Diseases of the Lens Practice Questions

Q: The SRK formula is used to calculate which of the following?

Power of intraocular lens. The **SRK (Sanders-Retzlaff-Kraff) formula** is the most widely used regression formula for calculating the power of an **Intraocular Lens (IOL)** prior to cataract surgery. ### **Explanation of the Correct Answer** The SRK formula is based on the relationship: **$P = A - 2.5L - 0.9K$** * **P:** Power of the IOL (in Diopters) * **A:** A-constant (specific to the lens design and manufacturer) * **L:** Axial length of the eyeball (measured via A-scan biometry) * **K:** Average keratometry reading (corneal power in Diopters) By inputting these variables, surgeons can determine the precise lens power required to achieve the desired postoperative refractive state (usually emmetropia). ### **Why Other Options are Incorrect** * **B. Corneal curvature:** This is measured using **Keratometry** or **Corneal Topography**. While corneal curvature is a *variable* in the SRK formula, the formula itself calculates IOL power, not the curvature. * **C. Corneal endothelial cell count:** This is assessed using **Specular Microscopy**. It is used to evaluate corneal health and compensation before surgery but is not part of the SRK calculation. * **D. Extent of retinal detachment:** This is evaluated clinically via **Indirect Ophthalmoscopy** or **B-scan ultrasonography**. ### **High-Yield Clinical Pearls for NEET-PG** * **SRK-II:** A modified version of the original formula that adjusts the A-constant based on the axial length to improve accuracy. * **SRK/T:** A "theoretical" formula preferred for **long (myopic) eyes**. * **Hoffer Q:** Preferred formula for **short (hyperopic) eyes**. * **Biometry:** The process of measuring the axial length and corneal power to calculate IOL power. **Optical biometry (IOL Master)** is now the gold standard over ultrasound A-scans.

Q: Modern intraocular lenses are NOT made up of which of the following materials?

Glass. **Explanation:** The evolution of Intraocular Lenses (IOLs) has moved toward materials that are biocompatible, lightweight, and foldable to allow for smaller surgical incisions. **Why Glass is the Correct Answer:** While the very first experimental attempts at intraocular lenses in the early 20th century (pre-dating Sir Nicholas Harold Ridley) occasionally explored glass, it is **not** used in modern IOL manufacturing. Glass is heavy, fragile, difficult to fixate within the capsular bag, and poses a significant risk of intraocular trauma if shattered. Modern ophthalmology relies exclusively on medical-grade polymers. **Analysis of Incorrect Options:** * **PMMA (Polymethylmethacrylate):** This was the first material used by Harold Ridley in 1949. It is a "rigid" lens material. While it is still used today (especially in low-cost settings or when a large incision is necessary), it is non-foldable. * **Silicon:** These were the first "foldable" lenses introduced. They allow for small-incision cataract surgery (SICS/Phacoemulsification). However, they are contraindicated if a patient might need future vitreoretinal surgery with silicone oil, as the oil can adhere to the lens. * **Acrylic Acid (Acrylates):** Modern foldable IOLs are most commonly made of hydrophobic or hydrophilic acrylic. Hydrophobic acrylic is currently the "gold standard" due to its high refractive index and lower rates of Posterior Capsular Opacification (PCO). **High-Yield Clinical Pearls for NEET-PG:** * **Father of Modern IOL:** Sir Nicholas Harold Ridley (inspired by Spitfire pilots with PMMA splinters in their eyes). * **Best material to prevent PCO:** Hydrophobic acrylic with a **square-edge design**. * **Ideal site for IOL placement:** Within the Capsular Bag (In-the-bag). * **Foldable vs. Rigid:** Silicon and Acrylic are foldable; PMMA is rigid.

Q: Typical appearance of diabetic cataract is:

Snowflake opacities. **Explanation:** **1. Why Snowflake Opacities is Correct:** True diabetic cataract (also known as "Snowflake cataract") is a rare but classic manifestation seen typically in young patients with uncontrolled Type 1 Diabetes Mellitus. The underlying pathophysiology involves the **Polyol pathway**: high glucose levels in the aqueous humor lead to the accumulation of **sorbitol** within the lens via the enzyme aldose reductase. Sorbitol acts as an osmotic agent, drawing water into the lens fibers, causing them to swell and rupture. This results in multiple, grayish-white subcapsular opacities that resemble snowflakes. **2. Analysis of Incorrect Options:** * **A. Blue dot cataract (Punctate cataract):** This is the most common type of **congenital cataract**. It appears as small, bluish, stationary dots and is usually asymptomatic. * **B. Posterior capsular cataract (PSC):** While diabetics are more prone to developing "senile" cataracts (like PSC or nuclear sclerosis) at an earlier age, PSC is specifically associated with **long-term steroid use**, ionizing radiation, or chronic intraocular inflammation (uveitis). * **D. Sunflower cataract:** This is the characteristic finding in **Wilson’s disease** (hepatolenticular degeneration) due to copper deposition in the anterior capsule, or following a copper-containing intraocular foreign body (Chalcosis). **3. High-Yield Clinical Pearls for NEET-PG:** * **Most common cataract in diabetics:** Senile cataract (specifically cortical or PSC), which occurs earlier and progresses faster than in non-diabetics. * **True Diabetic Cataract:** Refers specifically to the "Snowflake" type. * **Reversibility:** Early osmotic changes (refractive errors) in diabetes are reversible with glycemic control, but mature snowflake opacities are not. * **Christmas Tree Cataract:** Often confused with snowflake; it is seen in **Myotonic Dystrophy**.

Q: Commonest type of cataract is:

Blue dot. The correct answer is **Blue dot cataract (Punctate cataract)**. **Why it is correct:** Blue dot cataract, also known as **Cataracta Punctata Caerulea**, is the most common type of congenital cataract. It is characterized by multiple, small, bluish-white opacities scattered throughout the lens. These are usually asymptomatic, non-progressive, and do not interfere with vision, which is why they are often discovered incidentally during routine slit-lamp examinations. **Analysis of Incorrect Options:** * **B. Zonular (Lamellar) Cataract:** This is the most common type of congenital cataract that **causes visual impairment**. It involves a specific "zone" or layer of the lens (usually around the nucleus) and is often associated with Vitamin D deficiency or hypocalcemia. * **C. Cupuliform (Posterior Subcapsular) Cataract:** This is an acquired cataract located right in front of the posterior capsule. While common in patients using steroids or those with diabetes, it is not the "commonest" overall. * **D. Cuneiform Cataract:** This is a subtype of **Senile Cortical Cataract** characterized by wedge-shaped opacities extending from the periphery to the center. While very common in the elderly, Blue dot remains the most frequent finding across the general population in the context of developmental opacities. **High-Yield Clinical Pearls for NEET-PG:** * **Most common congenital cataract:** Blue dot cataract. * **Most common congenital cataract requiring surgery:** Zonular (Lamellar) cataract. * **Most common cause of childhood cataract:** Idiopathic (followed by genetic/hereditary). * **Snowflake cataract:** Seen in Diabetes Mellitus. * **Sunflower cataract:** Seen in Wilson’s Disease (Chalcosis). * **Christmas tree cataract:** Seen in Myotonic Dystrophy. Some systemic conditions like Stickler syndrome also include cataracts as a known clinical feature [1].

Q: The youngest lens fibres are present in which part of the lens?

Superficial layer of the cortex. **Explanation:** The lens is a unique structure that continues to grow throughout life. To understand the arrangement of lens fibers, one must understand its embryological development and growth pattern. **Why the correct answer is right:** New lens fibers are continuously formed by the mitotic division of the **equatorial lens epithelium**. Once formed, these new fibers elongate and are laid down concentrically over the pre-existing fibers. Because growth occurs from the periphery inward, the **most recently formed (youngest) fibers** are always located in the **superficial layer of the cortex**, just beneath the lens capsule. **Why the incorrect options are wrong:** * **A & B (Nucleus):** The nucleus represents the oldest part of the lens. The **central core (embryonic nucleus)** contains the very first fibers formed during the first 1-3 months of gestation. As we move from the center to the outer layers of the nucleus (fetal, infantile, and adult nuclei), the fibers become progressively younger than the core but are still significantly older than cortical fibers. * **C (Deeper layer of the cortex):** While these are younger than the nucleus, they have been pushed inward by the even newer fibers forming at the surface. **NEET-PG High-Yield Pearls:** * **Arrangement:** Oldest fibers are central (Nucleus); youngest fibers are peripheral (Cortex). * **Sutures:** The meeting points of lens fibers form the **Y-sutures**. The anterior Y-suture is upright (Y), and the posterior is inverted (⅄). * **Metabolism:** The lens is avascular; it derives its nutrition from the aqueous humor via anaerobic glycolysis (90%). * **Hardness:** As fibers age, they lose their nuclei and become dehydrated and compressed, leading to the increased density of the nucleus (nuclear sclerosis) seen in aging.

Q: Which of the following is NOT true about mercurial lentis?

Due to organic mercury. **Mercurialentis** (or Mercurial Lentis) is a specific ocular manifestation resulting from chronic exposure to mercury. ### **Explanation of the Correct Option** **A. Due to organic mercury (Incorrect Statement/Correct Answer):** Mercurialentis is caused by chronic exposure to **inorganic mercury** (elemental or salts), not organic mercury. It was historically seen in workers in the felt-hat industry (mercuric nitrate) or those using mercury-containing skin-lightening creams and eye drops (e.g., phenylmercuric nitrate used as a preservative). Organic mercury (like methylmercury) typically causes systemic neurotoxicity (Minamata disease) rather than this specific lens change. ### **Analysis of Other Options** * **B. Bilateral:** The deposition occurs systemically or through chronic local absorption, leading to a **symmetrical, bilateral** presentation. * **C. MALT brown reflex:** This is the pathognomonic clinical sign. On slit-lamp examination, a characteristic **dull rose-brown or "Maltese" brown** discoloration is seen on the anterior capsule of the lens. * **D. Visual acuity normal:** Unlike most cataracts, mercurialentis is a surface deposition (pigmentation) rather than an opacification of the lens fibers. Therefore, it **does not affect visual acuity**. ### **High-Yield Clinical Pearls for NEET-PG** * **Location:** The pigment deposits specifically on the **anterior capsule** of the lens. * **Associated Sign:** It is often associated with **Atkinson’s Sign** (the brown discoloration of the anterior lens capsule). * **Systemic Association:** Look for "Erethism" (behavioral changes/irritability) and tremors in the clinical vignette, often referred to as "Mad Hatter’s Syndrome." * **Differential Diagnosis:** Do not confuse this with **Chalcosis** (sunflower cataract due to copper) or **Siderosis** (rusty discoloration due to iron).

Q: A patient presents to the emergency department with uniocular diplopia. Examination with oblique illumination shows a golden crescent while examination with coaxial illumination shows a dark crescent line. Which of the following is the most likely diagnosis?

Ectopia lentis. ### Explanation **Correct Answer: D. Ectopia lentis** The clinical presentation describes the classic signs of **subluxation of the lens (Ectopia lentis)**. * **Mechanism:** When the lens is partially displaced, the edge of the lens (equator) becomes visible within the pupillary area. * **Optical Signs:** * **Oblique Illumination:** The edge of the lens reflects light, appearing as a **golden crescent**. * **Coaxial Illumination (Retroillumination):** The edge of the lens refracts light away from the observer’s eye, appearing as a **dark crescentic line**. * **Uniocular Diplopia:** This occurs because light enters the eye through two different zones: the phakic area (through the lens) and the aphakic area (outside the lens), creating two images on the retina. --- ### Why other options are incorrect: * **A. Lenticonus:** This is a cone-shaped protrusion of the lens capsule. On retroillumination, it presents with an **"Oil droplet" appearance**, not a crescentic edge. * **B. Coloboma:** This is a localized notch or defect in the lens periphery (usually inferiorly) due to defective zonules. While it can cause irregular astigmatism, it does not typically present with the "golden/dark crescent" sign of a displaced equator. * **C. Microspherophakia:** The lens is small and spherical. While the entire equator might be visible 360° upon dilation, it is classically associated with **inverse glaucoma** and high myopia rather than the specific crescentic signs of partial displacement. --- ### High-Yield Clinical Pearls for NEET-PG: * **Most common cause of Ectopia Lentis:** Trauma. * **Marfan Syndrome:** Most common genetic cause; displacement is typically **Superotemporal**. * **Homocystinuria:** Displacement is typically **Inferonasal**; associated with a high risk of secondary glaucoma and thromboembolism. * **Iridodonesis:** Tremulousness of the iris, a key clinical sign of lens subluxation/dislocation.

Question 1

The SRK formula is used to calculate which of the following?

Accepted Answer

Power of intraocular lens

Answer

Corneal curvature

Answer

Corneal endothelial cell count

Answer

Extent of retinal detachment

Question 2

Modern intraocular lenses are NOT made up of which of the following materials?

Accepted Answer

Glass

Answer

Silicon

Answer

Acrylic acid

Answer

PMMA

Question 3

Typical appearance of diabetic cataract is:

Accepted Answer

Snowflake opacities

Answer

Blue dot cataract

Answer

Posterior capsular cataract

Answer

Sunflower cataract

Question 4

Commonest type of cataract is:

Accepted Answer

Blue dot

Answer

Zonular

Answer

Cupuliform

Answer

Cuneiform

Question 5

The youngest lens fibres are present in which part of the lens?

Accepted Answer

Superficial layer of the cortex

Answer

Central core of the lens nucleus

Answer

Outer layer of the nucleus

Answer

Deeper layer of the cortex

Question 6

Which of the following is NOT true about mercurial lentis?

Accepted Answer

Due to organic mercury

Answer

Bilateral

Answer

MALT brown reflex

Answer

Visual acuity normal

Question 7

Festooned pupil results from:

Accepted Answer

Irregular dilatation of the pupil with atropine in the presence of segmental posterior synechiae

Answer

Annular synechiae

Answer

Occlusion pupillae

Answer

All of the above

Question 8

Which of the following is NOT a cause of early-onset cataract?

Accepted Answer

Smoking

Answer

Diabetes mellitus

Answer

Trauma

Answer

Recurrent episodes of diarrhoea

Question 9

What is the treatment of congenital cataract?

Accepted Answer

Extracapsular extraction

Answer

Needling and aspiration

Answer

Intracapsular extraction

Answer

Cryotherapy

Question 10

A patient presents to the emergency department with uniocular diplopia. Examination with oblique illumination shows a golden crescent while examination with coaxial illumination shows a dark crescent line. Which of the following is the most likely diagnosis?

Accepted Answer

Ectopia lentis

Answer

Lenticonus

Answer

Coloboma

Answer

Microspherophakia

Diseases of the Lens — MCQs

Diseases of the Lens — MCQs

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