Optics and Refraction — MCQs

$Optics and Refraction — MCQs$

Optics and Refraction Indian Medical PG Practice Questions and MCQs

Question 261: What is the SI unit of illuminance (brightness of light on a surface)?

A. Luminance
B. Lux (Correct Answer)
C. Candela
D. Lumen

Explanation: ***Lux*** - **Lux** is the SI unit specifically designated for **illuminance**, which measures the **luminous flux** incident on a surface per unit area. - It quantifies the perceived **brightness** of light on a surface, taking into account the human eye's sensitivity to different wavelengths. *Luminance* - **Luminance** is a measure of the **intensity of light emitted or reflected from a surface** in a given direction, expressed in candelas per square meter (cd/m²). - It describes the brightness of a surface as perceived by the eye, but unlike illuminance, it is **independent of the incident light**. *Candela* - The **candela** is the SI base unit of **luminous intensity**, measuring the **power emitted by a light source in a particular direction**. - It doesn't describe the **brightness on a surface** but rather the output of the light source itself. *Lumen* - The **lumen** is the SI unit of **luminous flux**, representing the total amount of **visible light emitted by a source per unit time**. - While related to brightness, it describes the **total light output** of a source, not the illuminance on a specific surface.

Question 262: 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 263: Campimetry is used to measure:

A. Squint
B. Field of Vision (Correct Answer)
C. Pattern of retina
D. Malignant melanoma

Explanation: ***Field of Vision*** - **Campimetry** is a diagnostic test specifically designed to map and assess a person's **field of vision**, identifying blind spots or areas of diminished sight. - This technique is crucial for detecting and monitoring conditions that affect the optic nerve or visual pathways, such as **glaucoma** or neurological disorders. *Squint* - A **squint**, also known as strabismus, refers to a misalignment of the eyes. - Its assessment primarily involves tests of **ocular motility** and alignment, such as the cover test, rather than perimetry. *Pattern of retina* - The **pattern of the retina** is evaluated through direct visualization using an **ophthalmoscope** or other retinal imaging techniques like fundus photography or optical coherence tomography (OCT). - These methods provide structural information about the retina, not its functional visual field. *Malignant melanoma* - **Malignant melanoma** (in the context of the eye) is a tumor that can affect various parts of the eye, including the choroid, iris, or conjunctiva. - Its diagnosis involves clinical examination, imaging studies (**ultrasound**, OCT, **fluorescein angiography**), and sometimes biopsy, not primarily visual field testing.

Question 264: Keratometry is done to assess:

A. Corneal thickness
B. Curvature of cornea (Correct Answer)
C. Corneal sensation
D. Corneal endothelium

Explanation: ***Curvature of cornea*** - **Keratometry** is specifically designed to measure the **radius of curvature of the anterior surface of the cornea**. - This measurement is essential for detecting and quantifying **astigmatism** and for fitting **contact lenses** and calculating **intraocular lens (IOL) power**. *Corneal thickness* - **Corneal thickness** is measured by **pachymetry**, not keratometry. - Pachymetry is used to assess conditions like **corneal edema** or prior to certain refractive surgeries. *Corneal sensation* - **Corneal sensation** is tested using a fine wisp of cotton or a **corneal aesthesiometer**. - This evaluates the integrity of the **corneal nerves** and blink reflex. *Corneal endothelium* - The **corneal endothelium** is assessed using **specular microscopy** to evaluate cell count, size, and shape. - This is important for surgical planning and monitoring **corneal dystrophies**.

Question 265: What is the true statement about retinoscopy with a plane mirror?

A. In myopia, the red glow moves in the same direction.
B. Retinoscopy is done at 1 meter away from the patient. (Correct Answer)
C. In hypermetropia, the red glow moves in the opposite direction.
D. In emmetropia, the red glow moves in the opposite direction.

Explanation: ***Retinoscopy is done at 1 meter away from the patient.*** - Retinoscopy is typically performed at a **working distance** of 67 cm or 1 meter, to allow for the examiner to observe the reflex and to incorporate a working distance lens in the final calculation. - A 1-meter working distance requires a **-1.00 D sphere correction** to be subtracted from the spherical power found in retinoscopy to find the patient's actual refractive error. *In myopia, the red glow moves in the same direction.* - In **myopia**, using a plane mirror, the retinal reflex appears to move in the **opposite direction** to the movement of the retinoscope. - This "against" movement needs **concave (minus)** lenses to neutralize it. *In hypermetropia, the red glow moves in the opposite direction.* - In **hypermetropia**, using a plane mirror, the retinal reflex appears to move in the **same direction** as the movement of the retinoscope. - This "with" movement needs **convex (plus)** lenses to neutralize it. *In emmetropia, the red glow moves in the opposite direction.* - In **emmetropia**, the light from the retinoscope is focused on the retina, and the reflex also moves in the **same direction** as the retinoscope (when using a plane mirror) until neutralization. - An **emmetropic eye** theoretically requires no corrective lens, other than the working distance correction, to neutralize the reflex.

Question 266: Keratometer is used to assess:

A. Curvature of lens
B. Curvature of cornea (Correct Answer)
C. Thickness of cornea
D. Diameter of cornea

Explanation: ***Curvature of cornea*** - A **keratometer** (or ophthalmometer) is specifically designed to measure the **radius of curvature** of the **anterior surface of the cornea**. - This measurement is crucial for fitting **contact lenses**, diagnosing **astigmatism**, and planning **refractive surgeries**. *Curvature of lens* - The curvature of the **crystalline lens** inside the eye is not directly measured by a keratometer. - Lens curvature changes with **accommodation** and is assessed more indirectly through an **autorefractor** or during cataract surgery planning with specific formulas. *Thickness of cornea* - The **thickness of the cornea** is measured using a **pachymeter**, not a keratometer. - **Pachymetry** is important for diagnosing conditions like **glaucoma** and evaluating suitability for **refractive surgery**. *Diameter of cornea* - The **diameter of the cornea** (from limbus to limbus) is typically measured using a **ruler or calipers**, not a keratometer. - This measurement is relevant for contact lens fitting and surgical planning.

Question 267: The eye in the newborn is:

A. Hypermetropia (Correct Answer)
B. Myopia
C. Hypermetropic with regular astigmatism
D. Hypermetropic with irregular astigmatism

Explanation: ***Hypermetropia*** - The newborn eye is typically **shorter in axial length** (approximately 16-17 mm vs. 24 mm in adults), leading to a state of **physiological hypermetropia** (farsightedness) of about **+2 to +4 diopters**. - This is a **universal finding** in newborns and represents the most fundamental refractive characteristic of the newborn eye. - The eye gradually grows and typically reaches emmetropia (normal vision) by about **6-7 years of age**. *Myopia* - **Myopia** (nearsightedness) occurs when the eye is too long or the refractive power is too strong, causing light to focus in front of the retina. - Myopia is **not the physiological state** of the newborn eye and is uncommon at birth. - When present in newborns, it may indicate pathology or very premature birth. *Hypermetropic with regular astigmatism* - While **most newborns do have some degree of astigmatism** (0.5-2D) in addition to hypermetropia, typically "against-the-rule" astigmatism that decreases during the first year, the question asks for the **primary refractive characteristic**. - **Hypermetropia alone** is the universal and defining feature, whereas the amount of astigmatism varies considerably between individuals. - In standard clinical terminology, when describing the typical newborn eye, "hypermetropic" is the complete answer. *Hypermetropic with irregular astigmatism* - **Irregular astigmatism** is uncommon and is typically associated with corneal pathology, trauma, or surgery. - It is **not a physiological finding** in the normal newborn eye and would indicate an underlying abnormality if present.

Question 268: Posterior staphyloma is seen in -

A. Degenerative high axial myopia (Correct Answer)
B. Corneal Ulcer
C. Chronic Uncontrolled glaucoma
D. Complication of cataract surgery

Explanation: ***Degenerative high axial myopia*** - **Posterior staphyloma** is a hallmark feature of **pathological** or **degenerative high axial myopia**, characterized by an outpouching of the posterior sclera. - This condition arises from excessive **axial elongation** of the eyeball, leading to thinning and weakening of the sclera at the posterior pole. *Corneal Ulcer* - A **corneal ulcer** is an open sore on the cornea, often caused by infection, and primarily affects the **anterior segment** of the eye. - It does not involve changes in the scleral structure or lead to **posterior staphyloma**. *Chronic Uncontrolled glaucoma* - **Chronic uncontrolled glaucoma** is characterized by progressive optic nerve damage and visual field loss, typically due to elevated intraocular pressure. - While it can lead to cupping of the optic disc, it does not directly cause **posterior staphyloma**. *Complication of cataract surgery* - Complications of **cataract surgery** include conditions like posterior capsule opacification, cystoid macular edema, or retinal detachment. - These complications do not involve the development of a **posterior staphyloma**.

Question 269: Which is the commonest cause of ocular morbidity globally?

A. Vitamin A deficiency
B. Ocular injury
C. Cataract
D. Refractive error (Correct Answer)

Explanation: ***Refractive error*** - **Uncorrected refractive errors** (myopia, hyperopia, astigmatism) are the **leading cause of visual impairment and ocular morbidity globally**, affecting approximately **2.6 billion people worldwide**. - They are **easily correctable** with glasses, contact lenses, or refractive surgery, but remain highly prevalent, especially in underserved regions. - Key distinction: Refractive errors cause the **most ocular morbidity** (overall eye health burden), while cataracts cause the **most blindness**. *Cataract* - **Cataracts** are the **leading cause of blindness globally** (not morbidity), accounting for **51% of world blindness**, particularly in older adults. - While cataracts cause significant vision loss, their prevalence affects primarily older age groups, whereas uncorrected refractive errors impact **all age groups**, making them the commonest cause of overall ocular morbidity. *Vitamin A deficiency* - **Vitamin A deficiency** is a major cause of **preventable childhood blindness** in developing countries, leading to **xerophthalmia, night blindness, and keratomalacia**. - Despite its severe consequences, its **global prevalence is much lower** than uncorrected refractive errors. *Ocular injury* - **Ocular injuries** cause significant morbidity with potential for **vision loss and structural damage**, often requiring emergency intervention. - However, they are **episodic events** rather than chronic conditions, making them far less prevalent globally than refractive errors.

Question 270: Most common cause of posterior staphyloma

A. Glaucoma
B. Myopia (Correct Answer)
C. Scleritis
D. Trauma

Explanation: ***Myopia*** - **Pathological myopia**, characterized by excessive axial elongation of the eyeball, is the most common cause of posterior staphyloma. - The stretching and thinning of the sclera in high myopia leads to localized outward bulging, clinically known as a posterior staphyloma. *Glaucoma* - While glaucoma can cause **optic nerve damage** and visual field loss, it is not directly associated with the formation of a posterior staphyloma. - Its primary effect is on intraocular pressure and its consequences on the **optic nerve head**. *Scleritis* - **Scleritis** is an inflammatory condition affecting the sclera, which can lead to scleral thinning and even perforation. - However, it typically causes localized inflammation and thinning rather than the characteristic outward bulging seen in posterior staphyloma. *Trauma* - Severe ocular **trauma** can lead to globe rupture or other structural changes. - While trauma could theoretically cause localized scleral weakness, it is not the most frequent cause of posterior staphyloma compared to the chronic, progressive changes seen in high myopia.

Practice by Chapter

Physical Optics

Practice Questions

Geometric Optics

Practice Questions

Optical System of Eye

Practice Questions

Visual Acuity and Contrast Sensitivity

Practice Questions

Refractive Errors

Practice Questions

Accommodation and Presbyopia

Practice Questions

Optical Instruments

Practice Questions

Lenses and Prisms

Practice Questions

Retinoscopy

Practice Questions

Subjective Refraction

Practice Questions

Contact Lens Optics

Practice Questions

Wavefront Technology

Practice Questions

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