The following light reflex is seen in a patient. How much is the deviation?
A patient presents with a down and out right eye with ptosis since birth. What is the nerve palsy?
A posterior staphyloma was observed on indirect ophthalmoscopy. What is the likely diagnosis?
FMGE 2025 - Ophthalmology FMGE Practice Questions and MCQs
Question 21: The following light reflex is seen in a patient. How much is the deviation?
- A. 45 PD (Correct Answer)
- B. 90 PD
- C. 30 PD
- D. 90°
Explanation: ***45 PD*** - The image displays the **Hirschberg test** (corneal light reflex test), which estimates the angle of strabismus. The light reflex is displaced nasally in the left eye, indicating an outward deviation (**exotropia**). - A reflex located approximately midway between the pupil margin and the limbus corresponds to a deviation of about 22.5 degrees, which is equivalent to **45 prism diopters (PD)**. *30 PD* - A deviation of 30 PD corresponds to approximately 15 degrees, where the light reflex would be seen at the **pupillary margin**. - This represents a smaller deviation than what is depicted in the image. *90 PD* - This value corresponds to a large deviation of 45 degrees, where the light reflex would be located at the **limbus** (the junction of the cornea and sclera). - The light reflex in the image is positioned midway between the pupil and limbus, indicating a smaller deviation than what would be seen with a full 90 PD deviation. *90°* - This is an extremely large deviation and is also an incorrect unit of measurement for this test; **prism diopters (PD)** are the standard unit used to quantify strabismus. - One degree of deviation is roughly equal to two prism diopters, making a 90-degree deviation (180 PD) anatomically inconsistent with the image.
Question 22: A patient presents with a down and out right eye with ptosis since birth. What is the nerve palsy?
- A. 4th nerve palsy
- B. 6th nerve palsy
- C. 7th nerve palsy
- D. 3rd nerve palsy (Correct Answer)
Explanation: ***3rd nerve palsy (Correct Answer)*** - The **oculomotor nerve (CN III)** supplies the levator palpebrae superioris, leading to **ptosis**, and most extraocular muscles (superior rectus, medial rectus, inferior rectus, and inferior oblique) - When CN III is paralyzed, the unopposed actions of **CN IV (superior oblique)** and **CN VI (lateral rectus)** pull the eye into the characteristic **"down and out"** position - **Congenital 3rd nerve palsy** presents with ptosis and the down-and-out eye position from birth - This is the classic triad: **ptosis + down and out eye + dilated pupil** (if pupil-involving) *4th nerve palsy (Incorrect)* - Palsy of the **trochlear nerve (CN IV)** affects only the superior oblique muscle - Presents with impaired **downward and inward movement** and **intorsion** - Typically causes **vertical diplopia** (especially on downward gaze) and compensatory **head tilt** to the opposite side - Does **NOT** cause ptosis or the pronounced "down and out" position *6th nerve palsy (Incorrect)* - Palsy of the **abducens nerve (CN VI)** affects only the lateral rectus muscle - Causes failure of **abduction** (outward movement), resulting in the eye being pulled **inward** (esotropia) - Does **NOT** cause ptosis or downward deviation of the eye *7th nerve palsy (Incorrect)* - The **facial nerve (CN VII)** controls facial muscles, including orbicularis oculi - Causes **lagophthalmos** (inability to close the eyelid) and facial weakness, NOT ptosis - Does **NOT** affect extraocular movements or eye position
Question 23: A posterior staphyloma was observed on indirect ophthalmoscopy. What is the likely diagnosis?
- A. Retinitis pigmentosa
- B. Primary open-angle glaucoma
- C. High myopia (Correct Answer)
- D. Hypermetropia
Explanation: ***High myopia*** - A **posterior staphyloma** is an outpouching of the sclera at the posterior pole of the eye, which is a pathognomonic sign of **pathological** or **high myopia** due to excessive axial elongation. - Other associated fundus findings in high myopia include **chorioretinal atrophy**, **lacquer cracks** (breaks in Bruch's membrane), and an increased risk of **retinal detachment**. *Hypermetropia* - Hypermetropia (farsightedness) is characterized by a **shorter axial length**, which is the opposite of the anatomical changes seen in high myopia that lead to staphyloma formation. - Fundus examination in hypermetropia may reveal a small, crowded optic disc, sometimes referred to as **pseudopapilledema**, but not scleral ectasia. *Primary open-angle glaucoma* - The primary funduscopic sign of glaucoma is progressive damage to the **optic nerve head**, manifesting as an increased **cup-to-disc ratio** and thinning of the neuroretinal rim. - While a myopic optic disc can be difficult to assess for glaucoma, a staphyloma itself is a feature of the sclera and retina, not a primary sign of glaucoma. *Retinitis pigmentosa* - This is an inherited retinal dystrophy with characteristic fundus findings including **bone-spicule pigmentation** in the mid-periphery, **arteriolar attenuation**, and **waxy pallor of the optic disc**. - These changes result from photoreceptor and retinal pigment epithelium degeneration, and are not associated with the formation of a posterior staphyloma.