Optical System of Eye — 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?
What is the true statement about retinoscopy with a plane mirror?
Keratometry is done to assess:
Which of the following is true during far accommodation of the eyes?
Which of the following is a true statement regarding the human eye?
Which is the most powerful refractive surface of the eye?
Pseudopapilledema with tigroid fundus appearance is seen in?
Average hypermetropia in a newborn is
Jack in box scotoma is seen after correction of Aphakia by?
Optical System of Eye 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: 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 4: 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 5: Which of the following is true during far accommodation of the eyes?
- A. The focal length of the lens is decreased to focus on distant objects
- B. The lens becomes more curved due to ciliary muscle contraction
- C. The ciliary muscles are relaxed (Correct Answer)
- D. The zonula fibers become slack to allow lens flattening
Explanation: ***The ciliary muscles are relaxed*** - During **far accommodation**, the eye is set to focus on distant objects, which requires the **lens** to be as thin and flat as possible. - This flattening of the lens is achieved when the **ciliary muscles relax**, increasing tension on the suspensory ligaments. *The lens becomes more curved due to ciliary muscle contraction* - This statement describes **near accommodation**, where the **ciliary muscles contract** to decrease the tension on the suspensory ligaments, allowing the lens to become more spherical and curved. - A more curved lens has greater refractive power, necessary for focusing on close objects. *The focal length of the lens is decreased to focus on distant objects* - A **decreased focal length** means the lens is more powerful and curved, which is needed for **near vision**, not distant vision. - For **distant vision**, the lens flattens, increasing its **focal length** to match the parallel light rays coming from far away. *The zonula fibers become slack to allow lens flattening* - When the **ciliary muscles relax** during far accommodation, they move away from the lens, which **increases the tension** on the zonula fibers (suspensory ligaments). - This increased tension pulls on the lens, causing it to flatten and become thinner.
Question 6: Which of the following is a true statement regarding the human eye?
- A. Lens will not reflect light
- B. Even after cataract surgery UV rays do not penetrate
- C. Normal eye medium will permit wavelengths of 400-700 nm (Correct Answer)
- D. Cornea cuts off wavelengths up to 400 nm
Explanation: ***Normal eye medium will permit wavelength of 400- 700 nm*** - The **normal human eye** can perceive light in the **visible spectrum**, which ranges approximately from **400 nm (violet)** to **700 nm (red)**. - This range of wavelengths is efficiently transmitted through the ocular media (cornea, aqueous humor, lens, vitreous humor) to reach the retina. *Lens will not reflect light* - The human **lens** does **reflect some light**, contributing to phenomena like **glare** and internal reflections, especially if there are opacities like cataracts. - While its primary function is to transmit and refract light, it is not perfectly non-reflective. *Even after cataract surgery UV rays are not penetrated* - Modern **intraocular lenses (IOLs)** implanted during **cataract surgery** are designed to **block UV light (UVA and UVB)** to protect the retina. - However, the natural lens also blocks UV light, and before the development of UV-blocking IOLs, patients sometimes experienced increased retinal exposure to UV post-surgery. *Cornea cut off wavelength upto 400 nm* - The **cornea** primarily absorbs and blocks **UVB (280-315 nm)** and **UVC (100-280 nm)** radiation, protecting the anterior segment structures and retina from harmful short-wavelength light. - It does **not cut off wavelengths up to 400 nm**; it primarily transmits wavelengths longer than approximately 300-310 nm into the eye.
Question 7: Which is the most powerful refractive surface of the eye?
- A. Conjunctiva
- B. Cornea (Correct Answer)
- C. Vitreous
- D. Lens
Explanation: ***Cornea*** - The **cornea** is the eye's outermost, transparent layer, responsible for approximately **two-thirds of the total refractive power** of the eye due to its highly curved anterior surface and the significant change in refractive index from air to corneal tissue. - Its fixed curvature and consistent refractive index make it the primary and most powerful component in bending light rays to focus them on the retina. *Conjunctiva* - The **conjunctiva** is a thin, translucent mucous membrane that lines the inner surface of the eyelids and covers the anterior sclera (white part of the eye). - Its primary function is protection and lubrication, producing mucus and tears, but it plays **no significant role in light refraction**. *Vitreous* - The **vitreous humor** is a transparent, gel-like substance that fills the space between the lens and the retina, maintaining the eye's shape. - It has a refractive index very similar to water (approximately 1.334) and contributes **minimally to the eye's total refractive power** because light has already been significantly refracted by the cornea and lens before reaching it. *Lens* - The **lens** is a transparent, biconvex structure located behind the iris, providing the remaining **one-third of the eye's refractive power**. - While crucial for **accommodation** (changing focal length to see objects at different distances), its refractive power is less than the cornea's, and its ability to change shape is what makes it unique, not its absolute power.
Question 8: Pseudopapilledema with tigroid fundus appearance is seen in?
- A. Astigmatism
- B. Presbyopia
- C. Hypermetropia
- D. Myopia (Correct Answer)
Explanation: ***Myopia*** - **Pseudopapilledema** with a **tigroid fundus** (tessellated or salt-and-pepper appearance) is characteristically observed in high myopia due to the oblique entry of the **optic nerve** into the globe and thinning of the choroid and retinal pigment epithelium. - The pseudopapilledema is caused by the crowding of axons and glial tissue within the optic disc, giving a raised appearance, and is distinct from true papilledema which involves **optic disc edema** due to increased **intracranial pressure**. - The tigroid fundus results from the visibility of underlying **choroidal vessels** through the attenuated retinal pigment epithelium in the stretched, elongated myopic eye. *Hypermetropia* - **Hypermetropia** (farsightedness) typically presents with a small, compact optic disc, but does not exhibit the specific findings of **pseudopapilledema** or tigroid fundus. - This condition is characterized by the eye being too short or the lens having insufficient power, causing light to focus behind the retina. *Astigmatism* - **Astigmatism** is characterized by an **irregularly shaped cornea** or lens, leading to blurred vision at all distances. - While it can cause some distortion, it is not associated with the specific optic disc appearance of **pseudopapilledema** or the fundus changes seen in high myopia. *Presbyopia* - **Presbyopia** is an age-related condition where the eye's natural lens loses its flexibility, making it difficult to focus on **near objects**. - It affects the **accommodative ability** of the eye and does not manifest with any characteristic changes in the optic disc morphology such as **pseudopapilledema** or retinal/choroidal changes.
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: Jack in box scotoma is seen after correction of Aphakia by?
- A. IOL
- B. Spectacles (Correct Answer)
- C. Contact lens
- D. None of the options
Explanation: ***Spectacles*** - **Jack-in-the-box scotoma** describes a visual phenomenon where objects appear to jump into and out of the field of vision. This occurs due to the **peripheral scotoma** and **ring scotoma** created by high-plus aphakic spectacle lenses. - Aphakic spectacles cause significant **magnification of the central visual field** (about 25-30%) and a corresponding minification/displacement of the peripheral field, leading to areas where objects are transiently obscured or reappear. *IOL* - An **intraocular lens (IOL)** replaces the natural lens within the eye, providing a much more stable and centered optical correction. - IOLs generally do not cause significant magnification changes or the peripheral scotoma associated with aphakic spectacles. *Contact lens* - **Contact lenses** sit directly on the cornea, offering a visual correction that is much closer to the nodal point of the eye than spectacles. - This placement results in less peripheral distortion and magnification compared to spectacles, making jack-in-the-box scotoma unlikely. *None of the options* - As **aphakic spectacles** are known to cause jack-in-the-box scotoma, this option is incorrect.
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