Diseases of the Lens — MCQs

Diseases of the Lens Indian Medical PG Practice Questions and MCQs

Question 31: What is the SRK formula used to calculate the power of an intraocular lens (IOL)?

A. IOL constant - 2.5 * corneal curvature - 0.9 * axial length
B. IOL constant - 2.5 * axial length - 0.9 * corneal curvature (Correct Answer)
C. 2.5 * IOL constant - axial length - 0.9 * corneal curvature
D. axial length - 0.9 * axial length - 2.5 * corneal curvature

Explanation: The **SRK (Sanders-Retzlaff-Kraff) formula** is a first-generation regression formula used to determine the power of an intraocular lens (IOL) required to achieve emmetropia after cataract surgery. ### **The Formula Breakdown** The correct formula is: **P = A - 2.5L - 0.9K** * **P:** Power of the IOL (in Diopters). * **A:** The **A-constant**, which is specific to the manufacturer and the design of the lens. * **L:** **Axial length** of the eye (measured in mm via biometry). * **K:** Average **corneal curvature** (measured in Diopters via keratometry). ### **Why Option B is Correct** The formula is derived from statistical regression analysis. It demonstrates that for every 1 mm increase in axial length, the IOL power must decrease by approximately 2.5 D. Similarly, for every 1 D increase in corneal power, the IOL power must decrease by 0.9 D. Option B correctly identifies these mathematical relationships. ### **Why Other Options are Incorrect** * **Option A:** Swaps the coefficients for axial length and corneal curvature. * **Option C & D:** These represent arbitrary mathematical arrangements that do not follow the established regression constants (2.5 and 0.9) used in ophthalmic biometry. ### **High-Yield Clinical Pearls for NEET-PG** * **SRK-II:** A modification of the original SRK formula that adjusts the A-constant based on the axial length (e.g., adding power for very short eyes). * **SRK/T:** A "theoretical" third-generation formula, currently preferred for **long (myopic) eyes**. * **Hoffer Q:** Preferred for **short (hyperopic) eyes** (Axial length < 22 mm). * **Barrett Universal II:** Currently considered one of the most accurate formulas across all axial lengths. * **Key Measurement:** Axial length is the most critical variable; a 1 mm error in axial length measurement results in approximately a **3 Diopter** refractive error.

Question 32: Anterior lenticonus may be associated with which of the following conditions?

A. Alport syndrome (Correct Answer)
B. Lowe syndrome
C. Marfan syndrome
D. Homocystinuria

Explanation: **Explanation:** **Anterior lenticonus** is a rare localized cone-shaped protrusion of the anterior lens pole into the anterior chamber. It is a pathognomonic clinical sign of **Alport syndrome**, an inherited disorder caused by mutations in the genes encoding **Type IV collagen** (specifically the $\alpha$3, $\alpha$4, and $\alpha$5 chains). Since Type IV collagen is a major structural component of the lens capsule and the glomerular basement membrane, its deficiency leads to thinning and fragility of these structures. In the eye, this results in the characteristic bulging of the lens. **Analysis of Options:** * **Alport Syndrome (Correct):** Classically presents with the triad of progressive hereditary nephritis (sensorineural deafness), anterior lenticonus, and "dot-and-fleck" retinopathy. * **Lowe Syndrome (Oculo-cerebro-renal syndrome):** Characteristically associated with **congenital cataracts** and glaucoma, rather than lenticonus. * **Marfan Syndrome:** The hallmark ocular finding is **ectopia lentis** (subluxation of the lens), typically in an **upward and outward** direction. * **Homocystinuria:** Also associated with ectopia lentis, but the displacement is typically **downward and inward**, often accompanied by secondary glaucoma. **High-Yield Clinical Pearls for NEET-PG:** * **Lenticonus vs. Lentiglobus:** Lenticonus is cone-shaped; Lentiglobus is hemispherical/spherical. * **Posterior Lenticonus:** More common than anterior; usually unilateral, sporadic, and **not** associated with Alport syndrome. * **Oil Droplet Sign:** On distant direct ophthalmoscopy, lenticonus appears as a dark, circular shadow resembling an oil droplet in water. * **Alport Triad:** 1. Hematuria/Renal failure, 2. Sensorineural hearing loss, 3. Anterior lenticonus.

Question 33: Which of the following statements is not true regarding congenital rubella cataract?

A. Pearly white cataract
B. May harbor virus inside the lens
C. Can be associated with cardiovascular anomalies
D. Reversible (Correct Answer)

Explanation: **Explanation:** Congenital Rubella Syndrome (CRS) occurs due to transplacental transmission of the Rubella virus, typically during the first trimester. The correct answer is **D (Reversible)** because a rubella cataract is a structural opacity of the lens that is **permanent and irreversible** without surgical intervention. **Analysis of Options:** * **A. Pearly white cataract:** This is the classic morphological description. The cataract is typically dense, central, and "pearly white," often involving the entire lens (total cataract) or the nucleus. * **B. May harbor virus inside the lens:** This is a critical clinical fact. The Rubella virus can persist within the lens fiber cells for several years after birth. This is why surgeons must ensure complete aspiration of the lens material; if lens matter is left behind, the sequestered virus can be released, leading to severe postoperative endophthalmitis. * **C. Associated with cardiovascular anomalies:** CRS is characterized by **Gregg’s Triad**: 1. **Ocular defects** (Cataract, Microphthalmos, "Salt and Pepper" retinopathy). 2. **Ear defects** (Sensorineural deafness). 3. **Cardiac defects** (Patent Ductus Arteriosus is most common, followed by Pulmonary Artery Stenosis). **High-Yield Clinical Pearls for NEET-PG:** * **Most common ocular finding in CRS:** "Salt and Pepper" Retinopathy (though it doesn't usually affect vision). * **Most common cause of blindness in CRS:** Cataract. * **Surgical Note:** Primary IOL implantation is generally avoided in infants with Rubella cataracts due to the high risk of chronic inflammation and the presence of the live virus. * **Other associations:** Microphthalmos and Glaucoma (infantile or late-onset).

Question 34: What is the approximate water content in the human lens?

A. 64% (Correct Answer)
B. 35%
C. 1%
D. 28%

Explanation: The human lens is a unique, transparent, and avascular structure. Understanding its chemical composition is high-yield for NEET-PG, as it explains the lens's physiological clarity and metabolic processes. ### **Correct Answer: A (64%)** The human lens consists of approximately **64% water** and **36% solids**. Of the solid component, proteins make up about 35% (the highest protein concentration of any tissue in the body), while the remaining 1% consists of lipids, electrolytes (high Potassium, low Sodium), and glucose. This specific hydration level is critical for maintaining the refractive index and transparency of the lens. ### **Analysis of Incorrect Options:** * **B (35%):** This represents the **protein content** of the lens, not the water content. Lens proteins are divided into water-soluble (Crystallins) and water-insoluble (Albuminoids). * **C (1%):** This represents the concentration of **lipids and electrolytes** within the lens. * **D (28%):** This is a distractor; however, in certain states of advanced nuclear cataract, the relative proportion of water may decrease slightly as insoluble protein aggregates increase, but it does not represent the physiological norm. ### **Clinical Pearls for NEET-PG:** * **Metabolism:** The lens derives its nutrition from the aqueous humor. 90% of its energy is generated via **Anaerobic Glycolysis** (Embden-Meyerhof pathway). * **Transparency:** Maintained by the regular arrangement of lens fibers and the "Pump-Leak" mechanism (Na+/K+ ATPase pump), which keeps the lens in a state of relative dehydration. * **Cataractogenesis:** Any disruption in the water-electrolyte balance (e.g., osmotic stress in Diabetes via the Sorbitol pathway) leads to increased water intake, causing lens opacification.

Question 35: What is the respiratory quotient of the lens?

A. 1 (Correct Answer)
B. 0.6
C. 0.7
D. 0.9

Explanation: **Explanation:** The **Respiratory Quotient (RQ)** is the ratio of the volume of carbon dioxide ($CO_2$) produced to the volume of oxygen ($O_2$) consumed during metabolism. The value of RQ depends entirely on the type of substrate being oxidized for energy. **1. Why Option A is Correct:** The crystalline lens is a unique structure that relies almost exclusively on **carbohydrates (Glucose)** for its energy requirements. In carbohydrate metabolism, the amount of $CO_2$ produced is equal to the $O_2$ consumed (e.g., $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O$). Therefore, the RQ for glucose is **1.0**. Since the lens does not significantly metabolize lipids or proteins for energy, its overall RQ remains 1. **2. Why Other Options are Incorrect:** * **Option B (0.6):** This value is lower than the physiological range for human metabolism (typically 0.7–1.0). * **Option C (0.7):** This is the RQ for **pure lipid (fat) metabolism**. While the lens contains lipids in its fiber membranes, they are not used as a primary fuel source. * **Option D (0.9):** This value is typically associated with **mixed diets** or the metabolism of **proteins** (which is approximately 0.8–0.9). **Clinical Pearls for NEET-PG:** * **Glucose Metabolism:** 80% of glucose in the lens is metabolized via **Anaerobic Glycolysis** (Embden-Meyerhof pathway) due to the relatively avascular/hypoxic environment. * **HMP Shunt:** About 10% of glucose is diverted here to produce NADPH, which is crucial for maintaining **Reduced Glutathione**, the lens's primary antioxidant. * **Sorbitol Pathway:** In diabetic states, hexokinase becomes saturated, and glucose is diverted to the Polyol pathway. Sorbitol accumulation leads to osmotic swelling and **snowflake cataracts**.

Question 36: What is the treatment of choice for congenital cataract?

A. Pharmacotherapy
B. Combined cataract surgery and goniotomy
C. Cataract surgery with IOL implant and primary posterior capsulotomy (Correct Answer)
D. Pars plana lensectomy with no IOL implant

Explanation: **Explanation:** The management of congenital cataract is a high-yield topic in NEET-PG, focusing on the prevention of **amblyopia** and **Posterior Capsular Opacification (PCO)**. **Why Option C is Correct:** In children, the visual system is still developing. Prompt surgery is required to provide a clear visual axis. **Cataract surgery with IOL implantation** is the standard of care to correct aphakia. However, children have a very high rate of PCO (nearly 100% if left alone) due to increased reactivity of the lens epithelial cells. Therefore, a **Primary Posterior Capsulotomy (PPC)** combined with **Anterior Vitrectomy** is mandatory to ensure a clear visual axis and prevent secondary opacification. **Why other options are incorrect:** * **Option A:** Pharmacotherapy has no role in treating a formed cataract; surgery is the only definitive treatment. * **Option B:** Goniotomy is a treatment for congenital glaucoma, not cataract. While both can coexist (e.g., in Lowe syndrome), it is not the standard treatment for isolated cataract. * **Option D:** Pars plana lensectomy was historically common, but leaving a child aphakic (no IOL) leads to severe refractive errors and poor compliance with heavy glasses/contact lenses, increasing the risk of amblyopia. **Clinical Pearls for NEET-PG:** * **Ideal Time for Surgery:** For unilateral cases, within 4–6 weeks of birth; for bilateral cases, within 8–10 weeks. * **IOL Choice:** Hydrophobic acrylic IOLs are preferred. * **IOL Power:** Aim for **hyperopia** (under-correction) because the child’s eye will grow and shift toward myopia (axial elongation). * **Most common cause:** Idiopathic (overall), but **Rubella** is the most common infectious cause.

Question 37: Which of the following subtypes of cataract is the most common cause of visual morbidity?

A. Senile (Correct Answer)
B. Congenital
C. Traumatic
D. Drug toxicity

Explanation: **Explanation:** **1. Why Senile Cataract is the Correct Answer:** Senile (age-related) cataract is the most common cause of visual morbidity and blindness worldwide. It is a degenerative condition of the crystalline lens that occurs due to cumulative oxidative stress, protein denaturation, and the accumulation of insoluble proteins (crystallins) as a person ages. Because aging is a universal physiological process, the sheer volume of the geriatric population makes senile cataract the leading cause of reversible vision loss globally and in India. **2. Why the Other Options are Incorrect:** * **Congenital Cataract:** While it is a significant cause of childhood blindness and requires urgent intervention to prevent amblyopia, its overall prevalence is much lower than age-related cases. * **Traumatic Cataract:** This is usually unilateral and occurs following blunt or penetrating injury (e.g., Rosette-shaped cataract). While common in specific demographics (young males), it does not match the public health burden of senile cataracts. * **Drug Toxicity:** Certain drugs (e.g., long-term Corticosteroids causing Posterior Subcapsular Cataract) can induce lens opacities, but these are considered secondary causes and represent a smaller fraction of the total cataract burden. **3. Clinical Pearls for NEET-PG:** * **Most common type of Senile Cataract:** Nuclear Sclerosis. * **Cataract with the most profound effect on vision:** Posterior Subcapsular Cataract (PSC), as it lies near the nodal point of the eye. * **Early symptom of Nuclear Cataract:** "Second sight" or myopic shift (improvement in near vision due to increased refractive index of the nucleus). * **WHO Definition:** Cataract remains the #1 cause of avoidable blindness globally.

Question 38: What is the thinnest part of the lens capsule?

A. Anterior part
B. Posterior part (Correct Answer)
C. Peripheral part
D. All of the above

Explanation: The lens capsule is a modified basement membrane (the thickest in the body) secreted by the lens epithelium. Understanding its varying thickness is crucial for surgical procedures like cataract surgery. ### **Explanation of the Correct Answer** The **posterior pole** of the lens capsule is the thinnest part, measuring approximately **2–4 μm**. This extreme thinness occurs because the lens epithelium is absent under the posterior capsule (epithelial cells are only present anteriorly and at the equator). This anatomical vulnerability makes the posterior capsule highly susceptible to rupture during cataract surgery (Phacoemulsification or SICS). ### **Analysis of Incorrect Options** * **Anterior part:** This is significantly thicker than the posterior part (approx. 14 μm). It increases in thickness with age. During surgery, a "Continuous Curvilinear Capsulorhexis" (CCC) is performed here because the thickness provides enough tensile strength to manipulate the lens. * **Peripheral part (Pre-equatorial/Equatorial):** The **anterior pre-equatorial zone** is actually the **thickest part** of the entire lens capsule (approx. 17–21 μm). This is where the zonular fibers attach, requiring extra structural integrity to withstand the tension of accommodation. ### **NEET-PG High-Yield Pearls** * **Thickest part of the capsule:** Anterior pre-equatorial dimension (~21 μm). * **Thinnest part of the capsule:** Posterior pole (~2–4 μm). * **Embryology:** The lens capsule is derived from the surface ectoderm. * **Clinical Correlation:** The fragility of the posterior capsule is the reason why **Posterior Capsular Rupture (PCR)** is a common intraoperative complication, potentially leading to vitreous loss. * **Metabolism:** The lens capsule is semi-permeable; it allows water and electrolytes but acts as a barrier to large molecules and bacteria.

Question 39: Which of the following is NOT a cause of complicated cataract?

A. Pars planitis
B. Retinitis pigmentosa
C. Retinal detachment
D. Posterior vitreous detachment (Correct Answer)

Explanation: **Explanation:** **Complicated cataract** refers to opacification of the lens resulting from metabolic disturbances caused by chronic intraocular inflammatory or degenerative diseases. The lens derives its nutrition from the aqueous humor; any condition that alters the composition of intraocular fluids or introduces toxins can lead to cataract formation. **Why Posterior Vitreous Detachment (PVD) is the correct answer:** PVD is a common, age-related physiological event where the vitreous membrane separates from the retina. It is generally an **isolated mechanical event** and does not involve chronic inflammation or significant metabolic derangement of the intraocular environment. Therefore, it does not cause a complicated cataract. **Analysis of incorrect options:** * **Pars planitis:** This is a form of intermediate uveitis. Chronic inflammation leads to the release of inflammatory mediators and cytokines into the aqueous and vitreous, which directly damages lens metabolism. * **Retinitis pigmentosa:** This degenerative retinal disease is classically associated with **Posterior Subcapsular Cataract (PSC)**. The mechanism involves the accumulation of metabolic byproducts or toxic substances from the degenerating retina. * **Retinal detachment:** Long-standing (chronic) retinal detachment leads to a "starved" intraocular environment and the release of degenerative products, frequently resulting in lens opacification. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Appearance:** Complicated cataracts typically present as a **Posterior Subcapsular Cataract (PSC)** with a characteristic **"Bread-crumb" appearance** and **polychromatic luster** (iridescence). * **Other Causes:** High myopia, anterior uveitis, and intraocular tumors (e.g., choroidal melanoma). * **Steroid-induced cataract:** Also presents as PSC, often making it difficult to distinguish from the underlying disease (like uveitis) causing the cataract.

Question 40: Rosette shaped cataract is seen in which of the following conditions?

A. Congenital rubella
B. Blunt trauma to the eye (Correct Answer)
C. Wilson's disease
D. Diabetes mellitus

Explanation: **Explanation:** **Rosette-shaped cataract** is a classic clinical sign of **blunt trauma** to the eye. When a blunt force impacts the globe, it generates hydraulic pressure waves that travel through the lens. This leads to the separation of lens fibers along their natural suture lines, typically at the interface between the lens cortex and the nucleus. The resulting opacification follows the anatomical pattern of the lens sutures, creating a characteristic "flower-shaped" or "rosette" appearance. This can occur shortly after the injury or may develop years later. **Analysis of Incorrect Options:** * **Congenital Rubella:** Typically presents with a **"Pearly White" nuclear cataract** or microphthalmos. * **Wilson’s Disease:** Characterized by a **"Sunflower cataract"** (due to copper deposition in the anterior capsule) and the pathognomonic Kayser-Fleischer (KF) ring in the cornea. * **Diabetes Mellitus:** Associated with **"Snowflake cataracts"** (subcapsular opacities) in young diabetics or early-onset senile cataracts in adults. **High-Yield Clinical Pearls for NEET-PG:** 1. **Vossius Ring:** A circular ring of iris pigment on the anterior lens capsule, also a hallmark of blunt trauma. 2. **Traumatic Rosette:** Can be "Early" (subcapsular) or "Late" (deeper in the cortex). 3. **Glass-blower’s Cataract:** Caused by Infrared radiation; presents with true exfoliation of the lens capsule. 4. **Electric Cataract:** Often presents as milky white subcapsular opacities following high-voltage injury.

Practice by Chapter

Lens Anatomy and Physiology

Practice Questions

Age-Related Cataract

Practice Questions

Congenital and Developmental Cataracts

Practice Questions

Traumatic Cataract

Practice Questions

Metabolic Cataracts

Practice Questions

Drug-Induced Cataracts

Practice Questions

Cataract Surgery Techniques

Practice Questions

Intraocular Lens Implants

Practice Questions

Complications of Cataract Surgery

Practice Questions

Posterior Capsular Opacification

Practice Questions

Lens Subluxation and Dislocation

Practice Questions

Specialty IOLs

Practice Questions

Want unlimited practice?

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

Start For Free