ABO NOCE Basic Opticianry Ocular Anatomy and Physiology Questions and Answers — Questions and Answers
Question 1: Which layer of the cornea constitutes approximately 90% of its thickness and is composed of highly organized collagen fibrils that are crucial for maintaining corneal transparency?
- Epithelium
- Stroma (Correct answer)
- Bowman's Layer
- Endothelium
Correct answer: Stroma
The stroma is the thickest layer of the cornea, making up about 90% of its total thickness. Its structure consists of regularly arranged collagen fibers and keratocytes, which is essential for the cornea's strength and transparency. Disruption to this organized arrangement can lead to light scattering and reduced visual clarity.
Question 2: A patient is having difficulty with tasks at close distances. The process of accommodation allows the eye to focus on near objects. Which of the following correctly describes the primary mechanism of accommodation?
- The ciliary muscle relaxes, increasing tension on the zonules, which flattens the crystalline lens.
- The iris constricts, increasing the depth of focus, which brings near objects into view.
- The ciliary muscle contracts, releasing tension on the zonules, which allows the crystalline lens to become more convex. (Correct answer)
- The extraocular muscles converge the eyes, which changes the focal point of the cornea.
Correct answer: The ciliary muscle contracts, releasing tension on the zonules, which allows the crystalline lens to become more convex.
Accommodation is the process where the eye increases its optical power to maintain a clear image of near objects. This is achieved when the ciliary muscle contracts, which in turn relaxes the tension on the suspensory ligaments (zonules). This release of tension allows the elastic crystalline lens to assume a more rounded or convex shape, thus increasing its refractive power.
Question 3: Which of the following photoreceptor cells are more numerous in the human retina, are responsible for vision in low-light (scotopic) conditions, and do not perceive color?
- Cones
- Bipolar Cells
- Rods (Correct answer)
- Ganglion Cells
Correct answer: Rods
Rods are the most numerous photoreceptors in the retina, with about 120 million compared to 6 million cones. They are highly sensitive to light, enabling vision in dim (scotopic) conditions, but they do not differentiate between colors, perceiving only shades of gray. Cones, on the other hand, are responsible for color vision in brighter (photopic) light.
Question 4: The aqueous humor is a clear fluid that fills the anterior and posterior chambers of the eye. What is its primary drainage pathway out of the eye?
- Through the vitreous humor to the optic nerve
- Via the uveoscleral outflow pathway
- Through the trabecular meshwork into Schlemm's canal (Correct answer)
- Direct absorption by the corneal endothelium
Correct answer: Through the trabecular meshwork into Schlemm's canal
The primary, or conventional, pathway for aqueous humor drainage involves the fluid flowing from the anterior chamber through the trabecular meshwork. From there, it enters Schlemm's canal and then drains into the episcleral venous system to return to the general circulation. This pathway regulates intraocular pressure.
Question 5: A client is instructed to look up and to the right during an extraocular muscle motility test. This movement primarily involves the contraction of which two muscles in the right eye?
- Superior Rectus and Medial Rectus
- Superior Rectus and Lateral Rectus (Correct answer)
- Inferior Oblique and Lateral Rectus
- Superior Oblique and Medial Rectus
Correct answer: Superior Rectus and Lateral Rectus
Looking up (elevation) is primarily accomplished by the Superior Rectus and Inferior Oblique muscles. Looking to the right (abduction for the right eye) is accomplished by the Lateral Rectus. Therefore, the combined action of looking up and to the right involves the right Superior Rectus and the right Lateral Rectus.
Question 6: Which transparent mucous membrane covers the anterior surface of the sclera and the inner surface of the eyelids, playing a key role in lubrication and protection?
- Choroid
- Retina
- Cornea
- Conjunctiva (Correct answer)
Correct answer: Conjunctiva
The conjunctiva is a thin, clear membrane that covers the white part of the eye (sclera) and lines the inside of the eyelids. It helps lubricate the eye by producing mucus and tears and acts as a protective barrier against foreign bodies and infection.
ABO NOCE Basic Opticianry Ocular Anatomy and Physiology Questions and Answers
Which layer of the cornea constitutes approximately 90% of its thickness and is composed of highly organized collagen fibrils that are crucial for maintaining corneal transparency?