Cranial Nerve Examination on Vision

Vision for Function

• Vision is assessed as part of a cranial nerve examination by the medical team.
• Visual acuity is the eye's ability to distinguish shapes and details at a specified distance. Optometrists use Snellen charts to assess this.
• A normal visual field spans 90 degrees temporally, 50 degrees nasally, 50 degrees superiorly, and 60 degrees inferiorly. Visual acuity improves from peripheral vision to over 20/20 in the centre.
• Physiotherapists evaluate visual field, fixing, and scanning during neurological rehabilitation.
• Visual field encompasses the entire area of peripheral vision while focusing on a central point.
• Input from visual fields is crucial for a complete view of the surroundings, enabling safe and efficient navigation. Lesions in this area can impede functionality.
• Visual acuity necessitates coordination between head and body movements to direct visual stimuli correctly on the retina. Fixing and scanning enable this.
• Visual fixing is the process of keeping the eyes oriented so that the image of a viewed object falls on the centre of the retina. Problems indicate a deficient vestibulo-ocular reflex (VOR) and potential issues with cranial nerves III or IV.
• Visual scanning is eye movement from point A to point B, systematically exploring from top to bottom and right to left, to identify environmental details. Problems here could involve cranial nerves III or IV.
• Deficits in fixing or scanning lead to poor balance and inaccurate movement.
• Approximately 40% of stroke patients and 50% of traumatic brain injury patients experience visual deficits.
• Cranial nerves involved in vision include (among others) Optic (II), Oculomotor (III), Trochlear (IV), and Abducens (VI).
• Key eye muscles include Superior Rectus, Superior Oblique, Lateral Rectus, Medial Rectus, Inferior Rectus, and Inferior Oblique.
• The visual pathway involves the optic nerve, optic tract, optic chiasm, and visual cortex.
• Right homonymous hemianopia (HH) frequently stems from occipital lobe lesions, followed by optic radiation damage, lesions to the optic tract or lateral geniculate nucleus (LGN), or a combination of the above.
• Depth perception involves seeing objects in three dimensions (length, width, and depth), and estimating their distance. Accurate depth perception usually requires binocular (two-eyed) vision.

This quiz covers the assessment of vision during a cranial nerve examination, focusing on visual acuity, fields, and movements. Understand how healthcare professionals evaluate visual capabilities and its importance in navigation and rehabilitation. Gain insights into the anatomical and functional aspects of vision assessments.