-Yield Clinical Pearls for NEET-PG:** * **Symptoms:** Patients typically present with **painless floaters** and blurred vision. Redness and pain are usually absent. * **Most common complication:** **Cystoid Macular Edema (CME)** is the leading cause of vision loss in pars planitis. * **Snowbanking:** This is most commonly found in the **inferior** quadrant of the pars plana and is best visualized using indirect ophthalmoscopy with scleral depression. * **Associations:** While pars planitis is idiopathic, intermediate uveitis can be associated with **Multiple Sclerosis** and **Sarcoidosis**.

Question 162: What instrument is used to measure corneal curvature?

A. Keratometry (Correct Answer)
B. Pachymetry
C. Gonioscopy
D. Perimetry

Explanation: **Explanation:** **1. Why Keratometry is Correct:** Keratometry (or a Keratometer) is the standard instrument used to measure the **curvature of the anterior corneal surface**. It works on the principle that the anterior surface of the cornea acts as a convex mirror. By measuring the size of the reflected image (Purkinje image I) of an object of known size, the radius of curvature can be calculated using the formula $r = 2uI/O$. This is essential for calculating Intraocular Lens (IOL) power before cataract surgery and for fitting contact lenses. **2. Why Other Options are Incorrect:** * **B. Pachymetry:** This measures **corneal thickness**. It is clinically vital for screening glaucoma (as Central Corneal Thickness affects IOP readings) and pre-operative evaluation for refractive surgeries like LASIK. * **C. Gonioscopy:** This is used to visualize the **iridocorneal angle** (drainage angle) of the anterior chamber. It is the gold standard for differentiating between Open-Angle and Angle-Closure Glaucoma. * **D. Perimetry:** This measures the **visual field**. It is used to map the peripheral and central field of vision to detect defects (scotomas) caused by glaucoma or neurological lesions. **High-Yield Clinical Pearls for NEET-PG:** * **Normal Corneal Curvature:** Approximately 44.00 Diopters (Radius of curvature $\approx$ 7.8 mm). * **Astigmatism:** Keratometry helps identify if astigmatism is "With-the-rule" (vertical meridian steeper) or "Against-the-rule" (horizontal meridian steeper). * **Corneal Topography:** While keratometry measures only the central 3mm, topography provides a detailed map of the entire corneal surface (useful for diagnosing Keratoconus). * **Specular Microscopy:** Used to study the corneal **endothelial cell count** (Normal: 2500–3000 cells/mm²).

Question 163: A 67-year-old man presents with complaints of deteriorating vision. A form of glaucoma is diagnosed in which the aqueous humor does not drain properly into the scleral venous sinus at the iridoscleral angle of the eyeball. The aqueous fluid is secreted by the epithelium of the ciliary body directly into which of the following spaces?

A. Iridoscleral angle
B. Posterior chamber (Correct Answer)
C. Pupil
D. Vitreous body

Explanation: **Explanation:** The correct answer is **B. Posterior chamber**. **Underlying Concept:** Aqueous humor is a clear fluid produced by the **non-pigmented epithelium of the ciliary processes** (part of the ciliary body). It is secreted directly into the **posterior chamber**, which is the narrow space bounded anteriorly by the iris, posteriorly by the lens and zonules, and peripherally by the ciliary body. From the posterior chamber, the fluid flows through the **pupil** into the anterior chamber and eventually drains via the trabecular meshwork into the **scleral venous sinus (Schlemm’s canal)** at the iridoscleral angle. **Analysis of Incorrect Options:** * **A. Iridoscleral angle:** This is the site of **drainage**, not secretion. Obstruction here leads to glaucoma. * **C. Pupil:** The pupil is the aperture through which aqueous humor passes to reach the anterior chamber; it is not the initial site of secretion. * **D. Vitreous body:** This is a gel-filled space behind the lens. While some fluid exchange occurs, the ciliary body does not secrete aqueous humor into the vitreous. **High-Yield NEET-PG Pearls:** * **Production Mechanism:** Aqueous is formed via three mechanisms: **Active secretion** (80% - most important), ultrafiltration, and simple diffusion. * **Enzyme involved:** Carbonic anhydrase II is crucial for production (target for Acetazolamide/Dorzolamide). * **Drainage Pathways:** 1. **Trabecular (Conventional):** 90% (Schlemm’s canal → Episcleral veins). 2. **Uveoscleral (Unconventional):** 10% (Ciliary muscle → Suprachoroidal space). Prostaglandin analogs increase this pathway. * **Volume:** The total volume of aqueous is approximately 0.25–0.30 mL, with a production rate of ~2–2.5 µL/min.

Question 164: In a fracture of the optic canal, which pair of structures is most likely to be damaged?

A. Optic nerve and ophthalmic vein
B. Ophthalmic vein and ophthalmic nerve
C. Ophthalmic artery and optic nerve (Correct Answer)
D. Ophthalmic nerve and optic nerve

Explanation: **Explanation:** The optic canal is a bony tunnel located in the **lesser wing of the sphenoid bone**. It serves as the primary gateway between the middle cranial fossa and the apex of the orbit. **Why Option C is Correct:** The optic canal transmits two major structures: 1. **Optic Nerve (CN II):** Surrounded by the three layers of meninges (dura, arachnoid, and pia mater). 2. **Ophthalmic Artery:** The first major branch of the internal carotid artery, which enters the canal inferolateral to the optic nerve within the dural sheath. Because these two structures are tightly packed within this narrow bony canal, a fracture of the lesser wing of the sphenoid directly compromises both, leading to traumatic optic neuropathy and vascular compromise. **Why Other Options are Incorrect:** * **Options A & B (Ophthalmic Veins):** The superior and inferior ophthalmic veins do not pass through the optic canal; they exit the orbit via the **Superior Orbital Fissure (SOF)**. * **Options B & D (Ophthalmic Nerve):** The ophthalmic nerve (CN V1) divides into three branches (Frontal, Lacrimal, Nasociliary), all of which enter the orbit through the **Superior Orbital Fissure**, not the optic canal. **High-Yield Clinical Pearls for NEET-PG:** * **Dimensions:** The optic canal is approximately 8–10 mm long. * **Surgical Landmark:** The optic canal is separated from the Superior Orbital Fissure by a thin bony bar called the **optic strut**. * **Clinical Sign:** A fracture here often results in an **Afferent Pupillary Defect (Marcus Gunn Pupil)** due to optic nerve damage, even if the eye appears structurally normal on external examination. * **Radiology:** The best view to visualize the optic canal is the **Rhiese view** (X-ray) or thin-cut CT scans.

Question 165: Where is the attachment of the vitreous strongest?

A. Foveal region
B. Back of lens
C. Across ora serrata (Correct Answer)
D. Margin of optic disc

Explanation: **Explanation:** The vitreous body is a transparent, gel-like structure that fills the posterior segment of the eye. It is not uniformly attached to the underlying retina; rather, it has specific sites of adherence with varying degrees of strength. **1. Why "Across ora serrata" is correct:** The strongest attachment of the vitreous is at the **vitreous base**. This is a 3–4 mm wide zone that straddles the **ora serrata** (extending approximately 2 mm anterior and 2 mm posterior to it). Here, the vitreous fibrils are firmly embedded into the basement membrane of the non-pigmented epithelium of the ciliary body and the internal limiting membrane of the peripheral retina. This attachment is so strong that surgical separation often results in retinal tearing rather than vitreous detachment. **2. Analysis of Incorrect Options:** * **Margin of optic disc:** This is the **second strongest** attachment (Weiss ring forms here during a Posterior Vitreous Detachment). * **Foveal region:** This is the **third strongest** attachment. Traction here can lead to macular holes or vitreomacular traction syndrome. * **Back of lens:** This is a circular attachment known as the **Ligament of Wieger** (hyaloideo-capsular ligament). It is strong in children but weakens significantly with age, allowing for intracapsular cataract surgery in adults. **3. Clinical Pearls for NEET-PG:** * **Hierarchy of Strength:** Vitreous Base (Ora serrata) > Optic Disc > Fovea > Along Retinal Vessels. * **Vitreous Base:** It is the only site where the vitreous cannot be surgically separated from the retina without causing damage. * **Shafer’s Sign:** The presence of "tobacco dust" (RPE cells) in the anterior vitreous following a tear at the vitreous base is a hallmark of retinal detachment.

Question 166: What infection is called a stye?

A. Hair follicles
B. Tarsal glands
C. Conjunctiva
D. Zeis glands (Correct Answer)

Explanation: ### Explanation A **stye**, medically known as an **External Hordeolum**, is an acute, focal, pyogenic inflammation of the eyelid margin. It is most commonly caused by a *Staphylococcus aureus* infection. **Why Option D is Correct:** The infection specifically involves the **Zeis glands** (sebaceous glands) or the **Moll glands** (modified sweat glands) located at the base of the eyelashes. Because these glands are superficial and associated with the lash follicle, the resulting abscess points outward on the lid margin, characterizing an external hordeolum. **Why Other Options are Incorrect:** * **Option A (Hair follicles):** While the infection occurs *at the base* of the hair follicle, the primary site of the glandular abscess is the Zeis or Moll gland. "Hair follicle" is a component, but "Zeis glands" is the more specific anatomical answer for the glandular involvement. * **Option B (Tarsal glands):** Infection of the Tarsal (Meibomian) glands is called an **Internal Hordeolum**. Since these glands are located deep within the tarsal plate, the abscess points toward the conjunctival side (inner surface) of the lid. * **Option C (Conjunctiva):** Infection of the conjunctiva is termed **Conjunctivitis**. While a stye may cause secondary conjunctival congestion, it is not an infection of the conjunctival tissue itself. **High-Yield Clinical Pearls for NEET-PG:** * **Internal Hordeolum:** Infection of Meibomian glands (more painful than external). * **Chalazion:** A **painless**, chronic granulomatous inflammation of the Meibomian glands (sterile, not acute infection). * **Treatment:** Most styes are self-limiting; management includes warm compresses and topical antibiotics. If it becomes a large abscess, incision and drainage (I&D) are performed (incision is made parallel to the lid margin for external hordeolum to avoid scarring).

Question 167: Dalén-Fuchs nodule is seen in which condition?

A. Bacterial endophthalmitis
B. Mycotic endophthalmitis
C. Sympathetic ophthalmitis (Correct Answer)
D. Phacotoxic endophthalmitis

Explanation: **Explanation:** **Sympathetic Ophthalmitis (SO)** is a rare, bilateral granulomatous panuveitis that occurs following a penetrating ocular injury or intraocular surgery in one eye (the "exciting eye"), subsequently affecting the other eye (the "sympathizing eye"). The hallmark histopathological feature of SO is the **Dalén-Fuchs nodule**. These are small, discrete, yellowish-white elevations found between the **Bruch’s membrane and the Retinal Pigment Epithelium (RPE)**. They consist of clusters of epithelioid cells, macrophages, and pigment-laden cells. Their presence is a classic diagnostic sign in histopathology for SO, alongside a diffuse non-necrotizing granulomatous inflammation of the uveal tract with "sparing of the choriocapillaris." **Analysis of Incorrect Options:** * **Bacterial and Mycotic Endophthalmitis:** These are acute or subacute suppurative inflammations of the inner coats of the eye caused by pathogens. The pathology is characterized by massive infiltration of polymorphonuclear leukocytes (neutrophils) and abscess formation, not granulomatous nodules. * **Phacotoxic Endophthalmitis:** This is a lens-induced uveitis (now more commonly termed lens-associated uveitis) caused by an inflammatory reaction to leaked lens proteins. While it involves inflammation, it does not manifest with Dalén-Fuchs nodules. **High-Yield Pearls for NEET-PG:** * **Latent Period:** SO usually occurs 2 weeks to 3 months after injury (90% within 1 year). * **Prevention:** Evisceration/Enucleation of the injured eye within 10–14 days of injury can prevent SO. * **Vogt-Koyanagi-Harada (VKH) Syndrome:** This is the other major condition where Dalén-Fuchs nodules can be seen, though they are most classically associated with SO in exams. * **Histology Tip:** Look for "Sparing of Choriocapillaris" and "Dalen-Fuchs Nodules" to confirm SO.

Question 168: Flexner-Wintersteiner rosettes in microscopy are seen in which condition?

A. Retinitis pigmentosa
B. Trauma
C. Retinoblastoma (Correct Answer)
D. Neuroblastoma

Explanation: **Explanation:** **Flexner-Wintersteiner rosettes** are the pathognomonic histological hallmark of **Retinoblastoma**. These structures consist of a ring of cuboidal or columnar cells surrounding a central lumen. This lumen represents an attempt by the primitive tumor cells to differentiate into photoreceptor elements (rods and cones). The presence of these rosettes indicates a degree of retinal differentiation. **Analysis of Options:** * **Retinoblastoma (Correct):** It is the most common intraocular malignancy of childhood. Flexner-Wintersteiner rosettes are highly specific for this condition. Other histological features include Homer-Wright rosettes (less specific) and fleurettes (representing high differentiation). * **Retinitis Pigmentosa:** This is a degenerative (not neoplastic) disease of the photoreceptors. Histology shows "bony spicule" pigmentation and atrophy of the retinal layers, not rosette formation. * **Trauma:** Ocular trauma leads to inflammation, scarring, or hemorrhage (e.g., Commotio retinae). It does not involve the cellular proliferation required to form rosettes. * **Neuroblastoma:** While neuroblastomas also feature rosettes, they are typically **Homer-Wright rosettes** (which lack a central lumen and contain a central tangle of nerve fibers/neuropil). Flexner-Wintersteiner rosettes are not characteristic of neuroblastoma. **High-Yield Clinical Pearls for NEET-PG:** * **Homer-Wright Rosettes:** Seen in Neuroblastoma, Medulloblastoma, and Retinoblastoma (non-specific). * **Flexner-Wintersteiner Rosettes:** Specific for Retinoblastoma and Pineoblastoma. * **Fleurettes:** Represent the highest level of photoreceptor differentiation in Retinoblastoma. * **Calcification:** Retinoblastoma is a "chalky white" tumor; presence of calcification on CT scan is a key diagnostic sign.

Question 169: Inheritance of colour blindness is:

A. Y linked
B. X linked recessive (Correct Answer)
C. Autosomal dominant
D. Autosomal recessive

Explanation: **Explanation:** The correct answer is **B. X-linked recessive.** **1. Why X-linked Recessive is Correct:** Congenital color blindness, specifically the most common types (Protanopia and Deuteranopia), is inherited in an **X-linked recessive** pattern. The genes responsible for the red (L-cone) and green (M-cone) photopigments are located on the **long arm of the X chromosome (Xq28)**. Because males have only one X chromosome, a single defective gene results in the condition. Females, having two X chromosomes, are typically asymptomatic carriers unless they are homozygous for the mutation. **2. Why Other Options are Incorrect:** * **A. Y-linked:** Y-linked (holandric) inheritance involves traits passed only from father to son. Color blindness genes are not located on the Y chromosome. * **C. Autosomal Dominant:** While rare forms of Tritanopia (blue-yellow deficiency) can show autosomal patterns, the standard "color blindness" referred to in exams follows the X-linked pattern. * **D. Autosomal Recessive:** Total color blindness (Achromatopsia) is autosomal recessive, but it is a rare condition involving a complete lack of cone function, distinct from common red-green color blindness. **Clinical Pearls for NEET-PG:** * **Prevalence:** It is significantly more common in **males (8%)** than in females (0.5%). * **Most Common Type:** **Deuteranomaly** (green-weakness) is the most frequent clinical subtype. * **Ishihara Charts:** The gold standard for screening red-green deficiency. It cannot detect blue-yellow (Tritan) defects. * **Nagel’s Anomaloscope:** The definitive diagnostic tool used to differentiate between dichromats and anomalous trichromats. * **Kollner’s Rule:** Acquired color vision defects due to outer retinal diseases/media changes result in blue-yellow defects, while optic nerve diseases result in red-green defects (Exception: Glaucoma and Papilledema cause blue-yellow defects).

Question 170: A stye is an inflammation of which gland?

A. Gland of Zeis (Correct Answer)
B. Meibomian gland
C. Gland of Manz
D. Lacrimal gland

Explanation: **Explanation:** A **Stye (Hordeolum Externum)** is an acute, focal, pyogenic inflammation (usually staphylococcal) of the eyelash follicle and its associated glands. The correct answer is the **Gland of Zeis**, which are sebaceous glands that open into the follicles of the eyelashes. In some cases, the Glands of Moll (modified sweat glands) are also involved. **Analysis of Options:** * **Gland of Zeis (Correct):** These are rudimentary sebaceous glands located at the lid margin. Their infection leads to the characteristic painful, red, and pointing swelling known as an external hordeolum. * **Meibomian Gland (Incorrect):** Inflammation of these tarsal glands leads to an **Internal Hordeolum**. If the inflammation becomes chronic and granulomatous, it is called a **Chalazion**. * **Gland of Manz (Incorrect):** These are small, flask-shaped glands found in the limbal conjunctiva. They are not involved in the formation of a stye. * **Lacrimal Gland (Incorrect):** This is the major tear-producing gland located in the superolateral orbit. Inflammation of this gland is termed **Dacryoadenitis**. **High-Yield Clinical Pearls for NEET-PG:** * **Causative Organism:** *Staphylococcus aureus* is the most common pathogen. * **Treatment:** Hot compresses and topical antibiotics. If pointing occurs, epilation of the involved eyelash facilitates drainage. * **Differential Diagnosis:** Always distinguish between an External Hordeolum (Zeis/Moll) and an Internal Hordeolum (Meibomian). * **Glands of Moll:** These are modified apocrine sweat glands; they are also involved in external hordeolum but Zeis is the primary sebaceous component often tested.

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