Refractive Errors — MCQs
What term describes a condition where the axial length of the eye does not match its refractive power?
A 50-year-old patient has difficulty reading close objects. Likely diagnosis?
A patient complains of an inability to read a newspaper, particularly in bright sunlight. What is the most likely diagnosis?
The refracting structures of the eye constitute a homocentric system of lenses. The refractive index of the cornea is:
Constantly changing refractive error is seen in:
What is regular astigmatism?
Maximum correction of myopia can be done by?
1mm change in axial length of the eyeball would change the refracting power of the eye by?
Average hypermetropia in a newborn is
Shortening of 2 mm of axial length of the eyeball causes?
Refractive Errors Indian Medical PG Practice Questions and MCQs
Question 1: What term describes a condition where the axial length of the eye does not match its refractive power?
- A. Anisokonia
- B. Axial Ametropia (Correct Answer)
- C. Emmetropia
- D. Curvature ametropia
Explanation: ***Axial Ametropia*** - This term precisely describes a refractive error where the **axial length** of the eye is either too long or too short relative to its **optical power**, leading to images focusing in front of or behind the retina. - Examples include **myopia** (eye too long) and **hyperopia** (eye too short), which are fundamentally caused by a mismatch in axial length. *Anisokonia* - This condition refers to a significant difference in the **perceived size of images** between the two eyes, often due to unequal refractive errors between the eyes. - It does not directly describe the mismatch between axial length and refractive power itself, but rather a perceptual consequence that can result from asymmetric refractive errors. *Curvature ametropia* - This type of ametropia occurs when the **curvature** of the cornea or lens is abnormal, causing light rays to converge incorrectly. - While it's a form of refractive error, it specifically relates to the curvature of refractive surfaces, not the overall **axial length** of the eyeball. *Emmetropia* - This is the state of having **perfect vision**, where the refractive power of the eye correctly matches its axial length, allowing light to focus precisely on the retina without accommodation. - It describes the absence of refractive error, which is the opposite of the condition described in the question.
Question 2: A 50-year-old patient has difficulty reading close objects. Likely diagnosis?
- A. Hypermetropia
- B. Astigmatism
- C. Myopia
- D. Presbyopia (Correct Answer)
Explanation: ***Presbyopia*** - This condition is characterized by the **loss of elasticity** in the lens of the eye, which occurs naturally with age, making it difficult to focus on **near objects**. - Its typical presentation, as seen in this 50-year-old patient, is **difficulty reading close objects** or performing other tasks requiring near vision. *Hypermetropia* - Often causes **farsightedness**, meaning distant objects are seen clearly, but near objects appear blurry due to the eye attempting to constantly accommodate. - While it can make near vision difficult, it is not primarily an age-related loss of accommodation and can affect individuals of various ages. *Astigmatism* - Results from an **irregular curvature of the cornea or lens**, causing blurred or distorted vision at all distances, rather than specifically difficulty with close objects. - This condition makes it difficult for the eye to focus light uniformly on the retina, leading to multiple focal points or streaks. *Myopia* - This is commonly known as **nearsightedness**, where distant objects appear blurry while near objects are seen clearly. - It occurs when the eyeball is too long or the cornea is too steeply curved, causing light to focus in front of the retina.
Question 3: A patient complains of an inability to read a newspaper, particularly in bright sunlight. What is the most likely diagnosis?
- A. Nuclear cataract
- B. Cortical cataract
- C. Posterior subcapsular cataract (Correct Answer)
- D. Congenital cataract
Explanation: ***Posterior subcapsular cataract*** - This type of cataract causes significant **glare** and **photophobia**, making it difficult to read in bright light due to opacities located at the **posterior lens capsule**. - The patient experiences worsening vision in **bright light** conditions because the constricted pupil directs more light through the **central posterior opacity**, which lies directly in the visual axis. *Nuclear cataract* - Patients with **nuclear cataracts** typically experience **myopic shift** and improved near vision (second sight) due to increased refractive power of the lens. - Vision is usually worse in **dim light** conditions because of pupillary dilation, which allows more light to pass through the central opacity. *Cortical cataract* - Characterized by **spoke-like opacities** that start in the periphery and extend inward. - While it can cause glare, vision often remains good until the opacities encroach upon the **visual axis**, and it doesn't specifically cause worsening vision in bright light to the same degree as PSC. *Congenital cataract* - Present at birth or shortly after, and symptoms depend on the density and location of the opacity. - While it affects vision, the specific complaint of difficulty reading in bright sunlight is not a typical distinguishing feature of **congenital cataracts**.
Question 4: The refracting structures of the eye constitute a homocentric system of lenses. The refractive index of the cornea is:
- A. 1.37 (Correct Answer)
- B. 1.42
- C. 1.31
- D. 1.33
Explanation: ***1.37*** - The **refractive index** of the **cornea** is approximately **1.376**. This value is crucial for the cornea's role as the primary refracting surface of the eye. - Its high refractive power, due to the significant change in refractive index between air (index ~1.00) and the corneal tissue, is responsible for about two-thirds of the eye's total focusing power. *1.31* - This value is lower than the actual refractive index of the cornea. A refractive index of 1.31 would imply less optical density and reduced refractive power compared to the physiological value. - While within the broader range of biological tissues, it is not the accurate specific value for the human cornea. *1.33* - The refractive index of **aqueous humor** and **vitreous humor**, as well as **water**, is approximately 1.33. The cornea has a slightly higher refractive index than these transparent fluids. - While close, this value is primarily associated with the intraocular fluids and not the corneal tissue itself. *1.42* - This value is higher than the actual refractive index of the cornea and would suggest a greater optical density and refractive power than is physiologically present. - A refractive index of 1.42 is closer to that of the lens nucleus, which has a higher refractive index than the cornea to provide fine-tuning of vision.
Question 5: Constantly changing refractive error is seen in:
- A. Morgagnian cataract
- B. Intumescent cataract
- C. Traumatic cataract
- D. Diabetic cataract (Correct Answer)
Explanation: ***Diabetic cataract*** - Fluctuating blood glucose levels in diabetes can cause changes in the **osmolarity of the aqueous humor**, which in turn affects the hydration of the lens and its refractive power. - This leads to a **constantly changing refractive error**, where a person's prescription might change rapidly over short periods of time. *Morgagnian cataract* - This is a type of **hypermature cataract** where the cortex has liquefied, allowing the nucleus to sink within the capsular bag. - While vision is severely impaired, it doesn't typically present with a constantly changing refractive error, but rather a stable, significant vision loss. *Intumescent cataract* - An **intumescent cataract** is a mature or hypermature cataract where the lens has become significantly swollen due to water absorption. - This swelling causes the anterior capsule to stretch, but it results in a fixed and profound vision loss, not a fluctuating refractive error. *Traumatic cataract* - A **traumatic cataract** develops as a result of blunt or penetrating ocular injury, causing damage to the lens fibers. - While the specific type of refractive error can vary depending on the trauma, it typically presents as a stable visual impairment rather than a constantly changing refractive error.
Question 6: What is regular astigmatism?
- A. Astigmatism in which the principal meridians are parallel
- B. Asymptomatic astigmatism
- C. Astigmatism as a result of cataract surgery
- D. Astigmatism where the principal meridians are at a 90-degree angle to each other (Correct Answer)
Explanation: ***Astigmatism where the principal meridians are at a 90-degree angle to each other.*** - In **regular astigmatism**, the two principal meridians of the eye's refractive power are **perpendicular** (90 degrees apart), meaning they are not random. - This perpendicularity allows for correction with **sphero-cylindrical lenses**, as the different focal powers are along well-defined axes. *Astigmatism in which the principal meridians are parallel* - This statement is incorrect as it describes a non-existent or mischaracterized form of astigmatism; for astigmatism to occur, there must be a **difference in curvature** and thus power between two meridians, which cannot be parallel and distinct. - While meridians are typically measured, the concept of **parallel principal meridians** does not align with the definition of astigmatism. *Asymptomatic astigmatism* - This describes the **presence of astigmatism without noticeable symptoms**, not the type of astigmatism itself. - Astigmatism can be asymptomatic, particularly if it is of a **low magnitude**, but this term does not define its optical characteristics. *Astigmatism as a result of cataract surgery* - This refers to **induced astigmatism**, often post-surgical, which can be regular or irregular. - **Surgically induced astigmatism** is a cause, not a classification of astigmatism based on the orientation of its principal meridians.
Question 7: Maximum correction of myopia can be done by?
- A. Radial keratotomy
- B. LASIK (Correct Answer)
- C. Photorefractive keratectomy
- D. Orthokeratology
Explanation: ***LASIK*** - **LASIK (Laser-Assisted In Situ Keratomileusis)** allows for significant correction of high myopia by reshaping the cornea with an excimer laser. - It involves creating a **corneal flap** and then ablating tissue underneath, offering precise and stable vision correction for a wide range of refractive errors. - Among the given corneal refractive procedures, LASIK can correct myopia up to **-10 to -12 D**. *Radial keratotomy* - **Radial keratotomy (RK)** involves making radial incisions in the cornea to flatten it, primarily used for low to moderate myopia (up to -3 to -4 D). - It has a higher risk of **unpredictable outcomes**, induced astigmatism, and glare compared to modern laser procedures. *Photorefractive keratectomy* - **Photorefractive keratectomy (PRK)** involves direct ablation of the corneal surface without creating a flap, which is suitable for moderate myopia (up to -8 to -10 D). - While effective, PRK typically has a **longer recovery period** and more post-operative pain than LASIK. *Orthokeratology* - **Orthokeratology (Ortho-K)** uses specially designed rigid contact lenses worn overnight to temporarily reshape the cornea and correct myopia. - The effect is **temporary**, requiring continuous lens wear to maintain vision correction, and is generally limited to low to moderate myopia (up to -4 to -6 D).
Question 8: 1mm change in axial length of the eyeball would change the refracting power of the eye by?
- A. 1D
- B. 2D
- C. 3D (Correct Answer)
- D. 4D
Explanation: ***3D*** - A 1mm change in the **axial length** of the eyeball leads to an approximate **3 diopter (D) change** in the refractive power of the eye. - This relationship is crucial for understanding **refractive errors** like myopia (if the eyeball is too long) or hyperopia (if it's too short). *1D* - A 1D change in refractive power corresponds to a much larger change in the **focal length** of the eye, not typically 1mm in axial length. - This value is too small to reflect the significant impact of a 1mm axial length alteration on the eye's focusing ability. *2D* - While a direct relationship exists, 2D is an **underestimation** of the actual refractive change caused by a 1mm alteration in axial length. - This value would imply a less sensitive optical system than the human eye. *4D* - A 4D change would represent an **overestimation** of the refractive power change for a 1mm alteration in axial length. - Such a high value is generally seen with more substantial anatomical variations or surgical interventions.
Question 9: Average hypermetropia in a newborn is
- A. + 2.5 D (Correct Answer)
- B. + 10 D
- C. + 1 D
- D. + 5 D
Explanation: ***+ 2.5 D*** - Most **newborns** are **hypermetropic** (farsighted) due to a shorter axial length of the eye. - The average hypermetropic correction needed at birth is approximately **+2.5 diopters (D)**. *+ 10 D* - A hyperopia of **+10 D** would represent a very significant degree of **hypermetropia**, far exceeding the typical physiological range for a newborn. - Such high hyperopia in a newborn might suggest an **ocular anomaly** or a condition like **microphthalmia**. *+ 1 D* - A hyperopia of **+1 D** is a mild degree of hypermetropia, which is less than the average physiological hyperopia found in **newborns**. - While within a normal range for some infants, it does not represent the typical average for **newborns**. *+ 5 D* - A hyperopia of **+5 D** is a higher degree of hypermetropia than the average seen in **newborns**. - While possible, it is not the most common or average refractive error at birth, which is typically around **+2.5 D**.
Question 10: Shortening of 2 mm of axial length of the eyeball causes?
- A. 3D myopia
- B. 2D myopia
- C. 6D hypermetropia (Correct Answer)
- D. 1D hypermetropia
Explanation: ***6D hypermetropia*** - A 1 mm shortening of the **axial length** of the eyeball typically results in approximately **3 diopters** of hypermetropia. - Therefore, a 2 mm shortening would cause **6 diopters** (2 mm x 3 D/mm) of hypermetropia. *3D myopia* - Myopia (nearsightedness) is caused by an **eyeball that is too long** or a cornea that is too steeply curved, not by a shortened axial length. - A 2 mm shortening would cause **hypermetropia** (farsightedness), not myopia. *2D myopia* - This option incorrectly identifies both the **type of refractive error** (myopia instead of hypermetropia) and the magnitude of the change. - Shortening of the axial length makes the eye effectively **farsighted**, not nearsighted. *1D hypermetropia* - While reflecting the correct type of refractive error (hypermetropia), the **magnitude is incorrect**. - A 1 mm change in axial length results in about 3 diopters, so 2 mm would be **6 diopters**, not 1 diopter.
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