Ocular Motility Evaluation & Binocular Vision Assessment Flashcards

What is the primary purpose of the cover test in ocular motility assessment?

Answer: To detect misalignment or latent eye deviations.

The cover test is a fundamental diagnostic tool in orthoptics used to assess ocular alignment. By alternately covering and uncovering each eye, the orthoptist can observe any movement of the uncovered eye, indicating a manifest deviation (strabismus) or a latent deviation (phoria) that is present when binocular fusion is disrupted. This helps identify the presence and type of eye misalignment.

Which cranial nerve is primarily responsible for lateral eye movement?

Answer: Abducens nerve (VI)

The abducens nerve (cranial nerve VI) innervates the lateral rectus muscle, which is primarily responsible for abducting the eye, meaning moving it away from the midline. Damage to this nerve results in an inability to move the eye laterally and can cause esotropia (inward turning of the eye). The other nerves control different eye movements or sensory functions.

What condition is typically diagnosed using Hirschberg’s test?

Answer: Strabismus

Hirschberg's test is a quick and simple screening tool used to detect strabismus, or ocular misalignment. It involves observing the reflection of a light source on the patient's corneas. If the light reflex is not symmetrically centered in both pupils, it indicates a deviation in eye alignment, suggesting the presence of strabismus.

What is the function of the superior oblique muscle in eye movement?

Answer: Depresses and intorts the eye

The superior oblique muscle is one of the extraocular muscles responsible for eye movement. Its primary actions are depression (moving the eye downwards) and intorsion (rotating the top of the eye inward towards the nose). It also has a secondary action of abduction (moving the eye outwards).

Which test measures a patient’s ability to maintain binocular vision under stress?

Answer: Prism bar vergence test

The prism bar vergence test is specifically designed to measure a patient’s fusional vergence amplitudes, which is their ability to maintain single binocular vision while the eyes converge or diverge. By introducing prisms of increasing strength, the test assesses the limits of the patient's ability to overcome prism-induced diplopia and maintain fusion, thereby indicating their binocular stability under stress.

A patient has difficulty converging their eyes. Which condition is most likely?

Answer: Convergence insufficiency

Convergence insufficiency is a common binocular vision disorder where the eyes have difficulty turning inward (converging) to maintain single vision when viewing near objects. This often leads to symptoms like eye strain, headaches, blurred vision, or double vision during reading or close work. Divergence excess, conversely, involves difficulty converging.

What tool is commonly used to measure eye deviations in prism diopters?

Answer: Prism bar

A prism bar is a diagnostic tool consisting of a series of prisms of increasing dioptric power, mounted in a linear fashion. It is commonly used in orthoptics to measure the magnitude of eye deviations (strabismus) and fusional vergence amplitudes, quantifying them in prism diopters. Other tools like the slit lamp, ophthalmoscope, and phoropter serve different diagnostic purposes.

Which of the following is a symptom of poor binocular vision?

Answer: Headache during reading

Poor binocular vision, such as from convergence insufficiency or uncorrected phorias, often causes symptoms related to eye strain and the effort to maintain single vision. Headaches, especially during prolonged near tasks like reading, are a classic symptom as the eyes struggle to work together efficiently. Other options like eye twitching or blurry peripheral vision are not typically primary symptoms of poor binocular vision.

What is suppression in binocular vision assessment?

Answer: Brain ignores input from one eye

Suppression in binocular vision refers to the brain's active mechanism of ignoring or 'turning off' the visual input from one eye. This occurs to avoid diplopia (double vision) when the eyes are misaligned (strabismus) or when there is a significant difference in image quality between the two eyes. While it prevents double vision, prolonged suppression can lead to amblyopia.