Basic Sciences as Related to Eye — MCQs

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

Question 131: What is the normal depth of the anterior chamber of the eye?

A. 2-3 mm (Correct Answer)
B. 3-4 mm
C. 4-5 mm
D. 5-6 mm

Explanation: The **Anterior Chamber (AC)** is the space between the posterior surface of the cornea and the anterior surface of the iris and lens. Understanding its dimensions is crucial for diagnosing glaucoma and planning intraocular surgeries. ### **Explanation of the Correct Answer** **Option A (2-3 mm)** is correct. In a normal emmetropic adult eye, the central depth of the anterior chamber typically ranges from **2.5 to 3.0 mm**. It is deepest at the center and becomes shallower toward the periphery (the AC angle). This depth is essential for maintaining proper aqueous humor outflow and preventing contact between the corneal endothelium and the iris. ### **Analysis of Incorrect Options** * **Option B (3-4 mm):** This is generally considered deeper than average. While seen in high myopes or aphakic patients, it is not the standard "normal" range. * **Options C & D (4-6 mm):** These values are pathologically deep. Such depths are only encountered in conditions like posterior lens dislocation, extreme myopia, or "buphthalmos" (congenital glaucoma). ### **Clinical Pearls for NEET-PG** 1. **Refractive Errors:** The AC is **shallower in hypermetropes** (predisposing them to Angle Closure Glaucoma) and **deeper in myopes**. 2. **Age Factor:** The AC depth decreases with age as the lens increases in thickness and moves forward. 3. **Volume:** The average volume of aqueous humor in the AC is approximately **0.25 ml**. 4. **Van Herick Technique:** A clinical method using a slit lamp to estimate AC depth by comparing the peripheral AC depth to the corneal thickness. 5. **Shallow AC Causes:** Primary Angle Closure Glaucoma (PACG), Ciliary block glaucoma (Malignant glaucoma), and penetrating trauma with a "leaking" wound (Seidel’s test positive).

Question 132: Snowball opacities are characteristic findings in which ocular condition?

A. Acute anterior uveitis
B. Posterior uveitis
C. Pars planitis (Correct Answer)
D. None of the above

Explanation: **Explanation:** **Pars planitis** is a specific subset of intermediate uveitis characterized by idiopathic inflammation of the *pars plana* (the posterior part of the ciliary body). The hallmark clinical findings are: 1. **Snowballs:** These are whitish, inflammatory vitreous condensations or aggregates of inflammatory cells, typically found in the inferior vitreous. 2. **Snowbanking:** This refers to the accumulation of inflammatory exudates (exudative plaques) over the pars plana, most commonly seen in the inferior quadrant. **Analysis of Options:** * **Option A (Acute anterior uveitis):** This primarily presents with aqueous cells, flare, and Keratic Precipitates (KPs) on the corneal endothelium. It does not typically involve the vitreous or pars plana. * **Option B (Posterior uveitis):** While this involves the retina and choroid (e.g., toxoplasmosis, CMV retinitis), "snowballs" are specifically associated with the intermediate compartment (vitreous/pars plana) rather than primary retinal inflammation. * **Option D:** Incorrect, as Pars planitis is the classic association. **High-Yield Clinical Pearls for NEET-PG:** * **Intermediate Uveitis:** The most common cause of vitreous haze/cells in a young patient. * **Most common complication:** Cystoid Macular Edema (CME), which is the primary cause of vision loss in these patients. * **Systemic Association:** Pars planitis is often idiopathic but can be associated with **Multiple Sclerosis (MS)** and Sarcoidosis. * **Treatment:** Usually involves periocular or systemic corticosteroids; "Double-freeze" cryotherapy or laser photocoagulation is used for the snowbank area in resistant cases.

Question 133: What cell type is most typically seen in the keratic precipitates of non-granulomatous uveitis?

A. Polymorphonuclear cells
B. Lymphocytes (Correct Answer)
C. Plasma cells
D. Epithelioid cells

Explanation: **Explanation:** Keratic precipitates (KPs) are inflammatory cell deposits on the corneal endothelium, typically forming in the lower triangular area (Arlt’s triangle) due to convection currents in the aqueous humor. The cellular composition of these precipitates is a key diagnostic indicator of the type of uveitis. **Why Lymphocytes are Correct:** In **non-granulomatous uveitis** (e.g., HLA-B27 associated, trauma, or idiopathic), the inflammatory response is acute and non-specific. The resulting KPs are typically **small, fine, and white**. Histologically, these are composed almost exclusively of **lymphocytes** and some neutrophils. They do not clump together, which explains their fine appearance on slit-lamp examination. **Analysis of Incorrect Options:** * **Polymorphonuclear cells (PMNs):** While present in very acute phases, they are not the hallmark cell of established KPs. * **Plasma cells:** These are often found in the uveal tissue itself during chronic inflammation but are not the primary component of the precipitates on the endothelium. * **Epithelioid cells:** These are modified macrophages characteristic of **granulomatous uveitis** (e.g., Sarcoidosis, TB). They fuse to form "Mutton-fat" KPs, which are large, greasy, and yellowish. **NEET-PG High-Yield Pearls:** * **Mutton-fat KPs:** Composed of epithelioid cells and macrophages; diagnostic of granulomatous uveitis. * **Arlt’s Triangle:** The classic distribution of KPs at the inferior 1/3rd of the cornea. * **Krukenberg Spindle:** Vertical pigment deposits (not inflammatory cells) seen in pigment dispersion syndrome. * **Stellate KPs:** Fine, star-shaped precipitates distributed over the entire endothelium; characteristic of **Fuchs’ Heterochromic Iridocyclitis** and Viral uveitis.

Question 134: What is true about heterochromic uveitis?

A. Involves the posterior surface of the iris
B. Involves the anterior surface of the iris (Correct Answer)
C. Involves the posterior chamber
D. Posterior synechiae

Explanation: **Explanation:** **Fuchs’ Heterochromic Iridocyclitis (FHI)** is a chronic, low-grade, non-granulomatous uveitis characterized by a classic triad of heterochromia, cyclitis, and cataract. **Why Option B is Correct:** The primary pathology in FHI involves **atrophy of the iris stroma**, which is located on the **anterior surface of the iris**. This stromal atrophy leads to a loss of pigment, making the iris appear lighter (hypochromic) in most patients. The loss of the anterior limiting layer and the underlying stroma is what clinically defines the characteristic "moth-eaten" appearance and the change in iris color. **Why Other Options are Incorrect:** * **Option A & C:** While the entire uveal tract can be mildly affected, the hallmark diagnostic feature is the involvement of the **anterior iris stroma**, not primarily the posterior surface or the posterior chamber. * **Option D:** A pathognomonic feature of Fuchs’ Heterochromic Uveitis is the **absence of posterior synechiae**, despite the presence of chronic inflammation. If posterior synechiae are present, the diagnosis should be reconsidered. **High-Yield Clinical Pearls for NEET-PG:** * **Presentation:** Usually unilateral; patients are often asymptomatic until they develop complications. * **Signs:** Small, white, stellate **Kerateous Precipitates (KPs)** distributed over the entire corneal endothelium; diffuse iris atrophy; and **Amsler’s Sign** (filiform hemorrhage on anterior chamber paracentesis). * **Complications:** Presenile cataract (most common) and secondary glaucoma (most difficult to manage). * **Treatment:** Steroids are generally **not** effective and not indicated for the chronic low-grade inflammation of FHI.

Question 135: The central artery of the retina is a branch of which artery?

A. External carotid artery
B. Internal carotid artery
C. Ophthalmic artery (Correct Answer)
D. Basilar artery

Explanation: ### Explanation **Correct Option: C. Ophthalmic artery** The **Central Artery of the Retina (CAR)** is the first and one of the most vital branches of the **Ophthalmic artery**. It arises as the ophthalmic artery crosses the optic nerve. The CAR pierces the dural sheath of the optic nerve approximately 10–12 mm behind the eyeball and runs forward in the center of the nerve to enter the eye at the optic disc. It is a **functional end-artery**, meaning it is the sole supplier of the inner layers of the retina; its occlusion leads to immediate and profound vision loss. **Why other options are incorrect:** * **A. External carotid artery:** While it supplies the face and scalp, it does not directly supply the retina. However, its branch (Maxillary artery) can provide collateral circulation via the orbital anastomosis in rare cases. * **B. Internal carotid artery:** The Ophthalmic artery is indeed the first major intradural branch of the **Internal Carotid Artery (ICA)**, but the CAR specifically branches off the Ophthalmic artery, not the ICA directly. * **D. Basilar artery:** This is part of the posterior circulation (Vertebrobasilar system) supplying the brainstem and occipital cortex, not the eyeball. **High-Yield Clinical Pearls for NEET-PG:** * **Cherry Red Spot:** Seen in **Central Retinal Artery Occlusion (CRAO)** because the thin foveola allows the vascular choroid to show through, contrasting with the pale, edematous ischemic retina. * **Blood Supply of Retina:** The inner 2/3 is supplied by the **CAR**, while the outer 1/3 (photoreceptors) is supplied by the **Choriocapillaris** (via Ciliary arteries). * **Cilioretinal Artery:** Present in ~20% of the population; it is a branch of the **Posterior Ciliary Artery**. It can preserve central vision in a patient with CRAO.

Question 136: Which vitamin deficiency causes circumcorneal vascularization?

A. Biotin
B. Riboflavin (Correct Answer)
C. Thiamine
D. Vitamin D

Explanation: **Explanation:** **Riboflavin (Vitamin B2)** is the correct answer. It serves as a precursor for FAD and FMN, which are essential coenzymes in the mitochondrial respiratory chain. The cornea is a non-vascularized structure that relies on atmospheric oxygen and limbal diffusion. In riboflavin deficiency, the corneal epithelium suffers from impaired oxidative metabolism. To compensate for this localized hypoxia and to provide a conduit for nutrients, the body initiates **circumcorneal vascularization** (neovascularization), where capillaries from the limbal plexus proliferate into the subepithelial layers of the cornea. **Analysis of Incorrect Options:** * **Biotin (B7):** Deficiency primarily manifests as dermatological issues (seborrheic dermatitis, alopecia) and neurological symptoms, but it does not typically cause corneal vascularization. * **Thiamine (B1):** Deficiency leads to Beriberi or Wernicke-Korsakoff syndrome. Ocular signs are usually limited to ophthalmoplegia or nystagmus, not structural corneal changes. * **Vitamin D:** Essential for calcium homeostasis. Deficiency causes Rickets/Osteomalacia. While it may be linked to dry eye, it is not a cause of circumcorneal vascularization. **High-Yield Clinical Pearls for NEET-PG:** * **Riboflavin Deficiency Triad:** Cheilosis (cracking of lips), Glossitis (magenta tongue), and Circumcorneal vascularization. * **Vitamin A Deficiency:** The most common vitamin deficiency affecting the eye; causes Xerophthalmia (Bitot’s spots, Keratomalacia, Night blindness). * **Differential for Corneal Neovascularization:** Chronic hypoxia (contact lens overwear), chemical burns, and chronic interstitial keratitis (Syphilis). * **Memory Aid:** "B2 for 2 eyes" – think of the vessels creeping into the cornea.

Question 137: What is the first sign of sympathetic ophthalmia?

A. Presence of aqueous flare
B. Presence of precipitates
C. Constriction of pupil
D. Retrolental flare (Correct Answer)

Explanation: **Explanation:** Sympathetic Ophthalmia (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 non-injured eye (the "sympathizing eye"). **Why Retrolental Flare is the correct answer:** The earliest clinical sign of sympathetic ophthalmia in the sympathizing eye is the appearance of **retrolental flare** (cells and protein leakage in the space behind the lens) or fine cells in the anterior vitreous. This occurs because the inflammatory process often begins in the posterior segment or the uveal tract before manifesting in the anterior chamber. Detecting these cells using a slit-lamp biomicroscope is crucial for early diagnosis. **Analysis of Incorrect Options:** * **A & B (Aqueous flare and Keratic Precipitates):** While these are classic signs of SO, they represent anterior uveitis. They typically appear *after* the initial inflammatory changes in the retrolental/vitreous space. Keratic precipitates in SO are characteristically "mutton-fat" (large and greasy). * **C (Constriction of pupil):** This is a non-specific sign of anterior segment irritation or ciliary spasm common to many types of uveitis, but it is not the earliest diagnostic sign. **High-Yield Clinical Pearls for NEET-PG:** * **Pathology:** Characterized by **Dalen-Fuchs nodules** (clusters of epithelioid cells between the RPE and Bruch’s membrane). * **Histology:** Non-necrotizing granulomatous inflammation with **sparing of the choriocapillaris**. * **Latent Period:** Usually occurs within 4–8 weeks of injury, but 90% of cases occur within the first year. * **Prevention:** Evisceration does not prevent SO as effectively as **enucleation**. Enucleation of the injured eye should ideally be performed within 2 weeks if the eye has no visual potential.

Question 138: Regarding color blindness, which of the following statements is true?

A. It is mainly congenital.
B. It can be tested with the Farnsworth 100 hue test.
C. The Ishihara test is used for red/green color blindness.
D. All of the above. (Correct Answer)

Explanation: **Explanation:** Color blindness (color vision deficiency) is a common high-yield topic in Ophthalmology. The correct answer is **D (All of the above)** because each statement accurately describes a facet of color vision assessment and pathology. 1. **Mainly Congenital (Option A):** Most cases are X-linked recessive, affecting approximately 8% of males and 0.5% of females. The most common type is **Deuteranomaly** (green weakness). While it can be acquired (e.g., optic neuritis, toxic amblyopia), the vast majority of cases encountered clinically are congenital. 2. **Farnsworth-Munsell 100 Hue Test (Option B):** This is a highly sensitive quantitative test used to assess the severity and type of color deficiency. It involves arranging 85 colored caps in a sequence of shifting hues. It is the gold standard for vocational testing and identifying subtle defects. 3. **Ishihara Test (Option C):** This is the most common screening tool used in clinical practice. It specifically utilizes pseudoisochromatic plates to detect **Red-Green** color blindness. It cannot detect Blue-Yellow (Tritan) defects. **Clinical Pearls for NEET-PG:** * **Kollner’s Rule:** Acquired outer retinal diseases (e.g., ARMD) usually cause Blue-Yellow defects, while inner retinal/optic nerve diseases (e.g., Optic Neuritis) cause Red-Green defects (Exception: Glaucoma causes Blue-Yellow). * **Nagel’s Anomaloscope:** The definitive "Gold Standard" for differentiating between dichromats and anomalous trichromats. * **Protanopia:** Red blindness; **Deuteranopia:** Green blindness; **Tritanopia:** Blue blindness. * **Hardy-Rand-Rittler (HRR) Plates:** Unlike Ishihara, these can detect all three types of defects (Red, Green, and Blue).

Question 139: What is the distance of the foveola from the optic disc margin?

A. 1 mm
B. 2 mm
C. 3 mm (Correct Answer)
D. 4 mm

Explanation: **Explanation:** The correct answer is **3 mm**. Understanding the topographical anatomy of the posterior pole is crucial for both clinical practice and NEET-PG. **Underlying Medical Concept:** The **foveola** is the central-most pit of the fovea, located within the macula lutea. Anatomically, the center of the fovea (foveola) is situated approximately **4 mm temporal to and 0.8 mm inferior** to the center of the optic disc. However, when measuring from the **temporal margin** of the optic disc, the distance to the foveola is approximately **3 mm** (since the average optic disc diameter is 1.5 mm, half of which is 0.75 mm). In standard ophthalmic textbooks (like Parsons or Khurana), this 3 mm distance is a high-yield anatomical landmark. **Analysis of Options:** * **A (1 mm) & B (2 mm):** These distances are too short. The area within 1-2 mm of the disc is considered the peripapillary region. * **D (4 mm):** This is a common distractor. 4 mm represents the distance from the **center** of the optic disc to the foveola, not the margin. **High-Yield Clinical Pearls for NEET-PG:** * **Dimensions:** The foveola is approximately 0.35 mm in diameter and is the thinnest part of the retina (0.13 mm). * **Histology:** The foveola contains only **cones** (no rods) and is devoid of the inner nuclear and ganglion cell layers. * **Foveal Avascular Zone (FAZ):** The foveola is located within the FAZ; it derives its nutrition solely from the underlying choriocapillaris. * **Henle’s Layer:** In the foveal region, the outer plexiform layer is known as Henle’s fiber layer, which is the site of "macular star" formation in neuroretinitis.

Question 140: Congenital colour blindness is transmitted as:

A. Recessive disorder
B. Autosomal dominant
C. Sex-linked disorder (Correct Answer)
D. All of the above

Explanation: ### Explanation **1. Why Sex-linked disorder is correct:** Congenital color blindness (specifically the most common red-green type) is inherited as an **X-linked recessive** disorder. The genes responsible for producing the photopigments in the **L-cones (red)** and **M-cones (green)** are located on the **X chromosome**. Because males have only one X chromosome (XY), a single defective gene results in the manifestation of the condition. Females (XX) are typically asymptomatic carriers and only express the condition if both X chromosomes are affected. **2. Why other options are incorrect:** * **Autosomal dominant:** While some rare forms of blue-yellow color blindness (Tritanopia) can follow autosomal patterns, the vast majority of "congenital color blindness" cases encountered in clinical practice and exams refer to red-green deficiency, which is strictly sex-linked. * **Recessive disorder:** While the inheritance is indeed recessive, "Sex-linked" is the more specific and accurate description required for NEET-PG. An "Autosomal recessive" label would be incorrect for the standard red-green type. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Prevalence:** It affects approximately **8% of males** and only **0.5% of females**. * **Types:** * **Protanopia:** Missing red cones (Long wavelength). * **Deuteranopia:** Missing green cones (Medium wavelength) — **Most common type.** * **Tritanopia:** Missing blue cones (Short wavelength) — Gene located on **Chromosome 7** (Autosomal). * **Screening:** The **Ishihara Pseudoisochromatic Plate** test is the most common screening tool (detects red-green deficiency but not blue-yellow). * **Confirmatory Test:** **Nagel’s Anomaloscope** is the gold standard for definitive diagnosis and differentiation.

Practice by Chapter

Embryology of Eye

Practice Questions

Ocular Anatomy

Practice Questions

Ocular Physiology

Practice Questions

Ocular Biochemistry

Practice Questions

Ocular Microbiology

Practice Questions

Ocular Pharmacology

Practice Questions

Ocular Pathology

Practice Questions

Ocular Genetics

Practice Questions

Ocular Immunology

Practice Questions

Visual Neuroscience

Practice Questions

Ocular Imaging Physics

Practice Questions

Laser Physics in Ophthalmology

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free