Optics and Refraction Practice Questions

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

Lux. ***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.

Q: Average hypermetropia in a newborn is

+ 2.5 D. ***+ 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**.

Q: Campimetry is used to measure:

Field of Vision. ***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.

Q: Keratometry is done to assess:

Curvature of cornea. ***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**.

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

Retinoscopy is done at 1 meter away from the patient.. ***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.

Q: Keratometer is used to assess:

Curvature of cornea. ***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.

Q: The eye in the newborn is:

Hypermetropia. ***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.

Q: Posterior staphyloma is seen in -

Degenerative high axial myopia. ***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**.

Q: Which is the commonest cause of ocular morbidity globally?

Refractive error. ***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.

Q: Most common cause of posterior staphyloma

Myopia. ***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.

Question 1

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

Accepted Answer

Lux

Answer

Luminance

Answer

Candela

Answer

Lumen

Question 2

Average hypermetropia in a newborn is

Accepted Answer

+ 2.5 D

Answer

+ 10 D

Answer

+ 1 D

Answer

+ 5 D

Question 3

Campimetry is used to measure:

Accepted Answer

Field of Vision

Answer

Squint

Answer

Pattern of retina

Answer

Malignant melanoma

Question 4

Keratometry is done to assess:

Accepted Answer

Curvature of cornea

Answer

Corneal thickness

Answer

Corneal sensation

Answer

Corneal endothelium

Question 5

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

Accepted Answer

Retinoscopy is done at 1 meter away from the patient.

Answer

In myopia, the red glow moves in the same direction.

Answer

In hypermetropia, the red glow moves in the opposite direction.

Answer

In emmetropia, the red glow moves in the opposite direction.

Question 6

Keratometer is used to assess:

Accepted Answer

Curvature of cornea

Answer

Curvature of lens

Answer

Thickness of cornea

Answer

Diameter of cornea

Question 7

The eye in the newborn is:

Accepted Answer

Hypermetropia

Answer

Myopia

Answer

Hypermetropic with regular astigmatism

Answer

Hypermetropic with irregular astigmatism

Question 8

Posterior staphyloma is seen in -

Accepted Answer

Degenerative high axial myopia

Answer

Corneal Ulcer

Answer

Chronic Uncontrolled glaucoma

Answer

Complication of cataract surgery

Question 9

Which is the commonest cause of ocular morbidity globally?

Accepted Answer

Refractive error

Answer

Vitamin A deficiency

Answer

Ocular injury

Answer

Cataract

Question 10

Most common cause of posterior staphyloma

Accepted Answer

Myopia

Answer

Glaucoma

Answer

Scleritis

Answer

Trauma

Optics and Refraction — MCQs

Optics and Refraction — MCQs

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