Subtitles in English for this video can be displayed by clicking on 
(first button on the bottom right hand corner of the video).
During the general inspection of the cranial nerves, we should look for whether the patient has any ptosis, abnormal eye movements and facial asymmetry. We should also inspect for whether there are any neuro-cutaneous features (for example in patients with tuberous sclerosis and neuro-fibromatosis), syndromal features etc.
Subtitles in English for this video can be displayed by clicking on (first button on the bottom right hand corner of the video).
Measuring the visual acuity of each eye is the first step of the neuro-ophthalmic examination. It should be carried out on every patient presenting with an ocular symptom. Distant visual acuity (at 6 metres or 20 feet) [lightbox full=”http://youtu.be/BUf_XrecQvc” title=”Distant Visual Acuity Examination”](see Distant visual acuity video)[/lightbox] is the measurement of choice in an ophthalmology specialist outpatient clinic. However, near visual acuity (at 35 cm or 14 inches) is a more practical measurement that can be performed at the bedside [lightbox full=”http://youtu.be/JKH-ICcRPIc” title=”Near Visual Acuity Exam “](see Near Visual Acuity video)[/lightbox].
The most common method of assessment is using a Snellen chart, which comprises of random letters, arranged in rows, decreasing in size in each row.
The measurement of visual acuity has medico-legal implications:
Hence, an accurate and repeatable visual acuity measurement is a key skill for every medical practitioner.
Different parts of the retina are particularly sensitive to certain hues. The majority of nerve fibres of the anterior visual pathways (optic nerve, optic chiasm and optic tract) serve our central vision, which is particularly sensitive to red and green light. Hence, diseases of the optic nerve (optic neuropathies) will cause red-green colour desaturation.
Subtitles in English for this video can be displayed by clicking on (first button on the bottom right hand corner of the video).
The confrontation test is a quick screening test for gross visual field defects that can be done at the bedside. Spectacles should not be worn during the test as they may cause spurious visual field defects.
The site of the lesion along the visual pathway determines the type of visual field defect seen. In general, because it measures only the outer edge of your visual field, the confrontation test is mainly useful in looking for large visual field defects, such as:
Inflammatory, toxic, hereditary and nutritional-deficiency related optic neuropathies tend to give central scotomas or centro-caecal scotomas, which are difficult to pick up on confrontation tests.
Glaucomatous optic neuropathies (glaucoma) commonly begin with nasal visual field defects, but are small and easily missed on confrontation tests.
Subtitles in English for this video can be displayed by clicking on (first button on the bottom right hand corner of the video).
The size of the pupillary aperture at any point in time is dependent on a balance between sympathetic tone, parasympathetic tone, the light reflex and the near reflex.
The light reflex is an important marker for optic nerve function. The afferent pathway of the light reflex is the optic nerve, with each one connecting to the parasympathetic fibers of the oculomotor nerves on both sides to form the efferent pathways. Hence, light shown on one eye causes equal pupil constriction in both eyes. An asymmetrical light reflex, as evidenced by a relative afferent pupillary defect, is an indicator for optic neuropathy.
Also known as anisocoria. The presence of this indicates an imbalance between pupil dilator (sympathetic) and constrictor muscles (parasympathetic). Before considering the possible neurological causes, it is important to take a history of previous ocular conditions (including acute glaucoma, uveitis), ocular trauma and ocular surgery (cataract surgery), as damage to the iris muscles can cause abnormalities in pupil size.
For a unilateral dilated pupil, the most important condition to look for is an oculomotor nerve palsy. Other signs to look for include ipsilateral ptosis, squint (the eye is deviated downwards and outwards). In pupil-involving oculomotor nerve palsy, it is vital to consider a space-occupying lesion (such as an aneurysm) compressing on the nerve on its route from the brainstem towards the eye.
For a unilateral constricted pupil, the most important condition to look for is Horner’s syndrome. The sympathetic nerve supply begins at the hypothalamus. The preganglionic neurons travel down the brainstem, and then along the lung apex towards the superior cervical ganglion. This lies deep to the sheath of the internal carotid artery and internal jugular vein at the level of the second and third cervical vertebrae. The postganglionic neurons then travel along the internal carotid artery towards the eye. Other signs to look for include ipsilateral partial ptosis, relative enophthalmos and occasionally anhidrosis. A confirmatory test is 4% cocaine drop test. Cocaine blocks the reuptake of noradrenaline at synaptic cleft. In Horner’s syndrome there is a lack of noradrenaline at the synaptic cleft due to loss of innervation. A positive sign is where the pupil fails to dilate to 4% cocaine solution. The most important lesion to look for is a pancoast tumor: bronchogenic carcinoma of the lung apex. A chest X-Ray may reveal an otherwise asymptomatic lung lesion.
Also known as a Marcus Gunn pupil. A paradoxical dilation of the pupil when a bright light is swung towards an eye indicates a positive relative afferent pupillary defect. Conditions to consider include lesions of the optic nerve, optic chiasm, optic tract as well as diffuse/severe retinal diseases. This is distinguished from a complete optic nerve lesion, where the pupil fails to constrict to light at all. To identify a relative afferent pupillary defect the efferent pathway must be intact. Hence anisocoria is absent during initial pupil assessment.