Q&A: Concerning Anatomy of the Optic Disc

The optic disc or optic nerve head is the point of exit for ganglion cell axons leaving the eye. The ganglion cell axons form the optic nerve after they leave the eye. The optic disc represents the beginning of the optic nerve and is the point where the axons of retinal ganglion cells come together. The optic disc in a normal human eye carries 1–1.2 million afferent nerve fibers from the eye towards the brain.

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This is a Question & Answer revision article designed for medical students and professionals preparing for the PLAB, MRCP or USMLE examinations. They are based on actual questions from these examinations. You may find the Anatomy of the Eye article more useful, or one of our many articles on Diseases & Conditions, Medical Syndromes, Health & Wellness or Home Remedies.

In this article:
Congenital vs acquired optic disc abnormalities
MCQ: clinical scenario
MCQ: answer
MCQ: explanation

Congenital vs acquired optic disc abnormalities

Optic nerve abnormalities can be categorized as congenital or acquired. Congenital optic nerve anomalies are distinguished by the appearance of the optic disc and surrounding retina. As a general rule, these anomalies are classified according to abnormalities of optic disc size or conformation and by the presence of abnormal tissue at the nerve head (pseudoswelling). Acquired abnormalities of the optic nerve are classified according to the reaction of the optic nerve to insult: cupping, swelling, and atrophy.

MCQ: clinical scenario

Which of the following is true of the optic disc?

a) no arteries pass through it
b) no veins pass through it
c) it appears dark red on fundoscopy
d) contains a concentration of photoreceptors
e) it is normally less than 1cm in diameter

MCQ: answer

The correct answer is E.

MCQ: explanation

This is the point at which axons leave the eyeball and join the optic nerve. Also, arteries enter and veins leave the retina at the optic disk. There are no photoreceptors here, hence it is known as the 'blind spot'. The normal optic nerve head (optic disc) usually is round or oval and pink or pinky-yellow in color; typically it is flat or mildly elevated and has a central depression called the cup. The horizontal diameter of the normal optic nerve is approximately 1.5-2 mm, and it is situated in the nasal retina. The ratio between the cup and disc diameters is important to note because acquired optic nerve damage can cause cupping, an increase in the cup/disc ratio.

Reference(s)
1). UpToDate: Congenital anomalies and acquired abnormalities of the optic nerve. Available online: https://www.uptodate.com/contents/congenital-anomalies-and-acquired-abnormalities-of-the-optic-nerve
2). Tasman, William; Jaeger, Edward A (2006). "Chapter 4: Anatomy of the Visual Sensory System". Duane's Ophthalmology. Philadelphia: Lippincott Williams & Wilkins. ISBN 9780781768559. OCLC 318288606